Signatures of unresolved binaries in stellar spectra: implications for spectral fitting. Issue 4 (26th October 2017)

• Record Type: Journal Article
• Authors: El-Badry, Kareem; Rix, Hans-Walter; Ting, Yuan-Sen; Weisz, Daniel R.; Bergemann, Maria; Cargile, Phillip; Conroy, Charlie; Eilers, Anna-Christina
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 473:Issue 4(2018)
• Page Start: 5043
• Page End: 5049
• Publication Date: 2017-10-26
• Subjects: methods: data analysis -- stars: abundances -- binaries: spectroscopic -- Galaxy: stellar content; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stx2758
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: The observable spectrum of an unresolved binary star system is a superposition of two single-star spectra. Even without a detectable velocity offset between the two stellar components, the combined spectrum of a binary system is in general different from that of either component, and fitting it with single-star models may yield inaccurate stellar parameters and abundances. We perform simple experiments with synthetic spectra to investigate the effect of unresolved main-sequence binaries on spectral fitting, modelling spectra similar to those collected by the APOGEE, GALAH and LAMOST surveys. We find that fitting unresolved binaries with single-star models introduces systematic biases in the derived stellar parameters and abundances that are modest but certainly not negligible, with typical systematic errors of 300 K in T eff, 0.1 dex in log g and 0.1 dex in [Fe/H] for APOGEE-like spectra of solar-type stars. These biases are smaller for spectra at optical wavelengths than in the near-infrared. We show that biases can be corrected by fitting spectra with a binary model, which adds only two labels to the fit and includes single-star models as a special case. Our model provides a promising new method to constrain the Galactic binary population, including systems with single-epoch spectra and no detectable velocity offset between the two stars.