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

Traven, G. and Feltzing, S. and Merle, T. and Van der Swaelmen, M. and Cotar, K. and Church, R. and Zwitter, T. and Ting, Y.-S. and Sahlholdt, C. and Asplund, M. and Bland-Hawthorn, J. and de Silva, G. and Freeman, K. and Martell, S. and Sharma, S. and Zucker, D. and Buder, S. and Casey, A. and D'Orazi, V. and Kos, J. and Lewis, G. and Lin, J. and Lind, K. and Simpson, J. and Stello, D. and Munari, U. and Wittenmyer, R. A. (2020) The GALAH survey: multiple stars and our Galaxy. I. A comprehensive method for deriving properties of FGK binary stars. Astronomy and Astrophysics, 638:A145. ISSN 0004-6361

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Abstract

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 DR2, 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: T-eff[1,T-2], logg([1,2]), [Fe/H], V-r[1,V-2], v(mic[1,2]), v(broad[1,2]), R-[1,R-2], 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, Delta 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 Delta 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 <less than or equal to>q <= 1.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to Published version in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Date Deposited: 08 Feb 2021 04:24
Last Modified: 10 Feb 2021 05:36
Uncontrolled Keywords: data analysis; radial velocities; catalogs; stars: statistics; binaries: spectroscopic; solar astrophysics; stellar astrophysics; astrophysics of galaxies; 85-XX
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
Identification Number or DOI: https://doi.org/10.1051/0004-6361/202037484
URI: http://eprints.usq.edu.au/id/eprint/41142

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