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we report on chandra x-ray observatory (cxo) observations of the pulsar wind nebula (pwn) associated with psr b0355+54 (eight observations with a 395 ks total exposure, performed over an eight month period). we investigated the spatial and spectral properties of the emission coincident with the pulsar, compact nebula (cn), and extended tail. we find that the cn morphology can be interpreted in a way that suggests a small angle between the pulsar spin axis and our line of sight, as inferred from the radio data. on larger scales, emission from the 7\prime (≈ 2 pc) tail is clearly seen. we also found hints of two faint extensions nearly orthogonal to the direction of the pulsar’s proper motion. the spectrum extracted at the pulsar position can be described with an absorbed power-law + blackbody model. the nonthermal component can be attributed to magnetospheric emission, while the thermal component can be attributed to emission from either a hot spot (e.g., a polar cap) or the entire neutron star surface. surprisingly, the spectrum of the tail shows only a slight hint of cooling with increasing distance from the pulsar. this implies either a low magnetic field with fast flow speed, or particle reacceleration within the tail. we estimate physical properties of the pwn and compare the morphologies of the cn and the extended tail with those of other bow shock pwne observed with long cxo exposures. | deep chandra observations of the pulsar wind nebula created by psr b0355+54 |
freely decaying, relativistic force-free turbulence is studied for the first time. we initiate the magnetic field at a short wavelength and simulate its relaxation toward equilibrium on two- and three-dimensional periodic domains in both helical and nonhelical settings. force-free turbulent relaxation is found to exhibit an inverse cascade in all settings and in three dimensions to have a magnetic energy spectrum consistent with the kolmogorov 5/3 power law. three-dimensional relaxations also obey the taylor hypothesis; they settle promptly into the lowest-energy configuration allowed by conservation of the total magnetic helicity. however, in two dimensions, the relaxed state is a force-free equilibrium whose energy greatly exceeds the taylor minimum and that contains persistent force-free current layers and isolated flux tubes. we explain this behavior in terms of additional topological invariants that exist only in two dimensions, namely the helicity enclosed within each level surface of the magnetic potential function. the speed and completeness of turbulent magnetic free-energy discharge could help account for rapidly variable gamma-ray emission from the crab nebula, gamma-ray bursts, blazars, and radio galaxies. | freely decaying turbulence in force-free electrodynamics |
we report on the discovery of ionised gas filaments in the circum-galactic halo of the extremely metal-poor compact starburst sbs 0335-052e in a 1.5 h integration with the muse integral-field spectrograph. we detect these features in hα and [o iii] emission down to a limiting surface-brightness of 5 × 10-19 erg s-1 cm-2 arcsec-2. the filaments have projected diameters of 2.1 kpc and extend more than 9 kpc to the north and north-west from the main stellar body. we also detect extended nebular he ii λ4686 emission that brightens towards the north-west at the rim of a starburst driven super-shell. we also present a velocity field of the ionised gas. the filaments appear to connect seamlessly in velocity space to the kinematical disturbances caused by the shell. similar to high-z star-forming galaxies, the ionised gas in this galaxy is dispersion dominated. we argue that the filaments were created via feedback from the starburst and that these ionised structures in the halo may act as escape channels for lyman continuum radiation in this gas-rich system. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programme 096.b-0690. | vlt/muse illuminates possible channels for lyman continuum escape in the halo of sbs 0335-52e |
the mammoth-i nebula at redshift 2.3 is one of the largest known lyα nebulae in the universe, spanning ∼440 kpc. enormous lyα nebulae like mammoth-i typically trace the densest and most active regions of galaxy formation. using sensitive low-surface-brightness observations of co(1-0) with the very large array, we trace the cold molecular gas in the inner 150 kpc of the mammoth-i nebula. co is found in four regions that are associated with either galaxies or groups of galaxies that lie inside the nebula. in three of the regions, the co stretches up to ∼30 kpc into the circumgalactic medium (cgm). in the centermost region, the co has a very low velocity dispersion (fwhmco ∼ 85 km s-1), indicating that this gas is dynamically cold. this dynamically cold gas coincides with diffuse rest-frame optical light in the cgm around a central group of galaxies, as discovered with the hubble space telescope. we argue that this likely represents cooling of settled and enriched gas in the center of mammoth-i. this implies that the dynamically cold gas in the cgm, rather than the obscured active galactic nucleus, marks the core of the potential well of this lyα nebula. in total, the co in the mammoth-i nebula traces a molecular gas mass of m h2 ∼ 1.4(α co/3.6) × 1011 m ⊙, with roughly 50% of the co(1-0) emission found in the cgm. our results add to the increasing evidence that extended reservoirs of molecular gas exist in the cgm of massive high-z galaxies and protoclusters. | the cold circumgalactic environment of mammoth-i: dynamically cold gas in the core of an enormous lyα nebula |
aims: r coronae australis (r cra) is the brightest star of the coronet nebula of the corona australis (cra) star forming region. this star is very red in color, probably due to dust absorption, and is strongly variable. high-contrast instruments allow for an unprecedented direct exploration of the immediate circumstellar environment of this star.methods: we observed r cra with the near-infrared (nir) channels (ifs and irdis) of sphere at the very large telescope (vlt). in this paper, we used four different epochs, three of which are from open time observations while one is from sphere guaranteed time. the data were reduced using the data reduction and handling pipeline and the sphere data center. we implemented custom idl routines on the reduced data with the aim to subtract the speckle halo. we have also obtained pupil-tracking h-band (1.45-1.85 μm) observations with the vlt/sinfoni nir medium-resolution (r ∼ 3000) spectrograph.results: a companion was found at a separation of 0.156″ from the star in the first epoch and increasing to 0.184″ in the final epoch. furthermore, several extended structures were found around the star, the most noteworthy of which is a very bright jet-like structure northeast from the star. the astrometric measurements of the companion in the four epochs confirm that it is gravitationally bound to the star. the sphere photometry and sinfoni spectrum, once corrected for extinction, point toward a spectral type object that is early m with a mass between 0.3 and 0.55 m⊙. the astrometric analyis provides constraints on the orbit paramenters: e ∼ 0.4, semimajor axis at 27-28 au, inclination of ∼70°, and a period larger than 30 yr. we were also able to put constraints of few mjup on the mass of possible other companions down to separations of few tens of au. based on observations made with european southern observatory (eso) telescopes at paranal observatory in chile, under programs id 095.c-0787(a), 097.c-0591(a), 1100.c-0481(h), 0101.c-0350(a) and 2101.c-5048(a).the sphere and sinfoni images 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/624/a4 | exploring the r cra environment with sphere. discovery of a new stellar companion |
one observational prediction for type ia supernovae (sne ia) explosions produced through white dwarf-white dwarf collisions is the presence of bimodal velocity distributions for the 56ni decay products, although this signature can also be produced by an off-centre ignition in a delayed detonation explosion. these bimodal velocity distributions can manifest as double-peaked or flat-topped spectral features in late-time spectroscopic observations for favourable viewing angles. we present nebular-phase spectroscopic observations of 17 sne ia obtained with the large binocular telescope. combining these observations with an extensive search of publicly available archival data, we collect a total sample of 48 sne ia and classify them based on whether they show compelling evidence for bimodal velocity profiles in three features associated with 56ni decay products: the [fe ii] and [fe iii] feature at ∼5300 å, the [co iii] λ5891 feature, and the [co iii] and [fe ii] feature at ∼6600 å. we identify nine bimodal sne in our sample, and we find that these sne have average peak mv about 0.3 mag fainter than those that do not. this is consistent with theoretical predictions for explosions created by nearly head-on collisions of white dwarfs due to viewing angle effects and 56ni yields. | signatures of bimodality in nebular phase type ia supernova spectra |
the nilsson et al. lyα nebula has often been cited as the most plausible example of an lyα nebula powered by gravitational cooling. in this paper, we bring together new data from the hubble space telescope and the herschel space observatory as well as comparisons to recent theoretical simulations in order to revisit the questions of the local environment and most likely power source for the lyα nebula. in contrast to previous results, we find that this lyα nebula is associated with six nearby galaxies and an obscured agn that is offset by ∼4″ ≈ 30 kpc from the lyα peak. the local region is overdense relative to the field, by a factor of ∼10, and at low surface brightness levels the lyα emission appears to encircle the position of the obscured agn, highly suggestive of a physical association. at the same time, we confirm that there is no compact continuum source located within ∼2-3″ ≈ 15-23 kpc of the lyα peak. since the latest cold accretion simulations predict that the brightest lyα emission will be coincident with a central growing galaxy, we conclude that this is actually a strong argument against, rather than for, the idea that the nebula is gravitationally powered. while we may be seeing gas within cosmic filaments, this gas is primarily being lit up, not by gravitational energy, but due to illumination from a nearby buried agn. | overturning the case for gravitational powering in the prototypical cooling lyα nebula |
a tremendous international effort is currently dedicated to observing the so-called primordial b modes of the cosmic microwave background (cmb) polarisation. if measured, this faint signal, caused by the primordial gravitational wave background, would be evidence of the inflation epoch and quantify its energy scale, providing a rigorous test of fundamental physics far beyond the reach of accelerators. at the unprecedented sensitivity level that the new generation of cmb experiments aims to reach, every uncontrolled instrumental systematic effect will potentially result in an analysis bias that is larger than the much sought-after cmb b-mode signal. the absolute calibration of the polarisation angle is particularly important in this context because any associated error will end up in leakage from the much larger e modes into b modes. the crab nebula (tau a), with its bright microwave synchrotron emission, is one of the few objects in the sky that can be used as absolute polarisation calibrators. in this paper we review the currently best constraints on its polarisation angle from 23 to 353 ghz at typical angular scales for cmb observations from wmap, xpol, planck, and nika data. these polarisation angle measurements are compatible with a constant angle of -88.26° ±0.27° (assuming that systematic errors are independent between frequencies and that the experiments fully capture the extent of the crab nebula). we study the uncertainty on this mean angle under different considerations for combinations of the individual measurement errors. for each of the cases, we study the potential effect on the cmb b-mode spectrum and on the recovered r parameter through a likelihood analysis. we find that current constraints on the crab polarisation angle, assuming it is constant through microwave frequencies, allow us to calibrate experiments with an accuracy enabling the measurement of r ∼ 0.01. on the other hand, even under the most optimistic assumptions, current constraints will lead to an important limitation for the detection of r ∼ 10-3. new realistic measurement of the crab nebula can change this situation by strengthening the assumption of the consistency across microwave frequencies and reducing the combined error. | absolute calibration of the polarisation angle for future cmb b-mode experiments from current and future measurements of the crab nebula |
recently, we have measured the ir absorptions of c60+, c60-, and c602+ in neon matrixes. many previously unknown absorptions were established. here we compare our laboratory ir absorption spectra for c60+ and c602+ to the ir emission spectra of several astronomical objects that show c60 emission. we find that ir bands of c60+ are possibly present in the objects tc1, smp smc 16, ngc 7023, ngc 2244, and smp lmc 02. infrared emission features possibly due to c602+ were identified in ngc 7023. to help with future observations of fullerene-related dibs, we also revisited the oscillator strengths of the nir absorptions of c60+, and report significantly revised values. additionally, we report the uv oscillator strengths of c60+. | on observing c60+ and c602+ in laboratory and space |
as the chemical compositions of ci chondrites closely resemble that of the sun's photosphere, their oxygen isotopic compositions represent a powerful tool to constrain the origin and dynamics of dust and water ice grains in the protoplanetary disk. however, parent-body alteration processes make straightforward estimation of the primordial isotopic compositions of ci chondritic water and anhydrous minerals difficult. in this contribution, we used in situ sims measurements to determine the oxygen isotope compositions of mechanically isolated olivine and carbonate grains from the ci chondrite orgueil and carbonates in a polished section of the ci chondrite ivuna. most ci olivine grains have earth-like o isotopic compositions (δ17o ≈ 0‰) plotting at the intersection of the terrestrial fractionation line and the primitive chondrule minerals line. ca-carbonates from orgueil and ivuna define a trend with δ17o = (0.50 ± 0.05) × δ18o + (0.9 ± 1.4) that differs from mass-independent variations observed in secondary phases of other carbonaceous chondrites. these data show that cis are chemically solar but isotopically terrestrial for oxygen isotopes. this supports models suggesting that primordial solar system dust was 16o-poor (δ17o ≈ 0‰) relative to the 16o-rich nebular gas. based on results, mass balance calculations reveal that the pristine o isotopic compositions of carbonaceous chondrite matrices differ significantly from the ci composition, except for cr chondrites (calculated δ17o values of cm, co, cv and cr matrices being -3.97 ± 1.19‰, -4.33 ± 1.45‰, -7.95 ± 1.95‰, and -0.07 ± 1.16‰, respectively). this confirms an open chondrule-matrix system with respect to oxygen isotopes where chondrule compositions reflect complex processes of chondrule precursor recycling and gas-melt interactions. as the mg-si-fe chondrule budget is also partially controlled by gas-melt interactions, the complementary formation of chondrules and matrix from a single solar-like reservoir -if it exists- require that (i) this reservoir must have been in a closed system with the gas or (ii) the gas had a ci composition to satisfy the elemental mass balance. | primordial water and dust of the solar system: insights from in situ oxygen measurements of ci chondrites |
we propose a scenario where a companion that is about to exit a common-envelope evolution (cee) with a giant star accretes mass from the remaining envelope outside its deep orbit and launches jets that facilitate the removal of the remaining envelope. the jets that the accretion disc launches collide with the envelope and form hot bubbles that energize the envelope. due to gravitational interaction with the envelope, which might reside in a circumbinary disc, the companion migrates farther in, but the inner boundary of the circumbinary disc continues to feed the accretion disc. while near the equatorial plane mass leaves the system at a very low velocity, along the polar directions velocities are very high. when the primary is an asymptotic giant branch star, this type of flow forms a bipolar nebula with very narrow waists. we compare this envelope-removal process with four other last-phase common-envelope-removal processes. we also note that the accreted gas from the envelope outside the orbit in the last phase of the cee might carry with it angular momentum that is anti-aligned to the orbital angular momentum. we discuss the implications to the possibly anti-aligned spins of the merging black hole event gw170104. | energizing the last phase of common-envelope removal |
we use the new non-local-thermodynamical-equilibrium (nlte) light curve and spectral synthesis code jekyll to evolve a macro-scopically mixed ejecta model of a type iib supernova (sn) originating from a star with an initial mass of 12 m⊙ through the photospheric and nebular phase. the ejecta model is adopted from earlier work and has a mass of 1.7 m⊙, has a kinetic energy of 0.7 foe, and contains 0.075 m⊙ of 56ni. the macroscopic mixing is simulated through a statistical representation of ejecta fragmented into small clumps but spherically symmetric on average. we compare our model with sn 2011dh and find that both the spectra and the light curves are well reproduced in both the photospheric and nebular phase, although there are also some differences. our work further strengthens the evidence that this sn originated from a star with an initial mass of ~12 m⊙ that had lost all but a tiny (<0.1 m⊙) fraction of its hydrogen envelope, strongly suggesting a binary origin. we also investigate the effects of the macroscopic mixing by comparing macroscopically and microscopically mixed models and by varying the clumping geometry. in the photospheric phase, we find strong effects on the effective opacity in the macroscopically mixed regions, which affects the model light curves. the diffusion peak is considerably narrower (rise time decreased by 11%) in the macroscopically mixed case and differs strongly (rise time decreased by 29%) if the radioactive material in the helium envelope is allowed to expand more than in our standard model. the effect is mainly geometrical and is driven by the expansion of the clumps that contain radioactive material, which tend to decrease the effective opacity. in the limit of optically thick clumps, the decrease is roughly given by the product of the (volume) expansion and filling factors for the radioactive material, and in our models values up to ~8 are explored. these findings have implications for light curve modelling of stripped-envelope sne in general, and the effect would increase the estimated ejecta masses. in the nebular phase, we find strong effects on the collisional cooling rates in the macroscopically mixed regions, which affects lines driven by collisional cooling, in particular the [ca ii] 7291, 7323 å and [o i] 6300, 6364 å lines. the effect is mainly related to differences in composition between macroscopically and microscopically mixed ejecta. as these lines are often used for mass determinations, this highlights the importance of how and to what extent the calcium- and oxygen-rich material is mixed. as shown in this and earlier work, both nlte and macroscopic mixing are essential ingredients for accurately modelling the light curves and spectra of type iib sne throughout their evolution. | spectral modelling of type iib supernovae. comparison with sn 2011dh and the effect of macroscopic mixing |
in unequilibrated chondrites, the ferromagnesian silicates in chondrules exhibit wide ranges of mg# = mg/(mg + fe), allowing to sub-divide porphyritic chondrules into either type i (mg# > 0.9) or type ii (mg# < 0.9). although both chondrule types formed under oxidizing conditions relative to the canonical solar nebula, it is generally inferred that type ii chondrules formed in more oxidizing conditions than type i. in order to check whether this redox difference was established during chondrule formation, or reflects differences in their precursors, we have undertaken a set of experiments aimed at heating type i olivine-rich (a) chondrule proxy, i.e. forsterite + fe metal + ca-mg-si-al glass mixtures, under oxidizing conditions. we show that high temperature (isothermal) oxidation of type ia-like assemblages is a very efficient and rapid process (e.g. few tens of minutes) to form textures similar to type iia chondrules. due to the rapid dissolution of fe metal blebs, a feo increase in the melt and in combination with the dissolution of magnesian olivine allows the melt to reach ferroan olivine saturation. crystallization of ferroan olivine occurs either as new crystal in the mesostasis or as overgrowths on the remaining unresorbed forsterite grains (relicts). interruption of this process at any time before its completion by rapid cooling allows to reproduce the whole range of textures and chemical diversity observed in type a chondrules, i.e. from type i to type ii. several implications on chondrule formation processes can be inferred from the presented experiments. type i chondrules or fragments of type i chondrules are very likely the main precursor material involved in the formation of most type ii chondrules. formation of porphyritic olivine type ii chondrules is very likely the result of processes generating crystal growth by chemical disequilibrium at high temperature rather than processes generating crystallization only by cooling rates. this questions the reliability of chondrule thermal history (e.g. cooling rate values) hitherto inferred for producing porphyritic textures from dynamical cooling rate experiments only. type a chondrule formation can be a very fast process. after periods of sub-isothermal heating or slow cooling (<50 k/h) as short as several tens of minutes and no longer than few hundreds of minutes at 1500-1800 °c, type a chondrules terminates their formation by a fast cooling (>103-104 k/h) in order to preserve their glassy mesostasis. such inferred thermal history being at odds with nebular shock models, we thus advocate that impacts on planetesimals causing rapid melting and vaporization may provide the high density and highly volatile-enriched gaseous environments required to form chondrules. in this scenario, chondrules and their diversity should result from various degrees of interaction of the ejected fragments with the impact vapor plume; the most oxidizing conditions recorded in type iia chondrules being very likely the closest to those imposed by the impact vapor plume. | relationships between type i and type ii chondrules: implications on chondrule formation processes |
we present one-dimensional non-local thermodynamic equilibrium time-dependent radiative transfer simulations (using cmfgen) of two sub-chandrasekhar (sub-mch), one mch and one super-mch type ia sn ejecta models. three originate from mch delayed detonation models, and the fourth is a sub-mch detonation model. ejecta masses are 1.02, 1.04, 1.40 and 1.70 m⊙, and all models have 0.62 m⊙ of 56ni. sub-mch model light curves evolve faster, reaching bolometric maximum 2-3 d earlier and having 3-4 d shorter bolometric half-light widths. the models vary by ∼12 per cent at maximum bolometric luminosity and by 0.17 mag in bmax. while δm15(b) increases with ejecta mass, it only varies by ∼5 per cent around 1 mag. sub-mch models are 0.25 mag bluer in b - r at bmax. optical spectra share many similarities, but lower mass models exhibit less uv line blanketing during the photospheric phase. at nebular times, significant near-infrared (nir) spectroscopic differences are seen. in particular, emission lines of the ca ii nir triplet; [s iii] λλ9068,9530; [ca ii] λλ7291,7324; [ar iii] λλ7135,7751 and [ni ii] 1.939 μm are stronger in higher mass models. the [ni ii] 1.939 μm line is absent in the sub-mch detonation model, and provides a valuable potential tool to distinguish sub-mch explosions from mch explosions. in general, the nebular phase models are too highly ionized. we attribute this to the neglect of clumping and/or the distribution of intermediate mass and iron group elements. the two sub-mch models, while exploded by different mechanisms, can be distinguished in the j and h bands at late times (e.g. +200 d). | ejecta mass diagnostics of type ia supernovae |
the unidentified very-high-energy (vhe; e > 0.1 tev) γ-ray source, hess j1826-130, was discovered with the high energy stereoscopic system (hess) in the galactic plane. the analysis of 215 h of hess data has revealed a steady γ-ray flux from hess j1826-130, which appears extended with a half-width of 0.21° ± 0.02stat° ± 0.05sys°. the source spectrum is best fit with either a power-law function with a spectral index γ = 1.78 ± 0.10stat ± 0.20sys and an exponential cut-off at 15.2-3.2+5.5 tev, or a broken power-law with γ1 = 1.96 ± 0.06stat ± 0.20sys, γ2 = 3.59 ± 0.69stat ± 0.20sys for energies below and above ebr = 11.2 ± 2.7 tev, respectively. the vhe flux from hess j1826-130 is contaminated by the extended emission of the bright, nearby pulsar wind nebula, hess j1825-137, particularly at the low end of the energy spectrum. leptonic scenarios for the origin of hess j1826-130 vhe emission related to psr j1826-1256 are confronted by our spectral and morphological analysis. in a hadronic framework, taking into account the properties of dense gas regions surrounding hess j1826-130, the source spectrum would imply an astrophysical object capable of accelerating the parent particle population up to ≳200 tev. our results are also discussed in a multiwavelength context, accounting for both the presence of nearby supernova remnants, molecular clouds, and counterparts detected in radio, x-rays, and tev energies. | an extreme particle accelerator in the galactic plane: hess j1826-130 |
while the radiation mechanism of fast radio bursts (frbs) is unknown, coherent curvature radiation and synchrotron maser are promising candidates. we find that both radiation mechanisms work for a neutron star (ns) central engine with b ≳ 1012 g, while for a synchrotron maser, the central engine can also be an accreting black hole (bh) with b ≳ 1012 g and a white dwarf (wd) with b ∼ 108 - 109 g. we study the electromagnetic counterparts associated with such central engines, i.e., nebulae for repeating frbs and afterglows for nonrepeating frbs. in general, the energy spectrum and flux density of the counterpart depend strongly on its size and total injected energy. we apply the calculation to the nebula of frb 121102 and find that the persistent radio counterpart requires the average energy injection rate into the nebula to be between 2.7 × 1039 erg s-1 and 1.5 × 1044 erg s-1, and the minimum injected energy to be 6.0 × 1047 erg in around 7 yr. consequently, we find that for frb 121102 and its nebula: (1) wd and accretion bh central engines are disfavored; (2) a rotation-powered ns central engine works when 1.2 × 1012 g ≲ b ≲ 7.8 × 1014 g with initial period p < 180 ms, but the radio emission must be more efficient than that in typical giant pulses of radio pulsars; and (3) a magnetic-powered ns central engine works when its internal magnetic field b ≳ 1016 g. we also find that the radio-emitting electrons in the nebula could produce a significant rotation measure (rm), but cannot account for the entire observed rm of frb 121102. | fast radio burst counterparts and their implications for the central engine |
we investigate ztf18aalrxas, a double-peaked type iib core-collapse supernova (sn) discovered during science validation of the zwicky transient facility. ztf18aalrxas was discovered while the optical emission was still rising toward the initial cooling peak (0.7 mag over 2 days). our observations consist of multi-band (ultraviolet and optical) light curves (lcs), and optical spectra spanning from ≈0.7 to ≈180 days past the explosion. we use a monte-carlo based non-local thermodynamic equilibrium model that simultaneously reproduces both the 56ni-powered bolometric lc and our nebular spectrum. this model is used to constrain the synthesized radioactive nickel mass (0.17 m ⊙) and the total ejecta mass (1.7 m ⊙) of the sn. the cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius (790-1050 r ⊙) at the time of explosion. our nebular spectrum shows signs of interaction with a dense circumstellar medium (csm), and this spectrum is modeled and analyzed to constrain the amount of ejected oxygen (0.3-0.5 m ⊙) and the total hydrogen mass (≈0.15 m ⊙) in the envelope of the progenitor. the oxygen mass of ztf18aalrxas is consistent with a low (12-13 m ⊙) zero-age main-sequence mass progenitor. the lcs and spectra of ztf18aalrxas are not consistent with massive single-star sn type iib progenitor models. the presence of an extended hydrogen envelope of low mass, the presence of a dense csm, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario. | ztf18aalrxas: a type iib supernova from a very extended low-mass progenitor |
context. complex bipolar shapes can be generated either as a planetary nebula or a symbiotic system. the origin of the material ionised by the white dwarf is very different in these two scenarios, and it complicates the understanding of the morphologies of planetary nebulae.aims: the physical properties, structure, and dynamics of the bipolar nebulae, m 2-9, mz 3, and hen 2-104, are investigated in detail with the aim of understanding their nature, shaping mechanisms, and evolutionary history. both a morpho-kinematic study and a spectroscopic analysis, can be used to more accurately determine the kinematics and nature of each nebula.methods: long-slit optical echelle spectra are used to investigate the morpho-kinematics of m 2-9, mz 3, and hen 2-104. the morpho-kinematic modelling software shape is used to constrain both the morphology and kinematics of each nebula by means of detailed 3d models. near-infrared (nir) data, as well as optical, spectra are used to separate galactic symbiotic-type nebulae from genuine planetary nebulae by means of a 2mass j-h/h-ks diagram and a λ4363/hγ vs. λ5007/hβ diagnostic diagram, respectively.results: the best-fitted 3d models for m 2-9, mz 3, and hen 2-104 provide invaluable kinematical information on the expansion velocity of its nebular components by means of synthetic spectra. the observed spectra match up very well with the synthetic spectra for each model, thus showing that each model is tightly constrained both morphologically and kinematically. kinematical ages of the different structures of m 2-9 and mz 3 have also been determined. both diagnostic diagrams show m 2-9 and hen 2-104 to fall well within the category of having a symbiotic source, whereas mz 3 borders the region of symbiotic and young planetary nebulae in the optical diagram but is located firmly in the symbiotic region of the nir colour-colour diagram. the optical diagnostic diagram is shown to successfully separate the two types of nebulae, however, the nir colour-colour diagram is not as accurate in separating these objects.conclusions: the morphology, kinematics, and evolutionary history of m 2-9, mz 3, and hen 2-104 are better understood using the interactive 3d modelling tool shape. the expansion velocities of the components for each nebula are better constrained and fitted with a vector field to reveal their direction of motion. the optical and nir diagnostic diagrams used are important techniques for separating galactic symbiotic-type nebulae from genuine planetary nebulae. | a morpho-kinematic and spectroscopic study of the bipolar nebulae: m 2-9, mz 3, and hen 2-104 |
we have observed the pulsar in the crab nebula at high radio frequencies and high time resolution. we present continuously sampled data at 640 ns time resolution and individual bright pulses recorded at down to 0.25 ns time resolution. combining our new data with previous data from our group and from the literature shows the dramatic changes in the pulsar’s radio emission between low and high radio frequencies. below about 5 ghz the mean profile is dominated by the bright main pulse and low-frequency interpulse. everything changes, however, above about 5 ghz; the main pulse disappears and the mean profile of the crab pulsar is dominated by the high-frequency interpulse (which is quite different from its low-frequency counterpart) and the two high-frequency components. we present detailed observational characteristics of these different components which future models of the pulsar’s magnetosphere must explain. | the crab pulsar at centimeter wavelengths. i. ensemble characteristics |
the clash x-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (bcgs) that exhibit significant (>5σ) extinction-corrected star formation rates (sfrs). star formation activity is inferred from photometric estimates of uv and hα+[n ii] emission in knots and filaments detected in clash hubble space telescope acs and wfc3 observations. uv-derived sfrs in these bcgs span two orders of magnitude, including two with a sfr ≳ 100 m⊙ yr-1. these measurements are supplemented with [o ii], [o iii], and hβ fluxes measured from spectra obtained with the soar telescope. we confirm that photoionization from ongoing star formation powers the line emission nebulae in these bcgs, although in many bcgs there is also evidence of a liner-like contribution to the line emission. coupling these data with chandra x-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. we also perform an in-depth study of the starburst history of the bcg in the cluster rxj1532.9+3021, and create 2d maps of stellar properties on scales down to ∼350 pc. these maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ∼0.5-1.0 gyr timescales, although some filaments are consistent with much younger (≲100 myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. the relationship between bcg sfrs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions. based on observations obtained at the southern astrophysical research (soar) telescope, which is a joint project of the ministério da ciência, tecnologia, e inovação (mcti) da república federativa do brasil, the u.s. national optical astronomy observatory (noao), the university of north carolina at chapel hill (unc), and michigan state university (msu). | star formation activity in clash brightest cluster galaxies |
in this work, we measure the lyα escape fraction of 935 [o iii]-emitting galaxies between 1.9 < z < 2.35 by comparing stacked spectra from the hubble space telescope/wfc3's near-ir grism to corresponding stacks from the hobby-eberly telescope dark energy experiment's internal data release 2. by measuring the stacks' hβ to lyα ratios, we determine the lyα escape fraction as a function of stellar mass, star-formation rate, internal reddening, size, and [o iii]/hβ ratio. we show that the escape fraction of lyα correlates with a number of parameters, such as galaxy size, star-formation rate, and nebular excitation. however, we also demonstrate that most of these relations are indirect, and that the primary variables controlling the escape of lyα are likely to be stellar mass and internal extinction. overall, the escape of lyα declines from ≳16% in galaxies with $\mathrm{log}m/{m}_{\odot }\lesssim 9$ to ≲1% for systems with $\mathrm{log}m/{m}_{\odot }\gtrsim 10$ , with the sample's mean escape fraction being ${6.0}_{-0.5 \% }^{+0.6 \% }$ . | the hetdex survey: the lyα escape fraction from 3d-hst emission-line galaxies at z ∼ 2 |
context. measuring star formation on a local scale is important to constrain star formation laws. it is not clear yet, however, whether and how the measure of star formation is affected by the spatial scale at which a galaxy is observed.aims: we wish to understand the impact of the resolution on the determination of the spatially resolved star formation rate (sfr) and other directly associated physical parameters such as the attenuation.methods: we carried out a multi-scale, pixel-by-pixel study of the nearby galaxy m 33. assembling fuv, hα, 8 μm, 24 μm, 70 μm, and 100 μm maps, we have systematically compared the emission in individual bands with various sfr estimators from a resolution of 33 pc to 2084 pc.results: there are strong, scale-dependent, discrepancies of up to a factor 3 between monochromatic sfr estimators and hα+24 μm. the scaling factors between individual ir bands and the sfr show a strong dependence on the spatial scale and on the intensity of star formation. finally, strong variations of the differential reddening between the nebular emission and the stellar continuum are seen, depending on the specific sfr (ssfr) and on the resolution. at the finest spatial scales, there is little differential reddening at high ssfr. the differential reddening increases with decreasing ssfr. at the coarsest spatial scales the differential reddening is compatible with the canonical value found for starburst galaxies.conclusions: our results confirm that monochromatic estimators of the sfr are unreliable at scales smaller than 1 kpc. furthermore, the extension of local calibrations to high-redshift galaxies presents non-trivial challenges because the properties of these systems may be poorly known. the maps (fits files) and the data cube used in this article 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/578/a8 | measuring star formation with resolved observations: the test case of m 33 |
we present a study of the galaxy environment of nine strong h i + c iv absorption line systems (16.2 < log(n(hi)) < 21.2) spanning a wide range in metallicity at z ∼ 4-5, using muse integral field and x-shooter spectroscopic data collected in a z ≈ 5.26 quasar field. we identify galaxies within a 250 kpc and ±1000 km s-1 window for six out of the nine absorption systems, with two of the absorption line systems showing multiple associated galaxies within the muse field of view. the space density of ly α emitting galaxies (laes) around the h i and c iv systems is ≈10-20 times the average sky density of laes given the flux limit of our survey, showing a clear correlation between the absorption and galaxy populations. further, we find that the strongest c iv systems in our sample are those that are most closely aligned with galaxies in velocity space, i.e. within velocities of ±500 km s-1. the two most metal-poor systems lie in the most dense galaxy environments, implying we are potentially tracing gas that is infalling for the first time into star-forming groups at high redshift. finally, we detect an extended ly α nebula around the z ≈ 5.26 quasar, which extends up to ≈50 kpc at the surface brightness limit of 3.8 × 10-18 erg s-1 cm-2 arcsec-2. after scaling for surface brightness dimming, we find that this nebula is centrally brighter, having a steeper radial profile than the average for nebulae studied at z ∼ 3 and is consistent with the mild redshift evolution seen from z ≈ 2. | into the ly α jungle: exploring the circumgalactic medium of galaxies at z ∼ 4-5 with muse |
the first detected gravitational wave gw170817 from a binary neutron star merger is associated with an important optical transient at 2017gfo, which is a direct observation of kilonova. recent observations suggest that the remnant compact object of the binary neutron star merger associated with gw170817/grb 170817a may be a stable long-lived magnetized neutron star. in this situation, there would be a pulsar wind nebula (pwn) embedded inside the dynamic ejecta. the pwn emission may be absorbed by the ejecta or leak out of the system. we study the effect of the pwn emission on the observed light curves and radiation spectra. different from previous works, the absorption and leakage of the pwn emission are all involved in our model, where the absorption of the pwn emission heats up the ejecta and alters its radiation. it is found that the characteristic emission of the embedded pwn quickly evolves. for the multiband and long-term observations of at 2017gfo, we find that the dynamic ejecta with a pwn emission can fit the observational data very well, especially for the light curves at t ∼ 5 days and those in the late phase. in addition, our model can naturally generate the thermal to nonthermal spectrum evolution of at 2017gfo. our fitting result suggests that a pwn is embedded in the at 2017gfo. | a pulsar wind nebula embedded in the kilonova at 2017gfo associated with gw170817/grb 170817a |
we present late-time hubble space telescope (hst) images of the site of supernova (sn) 2009ip taken almost 3 yr after its bright 2012 luminosity peak. sn 2009ip is now slightly fainter in broad filters than the progenitor candidate detected by hst in 1999. the current source continues to be dominated by ongoing late-time circumstellar material interaction that produces strong hα emission and a weak pseudo-continuum, as found previously for 1-2 yr after explosion. the intent of these observations was to search for evidence of recent star formation in the local (∼1 kpc; 10 arcsec) environment around sn 2009ip, in the remote outskirts of its host spiral galaxy ngc 7259. we can rule out the presence of any massive star-forming complexes like 30 dor or the carina nebula at the sn site or within a few kpc. if the progenitor of sn 2009ip was really a 50-80 m⊙ star as archival hst images suggested, then it is strange that there is no sign of this type of massive star formation anywhere in the vicinity. a possible explanation is that the progenitor was the product of a merger or binary mass transfer, rejuvenated after a lifetime that was much longer than 4-5 myr, allowing its natal h ii region to have faded. a smaller region like the orion nebula would be an unresolved but easily detected point source. this is ruled out within ∼1.5 kpc around sn 2009ip, but a small h ii region could be hiding in the glare of sn 2009ip itself. later images after a few more years have passed are needed to confirm that the progenitor candidate is truly gone and to test for the possibility of a small h ii region or cluster at the sn position. | massive stars dying alone: the extremely remote environment of sn 2009ip |
we search for far-infrared (fir) counterparts of known supernova remnants (snrs) in the galactic plane (360° in longitude and $b = \pm \, 1^{\circ }$ ) at 70-500 μm with herschel. we detect dust signatures in 39 snrs out of 190, made up of 13 core-collapse supernovae (ccsne), including 4 pulsar wind nebulae (pwne), and 2 type ia sne. a further 24 fir detected snrs have unknown types. we confirm the fir detection of ejecta dust within g350.1-0.3, adding to the known sample of ∼ 10 snrs containing ejecta dust. we discover dust features at the location of a radio core at the centre of g351.2+0.1, indicating fir emission coincident with a possible crab-like compact object, with dust temperature and mass of td = 45.8 k and md = 0.18 m⊙, similar to the pwn g54.1+0.3. we show that the detection rate is higher among young snrs. we produce dust temperature maps of 11 snrs and mass maps of those with distance estimates, finding dust at temperatures $15\, \lesssim \, t_d\, \lesssim \, 40$ k. if the dust is heated by shock interactions the shocked gas must be relatively cool and/or have a low density to explain the observed low grain temperatures. | a complete catalogue of dusty supernova remnants in the galactic plane |
it has been demonstrated that planets belonging to the same close-in, compact multiple-planet system tend to exhibit a striking degree of uniformity in their sizes. a similar trend has also been found to hold for the masses of such planets, but considerations of such intra-system mass uniformity have generally been limited to statistical samples wherein a majority of systems have constituent planetary mass measurements obtained via analysis of transit timing variations (ttvs). since systems with strong ttv signals typically lie in or near mean motion resonance, it remains to be seen whether intra-system mass uniformity is still readily emergent for nonresonant systems with non-ttv mass provenance. we thus present in this work a mass uniformity analysis of 17 non-ttv systems with masses measured via radial velocity measurements. using the gini index, a common statistic for economic inequality, as our primary metric for uniformity, we find that our sample of 17 non-ttv systems displays intra-system mass uniformity at a level of ~2.5σ confidence. we provide additional discussion of possible statistical and astrophysical underpinnings for this result. we also demonstrate the existence of a correlation (r = 0.25) between characteristic solid surface density (σ0) of the minimum-mass extrasolar nebula and system mass gini index, suggesting that more-massive disks may generally form systems with more-unequal planetary masses. | generalized peas in a pod: extending intra-system mass uniformity to non-ttv systems via the gini index |
context. dynamical interactions in young stellar clusters can eject massive stars early in their lives and significantly alter their mass functions. if all of the most massive stars are lost, we are left with an orphan cluster.aims: we study the bermuda cluster (villafranca o-014 nw), the most significant young stellar group in the north america and pelican nebulae, and the massive stars that may have been ejected from it to test if it has been orphaned.methods: we use gaia edr3 parallaxes and proper motions to search for walkaway and runaway stars in the vicinity of the north america and pelican nebulae. the candidates are analyzed with a combination of spectroscopy and photometry to assess their nature and their trajectories are traced back in time to determine at what time they left the bermuda cluster.results: we detect three ejection events, dubbed the bajamar, toronto, and hd 201 795 events, which expelled (a minimum of) five, two, and two systems, respectively, or six, three, and three stars if we count the individual components in spectroscopic and eclipsing binaries. the events took place 1.611 ± 0.011 ma, 1.496 ± 0.044 ma, and 1.905 ± 0.037 ma ago, respectively, but our analysis is marginally consistent with the first two being simultaneous. we detect bow shocks in wise images associated with four of the ejected systems; their orientation agrees with that of their relative proper motions with respect to the cluster. combining the three events, the bermuda cluster has lost over 200 m⊙, including its three most massive stars, so it can be rightfully considered an orphan cluster. one consequence is that the present-day mass function of the cluster has been radically altered from its top-heavy initial value to one compatible with a kroupa-like function. another is that the cluster is currently expanding with a dynamical timescale consistent with the cause being the ejection events. a scenario in which the bermuda cluster was formed in a conveyor-belt fashion over several hundreds of ka or even 1 ma is consistent with all the observables. | escape from the bermuda cluster: orphanization by multiple stellar ejections |
v392 persei is a known dwarf nova (dn) that underwent a classical nova eruption in 2018. here we report ground-based optical, swift uv and x-ray, and fermi-lat γ-ray observations following the eruption for almost three years. v392 per is one of the fastest evolving novae yet observed, with a t2 decline time of 2 d. early spectra present evidence for multiple and interacting mass ejections, with the associated shocks driving both the γ-ray and early optical luminosity. v392 per entered sun-constraint within days of eruption. upon exit, the nova had evolved to the nebular phase, and we saw the tail of the supersoft x-ray phase. subsequent optical emission captured the fading ejecta alongside a persistent narrow line emission spectrum from the accretion disc. ongoing hard x-ray emission is characteristic of a standing accretion shock in an intermediate polar. analysis of the optical data reveals an orbital period of 3.230 ± 0.003 d, but we see no evidence for a white dwarf (wd) spin period. the optical and x-ray data suggest a high mass wd, the pre-nova spectral energy distribution (sed) indicates an evolved donor, and the post-nova sed points to a high mass accretion rate. following eruption, the system has remained in a nova-like high mass transfer state, rather than returning to the pre-nova dn low mass transfer configuration. we suggest that this high state is driven by irradiation of the donor by the nova eruption. in many ways, v392 per shows similarity to the well-studied nova and dn gk persei. | v392 persei: a γ-ray bright nova eruption from a known dwarf nova |
in this work, we present a new catalogue of >40 000 ionised nebulae distributed across the 19 galaxies observed by the phangs-muse survey. the nebulae have been classified using a new model-comparison-based algorithm that exploits the odds ratio principle to assign a probabilistic classification to each nebula in the sample. the resulting catalogue is the largest catalogue containing complete spectral and spatial information for a variety of ionised nebulae available so far in the literature. we developed this new algorithm to address some of the main limitations of the traditional classification criteria, such as their binarity, the sharpness of the involved limits, and the limited amount of data they rely on for the classification. the analysis of the catalogue shows that the algorithm performs well when selecting h ii regions. in fact, we can recover their luminosity function, and its properties are in line with what is available in the literature. we also identify a rather significant population of shock-ionised regions (mostly composed of supernova remnants), which is an order of magnitude larger than any other homogeneous catalogue of supernova remnants currently available in the literature. the number of supernova remnants we identify per galaxy is in line with results in our galaxy and in other very nearby sources. however, limitations in the source detection algorithm result in an incomplete sample of planetary nebulae, even though their classification seems robust. finally, we demonstrate how applying a correction for the contribution of the diffuse ionised gas to the nebulae's spectra is essential to obtain a robust classification of the objects and how a correct measurement of the extinction using diffuse-ionised-gas-corrected line fluxes prompts the use of a higher theoretical hα/hβ ratio (3.03) than what is commonly used when recovering the e(b - v) via the balmer decrement technique in massive star-forming galaxies. the catalogue of nebulae is 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/672/a148. the catalogue, together with the segmentation maps, is also available through the cadc via http://dx.doi.org/10.11570/23.0006 | phangs-muse: detection and bayesian classification of40 000 ionised nebulae in nearby spiral galaxies |
cosmic ray electrons and positrons are tracers of particle propagation in the interstellar medium (ism). a recent measurement performed using the high energy stereoscopic system extends the all-electron (electron +positron ) spectrum up to 20 tev, probing very local sources and transport due to the ∼10 kyr cooling time of these particles. an additional key local measurement was the recent estimation of the ism diffusion coefficient around geminga performed using the high-altitude water cherenkov observatory. the inferred diffusion coefficient is much lower than typically assumed values. it has been argued that if this diffusion coefficient is representative of the local ism, pulsars would not be able to account for the all-electron spectrum measured at earth. here we show that a low diffusion coefficient in the local ism is compatible with a pulsar wind nebula origin of the highest energy electrons, if a so-far-undiscovered pulsar with spin-down power ∼1 033 - 34 erg /s exists within 30-80 pc of earth. the existence of such a pulsar is broadly consistent with the known population and may be detected in near future survey observations. | undiscovered pulsar in the local bubble as an explanation of the local high energy cosmic ray all-electron spectrum |
in order to further elucidate possible temporal relationships between different varieties of calcium-, aluminum-rich inclusions (cais), we measured the aluminum-magnesium isotopic systematics of seven examples of the rare type known as forsterite-bearing type b (fob) inclusions from four different cv3 carbonaceous chondrites: allende, efremovka, nwa 3118, and vigarano. the primary phases (forsterite, al-ti-rich diopside, spinel, melilite, and anorthite) in each inclusion were analyzed in situ using high-precision secondary ion mass-spectrometry (sims). in all cases, minerals with low al/mg ratios (all except anorthite) yield well-defined internal al-mg isochrons, with a range of initial 26al/27al ratios [(26al/27al)0] ranging from (5.30 ± 0.22) × 10-5 down to (4.17 ± 0.43) × 10-5. anorthite in all cases is significantly disturbed relative to the isochrons defined by the other phases in the same cais, and in several cases contains no resolved excesses of radiogenic 26mg (δ26mg∗) even at 27al/24mg ratios greater than 1000. the fact that some fobs preserve (26al/27al)0 of ∼5.2 × 10-5, close to the canonical value of (5.23 ± 0.13) × 10-5 inferred from bulk magnesium-isotope measurements of cv cais (b. jacobsen et al., 2008), demonstrates that fobs began forming very early, contemporaneous with other more-refractory cais. the range of (26al/27al)0 values further shows that fobs continued to be reprocessed over ∼200,000 years of nebular history, consistent with results obtained for other types of igneous cais in cv chondrites. the absence of any correlation between of cai + fob formation or reprocessing times with bulk composition or cai type means that there is no temporal evolutionary sequence between the diverse cai types. the initial δ26mg∗ value in the most primitive fob (sj101) is significantly lower than the canonical solar system value of -0.040 ± 0.029‰. | high precision al-mg systematics of forsterite-bearing type b cais from cv3 chondrites |
five type a cais from three cv3 chondrites (vigarano, northwest africa 3118, allende), which differ in age by no more than ∼105 years, show mineralogical and textural evidence of gradual transition into type bs, indicating that type b inclusions formed by evolution of type a cais in the solar nebula. this model differs from the conventional condensation model in which aggregates of condensate grains form different kinds of cais depending on the relative populations of different kinds of grains. in our model the pyroxene forms nearly isochemically by reaction of perovskite with melilite under highly reducing conditions. anorthite requires the addition of silica from the gas, and originally forms as veins and reaction rims on gehlenitic melilite within fluffy type as. later partial re-melting of these assemblages results in the formation of poikilitic pyroxene and anorthite that enclose rounded (partially melted) tablets of melilite. oxygen isotopes in four of the cais support the formation of ti-rich 16o-depleted pyroxene from 16o-depleted perovskite, but not in the fifth cai. an alternative possibility is that ti-rich 16o-depleted pyroxene is the result of later solid-state exchange that preferentially affects the most ti-rich pyroxene. regardless of the origin of the 16o-depleted pyroxene, we give a model for nebular reservoir evolution based on sporadic fu-orionis flare-ups in which the 16o-rich region near the proto-sun fluctuated in size depending on whether the proto-sun was in flare-up stage or quiescent. | the formation of type b cais: evolution from type a cais |
the large high altitude air shower observatory (lhaaso) is one of the most sensitive gamma-ray detector arrays, whose ultrahigh-energy (uhe) work bands not only help to study the origin and acceleration mechanism of uhe cosmic rays, but also provide the opportunity to test fundamental physics concepts such as lorentz symmetry. lhaaso directly observes the 1.42pev highest-energy photon. by adopting the synchrotion self-compton model, lhaaso also suggests that the 1.12pev high-energy photon from crab nebula corresponds to a 2.3pev high-energy electron. we study the 1.42pev photon decay and the 2.3pev electron decay to perform a joint analysis on photon and electron two-dimensional lorentz violation (lv) parameter plane. our analysis is systematic and comprehensive, and we naturally get the strictest constraints from merely considering photon lv effect in photon decay and electron lv effect in electron decay. our result also permits the parameter space for new physics beyond relativity. | joint photon-electron lorentz violation parameter plane from lhaaso data |
we analyse a 3d hydrodynamic simulation of common envelope evolution to understand how energy is transferred between various forms and whether theory and simulation are mutually consistent given the set-up. virtually all of the envelope unbinding in the simulation occurs before the end of the rapid plunge-in phase, here defined to coincide with the first periastron passage. in contrast, the total envelope energy is nearly constant during this time because positive energy transferred to the gas from the core particles is counterbalanced by the negative binding energy from the closer proximity of the inner layers to the plunged-in secondary. during the subsequent slow spiral-in phase, energy continues to transfer to the envelope from the red giant core and secondary core particles. we also propose that relative motion between the centre of mass of the envelope and the centre of mass of the particles could account for the offsets of planetary nebula central stars from the nebula's geometric centre. | energy budget and core-envelope motion in common envelope evolution |
we present atacama large millimeter/sub-millimeter array cycle-2 observations of the hbc 494 molecular outflow and envelope. hbc 494 is an fu ori-like object embedded in the orion a cloud and is associated with the reflection nebulae re50 and re50n. we use 12co, 13co and c18o spectral line data to independently describe the outflow and envelope structures associated with hbc 494. the moment-1 map of the 12co emission shows the widest outflow cavities in a class i object known to date (opening angle ∼150°). the morphology of the wide outflow is likely to be due to the interaction between winds originating in the inner disc and the surrounding envelope. the low-velocity blueshifted and redshifted 13co and c18o emission trace the rotation and infall motion of the circumstellar envelope. using molecular line data and adopting standard methods for correcting optical depth effects, we estimate its kinematic properties, including an outflow mass of the order of 10-1 m⊙. considering the large estimated outflow mass for hbc 494, our results support recent theoretical work suggesting that wind-driven processes might dominate the evolution of protoplanetary discs via energetic outflows. | the alma early science view of fuor/exor objects - ii. the very wide outflow driven by hbc 494 |
we use x-ray computed tomography (xct) to examine the 3d morphology and spatial relationship of fine-grained rims (fgrs) of type i chondrules in the cm carbonaceous chondrite murchison to investigate the formation setting (nebular vs. parent body) of the fgrs. we quantify the sizes, shapes, and orientations of the chondrules and fgrs and develop a new algorithm to examine the 3d variation of fgr thickness around each chondrule. we find that the average proportion of chondrule volume contained in the rim for murchison chondrules is 35.9%. the fgr volume in relation to the interior chondrule radius is well described by a power law function as proposed for accretion of fgrs in a weakly turbulent nebula by cuzzi (2004). the power law exponent indicates that the rimmed chondrules behaved as stokes number stη > 1 nebular particles in kolmogorov η scale turbulence. fgr composition as inferred from xct number appears essentially uniform across interior chondrule types and compositions, making formation by chondrule alteration unlikely. we determine that the fgrs were compressed by the impact event(s) that deformed murchison (hanna et al., 2015), resulting in rims that are thicker in the plane of foliation but that still preserve their nebular morphological signature. finally, we propose that the irregular shape of some chondrules in murchison is a primary feature resulting from chondrule formation and that chondrules with a high degree of surface roughness accreted a relatively larger amount of nebular dust compared to smoother chondrules. | evidence for accretion of fine-grained rims in a turbulent nebula for cm murchison |
concerning the electroconvective analyte manipulation in microfluidics, we describe the basic physics of fluid flow driven by rotating induced-charge electro-osmosis (rot-iceo), which occurs on the planar surface of a single floating electrode in an external rotating electric field. first, based on a linear asymptotic analysis, the dynamic flow stagnation line in rot-iceo induced on the bipolar electrode from a rotary debye screening charge revolves synchronously with the applied rotating fields. a net hydrodynamic torque is then generated that acts on any fluid or particle sample to produce either a synchronous or asynchronous co-field rotation depending on the frequency of the ac signal. next, from the synergy between the hydrodynamic and electrochemical ion relaxations, an analytical solution of the sample rotation rate subject to rot-iceo slipping on an ideally polarizable surface is obtained for different frequency ranges and determined by the transient nature of the rotating electro-osmotic flow oscillating at twice the field frequency. to visualize the flow field in rot-iceo, experiments were performed with fluorescent tracer nanoparticles; they exhibited concentric rotational behavior at the polarized phase interface. formed like the arms of a nebula disk, the four twisted tails of nanoparticles can be arbitrarily directed under voltage-phase rectification. these experimental results are in good agreement with our mathematical simulations using the debye-hückel approximation on rot-iceo. | induced-charge electrokinetics in rotating electric fields: a linear asymptotic analysis |
supernova remnants (snrs) contain information on the influence of supernova explosions on dust properties. based on the color indices from the two micron all sky survey and the stellar parameters from the sdss-dr12/apache point observatory galactic evolution experiment and lamost-dr2/lamost experiment for galactic understanding and exploration spectroscopic surveys, the near-infrared extinction law of and the distance to the monoceros snr are derived together with those of two nebulae close to it, the rosette nebula and ngc 2264. the distance is found at the position of the sharp increase of the interstellar extinction with distance, and the nebular extinction is calculated by subtracting the foreground interstellar extinction. the distance to the monoceros snr is determined to be 1.98 kpc, larger than previous values. meanwhile, the distance to the rosette nebula is 1.55 kpc, which is generally consistent with previous work. the distance between these two nebulae suggests no interaction between them. the distance to ngc 2264, 1.20 kpc, exceeds previous values. the color excess ratio, {e}{jh}/{e}{{jk}s}, is 0.657 for the monoceros snr, consistent with the average value of 0.652 for the milky way. this consistency results from the fact that the snr material is dominated by interstellar dust rather than by supernova ejecta. {e}{jh}/{e}{{jk}s} is equal to 0.658 for the rosette nebula, further proving the universality of the near-infrared extinction law. | the distance to and the near-infrared extinction of the monoceros supernova remnant |
in this paper, we investigate the formation and growth of rayleigh-taylor instability (rti) in an ultra-dense celestial body like a neutron star which gradually accretes mass in it. such an accretion process occurs at the magnetospheric boundary of the accreting star. since the density is very high we have considered relativistic degeneracy pressure as well as quantum diffraction effect. employing quantum hydrodynamic model (qhd), we have carried out the linear and non-linear analysis for this problem. further by employing standard method we analyzed the instability criteria, its growth rate and other (physical) properties. we obtained four wave modes and analysed the growth rate of rti and its dependence on various physical parameters. the results obtained here will be helpful in understanding many deep space phenomena. many observations made by space missions like polar, chandra, hubble, etc. regarding neutron stars, dwarfs, and nebulae can be explained in a more meaningful way with our theoretical findings. | growth of rt instability at the accreting magnetospheric boundary of neutron stars |
calcium-aluminum-rich inclusions (cais) are the oldest dated objects that formed inside the solar system. among these are rare, enigmatic objects with large mass-dependent fractionation effects (f cais), which sometimes also have large nucleosynthetic anomalies and a low initial abundance of the short-lived radionuclide 26al (fun cais). we have studied seven refractory hibonite-rich cais and one grossite-rich cai from the murchison (cm2) meteorite for their oxygen, calcium, and titanium isotopic compositions. the 26al-26mg system was also studied in seven of these cais. we found mass-dependent heavy isotope enrichment in all measured elements, but never simultaneously in the same cai. the data are hard to reconcile with a single-stage melt evaporation origin and may require reintroduction or reequilibration for magnesium, oxygen and titanium after evaporation for some of the studied cais. the initial 26al/27al ratios inferred from model isochrons span a range from <1 × 10-6 to canonical (∼5 × 10-5). the cais show a mutual exclusivity relationship between inferred incorporation of live 26al and the presence of resolvable anomalies in 48ca and 50ti. furthermore, a relationship exists between 26al incorporation and δ17o in the hibonite-rich cais (i.e., 26al-free cais have resolved variations in δ17o, while cais with resolved 26mg excesses have δ17o values close to -23‰). only the grossite-rich cai has a relatively enhanced δ17o value (∼-17‰) in spite of a near-canonical 26al/27al. we interpret these data as indicating that fractionated hibonite-rich cais formed over an extended time period and sampled multiple stages in the isotopic evolution of the solar nebula, including: (1) an 26al-poor nebula with large positive and negative anomalies in 48ca and 50ti and variable δ17o; (2) a stage of 26al-admixture, during which anomalies in 48ca and 50ti had been largely diluted and a δ17o value of ∼-23‰ had been achieved in the cai formation region; and (3) a nebula with an approximately canonical level of 26al and a δ17o value of ∼-23‰ in the cai formation region. | a multielement isotopic study of refractory fun and f cais: mass-dependent and mass-independent isotope effects |
the 30 doradus nebula in the large magellanic cloud (lmc) contains the massive starburst cluster ngc 2070 with a massive and probably younger stellar sub clump at its centre: r136. it is not clear how such a massive inner cluster could form several million years after the older stars in ngc 2070, given that stellar feedback is usually thought to expel gas and inhibit further star formation. using the recently developed 1d feedback scheme warpfield to scan a large range of cloud and cluster properties, we show that an age offset of several million years between the stellar populations is in fact to be expected given the interplay between feedback and gravity in a giant molecular cloud with a density ≳500 cm-3 due to re-accretion of gas on to the older stellar population. neither capture of field stars nor gas retention inside the cluster have to be invoked in order to explain the observed age offset in ngc 2070 as well as the structure of the interstellar medium around it. | forming clusters within clusters: how 30 doradus recollapsed and gave birth again |
we describe results from particle-in-cell simulations of driven turbulence in collisionless, magnetized, relativistic pair plasma. this physical regime provides a simple setting for investigating the basic properties of kinetic turbulence and is relevant for high-energy astrophysical systems such as pulsar wind nebulae and astrophysical jets. in this paper, we investigate the statistics of turbulent fluctuations in simulations on lattices of up to 10243 cells and containing up to 2 × 1011 particles. due to the absence of a cooling mechanism in our simulations, turbulent energy dissipation reduces the magnetization parameter to order unity within a few dynamical times, causing turbulent motions to become sub-relativistic. in the developed stage, our results agree with predictions from magnetohydrodynamic turbulence phenomenology at inertial-range scales, including a power-law magnetic energy spectrum with index near -5/3, scale-dependent anisotropy of fluctuations described by critical balance, lognormal distributions for particle density and internal energy density (related by a 4/3 adiabatic index, as predicted for an ultra-relativistic ideal gas), and the presence of intermittency. we also present possible signatures of a kinetic cascade by measuring power-law spectra for the magnetic, electric and density fluctuations at sub-larmor scales. | numerical investigation of kinetic turbulence in relativistic pair plasmas - i. turbulence statistics |
the spectrometer on integral (spi) instrument has observed the hard x-ray sky from 20 kev up to a few mev for more than 15 yr. in this energy domain, the main emitters are compact objects for which spi provides spectral information of prime interest. recently, two transient sources reached very unusual flux levels and have been detected up to a few hundreds of kev with a high significance level. a drastic reduction of the systematic errors is thus required to obtain reliable spectra. this objective is achieved through an analysis including a detailed understanding of the instrument behavior. this paper presents both aspects of the data analysis: we first give a basic description of the instrumental issues, then we present the solution implemented in the spi data analysis (at the event selection stage) and illustrate with a few examples the reliability of the spi results in the high-energy domain when the data analysis is performed properly. we benefit from this refined analysis procedure and propose an updated model of the hard x-ray spectral shape of the crab nebula. we revisit the high-energy emission observed in gs 2023+338 spectra during its 2015 outburst and present the first results from the spi observations dedicated to the recently discovered transient maxi j1820+070. based on observations with integral, an esa project with instruments and science data center funded by esa member states (especially the pi countries: denmark, france, germany, italy, spain, and switzerland), czech republic and poland with participation of russia and usa. | on the high-energy emissions of compact objects observed with integral spi: event selection impact on source spectra and scientific results for the bright sources crab nebula, gs 2023+338 and maxi j1820+070 |
in this work we report deep muse observations of a broad absorption line (bal) quasar at z ∼ 5, revealing a ly α nebula with a maximum projected linear size of ∼60 kpc around the quasar (down to our 2σ sb limit per layer of ∼ 9× 10^{-19} erg s^{-1} cm^{-2} arcsec^{-2} for a 1 arcsec2 aperture). after correcting for the cosmological surface brightness dimming, we find that our nebula, at z ∼ 5, has an intrinsically less extended ly α emission than nebulae at lower redshift. however, such a discrepancy is greatly reduced when referring to comoving distances, which take into account the cosmological growth of dark matter (dm) haloes, suggesting a positive correlation between the size of ly α nebulae and the sizes of dm haloes/structures around quasars. differently from the typical nebulae around radio-quiet non-bal quasars, in the inner regions (∼10 kpc) of the circumgalactic medium of our source, the velocity dispersion of the ly α emission is very high (fwhm > 1000 km s-1), suggesting that in our case we may be probing outflowing material associated with the quasar. | extended and broad ly α emission around a bal quasar at z ∼ 5 |
context. we have compiled a catalogue of central stars of planetary nebulae (cspn) with reliable distances and positions obtained from gaia data release 2 (dr2) astrometry. distances derived from parallaxes allow us to analyse the galactic distribution and estimate other parameters such as sizes, kinematical ages, bolometric magnitudes, and luminosities.aims: our objective is to analyse the information regarding distances together with other available literature data about photometric properties, nebular kinematics, and stellar effective temperatures to throw new light on this rapid and rather unknown evolutionary phase. we seek to understand how gaia distances compare with other indirect methods commonly used and, in particular, with those derived from non-local thermodynamic equilibrium (non-lte) models; how many planetary nebulae (pne) populate the galaxy; and how are they spatially distributed. we also aim to comprehend their intrinsic luminosities, range of physical sizes of the nebulae; how to derive the values for their kinematical ages; and whether those ages are compatible with those derived from evolutionary models.methods: we considered all pne listed in catalogues from different authors and in hong kong/aao/strasbourg/hα (hash) database. by x-matching their positions with gaia dr2 astrometry we were able to identify 1571 objects in gaia second archive, for which we assumed distances calculated upon a bayesian statistical approach. from those objects, we selected a sample of pne with good quality parallax measurements and distance derivations, we which refer to as our golden astrometry pne sample (gapn), and obtained literature values of their apparent sizes, radial and expansion velocities, visual magnitudes, interstellar reddening, and effective temperatures.results: we found that the distances derived from dr2 parallaxes compare well with previous astrometric derivations of the united states naval observatory and hubble space telescope, but that distances inferred from non-lte model fitting are overestimated and need to be carefully reviewed. from literature apparent sizes, we calculated the physical radii for a subsample of nebulae that we used to derive the so-called kinematical ages, taking into account literature expansion velocities. luminosities calculated with dr2 distances were combined with literature central stars teff values in a hertzsprung-russell (hr) diagram to infer information on the evolutionary status of the nebulae. we compared their positions with updated evolutionary tracks finding a rather consistent picture. stars with the smallest associated nebular radii are located in the flat luminosity region of the hr diagram, while those with the largest radii correspond to objects in a later stage, getting dimmer on their way to become a white dwarf. finally, we commented on the completeness of our catalogue and calculated an approximate value for the total number of pne in the galaxy. full table a.1 is 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/cat/j/a+a/630/a150 | properties of central stars of planetary nebulae with distances in gaia dr2 |
we explain the early excess emission of the type ia supernova 2018oh by an interaction of the supernova ejecta with disk-originated matter (dom). such dom can form in the merger process of two white dwarfs in the double-degenerate scenario of type ia supernovae (sne ia). we find that an ejecta-dom interaction can fit the early light curve of sn 2018oh better than an ejecta-companion interaction in the single-degenerate scenario. by composing the dom from two components that were ejected in the merger process with two different velocities, we show that the ejecta-dom interaction can account for the linear rise in the light curve, while the ejecta-companion interaction predicts too steep of a rise. in addition, the ejecta-dom interaction does not predict the presence of hydrogen and helium lines in nebular spectra, and hence does not suffer from this major drawback of the ejecta-companion model. we consider the ejecta-dom interaction to be the most likely explanation for the early excess emission in sn 2018oh. by that we show that the double-degenerate scenario can account for early excess emission in sne ia. | explaining the early excess emission of the type ia supernova 2018oh by the interaction of the ejecta with disk-originated matter |
context. the transient iptf15dtg is a type-ic supernova (sn) showing a broad light curve around maximum light, consistent with massive ejecta if we assume a radioactive-powering scenario.aims: we aim to study the late-time light curve of iptf15dtg, which turned out to be extraordinarily luminous for a stripped-envelope (se) sn, and investigate possible powering mechanisms.methods: we compare the observed light curves to those of other se sne and also to models for the 56co decay. we analyze and compare the spectra to nebular spectra of other se sne. we build a bolometric light curve and fit it with different models, including powering by radioactivity, magnetar powering, and a combination of the two.results: between 150 and 750 d post-explosion, the luminosity of iptf15dtg declined by merely two magnitudes instead of the six magnitudes expected from 56co decay. this is the first spectroscopically regular se sn found to show this behavior. the model with both radioactivity and magnetar powering provides the best fit to the light curve and appears to be the most realistic powering mechanism. an alternative mechanism might be circumstellar-medium (csm) interaction. however, the spectra of iptf15dtg are very similar to those of other se sne, and do not show signs of strong csm interaction.conclusions: the object iptf15dtg is the first spectroscopically regular se sn whose light curve displays such clear signs of a magnetar contributing to its late-time powering. given this result, the mass of the ejecta needs to be revised to a lower value, and therefore the progenitor mass could be significantly lower than the previously estimated > 35 m⊙. | the luminous late-time emission of the type-ic supernova iptf15dtg - evidence for powering from a magnetar? |
nebular he ii emission implies the presence of energetic photons (e ≥ 54 ev). despite the great deal of effort dedicated to understanding he ii ionization, its origin has remained mysterious, particularly in metal-deficient star-forming (sf) galaxies. unfolding he ii-emitting, metal-poor starbursts at z ∼ 0 can yield insight into the powerful ionization processes occurring in the primordial universe. here we present a new study on the effects that x-ray sources have on the he ii ionization in the extremely metal-poor galaxy izw18 (z ∼ 3% z⊙), whose x-ray emission is dominated by a single high-mass x-ray binary (hmxb). this study uses optical integral field spectroscopy, archival hubble space telescope observations, and all of the x-ray data sets publicly available for izw18. we investigate the time-variability of the izw18 hmxb for the first time; its emission shows small variations on timescales from days to decades. the best-fit models for the hmxb x-ray spectra cannot reproduce the observed he ii ionization budget of izw18, nor can recent photoionization models that combine the spectra of both very low metallicity massive stars and the emission from hmxb. we also find that the izw18 hmxb and the he ii-emission peak are spatially displaced at a projected distance of ≃200 pc. these results reduce the relevance of x-ray photons as the dominant he ii ionizing mode in izw18, which leaves uncertain what process is responsible for the bulk of its he ii ionization. this is in line with recent work discarding x-ray binaries as the main source responsible for he ii ionization in sf galaxies. | on the contribution of the x-ray source to the extended nebular he ii emission in izw18 |
we present an analysis of the photometry and spectroscopy of the host galaxy of swift-detected grb 080517. from our optical spectroscopy, we identify a redshift of z = 0.089 ± 0.003, based on strong emission lines, making this a rare example of a very local, low-luminosity, long gamma-ray burst. the galaxy is detected in the radio with a flux density of s4.5 ghz = 0.22 ± 0.04 mjy - one of relatively few known gamma-ray bursts hosts with a securely measured radio flux. both optical emission lines and a strong detection at 22 μm suggest that the host galaxy is forming stars rapidly, with an inferred star formation rate ∼16 m⊙ yr-1 and a high dust obscuration (e(b - v) > 1, based on sightlines to the nebular emission regions). the presence of a companion galaxy within a projected distance of 25 kpc, and almost identical in redshift, suggests that star formation may have been triggered by galaxy-galaxy interaction. however, fitting of the remarkably flat spectral energy distribution from the ultraviolet through to the infrared suggests that an older, 500 myr post-starburst stellar population is present along with the ongoing star formation. we conclude that the host galaxy of grb 080517 is a valuable addition to the still very small sample of well-studied local gamma-ray burst hosts. | grb 080517: a local, low-luminosity gamma-ray burst in a dusty galaxy at z = 0.09 |
the nature of the supernova leading to the crab nebula has long been controversial because of the low energy that is present in the observed nebula. one possibility is that there is significant energy in extended fast material around the crab but searches for such material have not led to detections. an electron capture supernova model can plausibly account for the low energy and the observed abundances in the crab. here, we examine the evolution of the crab pulsar wind nebula inside a freely expanding supernova and find that the observed properties are most consistent with a low energy event. both the velocity and radius of the shell material, and the amount of gas swept up by the pulsar wind point to a low explosion energy (∼1050 erg). we do not favor a model in which circumstellar interaction powers the supernova luminosity near maximum light because the required mass would limit the freely expanding ejecta. | evolution of the crab nebula in a low energy supernova |
we acquired spectra of 141 h ii regions in 10 late-type low surface brightness galaxies (lsbgs). the analysis of the chemical abundances obtained from the nebular emission lines shows that metallicity gradients are a common feature of lsbgs, contrary to previous claims concerning the absence of such gradients in this class of galaxies. the average slope, when expressed in units of the isophotal radius, is found to be significantly shallower in comparison to galaxies of high surface brightness. this result can be attributed to the reduced surface brightness range measured across their discs, when combined with a universal surface mass density-metallicity relation. with a similar argument we explain the common abundance gradient observed in high surface brightness galaxy (hsbg) discs and its approximate dispersion. this conclusion is reinforced by our result that lsbgs share the same common abundance gradient with hsbgs, when the slope is expressed in terms of the exponential disc scalelength. | abundance gradients in low surface brightness spirals: clues on the origin of common gradients in galactic discs |
context. a currently unsolved question in supernova (sn) research is the origin of stripped-envelope supernovae (sesne). such sne lack spectral signatures of hydrogen (type ib), or hydrogen and helium (type ic), indicating that the outer stellar layers have been stripped during their evolution. the mechanism for this is not well understood, and to disentangle the different scenarios' determination of nucleosynthesis yields from observed spectra can be attempted. however, the interpretation of observations depends on the adopted spectral models. a previously missing ingredient in these is the inclusion of molecular effects, which can be significant.aims: we aim to investigate how the molecular chemistry in sesne affect physical conditions and optical spectra, and produce ro-vibrational emission in the mid-infrared (mir). we also aim to assess the diagnostic potential of observations of such mir emission with jwst.methods: we coupled a chemical kinetic network including carbon, oxygen, silicon, and sulfur-bearing molecules into the nonlocal thermal equilibrium (nlte) spectral synthesis code sumo. we let four species - co, sio, sis, and so - participate in nlte cooling of the gas to achieve self-consistency between the molecule formation and the temperature. we applied the new framework to model the spectrum of a type ic sn in the 100-600 days time range.results: molecules are predicted to form in sesn ejecta in significant quantities (typical mass 10−3 m⊙) throughout the 100-600 days interval. the impact on the temperature and optical emission depends on the density of the oxygen zones and varies with epoch. for example, the [o i] 6300, 6364 feature can be quenched by molecules from 200 to 450 days depending on density. the mir predictions show strong emission in the fundamental bands of co, sio, and sis, and in the co and sio overtones.conclusions: type ibc sn ejecta have a rich chemistry and considering the effect of molecules is important for modeling the temperature and atomic emission in the nebular phase. observations of sesne with jwst hold promise to provide the first detections of sis and so, and to give information on zone masses and densities of the ejecta. combined optical, near-infrared, and mir observations can break degeneracies and achieve a more complete picture of the nucleosynthesis, chemistry, and origin of type ibc sne. | the molecular chemistry of type ibc supernovae and diagnostic potential with the james webb space telescope |
current methods of identifying the ionizing source of nebular emission in galaxies are well defined for the era of single-fiber spectroscopy, but still struggle to differentiate the complex and overlapping ionization sources in some galaxies. with the advent of integral field spectroscopy, the limits of these previous classification schemes are more apparent. we propose a new method for distinguishing the ionizing source in resolved galaxy spectra by use of a multidimensional diagnostic diagram that compares emission-line ratios with velocity dispersion on a spaxel-by-spaxel basis within a galaxy. this new method is tested using the sydney-australian-astronomical-observatory multi-object integral-field spectrograph galaxy survey (sami) data release 3 (dr3), which contains 3068 galaxies at z < 0.12. our results are released as ionization maps available alongside the sami dr3 public data. our method accounts for a more diverse range of ionization sources than the standard suite of emission-line diagnostics; we find 1433 galaxies with a significant contribution from non-star-forming ionization using our improved method as compared to 316 galaxies identified using only emission-line ratio diagnostics. within these galaxies, we further identify 886 galaxies hosting unique signatures inconsistent with standard ionization by h ii regions, active galactic nuclei, or shocks. these galaxies span a wide range of masses and morphological types and comprise a sizable portion of the galaxies used in our sample. with our revised method, we show that emission-line diagnostics alone do not adequately differentiate the multiple ways to ionize gas within a galaxy. | beyond bpt: a new multidimensional diagnostic diagram for classifying power sources tested using the sami galaxy survey |
there are several studies proposing phenomenological consequences of a deformation of special and general relativity. here, we cast novel constraints on the deformation parameter of a metric in the cotangent bundle accounting for a curved momentum space. in an expanding universe, we study three possible observations that could restrict our model, focusing on the deformations of velocity, redshift and luminosity distance, which in the aforementioned framework, depend on the energy of the particles. we find that for an energy dependent velocity there would be no time delay for massless particles since also the observed distance to the source depends on the energy. for the redshift and luminosity distance we see that a scale of the order of some kev could be compatible with our model. this shows that the constraints on the high-energy scale parametrizing the momentum dependent deviation from a friedmann-robertson-walker metric are at the moment weak due to the fact that the precision (rather than energies) needed in the observational constraints are extremely high. however, this is not the case when considering the synchrotron radiation. indeed, the observation of such emission from the crab nebula, for deformations leading to subluminal propagation at high energies, leads to a constraint for the high-energy scale of the order of 1 pev. | constraints on the deformation scale of a geometry in the cotangent bundle |
aims: we aim to study the presence of both rotation and expansion in post-agb nebulae, in particular around iw car, a binary post-agb star that was suspected to be surrounded by a keplerian disk.methods: we obtained high-quality alma observations of 12co and 13co j = 3-2 lines in iw car. the maps were analyzed by means of a simplified model of co emission, based on those used for similar objects.results: our observations clearly show the presence of gas components in rotation, in an equatorial disk, and expansion, which shows an hourglass-like structure with a symmetry axis perpendicular to the rotation plane and is probably formed of material extracted from the disk. our modeling can reproduce the observations and shows moderate uncertainties. the rotation velocity corresponds to a central stellar mass of approximately 1 m⊙. we also derive the total mass of the molecule-rich nebula, found to be of 4 × 10-3m⊙; the outflow is approximately eight times less massive than the disk. from the kinematical age of the outflow and the mass values derived for both components, we infer a (future) lifetime of the disk of approximately 5000-10 000 yr. | a second post-agb nebula that contains gas in rotation and in expansion: alma maps of iw carinae |
herein we analyse late-time (post-plateau; 103 < t < 1229 d) optical spectra of low-redshift (z < 0.016), hydrogen-rich type iip supernovae (sne iip). our newly constructed sample contains 91 nebular spectra of 38 sne iip, which is the largest data set of its kind ever analysed in one study, and many of the objects have complementary photometric data. the strongest and most robust result we find is that the luminosities of all spectral features (except those of helium) tend to be higher in objects with steeper late-time v-band decline rates. a steep late-time v-band slope likely arises from less efficient trapping of γ-rays and positrons, which could be caused by multidimensional effects such as clumping of the ejecta or asphericity of the explosion itself. furthermore, if γ-rays and positrons can escape more easily, then so can photons via the observed emission lines, leading to more luminous spectral features. it is also shown that sne iip with larger progenitor stars have ejecta with a more physically extended oxygen layer that is well-mixed with the hydrogen layer. in addition, we find a subset of objects with evidence for asymmetric 56ni ejection, likely bipolar in shape. we also compare our observations to theoretical late-time spectral models of sne iip from two separate groups and find moderate-to-good agreement with both sets of models. our sne iip spectra are consistent with models of 12-15 m⊙ progenitor stars having relatively low metallicity (z ≤ 0.01). | after the fall: late-time spectroscopy of type iip supernovae |
we have mapped 12co j = 3-2 and other molecular lines from the “water fountain” bipolar pre-planetary nebula (ppn) iras 16342-3814 with ∼0.″35 resolution using atacama large millimeter/submillimeter array. we find (i) two very high-speed knotty, jet-like molecular outflows; (ii) a central high-density (> {few}× {10}6 cm-3), expanding torus of diameter 1300 au; and (iii) the circumstellar envelope of the progenitor agb, generated by a sudden, very large increase in the mass-loss rate to > 3.5× {10}-4 m⊙ yr-1 in the past ∼455 years. strong continuum emission at 0.89 mm from a central source (690 mjy), if due to thermally emitting dust, implies a substantial mass (0.017 m⊙) of very large (∼millimeter-sized) grains. the measured expansion ages of the above structural components imply that the torus (age ∼160 years) and the younger high-velocity outflow (age ∼110 years) were formed soon after the sharp increase in the agb mass-loss rate. assuming a binary model for the jets in iras 16342, the high momentum rate for the dominant jet-outflow in iras 16342 implies a high minimum accretion rate, ruling out standard bondi-hoyle-lyttleton wind accretion and wind roche-lobe overflow (rlof) models with white-dwarf or main-sequence companions. most likely, enhanced rlof from the primary or accretion modes operating within common-envelope evolution are needed. | alma observations of the water fountain pre-planetary nebula iras 16342-3814: high-velocity bipolar jets and an expanding torus |
the interaction between a pulsar wind nebula (pwn) and its host supernova remnant (snr) can produce a vast array of observable structures. asymmetry present within these structures derives from the complexity of the composite system, where many factors take turns playing a dominating hand throughout the stages of composite snr evolution. of particular interest are systems characterized by blastwave expansion within a nonuniform interstellar medium (ism), which contain an active pulsar having a substantial “kick” velocity (upward of 300 {km} {{{s}}}-1), because these systems tend to produce complex morphologies. we present a numerical model that employs these and several other factors in an effort to generate asymmetry similar to that seen in various x-ray and radio observations. we find that the main parameters driving structure are ism uniformity and total pulsar spin-down energy, with secondary contributions from factors such as pulsar trajectory and initial spin-down luminosity. we also investigate the dynamics behind pwn “tails,” which may form to link active pulsars to a crushed, relic nebula as the reverse shock passes. we find that the directions of such tails are not good indicators of pulsar motion, but direction does reveal the flow of ejecta created by the passage of a reverse shock. | evolution of a pulsar wind nebula within a composite supernova remnant |
the scanning fabry-perot interferometer (fpi) - is the oldest method of optical 3d spectroscopy. it is still in use because of the high spectral resolution it provides over a large field of view. the history of the application of this method for the study of extended ob jects (nebulae and galaxies) and the technique of data reduction and analysis are discussed. the paper focuses on the performing observations with the scanning fpi on the 6-m telescope of the special astrophysical observatory of the russian academy of sciences (sao ras). the instrument is currently used as a part of the scorpio-2 multimode focal reducer. the results of studies of various galactic and extragalactic objects with the scanning fpi on the 6-m telescope - star-forming regions and young stellar objects, spiral, ring, dwarf and interacting galaxies, ionization cones of active galactic nuclei, galactic winds, etc. are briefly discussed. further prospects for research with the scanning fpi of the sao ras are discussed. | scanning fabry–perot interferometer of the 6-m sao ras telescope |
for the extremely bright lensed galaxy sdss j1723+3411 at z = 1.3293, we analyze spatially integrated mmt, keck, and hubble space telescope spectra that fully cover the rest-frame wavelength range of 1400-7200 å. we also analyze near-ir spectra from gemini that cover hα for a portion of the lensed arc. we report fluxes for 42 detected emission lines, and upper limits for an additional 22. this galaxy has extreme emission-line ratios and high equivalent widths that are characteristic of extreme emission-line galaxies. we compute strong emission-line diagnostics from both the rest-frame optical and rest-frame ultraviolet (uv), to constrain physical conditions and test the spectral diagnostics themselves. we tightly determine the nebular physical conditions using the most reliable diagnostics, and then compare to results from other diagnostics. we find disappointing performance from the uv-only diagnostics: they either are unable to measure the metallicity or dramatically underestimate it; they overestimate the pressure; and the uv diagnostic of ionization parameter has a strong metallicity dependence in this regime. based on these results, we suggest that upcoming james webb space telescope (jwst) spectroscopic surveys of galaxies in the reionization epoch should invest the additional integration time to capture the optical [o ii] and [o iii] emission lines, and not rely solely on the rest-frame uv emission lines. we make available the spectra; they represent one of the highest-quality emission-line spectral atlases of star-forming galaxies available beyond the local universe, and will aid the planning of observations with jwst. | a comparison of rest-frame ultraviolet and optical emission-line diagnostics in the lensed galaxy sdss j1723+3411 at redshift z = 1.3293 |
we present an infrared (ir) characterization of the born-again planetary nebulae (pne) a 30 and a 78 using ir images and spectra. we demonstrate that the carbon-rich dust in a 30 and a 78 is spatially coincident with the h-poor ejecta and coexists with hot x-ray-emitting gas up to distances of 50 arcsec from the central stars of pne (cspne). dust forms immediately after the born-again event and survives for 1000 yr in the harsh environment around the cspn as it is destroyed and pushed away by radiation pressure and dragged by hydrodynamical effects. spitzer irs spectral maps showed that the broad spectral features at 6.4 and 8.0 μm, attributed to amorphous carbon formed in h-deficient environments, are associated with the disrupted disc around their cspn, providing an optimal environment for charge exchange reactions with the stellar wind that produces the soft x-ray emission of these sources. nebular and dust properties are modelled for a 30 with cloudy taking into account different carbonaceous dust species. our models predict dust temperatures in the 40-230 k range, five times lower than predicted by previous works. gas and dust masses for the born-again ejecta in a 30 are estimated to be $m_\mathrm{gas}=4.41^{+0.55}_{-0.14}\times 10^{-3}$ m⊙ and $m_\mathrm{dust}=3.20^{+3.21}_{-2.06}\times 10^{-3}$ m⊙, which can be used to estimate a total ejected mass and mass-loss rate for the born-again event of $7.61^{+3.76}_{-2.20}\times 10^{-3}$ m⊙ and $\dot{m}=(5{\!-\!}60)\times 10^{-5}$ m⊙ yr-1, respectively. taking into account the carbon trapped into dust grains, we estimate that the c/o mass ratio of the h-poor ejecta of a 30 is larger than 1, which favours the very late thermal pulse model over the alternate hypothesis of a nova-like event. | carbon dust in the evolved born-again planetary nebulae a 30 and a 78 |
in this work, we present photometric and spectroscopic data of the low-luminosity (ll) type iip supernova (sn) 2018hwm. the object shows a faint (mr = -15 mag) and very long (~130 d) plateau, followed by a 2.7 mag drop in the r band to the radioactive tail. the first spectrum shows a blue continuum with narrow balmer lines, while during the plateau the spectra show numerous metal lines, all with strong and narrow p-cygni profiles. the expansion velocities are low, in the 1000-1400 km s-1 range. the nebular spectrum, dominated by h α in emission, reveals weak emission from [o i] and [ca ii] doublets. the absolute light curve and spectra at different phases are similar to those of ll sne iip. we estimate that 0.002 m⊙ of 56ni mass were ejected, through hydrodynamical simulations. the best fit of the model to the observed data is found for an extremely low explosion energy of 0.055 foe, a progenitor radius of 215 r⊙, and a final progenitor mass of 9-10 m⊙. finally, we performed a modelling of the nebular spectrum, to establish the amount of oxygen and calcium ejected. we found a low m(16o)$\approx 0.02\, \mathrm{ m}_{\odot }$, but a high m(40ca) of 0.3 m⊙. the inferred low explosion energy, the low ejected 56ni mass, and the progenitor parameters, along with peculiar features observed in the nebular spectrum, are consistent with both an electron-capture sn explosion of a superasymptotic giant branch star and with a low-energy, ni-poor iron core-collapse sn from a 10-12 m⊙ red supergiant. | low-luminosity type ii supernovae - iii. sn 2018hwm, a faint event with an unusually long plateau |
we present 3d hydrodynamic models of the interaction between the outflows of evolved, pulsating, asymptotic giant branch (agb) stars and nearby (<3 stellar radii) substellar companions (mcomp ≲ 40 mj). our models show that due to resonances between the orbital period of the companion and the pulsation period of the agb star, multiple spiral structures can form; the shocks driven by the pulsations are enhanced periodically in different regions as they encounter the denser material created by the substellar companion's wake. we discuss the properties of these spiral structures and the effect of the companion parameters on them. we also demonstrate that the gravitational potential of the nearby companion enhances the mass-loss from the agb star. for more massive (mcomp > 40 mj) and more distant companions (>4 stellar radii), a single spiral arm forms. we discuss the possibility of observing these structures with the new generations of high-resolution, high-sensitivity instruments, and using them to 'find' substellar companions around bright, evolved stars. our results also highlight possible structures that could form in our solar system when the sun turns into an agb star. | 3d models of the circumstellar environments of evolved stars: formation of multiple spiral structures |
the nature of the sources powering nebular he ii emission in star-forming galaxies remains debated, and various types of objects have been considered, including wolf-rayet stars, x-ray binaries, and population iii stars. modern x-ray observations show the ubiquitous presence of hot gas filling star-forming galaxies. we use a collisional ionization plasma code to compute the specific he ii ionizing flux produced by hot gas and show that if its temperature is not too high (≲2.5 mk), then the observed levels of soft diffuse x-ray radiation could explain he ii ionization in galaxies. to gain a physical understanding of this result, we propose a model that combines the hydrodynamics of cluster winds and hot superbubbles with observed populations of young massive clusters in galaxies. we find that in low-metallicity galaxies, the temperature of hot gas is lower and the production rate of he ii ionizing photons is higher compared to high-metallicity galaxies. the reason is that the slower stellar winds of massive stars in lower-metallicity galaxies input less mechanical energy in the ambient medium. furthermore, we show that ensembles of star clusters up to ∼10−20 myr old in galaxies can produce enough soft x-rays to induce nebular he ii emission. we discuss observations of the template low-metallicity galaxy i zw 18 and suggest that the he ii nebula in this galaxy is powered by a hot superbubble. finally, appreciating the complex nature of stellar feedback, we suggest that soft x-rays from hot superbubbles are among the dominant sources of he ii ionizing flux in low-metallicity star-forming galaxies. | ionization of he ii in star-forming galaxies by x-rays from cluster winds and superbubbles |
galactic pev cosmic-ray accelerators (pevatrons) are galactic sources theorized to accelerate cosmic rays up to pev in energy. the accelerated cosmic rays are expected to interact hadronically with nearby ambient gas or the interstellar medium, resulting in γ-rays and neutrinos. recently, the large high altitude air shower observatory (lhaaso) identified 12 γ-ray sources with emissions above 100 tev, making them candidates for pevatrons. while at these high energies the klein-nishina effect exponentially suppresses leptonic emission from galactic sources, evidence for neutrino emission would unequivocally confirm hadronic acceleration. here, we present the results of a search for neutrinos from these γ-ray sources and stacking searches testing for excess neutrino emission from all 12 sources as well as their subcatalogs of supernova remnants and pulsar wind nebulae with 11 yr of track events from the icecube neutrino observatory. no significant emissions were found. based on the resulting limits, we place constraints on the fraction of γ-ray flux originating from the hadronic processes in the crab nebula and lhaaso j2226+6057. | searches for neutrinos from large high altitude air shower observatory ultra-high-energy γ-ray sources using the icecube neutrino observatory |
integral field spectroscopy (ifs) provides a unique capability to spectroscopically study extended sources over a 2d field of view, but it also requires new techniques and tools. in this paper, we present an automatic code, spectroscopic analysis tool for integral field unit datacubes, satellite, designed to fully explore such capability in the characterization of extended objects, such as planetary nebulae, h ii regions, galaxies, etc. satellite carries out 1d and 2d spectroscopic analysis through a number of pseudo-slits that simulate slit spectrometry, as well as emission line imaging. the 1d analysis permits direct comparison of the integral field unit (ifu) data with previous studies based on long-slit spectroscopy, while the 2d analysis allows the exploration of physical properties in both spatial directions. interstellar extinction, electron temperatures and densities, ionic abundances from collisionally excited lines, total elemental abundances, and ionization correction factors are computed employing the pyneb package. a monte carlo approach is implemented in the code to compute the uncertainties for all the physical parameters. satellite provides a powerful tool to extract physical information from ifs observations in an automatic and user configurable way. the capabilities and performance of satellite are demonstrated by means of a comparison between the results obtained from the multi unit spectroscopic explorer (muse) data of the planetary nebula ngc 7009 with the results obtained from long-slit and ifu data available in the literature. the satellite characterization of ngc 6778 based on muse data is also presented. | spectroscopic analysis tool for integral field unit datacubes (satellite): case studies of ngc 7009 and ngc 6778 with muse |
in this work we use the first data release of the gaia mission to explore the three-dimensional arrangement and age ordering of the many stellar groups toward the orion ob association, aiming at a new classification and characterization of the stellar population not embedded in the orion a and b molecular clouds. we make use of the parallaxes and proper motions provided in the tycho gaia astrometric solution (tgas) subset of the gaia data release 1 (dr1) catalog and of the combination of gaia dr1 and 2mass photometry. in tgas, we find evidence for the presence of a young population at a parallax ϖ 2.65 mas, which is loosely distributed around the following known clusters: 25 ori, ɛ ori, and σ ori, and ngc 1980 (ι ori) and the orion nebula cluster (onc). the low mass counterpart of this population is visible in the color magnitude diagrams constructed by combining gaia dr1 g-band photometry and 2mass. we study the density distribution of the young sources in the sky using a kernel density estimation (kde). we find the same groups as in tgas and also some other density enhancements that might be related to the recently discovered orion x group, orion dust ring, and λ ori complex. the maps also suggest that the 25 ori group presents a northern elongation. we estimated the ages of this population using a bayesian isochronal fitting procedure assuming a unique parallax value for all the sources, and we inferred the presence of an age gradient going from 25 ori (13-15 myr) to the onc (1-2 myr). we confirmed this age ordering by repeating the bayesian fit using the pan-starrs1 data. intriguingly, the estimated ages toward the ngc 1980 cluster span a broad range of values. this can either be due to the presence of two populations coming from two different episodes of star formation or to a large spread along the line of sight of the same population. some confusion might arise from the presence of unresolved binaries, which are not modeled in the fit, and usually mimic a younger population. finally, we provisionally relate the stellar groups to the gas and dust features in orion. our results form the first step toward using gaia data to unravel the complex star formation history of the orion region in terms of the various star formation episodes, their duration, and their effects on the surrounding interstellar medium. the data and some relevant ipython notebooks used in the preparation of this paper are available at https://github.com/eleonorazari/oriondr1, and also 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/608/a148 | mapping young stellar populations toward orion with gaia dr1 |
we present an aca search for [c i] 1-0 emission at 492 ghz toward large t tauri disks (gas radii ≳ 200 au) in the ~1-3 myr-old lupus star-forming region. combined with atacama large millimeter/submillimeter array 12 m archival data for im lup, we report [c i] 1-0 detections in six out of 10 sources, thus doubling the known detections toward t tauri disks. we also identify four keplerian double-peaked profiles and demonstrate that the [c i] 1-0 fluxes correlate with 13co, c18o, and 12co(2-1) fluxes, as well as with the gas disk outer radius measured from the latter transition. these findings are in line with the expectation that atomic carbon traces the disk surface. in addition, we compare the carbon and carbon monoxide (co) line luminosities of a lupus and literature sample with [c i] 1-0 detections with predictions from the self-consistent disk thermo-chemical models of ruaud et al. these models adopt interstellar medium carbon and oxygen elemental abundances as input parameters. with the exception of the disk around sz 98, we find that these models reproduce all the available line luminosities and upper limits, with gas masses comparable to or higher than the minimum-mass solar nebula and gas-to-dust mass ratios ≥10. thus, we conclude that the majority of large myr-old disks conform to the simple expectation that they are not significantly depleted in gas, co, or carbon. | large myr-old disks are not severely depleted of gas-phase co or carbon |
magnetic fields in the early solar system may have driven the inward accretion of the protoplanetary disk (ppd) and generated instabilities that led to the formation of planets and ring and gap structures. the allende carbonaceous chondrite meteorite records a strong early solar system magnetic field that has been interpreted to have a ppd, dynamo, or impact-generated origin. using high-resolution magnetic field imaging to isolate the magnetization of individual grain assemblages, we find that only fe-sulfides carry a coherent magnetization. combined with rock magnetic analyses, we conclude that allende carries a magnetization acquired during parent body chemical alteration at ~3.0-4.2 my after calcium aluminum-rich inclusions in an >40 µt magnetic field. this early age strongly favors a magnetic field of nebular origin instead of dynamo or solar wind alternatives. when compared to other paleomagnetic data from meteorites, this strong intensity supports a central role for magnetic instabilities in disk accretion and the presence of temporal variations or spatial heterogeneities in the disk, such as ring and gap structures. | the fine-scale magnetic history of the allende meteorite: implications for the structure of the solar nebula |
terrestrial planets (mercury, venus, earth, and mars) are differentiated into three layers: a metallic core, a silicate shell (mantle and crust), and a volatile envelope of gases, ices, and, for the earth, liquid water. each layer has different dominant elements (e.g., increasing iron content with depth and increasing oxygen content to the surface). chondrites, the building blocks of the terrestrial planets, have mass and atomic proportions of oxygen, iron, magnesium, and silicon totaling ≥ 90% and variable mg/si (∼ 25%), fe/si (factor of ≥2), and fe/o (factor of ≥ 3). what remains an unknown is to what degree did physical processes during nebular disk accretion versus those during post-nebular disk accretion (e.g., impact erosion) influence these planets final bulk compositions. here we predict terrestrial planet compositions and show that their core mass fractions and uncompressed densities correlate with their heliocentric distance, and follow a simple model of the magnetic field strength in the protoplanetary disk. our model assesses the distribution of iron in terms of increasing oxidation state, aerodynamics, and a decreasing magnetic field strength outward from the sun, leading to decreasing core size of the terrestrial planets with radial distance. this distribution enhances habitability in our solar system and may be equally applicable to exoplanetary systems. | terrestrial planet compositions controlled by accretion disk magnetic field |
context. planet formation remains an open field of research, and many fundamental physical processes regarding planetary formation in protoplanetary disks are still imperfectly understood. it remains to be investigated how different conditions in these protoplanetary disks affect the emergence of different types of observed systems. an elusive phenomenon is the turbulence in these disks. observations are available of planetary systems and of some protoplanetary disks, which can serve as a starting point for these investigations. the detected systems reveal different architectures of planets. one particularly interesting case to consider is the kepler-223 system, which contains a rare configuration of four planets in a resonance chain. this implies a certain migration history.aims: we aim to use the orbital configuration of the kepler-223 planets to constrain the parameters of the protoplanetary disk that allow the formation of a chain of mean-motion resonances that resembles the resonances of kepler-223. we primarily investigate the disk viscosity and surface density.methods: we used the swift_symba n-body integrator with additional dissipative forces to mimic planet-disk interactions.results: we constrained the surface densities and viscosities that allow the formation of a resonant chain like that of kepler-223. we find that surface densities of up to a few minimum mass solar nebula surface densities and disk viscosity parameters α of a few × 10−3 up to × 10−2 are most successful at reproducing the architecture of this particular planetary system. we describe the connection of these two quantities with each other, considering the success of reproducing the chain. we find that higher disk surface densities in turn require lower viscosities to build the chain.conclusions: our results show that well-characterized observed planetary systems hold information about their formation conditions in the protoplanetary disks and that it is possible to extract this information, namely the initial disk surface density and viscosity. this helps to constrain planet formation. | kepler-223 resonance holds information about turbulence during the gas-disk phase |
context. the fundamental metallicity relation (fmr) of galaxies is a 3d relation between the gas-phase metallicity, stellar mass, and star-formation rate (sfr). so far, it has only been studied for galaxies identified as star forming (sf) on the bpt diagrams (bpt-sf), but not for galaxies with li(n)er/agn classification (bpt-non-sf), mainly because of the lack of diagnostics for estimating their gas-phase metallicities in the latter cases.aims: we extend the fmr to bpt-non-sf galaxies.methods: to this end, we exploit the recent nebular line empirical calibrations derived specifically for galaxies classified as non-sf in the bpt diagrams. moreover, we study an alternative representation of the fmr where we consider the offsets in metallicity and sfr with respect to main sequence (ms) galaxies.results: we find that galaxies with sfr higher than the ms are more metal-poor than their counterparts on the ms, which is interpreted in terms of gas accretion boosting star formation and diluting the metallicity. low-mass galaxies below the ms (i.e. towards quiescence) have higher metallicities than their ms counterparts, which is interpreted in terms of starvation (i.e. suppression of fresh gas supply) hampering star formation and reducing the dilution effect, hence resulting in a higher level of internal chemical enrichment. massive galaxies below the ms have a gas metallicity that is much closer to their ms counterparts and much lower than expected from their stellar metallicities; this result suggests a scenario where massive nearly quiescent galaxies with li(n)er-like nebular emission have recently accreted gas from the circum/intergalactic medium. | the extension of the fundamental metallicity relation beyond the bpt star-forming sequence: evidence for both gas accretion and starvation |
mean motion commensurabilities in multi-planet systems are an expected outcome of protoplanetary disk-driven migration, and their relative dearth in the observational data presents an important challenge to current models of planet formation and dynamical evolution. one natural mechanism that can lead to the dissolution of commensurabilities is stochastic orbital forcing, induced by turbulent density fluctuations within the nebula. while this process is qualitatively promising, the conditions under which mean motion resonances can be broken are not well understood. in this work, we derive a simple analytic criterion that elucidates the relationship among the physical parameters of the system, and find the conditions necessary to drive planets out of resonance. subsequently, we confirm our findings with numerical integrations carried out in the perturbative regime, as well as direct n-body simulations. our calculations suggest that turbulent resonance disruption depends most sensitively on the planet-star mass ratio. specifically, for a disk with properties comparable to the early solar nebula with α ={10}-2, only planet pairs with cumulative mass ratios smaller than ({m}1+{m}2)/m≲ {10}-5∼ 3{m}\oplus /{m}⊙are susceptible to breaking resonance at semimajor axis of order a∼ 0.1 {au}. although turbulence can sometimes compromise resonant pairs, an additional mechanism (such as suppression of resonance capture probability through disk eccentricity) is required to adequately explain the largely non-resonant orbital architectures of extrasolar planetary systems. | an analytic criterion for turbulent disruption of planetary resonances |
massive stars that have been ejected from their parent cluster and supersonically sailing away through the interstellar medium (ism) are classified as exiled. they generate circumstellar bow-shock nebulae that can be observed. we present two-dimensional, axisymmetric hydrodynamical simulations of a representative sample of stellar wind bow shocks from galactic ob stars in an ambient medium of densities ranging from nism = 0.01 up to 10.0 cm- 3. independently of their location in the galaxy, we confirm that the infrared is the most appropriated waveband to search for bow shocks from massive stars. their spectral energy distribution is the convenient tool to analyse them since their emission does not depend on the temporary effects which could affect unstable, thin-shelled bow shocks. our numerical models of galactic bow shocks generated by high-mass ( ≈ 40 m⊙) runaway stars yield h α fluxes which could be observed by facilities such as the supercosmos h-alpha survey. the brightest bow-shock nebulae are produced in the denser regions of the ism. we predict that bow shocks in the field observed at h α by means of rayleigh-sensitive facilities are formed around stars of initial mass larger than about 20 m⊙. our models of bow shocks from ob stars have the emission maximum in the wavelength range 3 ≤ λ ≤ 50 μm which can be up to several orders of magnitude brighter than the runaway stars themselves, particularly for stars of initial mass larger than 20 m⊙. | on the observability of bow shocks of galactic runaway ob stars |
we present an optical spectrum of the energetic type ib supernova (sn) 2012au obtained at an unprecedented epoch of 6.2 yr after explosion. forbidden transition emission lines of oxygen and sulfur are detected with expansion velocities of ≈2300 km s-1. the lack of narrow h balmer lines suggests that interaction with circumstellar material is not a dominant source of the observed late-time emission. we also present a deep chandra observation that reveals no x-ray emission down to a luminosity of lx< 2 × 1038 erg s-1 (0.5-10 kev). our findings are consistent with the notion that sn 2012au is associated with a diverse subset of sne, including long-duration gamma-ray burst sne and superluminous sne, harboring pulsar/magnetar wind nebulae that influence core-collapse explosion dynamics on a wide range of energy scales. we hypothesize that these systems may all evolve into a similar late-time phase dominated by forbidden oxygen transitions, and predict that emission line widths should remain constant or broaden a few percent per year due to the acceleration of ejecta by the pulsar/magnetar bubble. | evidence for a pulsar wind nebula in the type ib peculiar supernova sn 2012au |
we present jansky very large array observations of 20-37 ghz absorption lines from nearby galactic diffuse molecular gas seen against four cosmologically distant compact radio continuum sources. the main new observational results are that l-c3h and ch3cn are ubiqitous in the local diffuse molecular interstellar medium at {\text{}}{a}{{v}} ≲ 1, while hc3n was seen only toward b0415 at {\text{}}{a}{{v}} > 4 mag. the linear/cyclic ratio is much larger in c3h than in c3h2 and the ratio ch3cn/hcn is enhanced compared to tmc-1, although not as much as toward the horsehead nebula. more consequentially, this work completes a long-term program assessing the abundances of small hydrocarbons (ch, c2h, linear and cyclic c3h and c3 {{{h}}}2, and c4h and c4h-) and the cn-bearing species (cn, hcn, hnc, hc3n, hc5n, and ch3cn): their systematics in diffuse molecular gas are presented in detail here. we also observed but did not strongly constrain the abundances of a few oxygen-bearing species, most prominently hnco. we set limits on the column density of ch2cn, such that the anion ch2cn- is only viable as a carrier of diffuse interstellar bands if the n(ch2cn)/n(ch2cn-) abundance ratio is much smaller in this species than in any others for which the anion has been observed. we argue that complex organic molecules (coms) are not present in clouds meeting a reasonable definition of diffuse molecular gas, i.e., {\text{}}{a}{{v}} ≲ 1 mag. based on observations obtained with the nrao jansky very large array (vla). | chemical complexity in local diffuse and translucent clouds: ubiquitous linear c3h and ch3cn, a detection of hc3n and an upper limit on the abundance of ch2cn |
we report new chandra x-ray observations of the shell supernova remnant kes 75 (g29.7-0.3) containing a pulsar and pulsar-wind nebula (pwn). expansion of the pwn is apparent across four epochs—2000, 2006, 2009, and 2016. we find an expansion rate between 2000 and 2016 of the northwest edge of the pwn of 0.249% ± 0.023% yr-1, for an expansion age r/(dr/dt) of 400 ± 40 yr and an expansion velocity of about 1000 km s-1. we suggest that the pwn is expanding into an asymmetric nickel bubble in a conventional type iip supernova. some acceleration of the pwn expansion is likely, giving a true age of 480 ± 50 yr. the pulsar’s birth luminosity was larger than the current value by a factor of 3-8, while the initial period was within a factor of 2 of its current value. we confirm directly that kes 75 contains the youngest known pwn, and hence the youngest known pulsar. the pulsar psr j1846-0258 has a spindown-inferred magnetic field of 5 × 1013 g; in 2006, it emitted five magnetar-like short x-ray bursts, but its spindown luminosity has not changed significantly. however, the flux of the pwn has decreased by about 10% between 2009 and 2016, almost entirely in the northern half. a bright knot has declined by 30% since 2006. during this time, the photon indices of the power-law models did not change. this flux change is too rapid to be due to normal pwn evolution in one-zone models. | expansion and brightness changes in the pulsar-wind nebula in the composite supernova remnant kes 75 |
context. the abundance ratio n/o is a useful tool to study the interplay of galactic processes, for example star formation efficiency, timescale of infall, and outflow loading factor.aims: we aim to trace log(n/o) versus [fe/h] in the milky way and to compare this ratio with a set of chemical evolution models to understand the role of infall, outflow, and star formation efficiency in the building up of the galactic disc.methods: we used the abundances from idr2-3, idr4, idr5 data releases of the gaia-eso survey both for galactic field and open cluster stars. we determined membership and average composition of open clusters and we separated thin and thick disc field stars. we considered the effect of mixing in the abundance of n in giant stars. we computed a grid of chemical evolution models, suited to reproduce the main features of our galaxy, exploring the effects of the star formation efficiency, infall timescale, and differential outflow.results: with our samples, we map the metallicity range -0.6 ≤ [fe/h] ≤ 0.3 with a corresponding -1.2 ≤ log(n/o) ≤ -0.2, where the secondary production of n dominates. thanks to the wide range of galactocentric distances covered by our samples, we can distinguish the behaviour of log(n/o) in different parts of the galaxy.conclusions: our spatially resolved results allow us to distinguish differences in the evolution of n/o with galactocentric radius. comparing the data with our models, we can characterise the radial regions of our galaxy. a shorter infall timescale is needed in the inner regions, while the outer regions need a longer infall timescale, coupled with a higher star formation efficiency. we compare our results with nebular abundances obtained in manga galaxies, finding in our galaxy a much wider range of log(n/o) than in integrated observations of external galaxies of similar stellar mass, but similar to the ranges found in studies of individual h ii regions. based on observations collected with the flames instrument at vlt/ut2 telescope (paranal observatory, eso, chile), for the gaia-eso large public spectroscopic survey (188.b-3002, 193.b-0936).full table a.1 is 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/618/a102 | the gaia-eso survey: the n/o abundance ratio in the milky way |
this study is dedicated to the systematic investigation of the effect of interferences on sr isotopic analyses in biological apatite and carbonate matrices using laser ablation multicollector inductively coupled plasma mass spectrometry (la-mc icp-ms). trends towards higher 87sr/86sr ratios for la-mc icp-ms compared to solution-nebulization based mc icp-ms when analysing bioapatite matrices (e.g. human teeth) and lower ratios in case of calcium carbonates (e.g. fish ear stones) were observed. this effect can be related to the presence of significant matrix-related interferences such as molecular ions (e.g. (40ca-31p-16o)+, (40ar-31p-16o)+, (42ca-44ca)+, (46ca40ar)+) as well as in many cases concomitant atomic ions (e.g. 87rb+, 174hf2 +). direct 87sr/86sr ratio measurements in ca-rich samples are conducted without the possibility of prior sample separation, which can be accomplished routinely for solution-based analysis. the presence of ca-ar and ca-ca molecular ion interferences in the mass range of sr isotopes is shown using the mass resolving capabilities of a single collector inductively coupled plasma sector field mass spectrometer operated in medium mass resolution when analysing bioapatites and calcium carbonate samples. the major focus was set on analysing human tooth samples, fish hard parts and geological carbonates. potential sources of interferences were identified and corrected for. the combined corrections of interferences and adequate instrumental isotopic fractionation correction procedures lead to accurate data even though increased uncertainties have to be taken into account. the results are discussed along with approaches presented in literature for data correction in laser ablation analysis. | 87sr/86sr isotope ratio measurements by laser ablation multicollector inductively coupled plasma mass spectrometry: reconsidering matrix interferences in bioapatites and biogenic carbonates |
context. alma observations of the serpens south star-forming region suggest that stellar protoclusters may be completely mass segregated at birth. independent observations also suggest that embedded clusters form segregated by mass.aims: as the primordial mass segregation seems to be lost over time, we aim to study on which timescale an initially perfectly mass-segregated star cluster becomes indistinguishable from an initially not mass-segregated cluster. as an example, the orion nebula cluster (onc) is also discussed.methods: we used n-body simulations of star clusters with various masses and two different degrees of primordial mass segregation. we analysed their energy redistribution through two-body relaxation to quantify the time when the models agree in terms of mass segregation, which sets in only dynamically in the models that are primordially not mass segregated. a comprehensive cross-matched catalogue combining optical, infrared, and x-ray surveys of onc members was also compiled and made available.results: the models evolve to a similar radial distribution of high-mass stars after the core collapse (about half a median two-body relaxation time, trh) and become observationally indistinguishable from the point of view of mass segregation at time τv ≈ 3.3 trh. in the case of the onc, using the distribution of high-mass stars, we may not rule out either evolutionary scenario (regardless of whether they are initially mass segregated). when we account for extinction and elongation of the onc, as reported elsewhere, an initially perfectly mass-segregated state seems to be more consistent with the observed cluster. full table 3 is 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/626/a79 | do star clusters form in a completely mass-segregated way? |
fast highly collimated outflows, including bipolar knots, jetlike features, and point-symmetric filaments or strings of knots, are common in planetary nebulae (pne). these features, generally known as jets, are thought to play an active role in the nebular shaping immediately before or while fast stellar winds and d-type ionization fronts shock and sweep up the nebular envelope. the space velocity, radial distance from the central star, and kinematic age of the jets in pne cannot be determined because the inclination angle with the line of sight is usually unknown. here we have used the large number of jets already detected in pne to derive orientation-independent properties from a statistical point of view. we find that jets in pne can be assigned to two different populations: most (about 70%) have space velocities below 100 km s-1, and only 30% have larger velocities. since a significant fraction of jets move at velocities similar to that of their parent pne and are found close to the nebular edge, we propose that these jets have been slowed down in their interaction with the nebular envelope, contributing to the expansion of their pne. the time spans before the jets dissolve are found to be generally shorter than 2500 yr. since most jets are found in young pne of similar (1000-3000 yr) age, it can be concluded that jets are mostly coeval with their pne. | space velocity and time span of jets in planetary nebulae |
the black hole transient v404 cygni exhibited a bright outburst in june 2015 that was intensively followed over a wide range of wavelengths. our team obtained high time resolution optical spectroscopy (! ∼ ! 90 s), which included a detailed coverage of the most active phase of the event. we present a data base consisting of 651 optical spectra obtained during this event, that we combine with 58 spectra gathered during the fainter december 2015 sequel outburst, as well as with 57 spectra from the 1989 event. we previously reported the discovery of wind-related features (p-cygni and broad-wing line profiles) during both 2015 outbursts. here, we build diagnostic diagrams that enable us to study the evolution of typical emission line parameters, such as line fluxes and equivalent widths, and develop a technique to systematically detect outflow signatures. we find that these are present throughout the outburst, even at very low optical fluxes, and that both types of outflow features are observed simultaneously in some spectra, confirming the idea of a common origin. we also show that the nebular phases depict loop patterns in many diagnostic diagrams, while p-cygni profiles are highly variable on time-scales of minutes. the comparison between the three outbursts reveals that the spectra obtained during june and december 2015 share many similarities, while those from 1989 exhibit narrower emission lines and lower wind terminal velocities. the diagnostic diagrams presented in this work have been produced using standard measurement techniques and thus may be applied to other active low-mass x-ray binaries. | the 1989 and 2015 outbursts of v404 cygni: a global study of wind-related optical features |
the microquasar ss433 features the most energetic jets known in our galaxy. a large fraction of the jet kinetic power is delivered to the surrounding w50 nebula at the jet termination shock, from which high-energy emission and cosmic-ray production have been anticipated. here, we report on the detection of a persistent gamma-ray signal obtained with the fermi large area telescope from an unidentified source that we tentatively associate, given its 99.9% confidence level position accuracy and the lack of any other high-energy emitter counterpart in the studied region, with ss433. the obtained spectral energy distribution displays a distinct maximum at ∼250 mev and only extends up to ∼800 mev. we discuss the possibility that the observed gamma-ray emission is produced through proton-proton collisions at the ss433/w50 interaction regions. if the same mechanism is operating in other baryon-loaded microquasar jets, their collective contribution could represent a significant fraction of the total galactic cosmic-ray flux at gev energies. | detection of persistent gamma-ray emission toward ss433/w50 |
while several observational investigations have revealed the presence of magnetic fields in the circumstellar envelopes, jets and outflows of post-asymptotic giant branch stars (pagbs) and planetary nebulae, none has clearly demonstrated their presence at the stellar surface. the lack of information on the strength of the surface magnetic fields prevents us from performing any thorough assessment of their dynamic capability (i.e. material mixing, envelope shaping, etc). we present new high-resolution spectropolarimetric (stokes v) observations of a sample of pagb stars, realized with the instruments espadons and narval, where we searched for the presence of photospheric magnetic fields. out of the seven targets investigated, the rv tauri stars u mon and r sct display a clear zeeman signature and return a definite detection after performing a least squares deconvolution analysis. the remaining five pagbs show no significant detection. we derived longitudinal magnetic fields of 10.2 ± 1.7 g for u mon and 0.6 ± 0.6 g for r sct. in both cases, the stokes profiles point towards an interaction of the magnetic field with the atmosphere dynamics. this first discovery of weak magnetic fields (e.g. ∼10 g level) at the stellar surface of pagb stars opens the door to a better understanding of magnetism in evolved stars. | first detection of surface magnetic fields in post-agb stars: the cases of u monocerotis and r scuti |
a strong super-alfvénic drift of energetic particles (or cosmic rays) in a magnetized plasma can amplify the magnetic field significantly through nonresonant streaming instability (nrsi). while the traditional analysis is done for an ion current, here we use kinetic particle-in-cell simulations to study how the nrsi behaves when it is driven by electrons or by a mixture of electrons and positrons. in particular, we characterize the growth rate, spectrum, and helicity of the unstable modes, as well the level of the magnetic field at saturation. our results are potentially relevant for several space/astrophysical environments (e.g., electron strahl in the solar wind, at oblique nonrelativistic shocks, around pulsar wind nebulae), and also in laboratory experiments. | lepton-driven nonresonant streaming instability |
we build a spitzer irac-complete catalog of objects complementing the ks-band selected ultravista catalog with objects detected in irac only. to identify massive (log ({{m}*}/{{m}⊙ })\gt 11) galaxies at 4\lt z\lt 7, we consider the systematic effects on photometric redshift measurements from the introduction of an old and dusty template and of a bayesian prior on luminosity, as well as the systematic effects from different star formation histories (sfhs) and from nebular emission lines in estimated stellar population properties. our results are most affected by the luminosity prior, while nebular lines and sfhs marginally increase the measurement dispersion; the samples include 52 to 382 galaxies, depending on the adopted configuration. using these results we investigate, for the first time, the evolution of the massive end of the stellar mass functions (smfs) at 4\lt z\lt 7. given the rarity of massive galaxies at these redshifts, cosmic variance and poisson noise dominate the total error budget. the smfs obtained excluding the luminosity prior show no evolution from z∼ 6.5 to z∼ 3.5, indicating that massive galaxies could already be present at early epochs. the luminosity prior reduces the number of z\gt 4 massive galaxies by 83%, implying a rapid growth of massive galaxies in the first 1.5 gyr of cosmic history. the stellar-mass complete sample includes one candidate of a very massive (log ({{m}*}/{{m}⊙ })∼ 11.5), quiescent galaxy at z∼ 5.4 with mips 24 μ m detection, suggesting the presence of an obscured active galactic nucleus. finally, we show that the observed number of 4\lt z\lt 7 massive galaxies matches the number of massive galaxies at 3\lt z\lt 6 predicted by current galaxy formation models. | stellar mass functions of galaxies at 4 < z < 7 from an irac-selected sample in cosmos/ultravista: limits on the abundance of very massive galaxies |
we report the first detection and high angular resolution (1.8″× 1.1″) imaging of acetic acid (ch3cooh) and ggg'-ethylene glycol (ggg'(ch2oh)2) toward the orion kleinmann-low (orion-kl) nebula. the observations were carried out at 1.3 mm with alma during cycle 2. a notable result is that the spatial distribution of the acetic acid and ethylene glycol emission differs from that of the other o-bearing molecules within orion-kl. while the typical emission of o-bearing species harbors a morphology associated with a v-shape linking the hot core region to the compact ridge (with an extension toward the bn object), the emission of acetic acid and ethylene glycol mainly peaks at about 2'' southwest from the hot core region (near sources i and n). we find that the measured ch3cooh:agg'(ch2oh)2 and ch3cooh:ggg'(ch2oh)2 ratios differ from those measured toward the low-mass protostar iras 16293-2422 by more than one order of magnitude. our best hypothesis to explain these findings is that ch3cooh, agg'(ch2oh)2, and ggg'(ch2oh)2 are formed on the icy surface of grains and are then released into the gas-phase via co-desorption with water, by way of a bullet of matter ejected during the explosive event that occurred in the heart of the nebula about 500-700 yr ago. | the complexity of orion: an alma view. ii. ggg'-ethylene glycol and acetic acid |
an analysis of the kinematics of ngc 6720 is performed on the commissioning data obtained with sitelle, the canada-france-hawaii telescope's new imaging fourier transform spectrometer. in order to measure carefully the small broadening effect of a shell expansion on an unresolved emission line, we have determined a computationally robust implementation of the convolution of a gaussian with a sinc instrumental line shape which avoids arithmetic overflows. this model can be used to measure line broadening of typically a few km s-1 even at low spectral resolution (r < 5000). we have also designed the corresponding set of gaussian apodizing functions that are now used by orbs, the sitelle's reduction pipeline. we have implemented this model in orcs, a fitting engine for sitelle's data, and used it to derive the [s ii] density map of the central part of the nebula. the study of the broadening of the [n ii] lines shows that the main ring and the central lobe are two different shells with different expansion velocities. we have also derived deep and spatially resolved velocity maps of the halo in [n ii] and hα and found that the brightest bubbles are originating from two bipolar structures with a velocity difference of more than 35 km s-1 lying at the poles of a possibly unique halo shell expanding at a velocity of more than 15 km s-1. | optimal fitting of gaussian-apodized or under-resolved emission lines in fourier transform spectra providing new insights on the velocity structure of ngc 6720 |
context. the large jet kinetic power and non-thermal processes occurring in the microquasar ss 433 make this source a good candidate for a very high-energy (vhe) gamma-ray emitter. gamma-ray fluxes above the sensitivity limits of current cherenkov telescopes have been predicted for both the central x-ray binary system and the interaction regions of ss 433 jets with the surrounding w50 nebula. non-thermal emission at lower energies has been previously reported, indicating that efficient particle acceleration is taking place in the system. aim. we explore the capability of ss 433 to emit vhe gamma rays during periods in which the expected flux attenuation due to periodic eclipses (porb 13.1 days) and precession of the circumstellar disk (ppre 162 days) periodically covering the central binary system is expected to be at its minimum. the eastern and western ss 433/w50 interaction regions are also examined using the whole data set available. we aim to constrain some theoretical models previously developed for this system with our observations.methods: we made use of dedicated observations from the major atmospheric gamma imaging cherenkov telescopes (magic) and high energy spectroscopic system (h.e.s.s.) of ss 433 taken from 2006 to 2011. these observation were combined for the first time and accounted for a total effective observation time of 16.5 h, which were scheduled considering the expected phases of minimum absorption of the putative vhe emission. gamma-ray attenuation does not affect the jet/medium interaction regions. in this case, the analysis of a larger data set amounting to 40-80 h, depending on the region, was employed.results: no evidence of vhe gamma-ray emission either from the central binary system or from the eastern/western interaction regions was found. upper limits were computed for the combined data set. differential fluxes from the central system are found to be ≲ 10-12-10-13 tev-1 cm-2 s-1 in an energy interval ranging from few × 100 gev to few tev. integral flux limits down to 10-12-10-13 ph cm-2 s-1 and 10-13-10-14 ph cm-2 s-1 are obtainedat 300 and 800 gev, respectively. our results are used to place constraints on the particle acceleration fraction at the inner jetregions and on the physics of the jet/medium interactions.conclusions: our findings suggest that the fraction of the jet kinetic power that is transferred to relativistic protons must be relatively small in ss 433, qp ≤ 2.5 × 10-5, to explain the lack of tev and neutrino emission from the central system. at the ss 433/w50 interface, the presence of magnetic fields ≳10 μg is derived assuming a synchrotron origin for the observed x-ray emission. this also implies the presence of high-energy electrons with ee- up to 50 tev, preventing an efficient production of gamma-ray fluxes in these interaction regions. | constraints on particle acceleration in ss433/w50 from magic and h.e.s.s. observations |
extreme high-frequency bl lacs (ehbl) feature their synchrotron peak of the broad-band spectral energy distribution (sed) at νs ≥ 1017 hz. the bl lac object 1es 2344+514 was included in the ehbl family because of its impressive shift of the synchrotron peak in 1996. during the following years, the source appeared to be in a low state without showing any extreme behaviours. in 2016 august, 1es 2344+514 was detected with the ground-based γ-ray telescope fact during a high γ-ray state, triggering multiwavelength (mwl) observations. we studied the mwl light curves of 1es 2344+514 during the 2016 flaring state, using data from radio to very-high-energy (vhe) γ-rays taken with ovro, kait, kva, not, some telescopes of the gasp-webt collaboration at the teide, crimean, and st. petersburg observatories, swift-uvot, swift-xrt, fermi-lat, fact, and magic. with simultaneous observations of the flare, we built the broad-band sed and studied it in the framework of a leptonic and a hadronic model. the vhe γ-ray observations show a flux level of 55 per cent of the crab nebula flux above 300 gev, similar to the historical maximum of 1995. the combination of magic and fermi-lat spectra provides an unprecedented characterization of the inverse-compton peak for this object during a flaring episode. the γ index of the intrinsic spectrum in the vhe γ-ray band is 2.04 ± 0.12stat ± 0.15sys. we find the source in an extreme state with a shift of the position of the synchrotron peak to frequencies above or equal to 1018 hz. | an intermittent extreme bl lac: mwl study of 1es 2344+514 in an enhanced state |
wolf-rayet stars are advanced evolutionary stages of massive stars. despite their large mass-loss rates and high wind velocities, none of them displays a bow shock, although a fraction of them are classified as runaway. our 2.5-d numerical simulations of circumstellar matter around a $60\mbox{-}\rm m_{\odot }$ runaway star show that the fast wolf-rayet stellar wind is released into a wind-blown cavity filled with various shocks and discontinuities generated throughout the preceding evolutionary phases. the resulting fast-wind-slow-wind interaction leads to the formation of spherical shells of swept-up dusty material similar to those observed in the near-infrared at $24\, \rm \mu \rm m$ with spitzer, which appear to be comoving with the runaway massive stars, regardless of their proper motion and/or the properties of the local ambient medium. we interpret bright infrared rings around runaway wolf-rayet stars in the galactic plane as an indication of their very high initial masses and complex evolutionary history. stellar-wind bow shocks become faint as stars run in diluted media, therefore our results explain the absence of bow shocks detected around galactic wolf-rayet stars, such as the high-latitude, very fast-moving objects wr71, wr124 and wr148. our results show that the absence of a bow shock is consistent with the runaway nature of some wolf-rayet stars. this questions the in situ star formation scenario of high-latitude wolf-rayet stars in favour of dynamical ejection from birth sites in the galactic plane. | on the ring nebulae around runaway wolf-rayet stars |
we present nebular-phase spectra of the type ia supernova (sn ia) 2016brx, a member of the 1991bg-like subclass that lies at the faint end of the sn ia luminosity function. nebular spectra are available for only three other 1991bg-like sne, and their co line centres are all within ≲500 km s-1 of each other. in contrast, the nebular co line centre of sn 2016brx is blue-shifted by >1500 km s-1 compared to them and by ≈1200 km s-1 compared to the rest frame. this is a significant shift relative to the narrow nebular line velocity dispersion of ≲2000 km s-1 of these sne. the large range of nebular line shifts implies that the 56ni in the ejecta of sn 1991bg-like events is off-centre by ∼1000 km s-1 rather than universally centrally confined as previously suggested. with the addition of sn 2016brx, the co nebular line shapes of 1991bg-like objects appear to connect with the brighter sne ia that show double-peaked profiles, hinting at a continuous distribution of line profiles among sne ia. one class of models to produce both off-centre and bimodal 56ni distributions is collisions of white dwarfs with unequal and equal masses. | a significantly off-centre 56ni distribution for the low-luminosity type ia supernova sn 2016brx from the 100ias survey |
massive ob stars are critical to the ecology of galaxies, and yet our knowledge of ob stars in the milky way, fainter than $v \sim 12$, remains patchy. data from the vst photometric h$\alpha$ survey (vphas+) permit the construction of the first deep catalogues of blue excess-selected ob stars, without neglecting the stellar field. a total of 14900 candidates with 2mass cross-matches are blue-selected from a 42 square-degree region in the galactic plane, capturing the carina arm over the galactic longitude range $282^{\circ} \lesssim \ell \lesssim 293^{\circ}$. spectral energy distribution fitting is performed on these candidates' combined vphas+ $u,g,r,i$ and 2mass $j,h,k$ magnitudes. this delivers: effective temperature constraints, statistically separating o from early-b stars; high-quality extinction parameters, $a_0$ and $r_v$ (random errors typically $< 0.1$). the high-confidence o-b2 candidates number 5915 and a further 5170 fit to later b spectral type. spectroscopy of 276 of the former confirms 97% of them. the fraction of emission line stars among all candidate b stars is 7--8% . greyer ($r_v > 3.5$) extinction laws are ubiquitous in the region, over the distance range 2.5--3 kpc to $\sim$10~kpc. near prominent massive clusters, $r_v$ tends to rise, with particularly large and chaotic excursions to $r_v \sim 5$ seen in the carina nebula. the data reveal a hitherto unnoticed association of 108 o-b2 stars around the o5if$+$ star lss 2063 ($\ell = 289.77^{\circ}$, $b = -1.22^{\circ}$). treating the ob star scale-height as a constant within the thin disk, we find an orderly mean relation between extinction ($a_0$) and distance in the galactic longitude range, $287.6^{\circ} < \ell < 293.5^{\circ}$, and infer the subtle onset of thin-disk warping. a halo around ngc 3603, roughly a degree in diameter, of $\sim$500 o-b2 stars with $4 < a_0 (\rm{mag}) < 7$ is noted. | the deep ob star population in carina from the vst photometric hα survey (vphas+) |
x-ray observations provide a potentially powerful tool to study starburst feedback. the analysis and interpretation of such observations remain challenging, however, due to various complications, including the non-isothermality of the diffuse hot plasma and the inhomogeneity of the foreground absorption. we here illustrate such complications and a way to mitigate their effects by presenting an x-ray spectroscopy of the 30 doradus nebula in the large magellanic clouds, based on a 100 ks suzaku observation. we measure the thermal and chemical properties of the hot plasma and quantitatively confront them with the feedback expected from embedded massive stars. we find that our spatially resolved measurements can be well reproduced by a global modelling of the nebula with a lognormal temperature distribution of the plasma emission measure and a lognormal foreground absorption distribution. the metal abundances and total mass of the plasma are consistent with the chemically enriched mass ejection expected from the central ob association and a $\sim 55{{\ \rm per\ cent}}$ mass-loading from the ambient medium. the total thermal energy of the plasma is smaller than what is expected from a simple superbubble model, demonstrating that important channels of energy loss are not accounted for. our analysis indeed shows tentative evidence for a diffuse non-thermal x-ray component, indicating that cosmic ray acceleration needs to be considered in such a young starburst region. finally, we suggest that the lognormal modelling may be suitable for the x-ray spectral analysis of other giant h ii regions, especially when spatially resolved spectroscopy is not practical. | x-ray spectroscopy of the starburst feedback in 30 doradus |
extragalactic planetary nebulae (pne) offer a way to determine the distance to their host galaxies thanks to the nearly universal shape of the planetary nebulae luminosity function (pnlf). accurate pne distance measurements rely on obtaining well-sampled pnlfs and the number of observed pne scales with the encompassed stellar mass. this means either disposing of wide-field observations or focusing on the bright central regions of galaxies. in this work we take this second approach and conduct a census of the pne population in the central regions of galaxies in the fornax cluster, using vlt/muse data for the early-type galaxies observed over the course of the fornax3d survey. using such integral-field spectroscopic observations to carefully separate the nebular emission from the stellar continuum, we isolated [o iii] 5007 å sources of interest, filtered out unresolved impostor sources or kinematic outliers, and present a catalogue of 1350 unique pne sources across 21 early-type galaxies, which includes their positions, [o iii] 5007 å line magnitudes, and line-of-sight velocities. using the pne catalogued within each galaxy, we present independently derived distance estimates based on the fit to the entire observed pnlf observed while carefully accounting for the pne detection incompleteness. with these individual measurements, we arrive at an average distance to the fornax cluster itself of 19.86 ± 0.32 mpc (μpnlf = 31.49 ± 0.04 mag). our pnlf distance measurements agree well with previous distances based on surface brightness fluctuations, finding no significant systematic offsets between the two methods as otherwise reported in previous studies. tables a.1 to a.36 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/653/a167 | the fornax3d project: planetary nebulae catalogue and independent distance measurements to fornax cluster galaxies |
we present new images and continuum spectral analysis for 14 resolved galactic supernova remnants (snrs) selected from the 74 mhz very large array low-frequency sky survey redux (vlssr). we combine new integrated measurements from the vlssr with, when available, flux densities extracted from the galactic and extragalactic all-sky murchison widefield array survey and measurements from the literature to generate improved integrated continuum spectra sampled from ~15 mhz to ~217 ghz. we present the vlssr images. when possible we combine them with publicly available images at 1.4 ghz, to analyse the resolved morphology and spectral index distribution across each snr. we interpret the results and look for evidence of thermal absorption caused by ionised gas either proximate to the snr itself, or along its line of sight. three of the snrs, g4.5+6.8 (kepler), g28.6−0.1, and g120.1+1.4 (tycho), have integrated spectra which can be adequately fit with simple power laws. the resolved spectral index map for tycho confirms internal absorption which was previously detected by the low frequency array, but it is insufficient to affect the fit to the integrated spectrum. two of the snrs are pulsar wind nebulae, g21.5−0.9 and g130.7+3.1 (3c 58). for those we identify high-frequency spectral breaks at 38 and 12 ghz, respectively. for the integrated spectra of the remaining nine snrs, a low frequency spectral turnover is necessary to adequately fit the data. in all cases we are able to explain the turnover by extrinsic thermal absorption. for g18.8+0.3 (kes 67), g21.8−0.6 (kes 69), g29.7−0.3 (kes 75), and g41.1−0.3 (3c 397), we attribute the absorption to ionised gas along the line of sight, possibly from extended h ii region envelopes. for g23.3−0.3 (w41) the absorption can be attributed to h ii regions located in its immediate proximity. thermal absorption from interactions at the ionised interface between snr forward shocks and the surrounding medium were previously identified as responsible for the low frequency turnover in snr g31.9+0.0 (3c 391); our integrated spectrum is consistent with the previous results. we present evidence for the same phenomenon in three additional snrs g27.4+0.0 (kes 73), g39.2-0.3 (3c 396), and g43.3-0.2 (w49b), and derive constraints on the physical properties of the interaction. this result indicates that interactions between snrs and their environs should be readily detectable through thermal absorption by future low frequency observations of snrs with improved sensitivity and resolution. | thermal radio absorption as a tracer of the interaction of snrs with their environments |
extreme emission line galaxies (eelgs) are a notable galaxy genus, ultimately being regarded as local prototypes of early galaxies at the cosmic noon. robust characterisation of their stellar content, however, is hindered by the exceptionally high nebular emission present in their optical spectroscopic data. this study is dedicated into recovering the stellar properties of a sample of 414 eelgs as observed by the sdss survey. such is achieved by means of the spectral synthesis code fado, which self-consistently considers the stellar and nebular emission in an optical spectrum. additionally, a comparative analysis was carried on, by further processing the eelgs sample with the purely stellar spectral synthesis code starlight, and by extending the analysis to a sample of 697 normal star-forming galaxies, expected to be less affected by nebular contribution. we find that, for both galaxy samples, stellar mass and mean age estimates by starlight are systematically biased towards higher values, and that an adequate determination of the physical and evolutionary properties of eelgs via spectral synthesis is only possible when nebular continuum emission is taken into account. moreover, the differences between the two population synthesis codes can be ascribed to the degree of star-formation activity through the specific star-formation rate and the sum of the flux of the most prominent emission lines. as expected, on the basis of the theoretical framework, our results emphasise the importance of considering the nebular emission while performing spectral synthesis, even for galaxies hosting typical levels of star-formation activity. | characterisation of the stellar content of sdss eelgs through self-consistent spectral modelling |
streaming instability is hypothesized to be triggered at particular protoplanetary disk locations where the volume density of the solid particles is enriched comparable to that of the gas. a ring of planetesimals thus forms when this condition is fulfilled locally. these planetesimals collide with each other and accrete inward drifting pebbles from the outer disk to further increase masses. we investigate the growth of the planetesimals that form in a ring-belt at various disk radii. their initial mass distributions are calculated based on the formula summarized from the streaming instability simulations. we simulate the subsequent dynamical evolution of the planetesimals with a protoplanetary disk model based either on the minimum mass solar nebula (mmsn) or on the toomre stability criterion. for the mmsn model, both pebble accretion and planetesimal accretion are efficient at a close-in orbit of 0.3 au, resulting in the emergence of several super-earth mass planets after 1 myr. for comparison, only the most massive planetesimals undergo substantial mass growth when they are born at r = 3 au, while the planetesimals at r = 30 au experience little or no growth. on the other hand, in the denser toomre disk, the most massive forming planets can reach earth mass at t = 1 myr and reach a mass between that of neptune and that of saturn within 3 myr at 30 au and 100 au. both the pebble and planetesimal accretion rate decrease with disk radial distance. nevertheless, planetesimal accretion is less pronounced than pebble accretion at more distant disk regions. taken together, the planets acquire higher masses when the disk has a higher gas density, a higher pebble flux, and/or a lower stokes number of pebbles. | growth after the streaming instability: the radial distance dependence of the planetary growth |
recent observations by the large high altitude air shower observatory (lhaaso) have paved the way for the observational detection of pevatrons in the milky way, thus revolutionizing the field of γ-ray astrophysics. in this paper, we study one such detected source, lhaaso j1908+0621, and explore the origin of multi-tev γ-ray emission from this source. a middle-aged radio supernova remnant snr g40.5-0.5 and a gev pulsar psr j1907+0602 are cospatial with lhaaso j1908+0621. dense molecular clouds are also found to be associated with snr g40.5-0.5. we explain the multi-tev γ-ray emission observed from the direction of lhaaso j1908+0621, by the hadronic interaction between accelerated protons that escaped from the snr shock front and cold protons present inside the dense molecular clouds, and the leptonic emission from the pulsar wind nebula (pwn) associated with the pulsar j1907+0602. moreover, we explain lower energy γ-ray emission by considering the radiative cooling of the electrons that escaped from snr g40.5-0.5. finally, the combined lepto-hadronic scenario was used to explain the multiwavelength spectral energy distribution of lhaaso j1908+0621. although not yet significant, an icecube hotspot of neutrino emission is spatially associated with lhaaso j1908+0621, indicating a possible hadronic contribution. in this paper, we show that if a hadronic component is present in lhaaso j1908+0621, then the second-generation icecube observatory will detect neutrinos from this source. | exploring the hadronic origin of lhaaso j1908+0621 |
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