Rediscussion of eclipsing binaries. Paper XXIX. The F-type twin system BS Draconis

TL;DR

This paper provides a detailed analysis of the eclipsing binary BS Draconis using TESS and spectroscopic data, accurately measuring stellar parameters and confirming its potential as a precise celestial clock.

Contribution

It offers the first definitive identification of the primary eclipse and combines TESS and Gaia data to refine stellar parameters and system age.

Findings

Masses of 1.305 and 1.284 Msun for the stars

Radii of 1.409 and 1.400 Rsun for the stars

Eclipse timing scatter of only 0.37 seconds

Abstract

We present an analysis of BS Dra, a detached eclipsing binary containing two almost-identical F3 V stars in a 3.36-d circular orbit, based on 40 sectors of observations from the Transiting Exoplanet Survey Satellite (TESS) and published spectroscopic results. We measure masses of 1.305 +/- 0.015 Msun and 1.284 +/- 0.017 Msun, and radii of 1.409 +/- 0.006 Rsun and 1.400 +/- 0.006 Rsun, for the two components. The high quality of the TESS data allow -- for the first time -- a definitive identification of the primary eclipse, which is 0.007 mag deeper than the secondary. The primary star is the hotter, larger and more massive of the two: the ratios of the radii and surface brightnesses are both slightly but significantly below unity. We find a distance concordant with the Gaia DR3 parallax and, by comparison to theoretical models, an age of 1600 +/- 300 Myr and a slightly sub-solar chemical composition. Our mean times of primary eclipse, each representing all eclipses in one sector, have a scatter of only 0.37 s around a linear ephemeris: BS Dra may be useful as a celestial clock.