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we present results from the intermediate redshift osiris chemo-kinematic survey (irocks) for sixteen z ∼ 1 and one z ∼ 1.4 star-forming galaxies. all galaxies were observed with osiris with the laser guide star adaptive optics system at keck observatory. we use rest-frame nebular hα emission lines to trace morphologies and kinematics of ionized gas in star-forming galaxies on sub-kiloparsec physical scales. we observe elevated velocity dispersions (σ ≳ 50 km s-1) seen in z > 1.5 galaxies persist at z ∼ 1 in the integrated galaxies. using an inclined disk model and the ratio of v/σ , we find that 1/3 of the z ∼ 1 sample are disk candidates while the other 2/3 of the sample are dominated by merger-like and irregular sources. we find that including extra attenuation toward h ii regions derived from stellar population synthesis modeling brings star formation rates (sfrs) using hα and stellar population fit into a better agreement. we explore the properties of the compact hα sub-component, or “clump,” at z ∼ 1 and find that they follow a similar size-luminosity relation as local h ii regions but are scaled-up by an order of magnitude with higher luminosities and sizes. comparing the z ∼ 1 clumps to other high-redshift clump studies, we determine that the clump sfr surface density evolves as a function of redshift. this suggests clump formation is directly related to the gas fraction in these systems and may support disk fragmentation as their formation mechanism since gas fraction scales with redshift. | irocks: spatially resolved kinematics of z ∼ 1 star-forming galaxies |
we investigate the dynamics of bow shock nebulae created by pulsars moving supersonically through a partially ionized interstellar medium. a fraction of interstellar neutral hydrogen atoms penetrating into the tail region of a pulsar wind will undergo photoionization due to the ultraviolet light emitted by the nebula, with the resulting mass loading dramatically changing the flow dynamics of the light leptonic pulsar wind. using a quasi-1d hydrodynamic model of both non-relativistic and relativistic flow, and focusing on scales much larger than the stand-off distance, we find that if a relatively small density of neutral hydrogen, as low as 10-4 cm-3, penetrate inside the pulsar wind, this is sufficient to strongly affect the tail flow. mass loading leads to the fast expansion of the pulsar wind tail, making the tail flow intrinsically non-stationary. the shapes predicted for the bow shock nebulae compare well with observations, both in hα and x-rays. | mass loading of bow shock pulsar wind nebulae |
we report the first spectroscopic observations of a background star seen through the region between the ionization front and the dissociation front of the nebula ic 63. this photodissociation region (pdr) exhibits intense extended red emission (ere) attributed to fluorescence by large molecules/ions. we detected strong diffuse interstellar bands (dib) in the stellar spectrum, including an exceptionally strong and broad dib at λ4428. the detection of strong dibs in association with ere could be consistent with the suggestion that the carriers of dibs and ere are identical. the likely ere process is recurrent fluorescence, enabled by inverse internal conversions from highly excited vibrational levels of the ground state to low-lying electronic states with subsequent transitions to ground. this provides a path to rapid radiative cooling for molecules/molecular ions, greatly enhancing their ability to survive in a strongly irradiated environment. the ratio of the equivalent widths (ews) of dibs λ5797 and λ5780 in ic 63 is the same as that observed in the low-density interstellar medium with ultraviolet (uv) interstellar radiation fields (isrf) weaker by at least two orders of magnitude. this falsifies suggestions that the ratio of these two dibs can serve as a measure of the uv strength of the isrf. observations of the nebular spectrum of the pdr of ic 63 at locations immediately adjacent to where dibs were detected failed to reveal any presence of sharp emission features seen in the spectrum of the red rectangle nebula. this casts doubts upon proposals that the carriers of these features are the same as those of dibs seen at slightly shorter wavelengths. | are the carriers of diffuse interstellar bands and extended red emission the same? |
jupiter's sodium nebula, which originates from io's volcanic gas, shows variations in its brightness due to the volcanic activity on io. imaging observation of d-line brightness in the sodium nebula was performed from 2013 through 2015 in a conjunction with the hisaki mission. the d-line brightness of the sodium nebula had been stably faint and dim until january 2015, but it showed a distinct enhancement from february through march, 2015. the brightness increased by three times during this enhancement. details in variations of jupiter's sodium nebula are shown in this paper. | brightening event seen in observations of jupiter's extended sodium nebula |
free-floating (or rogue) planets are planets that are liberated (or ejected) from their host systems. although simulations predict their existence in substantial numbers, direct observational evidence for free-floating planets with masses below ~5 m jup is still lacking. several cycle-1 observing programs with jwst aim to hunt for them in four different star-forming clusters. these surveys are designed to be sensitive to masses of 1-15 m jup (assuming a hot-start formation), which corresponds to spectral types of early l to late t for the ages of these clusters. if the existing simulations are not wide off the mark, we show here that the planned programs are likely to find up to 10-20 giant rogue planets in moderate density clusters like ngc1333 or ic348, and several dozen to ~100 in high-density regions like ngc2024 and the orion nebula cluster. these numbers correspond to 1%-5% of the total cluster population; they could be substantially higher if stars form multiple giant planets at birth. in contrast, the number of free-floating brown dwarfs, formed from core collapse (like stars) is expected to be significantly lower, only about 0.25% of the number of stars, or 1-7 for the clusters considered here. below 10 m jup that number drops further by an order of magnitude. we also show that the planned surveys are not at risk of being significantly contaminated by field brown dwarfs in the foreground or background, after spectroscopic confirmation. taken together, our results imply that if a population of l and t dwarfs were to be found in these jwst surveys, it is expected to be predominantly made up of rogue planets. | rogue planets and brown dwarfs: predicting the populations free-floating planetary mass objects observable with jwst |
the ic 5146 cloud is a nearby star-forming region in cygnus, consisting of molecular gas filaments in a variety of evolutionary stages. we used optical and near-infrared polarization data toward the ic 5146 cloud, reported in the first paper of this series, to reveal the magnetic fields in this cloud. using the newly released gaia data, we found that the ic 5146 cloud may contain two separate clouds: a first cloud, including the densest main filament at a distance of ∼600 pc, and a second cloud, associated with the cocoon nebula at a distance of ∼800 pc. the spatially averaged h-band polarization map revealed a well-ordered magnetic field morphology, with the polarization segments perpendicular to the main filament but parallel to the nearby subfilaments, consistent with models assuming that the magnetic field is regulating cloud evolution. we estimated the magnetic field strength using the davis-chandrasekhar-fermi method and found that the magnetic field strength scales with volume density with a power-law index of ∼0.5 in the density range from {n}{{{h}}2}∼ 10 to 3000 cm-3, which indicates an anisotropic cloud contraction with a preferred direction along the magnetic field. in addition, the mass-to-flux ratio of the cloud gradually changes from subcritical to supercritical from the cloud envelope to the deep regions. these features are consistent with strong magnetic field star formation models and suggest that the magnetic field is important in regulating the evolution of the ic 5146 cloud. | multiwavelength polarimetry of the filamentary cloud ic 5146. ii. magnetic field structures |
common features of all carbonaceous chondrite groups are invariant refractory element ratios, depletions of moderately volatile elements as a function of their condensation temperature (tc), and strongly depleted highly volatile element concentrations independent of tc. the depletion of volatile elements with respect to the bulk solar system composition requires a separation of gas from solids in the solar nebula. several models have been proposed to explain the decoupling of gas and solids, but not all are compatible with astrophysical, chemical, and petrologic constraints. here existing physical models are integrated with measured element concentrations, measured and modeled physical properties of protoplanetary disks, and planetary-scale nucleosynthetic and stable isotope variations to establish a conceptual model for the condensation and accretion of elements into planetesimals. in this model, the chemical composition of chondrites is established by element condensation in a cooling solar nebula that changed its surface density as a function of time and temperature. the model predicts peak temperatures at the condensation sites of about 1400 k that consequently decreased due to a diminishing heat source originating from viscous heating and radiation, accompanied by continuous removal of gas from the nebula surface by photoevaporation. the coupled evolution of condensing solids from a nebula of diminishing surface density resulted in a pattern of decreasing moderately volatile abundances with decreasing tc. the reduction of nebula opacity due to the chondrule-forming process significantly increased nebula cooling rates and led to the near-chondritic relative abundances of highly volatile elements observed in carbonaceous chondrites. | carbonaceous chondrites and the condensation of elements from the solar nebula |
cool gas (t~104 k) traced by hydrogen ly α emission is now routinely detected around z ~ 3 quasars, but little is known about their molecular gas reservoirs. here, we present an apex spectroscopic survey of the co(6-5), co(7-6), and [c i](2-1) emission lines for nine quasars from the qso museum survey, which have similar uv luminosities, but very diverse ly α nebulae. these observations ($\lesssim ngle ~\rm rms~\rangle =2.6$ mjy in 300 km s-1) detected three co(6-5) lines with 3.4≤ico(6-5) ≤5.1 jy km s-1, 620≤fwhm≤707 km s-1, and three [c i](2-1) lines with 2.3$\le i_{\rm [c{\small i}](2-1)} \le$15.7 jy km s-1, 329≤fwhm≤943 km s-1. for the co and [c i] detected sources, we constrain the molecular gas reservoirs to be $\rm m_{h_{2}} = (0.4-6.9) \times 10^{11}\, m_{\odot }$, while the non-detections imply $\rm m_{h_{2}} \lt 1.1\times 10^{11}\, m_{\odot }$. we compare our observations with the extended ly α properties to understand the link between the cool and the molecular gas phases. we find large velocity shifts between the bulk of ly α and the molecular gas systemic redshift in five sources (from ~-400 to ~+1200 km s-1). the sources with the largest shifts have the largest ly α line widths in the sample, suggesting more turbulent gas conditions and/or large-scale inflows/outflows around these quasars. we also find that the brightest ($i_{\rm [c{\small i}](2-1)}=15.7\pm 3.7~\rm jy~km~s^{-1}$) and the widest (fwhm~900 km s-1) lines are detected for the smallest and dimmest ly α nebulae. from this, we speculate that host galaxy obscuration can play an important role in reducing the ionizing and ly α photons able to escape to halo scales, and/or that these systems are hosted by more massive haloes. | apex at the qso museum: molecular gas reservoirs associated with z 3 quasars and their link to the extended ly α emission |
secondary ionisation mass spectrometry (sims) u-th-pb dating of cassiterite with very low to sub-ppm u contents, zircon and monazite has provided direct measurements of the ages of mesoproterozoic-neoproterozoic pegmatite and quartz vein sn mineralisation in the karagwe-ankole belt (kab), rwanda, and through dates on local igneous rocks, helped to place the mineralisation in a tectonic context. three generations of sn mineralisation have been identified, each associated with magmatic and metamorphic processes during different periods of rodinian and gondwanan assembly. the first generation of mineralisation occurred in pegmatite at ca. 1145 ma. the second generation, the main episode of sn mineralisation, occurred from ca. 1090 to 960 ma in quartz veins and intra-pegmatitic greisen. it started during the period ca. 1090-1040 ma with fault-controlled sn mineralisation in quartz veins hosted in quartzite and intra-pegmatitic greisen. this was mainly associated with the ca. 1078 ma d2 orogenic event in the kab during the final amalgamation of rodinia. peak sn mineralisation occurred during the period ca. 1040-960 ma in quartz veins hosted in mica schists related to shear zones. it was associated with g4 s-type granitic magmatism, with zircon u-pb and monazite th-pb ages between 1011 ± 18 and 976 ± 11 ma, possibly related to a late/-post-collisional setting linked to the amalgamation of rodinia. the third and distinct generation of sn mineralisation occurred at ca. 530 ma in quartz veins hosted in mica schists within a shear zone located close to reworked basement rocks with meridional foliation. this sn generation is attributed to hydrothermal fluids, possibly induced by a post-tectonic event associated with the emplacement of g5 s-type granite at 614 ± 9 ma, during the pan-african orogeny. recognition of the nebulous sn-mineralised, cross-structural, satinsyi-rutongo fault zone, and the links established between the mode of sn mineralisation, its local geological setting, igneous activity and regional tectonism, will help in targeting exploration for ore-grade sn deposits in rwanda and nearby countries. | shrimp u-pb dating of cassiterite: insights into the timing of rwandan tin mineralisation and associated tectonic processes |
we model callisto's exosphere based on its ice as well as non-ice surface via the use of a monte-carlo exosphere model. for the ice component we implement two putative compositions that have been computed from two possible extreme formation scenarios of the satellite. one composition represents the oxidizing state and is based on the assumption that the building blocks of callisto were formed in the protosolar nebula and the other represents the reducing state of the gas, based on the assumption that the satellite accreted from solids condensed in the jovian sub-nebula. for the non-ice component we implemented the compositions of typical ci as well as l type chondrites. both chondrite types have been suggested to represent callisto's non-ice composition best. as release processes we consider surface sublimation, ion sputtering and photon-stimulated desorption. particles are followed on their individual trajectories until they either escape callisto's gravitational attraction, return to the surface, are ionized, or are fragmented. our density profiles show that whereas the sublimated species dominate close to the surface on the sun-lit side, their density profiles (with the exception of h and h2) decrease much more rapidly than the sputtered particles. the neutral gas and ion mass (nim) spectrometer, which is part of the particle environment package (pep), will investigate callisto's exosphere during the juice mission. our simulations show that nim will be able to detect sublimated and sputtered particles from both the ice and non-ice surface. nim's measured chemical composition will allow us to distinguish between different formation scenarios. | monte-carlo simulation of callisto's exosphere |
accurate radial velocity determinations of optical emission lines (i.e., [nii] λλ 6548, 6584, hα and [s ii] λλ 6717, 6731) are very important for investigating the kinematic and dynamic properties of nebulae. the second stage survey program of large sky area multi-object fiber spectroscopic telescope (lamost) has started a sub-survey of nebulae (mrs-n) which will spectroscopically observe the optical emission lines of a large sample of nebulae near the galactic plane. until now, 15 mrs-n plates have been observed from september 2017 to june 2019. based on fitting the sky emission lines in the red band spectra of mrs-n, we investigate the precision of wavelength calibration and find there are systematic deviations of radial velocities (rvs) from ∼ 0.2 to 4 km s-1 for different plates. especially for the plates obtained in march 2018, the systematic deviations of rvs can be as large as ∼ 4 km s-1, which then go down to ∼ 0.2 - 0.5 km s-1 at the end of 2018 and january 2019. an rv calibration function is proposed for these mrs-n plates, which can simultaneously and successfully calibrate the systematic deviations and improve the precision of rvs. | on the radial velocity calibrations in the lamost medium-resolution spectroscopic survey of nebulae |
we find that the remnant of supernova (sn) 1987a shares some morphological features with four supernova remnants (snrs) that have signatures of shaping by jets, and from that we strengthen the claim that jets played a crucial role in the explosion of sn 1987a. some of the morphological features appear also in planetary nebulae (pne) where jets are observed. the clumpy ejecta brings us to support the claim that the jittering jets explosion mechanism can account for the structure of the remnant of sn 1987a, i.e. snr 1987a. we conduct a preliminary attempt to quantify the fluctuations in the angular momentum of the mass that is accreted on to the newly born neutron star via an accretion disc or belt. the accretion disc/belt launches jets that explode core collapse supernovae (ccsne). the relaxation time of the accretion disc/belt is comparable to the duration of a typicalfigu jet-launching episode in the jittering jets explosion mechanism, and hence the disc/belt has no time to relax. we suggest that this might explain the two unequal opposite jets that later lead to the unequal sides of the elongated structures in some snrs of ccsne. we reiterate our earlier call for a paradigm shift from a neutrino-driven explosion to a jet-driven explosion of ccsne. | explaining the morphology of supernova remnant (snr) 1987a with the jittering jets explosion mechanism |
we report a computational study of the stability and infrared (ir) vibrational spectra of neutral and singly ionized fullerene cages containing between 44 and 70 carbon atoms. the stability is characterized in terms of the standard enthalpy of formation per cc bond, the homo-lumo gap, and the energy required to eliminate a c2 fragment. we compare the simulated ir spectra of these fullerene species to the observed emission spectra of several planetary nebulae (tc 1, smp smc 16, and smp lmc 56) where strong c60 emission has been detected. although we could not conclusively identify fullerenes other than c60 and c70, our results point to the possible presence of smaller (44, 50, and 56-atom) cages in those astronomical objects. observational confirmation of our prediction should become possible when the james webb space telescope comes online. | searching for stable fullerenes in space with computational chemistry |
the lines of sight to highly reddened sne ia show peculiar continuum polarization curves, growing towards blue wavelengths and peaking at λmax ≲ 0.4 μ m like no other sightline to any normal galactic star. we examined continuum polarization measurements of a sample of asymptotic giant branch (agb) and post-agb stars from the literature, finding that some proto-planetary nebulae (ppne) have polarization curves similar to those observed along sn ia sightlines. these polarization curves are produced by scattering on circumstellar dust. we discuss the similarity and the possibility that at least some sne ia might explode during the post-agb phase of their binary companion. furthermore, we speculate that the peculiar sn ia polarization curves might provide observational support to the core-degenerate progenitor model. | common continuum polarization properties: a possible link between proto-planetary nebulae and type ia supernova progenitors |
we have performed combined photoionization and photodissociation region (pdr) modelling of a crab nebula filament subjected to the synchrotron radiation from the central pulsar wind nebula, and to a high flux of charged particles; a greatly enhanced cosmic-ray ionization rate over the standard interstellar value, ζ0, is required to account for the lack of detected [c i] emission in published herschel spire fts observations of the crab nebula. the observed line surface brightness ratios of the oh+ and arh+ transitions seen in the spire fts frequency range can only be explained with both a high cosmic-ray ionization rate and a reduced arh+ dissociative recombination rate compared to that used by previous authors, although consistent with experimental upper limits. we find that the arh+/oh+ line strengths and the observed h2 vibration-rotation emission can be reproduced by model filaments with nh = 2 × 104 cm-3, ζ = 107ζ0 and visual extinctions within the range found for dusty globules in the crab nebula, although far-infrared emission from [o i] and [c ii] is higher than the observational constraints. models with nh = 1900 cm-3 underpredict the h2 surface brightness, but agree with the arh+ and oh+ surface brightnesses and predict [o i] and [c ii] line ratios consistent with observations. these models predict heh+ rotational emission above detection thresholds, but consideration of the formation time-scale suggests that the abundance of this molecule in the crab nebula should be lower than the equilibrium values obtained in our analysis. | modelling the arh+ emission from the crab nebula |
we have determined δ‧26mgdsm-3, the mass-independent variations in 26mg/24mg, of primitive, bulk meteorites to precisions better than ±3 ppm (2se). our measurements of samples from 10 different chondrite groups show δ‧26mgdsm-3 that vary from -5 to 22 ppm. our data define an array with a positive slope in a plot of δ‧26mgdsm-3 against 27al/24mg, which can be used to determine (26al/27al)0, i.e. initial 26al/27al, and (δ‧26mgdsm-3)0, i.e. initial δ‧26mgdsm-3. on such an isochron plot, the best fit of our new measurements combined with literature data implies (26al/27al)0 of (4.67 ± 0.78) ×10-5 and (δ‧26mgdsm-3)0 of -31.6 ± 5.7 ppm (2se) for ordinary and carbonaceous chondrites, other than cr chondrites, which have anomalously low δ‧26mgdsm-3. these parameters are within uncertainty of those defined by previous measurements of bulk calcium-, aluminium-rich inclusions (cais) that set canonical (26al/27al)0∼ 5 ×10-5. the most straightforward interpretation of all these observations is that differences in the al/mg of bulk ordinary and carbonaceous chondrites are dominantly controlled by variable contributions of early-formed refractory and major silicate components derived from a common, canonical reservoir. the δ‧26mgdsm-3 of enstatite chondrites are slightly more radiogenic (∼3 ppm) at similar al/mg to the ordinary chondrites. we speculate that this is related to the timing of removal of a refractory component from the source reservoirs of these different meteorite groups; the higher δ‧26mgdsm-3 of the enstatite chondrites suggests later (∼0.5 ma post cais) condensation and loss of this refractory component. despite inferred consistency of (26al/27al)0 and (δ‧26mgdsm-3)0 across most chondrite groups, some nebular heterogeneity is required to account for the compositions of cr chondrites. our preferred interpretation is that the cr source region has lower (δ‧26mgdsm-3)0. as the most appropriate isotopic reference for the earth, our new mean enstatite chondrite composition allows us to assess possible ingrowth of 26mg from live 26al during accretion of the earth. the earth has δ‧26mgdsm-3 within uncertainty of enstatite chondrites, despite its higher al/mg. this requires that the terrestrial increase in al/mg, which we attribute to vapour loss during accretion, must have happened >1.5 ma post cai formation, in an instantaneous fractionation model. | bulk chondrite variability in mass independent magnesium isotope compositions - implications for initial solar system 26al/27al and the timing of terrestrial accretion |
aims: the spatial structure of the emission lines and continuum over the 50″ extent of the nearby, o-rich, pn ngc 7009 (saturn nebula) have been observed with the muse integral field spectrograph on the eso very large telescope. this study concentrates on maps of line emission and their interpretation in terms of physical conditions.methods: muse science verification data, in <0.6″ seeing, have been reduced and analysed as maps of emission lines and continuum over the wavelength range 4750-9350 å. the dust extinction, the electron densities and temperatures of various phases of the ionized gas, abundances of species from low to high ionization and some total abundances are determined using standard techniques.results: emission line maps over the bright shells are presented, from neutral to the highest ionization available (he ii and [mn v]). for collisionally excited lines (cels), maps of electron temperature (te from [n ii] and [s iii]) and density (ne from [s ii] and [cl iii]) are available and for optical recombination lines (orls) temperature (from the paschen jump and ratio of he i lines) and density (from high paschen lines). these estimates are compared: for the first time, maps of the differences in cel and orl te's have been derived, and correspondingly a map of t2 between a cel and orl temperature, showing considerable detail. total abundances of only he and o were formed, the latter using three ionization correction factors. however, the map of he/h is not flat, departing by 2% from a constant value, with remnants corresponding to ionization structures. an integrated spectrum over an area of 2340 arcsec2 was also formed and compared to 1d photoionization models.conclusions: the spatial variation of a range of nebular parameters illustrates the complexity of the ionized media in ngc 7009. these muse data are very rich with detections of hundreds of lines over areas of hundreds of arcsec2 and follow-on studies are outlined. based on observations collected at the european organisation for astronomical research in the southern hemisphere, chile in science verification (sv) observing proposal 60.a-9347(a).fits files of all the individual maps are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/620/a169 | an imaging spectroscopic survey of the planetary nebula ngc 7009 with muse★ |
the very high energy gamma-ray emission reported from a number of pulsar wind nebulae (pwne) is naturally explained by the inverse compton scattering of multi-tev electrons. however, the physical dimensions of some gamma-ray-emitting pwne significantly exceed the scales anticipated by the standard hydrodynamical paradigm of pwn formation. the most “disturbing” case in this regard is hess j1825-137, which extends to distances of r ≈ 70 pc from the central pulsar psr j1826-1334. if the gamma-ray emission is indeed produced inside the pwn, but not by electrons that escaped the nebula and diffuse in the interstellar medium (ism), the formation of such an anomalously extended plerion could be realized, in a diluted environment with the hydrogen number density {n}{{ism}}≤slant {10}-2 {cm}}-3. in this paper, we explore an alternative scenario assuming that the pulsar responsible for the formation of the nebula initially had a very short rotation period. in this case, the sizes of both the pwn and the surrounding supernova remnant depend on the initial pulsar period, the braking index, and the ism density. to check the feasibility of this scenario, we study the parameter space that would reproduce the size of hess j1825-137. we show that this demand can be achieved if the braking index is small, n≤slant 2, and the pulsar birth period is short, {p}{{b}}≃ 1 {ms}. this scenario can reproduce the wind termination position, which is expected at {r}{{ts}}≃ 0.03 {pc}, only in a dense environment with {n}{{ism}}≥slant 1 {cm}}-3. the requirement of the dense surrounding gas is supported by the presence of molecular clouds found in the source vicinity. | on the anomalously large extension of the pulsar wind nebula hess j1825-137 |
radial abundance gradients are observed in the galaxy and other galaxies as well, and include several chemical elements in different stellar systems. possibly the most accurate gradients in the galaxy are those determined from chepheid variable stars. these objects have very accurate abundances for many elements and are generally considered as standard candles, so that their galactocentric distances are very well determined. these stars are relatively young, with ages between the main types of photoionized nebulae, namely the younger hii regions and the older planetary nebulae. in this paper we consider the o/h and fe/h gradients based on a large sample of galactic cepheids, and compare the results with recent determinations from photoionized nebulae. | galactic radial abundance gradients: cepheids and photoionized nebulae |
based on imaging and spectroscopic data, we develop a 3d model for the huygens region of the orion nebula. θ^{1} ori c, the hottest star in the trapezium, is surrounded by a wind-blown central bubble that opens sw into the extended orion nebula. outside of this feature lies a layer of ionized gas at about 0.4 pc from θ^{1} ori c. both of these features are moving rapidly away from θ^{1} ori c with an expansion age for the central bubble of only 15,000 yr. | deciphering the 3d orion nebula-i: expanding shells in the huygens region |
the wolf-rayet 98a (wr 98a) system is a prime target for interferometric surveys, since its identification as a `rotating pinwheel nebulae', where infrared images display a spiral dust lane revolving with a 1.4 yr periodicity. wr 98a hosts a wc9+ob star, and the presence of dust is puzzling given the extreme luminosities of wolf-rayet stars. we present 3d hydrodynamic models for wr 98a, where dust creation and redistribution are self-consistently incorporated. our grid-adaptive simulations resolve details in the wind collision region at scales below one percent of the orbital separation (∼4 au), while simulating up to 1300 au. we cover several orbital periods under conditions where the gas component alone behaves adiabatic, or is subject to effective radiative cooling. in the adiabatic case, mixing between stellar winds is effective in a well-defined spiral pattern, where optimal conditions for dust creation are met. when radiative cooling is incorporated, the interaction gets dominated by thermal instabilities along the wind collision region, and dust concentrates in clumps and filaments in a volume-filling fashion, so wr 98a must obey close to adiabatic evolutions to demonstrate the rotating pinwheel structure. we mimic keck, alma or future e-elt observations and confront photometric long-term monitoring. we predict an asymmetry in the dust distribution between leading and trailing edge of the spiral, show that alma and e-elt would be able to detect fine-structure in the spiral indicative of kelvin-helmholtz development, and confirm the variation in photometry due to the orientation. historic keck images are reproduced, but their resolution is insufficient to detect the details we predict. | pinwheels in the sky, with dust: 3d modelling of the wolf-rayet 98a environment |
we estimate the accretion rates of 235 classical t tauri star (ctts) candidates in the lagoon nebula using ugri h α photometry from the vst photometric h α survey+. our sample consists of stars displaying h α excess, the intensity of which is used to derive accretion rates. for a subset of 87 stars, the intensity of the u-band excess is also used to estimate accretion rates. we find the mean variation in accretion rates measured using h α and u-band intensities to be ∼0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. the spatial distribution of ctts align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. strong accretors are concentrated spatially, while weak accretors are more distributed. our results do not support the sequential star-forming processes suggested in the literature. | classical t tauri stars with vphas+ - i. h α and u-band accretion rates in the lagoon nebula m8 |
the argo-ybj air shower detector monitored the crab nebula gamma-ray emission from 2007 november to 2013 february. the integrated signal, consisting of ~3.3 × 105 events, reached the statistical significance of 21.1 standard deviations. the obtained energy spectrum in the energy range 0.3-20 tev can be described by a power law function dn/de = i 0 (e/2 tev)-α, with a flux normalization i 0 = (5.2 ± 0.2) × 10-12 photons cm-2 s-1 tev-1 and α = 2.63 ± 0.05, corresponding to an integrated flux above 1 tev of 1.97 × 10-11 photons cm-2 s-1. the systematic error is estimated to be less than 30% for the flux normalization and 0.06 for the spectral index. assuming a power law spectrum with an exponential cutoff dn/de = i 0 (e/2 tev)-α exp (-e/e cut), the lower limit of the cutoff energy e cut is 12 tev, at 90% confidence level. our extended data set allows the study of the tev emission over long timescales. over five years, the light curve of the crab nebula in 200-day bins is compatible with a steady emission with a probability of 7.3 × 10-2. a correlated analysis with fermi-lat data over ~4.5 yr using the light curves of the two experiments gives a pearson correlation coefficient r = 0.56 ± 0.22. concerning flux variations on timescales of days, a "blind" search for flares with a duration of 1-15 days gives no excess with a significance higher than four standard deviations. the average rate measured by argo-ybj during the three most powerful flares detected by fermi-lat is 205 ± 91 photons day-1, consistent with the average value of 137 ± 10 day-1. | crab nebula: five-year observation with argo-ybj |
planetary nebulae are ionized clouds of gas formed by the hydrogen-rich envelopes of low- and intermediate-mass stars ejected at late evolutionary stages. the strong uv flux from their central stars causes a highly stratified ionization structure, with species of higher ionization potential closer to the star. here, we report on the exceptional case of hubi 1, a double-shell planetary nebula whose inner shell presents emission from low-ionization species close to the star and emission from high-ionization species farther away. spectral analysis demonstrates that the inner shell of hubi 1 is excited by shocks, whereas its outer shell is recombining. the anomalous excitation of these shells can be traced to its low-temperature [wc10] central star whose optical brightness has declined continuously by 10 magnitudes in a period of 46 years. evolutionary models reveal that this star is the descendant of a low-mass star (≃1.1 m⊙) that has experienced a `born-again' event1 whose ejecta shock-excite the inner shell. hubi 1 represents the missing link in the formation of metal-rich central stars of planetary nebulae from low-mass progenitors, offering unique insight regarding the future evolution of the born-again sakurai's object2. coming from a solar-mass progenitor, hubi 1 represents a potential end-state for our sun. | the inside-out planetary nebula around a born-again star |
we present optical and near-infrared observations of the type iib supernova (sn) 2011fu from a few days to ∼300 d after explosion. the sn presents a double-peaked light curve (lc) similar to that of sn 1993j, although more luminous and with a longer cooling phase after the primary peak. the spectral evolution is also similar to sn 1993j's, with hydrogen dominating the spectra to ∼40 d, then helium gaining strength, and nebular emission lines appearing from ∼60 d post-explosion. the velocities derived from the p-cygni absorptions are overall similar to those of other type iib sne. we have found a strong similarity between the oxygen and magnesium line profiles at late times, which suggests that these lines are forming at the same location within the ejecta. the hydrodynamical modelling of the pseudo-bolometric lc and the observed photospheric velocities suggest that sn 2011fu was the explosion of an extended star (r∼ 450 r⊙), in which 1.3 × 1051 erg of kinetic energy were released and 0.15 m⊙ of 56ni were synthesized. in addition, a better reproduction of the observed early pseudo-bolometric lc is achieved if a more massive h-rich envelope than for other type iib sne is considered (0.3 m⊙). the hydrodynamical modelling of the lc and the comparison of our late-time spectra with nebular spectral models for type iib sne, point to a progenitor for sn 2011fu with a zero age main sequence (zams) mass of 13-18 m⊙. | sn 2011fu: a type iib supernova with a luminous double-peaked light curve |
we present a sample of resolved galactic h ii regions and photodissociation regions (pdrs) observed with the spitzer infrared spectrograph in spectral mapping mode between the wavelengths of 5-15 μm. for each object we have spectral maps at a spatial resolution of ∼4″ in which we have measured all of the mid-infrared emission and absorption features. these include the polycyclic aromatic hydrocarbon (pah) emission bands, primarily at 6.2, 7.7, 8.6, 11.2, and 12.7 μm, as well as the spectral emission lines of neon and sulfur and the absorption band caused by silicate dust at around 9.8 μm. in this work we describe the data in detail, including the data reduction and measurement strategies, and subsequently present the pah emission band intensity correlations for each of the objects and the sample as a whole. we find that there are distinct differences between the sources in the sample, with two main groups: the first comprising the h ii regions and the second the reflection nebulae (rne). three sources—the reflection nebula ngc 7023, the horsehead nebula pdr (an interface between the h ii region ic 434 and the orion b molecular cloud), and m17—resist this categorization, with the horsehead pdr points mimicking the rne and the ngc 7023 fluxes displaying a unique bifurcated appearance in our correlation plots. these discrepancies seem to be due to the very low radiation field experienced by the horsehead pdr and the very clean separation between the pdr environment and a diffuse environment in the ngc 7023 observations. | polycyclic aromatic hydrocarbon emission in spitzer/irs maps. i. catalog and simple diagnostics |
we discuss recent claims that the free electrons in ionized nebulae may not have a significantly maxwellian velocity distribution. supra-thermal electrons, electrons with much more energy than is encountered at electron temperatures found in nebulae, may solve the t^2/adf puzzle, the observations that abundances obtained from recombination and collisionally excited lines do not agree, and that different temperature indicators give different results. these non-maxwellian electrons can be designated by the kappa formalism. we show that the distance over which heating rates change are much longer than the distance supra-thermal electrons can travel, and that the timescale to thermalize these electrons are much shorter than the heating or cooling timescales. these estimates show that supra-thermal electrons will have disappeared into the maxwellian velocity distribution long before they affect the collisionally-excited forbidden and recombination lines, so the electron velocity distribution will be closely thermal. | the abundance discrepancy factor and t^2 in nebulae: are non-thermal electrons the culprits? |
in this contribution we review the recent progress in the modelling of pulsar wind nebulae (pwn). we start with a brief overview of the relevant physical processes in the magnetosphere, the wind-zone and the inflated nebula bubble. radiative signatures and particle transport processes obtained from 3d simulations of pwn are discussed in the context of optical and x-ray observations. we then proceed to consider particle acceleration in pwn and elaborate on what can be learned about the particle acceleration from the dynamical structures called gwispsg observed in the crab nebula. we also discuss recent observational and theoretical results of gamma-ray flares and the inner knot of the crab nebula, which had been proposed as the emission site of the flares. we extend the discussion to gev flares from binary systems in which the pulsar wind interacts with the stellar wind from a companion star. the chapter concludes with a discussion of solved and unsolved problems posed by pwn. | modelling jets, tori and flares in pulsar wind nebulae |
context. ag peg is known as the slowest symbiotic nova, which experienced its nova-like outburst around 1850. after 165 yr, during june of 2015, it erupted again showing characteristics of the z and-type outburst.aims: the primary objective is to determine basic characteristics, the nature and type of the 2015 outburst of ag peg.methods: we achieved this aim by modelling the spectral energy distribution using low-resolution spectroscopy (330-750 nm; r = 500-1000), medium-resolution spectroscopy (420-720 nm; r 11 000), and ubvrcic photometry covering the 2015 outburst with a high cadence. optical observations were complemented with the archival hst and fuse spectra from the preceding quiescence.results: during the outburst, the luminosity of the hot component was in the range of 2-11 × 1037 (d/ 0.8 kpc)2 erg s-1, being in correlation with the light curve (lc) profile. to generate the maximum luminosity by the hydrogen burning, the white dwarf (wd) had to accrete at 3 × 10-7 m⊙ yr-1, which exceeds the stable-burning limit and thus led to blowing optically thick wind from the wd. we determined its mass-loss rate to a few × 10-6 m⊙ yr-1. at the high temperature of the ionising source, 1.5-2.3 × 105 k, the wind converted a fraction of the wd's photospheric radiation into the nebular emission that dominated the optical. a one order of magnitude increase of the emission measure, from a few × 1059 (d/ 0.8 kpc)2 cm-3 during quiescence, to a few × 1060 (d/ 0.8 kpc)2 cm-3 during the outburst, caused a 2 mag brightening in the lc, which is classified as the z and-type of the outburst.conclusions: the very high nebular emission and the presence of a disk-like h i region encompassing the wd, as indicated by a significant broadening and high flux of the raman-scattered o vi 6825 å line during the outburst, is consistent with the ionisation structure of hot components in symbiotic stars during active phases. full table 1 and table 6 are only available at the cds are available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/604/a48 | new outburst of the symbiotic nova ag pegasi after 165 yr |
low-luminosity active galactic nuclei (llagn) are special among their kind due to the profound structural changes that the central engine experiences at low accretion rates (≲ 10−3 in eddington units). the disappearance of the accretion disc - the blue bump - leaves behind a faint optical nuclear continuum whose nature has been largely debated. this is mainly due to serious limitations on the observational side imposed by the starlight contamination from the host galaxy and the absorption by hydrogen, preventing the detection of these weak nuclei in the infrared (ir) to ultraviolet (uv) range. we addressed these challenges by combining multi-wavelength sub-arcsecond resolution observations - able to isolate the genuine nuclear continuum - with nebular lines in the mid-ir, which allowed us to indirectly probe the shape of the extreme uv continuum. we found that eight of the nearest prototype llagn are compatible with pure compact jet emission over more than ten orders of magnitude in frequency. this consists of self-absorbed synchrotron emission from radio to the uv plus the associated synchrotron self-compton component dominating the emission in the uv to x-ray range. additionally, the llagn continua show two particular characteristics when compared with the typical jet spectrum seen in radio galaxies: (i) a very steep spectral slope in the ir-to-optical/uv range (−3.7 < α0 < −1.3; fν ∝ να0); and (ii) a very high turnover frequency (0.2-30 thz; 1.3 mm-10 μm) that separates the optically thick radio emission from the optically thin continuum in the ir-to-optical/uv range. these attributes can be explained if the synchrotron continuum is mainly dominated by thermalised particles at the jet base or the corona with considerably high temperatures, whereas only a small fraction of the energy (∼20%) would be distributed along the high-energy power-law tail of accelerated particles. on the other hand, the nebular gas excitation in llagn is in agreement with photo-ionisation from inverse compton radiation (αx ∼ −0.7), which would dominate the nuclear continuum shortwards of ∼3000 å, albeit a possible contribution from low-velocity shocks (< 500 km s−1) to the line excitation cannot be discarded. no sign of a standard hot accretion disc is seen in our sample of llagn, nevertheless, a weak cold disc (< 3000 k) is detected at the nucleus of the sombrero galaxy, though its contribution to the nebular gas excitation is negligible. our results suggest that the continuum emission in llagn is dominated at all wavelengths by undeveloped jets, powered by a thermalised particle distribution with high energies, on average. this is in agreement with their compact morphology and their high turnover frequencies. this behaviour is similar to that observed in peaked-spectrum radio sources and also compact jets in quiescent black hole x-ray binaries. nevertheless, the presence of extended jet emission at kiloparsec scales for some of the objects in the sample is indicative of past jet activity, suggesting that these nuclei may undergo a rejuvenation event after a more active phase that produced their extended jets. these results imply that the dominant channel for energy release in llagn is mainly kinetic via the jet, rather than the radiative one. this has important implications in the context of galaxy evolution, since llagn probably represent a major but underestimated source of kinetic feedback in galaxies. the flux distribution of the nine llagn in the sample are only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/670/a22 | compact jets dominate the continuum emission in low-luminosity active galactic nuclei |
we matched the astrometry of central stars (css) of spectroscopically confirmed galactic planetary nebulae (pne) with dr2 gaia parallaxes (p), finding 430 targets in common with p > 0 and $| {\sigma }_{{\rm{p}}}/p| \lt 1$ ∣ σ p / p ∣ < 1 . a catalog of pne whose css have dr2 gaia parallaxes is presented in table 1. we compared dr2 parallaxes with those in the literature, finding good correlation between the two samples. we used pne parallaxes to calibrate the galactic pn distance scale. restricting the sample to objects with 20% parallax accuracy, we derive the distance scale $\mathrm{log}({r}_{\mathrm{pc}})\,=-(0.226\pm 0.0155)\times \mathrm{log}({s}_{{\rm{h}}\beta })$ log ( r pc ) = - ( 0.226 ± 0.0155 ) × log ( s h β ) $-\,(3.920\pm 0.215)$ - ( 3.920 ± 0.215 ) , which represents a notable improvement with respect to previous ones. we found that the ionized mass versus optical thickness distance scale for galactic pne is not as constrained by the gaia calibrators, but gives important insight into the nature of the pne, and is essential to define the domain for our distance scale application. we placed the css whose distance has been determined directly by parallax on the hr diagram, and found that their location on the post-asymptotic-giant-branch (agb) h-burning evolutionary tracks is typical for post-agb stars. | the population of galactic planetary nebulae: a study of distance scales and central stars based on the second gaia release |
we report the results from a pilot search for radio recombination line (rrl) emission at millimeter wavelengths in a small sample of pre-planetary nebulae (ppne) and young pne (ypne) with emerging central ionized regions. observations of the h30α, h31α, h39α, h41α, h48β, h49β, h51β, and h55γ lines at 1 and 3 mm have been performed with the iram 30 m radio telescope. these lines are excellent probes of the dense inner (≲150 au) and heavily obscured regions of these objects, where the yet unknown agents for pn-shaping originate. we detected mm-rrls in three objects: crl 618, mwc 922, and m 2-9. for crl 618, the only ppn with previous published detections of h41α, h35α, and h30α emission, we find significant changes in the line profiles indicating that current observations are probing regions of the ionized wind with larger expansion velocities and mass-loss rate than 29 yr ago. in the case of mwc 922, we observe a drastic transition from single-peaked profiles at 3 mm (h39α and h41α) to double-peaked profiles at 1 mm (h31α and h30α), which is consistent with maser amplification of the highest frequency lines; the observed line profiles are compatible with rotation and expansion of the ionized gas, probably arranged in a disk+wind system around a 5-10 m⊙ central mass. in m 2-9, the mm-rrl emission appears to be tracing a recent mass outburst by one of the stars of the central binary system. we present the results from non-lte line and continuum radiative transfer models, which enables us to constrain the structure, kinematics, and physical conditions (electron temperature and density) of the ionized cores of our sample. we find temperatures te 6000-17 000 k, mean densities ne 105-108 cm-3, radial density gradients ne ∝ r- αn with αn 2-3.5, and motions with velocities of 10-30 km s-1 in the ionized wind regions traced by these mm-wavelength observations. we deduce mass-loss rates of ṁpagb ≈ 10-6-10-7 m⊙ yr-1, which are significantly higher than the values adopted by stellar evolution models currently in use and would result in a transition from the asymptotic giant branch to the pn phase faster than hitherto assumed. the reduced spectra as fits files are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/603/a67 | a pilot search for mm-wavelength recombination lines from emerging ionized winds in pre-planetary nebulae candidates |
magnetic energy around compact objects often dominates over plasma rest mass, and its dissipation can power the object's luminosity. we describe a dissipation mechanism that works faster than magnetic reconnection. the mechanism involves two strong alfvén waves with anti-aligned magnetic fields b1 and b2 that propagate in opposite directions along the background magnetic field b0 and collide. the collision forms a thin current sheet perpendicular to b0, which absorbs the incoming waves. the current sheet is sustained by an electric field e breaking the magnetohydrodynamic condition e < b and accelerating particles to high energies. we demonstrate this mechanism with kinetic plasma simulations using a simple setup of two symmetric plane waves with amplitude a = b1/b0 = b2/b0 propagating in a uniform b0. the mechanism is activated when a > 1/2. it dissipates a large fraction of the wave energy, f = (2a - 1)/a2, reaching 100% when a = 1. the plane geometry allows one to see the dissipation process in a one-dimensional simulation. we also perform two-dimensional simulations, enabling spontaneous breaking of the plane symmetry by the tearing instability of the current sheet. at moderate a of main interest, the tearing instability is suppressed. dissipation transitions to normal, slower, magnetic reconnection at a ≫ 1. the fast dissipation described in this paper may occur in various objects with perturbed magnetic fields, including magnetars, jets from accreting black holes, and pulsar wind nebulae. | fast dissipation of colliding alfvén waves in a magnetically dominated plasma |
we present a hyperspectral cube of the crab nebula obtained with the imaging fourier transform spectrometer sitelle on the canada-france-hawaii telescope. we describe our techniques used to deconvolve the 310 000 individual spectra ($r = 9\, 600$) containing hα, [n ii] λλ6548, 6583, and [s ii] λλ6716, 6731 emission lines and create a detailed 3d reconstruction of the supernova (sn) remnant (snr) assuming uniform global expansion. we find that the general boundaries of the 3d volume occupied by the crab are not strictly ellipsoidal as commonly assumed, and instead appear to follow a 'heart-shaped' distribution that is symmetrical about the plane of the pulsar wind torus. conspicuous restrictions in the bulk distribution of gas consistent with constrained expansion coincide with positions of the dark bays and east-west band of he-rich filaments, which may be associated with interaction with a pre-existing circumstellar disc. the distribution of filaments follows an intricate honeycomb-like arrangement with straight and rounded boundaries at large and small scales that are anticorrelated with distance from the centre of expansion. the distribution is not unlike the large-scale rings observed in snrs 3c 58 and cassiopeia a, where it has been attributed to turbulent mixing processes that encouraged outwardly expanding plumes of radioactive 56ni-rich ejecta. these characteristics reflect critical details of the original sn of 1054 ce and its progenitor star, and may favour a low-energy explosion of an iron-core progenitor. we demonstrate that our main findings are robust despite regions of non-homologous expansion driven by acceleration of material by the pulsar wind nebula. | 3d mapping of the crab nebula with sitelle - i. deconvolution and kinematic reconstruction |
wide-field h α images of the galactic plane have revealed a new supernova remnant (snr) nearly 3 deg in diameter centred at l = 107.0, b = +9.0. deep and higher resolution h α and [o iii] 5007 å images show dozens of h α filaments along the remnant's northern, western, and southwestern limbs, but few [o iii] bright filaments. the nebula is well detected in the h α virginia tech spectral-line survey images, with many of its brighter filaments even visible on digital sky survey images. low-dispersion spectra of several filaments show either balmer dominated, non-radiative filaments, or the more common snr radiative filaments with [s ii]/h α ratios above 0.5, consistent with shock-heated line emission. emission line ratios suggest shock velocities ranging from ≤70 km s-1 along its western limb to ≃ 100 km s-1 along its northwestern boundary. while no associated x-ray emission is seen in rosat images, faint 1420 mhz radio emission appears coincident with its western and northern limbs. based on an analysis of the remnant's spatially resolved h α and [o iii] emissions, we estimate the remnant's distance at ∼1.5-2.0 kpc implying a physically large (dia. = 75-100 pc) and old (90-110 × 103 yr) snr in its post-sedov radiative phase of evolution expanding into a low-density interstellar medium (n0 = 0.05-0.2 cm-3) and lying some 250-300 pc above the galactic plane. | g107.0+9.0: a new large optically bright, radio, and x-ray faint galactic supernova remnant in cepheus |
we investigate the effects of stellar populations and sizes on lyα escape in 27 spectroscopically confirmed and 35 photometric lyα emitters (laes) at z ≈ 2.65 in seven fields of the boötes region of the noao deep wide-field survey. we use deep hst/wfc3 imaging to supplement ground-based observations and infer key galaxy properties. compared to typical star-forming galaxies (sfgs) at similar redshifts, the laes are less massive (m ⋆ ≈ 107-109 m ⊙), younger (ages ≲1 gyr), smaller (re< 1 kpc), and less dust-attenuated (e(b-v) ≤ 0.26 mag) but have comparable star formation rates (sfrs ≈ 1-100 m ⊙ yr-1). some of the laes in the sample may be very young galaxies having low nebular metallicities (z neb ≲ 0.2 z ⊙) and/or high ionization parameters ( $\mathrm{log}({\rm{u}})\,\gtrsim \,-2.4$ ). motivated by previous studies, we examine the effects of the concentration of star formation and gravitational potential on lyα escape by computing sfr surface density, σsfr, and specific sfr surface density, σssfr. for a given σsfr, the lyα escape fraction is higher for laes with lower stellar masses. the laes have a higher σssfr, on average, compared to sfgs. our results suggest that compact star formation in a low gravitational potential yields conditions amenable to the escape of lyα photons. these results have important implications for the physics of lyα radiative transfer and for the type of galaxies that may contribute significantly to cosmic reionization. | lyα escape from low-mass, compact, high-redshift galaxies |
new x-ray and optical observations shed light on the remarkable x-ray filament of the gamma-ray pulsar psr j2030+4415. images of the associated hα bow shock's evolution over the past decade compared with its velocity structure provide an improved kinematic distance of ~0.5 kpc. these velocities also imply that the pulsar spin axis lies ~15° from the proper motion axis, which is close to the plane of the sky. the multi-bubble shock structure indicates that the bow shock standoff was compressed to a small value ~20-30 yr ago when the pulsar broke through the bow shock to its present bubble. this compression allowed multi-tev pulsar e ± to escape to the external interstellar medium (ism), lighting up an external magnetic field structure as the filament. the narrow filament indicates excellent initial confinement and the full 15' (2.2 pc = 7 lt-yr) projected length of the filament indicates rapid e ± propagation to its end. spectral variation along the filament suggests that the injected particle energy evolved during the breakthrough event. | the long filament of psr j2030+4415 |
we use medium-resolution keck/echellette spectrograph and imager spectroscopy of bright quasars to study cool gas traced by ca ii λλ3934, 3969 and na i λλ5891, 5897 absorption in the interstellar/circumgalactic media of 21 foreground star-forming galaxies at redshifts 0.03 < z < 0.20 with stellar masses 7.4 ≤ log m */m ⊙ ≤ 10.6. the quasar-galaxy pairs were drawn from a unique sample of sloan digital sky survey quasar spectra with intervening nebular emission, and thus have exceptionally close impact parameters (r ⊥ < 13 kpc). the strength of this line emission implies that the galaxies' star formation rates (sfrs) span a broad range, with several lying well above the star-forming sequence. we use voigt profile modeling to derive column densities and component velocities for each absorber, finding that column densities n(ca ii) > 1012.5 cm-2 (n(na i) > 1012.0 cm-2) occur with an incidence f c(ca ii) = 0.63+0.10 -0.11 (f c(na i) = 0.57+0.10 -0.11). we find no evidence for a dependence of f c or the rest-frame equivalent widths wr (ca ii k) or wr (na i 5891) on r ⊥ or m *. instead, wr (ca ii k) is correlated with local sfr at >3σ significance, suggesting that ca ii traces star formation-driven outflows. while most of the absorbers have velocities within ±50 km s-1 of the host redshift, their velocity widths (characterized by δv 90) are universally 30-177 km s-1 larger than that implied by tilted-ring modeling of the velocities of interstellar material. these kinematics must trace galactic fountain flows and demonstrate that they persist at r ⊥ > 5 kpc. finally, we assess the relationship between dust reddening and wr (ca ii k) (wr (na i 5891)), finding that 33% (24%) of the absorbers are inconsistent with the best-fit milky way e(b-v)-wrrelations at >3σ significance. | on the kinematics of cold, metal-enriched galactic fountain flows in nearby star-forming galaxies |
the central star of the planetary nebula (pn) hubi 1 has been recently proposed to have experienced a very late thermal pulse (vltp), but the dilution of the emission of the recent ejecta by that of the surrounding h-rich old outer shell has so far hindered confirming its suspected h-poor nature. we present here an analysis of the optical properties of the ejecta in the innermost regions of hubi 1 using megara high-dispersion integral field and osiris intermediate-dispersion long-slit spectroscopic observations obtained with the 10.4-m gran telescopio de canarias. the unprecedented tomographic capability of megara to resolve structures in velocity space allowed us to disentangle for the first time the hα and hβ emission of the recent ejecta from that of the outer shell. the recent ejecta is found to have much higher extinction than the outer shell, implying the presence of large amounts of dust. the spatial distribution of the emission from the ejecta and the locus of key line ratios in diagnostic diagrams probe the shock excitation of the inner ejecta in hubi 1, in stark contrast with the photoionization nature of the h-rich outer shell. the abundances of the recent ejecta have been computed using the mappings v code under a shock scenario. they are found to be consistent with a born-again ejection scenario experienced by the progenitor star, which is thus firmly confirmed as a new 'born-again' star. | chemistry and physical properties of the born-again planetary nebula hubi 1 |
one of the great surprises of the late 1980s was the discovery that the [o iii] λ5007 planetary nebula luminosity function (pnlf) could be used as a precision extragalactic standard candle. despite the lack of any robust theory for the phenomenon, the technique passed a myriad of internal and external tests, and became an extremely reliable tool for obtaining distances to large galaxies within ∼20 mpc. but in more recent years, the use of the technique has declined, due in part to the changing landscape of cosmology. here we review the history of the pnlf, the experiments that confirmed its utility, and the reasons why interest in the method faded at the turn of the millennium. we also describe how and why the pnlf is making a comeback, and present some of the method's recent results. finally, we discuss how the pnlf must be analyzed in the era of precision cosmology, and detail the issues that must be overcome in order to address the current tension between local measures of the hubble constant and values derived from the microwave background. if these issues can be understood, then the pnlf can provide a useful cross-check on distance measurements out to ∼40 mpc. | the planetary nebula luminosity function in the era of precision cosmology |
we used archival very long baseline interferometry (vlbi) data of active galactic nuclei (agn) observed from 1.4 to 86 ghz to measure the angular size of vlbi radio cores in 8959 agns. we analysed their sky distributions, frequency dependencies, and created the most densely sampled and complete to date distribution map of large-scale scattering properties of the interstellar medium in our galaxy. significant angular broadening of the measured agn core sizes is detected for the sources seen through the galactic plane, and this effect is especially strong at low frequencies (e.g. at 2 ghz). the scattering screens containing electron density fluctuations of hot plasma are mainly concentrated in the galactic plane and manifest clumpy distribution. the region of the strongest scattering is the galactic centre, where the galactic bar and the compact radio source sagittarius a* are located. we have also found the enhancement of scattering strength in regions of the cygnus constellation, supernova remnants taurus a, vela, w78 and cassiopeia a, and the orion nebula. using multifrequency observational data of agn core sizes, we separated the contribution of the intrinsic and scattered sizes to the measured angular diameter for 1411 sources. for the sources observed through the galactic plane, the contribution of the scattered size component is systematically larger than for those seen outside the galactic plane. the derived power-law scattering indices are found to be in good agreement with theoretical predictions for the diffractive-dominated scattering of radio emission in a hot plasma with gaussian distribution of density inhomogeneities. | tracing milky way scattering by compact extragalactic radio sources |
directly characterising the first generations of stars in distant galaxies is a key quest of observational cosmology. we present a case study of id53 at z = 4.77, the uv-brightest (but l⋆) star-forming galaxy at z > 3 in the muse extremely deep field with a mass of ≈109 m⊙. in addition to very strong lyman-α (lyα) emission, we clearly detect the (stellar) continuum and an n v p cygni feature, interstellar absorption, fine-structure emission and nebular c iv emission lines in the 140 h spectrum. continuum emission from two spatially resolved components in hubble space telescope data are blended in the muse data, but we show that the nebular c iv emission originates from a subcomponent of the galaxy. the uv spectrum can be fit with recent bpass stellar population models combined with single-burst or continuous star formation histories (sfhs), a standard initial mass function, and an attenuation law. models with a young age and low metallicity (log10(age/yr) = 6.5-7.6 and [z/h] = −2.15 to −1.15) are preferred, but the details depend on the assumed sfh. the intrinsic hα luminosity of the best-fit models is an order of magnitude higher than the hα luminosity inferred from spitzer/irac data, which either suggests a high escape fraction of ionising photons, a high relative attenuation of nebular to stellar dust, or a complex sfh. the metallicity appears lower than the metallicity in more massive galaxies at z = 3 − 5, consistent with the scenario according to which younger galaxies have lower metallicities. this chemical immaturity likely facilitates lyα escape, explaining why the lyα equivalent width is anti-correlated with stellar metallicity. finally, we stress that uncertainties in sfhs impose a challenge for future inferences of the stellar metallicity of young galaxies. this highlights the need for joint (spatially resolved) analyses of stellar spectra and photo-ionisation models. based on observations obtained with the very large telescope under the large program 1101.a-0127. | deciphering stellar metallicities in the early universe: case study of a young galaxy at z = 4.77 in the muse extremely deep field |
recently, the large high altitude air shower observatory (lhaaso) reported the discovery of 12 ultrahigh-energy (uhe; ɛ ≥ 100 tev) gamma-ray sources located in the galactic plane. a few of these uhe gamma-ray emitting regions are in spatial coincidence with pulsar wind nebulae (pwne). we consider a sample of five sources: two of them are lhaaso sources (lhaaso j1908+0621 and lhaaso j2226+6057) and the remaining three are gev-tev gamma-ray emitters. in addition, x-rays, radio observations, or upper limits are also available for these objects. we study multiwavelength radiation from these sources by considering a pwn origin, where the emission is powered by spin-down luminosity of the associated pulsars. in this leptonic emission model, the electron population is calculated at different times under the radiative (synchrotron and inverse-compton) and adiabatic cooling. we also include the onset of the reverberation phase for the pwn, by assuming radially symmetric expansion. however, in this work, we find that multiwavelength emission can be interpreted before the onset of this phase. the maximum energy of the electrons based on the spectral fit is found to be above 0.1 pev and close to 1 pev. for lhaaso j2226+6057, using its observations in radio to uhe gamma-rays, we find that uhe gamma-rays can be interpreted using electrons with maximum energy of 1 pev. we estimate the upper limits on the minimum lorentz factor of the electrons and it also infers the minimum value of the pair-multiplicity of charged pairs. | study of maximum electron energy of sub-pev pulsar wind nebulae by multiwavelength modelling |
rejuvenating galaxies are unusual galaxies that fully quench and then subsequently experience a "rejuvenation" event to become star-forming once more. rejuvenation rates vary substantially in models of galaxy formation: 10%-70% of massive galaxies are expected to experience rejuvenation by z = 0. measuring the rate of rejuvenation is therefore important for calibrating the strength of star-formation feedback mechanisms. however, these observations are challenging because rejuvenating systems blend in with normal star-forming galaxies in broadband photometry. in this paper, we use the galaxy spectral energy distribution-fitting code prospector to search for observational markers that distinguish normal star-forming galaxies from rejuvenating galaxies. we find that rejuvenating galaxies have smaller balmer absorption line equivalent widths (ews) than normal star-forming galaxies. this is analogous to the well-known "k+a" or post-starburst galaxies, which have strong balmer absorption due to a-stars dominating the light: in this case, rejuvenating systems have a lack of a-stars, instead resembling "o-a" systems. we find star-forming galaxies that have hβ, hγ, and/or hδ absorption ews ≲3 å corresponds to a highly pure selection of rejuvenating systems. interestingly, while this technique is highly effective at identifying mild rejuvenation, "strongly" rejuvenating systems remain nearly indistinguishable from star-forming galaxies due to the well-known stellar outshining effect. we conclude that measuring balmer absorption line ews in star-forming galaxy populations is an efficient method to identify rejuvenating populations, and discuss several techniques to either remove or resolve the nebular emission which typically lies on top of these absorption lines. | a simple spectroscopic technique to identify rejuvenating galaxies |
we present the results from the hitomi soft gamma-ray detector (sgd) observation of the crab nebula. the main part of sgd is a compton camera, which in addition to being a spectrometer, is capable of measuring polarization of gamma-ray photons. the crab nebula is one of the brightest x-ray/gamma-ray sources on the sky, and the only source from which polarized x-ray photons have been detected. sgd observed the crab nebula during the initial test observation phase of hitomi. we performed data analysis of the sgd observation, sgd background estimation, and sgd monte carlo simulations, and successfully detected polarized gamma-ray emission from the crab nebula with only about 5 ks exposure time. the obtained polarization fraction of the phase-integrated crab emission (sum of pulsar and nebula emissions) is (22.1% ± 10.6%), and the polarization angle is {110{^{circ}.}7} +{13{^{circ}.}2}/-{13{^{circ}.}0} in the energy range of 60-160 kev (the errors correspond to the 1 σ deviation). the confidence level of the polarization detection was 99.3%. the polarization angle measured by sgd is about one sigma deviation with the projected spin axis of the pulsar, {124{^{circ}.}0} ± {0{^{circ}.}1}. | detection of polarized gamma-ray emission from the crab nebula with the hitomi soft gamma-ray detector |
we present the largest compilation to date of optical observations during and following fast radio bursts (frbs). the data set includes our dedicated simultaneous and follow-up observations, as well as serendipitous archival survey observations, for a sample of 15 well-localized frbs: eight repeating and seven one-off sources. our simultaneous (and nearly simultaneous with a 0.4 s delay) optical observations of 13 (1) bursts from the repeating frb 20220912a provide the deepest such limits to date for any extragalactic frb, reaching a luminosity limit of ν lν≲ 1042 erg s-1 (≲2 × 1041 erg s-1) with 15-400 s exposures; an optical-flux-to-radio-fluence ratio of f opt/f radio ≲ 10-7 ms-1 (≲10-8 ms-1); and a flux ratio of f opt/f radio ≲ 0.02-≲2 × 10-5 (≲10-6) on millisecond to second timescales. these simultaneous limits provide useful constraints in the context of frb emission models, such as the pulsar magnetosphere and pulsar nebula models. interpreting all available optical limits in the context of the synchrotron maser model, we find that they constrain the flare energies to ≲1043-1049 erg (depending on the distances of the various repeating frbs, with ≲1039 erg for the galactic sgr 1935+2154). these limits are generally at least an order of magnitude larger than those inferred from the frbs themselves, although in the case of frb 20220912a our simultaneous and rapid follow-up observations severely restrict the model parameter space. we conclude by exploring the potential of future simultaneous and rapid-response observations with large optical telescopes. | limits on simultaneous and delayed optical emission from well-localized fast radio bursts |
this is the first in a series of papers that present sets of different results for 136 compact, known planetary nebulae within a 10 × 10 degree region of the galactic bulge. we use a large, previously unpublished sample of our own extensive eso 8-m vlt deep imaging and spectroscopic data. this is combined with archival deep hubble space telescope imaging where available to provide a detailed morphological classification and study. the influence of angular resolution and sensitivity when assigning a morphology is discussed. a large fraction (68 per cent) of the sample are shown to be bipolars and the implications for this in the context of planetary nebulae progenitors are explored. four new planetary nebula central stars are also identified which are not in gaia. this is based on both very large telescope (vlt) and deep archival pan-starrs broad-band imagery. some 11 putative central stars previously reported, based on gaia positions, are also not the true central star. in other cases, the gaia central stars reported in the literature are actually based on the overall centroid position of a very compact planetary nebula rather than the actual central star within it. gaia parallax distances and kinematic ages for pne in this sample are provided where possible based on fresh angular size measures from the new vlt imagery and gaia distances and literature expansion velocities when available. all these results are discussed within the context of the overall characteristics of the galactic bulge and its planetary nebula population. | morphologies and central stars of planetary nebulae in the galactic bulge from vlt, hst and pan-starrs imaging |
we characterize massive stars (m > 8 m ⊙) in the nearby (d ∼ 0.8 mpc) extremely metal-poor (z ∼ 5% z ⊙) galaxy leo a using hubble space telescope ultraviolet (uv), optical, and near-infrared (nir) imaging along with keck/low-resolution imaging spectrograph and mmt/binospec optical spectroscopy for 18 main-sequence ob stars. we find that: (a) 12 of our 18 stars show emission lines, despite not being associated with an h ii region, suggestive of stellar activity (e.g., mass loss, accretion, binary star interaction), which is consistent with previous predictions of enhanced activity at low metallicity; (b) six are be stars, which are the first to be spectroscopically studied at such low metallicity-these be stars have unusual panchromatic seds; (c) for stars well fit by the tlusty nonlocal thermodynamic equilibrium models, the photometric and spectroscopic values of log(teff) and log(g) agree to within ∼0.01 dex and ∼0.18 dex, respectively, indicating that near-uv/optical/nir imaging can be used to reliably characterize massive (m ∼8-30 m ⊙) main-sequence star properties relative to optical spectroscopy; (d) the properties of the most-massive stars in h ii regions are consistent with constraints from previous nebular emission line studies; and (e) 13 stars with m > 8m ⊙ are >40 pc from a known star cluster or h ii region. our sample comprises ∼50% of all known massive stars at z ≲ 10% z ⊙with derived stellar parameters, high-quality optical spectra, and panchromatic photometry. *this paper includes data gathered with the 10 m keck telescopes located at w. m. keck observatory, hawaii and with the 6.5 m multiple mirror telescope (mmt) located at mt. hopkins, arizona. | a panchromatic study of massive stars in the extremely metal-poor local group dwarf galaxy leo a |
evolved low- to intermediate-mass stars are known to shed their gaseous envelope into a large, dusty, molecule-rich circumstellar nebula which typically develops a high degree of structural complexity. most of the large-scale, spatially correlated structures in the nebula are thought to originate from the interaction of the stellar wind with a companion. as part of the atomium large programme, we observed the m-type asymptotic giant branch (agb) star r hydrae with the atacama large millimeter/submillimeter array. the morphology of the inner wind of r hya, which has a known companion at ∼3500 au, was determined from maps of co and sio obtained at high angular resolution. a map of the co emission reveals a multi-layered structure consisting of a large elliptical feature at an angular scale of ∼10″ that is oriented along the north-south axis. the wind morphology within the elliptical feature is dominated by two hollow bubbles. the bubbles are on opposite sides of the agb star and lie along an axis with a position angle of ∼115°. both bubbles are offset from the central star, and their appearance in the sio channel maps indicates that they might be shock waves travelling through the agb wind. an estimate of the dynamical age of the bubbles yields an age of the order of 100 yr, which is in agreement with the previously proposed elapsed time since the star last underwent a thermal pulse. when the co and sio emission is examined on subarcsecond angular scales, there is evidence for an inclined, differentially rotating equatorial density enhancement, strongly suggesting the presence of a second nearby companion. the position angle of the major axis of this disc is ∼70° in the plane of the sky. we tentatively estimate that a lower limit on the mass of the nearby companion is ∼0.65 m⊙ on the basis of the highest measured speeds in the disc and the location of its inner rim at ∼6 au from the agb star. | atomium: the astounding complexity of the near circumstellar environment of the m-type agb star r hydrae. i. morpho-kinematical interpretation of co and sio emission |
we discuss the origin of the neon isotopic signatures in chondrites and in the terrestrial mantle. there are two primary possible origins for neon in the earth's mantle. one origin is the dissolution of a dense primordial atmosphere with a solar composition of 20ne/22ne >13.4 into the mantle in a possible magma ocean stage during earth's accretion. the second origin, developed in this study, is that mantle neon was already in earth's parent bodies because of refractory grain irradiation by solar wind. we propose that solar wind implantation occurred early on dust within the accretion disk to allow such irradiation. because solar wind implantation fractionates neon isotopes, the heavier isotopes are implanted deeper than the lighter ones because of different kinetic energies, and the process of implantation, if coupled with sputtering, leads to a steady state neon isotopic ratio (20ne/22ne ∼12.7) that is similar to what is observed in mantle-derived rocks (12.5-12.9), lunar soil grains (∼12.9) and certain gas-rich chondrites from all classes (enstatite, ordinary, rumuruti). using a dust transport model in a turbulent and irradiated solar nebula, we estimated the equivalent irradiation age of a population of dust particles at three different distances from the sun (0.8, 1, 1.2 au) and converted these ages into neon concentrations and isotopic ratios. the dust subsequently coagulated to form earth's parent bodies, which have the mean neon isotopic composition of the irradiated dust (non-irradiated dust is assumed to be free of neon). if this scenario of solar wind implantation coupled with sputtering in the precursors of earth's parent bodies is correct, it offers a simple alternative to the model of solar nebula gas incorporation by dissolution in a magma ocean. | the origin of the neon isotopes in chondrites and on earth |
in order to study the nature, origin, and impact of turbulent velocity fluctuations in the ionized gas of the orion nebula, we apply a variety of statistical techniques to observed velocity cubes. the cubes are derived from high resolving power (r ≈ 40 000) longslit spectroscopy of optical emission lines that span a range of ionizations. from velocity channel analysis (vca), we find that the slope of the velocity power spectrum is consistent with predictions of kolmogorov theory between scales of 8 and 22 arcsec (0.02 to 0.05 pc). the outer scale, which is the dominant scale of density fluctuations in the nebula, approximately coincides with the autocorrelation length of the velocity fluctuations that we determine from the second-order velocity structure function. we propose that this is the principal driving scale of the turbulence, which originates in the autocorrelation length of dense cores in the orion molecular filament. by combining analysis of the non-thermal linewidths with the systematic trends of velocity centroid versus ionization, we find that the global champagne flow and smaller scale turbulence each contribute in equal measure to the total velocity dispersion, with respective root-mean-square widths of 4-5 km s-1. the turbulence is subsonic and can account for only one half of the derived variance in ionized density, with the remaining variance provided by density gradients in photoevaporation flows from globules and filaments. intercomparison with results from simulations implies that the ionized gas is confined to a thick shell and does not fill the interior of the nebula. | turbulence in the ionized gas of the orion nebula |
the abundance of volatile elements in the silicate earth relative to primitive chondrites provides an important constraint on the thermochemical evolution of the planet. however, an overabundance of indium relative to elements with similar nebular condensation temperatures is a source of debate. here we use ab initio molecular dynamics simulations to explore the vaporization behavior of indium from pyrolite melt at conditions of the early magma ocean just after the moon-forming impact. we then compare this to the vaporization behavior of other minor elements. when considering the volatility of the elements from the magma ocean in the absence of the solar nebula gas, we find that there is no overabundance of indium. on the contrary, there is a slight deficit in the abundance of indium, which is consistent with its moderately siderophile nature. thus, we propose that a high-energy moon-forming impact may have had a more significant contribution to volatile depletion than previously believed. | earth's volatile depletion trend is consistent with a high-energy moon-forming impact |
legionella pneumophila is, by far, the species most frequently associated with legionnaires’ disease (ld). human infection occurs almost exclusively by aerosol inhalation which places the bacteria in juxtaposition with alveolar macrophages. ld risk management is based on controlling water quality by applying standardized procedures. however, to gain a better understanding of the real risk of exposure, there is a need (i) to investigate under which conditions legionella may be aerosolized and (ii) to quantify bacterial deposition into the respiratory tract upon nebulization. in this study, we used an original experimental set-up that enables the generation of aerosol particles containing l. pneumophila under various conditions. using flow cytometry in combination with qpcr and culture, we determined (i) the size of the aerosols and (ii) the concentration of viable legionella forms that may reach the thoracic region. we determined that the 0.26-2.5 μm aerosol size range represents 7% of initial bacterial suspension. among the viable forms, 0.7% of initial viable bacterial suspension may reach the pulmonary alveoli. in conclusion, these deposition profiles can be used to standardize the size of inoculum injected in any type of respiratory tract model to obtain new insights into the dose response for ld. | characterization of aerosols containing legionella generated upon nebulization |
in this work, i estimate the δ18 o and δ17 o values of primordial water in cm chondrites to be 55 ± 13 and 35 ± 9‰, respectively, based on whole-rock o and h data. also, i found that the o and/or h data of antarctic meteorites are biased, which is attributed to terrestrial weathering. this characteristic o isotopic ratio of water together with corresponding water abundances in cm chondrites are consistent with the origin of water as ice processed by photochemical reactions at the outer regions of the solar nebula, where mass-independent o isotopic fractionation and water destruction may have occurred. another possible mechanism to produce the inferred o isotopic ratio of water would be o isotopic fractionation between water vapor and ice, which likely occurred near the condensation front of h2o (snow line) in the solar nebula. the inferred o isotopic ratio of water suggests that carbonate in cm chondrites formed at low temperatures of <150 °c. the o isotopic ratios of primordial water in chondrites other than cm chondrites are not well constrained. | oxygen isotopic ratios of primordial water in carbonaceous chondrites |
context. most planetary nebulae (pne) show beautiful, axisymmetric morphologies despite their progenitor stars being essentially spherical. close binarity is widely invoked to help eject an axisymmetric nebula, after a brief phase of engulfment of the secondary within the envelope of the asymptotic giant branch (agb) star, known as the common envelope (ce). the evolution of the agb would thus be interrupted abruptly, with its still quite massive envelope being rapidly ejected to form the pn, which a priori would be more massive than the pn coming from a single version of the same star.aims: we aim to test this hypothesis by investigating the ionised and molecular masses of a sample consisting of 21 post-ce pne, roughly one-fifth of the known total population of these objects, and to compare them to a large sample of `regular' (i.e. not known to arise from close-binary systems) pne.methods: we gathered data on the ionised and molecular content of our sample from the literature, and carried out molecular observations of several previously unobserved objects. we derived the ionised and molecular masses of the sample by means of a systematic approach, using tabulated, dereddened hβ fluxes to find the ionised mass, and 12co j = 2-1 and j = 3-2 observations to estimate the molecular mass.results: there is a general lack of molecular content in post-ce pne. our observations only reveal molecule-rich gas around ngc 6778, which is distributed into a low-mass, expanding equatorial ring lying beyond the ionised broken ring previously observed in this nebula. the only two other objects showing molecular content (from the literature) are ngc 2346 and ngc 7293. once we derive the ionised and molecular masses, we find that post-ce pne arising from single-degenerate (sd) systems are just as massive, on average, as members of the `regular' pne sample, whereas post-ce pne arising from double-degenerate systems are considerably more massive, and show substantially higher linear momentum and kinetic energy than sd systems and `regular' pne. reconstruction of the ce of four objects, for which a wealth of data on the nebulae and complete orbital parameters are available, further suggests that the mass of sd nebulae actually amounts to a very small fraction of the envelope of their progenitor stars. this leads to the uncomfortable questions of where the rest of the envelope is and why we cannot detect it in the stars' vicinity, raising serious doubts about our understanding of these intriguing objects. reduced data are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/658/a17 | the ionised and molecular mass of post-common-envelope planetary nebulae. the missing mass problem |
we examine the evolution of late-time, optical nebular features of type ia supernovae (sne ia) using a sample consisting of 160 spectra of 27 normal sne ia taken from the literature as well as unpublished spectra of sn 2008q and asassn-14lp. particular attention was given to nebular features between 4000 and 6000 å in terms of temporal changes in width and central wavelength. analysis of the prominent late-time 4700 å feature shows a progressive central wavelength shift from ∼4600 å to longer wavelengths out to at least day +300 for our entire sample. we find no evidence for the feature's redward shift slowing or halting at an [fe iii] blend centroid ∼4700 å as has been proposed. the width of this feature also steadily increases with a fwhm ∼170 å at day +100 growing to 200 å or more by day +350. two weaker adjacent features at around 4850 and 5000 å exhibit similar redshifts to that of the 4700 å feature but show no change in width until very late times. we discuss possible causes for the observed redshifts of these late-time optical features including contribution from [co ii] emission at early nebular epochs and the emergence of additional features at later times. we conclude that the ubiquitous redshift of these common late-time sn ia spectral features is not mainly due to a decrease in line velocities of forbidden fe emissions, but the result of decreasing line velocities and opacity of permitted fe absorption lines. | progressive redshifts in the late-time spectra of type ia supernovae |
we develop a framework for a new definition of the galactic midplane, allowing for tilt ({θ }tilt}; rotation about galactic azimuth 90°) and roll ({θ }roll}; rotation about galactic azimuth 0°) of the midplane with respect to the current definition. derivation of the tilt and roll angles also determines the solar height above the midplane. here we use nebulae from the wide-field infrared survey explorer (wise) catalog of galactic h ii regions to define the galactic high-mass star formation (hmsf) midplane. we analyze various subsamples of the wise catalog and find that all have galactic latitude scale heights near 0.°30 and z-distribution scale heights near 30 {pc}. the vertical distribution for small (presumably young) h ii regions is narrower than that of larger (presumably old) h ii regions (∼25 {pc} versus ∼40 {pc}), implying that the larger regions have migrated further from their birth sites. for all h ii region subsamples and for a variety of fitting methodologies, we find that the hmsf midplane is not significantly tilted or rolled with respect to the currently defined midplane, and, therefore, the sun is near to the hmsf midplane. these results are consistent with other studies of hmsf, but are inconsistent with many stellar studies, perhaps because of asymmetries in the stellar distribution near the sun. our results are sensitive to latitude restrictions and also to the completeness of the sample, indicating that similar analyses cannot be done accurately with less complete samples. the midplane framework we develop can be used for any future sample of galactic objects to redefine the midplane. | a galactic plane defined by the milky way h ii region distribution |
whether planetary nebulae (pne) are predominantly the product of binary stellar evolution as some population synthesis models (psm) suggest remains an open question. around 50 short-period binary central stars (p ∼ 1 d) are known, but with only four with measured orbital periods over 10 d, our knowledge is severely incomplete. here we report on the first discovery from a systematic southern african large telescope (salt) high resolution spectrograph (hrs) survey for long-period binary central stars. we find a 142 d orbital period from radial velocities of the central star of ngc 1360, hip 16566. ngc 1360 appears to be the product of common-envelope (ce) evolution, with nebula features similar to post-ce pne, albeit with an orbital period considerably longer than expected to be typical of post-ce psm. the most striking feature is a newly identified ring of candidate low-ionization structures. previous spatiokinematic modelling of the nebula gives a nebula inclination of 30° ± 10°, and assuming the binary nucleus is coplanar with the nebula, multiwavelength observations best fit a more massive, evolved white dwarf (wd) companion. a wd companion in a 142 d orbit is not the focus of many psm, making ngc 1360 a valuable system with which to improve future psm work. hip 16566 is amongst many central stars in which large radial velocity variability was found by low-resolution surveys. the discovery of its binary nature may indicate long-period binaries may be more common than psm models predict. | salt hrs discovery of a long-period double-degenerate binary in the planetary nebula ngc 1360 |
we present narrowband near-infrared images of a sample of 11 galactic planetary nebulae (pne) obtained in the h2 2.122 μm and brγ 2.166 μm emission lines and the k c 2.218 μm continuum. these images were collected with the wide-field infrared camera on the 3.6 m canada-france-hawaii telescope (cfht); their unprecedented depth and wide field of view allow us to find extended nebular structures in h2 emission in several pne, some of these being the first detection. the nebular morphologies in h2 emission are studied in analogy with the optical images, and indication of stellar wind interactions is discussed. in particular, the complete structure of the highly asymmetric halo in ngc 6772 is witnessed in h2, which strongly suggests interaction with the interstellar medium. our sample confirms the general correlation between h2 emission and the bipolarity of pne. the knotty or filamentary fine structures of the h2 gas are resolved in the inner regions of several ring-like pne, also confirming the previous argument that h2 emission mostly comes from knots or clumps embedded within fully ionized material at the equatorial regions. moreover, the h2 image of the butterfly-shaped sh 1-89, after removal of field stars, clearly reveals a tilted ring structure at the waist. these high-quality cfht images justify follow-up detailed morphokinematic studies that are desired in order to deduce the true physical structures of a few pne in the sample. based on observations obtained with wircam, a joint project of cfht, taiwan, korea, canada, and france, at the canada-france-hawaii telescope (cfht), which is operated by the national research council (nrc) of canada, the institut national des sciences de l’univers of the centre national de la recherche scientifique of france, and the university of hawaii. | extended structures of planetary nebulae detected in h2 emission |
we explore the well-observed type iip supernova 2013ej with peculiar luminosity evolution. it is found that the hydrodynamic model cannot reproduce in detail the bolometric luminosity at both the plateau and the radioactive tail. yet the ejecta mass of 23-26 m⊙ and the kinetic energy of (1.2-1.4) × 1051 erg are determined rather confidently. we suggest that the controversy revealed in hydrodynamic simulations stems from the strong asphericity of the 56ni ejecta. an analysis of the asymmetric nebular h α line and of the peculiar radioactive tail made it possible to recover parameters of the asymmetric bipolar 56ni ejecta with the heavier jet residing in the rear hemisphere. the inferred 56ni mass is 0.039 m⊙, twice as large compared to a straightforward estimate from the bolometric luminosity at the early radioactive tail. the bulk of ejected 56ni has velocities in the range of 4000-6500 km s-1. the linear polarization predicted by the model with the asymmetric ionization produced by bipolar 56ni ejecta is consistent with the observational value. | luminous type iip sn 2013ej with high-velocity 56ni ejecta |
wr 112 is a dust-forming carbon-rich wolf-rayet (wc) binary with a dusty circumstellar nebula that exhibits a complex asymmetric morphology, which traces the orbital motion and dust formation in the colliding winds of the central binary. unraveling the complicated circumstellar dust emission around wr 112 therefore provides an opportunity to understand the dust formation process in colliding-wind wc binaries. in this work, we present a multi-epoch analysis of the circumstellar dust around wr 112 using seven high spatial resolution (fwhm ∼ 0"3-0"4) n-band (λ ∼ 12 μm) imaging observations spanning almost 20 yr and that includes images obtained from subaru/comics in 2019 october. in contrast to previous interpretations of a face-on spiral morphology, we observe clear evidence of proper motion of the circumstellar dust around wr 112 consistent with a nearly edge-on spiral with a θs = 55° half-opening angle and a ∼20 yr period. the revised near edge-on geometry of wr 112 reconciles previous observations of highly variable nonthermal radio emission that was inconsistent with a face-on geometry. we estimate a revised distance to wr 112 of $d={3.39}_{-0.84}^{+0.89}$ kpc based on the observed dust expansion rate and a spectroscopically derived wc terminal wind velocity of ${v}_{\infty }=1230\pm 260$ km s-1. with the newly derived wr 112 parameters, we fit optically thin dust spectral energy distribution models and determine a dust production rate of ${\dot{m}}_{{\rm{d}}}={2.7}_{-1.3}^{+1.0}\times {10}^{-6}$ m⊙ yr-1, which demonstrates that wr 112 is one of the most prolific dust-making wc systems known. | resolving decades of periodic spirals from the wolf-rayet dust factory wr 112 |
we develop a physical framework for interpreting high-resolution images and kinematics of pre-planetary nebulae (“prepne”). we use hydrodynamical models to infer the historical properties of fast collimated nuclear flows (“jet”) that successfully form hollow, candle-shaped lobes over ≈103 yr, including the density, momenta, and geometry of the jet and its environment. next we vary the most influential parameters of this “baseline” model to investigate how changes in the flow parameters affect the model outcomes after 900 yr. several generic conclusions emerge, such as the injected flows that create the hollow lobes must be light, “tapered,” and injected considerably faster than the lobe expansion speed. multipolar and starfish prepne probably evolve from wide-angle flows in which thin-shell instabilities corrugate their leading edges. we show how the common linear correlation of doppler shift and position along the lobe is a robust outcome of the interaction of tapered diverging streamlines with the lobes’ curved walls. finally, we probe how modest toroidal magnetic fields added to the fast flow affect the outcome of the baseline model. we conclude that the light, field-free, tapered baseline flow model is not only a successful and universal paradigm for unraveling the histories of lobe formation in prepne, but also provides a comprehensive, inclusive framework for understanding the details of the shapes, sizes, and internal kinematics of their edges. | models of the mass-ejection histories of pre-planetary nebulae. iii. the shaping of lobes by post-agb winds |
we present the results of a binary population study in the orion nebula cluster (onc) using archival hubble space telescope (hst) data obtained with the advanced camera for surveys in johnson v filter (hst proposal 10246, pi m. robberto). young clusters and associations hold clues to the origin and properties of multiple star systems. binaries with separations <100 au are useful as tracers of the initial binary population because they are not as likely to be destroyed through dynamical interactions. low-mass, low stellar density, star-forming regions such as taurus-auriga, reveal an excess of multiples compared to the galactic field. studying the binary population of higher mass, higher stellar density star-forming regions like the onc provides useful information concerning the origin of the galactic field star population. in this survey, we characterize the previously unexplored (and incomplete) separation parameter space of binaries in the onc (15-160 au) by fitting a double-point-spread function (psf) model built from empirical psfs. we identified 14 candidate binaries (11 new detections) and find that {8}-2 % +4 %of our observed sample are in binary systems, complete over mass ratios and separations of 0.6 < q < 1.0 and 30 < a < 160 au. this is consistent with the galactic field m-dwarf population over the same parameter ranges, 6.5% ± 3%. therefore, high-mass star-forming regions like the onc would not require further dynamical evolution for their binary population to resemble the galactic field, as some models have hypothesized for young clusters. | a search for intermediate-separation low-mass binaries in the orion nebula cluster |
the classification of gapped phases of non-interacting fermions hinges on the tenfold symmetries and on the spatial dimension. the notion of dimension leads to a well defined demarcation between bulk and edge. here we explore the nature of topological phases in systems where the distinction between bulk and edge is nebulous, of which fractal lattices are canonical examples. our key finding is that in homogeneous fractal lattices (where every site is equally coordinated), there are no gapped topological phases. what appears instead is a novel metallic state -- the fractalized metal -- whose low energy states arrange hierarchically on the structure of the fractal that hosts them. we study the properties (such as chiral transport) of this metal and demonstrate its robustness to disorder. further, by studying a variety of fractal models we establish that the homogeneity of the fractal is a key condition for the realization of such fractalized metallic states. | fractalized metals |
abell 14 is a poorly studied object despite being considered a born-again planetary nebula. we performed a detailed study of its 3d morphology and ionization structure using the shape and mocassin codes. we found that abell 14 is a highly evolved, bipolar nebula with a kinematical age of ∼19 400 yr for a distance of 4 kpc. the high he abundance, and n/o ratio indicate a progenitor of 5 m⊙ that has experienced the third dredge-up and hot bottom burning phases. the stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born-again scenario. the nebula shows unexpectedly strong [n i] λ5200 and [o i] λ6300 emission lines indicating possible shock interactions. abell 14 appears to be a member of a small group of highly evolved, extreme type-i planetary nebulae (pne). the members of this group lie at the lower-left corner of the pne regime on the [n ii]/hα versus [s ii]/hα diagnostic diagram, where shock-excited regions/objects are also placed. the low luminosity of their central stars, in conjunction with the large physical size of the nebulae, result in a very low photoionization rate, which can make any contribution of shock interaction easily perceptible, even for small velocities. | deciphering the bipolar planetary nebula abell 14 with 3d ionization and morphological studies |
aims: we wish to assess the role of kinematics and neutral hydrogen column density in the escape and distribution of lyα photons.methods: we selected a sample of 76 lyα emitting galaxies from the vimos ultra deep survey (vuds) at 2 ≤ z ≤ 4. we estimated the velocity of the neutral gas flowing out of the interstellar medium as the velocity offset, δv, between the systemic redshift (zsys) and the center of low-ionization absorption line systems (lis). to increase the s/n of vuds spectra, we stacked subsamples defined based on median values of their photometric and spectroscopic properties. we measured the systemic redshift from the rest-frame uv spectroscopic data using the ciii]1908 nebular emission line, and we considered siii1526 as the highest signal-to-noise lis line. we calculated the lyα peak shift with respect to the zsys, the ew(lyα), and the lyα spatial extension, ext(lyα-c), from the in the 2d stacked spectra.results: the galaxies that are faint in the rest-frame uv continuum, strong in lyα and ciii], with compact uv morphology, and localized in an underdense environment are characterized by outflow velocities of the order of a few hundreds of km s-1. the subsamples with smaller δv are characterized by larger lyα peak shifts, larger ext(lyα-c), and smaller ew(lyα). in general we find that ew(lyα) anti-correlates with ext(lyα-c) and lyα peak shift.conclusions: we interpret these trends using a radiative-transfer shell model. the model predicts that an hi gas with a column density larger than 1020 cm-2 is able to produce lyα peak shifts larger than >300 km s-1. an ism with this value of nhi would favour a large amount of scattering events, especially when the medium is static, so it can explain large values of ext(lyα-c) and small ew(lyα). on the contrary, an ism with a lower nhi, but large velocity outflows would lead to a lyα spatial profile peaked at the galaxy center (i.e. low values of ext(lyα-c)) and to a large ew(lyα), as we see in our data. our results and their interpretation via radiative-transfer models tell us that it is possible to use lyα to study the properties of the hi gas. also, the fact that lyα emitters are characterized by large δv could give hints about their stage of evolution in the sense that they could be experiencing short bursts of star formation that push strong outflows. based on data obtained with the european southern observatory very large telescope, paranal, chile, under large program 185.a-0791. | the vimos ultra deep survey. the role of hi kinematics and hi column density on the escape of lyα photons in star-forming galaxies at 2 < z < 4 |
a wide variety of molecules have recently been detected in the horsehead nebula photodissociation region (pdr) suggesting that: (i) gas-phase and grain chemistries should both contribute to the formation of organic molecules; and (ii) far-ultraviolet (fuv) photodesorption may explain the release into the gas phase of grain surface species. in order to tackle these specific problems and more generally in order to better constrain the chemical structure of these types of environments we present a study of the horsehead nebula gas-grain chemistry. to do so we used the 1d astrochemical gas-grain code nautilus with an appropriate physical structure computed with the meudon pdr code and compared our modeled outcomes with published observations and with previously modeled results when available. the use of a large set of chemical reactions coupled with the time-dependent code nautilus allows us to reproduce most of the observations well, including those of the first detections in a pdr of the organic molecules hcooh, ch2co, ch3cho and ch3cch, which are mostly associated with hot cores. we also provide some abundance predictions for other molecules of interest. understanding the chemistry behind the detection of these organic molecules is crucial to better constrain the environments these molecules can probe. | a new study of the chemical structure of the horsehead nebula: the influence of grain-surface chemistry |
we present the discovery of a giant ≳100 kpc lyα nebula detected in the core of the x-ray emitting cluster cl j1449+0856 at z = 1.99 through keck/lris narrow-band imaging. this detection extends the known relation between lyα nebulae and overdense regions of the universe to the dense core of a 5-7 × 1013 m ⊙ cluster. the most plausible candidates to power the nebula are two chandra-detected agn host cluster members, while cooling from the x-ray phase and cosmological cold flows are disfavored primarily because of the high lyα to x-ray luminosity ratio ({l}{lyα }/{l}{{x}}≈ 0.3, ≳10-1000 times higher than in local cool-core clusters) and by current modeling. given the physical conditions of the lyα-emitting gas and the possible interplay with the x-ray phase, we argue that the lyα nebula would be short-lived (≲10 myr) if not continuously replenished with cold gas at a rate of ≳1000 m ⊙ yr-1. we investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. this scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (icm), as required to explain the thermodynamic properties of local clusters. we estimate an energy injection of the order of ≈ 2 {{kev}} per particle in the icm over a 2 gyr interval. in our baseline calculation, agns provide up to 85% of the injected energy and two-thirds of the mass, while the rest is supplied by supernovae-driven winds. | a giant lyα nebula in the core of an x-ray cluster at z = 1.99: implications for early energy injection |
we report the discovery and timing measurements of psr j1208-6238, a young and highly magnetized gamma-ray pulsar, with a spin period of 440 ms. the pulsar was discovered in gamma-ray photon data from the fermi large area telescope (lat) during a blind-search survey of unidentified lat sources, running on the distributed volunteer computing system einstein@home. no radio pulsations were detected in dedicated follow-up searches with the parkes radio telescope, with a flux density upper limit at 1369 mhz of 30 μjy. by timing this pulsar’s gamma-ray pulsations, we measure its braking index over five years of lat observations to be n = 2.598 ± 0.001 ± 0.1, where the first uncertainty is statistical and the second estimates the bias due to timing noise. assuming its braking index has been similar since birth, the pulsar has an estimated age of around 2700 years, making it the youngest pulsar to be found in a blind search of gamma-ray data and the youngest known radio-quiet gamma-ray pulsar. despite its young age, the pulsar is not associated with any known supernova remnant or pulsar wind nebula. the pulsar’s inferred dipolar surface magnetic field strength is 3.8 × 1013 g, almost 90% of the quantum-critical level. we investigate some potential physical causes of the braking index deviating from the simple dipole model but find that lat data covering a longer time interval will be necessary to distinguish between these. | the braking index of a radio-quiet gamma-ray pulsar |
context. in the very first steps of the formation of a new planetary system, dust agglomerates grow inside the protoplanetary disk that rotates around the newly formed star. in this disk, collisions between the dust particles, induced by interactions with the surrounding gas, lead to sticking. aggregates start growing until their sizes and relative velocities are high enough for collisions to result in bouncing or fragmentation. with the aim of investigating the transitions between sticking and bouncing regimes for colliding dust aggregates and the formation of clusters from multiple aggregates, the suborbital particle and aggregation experiment (space) was flown on the rexus 12 suborbital rocket.aims: the collisional and sticking properties of sub-mm-sized aggregates composed of protoplanetary dust analogue material are measured, including the statistical threshold velocity between sticking and bouncing, their surface energy and tensile strength within aggregate clusters.methods: we performed an experiment on the rexus 12 suborbital rocket. the protoplanetary dust analogue materials were micrometre-sized monodisperse and polydisperse sio2 particles prepared into aggregates with sizes around 120 μm and 330 μm, respectively and volume filling factors around 0.37. during the experimental run of 150 s under reduced gravity conditions, the sticking of aggregates and the formation and fragmentation of clusters of up to a few millimetres in size was observed.results: the sticking probability of the sub-mm-sized dust aggregates could be derived for velocities decreasing from ~22 to 3 cm s-1. the transition from bouncing to sticking collisions happened at 12.7+2.1-1.4 cm s-1 for the smaller aggregates composed of monodisperse particles and at 11.5+1.9-1.3 and 11.7+1.9-1.3 cm s-1 for the larger aggregates composed of mono- and polydisperse dust particles, respectively. using the pull-off force of sub-mm-sized dust aggregates from the clusters, the surface energy of the aggregates composed of monodisperse dust was derived to be 1.6 × 10-5 j m-2, which can be scaled down to 1.7 × 10-2 j m-2 for the micrometre-sized monomer particles and is in good agreement with previous measurements for silica particles. the tensile strengths of these aggregates within the clusters were derived to be 1.9+2.2-1.2 pa and 1.6+0.7-0.6 pa for the small and large dust aggregates, respectively. these values are in good agreement with recent tensile strength measurements for ~mm-sized silica aggregates.conclusions: using our data on the sticking-bouncing threshold, estimates of the maximum aggregate size can be given. for a minimum mass solar nebula model, aggregates can reach sizes of ~1 cm. | submillimetre-sized dust aggregate collision and growth properties. experimental study of a multi-particle system on a suborbital rocket |
the carina star-forming region is one of the largest in the galaxy, and its massive star population is still being unveiled. the large number of stars combined with high, and highly variable, interstellar extinction makes it inherently difficult to find ob stars in this type of young region. we present the results of a spectroscopic campaign to study the massive star population of the carina nebula, with the primary goal to confirm or reject previously identified carina ob star candidates. a total of 141 known o- and b-type stars and 94 candidates were observed, of which 73 candidates had high enough signal-to-noise ratio to classify. we find 23 new ob stars within the carina nebula, a 32% confirmation rate. one of the new ob stars has blended spectra and is suspected to be a double-lined spectroscopic binary (sb2). we also reclassify the spectral types of the known ob stars and discover nine new sb2s among this population. finally, we discuss the spatial distribution of these new ob stars relative to known structures in the carina nebula. | a catalog of new spectroscopically confirmed massive ob stars in carina |
we have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. we selected z < 0.035 spiral galaxies that have wise colours consistent with little mid-infrared emission from warm dust. matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. six galaxies form a spectroscopic pilot study and were observed using the wide-field spectrograph to check for signs of nebular emission from star formation. we see no evidence of substantial nebular emission found in previous red spiral samples. these six galaxies possess absorption-line spectra with 4000 å breaks consistent with an average luminosity-weighted age of 2.3 gyr. our photometric and integral field spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation. | a photometrically and spectroscopically confirmed population of passive spiral galaxies |
we present the results of an expanded, long-term radial velocity search (25 years) for evidence of binarity in a sample of seven bright proto-planetary nebulae (ppne). the goal is to investigate the widely held view that the bipolar or point-symmetric shapes of planetary nebulae (pne) and ppne are due to binary interactions. observations from three observatories were combined from 2007 to 2015 to search for variations on the order of a few years and then combined with earlier observations from 1991 to 1995 to search for variations on the order of decades. all seven show velocity variations due to periodic pulsation in the range of 35-135 days. however, in only one ppn, iras 22272+5435, did we find even marginal evidence for multi-year variations that might be due to a binary companion. this object shows marginally significant evidence of a two-year period of low semi-amplitude, which could be due to a low-mass companion, and it also displays some evidence of a much longer period of >30 years. the absence of evidence in the other six objects for long-period radial velocity variations due to a binary companion sets significant constraints on the properties of any undetected binary companions: they must be of low mass, ≤0.2 m ⊙, or long period, >30 years. thus the present observations do not provide direct support for the binary hypothesis to explain the shapes of pne and ppne and severely constrains the properties of any such undetected companions. | where are the binaries? results of a long-term search for radial velocity binaries in proto-planetary nebulae |
while ml generates much economic value, many of us have problematic relationships with social media and other ml-powered applications. one reason is that ml often optimizes for what we want in the moment, which is easy to quantify but at odds with what is known scientifically about human flourishing. thus, through its impoverished models of us, ml currently falls far short of its exciting potential, which is for it to help us to reach ours. while there is no consensus on defining human flourishing, from diverse perspectives across psychology, philosophy, and spiritual traditions, love is understood to be one of its primary catalysts. motivated by this view, this paper explores whether there is a useful conception of love fitting for machines to embody, as historically it has been generative to explore whether a nebulous concept, such as life or intelligence, can be thoughtfully abstracted and reimagined, as in the fields of machine intelligence or artificial life. this paper forwards a candidate conception of machine love, inspired in particular by work in positive psychology and psychotherapy: to provide unconditional support enabling humans to autonomously pursue their own growth and development. through proof of concept experiments, this paper aims to highlight the need for richer models of human flourishing in ml, provide an example framework through which positive psychology can be combined with ml to realize a rough conception of machine love, and demonstrate that current language models begin to enable embodying qualitative humanistic principles. the conclusion is that though at present ml may often serve to addict, distract, or divide us, an alternative path may be opening up: we may align ml to support our growth, through it helping us to align ourselves towards our highest aspirations. | machine love |
we examine the assembly process and the observability of a first galaxy (m_vir≈ 10^9{ m_⊙ } at z ≈ 8) with cosmological zoom-in, hydrodynamic simulations, including the radiative, mechanical, and chemical feedback exerted by the first generations of stars. to assess the detectability of such dwarf systems with the upcoming james webb space telescope (jwst), we construct the spectral energy distribution for the simulated galaxy in a post-processing fashion. we find that while the non-ionizing uv continuum emitted by the simulated galaxy is expected to be below the jwst detection limit, the galaxy might be detectable using its nebular emission, specifically in the h α recombination line. this requires that the galaxy experiences an active starburst with a star formation rate of \dot{m}_{\ast }≳ 0.1 { m_⊙ }{ yr}^{-1} at z ≈ 9. due to the bursty nature of star formation in the first galaxies, the time interval for strong nebular emission is short, less than 2-3 myr. the probability of capturing such primordial dwarf galaxies during the observable part of their duty cycle is thus low, resulting in number densities of the order of one source in a single pointing with miri onboard the jwst, for very deep exposures. gravitational lensing, however, will boost their observability beyond this conservative baseline. the first sources of light will thus come firmly within our reach. | signature of the first galaxies in jwst deep field observations |
context. endogenous or exogenous, dry or wet, various scenarios have been depicted for the origin of water on the rocky bodies in our solar system. hydrated silicates found in meteorites and in interplanetary dust particles, together with observations of abundant water reservoirs in the habitable zone of protoplanetary disks, are evidence that support aqueous alteration of silicate dust grains by water vapor condensation in a nebular setting.aims: we investigate the thermodynamics (temperature and pressure dependencies) and kinetics (adsorption rates and energies, surface diffusion and cluster formation) of water adsorption on surfaces of forsterite grains, constraining the location in the solar nebula where aqueous alteration of silicates by water vapor adsorption can occur efficiently and leads to the formation of phyllosilicates. we analyze the astrophysical conditions favorable for such hydration mechanism and the implications for water on solid bodies.methods: the protoplanetary disk model (prodimo) code is tuned to simulate the thermochemical disk structure of the early solar nebula at three evolutionary stages. pressure, temperature, and water vapor abundance within 1 au of the protosun were extracted and used as input for a monte carlo code to model water associative adsorption using adsorption energies that resemble the forsterite [1 0 0] crystal lattice.results: hydration of forsterite surfaces by water vapor adsorption could have occurred within the nebula lifetime already at a density of 108 cm-3, with increasing surface coverage for higher water vapor densities. full surface coverage is attained for temperatures lower than 500 k, while for hotter grain surfaces water cluster formation plays a crucial role. between 0.5 and 10 earth oceans can arise from the agglomeration of hydrated 0.1 μm grains into an earth-sized planet. however, if grain growth occurs dry and water vapor processes the grains afterward, this value can decrease by two orders of magnitude.conclusions: this work shows that water cluster formation enhances the water surface coverage and enables a stable water layer to form at high temperature and low water vapor density conditions. finally, surface diffusion of physisorbed water molecules shortens the timescale for reaching steady state, enabling phyllosilicate formation within the solar nebula timescale. | water delivery in the inner solar nebula. monte carlo simulations of forsterite hydration |
we present a catalog of high-precision proper motions in the orion nebula cluster (onc), based on treasury program observations with the hubble space telescope's (hst) acs/wfc camera. our catalog contains 2454 objects in the magnitude range of 14.2 < mf775w < 24.7, thus probing the stellar masses of the onc from ∼0.4 m⊙ down to ∼0.02 m⊙ over an area of ∼550 arcmin2. we provide a number of internal velocity dispersion estimates for the onc that indicate a weak dependence on stellar location and mass. there is good agreement with the published velocity dispersion estimates, although nearly all of them (including ours at ${\sigma }_{v,x}=0.94$ and ${\sigma }_{v,y}=1.25$ mas yr-1) might be biased by the overlapping young stellar populations of orion a. we identified four new onc candidate runaways based on hst and the gaia dr 2 data, all with masses less than ∼1 m⊙. the total census of known candidate runaway sources is 10—one of the largest samples ever found in any milky way open star cluster. surprisingly, none of them have tangential velocities exceeding 20 km s-1. if most of them indeed originated in the onc, it may compel the re-examination of dynamical processes in very young star clusters. it appears that the mass function of the onc is not significantly affected by the lost runaways. | hubble space telescope astrometry in the orion nebula cluster: census of low-mass runaways |
the formation of jupiter is modeled via core-nucleated accretion, and the planet's evolution is simulated up to the present epoch. throughout the phases when the planet acquires most of its heavy-element content, the calculation of solids' accretion accounts for interactions with an evolving disk of planetesimals. the phase of growth from an embryo of a few hundred kilometers in radius until the time when the accretion of gas overtakes solids' accretion was presented by d'angelo et al. (2014), and the same numerical methods are applied here. those calculations followed the formation for about 4 × 105 years, until the epoch when the heavy-element and hydrogen/helium masses were mz ≈ 7.3 and mxy ≈ 0.15 earth's masses (m⊕), respectively, and ṁxy ≈ṁz. herein, the calculation is continued through the phase when mxy grows to equal mz , at which age, about 2.4 × 106 years, the total mass of the planet is mp ≈ 20 m⊕. about 9 × 105 years later, mp is approximately 60 m⊕ and mz ≈ 16 m⊕, three-quarters of which are delivered by planetesimals larger than 10 km in radius. around this epoch, the contraction of the envelope dictates gas accretion rates a few times 10-3 m⊕ per year, initiating the regime of disk-limited accretion, whereby the planet can accrete all the gas provided by the disk, and its evolution is therefore tied to disk's evolution. growth is continued by constructing simplified models of protosolar accretion disks that evolve through viscous diffusion, winds, and accretion on the planet. jupiter's formation ends after ≈ 3.4-4.2 myr, depending on the applied disk viscosity parameter, when nebula gas disperses. the young jupiter is 4.5-5.5 times as voluminous as it is presently and thousands of times as luminous, ~10-5 l⊙. the heavy-element mass is ≈ 20 m⊕. the evolution proceeds through the cooling and contraction phase, in isolation except for solar irradiation. after 4570 myr, the age of the solar system, radius and luminosity of the planet are within 10% of current values, accounting also for uncertainties in the power absorbed from the sun. during formation, and soon thereafter, the planet exhibits features, e.g., luminosity and effective temperature, that may probe aspects of the latter stages of formation, if observable. these possibly distinctive features, however, seem to disappear within a few tens of myr | growth of jupiter: formation in disks of gas and solids and evolution to the present epoch |
in order to obtain a complete census of the stellar and substellar population, down to a few ${m}_{\mathrm{jup}}$ in the ∼1 myr old orion nebula cluster, we used the infrared channel of the wide field camera 3 of the hubble space telescope with the f139m and f130n filters. these bandpasses correspond to the 1.4 μm h2o absorption feature and an adjacent line-free continuum region. out of 4504 detected sources, 3352 (about 75%) appear fainter than m130 = 14 (vega mag) in the f130n filter, a brightness corresponding to the hydrogen-burning limit mass ( $m\simeq 0.072\,{m}_{\odot }$ ) at ∼1 myr. of these, however, only 742 sources have a negative f130m-f139n color index, indicative of the presence of h2o vapor in absorption, and can therefore be classified as bona fide m and l dwarfs, with effective temperatures t ≲ 2850 k at an assumed 1 myr cluster age. on our color-magnitude diagram (cmd), this population of sources with h2o absorption appears clearly distinct from the larger background population of highly reddened stars and galaxies with positive f130m-f139n color index and can be traced down to the sensitivity limit of our survey, m130 ≃ 21.5, corresponding to a 1 myr old ≃3 ${m}_{\mathrm{jup}}$ planetary-mass object under about 2 mag of visual extinction. theoretical models of the bt-settl family predicting substellar isochrones of 1, 2, and 3 myr down to ∼1 ${m}_{\mathrm{jup}}$ fail to reproduce the observed h2o color index at m ≲ 20 ${m}_{\mathrm{jup}}$ . we perform a bayesian analysis to determine extinction, mass, and effective temperature of each substellar member of our sample, together with its membership probability. | hst survey of the orion nebula cluster in the h2o 1.4 μm absorption band. i. a census of substellar and planetary-mass objects |
very high energy γ -rays are one of the most important messengers of the relativistic non-thermal universe. the major motivation of very high energy γ -ray astronomy is to find sources of high energy cosmic rays. several astrophysical sources are known to accelerate cosmic rays to very high energies under extreme conditions. very high energy γ -rays are produced at these astrophysical sites or in their vicinity through interactions of cosmic rays in the surrounding medium close to the sources. gamma rays, being neutral, travel in a straight line and thus give us valuable information about the cosmic ray sources and their surroundings. additionally, very high energy γ -ray astronomy can probe many fundamental physics questions. ground-based γ -ray astronomy began its journey in 1989 when whipple telescope detected tev γ -rays from the crab, a pulsar wind nebula in our galaxy. in the last 2 decades, technological improvements have facilitated the development of the latest generation of very high energy detectors and telescopes which have delivered exciting new results. until now, over two hundred very high energy γ -ray sources, both galactic and extra-galactic, have been detected. these observations have provided a deeper insight into a large number of important questions in high energy astrophysics and astroparticle physics. this review article is an attempt to enumerate the most important results in the exciting and rapidly developing field of very high energy γ -ray astronomy. | galactic and extragalactic sources of very high energy gamma rays |
we report on broadband x-ray properties of the rabbit pulsar wind nebula (pwn) associated with the pulsar psr j1418-6058 using archival chandra and xmm-newton data, as well as a new nustar observation. nustar data above 10 kev allowed us to detect the 110 ms spin period of the pulsar, characterize its hard x-ray pulse profile, and resolve hard x-ray emission from the pwn after removing contamination from the pulsar and other overlapping point sources. the extended pwn was detected up to ~20 kev and is described well by a power-law model with a photon index γ ≈ 2. the pwn shape does not vary significantly with energy, and its x-ray spectrum shows no clear evidence of softening away from the pulsar. we modeled the spatial profile of x-ray spectra and broadband spectral energy distribution in the radio to tev band to infer the physical properties of the pwn. we found that a model with low magnetic field strength (b ~ 10 μg) and efficient diffusion (d ~ 1027 cm2 s-1) fits the pwn data well. the extended hard x-ray and tev emission, associated respectively with synchrotron radiation and inverse compton scattering by relativistic electrons, suggest that particles are accelerated to very high energies (≳500 tev), indicating that the rabbit pwn is a galactic pevatron candidate. | a broadband x-ray study of the rabbit pulsar wind nebula powered by psr j1418-6058 |
phosphorus is a minor element that controls the formation of several key planetary minerals. it is also an element critical to the development of life. a common assumption of phosphorus chemistry is that at low temperatures, phosphorus would have been a volatile component of ices or gases in the outer solar system. here i propose that phosphorus was depleted as a volatile throughout the developing solar system, and as a result, volatile forms of phosphorus would have been minimal, even in the colder regions of the solar nebula. based on thermodynamic equilibrium models and metal phosphidation kinetics coupled to a simple 1d gas diffusion model, phosphorus migrated rapidly to the inner solar system, forming solids such as phosphides and phosphates, and removing volatile phosphorus across large portions of the solar system. | phosphorus volatility in the early solar nebula |
context. in recent years, winds from massive stars have been considered promising sites for investigating relativistic particle acceleration. in particular, the resulting bow-shaped shocks from the interaction of the supersonic winds of runaway stars with interstellar matter have been intensively observed at many different wavelengths, from radio to γ-rays.aims: in this study we investigate the o4if star, bd+43° 3654, the bow shock of which is, so far, the only one proven to radiate both thermal and non-thermal emission at radio frequencies. in addition, we consider ngc 7635, the bubble nebula, as a bow shock candidate and examine its apex for indications of thermal and non-thermal radio emission.methods: we observed both bow shocks in radio frequencies with the very large array (vla) in the c and x bands (4-8 ghz and 8-12 ghz) and with the effelsberg telescope at 4-8 ghz. we analysed single-dish and interferometric results individually, in addition to their combined emission, obtained spectral index maps for each source, and calculated their spectral energy distributions.results: we find that both sources emit non-thermal emission in the radio regime, with the clearest evidence for ngc 7635, whose radio emission has a strongly negative spectral index along the northern rim of the bubble. we present the first high-resolution maps of radio emission from ngc 7635, finding that the morphology closely follows the optical nebular emission. our results are less conclusive for the bow shock of bd+43° 3654, as its emission becomes weaker and faint at higher frequencies in vla data. effelsberg data show a much larger emitting region (albeit a region of thermal emission) than is detected with the vla for this source.conclusions: our results extend the previous radio results from the bd+43° 3654 bow shock to higher frequencies, and with our ngc 7635 results we double the number of bow shocks around o stars with detected non-thermal emission, from one to two. modelling of the multi-wavelength data for both sources shows that accelerated electrons at the wind termination shock are a plausible source for the non-thermal radio emission, but energetics arguments suggest that any non-thermal x-ray and γ-ray emission could be significantly below existing upper limits. enhanced synchrotron emission from compressed galactic cosmic rays in the radiative bow shock could also explain the radio emission from the bd+43° 3654 bow shock, but not from ngc 7635. the non-detection of point-like radio emission from bd+43° 3654 puts an upper limit on the mass-loss rate of the star that is lower than values quoted in the literature. | and then they were two: detection of non-thermal radio emission from the bow shocks of two runaway stars |
the large high altitude air shower observatory (lhaaso) detected 12 gamma-ray sources above 100 tev, which are the possible origins of galactic cosmic-rays. we summarize the neutrino measurements by icecube and antares in the vicinity of lhaaso sources to constrain the contribution of hadronic gamma-rays in these sources. we find that the current observations constrain hadronic gamma-rays to contribute no more than ~60% of the gamma-rays from the crab nebula. gamma-rays from two lhaaso sources, lhaaso j1825-1326 and lhaaso j1907+0626, are dominated by leptonic components up to ~200 tev, under the hypotheses in the analysis by icecube. the uncertainties of the constraint on the hadronic gamma-ray emission are discussed. we also constrain the total 100 tev gamma-ray emission from tev pulsar wind nebulae by relying on the remarkable sensitivity of lhaaso at that energy. | constraints on hadronic contributions to lhaaso sources with neutrino observations |
short rise times of fast blue optical transients (fbots) require very light ejected envelopes, $m_{\rm ej} \le 10^{-1} \, \mathrm{m}_\odot$, much smaller than of a typical supernova. the detection by chandra of x-ray emission in at2020mrf of lx ~ 1042 erg s-1 after 328 d implies total, overall dominant, x-ray energetics at the gamma-ray burst level of ~6 × 1049 erg. we further develop a model of lyutikov and toonen, whereby fbots are the results of a late accretion-induced collapse of the product of double white dwarf (wd) merger between onemg wd and another wd. small ejecta mass, and the rarity of fbots, results from the competition between mass-loss from the merger product to the wind, and ashes added to the core, on a time-scale of ~103-104 yr. fbots proper come from central engine-powered radiation-dominated forward shock as it propagates through ejecta. all the photons produced by the central source deep inside the ejecta escape almost simultaneously, producing a short bright event. the high-energy emission is generated at the highly relativistic and highly magnetized termination shock, qualitatively similar to pulsar wind nebulae. the x-ray bump observed in at2020mrf by srg/erosita, predicted by lyutikov and toonen, is coming from the breakout of the engine-powered shock from the ejecta into the preceding wind. the model requires total energetics of just few × 1050 erg, slightly above the observed x-rays. we predict that the system is hydrogen poor. | on the nature of fast blue optical transients |
many double white dwarf (wd) mergers likely do not lead to a prompt thermonuclear explosion. we investigate the prospects for observationally detecting the surviving remnants of such mergers, focusing on the case of mergers of double carbon-oxygen wds. for ~104 yr, the merger remnant is observationally similar to an extreme agb star evolving to become a massive wd. identifying merger remnants is thus easiest in galaxies with high-stellar masses (high wd merger rate) and low star formation rates (low birth rate of ~6-10 m⊙ stars). photometrically identifying merger remnants is challenging even in these cases because the merger remnants appear similar to he stars and post-outburst classical novae. we propose that the most promising technique for discovering wd merger remnants is through their unusual surrounding photoionized nebulae. we use cloudy photoionization calculations to investigate their unique spectral features. merger remnants should produce weak hydrogen lines, strong carbon and oxygen recombination, and fine-structure lines in the uv, optical and ir. with narrow-band imaging or integral field spectrographs, we predict that multiple candidates are detectable in the bulge of m31, the outskirts of m87 and other nearby massive galaxies, and the milky way. our models roughly reproduce the wise nebula surrounding the galactic wd merger candidate iras 00500+6713; we predict detectable [ne vi] and [mg vii] lines with jwst but that the mid-ir wise emission is dominated by dust not fine-structure lines. | observational signatures of carbon-oxygen white dwarf merger remnants |
we present the results from the hst wfc3 and acs data on an archetypal galaxy undergoing ram pressure stripping (rps), eso 137-001, in the nearby cluster abell 3627. eso 137-001 is known to host a prominent stripped tail detected in many bands from x-rays, h α to co. the hst data reveal significant features indicative of rps such as asymmetric dust distribution and surface brightness as well as many blue young star complexes in the tail. we study the correlation between the blue young star complexes from hst, h ii regions from h α (muse), and dense molecular clouds from co (alma). the correlation between the hst blue star clusters and the h ii regions is very good, while their correlation with the dense co clumps are typically not good, presumably due in part to evolutionary effects. in comparison to the starburst99 + cloudy model, many blue regions are found to be young (<10 myr) and the total star formation (sf) rate in the tail is 0.3-0.6 m⊙ yr-1 for sources measured with ages less than 100 myr, about 40 per cent of the sf rate in the galaxy. we trace sf over at least 100 myr and give a full picture of the recent sf history in the tail. we also demonstrate the importance of including nebular emissions and a nebular to stellar extinction correction factor when comparing the model to the broad-band data. our work on eso 137-001 demonstrates the importance of hst data for constraining the sf history in stripped tails. | hst viewing of spectacular star-forming trails behind eso 137-001 |
jets (fast collimated outflows) are claimed to be the main shaping agent of the most asymmetric planetary nebulae (pns), as they impinge on the circumstellar material at late stages of the asymptotic giant branch phase. the first jet detected in a pn was that of ngc 2392, yet there is no available image because of its low surface brightness contrast with the bright nebular emission. here we take advantage of the tomographic capabilities of gran telescopio de canarias multi-espectrógrafo en gtc de alta resolución para astronomía high-dispersion integral field spectroscopic observations of the jet in ngc 2392 to gain unprecedented details of its morphology and kinematics. the jet of ngc 2392 is found to emanate from the central star, break through the walls of the inner shell of this iconic pn and extend outside the nebula's outermost regions with an s-shaped morphology suggestive of precession. at odds with the fossil jets found in mature pns, the jet in ngc 2392 is currently being collimated and launched. the high nebular excitation of ngc 2392, which implies an he++/he ionization fraction too high to be attributed to the known effective temperature of the star, has been proposed in the past to hint at the presence of a hot white dwarf companion. in conjunction with the hard x-ray emission from the central star, the present-day jet collimation would support the presence of such a double-degenerate system where one component undergoes accretion from a remnant circumbinary disk of the common envelope phase. | tomography of the unique ongoing jet in the planetary nebula ngc 2392 |
u-pb ages and hf isotope compositions of zircons from the chencai complex in zhejiang province have been determined to provide constraints on mechanisms of migmatization and tectonic evolution related to the early palaeozoic orogeny in the cathaysia block, south china. zircons from leucosome samples of migmatites are characterized by nebulous overgrowths enclosing inherited cores or occur as newly formed grains with weak zoning. five samples gave weighted mean ages ranging from 438±3 ma to 432±4 ma, which are interpreted as recording the time of anatexis of a regional tectono-thermal event. theirεhf(t) values range from −21.4 to −4.8 (with peak at −11), with correspondingtdm2ages of 1.73-2.77 ga (with peak atc.1.9-2.3 ga), suggesting that the protoliths formed by reworking of ancient crust evolved from late palaeoproterozoic - early archaean crust-mantle differentiation. the migmatization was spatially and temporally associated with reported 460-435 ma metamorphism with a clockwise pressure-temperature (p-t) path and was most likely controlled by crustal thickening driven by the early palaeozoic orogenesis. thetdm2ages of the chencai complex are consistent with those of the wuyi-yunkai structural belt in the cathaysia block, but distinct from those (with peak at 2.7-3.0 ga) of the badu complex which lacks early palaeozoic tectono-thermal records. the data support the suggestion that a postulated geological entity, instead of the east domain (the badu complex being its main part) of the cathaysia block, was probably involved in the early palaeozoic orogeny. | zircon u-pb ages and hf isotope compositions of the chencai migmatite, central zhejiang province, south china: constraints on the early palaeozoic orogeny |
the sun's astrophysical birth environment affected the formation and composition of the solar system. primitive meteorites display mass-independent oxygen isotope anomalies that were likely caused by ultraviolet (uv) photochemistry of co gas-phase molecules, either (i) in the outer solar nebula by light from the young sun or (ii) in the parent molecular cloud by light from nearby stars. however, measurements of oxygen isotopes alone cannot unambiguously constrain the uv spectrum of the source responsible for the photochemistry. sulfur, with four stable isotopes, can be used as a more direct probe of the astrophysical environment of mass-independent photochemistry. here, we report the in situ isotopic analysis of paired oxygen and sulfur isotope systematics in cosmic symplectite (cos), magnetite-pentlandite intergrowths, in the primitive ungrouped carbonaceous chondrite acfer 094. we show that cos grains contain mass-independent sulfur isotope anomalies (weighted means of δ33s = +3.84 ± 0.72‰ and δ36s = -6.05 ± 2.25‰, 2se) consistent with h2s photochemistry by uv from massive o and b stars close to the solar system's parent molecular cloud, and inconsistent with uv from the protosun. the presence of coupled mass-independent sulfur and oxygen (δ17o = 86 ± 6‰, 2se) isotope anomalies in cos imply that these anomalies originated in the same astrophysical environment. we propose that this environment is the photodissociation region (pdr) of the solar system's parent molecular cloud, where nearby massive stars irradiated the edge of the cloud. we conclude that the sun's stellar neighbors, likely o and b stars in a massive-star-forming region, affected the composition of the solar system's primordial building blocks. | cosmic symplectite recorded irradiation by nearby massive stars in the solar system's parent molecular cloud |
we analyse particle acceleration in explosive reconnection events in magnetically dominated proton-electron plasmas. reconnection is driven by large-scale magnetic stresses in interacting current-carrying flux tubes. our model relies on development of current-driven instabilities on macroscopic scales. these tilt-kink instabilities develop in an initially force-free equilibrium of repelling current channels. using magnetohydrodynamics (mhd) methods we study a 3d model of repelling and interacting flux tubes in which we simultaneously evolve test particles, guided by electromagnetic fields obtained from mhd. we identify two stages of particle acceleration; initially particles accelerate in the current channels, after which the flux ropes start tilting and kinking and particles accelerate due to reconnection processes in the plasma. the explosive stage of reconnection produces non-thermal energy distributions with slopes that depend on plasma resistivity and the initial particle velocity. we also discuss the influence of the length of the flux ropes on particle acceleration and energy distributions. this study extends previous 2.5d results to 3d setups, providing all ingredients needed to model realistic scenarios like solar flares, black hole flares and particle acceleration in pulsar wind nebulae: formation of strong resistive electric fields, explosive reconnection and non-thermal particle distributions. by assuming initial energy equipartition between electrons and protons, applying low resistivity in accordance with solar corona conditions and limiting the flux rope length to a fraction of a solar radius, we obtain realistic energy distributions for solar flares with non-thermal power-law tails and maximum electron energies up to 11 mev and maximum proton energies up to 1 gev. | reconnection and particle acceleration in interacting flux ropes - ii. 3d effects on test particles in magnetically dominated plasmas |
we present emission-line templates for passively-evolving (`retired') galaxies, useful for investigation of the evolution of the interstellar medium in these galaxies, and characterization of their high-temperature source populations. the templates are based on high signal-to-noise (>800) co-added spectra (3700-6800 å) of ∼11 500 gas-rich sloan digital sky survey galaxies devoid of star formation and active galactic nuclei. stacked spectra are provided for the entire sample and sub-samples binned by mean stellar age. in our previous paper, johansson et al., these spectra provided the first measurements of the he ii 4686 å line in passively-evolving galaxies, and the observed he ii/hβ ratio constrained the contribution of accreting white dwarfs (the `single-degenerate' scenario) to the type ia supernova rate. in this paper, the full range of unambiguously detected emission lines are presented. comparison of the observed [o i] 6300 å/hα ratio with photoionization models further constrains any high-temperature single-degenerate scenario for type ia supernovae (with 1.5 ≲ t/105 k ≲ 10) to ≲3-6 per cent of the observed rate in the youngest age bin (i.e. highest sn ia rate). hence, for the same temperatures, in the presence of an ambient population of post-asymptotic giant branch stars, we exclude additional high-temperature sources with a combined ionizing luminosity of ≈1.35 × 1030 l⊙/m⊙,* for stellar populations with mean ages of 1-4 gyr. furthermore, we investigate the extinction affecting both the stellar and nebular continuum. the latter shows about five times higher values. this contradicts isotropically distributed dust and gas that renders similar extinction values for both cases. | diffuse gas in retired galaxies: nebular emission templates and constraints on the sources of ionization |
we present observations of the trumpler 14/carina i region carried out using the stratospheric terahertz observatory 2. the trumpler 14/carina i region is in the western part of the carina nebula complex (cnc), which is one of the most extreme star-forming regions in the milky way. we observed trumpler 14/carina i in the 158 μm transition of [c ii] with a spatial resolution of 48″ and a velocity resolution of 0.17 km s-1. the observations cover a 0.°25 by 0.°28 area with central position l = 297.°34, b = -0.°60. the kinematics show that bright [c ii] structures are spatially and spectrally correlated with the surfaces of co clouds, tracing the photodissociation region (pdr) and ionization front of each molecular cloud. along seven lines of sight (loss) that traverse tr 14 into the dark ridge to the southwest, we find that the [c ii] luminosity from the h ii region is 3.7 times that from the pdr. in the same los, we find in the pdrs an average ratio of 1 : 4.1 : 5.6 for the mass in atomic gas : dark co gas : molecular gas traced by co. comparing multiple gas tracers, including h i 21 cm, [c ii], co, and radio recombination lines, we find that the h ii regions of the cnc are well described as h ii regions with one side freely expanding toward us, consistent with the champagne model of ionized gas evolution. the dispersal of the gmc in this region is dominated by euv photoevaporation; the dispersal timescale is 20-30 myr. | probing ism structure in trumpler 14 and carina i using the stratospheric terahertz observatory 2 |
the well-known quasar sdss j095253.83+011421.9 (j0952+0114) at z = 3.02 has one of the most peculiar spectra discovered so far, showing the presence of narrow lyα and broad metal emission lines. although recent studies have suggested that a proximate damped lyα absorption (pdla) system causes this peculiar spectrum, the origin of the gas associated with the pdla is unknown. here we report the results of observations with the multi unit spectroscopic explorer (muse) that reveal a new giant (≈100 physical kpc) lyα nebula. the detailed analysis of the lyα velocity, velocity dispersion, and surface brightness profiles suggests that the j0952+0114 lyα nebula shares similar properties with other qso nebulae previously detected with muse, implying that the pdla in j0952+0144 is covering only a small fraction of the solid angle of the qso emission. we also detected bright and spectrally narrow c iv λ1550 and he ii λ1640 extended emission around j0952+0114 with velocity centroids similar to the peak of the extended and central narrow lyα emission. the presence of a peculiarly bright, unresolved, and relatively broad he ii λ1640 emission in the central region at exactly the same pdla redshift hints at the possibility that the pdla originates in a clumpy outflow with a bulk velocity of about 500 km s-1. the smaller velocity dispersion of the large-scale lyα emission suggests that the high-speed outflow is confined to the central region. lastly, the derived spatially resolved he ii/lyα and c iv/lyα maps show a positive gradient with the distance to the qso, hinting at a non-homogeneous distribution of the ionization parameter. based on observations obtained at the very large telescope (vlt) of the european southern observatory, paranal, chile (eso programme id 096.a-0345). | a giant lyα nebula and a small-scale clumpy outflow in the system of the exotic quasar j0952+0114 unveiled by muse |
high- and low-resolution international ultraviolet explorer (iue) spectra of v838 her in the early outburst stages exhibit a strong absorption feature shortward of λ3130. we discuss the nature of this spectral feature and provide convincing evidence that it corresponds to the blueshifted resonance doublet of singly ionized 7be recently discovered in other novae. during the evolution of the outburst the appearance of an emission feature close to λ3130 å is also identified as 7be ii λ3132 because the usual identification as the o iii λ3133.7 bowen fluorescence line is hardly compatible with both the known oxygen underabundance in the nova ejecta and the low optical depths in the nebula due to the high outflow velocity. the average 7be abundance relative to hydrogen, estimated by four different methods, i.e. the 7be ii/mg ii absorption ratio, and the 7be ii/mg ii, 7be ii/he ii1640, and 7be ii/hβ emission ratios, is n(be)/n(h) ≈2.5 × 10-5 (by number), i.e. ≈1.7 × 10-4 by mass. this corresponds to an overproduction of 7be by about 1 dex in comparison with the theoretical models of massive co and one novae. since 7be all converts into 7li, the 7be/h abundance implies a 7li/h overabundance of about 4 dex over the 7li/h meteoritic value and indicates a total ejected mass of 7li of ≈9.5 × 10-10 m⊙. these data are in line with previous observations and indicate that large amounts of 7li can be synthesized in a variety of novae, including very fast one novae. | absorption and emission features of 7be ii in the outburst spectra of v838 her (nova her 1991) |
projected quasar galaxy pairs provide powerful means to study the circumgalactic medium (cgm) that maintains the relics of galactic feedback and the accreted gas from the intergalactic medium. here, we study the nature of a lyman limit system (lls) with n(h i) = 1019.1 ± 0.3 cm-2 and a dust-uncorrected metallicity of [fe/h] = -1.1 ± 0.3 at z = 0.78 towards q0152 - 020. the mg ii absorption profiles are composed of a main saturated and a few weaker optically thin components. using muse observations, we detect one galaxy close to the absorption redshift at an impact parameter of 54 kpc. this galaxy exhibits nebular emission lines from which we measure a dust-corrected star formation rate of 10^{+8}_{-5} m⊙ yr-1 and an emission metallicity of [o/h] = -0.1 ± 0.2. by combining the absorption line kinematics with the host galaxy morphokinematics we find that while the main absorption component can originate from a galactic wind at vw = 110 ± 4 km s-1 the weaker components cannot. we estimate a mass ejection rate of \dot{m}≳ 0.8 m⊙ yr-1 that translates to a loading factor of η ≳ 0.1. since the local escape velocity of the halo, vesc ≃ 430 km s-1, is a few times larger than vw, we expect this gas will remain bound to the host galaxy. these observations provide additional constraints on the physical properties of winds predicted by galaxy formation models. we also present the vlt/x-shooter data analysis of four other absorbing systems at 1.1 < z < 1.5 in this sightline with their host galaxies identified in the muse data. | a lyman limit system associated with galactic winds |
the crab nebula is an extreme particle accelerator that boosts the energy of electrons up to a few pev (10^{15} ev), close to the maximum energy allowed theoretically. the physical conditions in the acceleration site and the nature of the acceleration process itself remain highly uncertain. the key information about the highest-energy accelerated particles is contained in the synchrotron and inverse compton (ic) channels of radiation at energies above 1 mev and 100 tev, respectively. a recent report of the detection of an ultra-high-energy gamma-ray signal from the crab nebula up to 300 tev allows us to determine the energy distribution of the highest-energy electrons and to derive the magnetic field strength in the acceleration region, b≤ 120 μ g, in a parameter-free way. this estimate brings new constraints on the properties of non-thermal particle distributions and places important constraints on the magnetohydrodynamic models for the crab nebula, in particular on the feasible magnetization and anisotropy of the pulsar wind. the calculations of synchrotron and ic emission show that future observations with instruments that allow detection of the crab nebula above 300 tev and above 1 mev will clarify the conditions that allow acceleration of electrons beyond pev energies in the crab nebula. in particular, we will be able to verify the hypothetical multicomponent composition of the electron energy distribution, and we will determine the magnetic field strength in the regions responsible for the acceleration of pev electrons. | detection of ultra-high-energy gamma rays from the crab nebula: physical implications |
respiratory infection by pathogens via aerosol remains a major concern for both natural disease transmission as well as intentional release of biological weapons. critical to understanding the disease course and pathogenesis of inhaled pathogens are studies in animal models conducted under tightly controlled experimental settings, including the inhaled dose. the route of administration, particle size, and dose can affect disease progression and outcome. damage to or loss of pathogens during aerosolization could increase the dose required to cause disease and could stimulate innate immune responses, altering outcome. aerosol generators that reduce pathogen loss would be ideal. this study compares two aerosol generators to determine which is superior for animal studies. aerosol research methods and equipment need to be well characterized to optimize the development of animal models for respiratory pathogens, including bioterrorism agents. this information will be critical for pivotal efficacy studies in animals to evaluate potential vaccines or treatments against these agents. abstract experimental infection of animals with aerosols containing pathogenic agents is essential for an understanding of the natural history and pathogenesis of infectious disease as well as evaluation of potential treatments. we evaluated whether the aeroneb nebulizer, a vibrating mesh nebulizer, would serve as an alternative to the collison nebulizer, the "gold standard" for generating infectious bioaerosols. while the collison possesses desirable properties that have contributed to its longevity in infectious disease aerobiology, concerns have lingered about the liquid volume and concentration of the infectious agent required to cause disease and the damage that jet nebulization causes to the agent. fluorescein salt was added to the nebulizer contents to assess pathogen loss during aerosolization. relative to fluorescein salt, loss of influenza virus during aerosolization was worse with the collison than with the aeroneb. four other viruses also had superior aerosol performance with the aeroneb. the aeroneb did not improve the aerosol performance for a vegetative bacterium, francisella tularensis . environmental parameters collected during the aerosol challenges indicated that the aeroneb generated a higher relative humidity in exposure chambers while not affecting other environmental parameters. the aerosol mass median aerodynamic diameter (mmad) was generally larger and more disperse for aerosols generated by the aeroneb than what is seen with the collison, but ≥80% of particles were within the range that would reach the lower respiratory tract and alveolar regions. the improved aerosol performance and generated particle size range suggest that for viral pathogens, the aeroneb is a suitable alternative to the collison three-jet nebulizer for use in experimental infection of animals. importance respiratory infection by pathogens via aerosol remains a major concern for both natural disease transmission as well as intentional release of biological weapons. critical to understanding the disease course and pathogenesis of inhaled pathogens are studies in animal models conducted under tightly controlled experimental settings, including the inhaled dose. the route of administration, particle size, and dose can affect disease progression and outcome. damage to or loss of pathogens during aerosolization could increase the dose required to cause disease and could stimulate innate immune responses, altering outcome. aerosol generators that reduce pathogen loss would be ideal. this study compares two aerosol generators to determine which is superior for animal studies. aerosol research methods and equipment need to be well characterized to optimize the development of animal models for respiratory pathogens, including bioterrorism agents. this information will be critical for pivotal efficacy studies in animals to evaluate potential vaccines or treatments against these agents. | a vibrating mesh nebulizer as an alternative to the collison three-jet nebulizer for infectious disease aerobiology |
we present atacama large millimeter/sub-millimeter array (alma) observations of the star-forming environment surrounding v1647 ori, an outbursting fuor/exor pre-main sequence star. dust continuum and the (j = 2 - 1) 12co, 13co, c18o molecular emission lines were observed to characterize the v1647 ori circumstellar disc and any large scale molecular features present. we detect continuum emission from the circumstellar disc and determine a radius r = 40 au, inclination i = 17°+6-9 and total disc mass of mdisc of ∼0.1 m⊙. we do not identify any disc structures associated with nearby companions, massive planets or fragmentation. the molecular cloud environment surrounding v1647 ori is both structured and complex. we confirm the presence of an excavated cavity north of v1647 ori and have identified dense material at the base of the optical reflection nebula (mcneil's nebula) that is actively shaping its surrounding environment. two distinct outflows have been detected with dynamical ages of ∼11 700 and 17 200 yr. these outflows are misaligned suggesting disc precession over ∼5500 yr as a result of anisotropic accretion events is responsible. the collimated outflows exhibit velocities of ∼2 km s-1, similar in velocity to that of other fuor objects presented in this series, but significantly slower than previous observations and model predictions. the v1647 ori system is seemingly connected by an 'arm' of material to a large unresolved structure located ∼20 arcsec to the west. the complex environment surrounding v1647 ori suggests it is in the early stages of star formation, which may relate to its classification as both a fuor and exor type object. | the alma early science view of fuor/exor objects - iv. misaligned outflows in the complex star-forming environment of v1647 ori and mcneil's nebula |
we analyze far-ultraviolet spectra and ancillary data of the super star cluster ssc-n and its surrounding h ii region in the nearby dwarf galaxy ii zw 40. from the ultraviolet spectrum, we derive a low internal reddening of e(b - v) = 0.07 ± 0.03, a mass of (9.1 ± 1.0) × 105 m ⊙, a bolometric luminosity of (1.1 ± 0.1) × 109 l ⊙, a number of ionizing photons of (6 ± 2) × 1052 s-1, and an age of (2.8 ± 0.1) myr. these parameters agree with the values derived from optical and radio data, indicating no significant obscured star formation, absorption of photons by dust, or photon leakage. ssc-n and its nebulosity are an order of magnitude more massive and luminous than 30 doradus and its ionizing cluster. photoionization modeling suggests a high ionization parameter and a c/o ratio where c is between primary and secondary. we calculate diagnostic emission-line ratios and compare ssc-n to local star-forming galaxies. the ssc-n nebula does not coincide with the locus defined by local galaxies. rather, it coincides with the location of “green pea” galaxies, objects that are often considered nearby analogs of the galaxies reionizing the universe. most stellar features are well reproduced by synthetic spectra. however, the ssc-n cluster has strong, broad, stellar he ii λ1640 emission that cannot be reproduced, suggesting a deficit of he-enhanced stars with massive winds in the models. we discuss possible sources for the broad he ii emission, including very massive stars and/or enhanced mixing processes. | physical properties of ii zw 40's super star cluster and nebula: new insights and puzzles from uv spectroscopy |
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