On the Binary Nature of Dust-encircled BD+20 307

TL;DR

This study reveals that BD+20 307 is a short-period spectroscopic binary with nearly identical stars, where only the primary shows lithium, suggesting an older age and recent large collision producing circumbinary dust.

Contribution

The paper provides the first detailed spectroscopic analysis of BD+20 307, identifying it as a binary with contrasting lithium signatures, implying recent dust-generating collisions in an older system.

Findings

BD+20 307 is a ~3.5 day binary with nearly identical stars.

Only the primary star shows a weak lithium line.

The system's dust likely results from a recent large collision.

Abstract

Three epochs of high resolution spectra of the star BD+20 307 show that it is a short period (~3.5 day) spectroscopic binary of two nearly identical stars. Surprisingly, the two stars, though differing in effective temperature by only ~250 K and having a mass ratio of 0.91, show very different Li line equivalent widths. A Li 6707 Angstrom line is only detected from the primary star, and it is weak. This star is therefore likely to be older than 1 Gyr. If so, the large amount of hot circumbinary dust must be from a very large and recent, but very late evolutionarily, collision of planetesimals.