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to constrain the formation history of an exoplanet, we need to know its chemical composition1-3. with an equilibrium temperature of about 4,050 kelvin4, the exoplanet kelt-9b (also known as hd 195689b) is an archetype of the class of ultrahot jupiters that straddle the transition between stars and gas-giant exoplanets and are therefore useful for studying atmospheric chemistry. at these high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles and exist solely in their atomic forms5. however, despite being the most abundant transition metal in nature, iron has not hitherto been detected directly in an exoplanet because it is highly refractory. the high temperatures of kelt-9b imply that its atmosphere is a tightly constrained chemical system that is expected to be nearly in chemical equilibrium5 and cloud-free6,7, and it has been predicted that spectral lines of iron should be detectable in the visible range of wavelengths5. here we report observations of neutral and singly ionized atomic iron (fe and fe+) and singly ionized atomic titanium (ti+) in the atmosphere of kelt-9b. we identify these species using cross-correlation analysis8 of high-resolution spectra obtained as the exoplanet passed in front of its host star. similar detections of metals in other ultrahot jupiters will provide constraints for planetary formation theories. | atomic iron and titanium in the atmosphere of the exoplanet kelt-9b |
fast radio bursts (frbs) are brief, intense flashes of radio waves from unidentified extragalactic sources. polarized frbs originate in highly magnetized environments. we report observations of the repeating frb 20190520b spanning 17 months, which show that the frb’s faraday rotation is highly variable and twice changes sign. the frb also depolarizes below radio frequencies of about 1 to 3 gigahertz. we interpret these properties as being due to changes in the parallel component of the magnetic field integrated along the line of sight, including reversing direction of the field. this could result from propagation through a turbulent magnetized screen of plasma, located 10–5 to 100 parsecs from the frb source. this is consistent with the bursts passing through the stellar wind of a binary companion of the frb source. | magnetic field reversal in the turbulent environment around a repeating fast radio burst |
the growing population of binary black holes (bbhs) observed by gravitational wave (gw) detectors is a potential rosetta stone for understanding their formation channels. here, we use an upgraded version of our semi-analytical codes fastcluster and cosmo $\mathcal {r}$ate to investigate the cosmic evolution of four different bbh populations: isolated bbhs and dynamically formed bbhs in nuclear star clusters (nscs), globular clusters (gcs), and young star clusters (yscs). with our approach, we can study different channels assuming the same stellar and binary input physics. we find that the merger rate density of bbhs in gcs and nscs is barely affected by stellar metallicity (z), while the rate of isolated bbhs changes wildly with z. bbhs in yscs behave in an intermediate way between isolated and gc/nsc bbhs. the local merger rate density of nth-generation black holes (bhs), obtained by summing up hierarchical mergers in gcs, nscs, and yscs, ranges from -1 to -4 gpc-3 yr-1 and is mostly sensitive to the spin parameter. we find that the mass function of primary bhs evolves with redshift in gcs and nscs, becoming more top-heavy at higher z. in contrast, the primary bh mass function almost does not change with redshift in yscs and in the field. this signature of the bh mass function has relevant implications for einstein telescope and cosmic explorer. finally, our analysis suggests that multiple channels contribute to the bbh population of the second gw transient catalogue. | the cosmic evolution of binary black holes in young, globular, and nuclear star clusters: rates, masses, spins, and mixing fractions |
we present the evolution of black holes (bhs) and their relationship with their host galaxies in astrid, a large-volume cosmological hydrodynamical simulation with box size 250 h-1mpc containing 2 × 55003 particles evolved to z = 3. astrid statistically models bh gas accretion and active galactic nucleus (agn) feedback to their environments, applies a power-law distribution for bh seed mass $\, m_{\rm sd}$, uses a dynamical friction model for bh dynamics, and executes a physical treatment of bh mergers. the bh population is broadly consistent with empirical constraints on the bh mass function, the bright end of the luminosity functions, and the time evolution of bh mass and accretion rate density. the bh mass and accretion exhibit a tight correlation with host stellar mass and star formation rate. we trace bhs seeded before z > 10 down to z = 3, finding that bhs carry virtually no imprint of the initial $\, m_{\rm sd}$ except those with the smallest $\, m_{\rm sd}$, where less than 50 per cent of them have doubled in mass. gas accretion is the dominant channel for bh growth compared to bh mergers. with dynamical friction, astrid predicts a significant delay for bh mergers after the first encounter of a bh pair, with a typical elapse time of about 200 myr. there are in total 4.5 × 105 bh mergers in astrid at z > 3, ~103 of which have x-ray detectable em counterparts: a bright $\, {\rm kpc}$ scale dual agn with lx > 1043 erg s-1. bhs with $\, m_{\rm bh}\sim 10^{7\!-\!8} \, m_{\odot }$ experience the most frequent mergers. galaxies that host bh mergers are unbiased tracers of the overall $\, m_{\rm bh}\!-\! m_*$ relation. massive ($\gt 10^{11}\, m_{\odot }$) galaxies have a high occupation number (≳10) of bhs, and hence host the majority of bh mergers. | the astrid simulation: the evolution of supermassive black holes |
the process of superradiance can extract angular momentum and energy from astrophysical black holes (bhs) to populate gravitationally bound states with an exponentially large number of light bosons. we analytically calculate superradiant growth rates for vectors around rotating bhs in the regime where the vector compton wavelength is much larger than the bh size. spin-1 bound states have superradiance times as short as a second around stellar bhs, growing up to a thousand times faster than their spin-0 counterparts. the fast rates allow us to use measurements of rapidly spinning bhs in x-ray binaries to exclude a wide range of masses for weakly coupled spin-1 particles, 5 ×10-14-2 ×10-11 ev ; lighter masses in the range 6 ×10-20-2 ×10-17 ev start to be constrained by supermassive bh spin measurements at a lower level of confidence. we also explore routes to detection of new vector particles possible with the advent of gravitational wave (gw) astronomy. the ligo-virgo collaboration could discover hints of a new light vector particle in statistical analyses of masses and spins of merging bhs. vector annihilations source continuous monochromatic gravitational radiation which could be observed by current gw observatories. at design sensitivity, advanced ligo may measure up to thousands of annihilation signals from within the milky way, while hundreds of bhs born in binary mergers across the observable universe may superradiate vector bound states and become new beacons of monochromatic gravitational waves. | black hole superradiance signatures of ultralight vectors |
we report new searches for solar axions and galactic axionlike dark matter particles, using the first low-background data from the pandax-ii experiment at china jinping underground laboratory, corresponding to a total exposure of about 2.7 ×104 kg day . no solar axion or galactic axionlike dark matter particle candidate has been identified. the upper limit on the axion-electron coupling (ga e) from the solar flux is found to be about 4.35 ×10-12 in the mass range from 10-5 to 1 kev /c2 with 90% confidence level, similar to the recent lux result. we also report a new best limit from the 57fe deexcitation. on the other hand, the upper limit from the galactic axions is on the order of 10-13 in the mass range from 1 to 10 kev /c2 with 90% confidence level, slightly improved compared with the lux. | limits on axion couplings from the first 80 days of data of the pandax-ii experiment |
atmospheric compositions can provide powerful diagnostics of formation and migration histories of planetary systems. we investigate constraints on atmospheric abundances of h2o, na, and k, in a sample of transiting exoplanets using the latest transmission spectra and new h2 broadened opacities of na and k. our sample of 19 exoplanets spans from cool mini-neptunes to hot jupiters, with equilibrium temperatures between ∼300 and 2700 k. using homogeneous bayesian retrievals we report atmospheric abundances of na, k, and h2o, and their detection significances, confirming 6 planets with strong na detections, 6 with k, and 14 with h2o. we find a mass-metallicity trend of increasing h2o abundances with decreasing mass, spanning generally substellar values for gas giants and stellar/superstellar for neptunes and mini-neptunes. however, the overall trend in h2o abundances, from mini-neptunes to hot jupiters, is significantly lower than the mass-metallicity relation for carbon in the solar system giant planets and similar predictions for exoplanets. on the other hand, the na and k abundances for the gas giants are stellar or superstellar, consistent with each other, and generally consistent with the solar system metallicity trend. the h2o abundances in hot gas giants are likely due to low oxygen abundances relative to other elements rather than low overall metallicities, and provide new constraints on their formation mechanisms. the differing trends in the abundances of species argue against the use of chemical equilibrium models with metallicity as one free parameter in atmospheric retrievals, as different elements can be differently enhanced. | mass-metallicity trends in transiting exoplanets from atmospheric abundances of h2o, na, and k |
we analyze the stellar ages obtained from a combination of lick indices in borghi et al. for 140 massive and passive galaxies selected in the lega-c survey at 0.6 < z < 0.9. from their median age-redshift relation, we derive a new direct measurement of h(z) without any cosmological model assumption using the cosmic chronometer approach. we thoroughly study the main systematics involved in this analysis: the choice of the lick indices combination, the binning method, the assumed stellar population model, and the adopted star formation history; these effects are included in the total error budget. we obtain h(z = 0.75) = 98.8 ± 33.6 km s-1 mpc-1. in parallel, we also propose a simple framework based on a cosmological model to describe the age-redshift relations in the context of galaxy downsizing. this allows us to derive constraints on the hubble constant h 0 and the typical galaxy formation time. this new h(z) measurement, whose accuracy is currently limited by the scarcity of the sample analyzed, paves the road for the joint study of the stellar populations of individual passive galaxies and the expansion history of the universe in light of future spectroscopic surveys. | toward a better understanding of cosmic chronometers: a new measurement of h(z) at z 0.7 |
we use the panchromatic spectral energy distribution (sed)-fitting code prospector to measure the galaxy logm*-logsfr relationship (the star-forming sequence) across 0.2 < z < 3.0 using the cosmos-2015 and 3d-hst uv-ir photometric catalogs. we demonstrate that the chosen method of identifying star-forming galaxies introduces a systematic uncertainty in the inferred normalization and width of the star-forming sequence, peaking for massive galaxies at ~0.5 and ~0.2 dex, respectively. to avoid this systematic, we instead parameterize the density of the full galaxy population in the logm*-logsfr-redshift plane using a flexible neural network known as a normalizing flow. the resulting star-forming sequence has a low-mass slope near unity and a much flatter slope at higher masses, with a normalization 0.2-0.5 dex lower than typical inferences in the literature. we show this difference is due to the sophistication of the prospector stellar populations modeling: the nonparametric star formation histories naturally produce higher masses while the combination of individualized metallicity, dust, and star formation history constraints produce lower star formation rates (sfrs) than typical uv+ir formulae. we introduce a simple formalism to understand the difference between sfrs inferred from sed fitting and standard template-based approaches such as uv+ir sfrs. finally, we demonstrate the inferred star-forming sequence is consistent with predictions from theoretical models of galaxy formation, resolving a long-standing ~ 0.2-0.5 dex offset with observations at 0.5 < z < 3. the fully trained normalizing flow including a nonparametric description of $\rho (\mathrm{log}{m}^{* },\mathrm{logsfr},z)$ is available online 20 20 https://github.com/jrleja/sfs_leja_trained_flow to facilitate straightforward comparisons with future work. | a new census of the 0.2 < z < 3.0 universe. ii. the star-forming sequence |
when determining absolute ages of identifiably young stellar populations, results strongly depend on which stars are studied. cooler (k, m) stars typically yield ages that are systematically younger than warmer (a, f, g) stars by a factor of two. i explore the possibility that these age discrepancies are the result of magnetic inhibition of convection in cool young stars by using magnetic stellar evolution isochrones to determine the median age of the upper scorpius subgroup of the scorpius-centaurus ob association. a median age of 10 myr consistent across spectral types a through m is found, except for a subset of f-type stars that appear significantly older. agreement is shown for ages derived from the hertzsprung-russell (hr) diagram and from the empirical mass-radius relationship defined by eclipsing multiple-star systems. surface magnetic field strengths required to produce agreement are approximately 2.5 kg and are predicted from a priori estimates of thermal equipartition values. a region in the hr diagram is identified that plausibly connects stars whose structures are weakly influenced by the presence of magnetic fields with those whose structures are strongly influenced by magnetic fields. the models suggest that this region is characterized by stars with rapidly thinning outer convective envelopes where the radiative core mass is greater than 75% of the total stellar mass. furthermore, depletion of lithium predicted from magnetic models appears in better agreement with observed lithium equivalent widths than predictions from non-magnetic models. these results suggest that magnetic inhibition of convection plays an important role in the early evolution of low-mass stars and that it may be responsible for noted age discrepancies in young stellar populations. | magnetic inhibition of convection and the fundamental properties of low-mass stars. iii. a consistent 10 myr age for the upper scorpius ob association |
we present an end-to-end, two-phase model for the origin of globular clusters (gcs). in the model, populations of stellar clusters form in the high-pressure discs of high-redshift (z > 2) galaxies (a rapid-disruption phase due to tidal perturbations from the dense interstellar medium), after which the galaxy mergers associated with hierarchical galaxy formation redistribute the surviving, massive clusters into the galaxy haloes, where they remain until the present day (a slow-disruption phase due to tidal evaporation). the high galaxy merger rates of z > 2 galaxies allow these clusters to be `liberated' into the galaxy haloes before they are disrupted within the high-density discs. this physically motivated toy model is the first to include the rapid-disruption phase, which is shown to be essential for simultaneously reproducing the wide variety of properties of observed gc systems, such as their universal characteristic mass-scale, the dependence of the specific frequency on metallicity and galaxy mass, the gc system mass-halo mass relation, the constant number of gcs per unit supermassive black hole mass, and the colour bimodality of gc systems. the model predicts that most of these observables were already in place at z = 1-2, although under rare circumstances gcs may still form in present-day galaxies. in addition, the model provides important constraints on models for multiple stellar populations in gcs by putting limits on initial gc masses and the amount of pristine gas accretion. the paper is concluded with a discussion of these and several other predictions and implications, as well as the main open questions in the field. | globular clusters as the relics of regular star formation in `normal' high-redshift galaxies |
we report chandra observations of gw170817, the first neutron star-neutron star merger discovered by the joint ligo-virgo collaboration, and the first direct detection of gravitational radiation associated with an electromagnetic counterpart, fermi short γ-ray burst grb 170817a. the event occurred on 2017 august 17 and subsequent observations identified an optical counterpart, sss17a, coincident with ngc 4993 (∼10″ separation). early chandra ({{δ }}t∼ 2 days) and swift ({{δ }}t∼ 1{--}3 days) observations yielded non-detections at the optical position, but ∼9 days post-trigger chandra monitoring revealed an x-ray point source coincident with sss17a. we present two deep chandra observations totaling ∼95 ks, collected on 2017 september 01-02 ({{δ }}t∼ 15{--}16 days). we detect x-ray emission from sss17a with {l}0.3{--10{kev}}={2.6}-0.4+0.5× {10}38 erg s-1, and a power law spectrum of {{γ }}=2.4+/- 0.8. we find that the x-ray light curve from a binary ns coalescence associated with this source is consistent with the afterglow from an off-axis short γ-ray burst, with a jet angled ≳23° from the line of sight. this event marks both the first electromagnetic counterpart to a ligo-virgo gravitational-wave source and the first identification of an off-axis short grb. we also confirm extended x-ray emission from ngc 4993 ({l}0.3{--10{kev}}∼ 9× {10}38 erg s-1) consistent with its e/s0 galaxy classification, and report two new chandra point sources in this field, cxou j130948 and cxou j130946. | a deep chandra x-ray study of neutron star coalescence gw170817 |
the detonation of a sub-chandrasekhar-mass white dwarf (wd) has emerged as one of the most promising type ia supernova (sn ia) progenitor scenarios. recent studies have suggested that the rapid transfer of a very small amount of helium from one wd to another is sufficient to ignite a helium shell detonation that subsequently triggers a carbon core detonation, yielding a “dynamically driven double-degenerate double-detonation” sn ia. because the helium shell that surrounds the core explosion is so minimal, this scenario approaches the limiting case of a bare c/o wd detonation. motivated by discrepancies in previous literature and by a recent need for detailed nucleosynthetic data, we revisit simulations of naked c/o wd detonations in this paper. we disagree to some extent with the nucleosynthetic results of previous work on sub-chandrasekhar-mass bare c/o wd detonations; for example, we find that a median-brightness sn ia is produced by the detonation of a 1.0 {m}⊙wd instead of a more massive and rarer 1.1 {m}⊙wd. the neutron-rich nucleosynthesis in our simulations agrees broadly with some observational constraints, although tensions remain with others. there are also discrepancies related to the velocities of the outer ejecta and light curve shapes, but overall our synthetic light curves and spectra are roughly consistent with observations. we are hopeful that future multidimensional simulations will resolve these issues and further bolster the dynamically driven double-degenerate double-detonation scenario’s potential to explain most sne ia. | sub-chandrasekhar-mass white dwarf detonations revisited |
understanding the impact of active m-dwarf stars on the atmospheric equilibrium and surface conditions of a habitable zone earth-like planet is key to assessing m dwarf planet habitability. previous modeling of the impact of electromagnetic (em) radiation and protons from a single large flare on an earth-like atmosphere indicated that significant and long-term reductions in ozone were possible, but the atmosphere recovered. these stars more realistically exhibit frequent flaring with a power-law distribution of energies. here we use a coupled 1d photochemical and radiative-convective model to investigate the effects of repeated flaring on the photochemistry and surface uv of an earth-like planet unprotected by an intrinsic magnetic field. we use time-resolved flare spectra obtained for the dm3 star ad leo, combined with flare occurrence frequencies and total energies (typically 10$^{30.5}$ to 10$^{34}$ erg) from the 4-year kepler light curve for the dm4 flare star gj1243. our model results show repeated em-only flares have little effect on the ozone column depth, but that multiple proton events can rapidly destroy the ozone column. combining the realistic flare and proton event frequencies with nominal cme & sep geometries, we find the ozone column for an earth-like planet can be depleted by 94% in 10 years, with a downward trend that makes recovery unlikely and suggests further destruction. for more extreme stellar inputs o3 depletion allows a constant 0.1-1 w m$^{-2}$ of uv-c at the planet's surface, which is likely detrimental to organic complexity. our results suggest that active m dwarf hosts may comprehensively destroy ozone shields and subject the surface of magnetically-unprotected earth-like planets to long-term radiation that can damage complex organic structures. however, this does not preclude habitability, as a safe haven for life could still exist below an ocean surface. | modeling repeated m dwarf flaring at an earth-like planet in the habitable zone: atmospheric effects for an unmagnetized planet |
we build on the evidence provided by our legacy survey of galactic globular clusters (gc) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in gcs. the observational constraints on multiple generations to be fulfilled are manifold, including gc specificity, ubiquity, variety, predominance, discreteness, supernova avoidance, p-capture processing, helium enrichment and mass budget. we argue that scenarios appealing to supermassive stars, fast rotating massive stars and massive interactive binaries violate in an irreparable fashion two or more among such constraints. also the scenario appealing to asymptotic giant branch (agb) stars as producers of the material for next generation stars encounters severe difficulties, specifically concerning the mass budget problem and the detailed chemical composition of second-generation stars. we qualitatively explore ways possibly allowing one to save the agb scenario, specifically appealing to a possible revision of the cross-section of a critical reaction rate destroying sodium, or alternatively by a more extensive exploration of the vast parameter space controlling the evolutionary behaviour of agb stellar models. still, we cannot ensure success for these efforts and totally new scenarios may have to be invented to understand how gcs formed in the early universe. | the hubble space telescope uv legacy survey of galactic globular clusters - v. constraints on formation scenarios |
we present an improved measurement of the carbon-nitrogen-oxygen (cno) solar neutrino interaction rate at earth obtained with the complete borexino phase-iii dataset. the measured rate, rcno=6.7-0.8+2.0 counts/(day ×100 tonnes ) , allows us to exclude the absence of the cno signal with about 7 σ c.l. the correspondent cno neutrino flux is 6.6-0.9+2.0×108 cm-2 s−1 , taking into account the neutrino flavor conversion. we use the new cno measurement to evaluate the c and n abundances in the sun with respect to the h abundance for the first time with solar neutrinos. our result of ncn=(5.7 8-1.00+1.86)×10-4 displays a ∼2 σ tension with the "low-metallicity" spectroscopic photospheric measurements. furthermore, our result used together with the 7be and 8b solar neutrino fluxes, also measured by borexino, permits us to disfavor at 3.1 σ c.l. the "low-metallicity" standard solar model b16-agss09met as an alternative to the "high-metallicity" standard solar model b16-gs98. | improved measurement of solar neutrinos from the carbon-nitrogen-oxygen cycle by borexino and its implications for the standard solar model |
the detection of gw170817 in gravitational waves provides unprecedented constraints on the equation of state (eos) of the ultradense matter within the cores of neutron stars (nss). we extend the nonparametric analysis first introduced by landry and essick (2019), and confirm that gw170817 favors soft eoss. we infer macroscopic observables for a canonical 1.4 m⊙ ns, including the tidal deformability λ1.4=211-137+312 (491-181+216) and radius r1.4=10.8 6-1.42+2.04 (12.51-0.88+1.00) km , as well as the maximum mass for nonrotating nss mmax=2.06 4-0.134+0.260 (2.017-0.087+0.238) m⊙ , with nonparametric priors loosely (tightly) constrained to resemble candidate eoss from the literature. furthermore, we find weak evidence that gw170817 involved at least one ns based on gravitational-wave data alone (bbbhns=3.3 ±1.4 ), consistent with the observation of electromagnetic counterparts. we also investigate gw170817's implications for the maximum spin frequency of millisecond pulsars, and find that the fastest known pulsar is spinning at more than 50% of its breakup frequency at 90% confidence. we additionally find modest evidence in favor of quark matter within nss, and gw170817 favors the presence of at least one disconnected hybrid star branch in the mass-radius relation over a single stable branch by a factor of 2. assuming there are multiple stable branches, we find a suggestive posterior preference for a sharp softening around nuclear density followed by stiffening around twice nuclear density, consistent with a strong first-order phase transition. while the statistical evidence in favor of new physics within ns cores remains tenuous with gw170817 alone, these tantalizing hints reemphasize the promise of gravitational waves for constraining the supranuclear eos. | nonparametric inference of neutron star composition, equation of state, and maximum mass with gw170817 |
neutrinos in core-collapse supernovae and neutron-star mergers are susceptible to flavor instabilities of three kinds: slow, fast, and collisional. prior work has established mappings of the first two onto abstract mechanical systems in flavor space, respectively named the slow and fast flavor pendula. here we introduce and analyze the flavor pendulum associated with the third class. we explain our results in terms of the recently developed theory of neutrino quantum thermodynamics. perhaps our most surprising finding is that there exists a limit in which decoherent interactions drive perfectly coherent flavor conversion. | collisional flavor pendula and neutrino quantum thermodynamics |
in dense astrophysical environments, notably core-collapse supernovae and neutron star mergers, neutrino-neutrino forward scattering can spawn flavor conversion on very short scales. scattering with the background medium can impact collective flavor conversion in various ways, either damping oscillations or possibly setting off novel collisional flavor instabilities (cfis). a key feature in this process is the slowness of collisions compared to the much faster dynamics of neutrino-neutrino refraction. assuming spatial homogeneity, we leverage this hierarchy of scales to simplify the description accounting only for the slow dynamics driven by collisions. we illustrate our new approach both in the case of cfis and in the case of fast instabilities damped by collisions. in both cases, our strategy provides new equations, the slow-dynamics equations, that simplify the description of flavor conversion and allow us to qualitatively understand the final state of the system after the instability, either collisional or fast, has saturated. | collisions and collective flavor conversion: integrating out the fast dynamics |
by combining the jwst/nircam jades and ceers extragalactic datasets, we have uncovered a sample of twenty-one t and y brown dwarf candidates at best-fit distances between 0.1 - 4.2 kpc. these sources were selected by targeting the blue 1$\mu$m - 2.5$\mu$m colors and red 3$\mu$m - 4.5$\mu$m colors that arise from molecular absorption in the atmospheres of t$_{\mathrm{eff}} < $ 1300k brown dwarfs. we fit these sources using multiple models of low-mass stellar atmospheres and present the resulting fluxes, sizes, effective temperatures and other derived properties for the sample. if confirmed, these fits place the majority of the sources in the milky way thick disk and halo. we observe proper motion for seven of the candidate brown dwarfs with directions in agreement with the plane of our galaxy, providing evidence that they are not extragalactic in nature. we demonstrate how the colors of these sources differ from selected high-redshift galaxies, and explore the selection of these sources in planned large-area jwst nircam surveys. deep imaging with jwst/nircam presents an an excellent opportunity for finding and understanding these very cold low-mass stars at kpc distances. | brown dwarf candidates in the jades and ceers extragalactic surveys |
we study the radioactively powered transients produced by accretion disc winds following a compact object merger. based on the outflows found in two-dimensional hydrodynamical disc models, we use wavelength-dependent radiative transfer calculations to generate synthetic light curves and spectra. we show that resulting kilonova transients generally produce both optical and infrared emission, with the brightness and colour carrying information about the merger physics. in those regions of the wind subject to high neutrino irradiation, r-process nucleosynthesis may halt before producing high-opacity, complex ions (the lanthanides). the kilonova light curves thus typically has two distinct components: a brief (∼2 d) blue optical transient produced in the outer lanthanide-free ejecta, and a longer (∼10 d) infrared transient produced in the inner, lanthanide line-blanketed region. mergers producing a longer lived neutron star, or a more rapidly spinning black hole, have stronger neutrino irradiation, generate more lanthanide-free ejecta and are optically brighter and bluer. at least some optical emission is produced in all disc wind models, which should enhance the detectability of electromagnetic counterparts to gravitational wave sources. however, the presence of even a small amount (10-4 m⊙) of overlying, neutron-rich dynamical ejecta will act as a `lanthanide-curtain', obscuring the optical wind emission from certain viewing angles. because the disc outflows have moderate velocities (∼10 000 km s-1), numerous resolved line features are discernible in the spectra, distinguishing disc winds from fast-moving dynamical ejecta, and offering a potential diagnostic of the detailed composition of freshly produced r-process material. | kilonova light curves from the disc wind outflows of compact object mergers |
over this last year we have published four independent refereed studies confirming the presence of a gravitational anomaly, from studying the relative velocities and separations on the plane of the sky, $v_{2d}$ and $s_{2d}$ respectively, of wide binary stars observed by the {\it gaia} satellite. these studies show results which are fully consistent with newtonian dynamics in a high acceleration $s_{2d}<2000$ au regime, but which conclusively identify mond phenomenology for the low acceleration $s_{2d}>2000$ au regime. these four studies span a range of sample selection strategies and cover also a range of statistical techniques, in all cases, results are consistent in identifying a change in the effective value of the gravitational constant in the low acceleration $s_{2d}>2000$ au regime of $g \to \gamma g$ with $\gamma=1.5 \pm \sigma_{\gamma}$, with $0.06<\sigma_{\gamma}<0.2$, depending on the sample selection strategy and the statistical modelling implemented. recently, a contradictory study appeared, banik et al. (2024) (originally arxiv:2311.03436 in 2023), claiming a 19$\sigma$ statistical preference of a purely newtonian model over a mond alternative, looking also at distributions of $v_{2d}$ and $s_{2d}$ for wide binaries from the {\it gaia} satellite, although only in the $s_{2d}>2000$ au regime. inspection of said study readily shows the use of a statistical treatment inconsistent with the error structure of the data used. related to the above, the best fit posterior physical parameters found in banik et al. (2024), show a lack of correlation with their inferred gravity index. in this brief comment we expand upon the above to show that the results of banik et al. (2024) are not due to the physics of the problem being treated, but to the methodological problems of that study. | on the methodological shortcomings in the wide binary gravity test of banik et al. 2024 |
we report the discovery of the closest known black hole candidate as a binary companion to v723 mon. v723 mon is a nearby ($d\sim 460\, \rm pc$), bright (v ≃ 8.3 mag), evolved (teff, giant ≃ 4440 k, and lgiant ≃ 173 l⊙) red giant in a high mass function, f(m) = 1.72 ± 0.01 m⊙, nearly circular binary (p = 59.9 d, e ≃ 0). v723 mon is a known variable star, previously classified as an eclipsing binary, but its all-sky automated survey, kilodegree extremely little telescope, and transiting exoplanet survey satellite light curves are those of a nearly edge-on ellipsoidal variable. detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of $87.0^{\circ ^{+1.7^\circ }}_{-1.4^\circ }$, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of mcomp = 3.04 ± 0.06 m⊙, a stellar radius of rgiant = 24.9 ± 0.7 r⊙, and a giant mass of mgiant = 1.00 ± 0.07 m⊙. we identify a likely non-stellar, diffuse veiling component with contributions in the b and v band of ${\sim }63{{\ \rm per\ cent}}$ and ${\sim }24{{\ \rm per\ cent}}$, respectively. the sed and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. we do observe eclipses of the balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion discs. the x-ray luminosity of the system is $l_{\rm x}\simeq 7.6\times 10^{29}~\rm ergs~s^{-1}$, corresponding to l/ledd ~ 10-9. the simplest explanation for the massive companion is a single compact object, most likely a black hole in the 'mass gap'. | a unicorn in monoceros: the 3 m⊙ dark companion to the bright, nearby red giant v723 mon is a non-interacting, mass-gap black hole candidate |
young star clusters are the most common birthplace of massive stars and are dynamically active environments. here, we study the formation of black holes (bhs) and binary black holes (bbhs) in young star clusters, by means of 6000 n-body simulations coupled with binary population synthesis. we probe three different stellar metallicities (z = 0.02, 0.002, and 0.0002) and two initial-density regimes (density at the half-mass radius ρh ≥ 3.4 × 104 and ≥1.5 × 102 m⊙ pc-3 in dense and loose star clusters, respectively). metal-poor clusters tend to form more massive bhs than metal-rich ones. we find ∼6, ∼2, and <1 per cent of bhs with mass mbh > 60 m⊙ at z = 0.0002, 0.002, and 0.02, respectively. in metal-poor clusters, we form intermediate-mass bhs with mass up to ∼320 m⊙. bbh mergers born via dynamical exchanges (exchanged bbhs) can be more massive than bbh mergers formed from binary evolution: the former (latter) reach total mass up to ∼140 m⊙ (∼80 m⊙). the most massive bbh merger in our simulations has primary mass ∼88 m⊙, inside the pair-instability mass gap, and a mass ratio of ∼0.5. only bbhs born in young star clusters from metal-poor progenitors can match the masses of gw 170729, the most massive event in first and second observing run (o1 and o2), and those of gw 190412, the first unequal-mass merger. we estimate a local bbh merger rate density ∼110 and ∼55 gpc-3 yr-1, if we assume that all stars form in loose and dense star clusters, respectively. | binary black holes in young star clusters: the impact of metallicity |
stars are extremely important astronomical objects that constitute the pillars on which the universe is built, and as such, their study has gained increasing interest over the years. white dwarf stars are not the exception. indeed, these stars constitute the final evolutionary stage for more than 95% of all stars. the galactic population of white dwarfs conveys a wealth of information about several fundamental issues and are of vital importance to study the structure, evolution and chemical enrichment of our galaxy and its components—including the star formation history of the milky way. several important studies have emphasized the advantage of using white dwarfs as reliable clocks to date a variety of stellar populations in the solar neighborhood and in the nearest stellar clusters, including the thin and thick disks, the galactic spheroid and the system of globular and open clusters. in addition, white dwarfs are tracers of the evolution of planetary systems along several phases of stellar evolution. not less relevant than these applications, the study of matter at high densities has benefited from our detailed knowledge about evolutionary and observational properties of white dwarfs. in this sense, white dwarfs are used as laboratories for astro-particle physics, being their interest focused on physics beyond the standard model, that is, neutrino physics, axion physics and also radiation from "extra dimensions", and even crystallization. the last decade has witnessed a great progress in the study of white dwarfs. in particular, a wealth of information of these stars from different surveys has allowed us to make meaningful comparison of evolutionary models with observations. while some information like surface chemical composition, temperature and gravity of isolated white dwarfs can be inferred from spectroscopy, and the total mass and radius can be derived as well when they are in binaries, the internal structure of these compact stars can be unveiled only by means of asteroseismology, an approach based on the comparison between the observed pulsation periods of variable stars and the periods predicted by appropriate theoretical models. the asteroseismological techniques allow us to infer details of the internal chemical stratification, the total mass, and even the stellar rotation profile. in this review, we first revise the evolutionary channels currently accepted that lead to the formation of white-dwarf stars, and then, we give a detailed account of the different sub-types of pulsating white dwarfs known so far, emphasizing the recent observational and theoretical advancements in the study of these fascinating variable stars. | pulsating white dwarfs: new insights |
the structure of magnetic flux ropes injected into the solar wind during reconnection in the coronal atmosphere is explored with particle-in-cell simulations and compared with in situ measurements of magnetic "switchbacks" from the parker solar probe. we suggest that multi-x-line reconnection between open and closed flux in the corona injects flux ropes into the solar wind and that these flux ropes convect outward over long distances before eroding due to reconnection. simulations that explore the magnetic structure of flux ropes in the solar wind reproduce the following key features of the switchback observations: a rapid rotation of the radial magnetic field into the transverse direction, which is a consequence of reconnection with a strong guide field; and the potential to reverse the radial field component. the potential implication of the injection of large numbers of flux ropes in the coronal atmosphere for understanding the generation of the solar wind is discussed. | switchbacks as signatures of magnetic flux ropes generated by interchange reconnection in the corona |
models for black hole (bh) formation from stellar evolution robustly predict the existence of a pair-instability supernova (pisn) mass gap in the range ∼50 to ∼120 solar masses. this theoretical prediction is supported by the binary black holes (bbhs) of ligo/virgo's first two observing runs, whose component masses are well fit by a power law with a maximum mass cutoff at ${m}_{\max }={40.8}_{-4.4}^{+11.8}\,{\text{}}{m}_{\odot }$ . meanwhile, the bbh event gw190521 has a reported primary mass of ${m}_{1}={85}_{-14}^{+21}\,{\text{}}{m}_{\odot }$ , firmly above the inferred ${m}_{\max }$ , and secondary mass ${m}_{2}={66}_{-18}^{+17}\ {\text{}}{m}_{\odot }$ . rather than concluding that both components of gw190521 belong to a new population of mass-gap bhs, we explore the conservative scenario in which gw190521's secondary mass belongs to the previously observed population of bhs. we replace the default priors on m1 and m2, which assume that bh detector-frame masses are uniformly distributed, with this population-informed prior on m2, finding ${m}_{2}\lt 48\,{\text{}}{m}_{\odot }$ at 90% credibility. moreover, because the total mass of the system is better constrained than the individual masses, the population prior on m2 automatically increases the inferred m1 to sit above the gap (39% for m1 > 120 ${\text{}}{m}_{\odot }$ , or 25% probability for m1 > 130 ${\text{}}{m}_{\odot }$ ). as long as the prior odds for a double-mass-gap bbh are smaller than $\sim 1\,:\,15$ , it is more likely that gw190521 straddles the pair-instability gap. we argue that gw190521 may be the first example of a straddling binary black hole, composed of a conventional stellar mass bh and a bh from the "far side" of the pisn mass gap. | minding the gap: gw190521 as a straddling binary |
context. the medium-resolution spectrometer (mrs) provides one of the four operating modes of the mid-infrared instrument (miri) on board the james webb space telescope (jwst). the mrs is an integral field spectrometer, measuring the spatial and spectral distributions of light across the 5-28 µm wavelength range with a spectral resolving power between 3700 and 1300.aims: we present the mrs's optical, spectral, and spectro-photometric performance, as achieved in flight, and we report on the effects that limit the instrument's ultimate sensitivity.methods: the mrs flight performance has been quantified using observations of stars, planetary nebulae, and planets in our solar system. the precision and accuracy of this calibration was checked against celestial calibrators with well-known flux levels and spectral features.results: we find that the mrs geometric calibration has a distortion solution accuracy relative to the commanded position of 8 mas at 5 µm and 23 mas at 28 µm. the wavelength calibration is accurate to within 9 km s−1 at 5 µm and 27 km s−1 at 28 µm. the uncertainty in the absolute spectro-photometric calibration accuracy was estimated at 5.6 ± 0.7%. the miri calibration pipeline is able to suppress the amplitude of spectral fringes to below 1.5% for both extended and point sources across the entire wavelength range. the mrs point spread function (psf) is 60% broader than the diffraction limit along its long axis at 5 µm and is 15% broader at 28 µm.conclusions: the mrs flight performance is found to be better than prelaunch expectations. the mrs is one of the most subscribed observing modes of jwst and is yielding many high-profile publications. it is currently humanity's most powerful instrument for measuring the mid-infrared spectra of celestial sources and is expected to continue as such for many years to come. | jwst miri flight performance: the medium-resolution spectrometer |
we present a novel strategy to systematically study complex-structure moduli stabilization in type iib and f-theory flux compactifications. in particular, we determine vacua in any asymptotic regime of the complex-structure moduli space by exploiting powerful tools of asymptotic hodge theory. in a leading approximation the moduli dependence of the vacuum conditions are shown to be polynomial with a dependence given by sl(2)-weights of the fluxes. this simple algebraic dependence can be extracted in any asymptotic regime, even though in nearly all asymptotic regimes essential exponential corrections have to be present for consistency. we give a pedagogical introduction to the sl(2)-approximation as well as a detailed step-by-step procedure for constructing the corresponding hodge star operator. to exemplify the construction, we present a detailed analysis of several calabi-yau three- and fourfold examples. for these examples we illustrate that the vacua in the sl(2)-approximation match the vacua obtained with all polynomial and essential exponential corrections rather well, and we determine the behaviour of the tadpole contribution of the fluxes. finally, we discuss the structure of vacuum loci and their relations to several swampland conjectures. in particular, we comment on the realization of the so-called linear scenario in view of the tadpole conjecture. | moduli stabilization in asymptotic flux compactifications |
the near-infrared imager and slitless spectrograph (niriss) is the science module of the canadian-built fine guidance sensor onboard the james webb space telescope (jwst). niriss has four observing modes: (1) broadband imaging featuring seven of the eight nircam broadband filters, (2) wide-field slitless spectroscopy at a resolving power of ~150 between 0.8 and 2.2 μm, (3) single-object cross-dispersed slitless spectroscopy (soss) enabling simultaneous wavelength coverage between 0.6 and 2.8 μm at r ~ 700, a mode optimized for exoplanet spectroscopy of relatively bright (j < 6.3) stars and (4) aperture masking interferometry (ami) between 2.8 and 4.8 μm enabling high-contrast (~10-3 - 10-4) imaging at angular separations between 70 and 400 mas for relatively bright (m < 8) sources. this paper presents an overview of the niriss instrument, its design, its scientific capabilities, and a summary of in-flight performance. niriss shows significantly better response shortward of ~2.5 μm resulting in 10%-40% sensitivity improvement for broadband and low-resolution spectroscopy compared to pre-flight predictions. two time-series observations performed during instrument commissioning in the soss mode yield very stable spectro-photometry performance within ~10% of the expected noise. the first space-based companion detection of the tight binary star ab dor ac through ami was demonstrated. | the near infrared imager and slitless spectrograph for the james webb space telescope. i. instrument overview and in-flight performance |
we investigate the bright co fundamental emission in the central regions of five class 0 protostars using the jwst's near-infrared spectrograph (nirspec) and provide clues to what processes excite the gas. co line emission images are extracted for a forest of $\sim$150 ro-vibrational transitions from two vibrational bands, $v=1-0$ and $v=2-1$. however, ${}^{13}$co is not detected, and thus we can only statistically constrain the ${}^{12}$co optical depth. using noise measurements to determine upper limits to the ${}^{13}$co emission, the flux ratio of ${}^{12}$co/${}^{13}$co indicates that the ${}^{12}$co emission itself is not optically thick for ro-vibrational transitions with upper state rotational quantum number $j_u \geq 15$. we construct population diagrams to estimate the rotational temperature and number of molecules from extinction-corrected co line fluxes assuming co emission is optically thin. two different temperature components are required for $v=1$ ($\sim600-1000$ k and $\sim1500-3500$ k), while one hotter component is required for $v=2$ ($\sim2000-6000$ k). the vibrational temperature is $\sim 900$ k among our sources and shows no trend with luminosity. using vibrational temperatures and the inferred total amount of co molecules for our sources, the total warm gas mass correlates strongly with luminosity ranging from $\sim$0.1 $\rm m_{earth}$ for the low-mass protostars to $\sim$1 m$_{\rm sun}$ for the high-mass protostars. interpreting the distribution of gas column densities and temperatures depends on radiative and chemical processes affecting co. the presence of a $v=2$ population may indicate co gas radiatively excited. selective uv photodissociation of co isotopologues around our high-mass sources may explain their depletion of ${}^{13}$co. | ipa. class 0 protostars viewed in co emission using jwst/nirspec |
it has recently become possible to zoom-in from cosmological to sub-pc scales in galaxy simulations to follow accretion onto supermassive black holes (smbhs). however, at some point the approximations used on ism scales (e.g. optically-thin cooling and stellar-population-integrated star formation [sf] and feedback [fb]) break down. we therefore present the first cosmological radiation-magnetohydrodynamic (rmhd) simulation which self-consistently combines the fire physics (relevant on galactic/ism scales where sf/fb are ensemble-averaged) and starforge physics (relevant on small scales where we track individual (proto)stellar formation and evolution), together with explicit rmhd (including non-ideal mhd and multi-band m1-rhd) which self-consistently treats both optically-thick and thin regimes. this allows us to span scales from ~100 mpc down to <100 au (~300 schwarzschild radii) around a smbh at a time where it accretes as a bright quasar, in a single simulation. we show that accretion rates up to $\sim 10-100\,{\rm m_{\odot}\,yr^{-1}}$ can be sustained into the accretion disk at $\ll 10^{3}\,r_{\rm schw}$, with gravitational torques between stars and gas dominating on sub-kpc scales until star formation is shut down on sub-pc scales by a combination of optical depth to cooling and strong magnetic fields. there is an intermediate-scale, flux-frozen disk which is gravitoturbulent and stabilized by magnetic pressure sustaining strong turbulence and inflow with persistent spiral modes. in this paper we focus on how gas gets into the small-scale disk, and how star formation is efficiently suppressed. | forge'd in fire: resolving the end of star formation and structure of agn accretion disks from cosmological initial conditions |
we present early-stage analyses of low-resolution (r = 1000) optical spectra and near-infrared light curves of the bright type ii supernova (sn ii) 2023ixf in the notable nearby face-on spiral galaxy m 101, which were obtained from t = 1.7 to 8.0 d. our first spectrum showed remarkable emission features of the balmer series, he ii, n iii, c iv, and n iv with a strong blue continuum. compared with the sne ii which show flash-ionized features, we suggest that this sn could be categorized as a high-luminosity sn ii with a nitrogen/helium-rich circumstellar material (csm), e.g., sne 2014g, 2017ahn, and 2020pni. the hα emission line can be tentatively explained by a narrower component with a velocity of <300 km s-1 and a broader one with ~2200 km s-1. the near-infrared light curves were well consistent with those of the another luminous sn 2017ahn, and its absolute magnitudes are located at the bright end of the luminosity distribution of sne ii. these observational facts support that sn 2023ixf is well consistent with high-luminosity sne ii showing evidence of a dense nitrogen/helium-rich csm. | bright type ii supernova 2023ixf in m 101: a quick analysis of the early-stage spectra and near-infrared light curves |
planet-forming disc evolution is not independent of the star formation and feedback process in giant molecular clouds. in particular, ob stars emit uv radiation that heats and disperses discs in a process called `external photoevaporation'. this process is understood to be the dominant environmental influence acting on planet-forming discs in typical star-forming regions. our best studied discs are nearby, in sparse stellar groups where external photoevaporation is less effective. however, the majority of discs are expected to reside in much stronger uv environments. understanding external photoevaporation is therefore key to understanding how most discs evolve, and hence, how most planets form. here, we review our theoretical and observational understanding of external photoevaporation. we also lay out key developments for the future to address existing unknowns and establish the full role of external photoevaporation in the disc evolution and planet formation process. | the external photoevaporation of planet-forming discs |
when the primary star in a close binary system evolves into a giant and engulfs its companion, its core and the companion temporarily orbit each other inside a common envelope. drag forces transfer orbital energy and angular momentum to the envelope material. depending on the efficiency of this process, the envelope may be ejected leaving behind a tight remnant binary system of two stellar cores, or the cores merge retaining part of the envelope material. the exact outcome of common-envelope evolution is critical for in the formation of x-ray binaries, supernova progenitors, the progenitors of compact-object mergers that emit detectable gravitational waves, and many other objects of fundamental astrophysical relevance. the wide ranges of spatial and temporal timescales that characterize common-envelope interactions and the lack of spatial symmetries present a substantial challenge to generating consistent models. therefore, these critical phases are one of the largest sources for uncertainty in classical treatments of binary stellar evolution. three-dimensional hydrodynamic simulations of at least part of the common-envelope interaction are the key to gain predictive power in modeling common-envelope evolution. we review the development of theoretical concepts and numerical approaches for such three-dimensional hydrodynamic simulations. the inherent multi-physics, multi-scale challenges have resulted in a wide variety of approximations and numerical techniques to be exercised on the problem. we summarize the simulations published to date and their main results. given the recent rapid progress, a sound understanding of the physics of common-envelope interactions is within reach and thus there is hope that one of the remaining fundamental problems of stellar astrophysics may be solved before long. | simulations of common-envelope evolution in binary stellar systems: physical models and numerical techniques |
the tidal love numbers (tlns) encode the deformability of a self-gravitating object immersed in a tidal environment and depend significantly both on the object's internal structure and on the dynamics of the gravitational field. an intriguing result in classical general relativity is the vanishing of the tlns of black holes. we extend this result in three ways, aiming at testing the nature of compact objects: (i) we compute the tlns of exotic compact objects, including different families of boson stars, gravastars, wormholes, and other toy models for quantum corrections at the horizon scale. in the black-hole limit, we find a universal logarithmic dependence of the tlns on the location of the surface. (ii) we compute the tlns of black holes beyond vacuum general relativity, including einstein-maxwell, brans-dicke, and chern-simons gravity. (iii) we assess the ability of present and future gravitational-wave detectors to measure the tlns of these objects, including the first analysis of tlns with lisa. both ligo, et, and lisa can impose interesting constraints on boson stars, while lisa is able to probe even extremely compact objects. we argue that the tlns provide a smoking gun of new physics at the horizon scale and that future gravitational-wave measurements of the tlns in a binary inspiral provide a novel way to test black holes and general relativity in the strong-field regime. | testing strong-field gravity with tidal love numbers |
we use observations of ultra-faint dwarf (ufd) galaxies to constrain the particle mass of ultra-light dark matter. potential fluctuations created by wave interference in virialized "fuzzy" dark matter (fdm) halos dynamically heat stellar orbits in ufds, some of which exhibit velocity dispersions of $\lesssim$ 3 km/s and sizes $\lesssim$ 40 pc. using simulations of fdm halos, and existing measurements of sizes and stellar radial velocities in segue 1 and segue 2 ufds, we derive a lower limit on the dark matter particle mass of $m_{fdm} > 3\times 10^{-19}$ ev at 99% confidence, marginalized over host halo circular velocity. this constraint is conservative as it is derived under the assumption that soliton heating is negligible, and that no other sources of non-fdm dynamical heating of stars operate to increase velocity dispersion. it can potentially be strengthened by future spectroscopic observations of additional stars in ultra-faint galaxies and by tightening theoretical constraints on the soliton size-halo mass relation. however, even the current conservative lower limit on the fdm mass makes this model indistinguishable from cold dark matter at the scales probed by existing astronomical observations. | not so fuzzy: excluding fdm with sizes and stellar kinematics of ultra-faint dwarf galaxies |
seven rocky planets orbit the nearby dwarf star trappist-1, providing a unique opportunity to search for atmospheres on small planets outside the solar system1. thanks to the recent launch of the james webb space telescope (jwst), possible atmospheric constituents such as carbon dioxide (co2) are now detectable2,3. recent jwst observations of the innermost planet trappist-1 b showed that it is most probably a bare rock without any co2 in its atmosphere4. here we report the detection of thermal emission from the dayside of trappist-1 c with the mid-infrared instrument (miri) on jwst at 15 µm. we measure a planet-to-star flux ratio of fp/f⁎ = 421 ± 94 parts per million (ppm), which corresponds to an inferred dayside brightness temperature of 380 ± 31 k. this high dayside temperature disfavours a thick, co2-rich atmosphere on the planet. the data rule out cloud-free o2/co2 mixtures with surface pressures ranging from 10 bar (with 10 ppm co2) to 0.1 bar (pure co2). a venus-analogue atmosphere with sulfuric acid clouds is also disfavoured at 2.6σ confidence. thinner atmospheres or bare-rock surfaces are consistent with our measured planet-to-star flux ratio. the absence of a thick, co2-rich atmosphere on trappist-1 c suggests a relatively volatile-poor formation history, with less than 9.5−2.3+7.5 earth oceans of water. if all planets in the system formed in the same way, this would indicate a limited reservoir of volatiles for the potentially habitable planets in the system. | no thick carbon dioxide atmosphere on the rocky exoplanet trappist-1 c |
we present alma deep spectroscopy for a lensed galaxy at $z_{\rm spec}=8.496$ with $\log(m_{\rm star}/m_{\odot})\sim7.8$ whose optical nebular lines and stellar continuum are detected by jwst/nirspec and nircam early release observations in smacs0723. our alma spectrum shows [oiii]88$\mu$m and [cii]158$\mu$m line detections at $4.0\sigma$ and $4.5\sigma$, respectively. the redshift and position of the [oiii] line coincide with those of the jwst source, while the [cii] line is blue-shifted by 90 km s$^{-1}$ with a spatial offset of $0.''5$ ($\approx0.5$ kpc in source plane) from the jwst source. the nircam f444w image, including [oiii]$\lambda$5007 and h$\beta$ line emission, spatially extends beyond the stellar components by a factor of $>8$. this indicates that the $z=8.5$ galaxy has already experienced strong outflows whose oxygen and carbon produce the extended [oiii]$\lambda$5007 and the offset [cii] emission, which would promote ionizing photon escape and facilitate reionization. with careful slit-loss corrections and removals of emission spatially outside the galaxy, we evaluate the [oiii]88$\mu$m/$\lambda$5007 line ratio, and derive the electron density $n_{\rm e}$ by photoionization modeling to be $220^{+170}_{-100}$ cm$^{-3}$, which is comparable with those of $z\sim2-3$ galaxies. we estimate an [oiii]88$\mu$m/[cii]158$\mu$m line ratio in the galaxy of $>4$, as high as those of known $z\sim6-9$ galaxies. this high [oiii]88$\mu$m/[cii]158$\mu$m line ratio is generally explained by the high $n_{\rm e}$ as well as the low metallicity ($z_{\rm gas}/z_{\odot}=0.04^{+0.02}_{-0.02}$), high ionization parameter ($\log u > -2.27$), and low carbon-to-oxygen abundance ratio ($\log$(c/o) $=[-0.52:-0.24]$) obtained from the jwst/nirspec data; further [cii] follow-up observations will constrain the covering fraction of photodissociation regions. | jwst and alma multiple-line study in and around a galaxy at $z=8.496$: optical to fir line ratios and the onset of an outflow promoting ionizing photon escape |
the early universe, spanning 400,000 to 400 million years after the big bang ($z\approx1100-11$), has been left largely unexplored as the light from luminous objects is too faint to be observed directly. while new experiments are pushing the redshift limit of direct observations, measurements in the low-frequency radio band promise to probe early star and black hole formation via observations of the hydrogen 21-cm line. in this work we explore synergies between 21-cm data from the hera and saras 3 experiments and observations of the unresolved radio and x-ray backgrounds using multi-wavelength bayesian analysis. we use the combined data set to constrain properties of population ii and population iii stars as well as early x-ray and radio sources. the joint fit reveals a 68 percentile disfavouring of population iii star formation efficiencies $\gtrsim5.5\%$. we also show how the 21-cm and the x-ray background data synergistically constrain opposite ends of the x-ray efficiency prior distribution to produce a peak in the 1d posterior of the x-ray luminosity per star formation rate. we find (at 68\% confidence) that early galaxies were likely 0.33 to 311 times as x-ray efficient as present-day starburst galaxies. we also show that the functional posteriors from our joint fit rule out global 21-cm signals deeper than $\lesssim-225\ \mathrm{mk}$ and power spectrum amplitudes at $k=0.34\ h\mathrm{mpc^{-1}}$ greater than $\delta_{21}^2 \gtrsim 4814\ \mathrm{mk}^2$ with $3\sigma$ confidence. | constraining the properties of population iii galaxies with multi-wavelength observations |
we make use of sensitive (9.3 μjy beam-1 rms) 1.2 mm continuum observations from the atacama large millimeter/submillimeter array (alma) spectroscopic survey in the hubble ultra-deep field (aspecs) large program to probe dust-enshrouded star formation from 1362 lyman-break galaxies spanning the redshift range z = 1.5-10 (to ∼7-28 m⊙ yr-1 at 4σ over the entire range). we find that the fraction of alma-detected galaxies in our z = 1.5-10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 109.0 m⊙ to ${85}_{-18}^{+9}$ % at >1010 m⊙. moreover, on stacking all 1253 low-mass (<109.25 m⊙) galaxies over the aspecs footprint, we find a mean continuum flux of -0.1 ± 0.4 μjy beam-1, implying a hard upper limit on the obscured star formation rate of <0.6 m⊙ yr-1 (4σ) in a typical low-mass galaxy. the correlation between the infrared excess (irx) of uv-selected galaxies (lir/luv) and the uv-continuum slope is also seen in our aspecs data and shows consistency with a calzetti-like relation at > ${10}^{9.5}\,{m}_{\odot }$ and an smc-like relation at lower masses. using stellar mass and β measurements for z ∼ 2 galaxies over the cosmic assembly near-infrared deep extragalactic legacy survey, we derive a new empirical relation between β and stellar mass and then use this correlation to show that our irx-β and irx-stellar mass relations are consistent with each other. we then use these constraints to express the irx as a bivariate function of β and stellar mass. finally, we present updated estimates of star formation rate density determinations at z > 3, leveraging present improvements in the measured irx and recent probes of ultraluminous far-ir galaxies at z > 2. | the alma spectroscopic survey large program: the infrared excess of z = 1.5-10 uv-selected galaxies and the implied high-redshift star formation history |
the discovery and characterization of exoplanets around nearby stars is driven by profound scientific questions about the uniqueness of earth and our solar system, and the conditions under which life could exist elsewhere in our galaxy. doppler spectroscopy, or the radial velocity (rv) technique, has been used extensively to identify hundreds of exoplanets, but with notable challenges in detecting terrestrial mass planets orbiting within habitable zones. we describe infrared rv spectroscopy at the 10 m hobby-eberly telescope that leverages a 30 ghz electro-optic laser frequency comb with nanophotonic supercontinuum to calibrate the habitable zone planet finder spectrograph. demonstrated instrument precision <10 cm/s and stellar rvs approaching 1 m/s open the path to discovery and confirmation of habitable zone planets around m-dwarfs, the most ubiquitous type of stars in our galaxy. | stellar spectroscopy in the near-infrared with a laser frequency comb |
pair-instability (pi) is expected to open a gap in the mass spectrum of black holes (bhs) between ≈40-65 and ≈120 m⊙. the existence of the mass gap is currently being challenged by the detection of gw190521, with a primary component mass of $85^{+21}_{-14}$ m⊙. here, we investigate the main uncertainties on the pi mass gap: the 12c(α, γ)16o reaction rate and the h-rich envelope collapse. with the standard 12c(α, γ)16o rate, the lower edge of the mass gap can be 70 m⊙ if we allow for the collapse of the residual h-rich envelope at metallicity z ≤ 0.0003. adopting the uncertainties given by the starlib database, for models computed with the 12c(α, γ)16o rate $-1\, \sigma$ , we find that the pi mass gap ranges between ≈80 and ≈150 m⊙. stars with mzams > 110 m⊙ may experience a deep dredge-up episode during the core helium-burning phase, that extracts matter from the core enriching the envelope. as a consequence of the he-core mass reduction, a star with mzams = 160 m⊙ may avoid the pi and produce a bh of 150 m⊙. in the $-2\, {}\sigma {}$ case, the pi mass gap ranges from 92 to 110 m⊙. finally, in models computed with 12c(α, γ)16o $-3\, {}\sigma {}$ , the mass gap is completely removed by the dredge-up effect. the onset of this dredge-up is particularly sensitive to the assumed model for convection and mixing. the combined effect of h-rich envelope collapse and low 12c(α, γ)16o rate can lead to the formation of bhs with masses consistent with the primary component of gw190521. | formation of gw190521 from stellar evolution: the impact of the hydrogen-rich envelope, dredge-up, and 12c(α, γ)16o rate on the pair-instability black hole mass gap |
we perform an extensive numerical study of the evolution of massive binary systems to predict the peculiar velocities that stars obtain when their companion collapses and disrupts the system. our aim is to (i) identify which predictions are robust against model uncertainties and assess their implications, (ii) investigate which physical processes leave a clear imprint and may therefore be constrained observationally, and (iii) provide a suite of publicly available model predictions to allow for the use of kinematic constraints from the gaia mission. we find that 22+26-8% of all massive binary systems merge prior to the first core-collapse in the system. of the remainder, 86+11-9% become unbound because of the core-collapse. remarkably, this rarely produces runaway stars (observationally defined as stars with velocities above 30 km s-1). these are outnumbered by more than an order of magnitude by slower unbound companions, or "walkaway stars". this is a robust outcome of our simulations and is due to the reversal of the mass ratio prior to the explosion and widening of the orbit, as we show analytically and numerically. for stars more massive than 15 m⊙, we estimate that 10+5-8% are walkaways and only 0.5+1.0-0.4% are runaways, nearly all of which have accreted mass from their companion. our findings are consistent with earlier studies; however, the low runaway fraction we find is in tension with observed fractions of about 10%. thus, astrometric data on presently single massive stars can potentially constrain the physics of massive binary evolution. finally, we show that the high end of the mass distributions of runaway stars is very sensitive to the assumed black hole natal kicks, and we propose this as a potentially stringent test for the explosion mechanism. we also discuss companions remaining bound that can evolve into x-ray and gravitational wave sources. outcome of the numerical simulations 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/a66 and at https://sandbox.zenodo.org/record/262858#.xjomiemo9hh | massive runaway and walkaway stars. a study of the kinematical imprints of the physical processes governing the evolution and explosion of their binary progenitors |
we perform a statistical standard siren analysis of gw170817. our analysis does not utilize knowledge of ngc 4993 as the unique host galaxy of the optical counterpart to gw170817. instead, we consider each galaxy within the gw170817 localization region as a potential host; combining the redshifts from all of the galaxies with the distance estimate from gw170817 provides an estimate of the hubble constant, h 0. considering all galaxies brighter than 0.626{l}b\staras equally likely to host a binary neutron star merger, we find {h}0={77}-18+37 km s-1 mpc-1 (maximum a posteriori and 68.3% highest density posterior interval; assuming a flat h 0 prior in the range ≤ft[10,220\right] km s-1 mpc-1). we explore the dependence of our results on the thresholds by which galaxies are included in our sample, and we show that weighting the host galaxies by stellar mass or star formation rate provides entirely consistent results with potentially tighter constraints. by applying the method to simulated gravitational-wave events and a realistic galaxy catalog we show that, because of the small localization volume, this statistical standard siren analysis of gw170817 provides an unusually informative (top 10%) constraint. under optimistic assumptions for galaxy completeness and redshift uncertainty, we find that dark binary neutron star measurements of h 0 will converge as 40 % /\sqrt{(n)}, where n is the number of sources. while these statistical estimates are inferior to the value from the counterpart standard siren measurement utilizing ngc 4993 as the unique host, {h}0={76}-13+19 km s-1 mpc-1 (determined from the same publicly available data), our analysis is a proof-of-principle demonstration of the statistical approach first proposed by bernard schutz over 30 yr ago. | a standard siren measurement of the hubble constant from gw170817 without the electromagnetic counterpart |
we present the first sample of tidal disruption events (tdes) discovered during the srg all-sky survey. these 13 events were selected among x-ray transients detected in the 0° < l < 180° hemisphere by erosita during its second sky survey (2020 june 10 to december 14) and confirmed by optical follow-up observations. the most distant event occurred at z = 0.581. one tde continued to brighten at least 6 months. the x-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to $10^8\, \mathrm{ m}_\odot$, although supercritical accretion is possibly taking place. in two tdes, a spectral hardening is observed 6 months after the discovery. four tdes showed an optical brightening apart from the x-ray outburst. the other nine tdes demonstrate no optical activity. all 13 tdes are optically faint, with lg/lx < 0.3 (lg and lx being the g band and 0.2-6 kev luminosity, respectively). we have constructed a tde x-ray luminosity function, which can be fit by a power law with a slope of -0.6 ± 0.2, similar to the trend observed for optically selected tdes. the total rate is estimated at (1.1 ± 0.5) × 10-5 tdes per galaxy per year, an order of magnitude lower than inferred from optical studies. this suggests that x-ray bright events constitute a minority of tdes, consistent with models predicting that x-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. our tde detection threshold can be lowered by a factor of ~2, which should allow a detection of ~700 tdes by the end of the srg survey. | first tidal disruption events discovered by srg/erosita: x-ray/optical properties and x-ray luminosity function at z < 0.6 |
we carry out 2d viscous hydrodynamical simulations of circumbinary accretion using the moving-mesh code arepo. we self-consistently compute the accretion flow over a wide range of spatial scales, from the circumbinary disk (cbd) far from the central binary, through accretion streamers, to the disks around individual binary components, resolving the flow down to 2% of the binary separation. we focus on equal-mass binaries with arbitrary eccentricities. we evolve the flow over long (viscous) timescales until a quasi-steady state is reached, in which the mass supply rate at large distances {\dot{m}}0 (assumed constant) equals the time-averaged mass transfer rate across the disk and the total mass accretion rate onto the binary components. this quasi-steady state allows us to compute the secular angular momentum transfer rate onto the binary, < {\dot{j}}{{b}}> , and the resulting orbital evolution. through direct computation of the gravitational and accretional torques on the binary, we find that < {\dot{j}}{{b}}> is consistently positive (i.e., the binary gains angular momentum), with {l}0\equiv < {\dot{j}}{{b}}> /{\dot{m}}0 in the range of (0.4-0.8){a}{{b}}2{{{ω }}}{{b}}, depending on the binary eccentricity (where {a}{{b}}, {{{ω }}}{{b}} are the binary semimajor axis and angular frequency); we also find that this < {\dot{j}}{{b}}> is equal to the net angular momentum current across the cbd, indicating that global angular momentum balance is achieved in our simulations. in addition, we compute the time-averaged rate of change of the binary orbital energy for eccentric binaries and thus obtain the secular rates < {\dot{a}}{{b}}> and < {\dot{e}}{{b}}> . in all cases, < {\dot{a}}{{b}}> is positive; that is, the binary expands while accreting. we discuss the implications of our results for the merger of supermassive binary black holes and for the formation of close stellar binaries. | hydrodynamics of circumbinary accretion: angular momentum transfer and binary orbital evolution |
magnetic reconnection, topological changes in magnetic fields, is a fundamental process in magnetized plasmas. it is associated with energy release in regions of magnetic field annihilation, but this is only one facet of this process. astrophysical fluid flows normally have very large reynolds numbers and are expected to be turbulent, in agreement with observations. in strong turbulence, magnetic field lines constantly reconnect everywhere and on all scales, thus making magnetic reconnection an intrinsic part of the turbulent cascade. we note in particular that this is inconsistent with the usual practice of magnetic field lines as persistent dynamical elements. a number of theoretical, numerical, and observational studies starting with the paper done by lazarian and vishniac [astrophys. j. 517, 700-718 (1999)] proposed that 3d turbulence makes magnetic reconnection fast and that magnetic reconnection and turbulence are intrinsically connected. in particular, we discuss the dramatic violation of the textbook concept of magnetic flux-freezing in the presence of turbulence. we demonstrate that in the presence of turbulence, the plasma effects are subdominant to turbulence as far as the magnetic reconnection is concerned. the latter fact justifies a magnetohydrodynamiclike treatment of magnetic reconnection on all scales much larger than the relevant plasma scales. we discuss the numerical and observational evidence supporting the turbulent reconnection model. in particular, we demonstrate that the tearing reconnection is suppressed in 3d, and unlike the 2d settings, 3d reconnection induces turbulence that makes magnetic reconnection independent of resistivity. we show that turbulent reconnection dramatically affects key astrophysical processes, e.g., star formation, turbulent dynamo, and acceleration of cosmic rays. we provide criticism of the concept of "reconnection-mediated turbulence" and explain why turbulent reconnection is very different from enhanced turbulent resistivity and hyper-resistivity and why the latter have fatal conceptual flaws. | 3d turbulent reconnection: theory, tests, and astrophysical implications |
we present a new, open source, free, semi-analytic model (sam) of galaxy formation, shark, designed to be highly flexible and modular, allowing easy exploration of different physical processes and ways of modelling them. we introduce the philosophy behind shark and provide an overview of the physical processes included in the model. shark is written in c++11 and has been parallelized with openmp. in the released version (v1.1), we implement several different models for gas cooling, active galactic nuclei, stellar and photo-ionization feedback, and star formation (sf). we demonstrate the basic performance of shark using the planck collaboration et al. (2016) cosmology surfs simulations, by comparing against a large set of observations, including: the stellar mass function (smf) and stellar-halo mass relation at z = 0-4; the cosmic evolution of the star formation rate density (sfrd), stellar mass, atomic and molecular hydrogen; local gas scaling relations; and structural galaxy properties, finding excellent agreement. significant improvements over previous sams are seen in the mass-size relation for discs/bulges, the gas-stellar mass and stellar mass-metallicity relations. to illustrate the power of shark in exploring the systematic effects of the galaxy formation modelling, we quantify how the scatter of the sf main sequence and the gas scaling relations changes with the adopted sf law, and the effect of the starbursts h2 depletion time-scale on the sfrd and ω _h_2. we compare shark with other sams and the hydrodynamical simulation eagle, and find that sams have a much higher halo baryon fractions due to large amounts of intra-halo gas, which in the case of eagle is in the intergalactic medium. | shark: introducing an open source, free, and flexible semi-analytic model of galaxy formation |
we show that the electron recoil excess around 2 kev claimed by the xenon collaboration can be fitted by dark matter (dm) or dm-like particles having a fast component with velocity of order ∼0.1 . those particles cannot be part of the cold dm halo of our galaxy, so we speculate about their possible nature and origin, such as fast-moving dm subhalos, semiannihilations of dm and relativistic axions produced by a nearby axion star. feasible new physics scenarios must accommodate exotic dm dynamics and unusual dm properties. | dark matter and the xenon1t electron recoil excess |
context. establishing the number of faint active galactic nuclei (agns) at z = 4-6 is crucial to understanding their cosmological importance as main contributors to the reionization of the universe.aims: in order to derive the agn contribution to the cosmological ionizing emissivity we have selected faint agn candidates at z> 4 in the candels goods-south field, which is one of the deepest fields with extensive multiwavelength coverage from chandra, hst, spitzer, and various ground-based telescopes.methods: we have adopted a relatively novel criterion. as a first step, high redshift galaxies are selected in the nir h band down to very faint levels (h ≤ 27) using reliable photometric redshifts. at z> 4 this corresponds to a selection criterion based on the galaxy rest-frame uv flux. agn candidates are then picked up from this parent sample if they show x-ray fluxes above a threshold of fx ∼ 1.5 × 10-17 erg cm-2 s-1 (0.5-2 kev), corresponding to a probability of spurious detections of 2 × 10-4 in the deep x-ray 4 ms chandra image.results: we have found 22 agn candidates at z> 4 and we have derived the first estimate of the uv luminosity function in the redshift interval 4 <z< 6.5 and absolute magnitude interval - 22.5 ≲ m1450 ≲ -18.5 typical of local seyfert galaxies. the faint end of the derived luminosity function is about two to four magnitudes fainter at z ∼ 4-6 than that derived from previous uv surveys. we estimated ionizing emissivities and hydrogen photoionization rates in the same redshift interval under reasonable assumptions and after discussion of possible caveats, the most important being the large uncertainties involved in the estimate of photometric redshift for sources with featureless, almost power-law seds and/or low average escape fraction of ionizing photons from the agn host galaxies. both effects could, in principle, significantly reduce the estimated average volume densities and/or ionizing emissivities, especially at the highest redshifts.conclusions: at z = 4-6.5 we argue that, under reasonable evaluations of possible biases, the probed agn population can produce photoionization rates consistent with that required to keep the intergalactic medium observed in the lyman-α forest of high redshift qso spectra highly ionized, providing an important contribution to the cosmic reionization. appendices are available in electronic form at http://www.aanda.org | faint agns at z > 4 in the candels goods-s field: looking for contributors to the reionization of the universe |
we exploit james webb space telescope (jwst) nircam observations from the glass-jwst-early release science program to investigate galaxy stellar masses at z > 7. we first show that jwst observations reduce the uncertainties on the stellar mass by a factor of at least 5-10, when compared with the highest-quality data sets available to date. we then study the uv mass-to-light ratio, finding that galaxies exhibit a a two orders of magnitude range of m/l uv values for a given luminosity, indicative of a broad variety of physical conditions and star formation histories. as a consequence, previous estimates of the cosmic stellar-mass density-based on an average correlation between uv luminosity and stellar mass-can be biased by as much as a factor of ~6. our first exploration demonstrates that jwst represents a new era in our understanding of stellar masses at z > 7 and, therefore, of the growth of galaxies prior to cosmic reionization. | early results from glass-jwst. xi. stellar masses and mass-to-light ratio of z > 7 galaxies |
we propose a set of standard assumptions for the modelling of class ii and iii protoplanetary disks, which includes detailed continuum radiative transfer, thermo-chemical modelling of gas and ice, and line radiative transfer from optical to cm wavelengths. the first paper of this series focuses on the assumptions about the shape of the disk, the dust opacities, dust settling, and polycyclic aromatic hydrocarbons (pahs). in particular, we propose new standard dust opacities for disk models, we present a simplified treatment of pahs in radiative equilibrium which is sufficient to reproduce the pah emission features, and we suggest using a simple yet physically justified treatment of dust settling. we roughly adjust parameters to obtain a model that predicts continuum and line observations that resemble typical multi-wavelength continuum and line observations of class ii t tauri stars. we systematically study the impact of each model parameter (disk mass, disk extension and shape, dust settling, dust size and opacity, gas/dust ratio, etc.) on all mainstream continuum and line observables, in particular on the sed, mm-slope, continuum visibilities, and emission lines including [oi] 63 μm, high-j co lines, (sub-)mm co isotopologue lines, and co fundamental ro-vibrational lines. we find that evolved dust properties, i.e. large grains, often needed to fit the sed, have important consequences for disk chemistry and heating/cooling balance, leading to stronger near- to far-ir emission lines in general. strong dust settling and missing disk flaring have similar effects on continuum observations, but opposite effects on far-ir gas emission lines. pah molecules can efficiently shield the gas from stellar uv radiation because of their strong absorption and negligible scattering opacities in comparison to evolved dust. the observable millimetre-slope of the sed can become significantly more gentle in the case of cold disk midplanes, which we find regularly in our t tauri models. we propose to use line observations of robust chemical tracers of the gas, such as o, co, and h2, as additional constraints to determine a number of key properties of the disks, such as disk shape and mass, opacities, and the dust/gas ratio, by simultaneously fitting continuum and line observations. | consistent dust and gas models for protoplanetary disks. i. disk shape, dust settling, opacities, and pahs |
recent studies have shown that atmospheric mass-loss powered by the cooling luminosity of a planet's core can explain the observed radius valley separating super-earths and sub-neptunes, even without photoevaporation. in this work, we investigate the dependence of this core-powered mass-loss mechanism on stellar mass (m*), metallicity (z*), and age (τ*). without making any changes to the underlying planet population, we find that the core-powered mass-loss model yields a shift in the radius valley to larger planet sizes around more massive stars with a slope given by dlog rp/dlog m* ≃ 0.35, in agreement with observations. to first order, this slope is driven by the dependence of core-powered mass-loss on the bolometric luminosity of the host star and is given by dlog rp/dlog m* ≃ (3α - 2)/36 ≃ 0.33, where (l*/l⊙) = (m*/m⊙)α is the stellar mass-luminosity relation and α ≃ 4.6 for the cks data set. we therefore find, in contrast to photoevaporation models, no evidence for a linear correlation between planet and stellar mass, but cannot rule it out either. in addition, we show that the location of the radius valley is, to first order, independent of stellar age and metallicity. since core-powered mass-loss proceeds over gyr time-scales, the abundance of super-earths relative to sub-neptunes increases with age but decreases with stellar metallicity. finally, due to the dependence of the envelope's cooling time-scale on metallicity, we find that the radii of sub-neptunes increase with metallicity and decrease with age with slopes given by dlog rp/dlog z* ≃ 0.1 and dlog rp/dlog τ* ≃ -0.1, respectively. we conclude with a series of observational tests that can differentiate between core-powered mass-loss and photoevaporation models. | signatures of the core-powered mass-loss mechanism in the exoplanet population: dependence on stellar properties and observational predictions |
galactic haloes in a λ-cdm universe are predicted to host today a swarm of debris resulting from cannibalized dwarf galaxies. the chemodynamical information recorded in their stellar populations helps elucidate their nature, constraining the assembly history of the galaxy. using data from apogee and gaia, we examine the chemical properties of various halo substructures, considering elements that sample various nucleosynthetic pathways. the systems studied are heracles, gaia-enceladus/sausage (ges), the helmi stream, sequoia, thamnos, aleph, lms-1, arjuna, i'itoi, nyx, icarus, and pontus. abundance patterns of all substructures are cross-compared in a statistically robust fashion. our main findings include: (i) the chemical properties of most substructures studied match qualitatively those of dwarf milky way satellites, such as the sagittarius dsph. exceptions are nyx and aleph, which are chemically similar to disc stars, implying that these substructures were likely formed in situ; (ii) heracles differs chemically from in situ populations such as aurora and its inner halo counterparts in a statistically significant way. the differences suggest that the star formation rate was lower in heracles than in the early milky way; (iii) the chemistry of arjuna, lms-1, and i'itoi is indistinguishable from that of ges, suggesting a possible common origin; (iv) all three sequoia samples studied are qualitatively similar. however, only two of those samples present chemistry that is consistent with ges in a statistically significant fashion; (v) the abundance patterns of the helmi stream and thamnos are different from all other halo substructures. | the chemical characterization of halo substructure in the milky way based on apogee |
the 2017 detection of the inspiral and merger of two neutron stars in gravitational waves and gamma rays was accompanied by a quickly reddening transient. such a transient was predicted to occur following a rapid neutron capture (r-process) nucleosynthesis event, which synthesizes neutron-rich, radioactive nuclei and can take place in both dynamical ejecta and in the wind driven off the accretion torus formed after a neutron star merger. we present the first three-dimensional general relativistic, full transport neutrino radiation magnetohydrodynamics simulations of the black hole-accretion disk-wind system produced by the gw170817 merger. we show that the small but non-negligible optical depths lead to neutrino transport globally coupling the disk electron fraction, which we capture by solving the transport equation with a monte carlo method. the resulting absorption drives up the electron fraction in a structured, continuous outflow, with electron fraction as high as ye∼ 0.4 in the extreme polar region. we show via nuclear reaction network and radiative transfer calculations that nucleosynthesis in the disk wind will produce a blue kilonova. | full transport model of gw170817-like disk produces a blue kilonova |
the electromagnetic transients accompanying compact binary mergers (γ-ray bursts, afterglows and `macronovae') are crucial to pinpoint the sky location of gravitational wave sources. macronovae are caused by the radioactivity from freshly synthesized heavy elements, e.g. from dynamic ejecta and various types of winds. we study macronova signatures by using multidimensional radiative transfer calculations. we employ the radiative transfer code supernu and state-of-the-art lte opacities for a few representative elements from the wind and dynamical ejecta (cr, pd, se, te, br, zr, sm, ce, nd, u) to calculate synthetic light curves and spectra for a range of ejecta morphologies. the radioactive power of the resulting macronova is calculated with the detailed input of decay products. we assess the detection prospects for our most complex models, based on the portion of viewing angles that are sufficiently bright, at different cosmological redshifts (z). the brighter emission from the wind is unobscured by the lanthanides (or actinides) in some of the models, permitting non-zero detection probabilities for redshifts up to z = 0.07. we also find that the nuclear mass model and the resulting radioactive heating rate are crucial for the detectability. while for the most pessimistic heating rate (from the finite range droplet model) no reasonable increase in the ejecta mass or velocity, or wind mass or velocity, can possibly make the light curves agree with the observed near-infrared excess after grb130603b, a more optimistic heating rate (from the duflo-zuker model) leads to good agreement. we conclude that future reliable macronova observations would constrain nuclear heating rates, and consequently help constrain nuclear mass models. | impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers |
the formation of planets depends on the underlying protoplanetary disc structure, which in turn influences both the accretion and migration rates of embedded planets. the disc itself evolves on time scales of several myr, during which both temperature and density profiles change as matter accretes onto the central star. here we used a detailed model of an evolving disc to determine the growth of planets by pebble accretion and their migration through the disc. cores that reach their pebble isolation mass accrete gas to finally form giant planets with extensive gas envelopes, while planets that do not reach pebble isolation mass are stranded as ice giants and ice planets containing only minor amounts of gas in their envelopes. unlike earlier population synthesis models, our model works without any artificial reductions in migration speed and for protoplanetary discs with gas and dust column densities similar to those inferred from observations. we find that in our nominal disc model, the emergence of planetary embryos preferably should occur after approximately 2 myr in order to not exclusively form gas giants, but also ice giants and smaller planets. the high pebble accretion rates ensure that critical core masses for gas accretion can be reached at all orbital distances. gas giant planets nevertheless experience significant reduction in semi-major axes by migration. considering instead planetesimal accretion for planetary growth, we show that formation time scales are too long to compete with the migration time scales and the dissipation time of the protoplanetary disc. all in all, we find that pebble accretion overcomes many of the challenges in the formation of ice and gas giants in evolving protoplanetary discs. appendices are available in electronic form at http://www.aanda.org | the growth of planets by pebble accretion in evolving protoplanetary discs |
in the present investigation an exact generalised model for anisotropic compact stars of embedding class 1 is sought with a general relativistic background. the generic solutions are verified by exploring different physical aspects, viz. energy conditions, mass-radius relation, stability of the models, in connection to their validity. it is observed that the model presented here for compact stars is compatible with all these physical tests and thus physically acceptable as far as the compact star candidates rxj 1856-37, sax j 1808.4-3658 ( ss1) and sax j 1808.4-3658 ( ss2) are concerned. | generalised model for anisotropic compact stars |
the origin of cosmic high-energy neutrinos remains largely unexplained. for high-energy neutrino alerts from icecube, a coincidence with time-variable emission has been seen for three different types of accreting black holes: (1) a gamma-ray flare from a blazar (txs 0506+056), (2) an optical transient following a stellar tidal disruption event (tde, at2019dsg), and (3) an optical outburst from an active galactic nucleus (agn, at2019fdr). for the latter two sources, infrared follow-up observations revealed a powerful reverberation signal due to dust heated by the optical/uv/x-ray emission of the flare. this discovery motivates a systematic study of neutrino emission from all black hole flares. because dust reprocessing is agnostic to the origin of the outburst near the black hole, this work unifies tdes and high-amplitude flares from agn. besides the two known events, we uncover a third flare with a dust echo that is coincident with a pev-scale neutrino (at2019aalc). based solely on the optical and infrared properties, we estimate a significance of 3.6$\sigma$ for the neutrino association for these three flares. this association is also supported by the shared radio and x-ray properties of the three flares with dust echoes. these accretion flares are rare--the total light from agn outshines them by several orders of magnitude--yet they could explain a large fraction of the cosmic high-energy neutrino flux. this tension could be resolved if the efficiency of particle acceleration in accretion disks rapidly increases towards the eddington limit. | establishing accretion flares from massive black holes as a major source of high-energy neutrinos |
uvex is a proposed medium class explorer mission designed to provide crucial missing capabilities that will address objectives central to a broad range of modern astrophysics. the uvex design has two co-aligned wide-field imagers operating in the fuv and nuv and a powerful broadband medium resolution spectrometer. in its two-year baseline mission, uvex will perform a multi-cadence synoptic all-sky survey 50/100 times deeper than galex in the nuv/fuv, cadenced surveys of the large and small magellanic clouds, rapid target of opportunity followup, as well as spectroscopic followup of samples of stars and galaxies. the science program is built around three pillars. first, uvex will explore the low-mass, low-metallicity galaxy frontier through imaging and spectroscopic surveys that will probe key aspects of the evolution of galaxies by understanding how star formation and stellar evolution at low metallicities affect the growth and evolution of low-metallicity, low-mass galaxies in the local universe. such galaxies contain half the mass in the local universe, and are analogs for the first galaxies, but observed at distances that make them accessible to detailed study. second, uvex will explore the dynamic universe through time-domain surveys and prompt spectroscopic followup capability will probe the environments, energetics, and emission processes in the early aftermaths of gravitational wave-discovered compact object mergers, discover hot, fast uv transients, and diagnose the early stages of stellar explosions. finally, uvex will become a key community resource by leaving a large all-sky legacy data set, enabling a wide range of scientific studies and filling a gap in the new generation of wide-field, sensitive optical and infrared surveys provided by the rubin, euclid, and roman observatories. this paper discusses the scientific potential of uvex, and the broad scientific program. | science with the ultraviolet explorer (uvex) |
the gaia sausage is an elongated structure in velocity space discovered by belokurov et al. using the kinematics of metal-rich halo stars. they showed that it could be created by a massive dwarf galaxy (∼5 × 1010 {m}⊙ ) on a strongly radial orbit that merged with the milky way at a redshift z ≲ 3. this merger would also have brought in globular clusters (gcs). we seek evidence for the associated sausage globular clusters (gcs) by analyzing the structure of 91 milky way gcs in action space using the gaia data release 2 catalog, complemented with hubble space telescope proper motions. there is a characteristic energy {e}crit} that separates the in situ objects, such as the bulge/disk clusters, from the accreted objects, such as the young halo clusters. there are 15 old halo gcs that have e > {e}crit}. eight of the high-energy, old halo gcs are strongly clumped in azimuthal and vertical action, yet strung out like beads on a chain at extreme radial action. they are very radially anisotropic (β ∼ 0.95) and move on orbits that are all highly eccentric (e ≳ 0.80). they also form a track in the age-metallicity plane compatible with a dwarf galaxy origin. these properties are consistent with gcs associated with the merger event that gave rise to the gaia sausage. | the sausage globular clusters |
the tip of the red giant branch has been used to measure distances to 500 nearby galaxies with the hubble space telescope (hst) which are available in the color-magnitude diagrams and tip of the red giant branch (cmds/trgb) catalog on the extragalactic distance database (edd). our established methods are employed to perform an independent reduction of the targets presented by the carnegie-chicago hubble program (cchp) in the series of papers culminating in freedman (2021). our distinct methodology involves modeling the observed luminosity function of red giant branch and asymptotic giant branch stars, which differs from the edge-detection algorithms employed by the cchp. we find excellent agreement between distances for 11 hosts with new imaging, all at d < 20 mpc. however, we are unable to measure the trgb for four hosts that use archival data designed to measure distances with cepheids, all at d > 23 mpc. with two new hst observations taken in the halo of the megamaser host ngc 4258, the first with the same acs f606w and f814w filters and state of the electronics used for sn ia hosts, we then calibrate our trgb distance scale to the geometric megamaser distance. using our trgb distances, we find a value of the hubble constant of h 0 = 71.5 ± 1.8 km s-1 mpc-1 when using either the pantheon or carnegie supernova project (csp) samples of supernovae. in the future, the james webb space telescope will extend measurements of the trgb to additional hosts of sn ia and surface-brightness fluctuation measurements for separate paths to h 0. | comparing tip of the red giant branch distance scales: an independent reduction of the carnegie-chicago hubble program and the value of the hubble constant |
in many cosmologies dark matter clusters on subkiloparsec scales and forms compact subhalos, in which the majority of galactic dark matter could reside. null results in direct detection experiments since their advent four decades ago could then be the result of extremely rare encounters between the earth and these subhalos. we investigate alternative and promising means to identify subhalo dark matter interacting with standard model particles: (1) subhalo collisions with old neutron stars can transfer kinetic energy and brighten the latter to luminosities within the reach of imminent infrared, optical, and ultraviolet telescopes; we identify new detection strategies involving single-star measurements and galactic disk surveys, and obtain the first bounds on self-interacting dark matter in subhalos from the coldest known pulsar, psr j2144-3933; (2) subhalo dark matter scattering with cosmic rays results in detectable effects; (3) historic earth-subhalo encounters can leave dark matter tracks in paleolithic minerals deep underground. these searches could discover dark matter subhalos weighing between gigaton and solar masses, with corresponding dark matter cross sections and masses spanning tens of orders of magnitude. | scattering searches for dark matter in subhalos: neutron stars, cosmic rays, and old rocks |
we present a detailed overview of the science goals and predictions for the prime-cam direct-detection camera-spectrometer being constructed by the ccat-prime collaboration for dedicated use on the fred young submillimeter telescope (fyst). the fyst is a wide-field, 6 m aperture submillimeter telescope being built (first light in late 2023) by an international consortium of institutions led by cornell university and sited at more than 5600 m on cerro chajnantor in northern chile. prime-cam is one of two instruments planned for fyst and will provide unprecedented spectroscopic and broadband measurement capabilities to address important astrophysical questions ranging from big bang cosmology through reionization and the formation of the first galaxies to star formation within our own milky way. prime-cam on the fyst will have a mapping speed that is over 10 times greater than existing and near-term facilities for high-redshift science and broadband polarimetric imaging at frequencies above 300 ghz. we describe details of the science program enabled by this system and our preliminary survey strategies. | ccat-prime collaboration: science goals and forecasts with prime-cam on the fred young submillimeter telescope |
the first systematic study of opacity dependence on atomic number at stellar interior temperatures is used to evaluate discrepancies between measured and modeled iron opacity [j. e. bailey et al., nature (london) 517, 56 (2015), 10.1038/nature14048]. high-temperature (>180 ev ) chromium and nickel opacities are measured with ±6 % - 10 % uncertainty, using the same methods employed in the previous iron experiments. the 10%-20% experiment reproducibility demonstrates experiment reliability. the overall model-data disagreements are smaller than for iron. however, the systematic study reveals shortcomings in models for density effects, excited states, and open l -shell configurations. the 30%-45% underestimate in the modeled quasicontinuum opacity at short wavelengths was observed only from iron and only at temperature above 180 ev. thus, either opacity theories are missing physics that has nonmonotonic dependence on the number of bound electrons or there is an experimental flaw unique to the iron measurement at temperatures above 180 ev. | systematic study of l -shell opacity at stellar interior temperatures |
we introduce the modelling star cluster population assembly in cosmological simulations within eagle (e-mosaics) project. e-mosaics incorporates models describing the formation, evolution, and disruption of star clusters into the eagle galaxy formation simulations, enabling the examination of the co-evolution of star clusters and their host galaxies in a fully cosmological context. a fraction of the star formation rate of dense gas is assumed to yield a cluster population; this fraction and the population's initial properties are governed by the physical properties of the natal gas. the subsequent evolution and disruption of the entire cluster population are followed accounting for two-body relaxation, stellar evolution, and gravitational shocks induced by the local tidal field. this introductory paper presents a detailed description of the model and initial results from a suite of 10 simulations of ∼l⋆ galaxies with disc-like morphologies at z = 0. the simulations broadly reproduce key observed characteristics of young star clusters and globular clusters (gcs), without invoking separate formation mechanisms for each population. the simulated gcs are the surviving population of massive clusters formed at early epochs (z ≳ 1-2), when the characteristic pressures and surface densities of star-forming gas were significantly higher than observed in local galaxies. we examine the influence of the star formation and assembly histories of galaxies on their cluster populations, finding that (at similar present-day mass) earlier-forming galaxies foster a more massive and disruption-resilient cluster population, while galaxies with late mergers are capable of forming massive clusters even at late cosmic epochs. we find that the phenomenological treatment of interstellar gas in eagle precludes the accurate modelling of cluster disruption in low-density environments, but infer that simulations incorporating an explicitly modelled cold interstellar gas phase will overcome this shortcoming. | the e-mosaics project: simulating the formation and co-evolution of galaxies and their star cluster populations |
we present new measurements of the quasar luminosity function (lf) at z ∼ 6 over an unprecedentedly wide range of the rest-frame ultraviolet luminosity m 1450 from -30 to -22 mag. this is the fifth in a series of publications from the subaru high-z exploration of low-luminosity quasars (shellqs) project, which exploits the deep multiband imaging data produced by the hyper suprime-cam subaru strategic program survey. the lf was calculated with a complete sample of 110 quasars at 5.7 ≤ z ≤ 6.5, which includes 48 shellqs quasars discovered over 650 deg2 and 63 brighter quasars discovered by the sloan digital sky survey and the canada-france-hawaii quasar survey (including one overlapping object). this is the largest sample of z ∼ 6 quasars with a well-defined selection function constructed to date, which has allowed us to detect significant flattening of the lf at its faint end. a double power-law function fit to the sample yields a faint-end slope α =-{1.23}-0.34+0.44, a bright-end slope β =-{2.73}-0.31+0.23, a break magnitude {m}1450* =-{24.90}-0.90+0.75, and a characteristic space density {{{φ }}}* ={10.9}-6.8+10.0 gpc-3 mag-1. integrating this best-fit model over the range -18 < m 1450 < -30 mag, quasars emit ionizing photons at the rate of {\dot{n}}ion}={10}48.8+/- 0.1 s-1 mpc-3 at z = 6.0. this is less than 10% of the critical rate necessary to keep the intergalactic medium ionized, which indicates that quasars are not a major contributor to cosmic reionization. | subaru high-zexploration of low-luminosity quasars (shellqs). v. quasar luminosity function and contribution to cosmic reionization at z = 6 |
we introduce massive black holes (bhs) in the feedback in realistic environments (fire) project and perform high-resolution cosmological hydrodynamic simulations of quasar-mass haloes [mhalo(z = 2) ≈ 1012.5 m⊙] down to z = 1. these simulations model stellar feedback by supernovae, stellar winds and radiation, and bh growth using a gravitational torque-based prescription tied to the resolved properties of galactic nuclei. we do not include bh feedback. we show that early bh growth occurs through short (≲1 myr) accretion episodes that can reach or even exceed the eddington rate. in this regime, bh growth is limited by bursty stellar feedback continuously evacuating gas from galactic nuclei, and bhs remain undermassive in low-mass galaxies relative to the local mbh-mbulgerelation. bh growth is more efficient at later times, when the nuclear stellar potential retains a significant gas reservoir, star formation becomes less bursty and galaxies settle into a more ordered state. bhs rapidly converge on to the observed scaling relations when the host reaches mbulge ∼ 1010 m⊙. we show that resolving the effects of stellar feedback on the gas supply in the inner ∼100 pc of galaxies is necessary to accurately capture the growth of central bhs. our simulations imply that bursty stellar feedback has important implications for bh-galaxy relations, agn demographics and time variability, the formation of early quasars and massive bh mergers. | black holes on fire: stellar feedback limits early feeding of galactic nuclei |
we present the first volume-limited sample of cataclysmic variables (cvs), selected using the accurate parallaxes provided by the second data release (dr2) of the european space agency gaia space mission. the sample is composed of 42 cvs within 150 pc, including two new systems discovered using the gaia data, and is $(77 \pm 10)$ per cent complete. we use this sample to study the intrinsic properties of the galactic cv population. in particular, the cv space density we derive, $\rho =(4.8^{+0.6}_{-0.8}) \times 10^{-6}\, \mbox{$\mathrm{pc}^{-3}$}$, is lower than that predicted by most binary population synthesis studies. we also find a low fraction of period bounce cvs, seven per cent, and an average white dwarf mass of $\langle m_\mathrm{wd} \rangle = (0.83 \pm 0.17)\, \mathrm{m}_\odot$ . both findings confirm previous results, ruling out the presence of observational biases affecting these measurements, as has been suggested in the past. the observed fraction of period bounce cvs falls well below theoretical predictions, by at least a factor of five, and remains one of the open problems in the current understanding of cv evolution. conversely, the average white dwarf mass supports the presence of additional mechanisms of angular momentum loss that have been accounted for in the latest evolutionary models. the fraction of magnetic cvs in the 150 pc sample is remarkably high at 36 per cent. this is in striking contrast with the absence of magnetic white dwarfs in the detached population of cv progenitors, and underlines that the evolution of magnetic systems has to be included in the next generation of population models. | a volume-limited sample of cataclysmic variables from gaia dr2: space density and population properties |
in 2021 may, the dark energy spectroscopic instrument (desi) began a 5 yr survey of approximately 50 million total extragalactic and galactic targets. the primary desi dark-time targets are emission line galaxies, luminous red galaxies, and quasars. in bright time, desi will focus on two surveys known as the bright galaxy survey and the milky way survey. desi also observes a selection of "secondary" targets for bespoke science goals. this paper gives an overview of the publicly available pipeline (desitarget) used to process targets for desi observations. highlights include details of the different desi survey targeting phases, the targeting id (targetid) used to define unique targets, the bitmasks used to indicate a particular type of target, the data model and structure of desi targeting files, and examples of how to access and use the desitarget code base. this paper will also describe "supporting" desi target classes, such as standard stars, sky locations, and random catalogs that mimic the angular selection function of desi targets. the desi target-selection pipeline is complex and sizable; this paper attempts to summarize the most salient information required to understand and work with desi targeting data. | the target-selection pipeline for the dark energy spectroscopic instrument |
the transformation of cold neutral intergalactic hydrogen into a highly ionized warm plasma marks the end of the cosmic dark ages and the beginning of the age of galaxies. the details of this process reflect the nature of the early sources of radiation and heat, the statistical characteristics of the large-scale structure of the universe, the thermodynamics and chemistry of cosmic baryons, and the histories of star formation and black hole accretion. a number of massive data sets from new ground- and space-based instruments and facilities over the next decade are poised to revolutionize our understanding of primeval galaxies, the reionization photon budget, the physics of the intergalactic medium (igm), and the fine-grained properties of hydrogen gas in the "cosmic web". in this review, we survey the physics and key aspects of reionization-era modeling and describe the diverse range of computational techniques and tools currently available in this field. | modeling cosmic reionization |
we present new theoretical stellar yields and surface abundances for three grids of metal-rich asymptotic giant branch (agb) models. post-processing nucleosynthesis results are presented for stellar models with initial masses between 1 m ⊙ and 7.5 m ⊙ for z = 0.007, and 1 m ⊙ and 8 m ⊙ for z = 0.014 (solar) and z = 0.03. we include stellar surface abundances as a function of thermal pulse on the agb for elements from c to bi and for a selection of isotopic ratios for elements up to fe and ni (e.g., {}12{{c}}/{}13{{c}}), which can be obtained from observations of molecules in stars and from the laboratory analysis of meteoritic stardust grains. ratios of elemental abundances of he/h, c/o, and n/o are also included, which are useful for direct comparison to observations of agb stars and their progeny, including planetary nebulae. the integrated elemental stellar yields are presented for each model in the grid for hydrogen, helium, and all stable elements from c to bi. yields of li are also included for intermediate-mass models with hot bottom burning. we present the first slow neutron-capture (s-process) yields for super solar metallicity agb stars with z = 0.03, and the first complete s-process yields for models more massive than 6 m ⊙ at all three metallicities. | stellar yields from metal-rich asymptotic giant branch models |
aims: we present new gravity and limb-darkening coefficients for a wide range of effective temperatures, gravities, metallicities, and microturbulent velocities. these coefficients can be used in many different fields of stellar physics as synthetic light curves of eclipsing binaries and planetary transits, stellar diameters, line profiles in rotating stars, and others.methods: the limb-darkening coefficients were computed specifically for the photometric system of the space mission tess and were performed by adopting the least-square method. in addition, the linear and bi-parametric coefficients, by adopting the flux conservation method, are also available. on the other hand, to take into account the effects of tidal and rotational distortions, we computed the passband gravity-darkening coefficients y(λ) using a general differential equation in which we consider the effects of convection and of the partial derivative (∂lni(λ) /∂lng)teff.results: to generate the limb-darkening coefficients we adopt two stellar atmosphere models: atlas (plane-parallel) and phoenix (spherical, quasi-spherical, and r-method). the specific intensity distribution was fitted using five approaches: linear, quadratic, square root, logarithmic, and a more general one with four terms. these grids cover together 19 metallicities ranging from 10-5 up to 10+1 solar abundances, 0 ≤ log g ≤ 6.0 and 1500 k ≤teff ≤ 50 000 k. the calculations of the gravity-darkening coefficients were performed for all plane-parallel atlas models. tables 2-29 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/600/a30 | limb and gravity-darkening coefficients for the tess satellite at several metallicities, surface gravities, and microturbulent velocities |
a homogeneous search for stellar flares has been performed using every available kepler light curve. an iterative light curve de-trending approach was used to filter out both astrophysical and systematic variability to detect flares. the flare recovery completeness has also been computed throughout each light curve using artificial flare injection tests, and the tools for this work have been made publicly available. the final sample contains 851,168 candidate flare events recovered above the 68% completeness threshold, which were detected from 4041 stars, or 1.9% of the stars in the kepler database. the average flare energy detected is ∼1035 erg. the net fraction of flare stars increases with g - i color, or decreasing stellar mass. for stars in this sample with previously measured rotation periods, the total relative flare luminosity is compared to the rossby number. a tentative detection of flare activity saturation for low-mass stars with rapid rotation below a rossby number of ∼0.03 is found. a power-law decay in flare activity with rossby number is found with a slope of -1, shallower than typical measurements for x-ray activity decay with rossby number. | the kepler catalog of stellar flares |
literature data are collated for 38 stripped-envelope core-collapse supernovae (se sne; i.e. sne iib, ib, ic and ic-bl) that have good light-curve coverage in more than one optical band. using bolometric corrections derived in previous work, the bolometric light curve of each sn is recovered and template bolometric light curves provided. peak light distributions and decay rates are investigated; sne subtypes are not cleanly distinguished in this parameter space, although some grouping of types does occur and there is a suggestion of a phillips-like relation for most sne ic-bl. the bolometric light curves are modelled with a simple analytical prescription and compared to results from more detailed modelling. distributions of the explosion parameters show the extreme nature of sne ic-bl in terms of their 56ni mass and the kinetic energy, however ejected masses are similar to other subtypes. sne ib and ic have very similar distributions of explosion parameters, indicating a similarity in progenitors. sne iib are the most homogeneous subtype and have the lowest average values for 56ni mass, ejected mass, and kinetic energy. ejecta masses for each subtype and se sne as a whole are inconsistent with those expected from very massive stars. the majority of the ejecta mass distribution is well described by more moderately massive progenitors in binaries, indicating these are the dominant progenitor channel for se sne. | bolometric light curves and explosion parameters of 38 stripped-envelope core-collapse supernovae |
one of the striking observations from the parker solar probe (psp) spacecraft is the prevalence in the inner heliosphere of large amplitude, alfvénic magnetic field reversals termed switchbacks. these $\delta {b}_{r}/b\sim { \mathcal o }(1$ ) fluctuations occur over a range of timescales and in patches separated by intervals of quiet, radial magnetic field. we use measurements from psp to demonstrate that patches of switchbacks are localized within the extensions of plasma structures originating at the base of the corona. these structures are characterized by an increase in alpha particle abundance, mach number, plasma β and pressure, and by depletions in the magnetic field magnitude and electron temperature. these intervals are in pressure balance, implying stationary spatial structure, and the field depressions are consistent with overexpanded flux tubes. the structures are asymmetric in carrington longitude with a steeper leading edge and a small (~1°) edge of hotter plasma and enhanced magnetic field fluctuations. some structures contain suprathermal ions to ~85 kev that we argue are the energetic tail of the solar wind alpha population. the structures are separated in longitude by angular scales associated with supergranulation. this suggests that these switchbacks originate near the leading edge of the diverging magnetic field funnels associated with the network magnetic field-the primary wind sources. we propose an origin of the magnetic field switchbacks, hot plasma and suprathermals, alpha particles in interchange reconnection events just above the solar transition region and our measurements represent the extended regions of a turbulent outflow exhaust. | a solar source of alfvénic magnetic field switchbacks: in situ remnants of magnetic funnels on supergranulation scales |
we survey our understanding of classical novae-nonterminal, thermonuclear eruptions on the surfaces of white dwarfs in binary systems. the recent and unexpected discovery of gev gamma rays from galactic novae has highlighted the complexity of novae and their value as laboratories for studying shocks and particle acceleration. we review half a century of nova literature through this new lens, and conclude the following: the basics of the thermonuclear runaway theory of novae are confirmed by observations. the white dwarf sustains surface nuclear burning for some time after runaway, and until recently, it was commonly believed that radiation from this nuclear burning solely determines the nova's bolometric luminosity. the processes by which novae eject material from the binary system remain poorly understood. mass loss from novae is complex (sometimes fluctuating in rate, velocity, and morphology) and often prolonged in time over weeks, months, or years. the complexity of the mass ejection leads to gamma-ray-producing shocks internal to the nova ejecta. when gamma rays are detected (around optical maximum), the shocks are deeply embedded and the surrounding gas is very dense. observations of correlated optical and gamma-ray light curves confirm that the shocks are radiative and contribute significantly to the bolometric luminosity of novae. novae are therefore the closest and most common interaction-powered transients. | new insights into classical novae |
we present a systematic numerical relativity study of the dynamical ejecta, winds, and nucleosynthesis in neutron star (ns) merger remnants. binaries with the chirp mass compatible with gw170817, different mass ratios, and five microphysical equations of state (eoss) are simulated with an approximate neutrino transport and a subgrid model for magnetohydrodynamic turbulence up to 100 ms postmerger. spiral density waves propagating from the ns remnant to the disk trigger a wind with mass flux ∼0.1-0.5 m⊙ s-1, which persists for the entire simulation as long as the remnant does not collapse to a black hole. this wind has average electron fraction ≳0.3 and average velocity ∼0.1-0.17 c and thus is a site for the production of weak r-process elements (mass number a < 195). disks around long-lived remnants have masses ∼0.1-0.2 m⊙, temperatures peaking at ≲10 mev near the inner edge, and a characteristic double-peak distribution in entropy resulting from shocks propagating through the disk. the dynamical and spiral-wave ejecta computed in our targeted simulations are not compatible with those inferred from at2017gfo using two-components kilonova models. rather, they indicate that multicomponent kilonova models including disk winds are necessary to interpret at2017gfo. the nucleosynthesis in the combined dynamical ejecta and spiral-wave wind in the long-lived mergers of comparable mass robustly accounts for all the r-process peaks, from mass number ∼75 to actinides in terms of solar abundances. total abundances are weakly dependent on the eos, while the mass ratio affects the production of first-peak elements. | numerical relativity simulations of the neutron star merger gw170817: long-term remnant evolutions, winds, remnant disks, and nucleosynthesis |
context. three-dimensional maps of the galactic interstellar medium are general astrophysical tools. reddening maps may be based on the inversion of color excess measurements for individual target stars or on statistical methods using stellar surveys. three-dimensional maps based on diffuse interstellar bands (dibs) have also been produced. all methods benefit from the advent of massive surveys and may benefit from gaia data.aims: all of the various methods and databases have their own advantages and limitations. here we present a first attempt to combine different datasets and methods to improve the local maps.methods: we first updated our previous local dust maps based on a regularized bayesian inversion of individual color excess data by replacing hipparcos or photometric distances with gaia data release 1 values when available. secondly, we complemented this database with a series of ≃5000 color excess values estimated from the strength of the λ15273 dib toward stars possessing a gaia parallax. the dib strengths were extracted from sdss/apogee spectra. third, we computed a low-resolution map based on a grid of pan-starrs reddening measurements by means of a new hierarchical technique and used this map as the prior distribution during the inversion of the two other datasets.results: the use of gaia parallaxes introduces significant changes in some areas and globally increases the compactness of the structures. additional dib-based data make it possible to assign distances to clouds located behind closer opaque structures and do not introduce contradictory information for the close structures. a more realistic prior distribution instead of a plane-parallel homogeneous distribution helps better define the structures. we validated the results through comparisons with other maps and with soft x-ray data.conclusions: our study demonstrates that the combination of various tracers is a potential tool for more accurate maps. an online tool makes it possible to retrieve maps and reddening estimations. our online tool is available at http://stilism.obspm.fr | three-dimensional mapping of the local interstellar medium with composite data |
we determine the orbital eccentricities of individual small kepler planets, through a combination of asteroseismology and transit light-curve analysis. we are able to constrain the eccentricities of 51 systems with a single transiting planet, which supplement our previous measurements of 66 planets in multi-planet systems. through a bayesian hierarchical analysis, we find evidence that systems with only one detected transiting planet have a different eccentricity distribution than systems with multiple detected transiting planets. the eccentricity distribution of the single-transiting systems is well described by the positive half of a zero-mean gaussian distribution with a dispersion σe= 0.32 ± 0.06, while the multiple-transit systems are consistent with {σ }e={0.083}-0.020+0.015. a mixture model suggests a fraction of {0.76}-0.12+0.21 of single-transiting systems have a moderate eccentricity, represented by a rayleigh distribution that peaks at {0.26}-0.06+0.04. this finding may reflect differences in the formation pathways of systems with different numbers of transiting planets. we investigate the possibility that eccentricities are self-excited in closely packed planetary systems, as well as the influence of long-period giant companion planets. we find that both mechanisms can qualitatively explain the observations. we do not find any evidence for a correlation between eccentricity and stellar metallicity, as has been seen for giant planets. neither do we find any evidence that orbital eccentricity is linked to the detection of a companion star. along with this paper, we make available all of the parameters and uncertainties in the eccentricity distributions, as well as the properties of individual systems, for use in future studies. | the orbital eccentricity of small planet systems |
the analysis of the central compact object within the supernova remnant hess j1731-347 suggests that it has a small radius and, even more interestingly, a mass of the order or smaller than one solar mass. this raises the question of which astrophysical process could lead to such a small mass, since the analysis of various types of sn explosions indicate that is it not possible to produce a neutron star with a mass smaller than about $1.17 m_\odot$. here we show that masses of the order or smaller than one solar mass can be obtained in the case of strange quark stars and that it is possible to build a coherent model explaining not only the mass and the radius of that object, but also its slow cooling suggested in various analyses. we also show that an astrophysical path exists which leads to the formation of such an object, and we discuss the role played in that scenario by strangelets assumed to constitute the dark matter. | is the compact object associated with hess j1731-347 a strange quark star? |
we study the evolution of the scaling relations that compare the effective density ({{{σ }}}{{e}},r< {r}{{e}}) and core density ({{{σ }}}1,r< 1 kpc) to the stellar masses of star-forming galaxies (sfgs) and quiescent galaxies. these relations have been fully in place since z∼ 3 and have exhibited almost constant slope and scatter since that time. for sfgs, the zero points in {{{σ }}}{{e}} and {{{σ }}}1 decline by only × 2. this fact plus the narrowness of the relations suggests that galaxies could evolve roughly along the scaling relations. quiescent galaxies follow different scaling relations that are offset to higher densities at the same mass and redshift. furthermore, the zero point of their core density has declined by only × 2 since z∼ 3, while the zero point of the effective density declines by × 10. when galaxies quench, they move from the star-forming relations to the quiescent relations. this involves an increase in the core and effective densities, which suggests that sfgs could experience a phase of significant core growth relative to the average evolution along the structural relations. the distribution of massive galaxies relative to the sfr-m {}\starand the quiescent {{σ }}{--}{m}\starrelations exhibits an l-shape that is independent of redshift. the knee of this relation consists of a subset of “compact” sfgs that are the most likely precursors of quiescent galaxies forming at later times. the compactness selection threshold in {{{σ }}}1 exhibits a small variation from z = 3 to 0.5, {{{σ }}}1-0.65({log} m* -10.5)> 9.6-9.3 m ⊙ kpc-2, allowing the most efficient identification of compact sfgs and quiescent galaxies at every redshift. | structural and star-forming relations since z ∼ 3: connecting compact star-forming and quiescent galaxies |
with the advent of more sensitive all-sky instruments, the transient universe is being probed in greater depth than ever before. taking advantage of available resources, we have established a comprehensive database of black hole (and black hole candidate) x-ray binary (bhxb) activity between 1996 and 2015 as revealed by all-sky instruments, scanning surveys, and select narrow-field x-ray instruments on board the international gamma-ray astrophysics laboratory, monitor of all-sky x-ray image, rossi x-ray timing explorer, and swift telescopes; the whole-sky alberta time-resolved comprehensive black-hole database of the galaxy or watchdog. over the past two decades, we have detected 132 transient outbursts, tracked and classified behavior occurring in 47 transient and 10 persistently accreting bhs, and performed a statistical study on a number of outburst properties across the galactic population. we find that outbursts undergone by bhxbs that do not reach the thermally dominant accretion state make up a substantial fraction (∼40%) of the galactic transient bhxb outburst sample over the past ∼20 years. our findings suggest that this “hard-only” behavior, observed in transient and persistently accreting bhxbs, is neither a rare nor recent phenomenon and may be indicative of an underlying physical process, relatively common among binary bhs, involving the mass-transfer rate onto the bh remaining at a low level rather than increasing as the outburst evolves. we discuss how the larger number of these “hard-only” outbursts and detected outbursts in general have significant implications for both the luminosity function and mass-transfer history of the galactic bhxb population. | watchdog: a comprehensive all-sky database of galactic black hole x-ray binaries |
we investigate the impact of cosmic rays (crs) on the circumgalactic medium (cgm) in fire-2 simulations, for ultra-faint dwarf through milky way (mw)-mass haloes hosting star-forming (sf) galaxies. our cr treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, and collisional and streaming losses, with constant parallel diffusivity $\kappa \sim 3\times 10^{29}\, \mathrm{cm^2\ s^{-1}}$ chosen to match γ-ray observations. with this, crs become more important at larger halo masses and lower redshifts, and dominate the pressure in the cgm in mw-mass haloes at z ≲ 1-2. the gas in these 'cr-dominated' haloes differs significantly from runs without crs: the gas is primarily cool (a few ${\sim}10^{4}\,$ k), and the cool phase is volume-filling and has a thermal pressure below that needed for virial or local thermal pressure balance. ionization of the 'low' and 'mid' ions in this diffuse cool gas is dominated by photoionization, with o vi columns ${\gtrsim}10^{14.5}\, \mathrm{cm^{-2}}$ at distances ${\gtrsim}150\, \mathrm{kpc}$. cr and thermal gas pressure are locally anticorrelated, maintaining total pressure balance, and the cgm gas density profile is determined by the balance of cr pressure gradients and gravity. neglecting crs, the same haloes are primarily warm/hot ($t\gtrsim 10^{5}\,$k) with thermal pressure balancing gravity, collisional ionization dominates, o vi columns are lower and ne viii higher, and the cool phase is confined to dense filaments in local thermal pressure equilibrium with the hot phase. | properties of the circumgalactic medium in cosmic ray-dominated galaxy haloes |
the equation of state (eos) of dense matter is an essential ingredient for numerical simulations of core-collapse supernovae and neutron star mergers. the properties of matter near and above nuclear saturation density are uncertain, which translates into uncertainties in astrophysical simulations and their multimessenger signatures. therefore, a wide range of eoss spanning the allowed range of nuclear interactions are necessary for determining the sensitivity of these astrophysical phenomena and their signatures to variations in input microphysics. we present a new set of finite temperature eoss based on experimentally allowed skyrme forces. we employ a liquid-drop model of nuclei to capture the nonuniform phase of nuclear matter at subsaturation density, which is blended into a nuclear statistical equilibrium eos at lower densities. we also provide a new, open-source code for calculating eoss for arbitrary skyrme parametrizations. we then study the effects of different skyrme parametrizations on thermodynamical properties of dense astrophysical matter, the neutron star mass-radius relationship, and the core collapse of 15 and 40 solar mass stars. | open-source nuclear equation of state framework based on the liquid-drop model with skyrme interaction |
this paper presents a cross-calibrated catalog of hipparcos and gaia astrometry to enable their use in measuring changes in proper motion, i.e., accelerations in the plane of the sky. the final catalog adopts the reference frame of the second gaia data release (dr2) and locally cross-calibrates both the scaled hipparcos-gaia dr2 positional differences and the hipparcos proper motions themselves to this frame. this gives three nearly independent proper motion measurements per star, with the scaled positional difference usually being the most precise. we find that a linear combination of the two hipparcos reductions is superior to either reduction on its own and address error inflation for both hipparcos and gaia dr2. our adopted error inflation is additive (in quadrature) for hipparcos and multiplicative for gaia. we provide the covariance matrices along with the central epochs of all measurements. our final proper motion differences are accurately gaussian with the appropriate variances and are suitable for acceleration measurements and orbit fitting. the catalog is constructed with an eye toward completeness; it contains nearly 98% of the hipparcos stars. it also includes a handful of spurious entries and a few stars with poor hipparcos reductions that the user must vet by hand. statistical distributions of accelerations derived from this catalog should be interpreted with caution. | the hipparcos-gaia catalog of accelerations |
gravitational waves (gws) provide a new tool to probe the nature of dark energy (de) and the fundamental properties of gravity. we review the different ways in which gws can be used to test theories of gravity and cosmology, emphasizing models for late-time cosmic acceleration. lagrangian-based gravitational theories beyond general relativity (gr) are classified into those breaking fundamental assumptions, containing additional fields and massive graviton(s). in addition to lagrangian based theories we present the effective theory of de and the μ-σ parametrization as general descriptions of cosmological gravity. multi-messenger gw detections can be used to measure the cosmological expansion (standard sirens), providing an independent test of the de equation of state and measuring the hubble parameter. several key tests of gravity involve the cosmological propagation of gws, including anomalous gw speed, massive graviton excitations, lorentz violating dispersion relation, modified gw luminosity distance and additional polarizations, which may also cause gw oscillations. we summarize present constraints and their impact on de models, including those arising from the binary neutron star merger gw170817. upgrades of ligo-virgo detectors to design sensitivity and the next generation facilities such as lisa or einstein telescope will significantly improve these constraints in the next two decades. | dark energy in light of multi-messenger gravitational-wave astronomy |
high-quality collections of type ii supernova (sn) light curves are scarce because they evolve for hundreds of days, making follow-up observations time consuming and often extending over multiple observing seasons. in light of these difficulties, the diversity of sne ii is not fully understood. here we present ultraviolet and optical photometry of 12 sne ii monitored by the las cumbres observatory global telescope network during 2013 to 2014, and compare them with previously studied sne having well-sampled light curves. we explore sn ii diversity by searching for correlations between the slope of the linear light-curve decay after maximum light (historically used to divide sne ii into iil and iip) and other measured physical properties. while sne iil are found to be on average more luminous than sne iip, sne iil do not appear to synthesize more 56ni than sne iip. finally, optical nebular spectra obtained for several sne in our sample are found to be consistent with models of red supergiant progenitors in the 12-16 m⊙ range. consequently, sne iil appear not to account for the deficit of massive red supergiants as sn ii progenitors. | the diversity of type ii supernova versus the similarity in their progenitors |
we perform neutrino radiation-hydrodynamics simulations for the merger of asymmetric binary neutron stars in numerical relativity. neutron stars are modeled by soft and moderately stiff finite-temperature equations of state (eos). we find that the properties of the dynamical ejecta such as the total mass, neutron richness profile, and specific entropy profile depend on the mass ratio of the binary systems for a given eos in a unique manner. for a soft eos (sfho), the total ejecta mass depends weakly on the mass ratio, but the average of electron number per baryon (ye ) and specific entropy (s ) of the ejecta decreases significantly with the increase of the degree of mass asymmetry. for a stiff eos (dd2), with the increase of the mass asymmetry degree, the total ejecta mass significantly increases while the average of ye and s moderately decreases. we find again that only for the sfho, the total ejecta mass exceeds 0.01 m⊙ irrespective of the mass ratio chosen in this paper. the ejecta have a variety of electron number per baryon with an average approximately between ye∼0.2 and ∼0.3 irrespective of the eos employed, which is well suited for the production of the rapid neutron capture process heavy elements (second and third peaks), although its averaged value decreases with the increase of the degree of mass asymmetry. | dynamical mass ejection from the merger of asymmetric binary neutron stars: radiation-hydrodynamics study in general relativity |
in the present paper we investigate the structure of relativistic stars in 4d einstein-gauss-bonnet gravity. the mass-radius relations are obtained for realistic hadronic and for strange quark star equations of state, and for a wide range of the gauss-bonnet coupling parameter α. even though the deviations from general relativity for nonzero values of α can be large enough, they are still comparable with the variations due to different modern realistic equations of state if we restrict ourselves to moderate values of α. that is why the current observations of the neutron star masses and radii alone can not impose stringent constraints on the value of the parameter α. nevertheless some rough constraints on α can be put. the existence of stable stellar mass black holes imposes √(α) ≲ 2.6 km for α > 0 while the requirement that the maximum neutron star mass should be greater than two solar masses gives √(|α|) ≲ 3.9 km for α < 0. we also present an exact solution describing the structure of relativistic stars with uniform energy density in 4d einstein-gauss-bonnet gravity. | relativistic stars in 4d einstein-gauss-bonnet gravity |
in dense stellar environments, the merger products of binary black hole mergers may undergo additional mergers. these hierarchical mergers are naturally expected to have higher masses than the first generation of black holes made from stars. the components of hierarchical mergers are expected to have significant characteristic spins, imprinted by the orbital angular momentum of the previous mergers. however, since the population properties of first-generation black holes are uncertain, it is difficult to know if any given merger is first-generation or hierarchical. we use observations of gravitational waves to reconstruct the binary black hole mass and spin spectrum of a population including the possibility of hierarchical mergers. we employ a phenomenological model that captures the properties of merging binary black holes from simulations of globular clusters. inspired by recent work on the formation of low-spin black holes, we include a zero-spin subpopulation. we analyze binary black holes from ligo and virgo's first two observing runs, and find that this catalog is consistent with having no hierarchical mergers. we find that the most massive system in this catalog, gw170729, is mostly likely a first-generation merger, having a 4% probability of being a hierarchical merger assuming a 5 × 105m⊙ globular cluster mass. using our model, we find that 99% of first-generation black holes in coalescing binaries have masses below $44$ m⊙, and the fraction of binaries with near-zero component spins is less than $0.16$ (90% probability). upcoming observations will determine if hierarchical mergers are a common source of gravitational waves. | black hole genealogy: identifying hierarchical mergers with gravitational waves |
we derive and publish data-driven estimates of stellar metallicity [m/h] for ~175 million stars with low-resolution xp spectra published in gaia dr3. the [m/h] values, along with t eff and $\mathrm{log}g$ , are derived using the xgboost algorithm, trained on stellar parameters from apogee, augmented by a set of very-metal-poor stars. xgboost draws on a number of data features: the full set of xp spectral coefficients, narrowband fluxes derived from xp spectra, and broadband magnitudes. in particular, we include catwise magnitudes, as they reduce the degeneracy of t eff and dust reddening. we also include the parallax as a data feature, which helps constrain $\mathrm{log}g$ and [m/h]. the resulting mean stellar parameter precision is 0.1 dex in [m/h], 50 k in t eff, and 0.08 dex in $\mathrm{log}g$ . this all-sky [m/h] sample is substantially larger than published samples of comparable fidelity across -3 ≲ [m/h] ≲ +0.5. additionally, we provide a catalog of over 17 million bright (g < 16) red giants whose [m/h] values are vetted to be precise and pure. we present all-sky maps of the milky way in different [m/h] regimes that illustrate the purity of the data set, and demonstrate the power of this unprecedented sample to reveal the milky way's structure from its heart to its disk. | robust data-driven metallicities for 175 million stars from gaia xp spectra |
we present results from the lyman continuum escape survey (laces), a hubble space telescope (hst) program designed to characterize the ionizing radiation emerging from a sample of lyα-emitting galaxies at redshift z ≃ 3.1. as many show intense [o iii] emission characteristic of z > 6.5 star-forming galaxies, they may represent valuable low-redshift analogs of galaxies in the reionization era. using hst wide field camera 3/uvis f336w to image lyman continuum emission, we investigate the escape fraction of ionizing photons in this sample. for 61 sources, of which 77% are spectroscopically confirmed and 53 have measures of [o iii] emission, we detect lyman continuum leakage in 20%, a rate significantly higher than is seen in individual continuum-selected lyman break galaxies. we estimate that there is a 98% probability that ≤2 of our detections could be affected by foreground contamination. fitting multiband spectral energy distributions (seds) to take account of the varying stellar populations, dust extinctions and metallicities, we derive individual lyman continuum escape fractions corrected for foreground intergalactic absorption. we find escape fractions of 15%-60% for individual objects and infer an average 20% escape fraction by fitting composite seds for our detected samples. surprisingly, however, even a deep stack of those sources with no individual f336w detections provides a stringent upper limit on the average escape fraction of less than 0.5%. we examine various correlations with source properties and discuss the implications in the context of the popular picture that cosmic reionization is driven by such compact, low-metallicity star-forming galaxies. | the lyman continuum escape survey: ionizing radiation from [o iii]-strong sources at a redshift of 3.1 |
the juno magnetic field investigation (mag) characterizes jupiter's planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of jupiter. the magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial fluxgate magnetometer (fgm) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. the imaging system sensors are part of a subsystem that provides accurate attitude information (to ∼20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. the two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of 's three solar array assemblies. the magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside juno's massive radiation shielded vault. the imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 gauss = 1.6 × 106 nt per axis) with a resolution of ∼0.05 nt in the most sensitive dynamic range (±1600 nt per axis). both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. the magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. the attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. the system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. a spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of juno's spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft. | the juno magnetic field investigation |
strong solar flares and coronal mass ejections, here defined not only as the bursts of electromagnetic radiation but as the entire process in which magnetic energy is released through magnetic reconnection and plasma instability, emanate from active regions (ars) in which high magnetic non-potentiality resides in a wide variety of forms. this review focuses on the formation and evolution of flare-productive ars from both observational and theoretical points of view. starting from a general introduction of the genesis of ars and solar flares, we give an overview of the key observational features during the long-term evolution in the pre-flare state, the rapid changes in the magnetic field associated with the flare occurrence, and the physical mechanisms behind these phenomena. our picture of flare-productive ars is summarized as follows: subject to the turbulent convection, the rising magnetic flux in the interior deforms into a complex structure and gains high non-potentiality; as the flux appears on the surface, an ar with large free magnetic energy and helicity is built, which is represented by δ -sunspots, sheared polarity inversion lines, magnetic flux ropes, etc; the flare occurs when sufficient magnetic energy has accumulated, and the drastic coronal evolution affects magnetic fields even in the photosphere. we show that the improvement of observational instruments and modeling capabilities has significantly advanced our understanding in the last decades. finally, we discuss the outstanding issues and future perspective and further broaden our scope to the possible applications of our knowledge to space-weather forecasting, extreme events in history, and corresponding stellar activities. | flare-productive active regions |
using cosmological simulations, we address the properties of high-redshift star-forming galaxies (sfgs) across their main sequence (ms) in the plane of star formation rate (sfr) versus stellar mass. we relate them to the evolution of galaxies through phases of gas compaction, depletion, possible replenishment, and eventual quenching. we find that the high-sfr galaxies in the upper envelope of the ms are compact, with high gas fractions and short depletion times (`blue nuggets'), while the lower sfr galaxies in the lower envelope have lower central gas densities, lower gas fractions, and longer depletion times, consistent with observed gradients across the ms. stellar-structure gradients are negligible. the sfgs oscillate about the ms ridge on time-scales ∼0.4thubble (∼1 gyr at z ∼ 3). the propagation upwards is due to gas compaction, triggered, e.g. by mergers, counter-rotating streams, and/or violent disc instabilities. the downturn at the upper envelope is due to central gas depletion by peak star formation and outflows while inflow from the shrunken gas disc is suppressed. an upturn at the lower envelope can occur once the extended disc has been replenished by fresh gas and a new compaction can be triggered, namely as long as the replenishment time is shorter than the depletion time. the mechanisms of gas compaction, depletion, and replenishment confine the sfgs to the narrow (±0.3 dex) ms. full quenching occurs in massive haloes (mvir > 1011.5 m⊙) and/or at low redshifts (z < 3), where the replenishment time is long compared to the depletion time, explaining the observed bending down of the ms at the massive end. | the confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment |
context. the public european southern observatory spectroscopic survey of transient objects (pessto) began as a public spectroscopic survey in april 2012. pessto classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. pessto runs for nine months of the year, january - april and august - december inclusive, and typically has allocations of 10 nights per month.aims: we describe the data reduction strategy and data products that are publicly available through the eso archive as the spectroscopic survey data release 1 (ssdr1).methods: pessto uses the new technology telescope with the instruments efosc2 and sofi to provide optical and nir spectroscopy and imaging. we target supernovae and optical transients brighter than 20.5m for classification. science targets are selected for follow-up based on the pessto science goal of extending knowledge of the extremes of the supernova population. we use standard efosc2 set-ups providing spectra with resolutions of 13-18 å between 3345-9995 å. a subset of the brighter science targets are selected for sofi spectroscopy with the blue and red grisms (0.935-2.53 μm and resolutions 23-33 å) and imaging with broadband jhks filters.results: this first data release (ssdr1) contains flux calibrated spectra from the first year (april 2012-2013). a total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via wiserep). the data in ssdr1 replace those released spectra. they have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard eso phase 3 formats. we estimate the absolute accuracy of the flux calibrations for efosc2 across the whole survey in ssdr1 to be typically ~15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. the standard nir reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying jhks imaging can improve this. whenever possible, reduced sofi images are provided to allow this.conclusions: future data releases will focus on improving the automated flux calibration of the data products. the rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey. based on observations collected at the european organisation for astronomical research in the southern hemisphere, chile, as part of programme 188.d-3003 (pessto). http://www.pessto.org | pessto: survey description and products from the first data release by the public eso spectroscopic survey of transient objects |
the gravitational-wave astronomical revolution began in 2015 with ligo's observation of the coalescence of two stellar-mass black holes. over the coming decades, ground-based detectors like laser interferometer gravitational-wave observatory (ligo), virgo and kagra will extend their reach, discovering thousands of stellar-mass binaries. in the 2030s, the space-based laser interferometer space antenna (lisa) will enable gravitational-wave observations of the massive black holes in galactic centres. between ground-based observatories and lisa lies the unexplored dhz gravitational-wave frequency band. here, we show the potential of a decihertz observatory (do) which could cover this band, and complement discoveries made by other gravitational-wave observatories. the dhz range is uniquely suited to observation of intermediate-mass (∼102-104m⊙) black holes, which may form the missing link between stellar-mass and massive black holes, offering an opportunity to measure their properties. dos will be able to detect stellar-mass binaries days to years before they merge and are observed by ground-based detectors, providing early warning of nearby binary neutron star mergers, and enabling measurements of the eccentricity of binary black holes, providing revealing insights into their formation. observing dhz gravitational-waves also opens the possibility of testing fundamental physics in a new laboratory, permitting unique tests of general relativity (gr) and the standard model of particle physics. overall, a do would answer outstanding questions about how black holes form and evolve across cosmic time, open new avenues for multimessenger astronomy, and advance our understanding of gravitation, particle physics and cosmology. | the missing link in gravitational-wave astronomy: discoveries waiting in the decihertz range |
in the past five years, deep imaging campaigns conducted with the hubble space telescope (hst) and ground-based observatories have delivered large samples of galaxies at 6.5<z<10, providing our first glimpse of the census of star formation activity in what is thought to be the heart of the reionization era. the space density of luminous galaxies has been shown to decrease by 15-20× over 4<z<8. over this same redshift interval, the faint-end slope of the uv luminosity function becomes steeper (α≃-2.0 at z≃7-8), revealing a dominant population of low-luminosity galaxies. analysis of multiwavelength imaging from hst and the spitzer space telescope demonstrates that z>6 uv-selected galaxies are relatively compact with blue uv continuum slopes, low stellar masses, and large specific star formation rates. in the last year, alma (the atacama large millimeter array) and ground-based infrared spectrographs have begun to complement this picture, revealing minimal dust obscuration and hard radiation fields, and providing evidence for metal-poor ionized gas. weak low-ionization absorption lines suggest a patchy distribution of neutral gas surrounds o and b stars, possibly aiding in the escape of ionizing radiation. gamma ray burst afterglows and lyman-α surveys have provided evidence that the intergalactic medium (igm) evolves from mostly ionized at z≃6-6.5 ([formula: see text]) to considerably neutral at z≃7-8 ([formula: see text]). the reionization history that emerges from considering the uv output of galaxies over 6<z<10 is consistent with these constraints on the igm ionization state. the latest measurements suggest that galaxies can complete reionization by z≃6 and reproduce the thomson scattering optical depth faced by cosmic microwave background photons if the luminosity function extends ≃4 mag below current surveys and a moderate fraction ([formula: see text]) of ionizing radiation escapes from galaxies. | galaxies in the first billion years after the big bang |
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