Double-lined spectroscopic binaries in the APOGEE DR16 and DR17 data

TL;DR

This paper develops an automated method to identify double-lined spectroscopic binaries in APOGEE data, revealing their prevalence, orbital characteristics, and potential for follow-up studies, especially in eclipsing systems.

Contribution

The authors created a code to autonomously detect SB2s and higher order multiples in APOGEE spectra, expanding the catalog of known spectroscopic binaries and analyzing their properties.

Findings

Approximately 3% of main sequence dwarfs are SB2s.

Most short-period systems (<10 days) have circularized orbits.

Higher SB2 fraction observed in lower metallicity sources.

Abstract

APOGEE spectra offer $\lesssim$1 km s$^{-1}$ precision in the measurement of stellar radial velocities (RVs). This holds even when multiple stars are captured in the same spectrum, as happens most commonly with double-lined spectroscopic binaries (SB2s), although random line of sight alignments of unrelated stars can also occur. We develop a code that autonomously identifies SB2s and higher order multiples in the APOGEE spectra, resulting in 7273 candidate SB2s, 813 SB3s, and 19 SB4s. We estimate the mass ratios of binaries, and for a subset of these systems with sufficient number of measurements we perform a complete orbital fit, confirming that most systems with period $<$10 days have circularized. Overall, we find a SB2 fraction ($F_{SB2}$) $\sim$3\% among main sequence dwarfs, and that there is not a significant trend in $F_{SB2}$ with temperature of a star. We are also able to recover a higher $F_{SB2}$ in sources with lower metallicity, however there are some observational biases. We also examine light curves from TESS to determine which of these spectroscopic binaries are also eclipsing. Such systems, particularly those that are also pre- and post-main sequence, are good candidates for a follow-up analysis to determine their masses and temperatures.