MINESweeper: Spectrophotometric Modeling of Stars in the Gaia Era

Cargile, Phillip A.; Conroy, Charlie; Johnson, Benjamin D.; Ting, Yuan-Sen; Bonaca, Ana; Dotter, Aaron; Speagle, Joshua S.

doi:10.48550/arxiv.1907.07690

Cited by 9 publications

(15 citation statements)

References 52 publications

(69 reference statements)

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“…The key outputs from the survey are radial velocities precise to 1 km s −1 , [Fe/H] and [α/Fe] abundances precise to 0.1 dex, and spectrophotometric distances precise to 10% (see Cargile et al 2019 for details on the stellar parameter pipeline). Combined with Gaia proper motions (SNR>3 for >90% of the sample), H3 thus provides the full 6D phase-space and 2D chemicalspace for the sample stars.…”

Section: Methodsmentioning

confidence: 99%

Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure

Naidu,

Conroy,

Bonaca

et al. 2020

Preprint

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In the ΛCDM paradigm the Galactic stellar halo is predicted to harbor the accreted debris of smaller systems. To identify these systems, the H3 Spectroscopic Survey, combined with Gaia, is gathering 6D phase-space and chemical information in the distant Galaxy. Here we present a comprehensive inventory of structure within 50 kpc from the Galactic center using a sample of 5684 giants at |b| > 40 • and |Z| > 2 kpc. We identify known structures including the high-α disk, the in-situ halo (disk stars heated to eccentric orbits), Sagittarius (Sgr), Gaia-Sausage-Enceladus (GSE), the Helmi Streams, Sequoia, and Thamnos. Additionally, we identify the following new structures: (i) Aleph ([Fe/H]= −0.5), a low eccentricity structure that rises a surprising 10 kpc off the plane, (ii, iii) Arjuna ([Fe/H]= −1.2) and I'itoi ([Fe/H]< −2), which comprise the high-energy retrograde halo along with Sequoia, and (iv) Wukong ([Fe/H]= −1.6), a prograde phase-space overdensity chemically distinct from GSE. For each structure we provide [Fe/H], [α/Fe], and orbital parameters. Stars born within the Galaxy are a major component at |Z| ∼2 kpc (≈60%), but their relative fraction declines sharply to 5% past 15 kpc. Beyond 15 kpc, >80% of the halo is built by two massive (M ∼ 10 8 − 10 9 M ) accreted dwarfs: GSE ([Fe/H]= −1.2) within 25 kpc, and Sgr ([Fe/H]= −1.0) beyond 25 kpc. This explains the relatively high overall metallicity of the halo ([Fe/H]≈ −1.2). We attribute 95% of the sample to one of the listed structures, pointing to a halo built entirely from accreted dwarfs and heating of the disk.

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Section: Methodsmentioning

confidence: 99%

Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure

Naidu,

Conroy,

Bonaca

et al. 2020

Preprint

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“…Stellar parameters including [Fe/H] and [α/Fe], distance, radial velocity, mass, and age are measured with MINESweeper (Cargile et al 2019). MINESweeper determines physical stellar parameters by using MIST (Choi et al 2016) stellar isochrones to determine the evolutionary state, mass, and initial bulk composition of stars 1 which are then "matched" to both model spectra and photometry using a custom grid of custom stellar spectral models.…”

Section: Introductionmentioning

confidence: 99%

“…Gaia parallaxes and a Galactic density and age model are included as priors. See Conroy et al (2019b) and Cargile et al (2019) for more details. The typical precision on derived parameters are 1 km s −1 for radial velocities, 0.1 dex for [Fe/H] and [α/Fe], and 10% for spectrophotometric distances.…”

Section: Introductionmentioning

confidence: 99%

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Ancient Very Metal-Poor Stars Associated With the Galactic Disk in the H3 Survey

Carter,

Conroy,

Zaritsky

et al. 2020

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Ancient, very metal-poor stars offer a window into the earliest epochs of galaxy formation and assembly. We combine data from the H3 Spectroscopic Survey and Gaia to measure metallicities, abundances of α elements, stellar ages, and orbital properties of a sample of 482 very metal-poor (VMP; [Fe/H]< −2) stars in order to constrain their origins. This sample is confined to 1 |Z| 3 kpc from the Galactic plane. We find that > 70% of VMP stars near the disk are on prograde orbits and this fraction increases toward lower metallicities. This result unexpected if metal-poor stars are predominantly accreted from many small systems with no preferred orientation, as such a scenario would imply a mostly isotropic distribution. Furthermore, we find there is some evidence for higher fractions of prograde orbits amongst stars with lower [α/Fe]. Isochrone-based ages for main sequence turn-off stars reveal that these VMP stars are uniformly old (≈ 12 Gyr) irrespective of the α abundance and metallicity, suggesting that the metal-poor population was not born from the same well-mixed gas disk. We speculate that the VMP population has a heterogeneous origin, including both in-situ formation in the ancient disk and accretion from a satellite with the same direction of rotation as the ancient disk at early times. Our precisely measured ages for these VMP stars on prograde orbits show that the Galaxy has had a relatively quiescent merging history over most of cosmic time, and implies the angular momentum alignment of the Galaxy has been in place for at least 12 Gyr.

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“…The philosophy and approach of combining all available observational data in order to extract the maximum amount of information from studied objects have previously been proposed and developed for example by Schönrich & Bergemann (2014), and recently by Cargile et al (2019). In contrast to these studies of single stars, we avoid using models of stellar evolution (e.g.…”

Section: Comparison To Previous Workmentioning

confidence: 99%

The GALAH survey: Multiple stars and our Galaxy. I. A comprehensive method for deriving properties of FGK binary stars

Traven,

Feltzing,

Merle

et al. 2020

Preprint

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Context. Binary stellar systems form a large fraction of the Galaxy's stars. They are useful as laboratories for studying the physical processes taking place within stars, and must be correctly taken into account when observations of stars are used to study the structure and evolution of the Galaxy. The advent of large-scale spectroscopic and photometric surveys allows us to obtain large samples of binaries that permit characterising their populations. Aims. We aim to obtain a large sample of double-lined spectroscopic binaries (SB2s) by analysis of spectra from the GALAH survey in combination with photometric and astrometric data. A combined analysis will provide stellar parameters of thousands of binary stars that can be combined to form statistical observables of a given population. We aim to produce a catalogue of well-characterised systems, which can in turn be compared to models of populations of binary stars, or to follow-up individual systems of interest. Methods. We obtained a list of candidate SB2 systems from a t-distributed stochastic neighbour embedding (t-SNE) classification and a cross-correlation analysis of GALAH spectra. To compute parameters of the primary and secondary star, we used a Bayesian approach that includes a parallax prior from Gaia DR2, spectra from GALAH, and apparent magnitudes from APASS, Gaia, 2MASS, and WISE. We used a Markov chain Monte Carlo approach to sample the posterior distributions of the following model parameters for the two stars:, and E(B − V). Results. We present results for 12 760 binary stars detected as SB2s. We construct the statistical observables T 1 /T 2 , ∆V r , and R 1 /R 2 , which demonstrate that our sample mostly consists of dwarfs, with a significant fraction of evolved stars and several dozen members of the giant branch. The majority of these binary stars is concentrated at the lower boundary of the ∆V r distribution, and the R 1 /R 2 ratio is mostly close to unity. The derived metallicity of our binary stars is statistically lower than that of single dwarf stars from the same magnitude-limited sample. Conclusions. Our sample of binary stars represents a large population of well-characterised double-lined spectroscopic binaries that are appropriate for statistical studies of the binary populations. The derived stellar properties and their distributions show trends that are expected for a population of close binary stars (a < 10 AU) detected through double lines in their spectra. Our detection technique allows us to probe binary systems with mass ratios 0.5 ≤ q ≤ 1.

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MINESweeper: Spectrophotometric Modeling of Stars in the Gaia Era

Cited by 9 publications

References 52 publications

Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure

Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure

Ancient Very Metal-Poor Stars Associated With the Galactic Disk in the H3 Survey

The GALAH survey: Multiple stars and our Galaxy. I. A comprehensive method for deriving properties of FGK binary stars

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