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context. previous theoretical works on planet formation around low-mass stars have often been limited to large planets and individual systems. as current surveys routinely detect planets down to terrestrial size in these systems, models have shifted toward a more holistic approach that reflects their diverse architectures.aims: here, we investigate planet formation around low-mass stars and identify differences in the statistical distribution of modeled planets. we compare the synthetic planet populations to observed exoplanets and we discuss the identified trends.methods: we used the generation iii bern global model of planet formation and evolution to calculate synthetic populations, while varying the central star from solar-like stars to ultra-late m dwarfs. this model includes planetary migration, n-body interactions between embryos, accretion of planetesimals and gas, and the long-term contraction and loss of the gaseous atmospheres.results: we find that temperate, earth-sized planets are most frequent around early m dwarfs (0.3 m⊙-0.5 m⊙) and that they are more rare for solar-type stars and late m dwarfs. the planetary mass distribution does not linearly scale with the disk mass. the reason behind this is attributed to the emergence of giant planets for m⋆ ≥ 0.5 m⊙, which leads to the ejection of smaller planets. given a linear scaling of the disk mass with stellar mass, the formation of earth-like planets is limited by the available amount of solids for ultra-late m dwarfs. for m⋆ ≥ 0.3 m⊙, however, there is sufficient mass in the majority of systems, leading to a similar amount of exo-earths going from m to g dwarfs. in contrast, the number of super-earths and larger planets increases monotonically with stellar mass. we further identify a regime of disk parameters that reproduces observed m-dwarf systems such as trappist-1. however, giant planets around late m dwarfs, such as gj 3512b, only form when type i migration is substantially reduced.conclusions: we are able to quantify the stellar mass dependence of multi-planet systems using global simulations of planet formation and evolution. the results fare well in comparison to current observational data and predict trends that can be tested with future observations. the data supporting these findings are available online at http://dace.unige.ch under section "formation & evolution". | the new generation planetary population synthesis (ngpps). iv. planetary systems around low-mass stars |
the highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. in particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. three such `pulsar timing arrays' (ptas) have been set up around the world over the past decades and collectively form the `international' pta (ipta). in this paper, we describe the first joint analysis of the data from the three regional ptas, i.e. of the first ipta data set. we describe the available pta data, the approach presently followed for its combination and suggest improvements for future pta research. particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. we identify and describe in detail several factors that complicate ipta research and provide recommendations for future pulsar timing efforts. the first ipta data release presented here (and available online) is used to demonstrate the ipta's potential of improving upon gravitational-wave limits placed by individual ptas by a factor of ∼2 and provides a 2σ limit on the dimensionless amplitude of a stochastic gravitational-wave background of 1.7 × 10-15 at a frequency of 1 yr-1. this is 1.7 times less constraining than the limit placed by shannon et al., due mostly to the more recent, high-quality data they used. | the international pulsar timing array: first data release |
exploring dark matter via observations of extreme astrophysical environments -- defined here as heavy compact objects such as white dwarfs, neutron stars, and black holes, as well as supernovae and compact object merger events -- has been a major field of growth since the last snowmass process. theoretical work has highlighted the utility of current and near-future observatories to constrain novel dark matter parameter space across the full mass range. this includes gravitational wave instruments and observatories spanning the electromagnetic spectrum, from radio to gamma-rays. while recent searches already provide leading sensitivity to various dark matter models, this work also highlights the need for theoretical astrophysics research to better constrain the properties of these extreme astrophysical systems. the unique potential of these search signatures to probe dark matter adds motivation to proposed next-generation astronomical and gravitational wave instruments. | dark matter in extreme astrophysical environments |
the trappist-1 system is remarkable for its seven planets that are similar in size, mass, density and stellar heating to the rocky planets venus, earth and mars in the solar system1. all the trappist-1 planets have been observed with transmission spectroscopy using the hubble or spitzer space telescopes, but no atmospheric features have been detected or strongly constrained2-5. trappist-1 b is the closest planet to the m-dwarf star of the system, and it receives four times as much radiation as earth receives from the sun. this relatively large amount of stellar heating suggests that its thermal emission may be measurable. here we present photometric secondary eclipse observations of the earth-sized exoplanet trappist-1 b using the f1500w filter of the mid-infrared instrument on the james webb space telescope (jwst). we detect the secondary eclipses in five separate observations with 8.7σ confidence when all data are combined. these measurements are most consistent with re-radiation of the incident flux of the trappist-1 star from only the dayside hemisphere of the planet. the most straightforward interpretation is that there is little or no planetary atmosphere redistributing radiation from the host star and also no detectable atmospheric absorption of carbon dioxide (co2) or other species. | thermal emission from the earth-sized exoplanet trappist-1 b using jwst |
we present and discuss the results of the herschel gould belt survey (hgbs) observations in an 11 deg2 area of the aquila molecular cloud complex at d 260 pc, imaged with the spire and pacs photometric cameras in parallel mode from 70 μm to 500 μm. using the multi-scale, multi-wavelength source extraction algorithm getsources, we identify a complete sample of starless dense cores and embedded (class 0-i) protostars in this region, and analyze their global properties and spatial distributions. we find a total of 651 starless cores, 60% ± 10% of which are gravitationally bound prestellar cores, and they will likely form stars inthe future. we also detect 58 protostellar cores. the core mass function (cmf) derived for the large population of prestellar cores is very similar in shape to the stellar initial mass function (imf), confirming earlier findings on a much stronger statistical basis and supporting the view that there is a close physical link between the stellar imf and the prestellar cmf. the global shift in mass scale observed between the cmf and the imf is consistent with a typical star formation efficiency of 40% at the level of an individual core. by comparing the numbers of starless cores in various density bins to the number of young stellar objects (ysos), we estimate that the lifetime of prestellar cores is 1 myr, which is typically 4 times longer than the core free-fall time, and that it decreases with average core density. we find a strong correlation between the spatial distribution of prestellar cores and the densest filaments observed in the aquila complex. about 90% of the herschel-identified prestellar cores are located above a background column density corresponding to av 7, and 75% of them lie within filamentary structures with supercritical masses per unit length ≳16 m⊙/pc. these findings support a picture wherein the cores making up the peak of the cmf (and probably responsible for the base of the imf) result primarily from the gravitational fragmentation of marginally supercritical filaments. given that filaments appear to dominate the mass budget of dense gas at av> 7, our findings also suggest that the physics of prestellar core formation within filaments is responsible for a characteristic "efficiency" {sfr/m_dense ∼ 5+2-2 × 10-8 yr-1} for the star formation process in dense gas. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa.figures 18, 19, and appendices are available in electronic form at http://www.aanda.orgherschel column density and temperature maps (fits format) and full tables a.1 and a.2 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/584/a91 | a census of dense cores in the aquila cloud complex: spire/pacs observations from the herschel gould belt survey |
context. in the last 15 years different ground-based spectroscopic surveys have been started (and completed) with the general aim of delivering stellar parameters and elemental abundances for large samples of galactic stars, complementing gaia astrometry. among those surveys, the gaia-eso public spectroscopic survey, the only one performed on a 8m class telescope, was designed to target 100 000 stars using flames on the eso vlt (both giraffe and uves spectrographs), covering all the milky way populations, with a special focus on open star clusters.aims: this article provides an overview of the survey implementation (observations, data quality, analysis and its success, data products, and releases), of the open cluster survey, of the science results and potential, and of the survey legacy. a companion article reviews the overall survey motivation, strategy, giraffe pipeline data reduction, organisation, and workflow.methods: we made use of the information recorded and archived in the observing blocks; during the observing runs; in a number of relevant documents; in the spectra and master catalogue of spectra; in the parameters delivered by the analysis nodes and the working groups; in the final catalogue; and in the science papers. based on these sources, we critically analyse and discuss the output and products of the survey, including science highlights. we also determined the average metallicities of the open clusters observed as science targets and of a sample of clusters whose spectra were retrieved from the eso archive.results: the gaia-eso survey has determined homogeneous good-quality radial velocities and stellar parameters for a large fraction of its more than 110 000 unique target stars. elemental abundances were derived for up to 31 elements for targets observed with uves. lithium abundances are delivered for about 1/3 of the sample. the analysis and homogenisation strategies have proven to be successful; several science topics have been addressed by the gaia-eso consortium and the community, with many highlight results achieved.conclusions: the final catalogue will be released through the eso archive in the first half of 2022, including the complete set of advanced data products. in addition to these results, the gaia-eso survey will leave a very important legacy, for several aspects and for many years to come. table b.5 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg. fr/viz-bin/cat/j/a+a/666/a121 | the gaia-eso public spectroscopic survey: implementation, data products, open cluster survey, science, and legacy |
the diffuse interstellar bands are absorption lines seen towards reddened stars. none of the molecules responsible for these bands have been conclusively identified. two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from c60+ molecules (ref. 3), on the basis of the proximity of these wavelengths to the absorption bands of c60+ measured in a neon matrix. confirmation of this assignment requires the gas-phase spectrum of c60+. here we report laboratory spectroscopy of c60+ in the gas phase, cooled to 5.8 kelvin. the absorption spectrum has maxima at 9,632.7 +/- 0.1 ångströms and 9,577.5 +/- 0.1 ångströms, and the full widths at half-maximum of these bands are 2.2 +/- 0.2 ångströms and 2.5 +/- 0.2 ångströms, respectively. we conclude that we have positively identified the diffuse interstellar bands at 9,632 ångströms and 9,577 ångströms as arising from c60+ in the interstellar medium. | laboratory confirmation of c60+ as the carrier of two diffuse interstellar bands |
the mass function of neutron stars (nss) contains information about the late evolution of massive stars, the supernova explosion mechanism, and the equation-of-state of cold, nuclear matter beyond the nuclear saturation density. a number of recent ns mass measurements in binary millisecond pulsar (msp) systems increase the fraction of massive nss (with $m > 1.8$ m$_{\odot}$) to $\sim 20\% $ of the observed population. in light of these results, we employ a bayesian framework to revisit the msp mass distribution. we find that a single gaussian model does not sufficiently describe the observed population. we test alternative empirical models and infer that the msp mass distribution is strongly asymmetric. the diversity in spin and orbital properties of high-mass nss suggests that this is most likely not a result of the recycling process, but rather reflects differences in the ns birth masses. the asymmetry is best accounted for by a bimodal distribution with a low mass component centred at $1.393_{-0.029}^{+0.031}$ m$_{\odot}$ and dispersed by $0.064_{-0.025}^{+0.064}$ m$_{\odot}$, and a high-mass component with a mean of $1.807_{-0.132}^{+0.081}$ and a dispersion of $0.177_{-0.072}^{+0.115}$ m$_{\odot}$. we also establish a lower limit of $m_{max} \ge 2.018$ m$_{\odot}$ at 98% c.l. for the maximum ns mass, from the absence of a high-mass truncation in the observed masses. using our inferred model, we find that the measurement of 350 msp masses, expected after the conclusion of pulsar surveys with the square-kilometre array, can result in a precise localization of a maximum mass up to 2.15 m$_{\odot}$, with a 5% accuracy. finally, we identify possible massive nss within the known pulsar population and discuss birth masses of msps. | the millisecond pulsar mass distribution: evidence for bimodality and constraints on the maximum neutron star mass |
for most of their existence, stars are fuelled by the fusion of hydrogen into helium. fusion proceeds via two processes that are well understood theoretically: the proton-proton (pp) chain and the carbon-nitrogen-oxygen (cno) cycle1,2. neutrinos that are emitted along such fusion processes in the solar core are the only direct probe of the deep interior of the sun. a complete spectroscopic study of neutrinos from the pp chain, which produces about 99 per cent of the solar energy, has been performed previously3; however, there has been no reported experimental evidence of the cno cycle. here we report the direct observation, with a high statistical significance, of neutrinos produced in the cno cycle in the sun. this experimental evidence was obtained using the highly radiopure, large-volume, liquid-scintillator detector of borexino, an experiment located at the underground laboratori nazionali del gran sasso in italy. the main experimental challenge was to identify the excess signal—only a few counts per day above the background per 100 tonnes of target—that is attributed to interactions of the cno neutrinos. advances in the thermal stabilization of the detector over the last five years enabled us to develop a method to constrain the rate of bismuth-210 contaminating the scintillator. in the cno cycle, the fusion of hydrogen is catalysed by carbon, nitrogen and oxygen, and so its rate—as well as the flux of emitted cno neutrinos—depends directly on the abundance of these elements in the solar core. this result therefore paves the way towards a direct measurement of the solar metallicity using cno neutrinos. our findings quantify the relative contribution of cno fusion in the sun to be of the order of 1 per cent; however, in massive stars, this is the dominant process of energy production. this work provides experimental evidence of the primary mechanism for the stellar conversion of hydrogen into helium in the universe. | experimental evidence of neutrinos produced in the cno fusion cycle in the sun |
the halo of the milky way provides a laboratory to study the properties of the shocked hot gas that is predicted by models of galaxy formation. there is observational evidence of energy injection into the halo from past activity in the nucleus of the milky way1-4; however, the origin of this energy (star formation or supermassive-black-hole activity) is uncertain, and the causal connection between nuclear structures and large-scale features has not been established unequivocally. here we report soft-x-ray-emitting bubbles that extend approximately 14 kiloparsecs above and below the galactic centre and include a structure in the southern sky analogous to the north polar spur. the sharp boundaries of these bubbles trace collisionless and non-radiative shocks, and corroborate the idea that the bubbles are not a remnant of a local supernova5 but part of a vast galaxy-scale structure closely related to features seen in γ-rays6. large energy injections from the galactic centre7 are the most likely cause of both the γ-ray and x-ray bubbles. the latter have an estimated energy of around 1056 erg, which is sufficient to perturb the structure, energy content and chemical enrichment of the circumgalactic medium of the milky way. | detection of large-scale x-ray bubbles in the milky way halo |
we use the illustris simulation to study the relative contributions of in situ star formation and stellar accretion to the build-up of galaxies over an unprecedentedly wide range of masses (m* = 109-1012 m⊙), galaxy types, environments, and assembly histories. we find that the `two-phase' picture of galaxy formation predicted by some models is a good approximation only for the most massive galaxies in our simulation - namely, the stellar mass growth of galaxies below a few times 1011 m⊙ is dominated by in situ star formation at all redshifts. the fraction of the total stellar mass of galaxies at z = 0 contributed by accreted stars shows a strong dependence on galaxy stellar mass, ranging from about 10 per cent for milky way-sized galaxies to over 80 per cent for m* ≈ 1012 m⊙ objects, yet with a large galaxy-to-galaxy variation. at a fixed stellar mass, elliptical galaxies and those formed at the centres of younger haloes exhibit larger fractions of ex situ stars than disc-like galaxies and those formed in older haloes. on average, ∼50 per cent of the ex situ stellar mass comes from major mergers (stellar mass ratio μ > 1/4), ∼20 per cent from minor mergers (1/10 < μ < 1/4), ∼20 per cent from very minor mergers (μ < 1/10), and ∼10 per cent from stars that were stripped from surviving galaxies (e.g. flybys or ongoing mergers). these components are spatially segregated, with in situ stars dominating the innermost regions of galaxies, and ex situ stars being deposited at larger galactocentric distances in order of decreasing merger mass ratio. | the stellar mass assembly of galaxies in the illustris simulation: growth by mergers and the spatial distribution of accreted stars |
we present a new version of the galform semi-analytical model of galaxy formation. this brings together several previous developments of galform into a single unified model, including a different initial mass function (imf) in quiescent star formation and in starbursts, feedback from active galactic nuclei suppressing gas cooling in massive haloes, and a new empirical star formation law in galaxy discs based on their molecular gas content. in addition, we have updated the cosmology, introduced a more accurate treatment of dynamical friction acting on satellite galaxies, and updated the stellar population model. the new model is able to simultaneously explain both the observed evolution of the k-band luminosity function and stellar mass function, and the number counts and redshift distribution of sub-mm galaxies selected at 850 μm. this was not previously achieved by a single physical model within the λcold dark matter framework, but requires having an imf in starbursts that is somewhat top-heavy. the new model is tested against a wide variety of observational data covering wavelengths from the far-uv to sub-mm, and redshifts from z = 0 to 6, and is found to be generally successful. these observations include the optical and near-infrared (ir) luminosity functions, h i mass function, fraction of early type galaxies, tully-fisher, metallicity-luminosity and size-luminosity relations at z = 0, as well as far-ir number counts, and far-uv luminosity functions at z ∼ 3-6. discrepancies are, however, found in galaxy sizes and metallicities at low luminosities, and in the abundance of low-mass galaxies at high-z, suggesting the need for a more sophisticated model of supernova feedback. | a unified multiwavelength model of galaxy formation |
to date, modern three-dimensional (3d) supernova (sn) simulations have not demonstrated that explosion energies of 1051 erg (=1 bethe=1 b) or more are possible for neutrino-driven sne of non/slow-rotating m < 20 m⊙ progenitors. we present the first such model, considering a nonrotating, solar-metallicity 18.88 m⊙ progenitor, whose final 7 minutes of convective oxygen-shell burning were simulated in 3d and showed a violent oxygen-neon shell merger prior to collapse. a large set of 3d sn models was computed with the prometheus-vertex code, whose improved convergence of the two-moment equations with boltzmann closure allows now to fully exploit the implicit neutrino-transport treatment. nuclear burning is treated with a 23-species network. we vary the angular grid resolution and consider different nuclear equations of state and muon formation in the proto-neutron star (pns), which requires six-species transport with coupling of all neutrino flavors across all energy-momentum groups. elaborate neutrino transport was applied until ~2 s after bounce. in one case, the simulation was continued to >7 s with an approximate treatment of neutrino effects that allows for seamless continuation without transients. a spherically symmetric neutrino-driven wind does not develop. instead, accretion downflows to the pns and outflows of neutrino-heated matter establish a monotonic rise of the explosion energy until ~7 s post-bounce, when the outgoing shock reaches ~50,000 km and enters the he layer. the converged value of the explosion energy at infinity (with overburden subtracted) is ~1 b and the ejected 56ni mass ≲0.087 m⊙, both within a few 10% of the sn 1987a values. the final ns mass and kick are ~1.65 m⊙ and >450 km s-1, respectively. | self-consistent 3d supernova models from -7 minutes to +7 s: a 1-bethe explosion of a 19 m⊙ progenitor |
this paper is concerned with offline reinforcement learning (rl), which learns using pre-collected data without further exploration. effective offline rl would be able to accommodate distribution shift and limited data coverage. however, prior algorithms or analyses either suffer from suboptimal sample complexities or incur high burn-in cost to reach sample optimality, thus posing an impediment to efficient offline rl in sample-starved applications. we demonstrate that the model-based (or "plug-in") approach achieves minimax-optimal sample complexity without burn-in cost for tabular markov decision processes (mdps). concretely, consider a finite-horizon (resp. $\gamma$-discounted infinite-horizon) mdp with $s$ states and horizon $h$ (resp. effective horizon $\frac{1}{1-\gamma}$), and suppose the distribution shift of data is reflected by some single-policy clipped concentrability coefficient $c^{\star}_{\text{clipped}}$. we prove that model-based offline rl yields $\varepsilon$-accuracy with a sample complexity of \[ \begin{cases} \frac{h^{4}sc_{\text{clipped}}^{\star}}{\varepsilon^{2}} & (\text{finite-horizon mdps}) \frac{sc_{\text{clipped}}^{\star}}{(1-\gamma)^{3}\varepsilon^{2}} & (\text{infinite-horizon mdps}) \end{cases} \] up to log factor, which is minimax optimal for the entire $\varepsilon$-range. the proposed algorithms are ``pessimistic'' variants of value iteration with bernstein-style penalties, and do not require sophisticated variance reduction. our analysis framework is established upon delicate leave-one-out decoupling arguments in conjunction with careful self-bounding techniques tailored to mdps. | settling the sample complexity of model-based offline reinforcement learning |
in this work, we shall exhaustively study the effects of modified gravity on the energy spectrum of the primordial gravitational waves background. s. weinberg has also produced significant works related to the primordial gravitational waves, with the most important one being the effects of neutrinos on primordial gravitational waves. with this short review, our main aim is to gather all the necessary information for studying the effects of modified gravity on primordial gravitational waves in a concrete and quantitative way and in a single paper. after reviewing all the necessary techniques for extracting the general relativistic energy spectrum, and how to obtain, in a wkb way, the modified gravity damping or amplifying factor, we concentrate on specific forms of modified gravity of interest. the most important parameter involved for the calculation of the effects of modified gravity on the energy spectrum is the parameter am, which we calculate for the cases of f(r,ϕ) gravity, chern–simons-corrected f(r,ϕ) gravity, einstein–gauss–bonnet-corrected f(r,ϕ) gravity, and higher derivative extended einstein–gauss–bonnet-corrected f(r,ϕ) gravity. the exact form of am is presented explicitly for the first time in the literature. with regard to einstein–gauss–bonnet-corrected f(r,ϕ) gravity, and higher derivative extended einstein–gauss–bonnet-corrected f(r,ϕ) gravity theories, we focus on the case in which the gravitational wave propagating speed is equal to that of light in a vacuum. we provide expressions for am expressed in terms of the cosmic time and in terms of the redshift, which can be used directly for the numerical calculation of the effect of modified gravity on the primordial gravitational wave energy spectrum. | spectrum of primordial gravitational waves in modified gravities: a short overview |
a new collection of photodissociation and photoionisation cross sections for 102 atoms and molecules of astrochemical interest has been assembled, along with a brief review of the basic physical processes involved. these have been used to calculate dissociation and ionisation rates, with uncertainties, in a standard ultraviolet interstellar radiation field (isrf) and for other wavelength-dependent radiation fields, including cool stellar and solar radiation, lyman-α dominated radiation, and a cosmic-ray induced ultraviolet flux. the new isrf rates generally agree within 30% with our previous compilations, with a few notable exceptions. comparison with other databases such as phidrates is made. the reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic c, and self-shielding column densities. the relative importance of these shielding types depends on the atom or molecule in question and the assumed dust optical properties. all of the new data are publicly available from the leiden photodissociation and ionisation database. sensitivity of the calculated rates to variation of temperature and isotope, and uncertainties in measured or calculated cross sections, are tested and discussed. tests were conducted on the new rates with an interstellar-cloud chemical model, and find general agreement (within a factor of two) in abundances obtained with the previous iteration of the leiden database assuming an isrf, and order-of-magnitude variations assuming various kinds of stellar radiation. the newly parameterised dust-shielding factors makes a factor-of-two difference to many atomic and molecular abundances relative to parameters currently in the udfa and kida astrochemical reaction databases. the newly-calculated cosmic-ray induced photodissociation and ionisation rates differ from current standard values up to a factor of 5. under high temperature and cosmic-ray-flux conditions the new rates alter the equilibrium abundances of abundant dark cloud abundances by up to a factor of two. the partial cross sections for h2o and nh3 photodissociation forming oh, o, nh2 and nh are also evaluated and lead to radiation-field-dependent branching ratios. | photodissociation and photoionisation of atoms and molecules of astrophysical interest |
the generation of magnetic field in an electrically conducting fluid generally involves the complicated nonlinear interaction of flow turbulence, rotation and field. this dynamo process is of great importance in geophysics, planetary science and astrophysics, since magnetic fields are known to play a key role in the dynamics of these systems. this paper gives an introduction to dynamo theory for the fluid dynamicist. it proceeds by laying the groundwork, introducing the equations and techniques that are at the heart of dynamo theory, before presenting some simple dynamo solutions. the problems currently exercising dynamo theorists are then introduced, along with the attempts to make progress. the paper concludes with the argument that progress in dynamo theory will be made in the future by utilising and advancing some of the current breakthroughs in neutral fluid turbulence such as those in transition, self-sustaining processes, turbulence/mean-flow interaction, statistical methods and maintenance and loss of balance. | the turbulent dynamo |
the rest-frame uv recombination emission line ly$\alpha$ can be powered by ionising photons from young massive stars in star forming galaxies, but its ability to be resonantly scattered by neutral gas complicates its interpretation. for reionization era galaxies, a neutral intergalactic medium (igm) will scatter ly$\alpha$ from the line of sight, making ly$\alpha$ a useful probe of the neutral fraction evolution. here, we explore ly$\alpha$ in jwst/nirspec spectra from the ongoing jades programme, which targets hundreds of galaxies in the well-studied goods-s and goods-n fields. these sources are uv-faint ($-20.4<\rm m_{\rm uv}<-16.4$), and thus represent a poorly-explored class of galaxies. the low spectral resolution ($r\sim100$) spectra of a subset of 84 galaxies in goods-s with $z_{spec}>5.6$ (as derived with optical lines) are fit with line and continuum models, in order to search for significant line emission. through exploration of the r100 data, we find evidence for ly$\alpha$ in 17 sources. this sample allows us to place observational constraints on the fraction of galaxies with ly$\alpha$ emission in the redshift range $5.6<z<7.5$, with a decrease from $z=6$ to $z=7$. we also find a positive correlation between ly$\alpha$ equivalent width and m$_{uv}$, as seen in other samples. these results are used to estimate the neutral gas fraction at $z\sim7$, agreeing with previous results ($x_{hi}\sim0.5-0.9$). | jades: the emergence and evolution of ly$\\alpha$ emission and constraints on the igm neutral fraction |
most stars become white dwarfs after they have exhausted their nuclear fuel (the sun will be one such). between one-quarter and one-half of white dwarfs have elements heavier than helium in their atmospheres, even though these elements ought to sink rapidly into the stellar interiors (unless they are occasionally replenished). the abundance ratios of heavy elements in the atmospheres of white dwarfs are similar to the ratios in rocky bodies in the solar system. this fact, together with the existence of warm, dusty debris disks surrounding about four per cent of white dwarfs, suggests that rocky debris from the planetary systems of white-dwarf progenitors occasionally pollutes the atmospheres of the stars. the total accreted mass of this debris is sometimes comparable to the mass of large asteroids in the solar system. however, rocky, disintegrating bodies around a white dwarf have not yet been observed. here we report observations of a white dwarf--wd 1145+017--being transited by at least one, and probably several, disintegrating planetesimals, with periods ranging from 4.5 hours to 4.9 hours. the strongest transit signals occur every 4.5 hours and exhibit varying depths (blocking up to 40 per cent of the star's brightness) and asymmetric profiles, indicative of a small object with a cometary tail of dusty effluent material. the star has a dusty debris disk, and the star's spectrum shows prominent lines from heavy elements such as magnesium, aluminium, silicon, calcium, iron, and nickel. this system provides further evidence that the pollution of white dwarfs by heavy elements might originate from disrupted rocky bodies such as asteroids and minor planets. | a disintegrating minor planet transiting a white dwarf |
we assess the science reach and technical feasibility of a satellite mission based on precision atomic sensors configured to detect gravitational radiation. conceptual advances in the past three years indicate that a two-satellite constellation with science payloads consisting of atomic sensors based on laser cooled atomic sr can achieve scientifically interesting gravitational wave strain sensitivities in a frequency band between the lisa and ligo detectors, roughly 30 mhz to 10 hz. the discovery potential of the proposed instrument ranges from from observation of new astrophysical sources (e.g. black hole and neutron star binaries) to searches for cosmological sources of stochastic gravitational radiation and searches for dark matter. | mid-band gravitational wave detection with precision atomic sensors |
we make an in-depth comparison of the illustristng cosmological simulations with observed quenched fractions of central and satellite galaxies, for mstars = 109-12 m⊙ at 0 ≤ z ≤ 3. we show how measurement choices [aperture, quenched definition, and star formation rate (sfr) indicator time-scale], as well as sample selection issues (projection effects, satellite/central misclassification, and host mass distribution sampling), impact this comparison. the quenched definition produces differences of up to 70 (30) percentage points for centrals (satellites) above ~1010.5 m⊙. at z ≳ 2, a larger aperture within which sfr is measured suppresses the quenched fractions by up to ~50 percentage points. proper consideration of the stellar and host mass distributions is crucial: naive comparisons to volume-limited samples from simulations lead to misinterpretation of the quenched fractions as a function of redshift by up to 20 percentage points. including observational uncertainties to theoretical values of mstars and sfr changes the quenched fraction values and their trend and/or slope with mass. taking projected rather than three-dimensional distances for satellites decreases the quenched fractions by up to 10 per cent. tng produces quenched fractions for both centrals and satellites broadly consistent with observations and predicts up to ~80 (90) per cent of quenched centrals at z = 0 (z = 2), in line with recent observations, and higher than other theoretical models. the quantitative agreement of tng and sloan digital sky survey for satellite quenched fractions in groups and clusters depends strongly on the galaxy and host mass range. our mock comparison highlights the importance of properly accounting for observational effects and biases. | quenched fractions in the illustristng simulations: comparison with observations and other theoretical models |
we investigate the nature of the double color-magnitude sequence observed in the gaia dr2 hr diagram of stars with high transverse velocities. the stars in the reddest-color sequence are likely dominated by the dynamically hot tail of the thick disk population. information from nissen & schuster and from the apogee survey suggests that stars in the blue-color sequence have elemental abundance patterns that can be explained by this population having a relatively low star formation efficiency during its formation. in dynamical and orbital spaces, such as the “toomre diagram,” the two sequences show a significant overlap, but with a tendency for stars on the blue-color sequence to dominate regions with no or retrograde rotation and high total orbital energy. in the plane defined by the maximal vertical excursion of the orbits versus their apocenters, stars of both sequences redistribute into discrete wedges. we conclude that stars that are typically assigned to the halo in the solar vicinity are actually both accreted stars lying along the blue sequence in the hr diagram, and the low rotational velocity tail of the old galactic disk, possibly dynamically heated by past accretion events. our results imply that a halo population formed in situ and responsible for the early chemical enrichment prior to the formation of the thick disk has yet to be robustly identified, and that what has been defined as the stars of the in situ stellar halo of the galaxy may in fact be fossil records of its last significant merger. | in disguise or out of reach: first clues about in situ and accreted stars in the stellar halo of the milky way from gaia dr2 |
we report the discovery of an extreme galaxy overdensity at $z = 5.4$ in the goods-s field using jwst/nircam imaging from jades and jems alongside jwst/nircam wide field slitless spectroscopy from fresco. we identified potential members of the overdensity using hst+jwst photometry spanning $\lambda = 0.4-5.0\ \mu\mathrm{m}$. these data provide accurate and well-constrained photometric redshifts down to $m \approx 29-30\,\mathrm{mag}$. we subsequently confirmed $n = 81$ galaxies at $5.2 < z < 5.5$ using jwst slitless spectroscopy over $\lambda = 3.9-5.0\ \mu\mathrm{m}$ through a targeted line search for $\mathrm{h} \alpha$ around the best-fit photometric redshift. we verified that $n = 42$ of these galaxies reside in the field while $n = 39$ galaxies reside in a density around $\sim 10$ times that of a random volume. stellar populations for these galaxies were inferred from the photometry and used to construct the star-forming main sequence, where protocluster members appeared more massive and exhibited earlier star formation (and thus older stellar populations) when compared to their field galaxy counterparts. we estimate the total halo mass of this large-scale structure to be $12.6 \lesssim \mathrm{log}_{10} \left( m_{\mathrm{halo}}/m_{\odot} \right) \lesssim 12.8$ using an empirical stellar mass to halo mass relation, which is likely an underestimate as a result of incompleteness. our discovery demonstrates the power of jwst at constraining dark matter halo assembly and galaxy formation at very early cosmic times. | the jwst advanced deep extragalactic survey: discovery of an extreme galaxy overdensity at $z = 5.4$ with jwst/nircam in goods-s |
with an instantaneous view of 70% of the sky, the fermi gamma-ray burst monitor (gbm) is an excellent partner in the search for electromagnetic counterparts to gravitational-wave (gw) events. gbm observations at the time of the laser interferometer gravitational-wave observatory (ligo) event gw150914 reveal the presence of a weak transient above 50 kev, 0.4 s after the gw event, with a false-alarm probability of 0.0022 (2.9σ). this weak transient lasting 1 s was not detected by any other instrument and does not appear to be connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. its localization is ill-constrained but consistent with the direction of gw150914. the duration and spectrum of the transient event are consistent with a weak short gamma-ray burst (grb) arriving at a large angle to the direction in which fermi was pointing where the gbm detector response is not optimal. if the gbm transient is associated with gw150914, then this electromagnetic signal from a stellar mass black hole binary merger is unexpected. we calculate a luminosity in hard x-ray emission between 1 kev and 10 mev of {1.8}-1.0+1.5× {10}49 erg s-1. future joint observations of gw events by ligo/virgo and fermi gbm could reveal whether the weak transient reported here is a plausible counterpart to gw150914 or a chance coincidence, and will further probe the connection between compact binary mergers and short grbs. | fermi gbm observations of ligo gravitational-wave event gw150914 |
understanding the origin of the elements has been a decades-long pursuit, with many open questions remaining. old stars found in the milky way and its dwarf satellite galaxies can provide answers because they preserve clean element abundance patterns of the nucleosynthesis processes that operated some 13 billion years ago, enabling reconstruction of the chemical evolution of the elements. this review focuses on the astrophysical signatures of heavy neutron-capture elements made in the s-, i-, and r-processes found in old stars. a highlight is the recently discovered r-process galaxy reticulum ii, which was enriched by a neutron star merger. these results show that old stars in dwarf galaxies provide a novel means to constrain the astrophysical site of the r-process, ushering in much-needed progress on this major outstanding question. this nuclear astrophysics research complements the many experimental and theoretical nuclear physics efforts into heavy-element formation, and also aligns with results on the gravitational-wave signature of neutron star mergers. | from nuclei to the cosmos: tracing heavy-element production with the oldest stars |
thomson optical depth τ measurements from planck provide new insights into the reionization of the universe. in pursuit of model-independent constraints on the properties of the ionizing sources, we determine the empirical evolution of the cosmic ionizing emissivity. we use a simple two-parameter model to map out the evolution in the emissivity at z ≳ 6 from the new planck optical depth τ measurements, from the constraints provided by quasar absorption spectra and from the prevalence of lyα emission in z ∼ 7-8 galaxies. we find the redshift evolution in the emissivity {\dot{n}}{ion}(z) required by the observations to be {({\text{}}d{{log}}10 {\dot{n}}{ion}/{dz})}z=8=-{0.15}-0.11+0.08 ({({\text{}}d{{log}}10 {\dot{n}}{ion}/{dz})}z=8=-{0.19}-0.11+0.09 for a flat prior), largely independent of the assumed clumping factor ch ii and entirely independent of the nature of the ionizing sources. the trend in {\dot{n}}{ion}(z) is well-matched by the evolution of the galaxy uv-luminosity density (d{{log}}10{ρ }{uv}/{dz}=-0.11+/- 0.04) to a magnitude limit ≳-13 mag, suggesting that galaxies are the sources that drive the reionization of the universe. the role of galaxies is further strengthened by the conversion from the uv luminosity density ρuv to {\dot{n}}{ion}(z) being possible for physically plausible values of the escape fraction fesc, the lyman-continuum photon production efficiency ξion, and faint-end cut-off mlim to the luminosity function. quasars/active galactic nuclei appear to match neither the redshift evolution nor normalization of the ionizing emissivity. based on the inferred evolution in the ionizing emissivity, we estimate that the z ∼ 10 uv-iuminosity density is 8-4+15× lower than at z ∼ 6, consistent with the observations. the present approach of contrasting the inferred evolution of the ionizing emissivity with that of the galaxy uv luminosity density adds to the growing observational evidence that faint, star-forming galaxies drive the reionization of the universe. based on observations made with the nasa/esa hubble space telescope, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | reionization after planck: the derived growth of the cosmic ionizing emissivity now matches the growth of the galaxy uv luminosity density |
the primary kepler mission provided nearly continuous monitoring of ∼200,000 objects with unprecedented photometric precision. we present the final catalog of eclipsing binary systems within the 105 deg2 kepler field of view. this release incorporates the full extent of the data from the primary mission (q0-q17 data release). as a result, new systems have been added, additional false positives have been removed, ephemerides and principal parameters have been recomputed, classifications have been revised to rely on analytical models, and eclipse timing variations have been computed for each system. we identify several classes of systems including those that exhibit tertiary eclipse events, systems that show clear evidence of additional bodies, heartbeat systems, systems with changing eclipse depths, and systems exhibiting only one eclipse event over the duration of the mission. we have updated the period and galactic latitude distribution diagrams and included a catalog completeness evaluation. the total number of identified eclipsing and ellipsoidal binary systems in the kepler field of view has increased to 2878, 1.3% of all observed kepler targets. an online version of this catalog with downloadable content and visualization tools is maintained at http://keplerebs.villanova.edu. | kepler eclipsing binary stars. vii. the catalog of eclipsing binaries found in the entire kepler data set |
in the past few years, new observations of neutron stars (nss) and ns mergers have provided a wealth of data that allow one to constrain the equation of state (eos) of nuclear matter at densities above nuclear saturation density. however, most observations were based on nss with masses of about 1.4 m⊙, probing densities up to ~three to four times the nuclear saturation density. even higher densities are probed inside massive nss such as psr j0740+6620. very recently, new radio observations provided an update to the mass estimate for psr j0740+6620, and x-ray observations by the nicer and xmm telescopes constrained its radius. based on these new measurements, we revisit our previous nuclear physics multimessenger astrophysics constraints and derive updated constraints on the eos describing the ns interior. by combining astrophysical observations of two radio pulsars, two nicer measurements, the two gravitational-wave detections gw170817 and gw190425, detailed modeling of the kilonova at 2017gfo, and the gamma-ray burst grb 170817a, we are able to estimate the radius of a typical 1.4 m⊙ ns to be ${11.94}_{-0.87}^{+0.76}\,\mathrm{km}$ at 90% confidence. our analysis allows us to revisit the upper bound on the maximum mass of nss and disfavors the presence of a strong first-order phase transition from nuclear matter to exotic forms of matter, such as quark matter, inside nss. | nuclear physics multimessenger astrophysics constraints on the neutron star equation of state: adding nicer's psr j0740+6620 measurement |
we calculate the motion of binary mass systems in gravity up to the sixth post-newtonian order to the gn3 terms ab initio using momentum expansions within an effective field theory approach based on feynman amplitudes in harmonic coordinates. for these contributions we construct a canonical transformation to isotropic and to eob coordinates at 5pn and agree with the results in the literature [1,2] by bern et al. and damour. at 6pn we compare to the hamiltonians in isotropic coordinates either given in [1] or resulting from the scattering angle. we find a canonical transformation from our hamiltonian in harmonic coordinates to [1], but not to [2]. this implies that we also agree on all observables with [1] to the sixth post-newtonian order to gn3 . | testing binary dynamics in gravity at the sixth post-newtonian level |
context. the third gaia data release (gaia dr3) contains, beyond the astrometry and photometry, dispersed light for hundreds of millions of sources from the gaia prism spectra (bp and rp) and the spectrograph (rvs). this data release opens a new window on the chemo-dynamical properties of stars in our galaxy, essential knowledge for understanding the structure, formation, and evolution of the milky way.aims: to provide insight into the physical properties of milky way stars, we used these data to produce a uniformly derived all-sky catalogue of stellar astrophysical parameters: atmospheric properties (teff, log g, [m/h], [α/fe], activity index, emission lines, and rotation), 13 chemical abundance estimates, evolution characteristics (radius, age, mass, and bolometric luminosity), distance, and dust extinction.methods: we developed the astrophysical parameter inference system (apsis) pipeline to infer astrophysical parameters of gaia objects by analysing their astrometry, photometry, bp/rp, and rvs spectra. we validate our results against those from other works in the literature, including benchmark stars, interferometry, and asteroseismology. here we assess the stellar analysis performance from apsis statistically.results: we describe the quantities we obtained, including the underlying assumptions and the limitations of our results. we provide guidance and identify regimes in which our parameters should and should not be used.conclusions: despite some limitations, this is the most extensive catalogue of uniformly inferred stellar parameters to date. they comprise teff, log g, and [m/h] (470 million using bp/rp, 6 million using rvs), radius (470 million), mass (140 million), age (120 million), chemical abundances (5 million), diffuse interstellar band analysis (half a million), activity indices (2 million), hα equivalent widths (200 million), and further classifications of spectral types (220 million) and emission-line stars (50 thousand). more precise and detailed astrophysical parameters based on epoch bp, rp, and rvs spectrophotometry are planned for the next gaia data release. our catalogue is available from the gaia archive and partner data centres https://gea.esac.esa.int/archive/documentation/gdr3/. | gaia data release 3. apsis. ii. stellar parameters |
we analyse an n-body simulation of the interaction of the milky way (mw) with a sagittarius-like dsph (sgr), looking for signatures which may be attributed to its orbital history in the phase space volume around the sun in light of gaia dr2 discoveries. the repeated impacts of sgr excite coupled vertical and radial oscillations in the disc which qualitatively, and to a large degree quantitatively are able to reproduce many features in the 6d gaia dr2 samples, from the median vr, vϕ, vz velocity maps to the local δρ(vz, z) phase-space spiral which is a manifestation of the global disc response to coupled oscillations within a given volume. the patterns in the large-scale velocity field are well described by tightly wound spirals and vertical corrugations excited from sgr's impacts. we show that the last pericentric passage of sgr resets the formation of the local present-day δρ(vz, z) spiral and situate its formation around 500-800 myr. as expected δρ(vz, z) grows in size and decreases in woundedness as a function of radius in both the gaia dr2 data and simulations. this is the first n-body model able to explain so many of the features in the data on different scales. we demonstrate how to use the full extent of the galactic disc to date perturbations dating from myr to gyr, probe the underlying potential and constrain the mass-loss history of sgr. δρ(vz, z) looks the same in all stellar populations age bins down to the youngest ages which rules out a bar buckling origin. | footprints of the sagittarius dwarf galaxy in the gaia data set |
the origins of the stellar-mass black hole mergers discovered by ligo/virgo are still unknown. here we show that if migration traps develop in the accretion disks of active galactic nuclei (agns) and promote the mergers of their captive black holes, the majority of black holes within disks will undergo hierarchical mergers—with one of the black holes being the remnant of a previous merger. 40% of agn-assisted mergers detected by ligo/virgo will include a black hole with mass ≳50 m⊙ , the mass limit from stellar core collapse. hierarchical mergers at traps in agns will exhibit black hole spins (anti)aligned with the binary's orbital axis, a distinct property from other hierarchical channels. our results suggest, although not definitively (with odds ratio of ∼1 ), that ligo's heaviest merger so far, gw170729, could have originated from this channel. | hierarchical black hole mergers in active galactic nuclei |
the asteroid terrestrial-impact last alert system (atlas) carries out its primary planetary defense mission by surveying about 13,000 deg2 at least four times per night. the resulting data set is useful for the discovery of variable stars to a magnitude limit fainter than r ∼ 18, with amplitudes down to 0.02 mag for bright objects. here, we present a data release one catalog of variable stars based on analyzing the light curves of 142 million stars that were measured at least 100 times in the first two years of atlas operations. using a lomb-scargle periodogram and other variability metrics, we identify 4.7 million candidate variables. through the space telescope science institute, we publicly release light curves for all of them, together with a vector of 169 classification features for each star. we do this at the level of unconfirmed candidate variables in order to provide the community with a large set of homogeneously analyzed photometry and to avoid pre-judging which types of objects others may find most interesting. we use machine learning to classify the candidates into 15 different broad categories based on light-curve morphology. about 10% (427,000 stars) pass extensive tests designed to screen out spurious variability detections: we label these as “probable” variables. of these, 214,000 receive specific classifications as eclipsing binaries, pulsating, mira-type, or sinusoidal variables: these are the “classified” variables. new discoveries among the probable variables number 315,000, while 141,000 of the classified variables are new, including about 10,400 pulsating variables, 2060 mira stars, and 74,700 eclipsing binaries. | a first catalog of variable stars measured by the asteroid terrestrial-impact last alert system (atlas) |
stars lose a significant amount of angular momentum between birth and death, implying that efficient processes transporting it from the core to the surface are active. space asteroseismology delivered the interior rotation rates of more than a thousand low- and intermediate-mass stars, revealing the following: single stars rotate nearly uniformly during the core-hydrogen and core-helium burning phases. stellar cores spin up to a factor of 10 faster than the envelope during the red giant phase. the angular momentum of the helium-burning core of stars is in agreement with the angular momentum of white dwarfs.observations reveal a strong decrease of core angular momentum when stars have a convective core. current theory of angular momentum transport fails to explain this. we propose improving the theory with a data-driven approach, whereby angular momentum prescriptions derived frommultidimensional (magneto)hydrodynamical simulations and theoretical considerations are continuously tested against modern observations. the tess and plato space missions have the potential to derive the interior rotation of large samples of stars, including high-mass and metal-poor stars in binaries and clusters. this will provide the powerful observational constraints needed to improve theory and simulations. | angular momentum transport in stellar interiors |
we discuss new keck/mosfire spectroscopic observations of four luminous galaxies at z ≃ 7-9 selected to have intense optical line emission by roberts-borsani et al. previous follow-up has revealed lyα in two of the four galaxies. our new mosfire observations confirm that lyα is present in the entire sample. we detect lyα emission in the galaxy cos-zs7-1, confirming its redshift as zlyα = 7.154, and we detect lyα in egs-zs8-2 at zlyα = 7.477, verifying an earlier tentative detection. the ubiquity of lyα in this sample is puzzling given that the igm is expected to be significantly neutral over 7 < z < 9. to investigate this result in more detail, we have initiated a campaign to target uv metal lines in the four lyα emitters as a probe of both the ionizing field and the lyα velocity offset at early times. here we present the detection of c iii] emission in the z = 7.73 galaxy egs-zs8-1, requiring an intense radiation field and moderately low metallicity. we argue that the radiation field is likely to affect the local environment, increasing the transmission of lyα through the galaxy. moreover, the centroid of c iii] indicates that lyα is redshifted by 340 km s-1. this velocity offset is larger than that seen in less luminous systems, providing an explanation for the transmission of lyα emission through the igm. since the transmission is further enhanced by the likelihood that such systems are also situated in large ionized bubbles, the visibility of lyα at z > 7 is expected to be strongly luminosity-dependent, with transmission accelerated in systems with intense star formation. | lyα and c iii] emission in z = 7-9 galaxies: accelerated reionization around luminous star-forming systems? |
measurement-device-independent quantum key distribution (mdi qkd) removes all detector side channels and enables secure qkd with an untrusted relay. it is suitable for building a star-type quantum access network, where the complicated and expensive measurement devices are placed in the central untrusted relay and each user requires only a low-cost transmitter, such as an integrated photonic chip. here, we experimentally demonstrate a 1.25-ghz silicon photonic chip-based mdi qkd system using polarization encoding. the photonic chip transmitters integrate the necessary encoding components for a standard qkd source. we implement random modulations of polarization states and decoy intensities, and demonstrate a finite-key secret rate of 31 bit /s over 36-db channel loss (or 180-km standard fiber). this key rate is higher than state-of-the-art mdi qkd experiments. the results show that silicon photonic chip-based mdi qkd, benefiting from miniaturization, low-cost manufacture, and compatibility with cmos microelectronics, is a promising solution for future quantum secure networks. | high-speed measurement-device-independent quantum key distribution with integrated silicon photonics |
galactic rotation curves exhibit diverse behavior in the inner regions while obeying an organizing principle; i.e., they can be approximately described by a radial acceleration relation or the modified newtonian dynamics phenomenology. we analyze the rotation curve data from the sparc sample and explicitly demonstrate that both the diversity and uniformity are naturally reproduced in a hierarchical structure formation model with the addition of dark matter self-interactions. the required concentrations of the dark matter halos are fully consistent with the concentration-mass relation predicted by the planck cosmological model. the inferred stellar mass-to-light (3.6 μ m ) ratios scatter around 0.5 m⊙/l⊙, as expected from population synthesis models, leading to a tight radial acceleration relation and a baryonic tully-fisher relation. the inferred stellar-halo mass relation is consistent with the expectations from abundance matching. these results provide compelling arguments in favor of the idea that the inner halos of galaxies are thermalized due to dark matter self-interactions. | reconciling the diversity and uniformity of galactic rotation curves with self-interacting dark matter |
we utilize medium-resolution jwst/nirspec observations of 164 galaxies at z = 2.0-9.3 from the cosmic evolution early release science (ceers) survey to investigate the evolution of the excitation and ionization properties of galaxies at high redshifts. our results represent the first statistical constraints on the evolution of the [o iii]/hβ versus [n ii]/hα, [s ii]/hα, and [o i]/hα "bpt" diagrams at z > 2.7, and the first analysis of the o32 versus r23 diagram at z > 4 with a large sample. we divide the sample into five redshift bins containing 30-40 galaxies each. the subsamples at z ~ 2.3, z ~ 3.3, and z ~ 4.5 are representative of the main-sequence star-forming galaxy population at these redshifts, while the z ~ 5.6 and z ~ 7.5 samples are likely biased toward high specific star formation rate, due to selection effects. using composite spectra, we find that each subsample at z = 2.0-6.5 falls on the same excitation sequence in the [n ii] and [s ii] bpt diagrams and the o32-r23 diagram on average, and is offset from the sequences followed by z = 0 h ii regions in the same diagrams. the direction of these offsets are consistent with high-redshift star-forming galaxies uniformly having harder ionizing spectra than typical local galaxies at fixed nebular metallicity. the similarity of the average line ratios suggests that the ionization conditions of the interstellar medium do not strongly evolve between z ~ 2 and z ~ 6. overall, the rest-optical line ratios suggest the z = 2.7-9.3 ceers/nirspec galaxies at log(m */m ⊙) ~ 7.5-10 have high degrees of ionization and moderately low oxygen abundances (~0.1-0.3 z ⊙), but are not extremely metal-poor (<0.1 z ⊙) even at z > 6.5. | excitation and ionization properties of star-forming galaxies at z = 2.0-9.3 with jwst/nirspec |
understanding strongly correlated phases of matter, such as the quark-gluon plasma and neutron stars, and in particular the dynamics of such systems, for example, following a hamiltonian quench (a sudden change in some hamiltonian parameter, such as the strength of interparticle interactions) is a fundamental challenge in modern physics. ultracold atomic gases are excellent quantum simulators for these problems, owing to their tunable interparticle interactions and experimentally resolvable intrinsic timescales. in particular, they provide access to the unitary regime, in which the interactions are as strong as allowed by quantum mechanics. this regime has been extensively studied in fermi gases1,2. the less-explored unitary bose gases3-11 offer possibilities12 such as universal physics controlled solely by the gas density13,14 and new forms of superfluidity15-17. here, through momentum- and time-resolved studies, we explore degenerate and thermal homogeneous bose gases quenched to unitarity. in degenerate samples, we observe universal post-quench dynamics in agreement with the emergence of a prethermal state18-24 with a universal non-zero condensed fraction22,24. in thermal gases, the dynamic and thermodynamic properties generally depend on the gas density and the temperature, but we find that they can still be expressed in terms of universal dimensionless functions. surprisingly, we find that the total quench-induced correlation energy is independent of the gas temperature. these measurements provide quantitative benchmarks and challenges for the theory of unitary bose gases. | universal prethermal dynamics of bose gases quenched to unitarity |
we investigate the long-term evolution of black hole accretion discs formed in neutron star mergers. these discs expel matter that contributes to an r-process kilonova, and can produce relativistic jets powering short gamma-ray bursts. here we report the results of a three-dimensional, general-relativistic magnetohydrodynamic (grmhd) simulation of such a disc which is evolved for long enough (∼9 s, or ∼6 × 105rg/c) to achieve completion of mass ejection far from the disc. our model starts with a poloidal field, and fully resolves the most unstable mode of the magnetorotational instability. we parametrize the dominant microphysics and neutrino cooling effects, and compare with axisymmetric hydrodynamic models with shear viscosity. the grmhd model ejects mass in two ways: a prompt mhd-mediated outflow and a late-time, thermally driven wind once the disc becomes advective. the total amount of unbound mass ejected (0.013 m_\odot, or {∼eq } 40{{ per cent}} of the initial torus mass) is twice as much as in hydrodynamic models, with higher average velocity (0.1c) and a broad electron fraction distribution with a lower average value (0.16). scaling the ejected fractions to a disc mass of {∼ } 0.1 m_\odot can account for the red kilonova from gw170817 but underpredicts the blue component. about {∼ } 10^{-3} m_\odot of material should undergo neutron freezout and could produce a bright kilonova precursor in the first few hours after the merger. with our idealized initial magnetic field configuration, we obtain a robust jet and sufficient ejecta with lorentz factor ∼1-10 to (over)produce the non-thermal emission from gw1708107. | long-term grmhd simulations of neutron star merger accretion discs: implications for electromagnetic counterparts |
this review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. it includes theoretical first-principle results from lattice and perturbative qcd, as well as chiral effective field theory results. from the experimental side, it includes heavy-ion collision and low-energy nuclear physics results, as well as observations from neutron stars and their mergers. the validity of different constraints, concerning specific conditions and ranges of applicability, is also provided. | theoretical and experimental constraints for the equation of state of dense and hot matter |
since protostars and planets vi (ppvi), our knowledge of the global properties of protoplanetary and debris disks, as well as of young stars, has dramatically improved. at the time of ppvi, mm-observations and optical to near-infrared spectroscopic surveys were largely limited to the taurus star-forming region, especially of its most massive disk and stellar population. now, near-complete surveys of multiple star-forming regions cover both spectroscopy of young stars and mm interferometry of their protoplanetary disks. this provides an unprecedented statistical sample of stellar masses and mass accretion rates, as well as disk masses and radii, for almost 1000 young stellar objects within 300 pc from us, while also sampling different evolutionary stages, ages, and environments. at the same time, surveys of debris disks are revealing the bulk properties of this class of more evolved objects. this chapter reviews the statistics of these measured global star and disk properties and discusses their constraints on theoretical models describing global disk evolution. our comparisons of observations to theoretical model predictions extends beyond the traditional viscous evolution framework to include analytical descriptions of magnetic wind effects. finally, we discuss how recent observational results can provide a framework for models of planet population synthesis and planet formation. | demographics of young stars and their protoplanetary disks: lessons learned on disk evolution and its connection to planet formation |
collisions between galaxy clusters provide a test of the nongravitational forces acting on dark matter. dark matter’s lack of deceleration in the “bullet cluster” collision constrained its self-interaction cross section σdm/m < 1.25 square centimeters per gram (cm2/g) [68% confidence limit (cl)] (σdm, self-interaction cross section; m, unit mass of dark matter) for long-ranged forces. using the chandra and hubble space telescopes, we have now observed 72 collisions, including both major and minor mergers. combining these measurements statistically, we detect the existence of dark mass at 7.6σ significance. the position of the dark mass has remained closely aligned within 5.8 ± 8.2 kiloparsecs of associated stars, implying a self-interaction cross section σdm/m < 0.47 cm2/g (95% cl) and disfavoring some proposed extensions to the standard model. | the nongravitational interactions of dark matter in colliding galaxy clusters |
we present an independent confirmation of the zero-point offset of gaia data release 2 parallaxes using asteroseismic data of evolved stars in the kepler field. using well-characterized red giant branch stars from the apokasc-2 catalog, we identify a gaia astrometric pseudocolor ({ν }eff})- and gaia g-band magnitude-dependent zero-point offset of {\varpi }seis} - {\varpi }{gaia} = 52.8 ± 2.4 (rand.) ± 8.6 (syst.) - (150.7 ± 22.7)({ν }eff} - 1.5) - (4.21 ± 0.77)(g - 12.2) μas, in the sense that gaia parallaxes are too small. the offset is found in high- and low-extinction samples, as well as among both shell h-burning red giant stars and core he-burning red clump stars. we show that errors in the asteroseismic radius and temperature scales may be distinguished from errors in the gaia parallax scale. we estimate systematic effects on the inferred global gaia parallax offset, c, due to radius and temperature systematics, as well as choices in bolometric correction and the adopted form for gaia parallax spatial correlations. because of possible spatially correlated parallax errors, as discussed by the gaia team, our gaia parallax offset model is specific to the kepler field, but broadly compatible with the magnitude- and color-dependent offset inferred by the gaia team and several subsequent investigations using independent methods. | confirmation of the gaia dr2 parallax zero-point offset using asteroseismology and spectroscopy in the kepler field |
context. the trappist-1 system hosts seven earth-sized, temperate exoplanets orbiting an ultra-cool dwarf star. as such, it represents a remarkable setting to study the formation and evolution of terrestrial planets that formed in the same protoplanetary disk. while the sizes of the trappist-1 planets are all known to better than 5% precision, their densities have significant uncertainties (between 28% and 95%) because of poor constraints on the planet's masses.aims: the goal of this paper is to improve our knowledge of the trappist-1 planetary masses and densities using transit-timing variations (ttvs). the complexity of the ttv inversion problem is known to be particularly acute in multi-planetary systems (convergence issues, degeneracies and size of the parameter space), especially for resonant chain systems such as trappist-1.methods: to overcome these challenges, we have used a novel method that employs a genetic algorithm coupled to a full n-body integrator that we applied to a set of 284 individual transit timings. this approach enables us to efficiently explore the parameter space and to derive reliable masses and densities from ttvs for all seven planets.results: our new masses result in a five- to eight-fold improvement on the planetary density uncertainties, with precisions ranging from 5% to 12%. these updated values provide new insights into the bulk structure of the trappist-1 planets. we find that trappist-1 c and e likely have largely rocky interiors, while planets b, d, f, g, and h require envelopes of volatiles in the form of thick atmospheres, oceans, or ice, in most cases with water mass fractions less than 5%. | the nature of the trappist-1 exoplanets |
a recently proposed experimental protocol for quantum gravity induced entanglement of masses (qgem) requires in principle realizable, but still very ambitious, set of parameters in matter-wave interferometry. motivated by easing the experimental realization, in this paper, we consider the parameter space allowed by a slightly modified experimental design, which mitigates the casimir potential between two spherical neutral test masses by separating the two macroscopic interferometers by a thin conducting plate. although this setup will reintroduce a casimir potential between the conducting plate and the masses, there are several advantages of this design. first, the quantum gravity induced entanglement between the two superposed masses will have no casimir background. secondly, the matter-wave interferometry itself will be greatly facilitated by allowing both the mass 10-16-10-15kg and the superposition size δ x ∼20 μ m to be a one-two order of magnitude smaller than those proposed earlier, and thereby also two orders of magnitude smaller magnetic field gradient of 104tm-1 to create that superposition through the stern-gerlach effect. in this context, we will further investigate the collisional decoherences and decoherence due to vibrational modes of the conducting plate. | quantum gravity witness via entanglement of masses: casimir screening |
we present a new flexible bayesian framework for directly inferring the fraction of neutral hydrogen in the intergalactic medium (igm) during the epoch of reionization (eor, z ∼ 6-10) from detections and non-detections of lyman alpha (lyα) emission from lyman break galaxies (lbgs). our framework combines sophisticated reionization simulations with empirical models of the interstellar medium (ism) radiative transfer effects on lyα. we assert that the lyα line profile emerging from the ism has an important impact on the resulting transmission of photons through the igm, and that these line profiles depend on galaxy properties. we model this effect by considering the peak velocity offset of lyα lines from host galaxies’ systemic redshifts, which are empirically correlated with uv luminosity and redshift (or halo mass at fixed redshift). we use our framework on the sample of lbgs presented in pentericci et al. and infer a global neutral fraction at z ∼ 7 of {\overline{x}}{{h}{{i}}}={0.59}-0.15+0.11, consistent with other robust probes of the eor and confirming that reionization is ongoing ∼700 myr after the big bang. we show that using the full distribution of lyα equivalent width detections and upper limits from lbgs places tighter constraints on the evolving igm than the standard lyα emitter fraction, and that larger samples are within reach of deep spectroscopic surveys of gravitationally lensed fields and james webb space telescope nirspec. | the universe is reionizing at z ∼ 7: bayesian inference of the igm neutral fraction using lyα emission from galaxies |
the merger of binary neutron stars, or of a neutron star and a stellar-mass black hole, can result in the formation of a massive rotating torus around a spinning black hole. in addition to providing collimating media for γ -ray burst jets, unbound outflows from these disks are an important source of mass ejection and rapid neutron capture (r -process) nucleosynthesis. we present the first three-dimensional general-relativistic magnetohydrodynamic (grmhd) simulations of neutrino-cooled accretion disks in neutron star mergers, including a realistic equation of state valid at low densities and temperatures, self-consistent evolution of the electron fraction, and neutrino cooling through an approximate leakage scheme. after initial magnetic field amplification by magnetic winding, we witness the vigorous onset of turbulence driven by the magnetorotational instability (mri). the disk quickly reaches a balance between heating from mri-driven turbulence and neutrino cooling, which regulates the midplane electron fraction to a low equilibrium value ye≈0.1 . over the 380-ms duration of the simulation, we find that a fraction ≈20 % of the initial torus mass is unbound in powerful outflows with asymptotic velocities v ≈0.1 c and electron fractions ye≈0.1 - 0.25 . postprocessing the outflows through a nuclear reaction network shows the production of a robust second- and third-peak r process. though broadly consistent with the results of previous axisymmetric hydrodynamical simulations, extrapolation of our results to late times suggests that the total ejecta mass from grmhd disks is significantly higher. our results provide strong evidence that postmerger disk outflows are an important site for the r process. | three-dimensional general-relativistic magnetohydrodynamic simulations of remnant accretion disks from neutron star mergers: outflows and r -process nucleosynthesis |
during reionization, neutral hydrogen in the intergalactic medium (igm) imprints a damping wing absorption feature on the spectrum of high-redshift quasars. a detection of this signature provides compelling evidence for a significantly neutral universe, and enables measurements of the hydrogen neutral fraction x h i (z) at that epoch. obtaining reliable quantitative constraints from this technique, however, is challenging due to stochasticity induced by the patchy inside-out topology of reionization, degeneracies with quasar lifetime, and the unknown unabsorbed quasar spectrum close to rest-frame lyα. we combine a large-volume semi-numerical simulation of reionization topology with 1d radiative transfer through high-resolution hydrodynamical simulations of the high-redshift universe to construct models of quasar transmission spectra during reionization. our state-of-the-art approach captures the distribution of damping wing strengths in biased quasar halos that should have reionized earlier, as well as the erosion of neutral gas in the quasar environment caused by its own ionizing radiation. combining this detailed model with our new technique for predicting the quasar continuum and its associated uncertainty, we introduce a bayesian statistical method to jointly constrain the neutral fraction of the universe and the quasar lifetime from individual quasar spectra. we apply this methodology to the spectra of the two quasars with the highest redshifts known, ulas j1120+0641 and ulas j1342+0928, and measure volume-averaged neutral fractions < {x}{{h}{{i}}}> (z=7.09)={0.48}-0.26+0.26 and < {x}{{h}{{i}}}> (z=7.54)={0.60}-0.23+0.20 (posterior medians and 68% credible intervals) when marginalized over quasar lifetimes of 103 ≤ t q ≤ 108 yr. | quantitative constraints on the reionization history from the igm damping wing signature in two quasars at z > 7 |
e-astrogam ('enhanced astrogam') is a breakthrough observatory space mission, with a detector composed by a silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of the non-thermal universe in the photon energy range from 0.3 mev to 3 gev - the lower energy limit can be pushed to energies as low as 150 kev for the tracker, and to 30 kev for calorimetric detection. the mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. thanks to its performance in the mev-gev domain, substantially improving its predecessors, e-astrogam will open a new window on the non-thermal universe, making pioneering observations of the most powerful galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. with a line sensitivity in the mev energy range one to two orders of magnitude better than previous generation instruments, e-astrogam will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our galaxy. the mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as ligo-virgo-geo600-kagra, ska, alma, e-elt, tmt, lsst, jwst, athena, cta, icecube, km3net, and lisa. | science with e-astrogam. a space mission for mev-gev gamma-ray astrophysics |
binary systems containing boson stars—self-gravitating configurations of a complex scalar field—can potentially mimic black holes or neutron stars as gravitational-wave sources. we investigate the extent to which tidal effects in the gravitational-wave signal can be used to discriminate between these standard sources and boson stars. we consider spherically symmetric boson stars within two classes of scalar self-interactions: an effective-field-theoretically motivated quartic potential and a solitonic potential constructed to produce very compact stars. we compute the tidal deformability parameter characterizing the dominant tidal imprint in the gravitational-wave signals for a large span of the parameter space of each boson star model, covering the entire space in the quartic case, and an extensive portion of interest in the solitonic case. we find that the tidal deformability for boson stars with a quartic self-interaction is bounded below by λmin≈280 and for those with a solitonic interaction by λmin≈1.3 . we summarize our results as ready-to-use fits for practical applications. employing a fisher matrix analysis, we estimate the precision with which advanced ligo and third-generation detectors can measure these tidal parameters using the inspiral portion of the signal. we discuss a novel strategy to improve the distinguishability between black holes/neutrons stars and boson stars by combining tidal deformability measurements of each compact object in a binary system, thereby eliminating the scaling ambiguities in each boson star model. our analysis shows that current-generation detectors can potentially distinguish boson stars with quartic potentials from black holes, as well as from neutron-star binaries if they have either a large total mass or a large (asymmetric) mass ratio. discriminating solitonic boson stars from black holes using only tidal effects during the inspiral will be difficult with advanced ligo, but third-generation detectors should be able to distinguish between binary black holes and these binary boson stars. | distinguishing boson stars from black holes and neutron stars from tidal interactions in inspiraling binary systems |
the dark energy spectroscopic instrument (desi) is carrying out a five-year survey that aims to measure the redshifts of tens of millions of galaxies and quasars, including 8 million luminous red galaxies (lrgs) in the redshift range 0.4 < z ≲ 1.0. here we present the selection of the desi lrg sample and assess its spectroscopic performance using data from survey validation (sv) and the first two months of the main survey. the desi lrg sample, selected using g, r, z, and w1 photometry from the desi legacy imaging surveys, is highly robust against imaging systematics. the sample has a target density of 605 deg-2 and a comoving number density of 5 × 10-4 h 3 mpc-3 in 0.4 < z < 0.8; this is a significantly higher density than previous lrg surveys (such as sdss, boss, and eboss) while also extending to z ~ 1. after applying a bright star veto mask developed for the sample, 98.9% of the observed lrg targets yield confident redshifts (with a catastrophic failure rate of 0.2% in the confident redshifts), and only 0.5% of the lrg targets are stellar contamination. the lrg redshift efficiency varies with source brightness and effective exposure time, and we present a simple model that accurately characterizes this dependence. in the appendices, we describe the extended lrg samples observed during sv. | target selection and validation of desi luminous red galaxies |
we present the initial-final mass relation (ifmr) based on the self-consistent analysis of sirius b and 79 white dwarfs from 13 star clusters. we have also acquired additional signal on eight white dwarfs previously analyzed in the ngc 2099 cluster field, four of which are consistent with membership. these re-observed white dwarfs have masses ranging from 0.72 to 0.97 m ⊙, with initial masses from 3.0 to 3.65 m ⊙, where the ifmr has an important change in slope that these new data help to observationally confirm. in total, this directly measured ifmr has small scatter (σ = 0.06 m ⊙) and spans from progenitors of 0.85 to 7.5 m ⊙. applying two different stellar evolutionary models to infer two different sets of white dwarf progenitor masses shows that, when the same model is also used to derive the cluster ages, the resulting ifmr has weak sensitivity to the adopted model at all but the highest initial masses (>5.5 m ⊙). the nonlinearity of the ifmr is also clearly observed with moderate slopes at lower masses (0.08 m final/m initial) and higher masses (0.11 m final/m initial) that are broken up by a steep slope (0.19 m final/m initial) between progenitors from 2.85 to 3.6 m ⊙. this ifmr shows total stellar mass loss ranges from 33% of m initial at 0.83 m ⊙ to 83% of m initial at 7.5 m ⊙. testing this total mass loss for dependence on progenitor metallicity, however, finds no detectable sensitivity across the moderate range of -0.15 < [fe/h] < +0.15. based on observations with the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, was made possible by the generous financial support of the w.m. keck foundation. | the white dwarf initial-final mass relation for progenitor stars from 0.85 to 7.5 m ⊙ |
strong gravitational lens systems with time delays between the multiple images allow measurements of time-delay distances, which are primarily sensitive to the hubble constant that is key to probing dark energy, neutrino physics and the spatial curvature of the universe, as well as discovering new physics. we present h0licow (h0 lenses in cosmograil's wellspring), a program that aims to measure h0 with <3.5 per cent uncertainty from five lens systems (b1608+656, rxj1131-1231, he 0435-1223, wfi2033-4723 and he 1104-1805). we have been acquiring (1) time delays through cosmograil and very large array monitoring, (2) high-resolution hubble space telescope imaging for the lens mass modelling, (3) wide-field imaging and spectroscopy to characterize the lens environment and (4) moderate-resolution spectroscopy to obtain the stellar velocity dispersion of the lenses for mass modelling. in cosmological models with one-parameter extension to flat λ cold dark matter, we expect to measure h0 to <3.5 per cent in most models, spatial curvature ωk to 0.004, w to 0.14 and the effective number of neutrino species to 0.2 (1σ uncertainties) when combined with current cosmic microwave background (cmb) experiments. these are, respectively, a factor of ∼15, ∼2 and ∼1.5 tighter than cmb alone. our data set will further enable us to study the stellar initial mass function of the lens galaxies, and the co-evolution of supermassive black holes and their host galaxies. this program will provide a foundation for extracting cosmological distances from the hundreds of time-delay lenses that are expected to be discovered in current and future surveys. | h0licow - i. h0 lenses in cosmograil's wellspring: program overview |
we report the detection of coherent pulsations from the ultraluminous x-ray source (ulx) ngc 7793 p13. the ≈0.42 s nearly sinusoidal pulsations were initially discovered in broadband x-ray observations using xmm-newton and nustar taken in 2016. we subsequently also found pulsations in archival xmm-newton data taken in 2013 and 2014. the significant (≫5σ) detection of coherent pulsations demonstrates that the compact object in p13 is a neutron star, and given the observed peak luminosity of ≈1040 {erg} {{{s}}}-1 (assuming isotropy), it is well above the eddington limit for a 1.4 {m}⊙accretor. this makes p13 the second ulx known to be powered by an accreting neutron star. the pulse period varies between epochs, with a slow but persistent spin-up over the 2013-2016 period. this spin-up indicates a magnetic field of b ≈ 1.5 × 1012 g, typical of many galactic accreting pulsars. the most likely explanation for the extreme luminosity is a high degree of beaming; however, this is difficult to reconcile with the sinusoidal pulse profile. | discovery of coherent pulsations from the ultraluminous x-ray source ngc 7793 p13 |
the unprecedented range of second-generation gravitational-wave (gw) observatories calls for refining the predictions of potential sources and detection rates. the coalescence of double compact objects (dcos)—i.e., neutron star-neutron star (ns-ns), black hole-neutron star (bh-ns), and black hole-black hole (bh-bh) binary systems—is the most promising source of gws for these detectors. we compute detection rates of coalescing dcos in second-generation gw detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown gravitational waveform models in our signal-to-noise ratio calculations. we find that (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for ns-ns and bh-ns systems, but it boosts rates by a factor of ∼1.5 for bh-bh systems; (2) in almost all of our models bh-bh systems yield by far the largest rates, followed by ns-ns and bh-ns systems, respectively; and (3) a majority of the detectable bh-bh systems were formed in the early universe in low-metallicity environments. we make predictions for the distributions of detected binaries and discuss what the first gw detections will teach us about the astrophysics underlying binary formation and evolution. | double compact objects iii: gravitational-wave detection rates |
the first two orbits of the parker solar probe spacecraft have enabled the first in situ measurements of the solar wind down to a heliocentric distance of 0.17 au (or 36 ${r}_{\odot }$ ). here, we present an analysis of this data to study solar wind turbulence at 0.17 au and its evolution out to 1 au. while many features remain similar, key differences at 0.17 au include increased turbulence energy levels by more than an order of magnitude, a magnetic field spectral index of -3/2 matching that of the velocity and both elsasser fields, a lower magnetic compressibility consistent with a smaller slow-mode kinetic energy fraction, and a much smaller outer scale that has had time for substantial nonlinear processing. there is also an overall increase in the dominance of outward-propagating alfvénic fluctuations compared to inward-propagating ones, and the radial variation of the inward component is consistent with its generation by reflection from the large-scale gradient in alfvén speed. the energy flux in this turbulence at 0.17 au was found to be ∼10% of that in the bulk solar wind kinetic energy, becoming ∼40% when extrapolated to the alfvén point, and both the fraction and rate of increase of this flux toward the sun are consistent with turbulence-driven models in which the solar wind is powered by this flux. | the evolution and role of solar wind turbulence in the inner heliosphere |
black hole (bh) mergers detectable with the laser interferometer gravitational-wave observatory (ligo) can occur in active galactic nucleus (agn) disks. here we parameterize the merger rates, the mass spectrum, and the spin spectrum of bhs in agn disks. the predicted merger rate spans ∼10-3-104 gpc-1 yr-1, so upper limits from ligo (<212 gpc-1 yr-1) already constrain it. the predicted mass spectrum has the form of a broken power law, consisting of a pre-existing bh power-law mass spectrum and a harder power-law mass spectrum resulting from mergers. the predicted spin spectrum is multipeaked with the evolution of retrograde spin bhs in the gas disk playing a key role. we outline the large uncertainties in each of these ligo observables for this channel and we discuss ways in which they can be constrained in the future. | constraining stellar-mass black hole mergers in agn disks detectable with ligo |
helium is the second-most abundant element in the universe after hydrogen and is one of the main constituents of gas-giant planets in our solar system. early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres1. searches for helium, however, have hitherto been unsuccessful2. here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. we measured the near-infrared transmission spectrum of the warm gas giant3 wasp-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms. the amplitude of the feature, in transit depth, is 0.049 ± 0.011 per cent in a bandpass of 98 angstroms, which is more than five times greater than what could be caused by nominal stellar chromospheric activity. this large absorption signal suggests that wasp-107b has an extended atmosphere that is eroding at a total rate of 1010 to 3 × 1011 grams per second (0.1-4 per cent of its total mass per billion years), and may have a comet-like tail of gas shaped by radiation pressure. | helium in the eroding atmosphere of an exoplanet |
we report spectroscopic and photometric follow-up of a dormant black hole (bh) candidate from gaia dr3. the system, which we call gaia bh2, contains a ~1 m⊙ red giant and a dark companion with mass $m_2 = 8.9\pm 0.3\, {\rm m}_{\odot }$ that is very likely a bh. the orbital period, porb = 1277 d, is much longer than that of any previously studied bh binary. our radial velocity (rv) follow-up over a 7-month period spans >90 per cent of the orbit's rv range and is in excellent agreement with the gaia solution. uv imaging and high-resolution optical spectra rule out plausible luminous companions that could explain the orbit. the star is a bright (g = 12.3), slightly metal-poor ($\rm [fe/h]=-0.22$) low-luminosity giant ($t_{\rm eff}=4600\, \rm k$; $r = 7.8\, r_{\odot }$; $\log \left[g/\left({\rm cm\, s^{-2}}\right)\right] = 2.6$). the binary's orbit is moderately eccentric (e = 0.52). the giant is enhanced in α-elements, with $\rm [\alpha /fe] = +0.26$, but the system's galactocentric orbit is typical of the thin disc. we obtained x-ray and radio non-detections of the source near periastron, which support bh accretion models in which the net accretion rate at the horizon is much lower than the bondi-hoyle-lyttleton rate. at a distance of 1.16 kpc, gaia bh2 is the second-nearest known bh, after gaia bh1. its orbit - like that of gaia bh1 - seems too wide to have formed through common envelope evolution. gaia bh1 and bh2 have orbital periods at opposite edges of the gaia dr3 sensitivity curve, perhaps hinting at a bimodal intrinsic period distribution for wide bh binaries. dormant bh binaries like gaia bh1 and gaia bh2 significantly outnumber their close, x-ray bright cousins, but their formation pathways remain uncertain. | a red giant orbiting a black hole |
gravitational waves from coalescing neutron stars encode information about nuclear matter at extreme densities, inaccessible by laboratory experiments. the late inspiral is influenced by the presence of tides, which depend on the neutron star equation of state. neutron star mergers are expected to often produce rapidly rotating remnant neutron stars that emit gravitational waves. these will provide clues to the extremely hot post-merger environment. this signature of nuclear matter in gravitational waves contains most information in the 2-4 khz frequency band, which is outside of the most sensitive band of current detectors. we present the design concept and science case for a neutron star extreme matter observatory (nemo): a gravitational-wave interferometer optimised to study nuclear physics with merging neutron stars. the concept uses high-circulating laser power, quantum squeezing, and a detector topology specifically designed to achieve the high-frequency sensitivity necessary to probe nuclear matter using gravitational waves. above 1 khz, the proposed strain sensitivity is comparable to full third-generation detectors at a fraction of the cost. such sensitivity changes expected event rates for detection of post-merger remnants from approximately one per few decades with two a+ detectors to a few per year and potentially allow for the first gravitational-wave observations of supernovae, isolated neutron stars, and other exotica. | neutron star extreme matter observatory: a kilohertz-band gravitational-wave detector in the global network |
motivated by the recent xenon1t results, we explore various new physics models that can be discovered through searches for electron recoils in o (kev)-threshold direct-detection experiments. first, we consider the absorption of axion-like particles, dark photons, and scalars, either as dark matter relics or being produced directly in the sun. in the latter case, we find that kev mass bosons produced in the sun provide an adequate fit to the data but are excluded by stellar cooling constraints. we address this tension by introducing a novel chameleon-like axion model, which can explain the excess while evading the stellar bounds. we find that absorption of bosonic dark matter provides a viable explanation for the excess only if the dark matter is a dark photon or an axion. in the latter case, photophobic axion couplings are necessary to avoid x-ray constraints. second, we analyze models of dark matter-electron scattering to determine which models might explain the excess. standard scattering of dark matter with electrons is generically in conflict with data from lower-threshold experiments. momentum-dependent interactions with a heavy mediator can fit the data with dark matter mass heavier than a gev but are generically in tension with collider constraints. next, we consider dark matter consisting of two (or more) states that have a small mass splitting. the exothermic (down)scattering of the heavier state to the lighter state can fit the data for kev mass splittings. finally, we consider a subcomponent of dark matter that is accelerated by scattering off cosmic rays, finding that dark matter interacting though an o (100 kev)-mass mediator can fit the data. the cross sections required in this scenario are, however, typically challenged by complementary probes of the light mediator. throughout our study, we implement an unbinned monte carlo analysis and use an improved energy reconstruction of the xenon1t events. | exploring new physics with o(kev) electron recoils in direct detection experiments |
we present the optical spectroscopic evolution of sn 2023ixf seen in subnight cadence spectra from 1.18 to 15 days after explosion. we identify high-ionization emission features, signatures of interaction with material surrounding the progenitor star, that fade over the first 7 days, with rapid evolution between spectra observed within the same night. we compare the emission lines present and their relative strength to those of other supernovae with early interaction, finding a close match to sn 2020pni and sn 2017ahn in the first spectrum and sn 2014g at later epochs. to physically interpret our observations, we compare them to cmfgen models with confined, dense circumstellar material around a red supergiant (rsg) progenitor from the literature. we find that very few models reproduce the blended n iii (λλ4634.0,4640.6)/c iii (λλ4647.5,4650.0) emission lines observed in the first few spectra and their rapid disappearance thereafter, making this a unique diagnostic. from the best models, we find a mass-loss rate of 10-3-10-2 m ⊙ yr-1, which far exceeds the mass-loss rate for any steady wind, especially for an rsg in the initial mass range of the detected progenitor. these mass-loss rates are, however, similar to rates inferred for other supernovae with early circumstellar interaction. using the phase when the narrow emission features disappear, we calculate an outer dense radius of circumstellar material r csm,out ≈ 5 × 1014 cm, and a mean circumstellar material density of ρ = 5.6 × 10-14 g cm-3. this is consistent with the lower limit on the outer radius of the circumstellar material we calculate from the peak hα emission flux, r csm,out ≳ 9 × 1013 cm. | early spectroscopy and dense circumstellar medium interaction in sn 2023ixf |
we present an overview of the large program, "early planet formation in embedded disks (edisk)," conducted with the atacama large millimeter/submillimeter array (alma). the ubiquitous detections of substructures, particularly rings and gaps, in protoplanetary disks around t tauri stars raise the possibility that at least some planet formation may have already started during the embedded stages of star formation. in order to address exactly how and when planet formation is initiated, the program focuses on searching for substructures in disks around 12 class 0 and 7 class i protostars in nearby (<200 pc) star-forming regions through 1.3 mm continuum observations at a resolution of ~7 au (0.″04). the initial results show that the continuum emission, mostly arising from dust disks around the sample protostars, has relatively few distinctive substructures, such as rings and spirals, in marked contrast to class ii disks. the dramatic difference may suggest that substructures quickly develop in disks when the systems evolve from protostars to class ii sources, or alternatively that high optical depth of the continuum emission could obscure internal structures. kinematic information obtained through co isotopologue lines and other lines reveals the presence of keplerian disks around protostars, providing us with crucial physical parameters, in particular, the dynamical mass of the central protostars. we describe the background of the edisk program, the sample selection and their alma observations, and the data reduction, and we also highlight representative first-look results. | early planet formation in embedded disks (edisk). i. overview of the program and first results |
the milky way halo was predominantly formed by the merging of numerous progenitor galaxies. however, our knowledge of this process is still incomplete, especially in regard to the total number of mergers, their global dynamical properties and their contribution to the stellar population of the galactic halo. here, we uncover the milky way mergers by detecting groupings of globular clusters, stellar streams, and satellite galaxies in action ( j ) space. while actions fully characterize the orbits, we additionally use the redundant information on their energy (e) to enhance the contrast between the groupings. for this endeavor, we use gaia edr3−based measurements of 170 globular clusters, 41 streams, and 46 satellites to derive their j and e. to detect groups, we use the enlink software, coupled with a statistical procedure that accounts for the observed phase-space uncertainties of these objects. we detect a total of n = 6 groups, including the previously known mergers sagittarius, cetus, gaia−sausage/enceladus, lms-1/wukong, arjuna/sequoia/i'itoi, and one new merger that we call pontus. all of these mergers, together, comprise 62 objects (≈25% of our sample). we discuss their members, orbital properties, and metallicity distributions. we find that the three most-metal-poor streams of our galaxy-"c-19" ([fe/h] = -3.4 dex), "sylgr" ([fe/h] = -2.9 dex), and "phoenix" ([fe/h] = -2.7 dex)-are associated with lms-1/wukong, showing it to be the most-metal-poor merger. the global dynamical atlas of milky way mergers that we present here provides a present-day reference for galaxy formation models. | the global dynamical atlas of the milky way mergers: constraints from gaia edr3-based orbits of globular clusters, stellar streams, and satellite galaxies |
understanding the properties of dust attenuation curves in galaxies and the physical mechanisms that shape them are among the fundamental questions of extragalactic astrophysics, with great practical significance for deriving the physical properties of galaxies. attenuation curves result from a combination of dust grain properties, dust content, and the spatial arrangement of dust and different populations of stars. in this review, we assess the state of the field, paying particular attention to extinction curves as the building blocks of attenuation laws. we introduce a quantitative framework to characterize extinction and attenuation curves, present a theoretical foundation for interpreting empirical results, overview an array of observational methods, and review observational results at low and high redshifts. our main conclusions include the following: attenuation curves exhibit a wide range of uv-through-optical slopes, from curves with shallow (milky way-like) slopes to those exceeding the slope of the small magellanic cloud extinction curve. the slopes of the curves correlate strongly with the effective optical opacities, in the sense that galaxies with lower dust column density (lower visual attenuation) tend to have steeper slopes, whereas the galaxies with higher dust column density have shallower (grayer) slopes. galaxies exhibit a range of 2175-å uv bump strengths, including no bump, but, on average, are suppressed compared with the average milky way extinction curve. theoretical studies indicate that both the correlation between the slope and the dust column as well as variations in bump strength may result from geometric and radiative transfer effects. | the dust attenuation law in galaxies |
the recently discovered layered kagome metals a v3sb5 (a =k , rb, cs) have attracted much attention because of their unique combination of superconductivity, charge density wave (cdw) order, and nontrivial band topology. the cdw order with an in-plane 2 ×2 reconstruction is found to exhibit exotic properties, such as time-reversal symmetry breaking and rotational symmetry breaking. however, the nature of the cdw, including its dimensionality, structural pattern, and effect on electronic structure, remains elusive despite intense research efforts. here, we present a comprehensive study on the electronic structure of a v3sb5 by combining polarization- and temperature-dependent angle-resolved photoemission spectroscopy with density-functional theory calculations. apart from the energy shift of van hove singularities, we observe double-band splittings for v d -orbital bands in the cdw phase, which provide essential information for revealing the dimensionality and pattern of the cdw order. our calculations show that three-dimensional cdw orders containing stacking of star-of-david and trihexagonal patterns along the c axis can quantitatively reproduce the experimental features. the characteristic splittings from the two patterns can be experimentally extracted and they are quantitatively consistent with calculations, clearly demonstrating intrinsic coexistence of the two patterns in the cdw order. these results provide crucial insights into the nature and distortion pattern of the cdw order, and its signature in the electronic structure, thereby laying down the basis for a substantiated understanding of the exotic properties in the family of a v3sb5 kagome metals. | coexistence of trihexagonal and star-of-david pattern in the charge density wave of the kagome superconductor a v3sb5 |
we consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the sun, in current and next-generation direct detection experiments. experiments sensitive to electron recoils can detect such particles with masses between a few ev to more than 10 kev. for dark photon dark matter, we update a previous bound based on xenon10 data and derive new bounds based on data from xenon100 and cdmslite. we find these experiments to disfavor previously allowed parameter space. moreover, we derive sensitivity projections for supercdms at snolab for silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). the projected sensitivity can probe large new regions of parameter space. for axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond known stellar cooling bounds. however, projected sensitivities of the upcoming supercdms snolab using germanium can go beyond these and even probe parameter space consistent with possible hints from the white dwarf luminosity function. we find similar results for dark photons from the sun. for all cases, direct-detection experiments can have unprecedented sensitivity to dark-sector particles. | searching for dark absorption with direct detection experiments |
here we present juliet, a versatile tool for the analysis of transits, radial velocities, or both. juliet is built over many available tools for the modelling of transits, radial velocities, and stochastic processes (here modelled as gaussian processes; gps) in order to deliver a tool/wrapper which can be used for the analysis of transit photometry and radial-velocity measurements from multiple instruments at the same time, using nested sampling algorithms which allows it to not only perform a thorough sampling of the parameter space, but also to perform model comparison via bayesian evidences. in addition, juliet allows us to fit transiting and non-transiting multiplanetary systems, and to fit gps which might share hyperparameters between the photometry and radial velocities simultaneously (e.g. stellar rotation periods), which might be useful for disentangling stellar activity in radial-velocity measurements. nested sampling, importance nested sampling, and dynamic nested sampling is performed with publicly available codes which in turn give juliet multithreading options, allowing it to scale the computing time of complicated multidimensional problems. we make juliet publicly available via github. | juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems |
both the mass and radius of the millisecond pulsar psr j0030+0451 have been inferred via pulse-profile modeling of x-ray data obtained by nasa’s neutron star interior composition explorer (nicer) mission. in this letter we study the implications of the mass-radius inference reported for this source by riley et al. for the dense matter equation of state (eos), in the context of prior information from nuclear physics at low densities. using a bayesian framework we infer central densities and eos properties for two choices of high-density extensions: a piecewise-polytropic model and a model based on assumptions of the speed of sound in dense matter. around nuclear saturation density these extensions are matched to an eos uncertainty band obtained from calculations based on chiral effective field theory interactions, which provide a realistic description of atomic nuclei as well as empirical nuclear matter properties within uncertainties. we further constrain eos expectations with input from the current highest measured pulsar mass; together, these constraints offer a narrow bayesian prior informed by theory as well as laboratory and astrophysical measurements. the nicer mass-radius likelihood function derived by riley et al. using pulse-profile modeling is consistent with the highest-density region of this prior. the present relatively large uncertainties on mass and radius for psr j0030+0451 offer, however, only a weak posterior information gain over the prior. we explore the sensitivity to the inferred geometry of the heated regions that give rise to the pulsed emission, and find a small increase in posterior gain for an alternative (but less preferred) model. lastly, we investigate the hypothetical scenario of increasing the nicer exposure time for psr j0030+0451. | a nicer view of psr j0030+0451: implications for the dense matter equation of state |
the sun's activity cycle governs the radiation, particle and magnetic flux in the heliosphere creating hazardous space weather. decadal-scale variations define space climate and force the earth's atmosphere. however, predicting the solar cycle is challenging. current understanding indicates a short window for prediction best achieved at previous cycle minima. utilizing magnetic field evolution models for the sun's surface and interior we perform the first century-scale, data-driven simulations of solar activity and present a scheme for extending the prediction window to a decade. our ensemble forecast indicates cycle 25 would be similar or slightly stronger than the current cycle and peak around 2024. sunspot cycle 25 may thus reverse the substantial weakening trend in solar activity which has led to speculation of an imminent maunder-like grand minimum and cooling global climate. our simulations demonstrate fluctuation in the tilt angle distribution of sunspots is the dominant mechanism responsible for solar cycle variability. | prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions |
recent work indicates that the nearby galactic halo is dominated by the debris from a major accretion event. we confirm that result from an analysis of apogee-dr14 element abundances and gaia-dr2 kinematics of halo stars. we show that ∼2/3 of nearby halo stars have high orbital eccentricities (e ≳ 0.8), and abundance patterns typical of massive milky way dwarf galaxy satellites today, characterized by relatively low [fe/h], [mg/fe], [al/fe], and [ni/fe]. the trend followed by high-e stars in the [mg/fe]-[fe/h] plane shows a change of slope at [fe/h] ∼ -1.3, which is also typical of stellar populations from relatively massive dwarf galaxies. low-e stars exhibit no such change of slope within the observed [fe/h] range and show slightly higher abundances of mg, al, and ni. unlike their low-e counterparts, high-e stars show slightly retrograde motion, make higher vertical excursions, and reach larger apocentre radii. by comparing the position in [mg/fe]-[fe/h] space of high-e stars with those of accreted galaxies from the eagle suite of cosmological simulations, we constrain the mass of the accreted satellite to be in the range 108.5 ≲ m* ≲ 109 m⊙. we show that the median orbital eccentricities of debris are largely unchanged since merger time, implying that this accretion event likely happened at z ≲ 1.5. the exact nature of the low-e population is unclear, but we hypothesize that it is a combination of in situ star formation, high-|z| disc stars, lower mass accretion events, and contamination by the low-e tail of the high-e population. finally, our results imply that the accretion history of the milky way was quite unusual. | the origin of accreted stellar halo populations in the milky way using apogee, gaia, and the eagle simulations |
penetration testing, a crucial industrial practice for ensuring system security, has traditionally resisted automation due to the extensive expertise required by human professionals. large language models (llms) have shown significant advancements in various domains, and their emergent abilities suggest their potential to revolutionize industries. in this research, we evaluate the performance of llms on real-world penetration testing tasks using a robust benchmark created from test machines with platforms. our findings reveal that while llms demonstrate proficiency in specific sub-tasks within the penetration testing process, such as using testing tools, interpreting outputs, and proposing subsequent actions, they also encounter difficulties maintaining an integrated understanding of the overall testing scenario. in response to these insights, we introduce pentestgpt, an llm-empowered automatic penetration testing tool that leverages the abundant domain knowledge inherent in llms. pentestgpt is meticulously designed with three self-interacting modules, each addressing individual sub-tasks of penetration testing, to mitigate the challenges related to context loss. our evaluation shows that pentestgpt not only outperforms llms with a task-completion increase of 228.6\% compared to the \gptthree model among the benchmark targets but also proves effective in tackling real-world penetration testing challenges. having been open-sourced on github, pentestgpt has garnered over 4,700 stars and fostered active community engagement, attesting to its value and impact in both the academic and industrial spheres. | pentestgpt: an llm-empowered automatic penetration testing tool |
we explore magnetic-field amplification due to the kelvin-helmholtz instability during binary neutron star mergers. by performing high-resolution general relativistic magnetohydrodynamics simulations with a resolution of 17.5 m for 4-5 ms after the onset of the merger on the japanese supercomputer "k", we find that an initial magnetic field of moderate maximum strength 1013 g is amplified at least by a factor of ≈103. we also explore the saturation of the magnetic-field energy and our result shows that it is likely to be ≳4 ×1050 erg , which is ≳0.1 % of the bulk kinetic energy of the merging binary neutron stars. | efficient magnetic-field amplification due to the kelvin-helmholtz instability in binary neutron star mergers |
we show that terrestrial planets in the habitable zones of m dwarfs older than $\sim$ 1 gyr could have been in runaway greenhouses for several hundred myr following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. such prolonged runaway greenhouses can lead to planetary evolution divergent from that of earth. during this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several earth oceans of water from planets throughout the habitable zone, regardless of whether the escape is energy-limited or diffusion-limited. we find that the amount of water lost scales with the planet mass, since the diffusion-limited hydrogen escape flux is proportional to the planet surface gravity. in addition to undergoing potential desiccation, planets with inefficient oxygen sinks at the surface may build up hundreds to thousands of bars of abiotically produced o$_2$, resulting in potential false positives for life. the amount of o$_2$ that builds up also scales with the planet mass; we find that o$_2$ builds up at a constant rate that is controlled by diffusion: $\sim$ 5 bars/myr on earth-mass planets and up to $\sim$ 25 bars/myr on super-earths. as a result, some recently discovered super-earths in the habitable zone such as gj 667cc could have built up as many as 2000 bars of o$_2$ due to the loss of up to 10 earth oceans of water. the fate of a given planet strongly depends on the extreme ultraviolet flux, the duration of the runaway regime, the initial water content, and the rate at which oxygen is absorbed by the surface. in general, we find that the initial phase of high luminosity may compromise the habitability of many terrestrial planets orbiting low mass stars. | extreme water loss and abiotic o2buildup on planets throughout the habitable zones of m dwarfs |
analysis of emission lines in gaseous nebulae yields direct measures of physical conditions and chemical abundances and is the cornerstone of nebular astrophysics. although the physical problem is conceptually simple, its practical complexity can be overwhelming since the amount of data to be analyzed steadily increases; furthermore, results depend crucially on the input atomic data, whose determination also improves each year. to address these challenges we created pyneb, an innovative code for analyzing emission lines. pyneb computes physical conditions and ionic and elemental abundances and produces both theoretical and observational diagnostic plots. it is designed to be portable, modular, and largely customizable in aspects such as the atomic data used, the format of the observational data to be analyzed, and the graphical output. it gives full access to the intermediate quantities of the calculation, making it possible to write scripts tailored to the specific type of analysis one wants to carry out. in the case of collisionally excited lines, pyneb works by solving the equilibrium equations for an n-level atom; in the case of recombination lines, it works by interpolation in emissivity tables. the code offers a choice of extinction laws and ionization correction factors, which can be complemented by user-provided recipes. it is entirely written in the python programming language and uses standard python libraries. it is fully vectorized, making it apt for analyzing huge amounts of data. the code is stable and has been benchmarked against iraf/nebular. it is public, fully documented, and has already been satisfactorily used in a number of published papers. | pyneb: a new tool for analyzing emission lines. i. code description and validation of results |
we present new upper limits on the volume-weighted neutral hydrogen fraction, bar{x}_{h i}, at z ∼ 5-6 derived from spectroscopy of bright quasars. the fraction of the lyα and lyβ forests that is `dark' (with zero flux) provides the only model-independent upper limit on bar{x}_{h i}, requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed uv continuum. in this work, we update our previous results using a larger sample (22 objects) of medium-depth (∼ few hours) spectra of high-redshift quasars obtained with the magellan, mmt, and vlt. this significantly improves the upper bound on bar{x}_{h i} derived from dark pixel analysis to bar{x}_{h i} ≤ 0.06{+0.05 (1σ )} at z = 5.9 and bar{x}_{h i} ≤ 0.04{+0.05 (1σ )} at z = 5.6. these results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z ≈ 6. | model-independent evidence in favour of an end to reionization by z ≈ 6 |
we present year-long, near-infrared hubble space telescope (hst) wfc3 observations used to search for mira variables in ngc 1559, the host galaxy of the type ia supernova (sn ia) sn 2005df. this is the first dedicated search for miras, highly evolved low-mass stars, in an sn ia host, and subsequently the first calibration of the sn ia luminosity using miras in a role historically played by cepheids. we identify a sample of 115 o-rich miras with p < 400 days based on their light-curve properties. we find that the scatter in the mira period-luminosity relation (plr) is comparable to cepheid plrs seen in sn ia host galaxies. using a sample of o-rich miras discovered in ngc 4258 with hstf160w and its maser distance, we measure a distance modulus for ngc 1559 of ${\mu }_{1559}=31.41\pm 0.050$ (statistical) $\pm 0.060$ (systematic) mag. based on the light curve of the normal, well-observed, low-reddening sn 2005df, we obtain a measurement of the fiducial sn ia absolute magnitude of ${m}_{b}^{0}=-19.27\pm 0.13$ mag. with the hubble diagram of sne ia we find ${h}_{0}=72.7\pm 4.6$ km s-1 mpc-1. combining the calibration from the ngc 4258 megamaser and the large magellanic cloud detached eclipsing binaries gives a best value of ${h}_{0}=73.3\pm 4.0$ km s-1 mpc-1. this result is within 1σ of the hubble constant derived using cepheids and multiple calibrating sne ia. this is the first of four expected calibrations of the sn ia luminosity from miras that should reduce the error in h0 via miras to ∼3%. in light of the present hubble tension and jwst, miras have utility in the extragalactic distance scale to check cepheid distances or calibrate nearby sne in early-type host galaxies that would be unlikely targets for cepheid searches. | hubble space telescope observations of mira variables in the sn ia host ngc 1559: an alternative candle to measure the hubble constant |
context. for gaia dr2, 280 million spectra collected by the radial velocity spectrometer instrument on board gaia were processed, and median radial velocities were derived for 9.8 million sources brighter than grvs = 12 mag.aims: this paper describes the validation and properties of the median radial velocities published in gaia dr2.methods: quality tests and filters were applied to select those of the 9.8 million radial velocities that have the quality to be published in gaia dr2. the accuracy of the selected sample was assessed with respect to ground-based catalogues. its precision was estimated using both ground-based catalogues and the distribution of the gaia radial velocity uncertainties.results: gaia dr2 contains median radial velocities for 7 224 631 stars, with teff in the range [3550, 6900] k, which successfully passed the quality tests. the published median radial velocities provide a full-sky coverage and are complete with respect to the astrometric data to within 77.2% (for g ≤ 12.5 mag). the median radial velocity residuals with respect to the ground-based surveys vary from one catalogue to another, but do not exceed a few 100 m s-1. in addition, the gaia radial velocities show a positive trend as a function of magnitude, which starts around grvs 9 mag and reaches about + 500 m s-1 at grvs = 11.75 mag. the origin of the trend is under investigation, with the aim to correct for it in gaia dr3. the overall precision, estimated from the median of the gaia radial velocity uncertainties, is 1.05 km s-1. the radial velocity precision is a function of many parameters, in particular, the magnitude and effective temperature. for bright stars, grvs ∈ [4, 8] mag, the precision, estimated using the full dataset, is in the range 220-350 m s-1, which is about three to five times more precise than the pre-launch specification of 1 km s-1. at the faint end, grvs = 11.75 mag, the precisions for teff = 5000 and 6500 k are 1.4 and 3.7 km s-1, respectively. | gaia data release 2. properties and validation of the radial velocities |
we present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. we study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. we systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. we find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. in all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad ∼60° angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. we find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. this is also reflected in the infrared and radio signatures of the binary. the final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. the yields for elements on the first peak vary between our simulations, but none of our models is able to explain the solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer time-scales after the mergers, or from core-collapse supernovae. | dynamical mass ejection from binary neutron star mergers |
we use high-resolution cosmological zoom-in simulations from the feedback in realistic environment (fire) project to study the galaxy mass-metallicity relations (mzr) from z = 0-6. these simulations include explicit models of the multiphase ism, star formation, and stellar feedback. the simulations cover halo masses mhalo = 109-1013 m⊙ and stellar masses m* = 104-1011 m⊙ at z = 0 and have been shown to produce many observed galaxy properties from z = 0-6. for the first time, our simulations agree reasonably well with the observed mass-metallicity relations at z = 0-3 for a broad range of galaxy masses. we predict the evolution of the mzr from z = 0-6, as log (z_gas/z_{{⊙}}) = {12 + log (o/h) - 9.0} = 0.35 [log (m_{*}/m_{{⊙}})-10] + 0.93 exp (-0.43z) - 1.05 and log (z*/z⊙) = [fe/h] + 0.2 = 0.40[log (m*/m⊙) - 10] + 0.67exp ( - 0.50z) - 1.04, for gas-phase and stellar metallicity, respectively. our simulations suggest that the evolution of mzr is associated with the evolution of stellar/gas mass fractions at different redshifts, indicating the existence of a universal metallicity relation between stellar mass, gas mass, and metallicities. in our simulations, galaxies above m* = 106 m⊙ are able to retain a large fraction of their metals inside the halo, because metal-rich winds fail to escape completely and are recycled into the galaxy. this resolves a longstanding discrepancy between `subgrid' wind models (and semi-analytic models) and observations, where common subgrid models cannot simultaneously reproduce the mzr and the stellar mass functions. | the origin and evolution of the galaxy mass-metallicity relation |
substantial populations of massive quiescent galaxies at $z\ge3$ challenge our understanding of rapid galaxy growth and quenching over short timescales. in order to piece together this evolutionary puzzle, more statistical samples of these objects are required. established techniques for identifying massive quiescent galaxies are increasingly inefficient and unconstrained at $z>3$. as a result, studies report that as much as 70\% of quiescent galaxies at $z>3$ may be missed from existing surveys. in this work, we propose a new empirical color selection technique designed to select massive quiescent galaxies at $3\lesssim z \lesssim 6$ using jwst nircam imaging data. we use empirically-constrained galaxy sed templates to define a region in the $f277w-f444w$ vs. $f150w-f277w$ color plane that captures quiescent galaxies at $z>3$. we apply this color selection criteria to the cosmic evolution early release science (ceers) survey and identify 44 candidate $z\gtrsim3$ quiescent galaxies. over half of these sources are newly discovered and, on average, exhibit specific star formation rates of post-starburst galaxies. we derive volume density estimates of $n\sim1-4\times10^{-5}$\,mpc$^{-3}$ at $3< z <5$, finding excellent agreement with existing reports on similar populations in the ceers field. thanks to nircam's wavelength coverage and sensitivity, this technique provides an efficient tool to search for large samples of these rare galaxies. | efficient nircam selection of quiescent galaxies at 3 < z < 6 in ceers |
we present the results from a new search for candidate galaxies at z ≈ 8.5-11 discovered over the 850 arcmin2 area probed by the cosmic assembly near-infrared deep extragalactic legacy survey (candels). we use a photometric-redshift selection including both hubble and spitzer space telescope photometry to robustly identify galaxies in this epoch at h 160 < 26.6. we use a detailed vetting procedure, including screening against persistence and stellar contamination, and the inclusion of ground-based imaging and follow-up hubble space telescope imaging to build a robust sample of 11 candidate galaxies, three presented here for the first time. the inclusion of spitzer/irac photometry in the selection process reduces contamination, and yields more robust redshift estimates than hubble alone. we constrain the evolution of the rest-frame ultraviolet luminosity function via a new method of calculating the observed number densities without choosing a prior magnitude bin size. we find that the abundance at our brightest probed luminosities (m uv = - 22.3) is consistent with predictions from simulations that assume that galaxies in this epoch have gas depletion times at least as short as those in nearby starburst galaxies. due to large poisson and cosmic variance uncertainties, we cannot conclusively rule out either a smooth evolution of the luminosity function continued from z = 4-8, or an accelerated decline at z > 8. we calculate that the presence of seven galaxies in a single field extended groth strip is an outlier at the 2σ significance level, implying the discovery of a significant over-density. these scenarios will be imminently testable to high confidence within the first year of observations of the james webb space telescope. | a census of the bright z = 8.5-11 universe with the hubble and spitzer space telescopes in the candels fields |
exoplanets orbiting close to their parent stars may lose some fraction of their atmospheres because of the extreme irradiation. atmospheric mass loss primarily affects low-mass exoplanets, leading to the suggestion that hot rocky planets might have begun as neptune-like, but subsequently lost all of their atmospheres; however, no confident measurements have hitherto been available. the signature of this loss could be observed in the ultraviolet spectrum, when the planet and its escaping atmosphere transit the star, giving rise to deeper and longer transit signatures than in the optical spectrum. here we report that in the ultraviolet the neptune-mass exoplanet gj 436b (also known as gliese 436b) has transit depths of 56.3 +/- 3.5% (1σ), far beyond the 0.69% optical transit depth. the ultraviolet transits repeatedly start about two hours before, and end more than three hours after the approximately one hour optical transit, which is substantially different from one previous claim (based on an inaccurate ephemeris). we infer from this that the planet is surrounded and trailed by a large exospheric cloud composed mainly of hydrogen atoms. we estimate a mass-loss rate in the range of about 108-109 grams per second, which is far too small to deplete the atmosphere of a neptune-like planet in the lifetime of the parent star, but would have been much greater in the past. | a giant comet-like cloud of hydrogen escaping the warm neptune-mass exoplanet gj 436b |
the object frb 20180916b is a well-studied repeating fast radio burst source. its proximity (∼150 mpc), along with detailed studies of the bursts, has revealed many clues about its nature, including a 16.3 day periodicity in its activity. here we report on the detection of 18 bursts using lofar at 110-188 mhz, by far the lowest-frequency detections of any frb to date. some bursts are seen down to the lowest observed frequency of 110 mhz, suggesting that their spectra extend even lower. these observations provide an order-of-magnitude stronger constraint on the optical depth due to free-free absorption in the source's local environment. the absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300-1700 mhz. compared with higher frequencies, the larger burst widths (∼40-160 ms at 150 mhz) and lower linear polarization fractions are likely due to scattering. we find ∼2-3 rad m-2 variations in the faraday rotation measure that may be correlated with the activity cycle of the source. we compare the lofar burst arrival times to those of 38 previously published and 22 newly detected bursts from the ugmrt (200-450 mhz) and chime/frb (400-800 mhz). simultaneous observations show five chime/frb bursts when no emission is detected by lofar. we find that the burst activity is systematically delayed toward lower frequencies by about 3 days from 600 to 150 mhz. we discuss these results in the context of a model in which frb 20180916b is an interacting binary system featuring a neutron star and high-mass stellar companion. | lofar detection of 110-188 mhz emission and frequency-dependent activity from frb 20180916b |
the cold interstellar medium (ism) plays a central role in the galaxy evolution process. it is the reservoir that fuels galaxy growth via star formation, the repository of material formed by these stars, and a sensitive tracer of internal and external processes that affect entire galaxies. consequently, significant efforts have gone into systematic surveys of the cold ism of the galaxies in the local universe. this review discusses the resulting network of scaling relations connecting the atomic and molecular gas masses of galaxies with their other global properties (stellar masses, morphologies, metallicities, star-formation activity…) and their implications for our understanding of galaxy evolution. key take-home messages are as follows: from a gas perspective, there are three main factors that determine the star-formation rate of a galaxy: the total mass of its cold ism, how much of that gas is molecular, and the rate at which any molecular gas is converted into stars. all three of these factors vary systematically across the local galaxy population. the shape and scatter of both the star-formation main sequence and the mass-metallicity relation are deeply linked to the availability of atomic and molecular gas. future progress will come from expanding our exploration of scaling relations into new parameter space (in particular, the regime of dwarf galaxies), better connecting the cold ism of large samples of galaxies with the environment that feeds them (the circumgalactic medium, in particular), and understanding the impact of these large scales on the efficiency of the star-formation process on molecular cloud scales. | the cold interstellar medium of galaxies in the local universe |
au microscopii (au mic) is the second closest pre-main-sequence star, at a distance of 9.79 parsecs and with an age of 22 million years1. au mic possesses a relatively rare2 and spatially resolved3 edge-on debris disk extending from about 35 to 210 astronomical units from the star4, and with clumps exhibiting non-keplerian motion5-7. detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic `activity' on the star8,9. here we report observations of a planet transiting au mic. the transiting planet, au mic b, has an orbital period of 8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4 jupiter radii, and a mass of less than 0.18 jupiter masses at 3σ confidence. our observations of a planet co-existing with a debris disk offer the opportunity to test the predictions of current models of planet formation and evolution. | a planet within the debris disk around the pre-main-sequence star au microscopii |
we describe the design and performance of the near-infrared (1.51-1.70 μm), fiber-fed, multi-object (300 fibers), high resolution (r = λ/δλ ∼ 22,500) spectrograph built for the apache point observatory galactic evolution experiment (apogee). apogee is a survey of ∼105 red giant stars that systematically sampled all milky way populations (bulge, disk, and halo) to study the galaxy’s chemical and kinematical history. it was part of the sloan digital sky survey iii (sdss-iii) from 2011 to 2014 using the 2.5 m sloan foundation telescope at apache point observatory, new mexico. the apogee-2 survey is now using the spectrograph as part of sdss-iv, as well as a second spectrograph, a close copy of the first, operating at the 2.5 m du pont telescope at las campanas observatory in chile. although several fiber-fed, multi-object, high resolution spectrographs have been built for visual wavelength spectroscopy, the apogee spectrograph is one of the first such instruments built for observations in the near-infrared. the instrument’s successful development was enabled by several key innovations, including a “gang connector” to allow simultaneous connections of 300 fibers; hermetically sealed feedthroughs to allow fibers to pass through the cryostat wall continuously; the first cryogenically deployed mosaic volume phase holographic grating; and a large refractive camera that includes mono-crystalline silicon and fused silica elements with diameters as large as ∼400 mm. this paper contains a comprehensive description of all aspects of the instrument including the fiber system, optics and opto-mechanics, detector arrays, mechanics and cryogenics, instrument control, calibration system, optical performance and stability, lessons learned, and design changes for the second instrument. | the apache point observatory galactic evolution experiment (apogee) spectrographs |
the data and analysis methodology used for the sdss/apogee data releases 13 and 14 are described, highlighting differences from the dr12 analysis presented in holtzman et al. some improvement in the handling of telluric absorption and persistence is demonstrated. the derivation and calibration of stellar parameters, chemical abundances, and respective uncertainties are described, along with the ranges over which calibration was performed. some known issues with the public data related to the calibration of the effective temperatures (dr13), surface gravity (dr13 and dr14), and c and n abundances for dwarfs (dr13 and dr14) are highlighted. we discuss how results from a data-driven technique, the cannon, are included in dr14 and compare those with results from the apogee stellar parameters and chemical abundances pipeline. we describe how using the cannon in a mode that restricts the abundance analysis of each element to regions of the spectrum with known features from that element leads to cannon abundances can lead to significantly different results for some elements than when all regions of the spectrum are used to derive abundances. | apogee data releases 13 and 14: data and analysis |
i introduce some improvements to the ppxf method, which measures the stellar and gas kinematics, star formation history (sfh) and chemical composition of galaxies. i describe the new optimization algorithm that ppxf uses and the changes i made to fit both spectra and photometry simultaneously. i apply the updated ppxf method to a sample of 3200 galaxies at redshift 0.6 < z < 1 (median z = 0.76, stellar mass $m_\ast \gtrsim 3\times 10^{10}$ m⊙), using spectroscopy from the lega-c survey (dr3) and 28-bands photometry from two different sources. i compare the masses from new jam dynamical models with the ppxf stellar population m* and show the latter are more reliable than previous estimates. i use three different stellar population synthesis (sps) models in ppxf and both photometric sources. i confirm the main trend of the galaxies' global ages and metallicity [m/h] with stellar velocity dispersion σ* (or central density), but i also find that [m/h] depends on age at fixed σ*. the sfhs reveal a sharp transition from star formation to quenching for galaxies with $\lg (\sigma _\ast /\mathrm{km}\, s^{-1})\gtrsim 2.3$ ($\sigma _\ast \gtrsim 200$$\mathrm{km}\, s^{-1}$), or average mass density within 1 kpc $\lg (\sigma _1^{\rm jam}/\mathrm{\mathrm{m}_{\odot }kpc^{-2}})\gtrsim 9.9$ ($\sigma _1^{\rm jam}\gtrsim 7.9\times 10^9\, \mathrm{\mathrm{m}_{\odot }\ kpc^{-2}}$), or with $[m/h]\gtrsim -0.1$, or with sersic index $\lg n_{\rm ser}\gtrsim 0.5$ ($n_{\rm ser}\gtrsim 3.2$). however, the transition is smoother as a function of m*. these results are consistent for two sps models and both photometric sources, but they differ significantly from the third sps model, which demonstrates the importance of comparing model assumptions. | full spectrum fitting with photometry in ppxf: stellar population versus dynamical masses, non-parametric star formation history and metallicity for 3200 lega-c galaxies at redshift z ≈ 0.8 |
we present a uniform catalog of accurate distances to local molecular clouds informed by the gaia dr2 data release. our methodology builds on that of schlafly et al. first, we infer the distance and extinction to stars along sightlines toward the clouds using optical and near-infrared photometry. when available, we incorporate knowledge of the stellar distances obtained from gaia dr2 parallax measurements. we model these per-star distance-extinction estimates as being caused by a dust screen with a 2d morphology derived from planck at an unknown distance, which we then fit for using a nested sampling algorithm. we provide updated distances to the schlafly et al. sightlines toward the dame et al. and magnani et al. clouds, finding good agreement with the earlier work. for a subset of 27 clouds, we construct interactive pixelated distance maps to further study detailed cloud structure, and find several clouds which display clear distance gradients and/or are comprised of multiple components. we use these maps to determine robust average distances to these clouds. the characteristic combined uncertainty on our distances is ≈5%-6%, though this can be higher for clouds at greater distances, due to the limitations of our single-cloud model. | a large catalog of accurate distances to local molecular clouds: the gaia dr2 edition |
ngc 7793 p13 is a variable (luminosity range ∼100) ultraluminous x-ray source proposed to host a stellar-mass black hole of less than 15 m⊙ in a binary system with orbital period of 64 d and a 18-23 m⊙ b9ia companion. within the extras (exploring the x-ray transient and variable sky) project, we discovered pulsations at a period of ∼0.42 s in two xmm-newton observations of ngc 7793 p13, during which the source was detected at lx ∼ 2.1 × 1039 and 5 × 1039 erg s-1 (0.3-10 kev band). these findings unambiguously demonstrate that the compact object in ngc 7793 p13 is a neutron star accreting at super-eddington rates. while standard accretion models face difficulties accounting for the pulsar x-ray luminosity, the presence of a multipolar magnetic field with b ∼ few × 1013 g close to the base of the accretion column appears to be in agreement with the properties of the system. | discovery of a 0.42-s pulsar in the ultraluminous x-ray source ngc 7793 p13 |
we present improved estimates of several global properties of the milky way, including its current star formation rate (sfr), the stellar mass contained in its disk and bulge+bar components, as well as its total stellar mass. we do so by combining previous measurements from the literature using a hierarchical bayesian (hb) statistical method that allows us to account for the possibility that any value may be incorrect or have underestimated errors. we show that this method is robust to a wide variety of assumptions about the nature of problems in individual measurements or error estimates. ultimately, our analysis yields an sfr for the galaxy of {{\dot{m}}\star }=1.65+/- 0.19 {{m}⊙ } y{{r}-1}, assuming a kroupa initial mass function (imf). by combining hb methods with monte carlo simulations that incorporate the latest estimates of the galactocentric radius of the sun, r0, the exponential scale length of the disk, ld, and the local surface density of stellar mass, {{σ}\star }({{r}0}), we show that the mass of the galactic bulge+bar is m\star b=0.91+/- 0.07× {{10}10} {{m}⊙ }, the disk mass is m\star d=5.17+/- 1.11× {{10}10} {{m}⊙ }, and their combination yields a total stellar mass of {{m}\star }=6.08+/- 1.14× {{10}10} {{m}⊙ } (assuming a kroupa imf and an exponential disk profile). this analysis is based upon a new compilation of literature bulge mass estimates, normalized to common assumptions about the stellar imf and galactic disk properties, presented herein. we additionally find a bulge-to-total mass ratio for the milky way of b/t=0.150-0.019+0.028 and a specific sfr of {{\dot{m}}\star }/{{m}\star }=2.71+/- 0.59× {{10}-11} yr-1. | improved estimates of the milky way's stellar mass and star formation rate from hierarchical bayesian meta-analysis |
our milky way should host an ancient, metal-poor, and centrally concentrated stellar population, which reflects the star formation and enrichment in the few most massive progenitors that coalesced at high redshift to form the proto-galaxy. while metal-poor stars are known to reside in the inner few kiloparsecs of our galaxy, current data do not yet provide a comprehensive picture of such a metal-poor "heart" of the milky way. we use information from gaia data release 3, especially the xp spectra, to construct a sample of 2 million bright (g bp < 15.5 mag) giant stars within 30° of the galactic center (gc) with robust [m/h] estimates, δ[m/h] ≲ 0.1. for ~1.25 million stars we calculate orbits from gaia radial velocity spectrometer velocities and astrometry. this sample reveals an extensive, ancient, and metal-poor population that includes ~18,000 stars with -2.7 < [m/h] < -1.5, representing a stellar mass of ≳5 × 107 m ⊙. the spatial distribution of these [m/h] < -1.5 stars has a gaussian extent of only ${\sigma }_{{{r}}_{{\rm{gc}}}}\sim 2.7\,\mathrm{kpc}$ around the gc, with most orbits confined to the inner galaxy. at high orbital eccentricities, there is clear evidence for accreted halo stars in their pericentral orbit phase. most stars show [α/fe] enhancement and [al/fe]-[mn/fe] abundances expected for an origin in the more massive portions of the proto-galaxy. stars with [m/h] < -2 show no net rotation, whereas those with [m/h] ~ -1 are rotation dominated. these central, metal-poor stars most likely predate the oldest disk population (τ age ≈ 12.5 gyr), which implies that they formed at z ≳ 5, forging the proto-milky way. | the poor old heart of the milky way |
star-forming regions show a rich and varied chemistry, including the presence of complex organic molecules—in both the cold gas distributed on large scales and the hot regions close to young stars where protoplanetary disks arise. recent advances in observational techniques have opened new possibilities for studying this chemistry. in particular, the atacama large millimeter/submillimeter array has made it possible to study astrochemistry down to solar system-size scales while also revealing molecules of increasing variety and complexity. in this review, we discuss recent observations of the chemistry of star-forming environments, with a particular focus on complex organic molecules, taking context from the laboratory experiments and chemical models that they have stimulated. the key takeaway points include the following: the physical evolution of individual sources plays a crucial role in their inferred chemical signatures and remains an important area for observations and models to elucidate. comparisons of the abundances measured toward different star-forming environments (high-mass versus low-mass, galactic center versus galactic disk) reveal a remarkable similarity, which is an indication that the underlying chemistry is relatively independent of variations in their physical conditions. studies of molecular isotopologues in star-forming regions provide a link with measurements in our own solar system, and thus may shed light on the chemical similarities and differences expected in other planetary systems. | astrochemistry during the formation of stars |
stellar-mass black holes and neutron stars represent extremes in gravity, density, and magnetic fields. they therefore serve as key objects in the study of multiple frontiers of physics. in addition, their origin (mainly in core-collapse supernovae) and evolution (via accretion or, for neutron stars, magnetic spindown and reconfiguration) touch upon multiple open issues in astrophysics. in this review, we discuss current mass and spin measurements and their reliability for neutron stars and stellar-mass black holes, as well as the overall importance of spins and masses for compact object astrophysics. current masses are obtained primarily through electromagnetic observations of binaries, although future microlensing observations promise to enhance our understanding substantially. the spins of neutron stars are straightforward to measure for pulsars, but the birth spins of neutron stars are more difficult to determine. in contrast, even the current spins of stellar-mass black holes are challenging to measure. as we discuss, major inroads have been made in black hole spin estimates via analysis of iron lines and continuum emission, with reasonable agreement when both types of estimate are possible for individual objects, and future x-ray polarization measurements may provide additional independent information. we conclude by exploring the exciting prospects for mass and spin measurements from future gravitational wave detections, which are expected to revolutionize our understanding of strong gravity and compact objects. | the masses and spins of neutron stars and stellar-mass black holes |
we derive analytic, closed form, numerically stable solutions for the total flux received from a spherical planet, moon, or star during an occultation if the specific intensity map of the body is expressed as a sum of spherical harmonics. our expressions are valid to arbitrary degree and may be computed recursively for speed. the formalism we develop here applies to the computation of stellar transit light curves, planetary secondary eclipse light curves, and planet-planet/planet-moon occultation light curves, as well as thermal (rotational) phase curves. in this paper, we also introduce starry, an open-source package written in c++ and wrapped in python that computes these light curves. the algorithm in starry is six orders of magnitude faster than direct numerical integration and several orders of magnitude more precise. starry also computes analytic derivatives of the light curves with respect to all input parameters for use in gradient-based optimization and inference, such as hamiltonian monte carlo (hmc), allowing users to quickly and efficiently fit observed light curves to infer properties of a celestial body’s surface map. (please see https://github.com/rodluger/starry, https://rodluger.github.io/starry/, and https://doi.org/10.5281/zenodo.1312286). | starry: analytic occultation light curves |
we present fitting formulae for the dynamical ejecta properties and remnant disk masses from the largest to date sample of numerical relativity simulations. the considered data include some of the latest simulations with microphysical nuclear equations of state (eos) and neutrino transport as well as other results with polytropic eos available in the literature. our analysis indicates that the broad features of the dynamical ejecta and disk properties can be captured by fitting expressions, that depend on mass ratio and reduced tidal parameter. the comparative analysis of literature data shows that microphysics and neutrino absorption have a significant impact on the dynamical ejecta properties. microphysical nuclear eos lead to average velocities smaller than polytropic eos, while including neutrino absorption results in larger average ejecta masses and electron fractions. hence, microphysics and neutrino transport are necessary to obtain quantitative models of the ejecta in terms of the binary parameters. | mapping dynamical ejecta and disk masses from numerical relativity simulations of neutron star mergers |
we present new, more precise measurements of the mass and distance of our galaxy’s central supermassive black hole, sgr a*. these results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting sgr a*, combining 2 decades of speckle imaging and adaptive optics data. specifically, we improve our analysis of the speckle images by using information about a star’s orbit from the deep adaptive optics data (2005-2013) to inform the search for the star in the speckle years (1995-2005). when this new analysis technique is combined with the first complete re-reduction of keck galactic center speckle images using speckle holography, we are able to track the short-period star s0-38 (k-band magnitude = 17, orbital period = 19 yr) through the speckle years. we use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of s0-38 and s0-2 and thereby improve our constraints of the mass (m bh) and distance (ro ) of sgr a*: m bh = (4.02 ± 0.16 ± 0.04) × 106 m ⊙ and 7.86 ± 0.14 ± 0.04 kpc. the uncertainties in m bh and roas determined by the combined orbital fit of s0-2 and s0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of s0-2 alone and a factor of ∼2.5 compared to previous results from stellar orbits. this analysis also limits the extended dark mass within 0.01 pc to less than 0.13 × 106 m ⊙ at 99.7% confidence, a factor of 3 lower compared to prior work. | an improved distance and mass estimate for sgr a* from a multistar orbit analysis |
the assembly and architecture of planetary systems strongly depend on the physical processes governing the evolution and dispersal of protoplanetary disks. since protostars and planets vi, new observations and theoretical insights favor disk winds as being one of those key processes. this chapter provides a comprehensive review of both observations and theory of disk winds. first, we summarize recent observations probing outflowing gas launched over a range of disk radii for a wide range of evolutionary stages, enabling an empirical understanding of how winds evolve. next, we review theoretical advancements in both magnetohydrodynamic and photoevaporative disk wind models and identify predictions that can be confronted with observations. finally, by linking theory and observations we critically assess the role of disk winds in the evolution and dispersal of protoplanetary disks. we conclude by exploring the impact of disk winds on planet formation and evolution and highlight theoretical work, observations, and critical tests for future progress. | the role of disk winds in the evolution and dispersal of protoplanetary disks |
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