What are the spectroscopic binaries with high mass functions near the Gaia DR3 main sequence?

Abstract

The 3rd data release of the Gaia mission includes orbital solutions for > 10 5 single-lined spectroscopic binaries, representing more than an order of magnitude increase in sample size over all previous studies. This dataset is a treasure trove for searches for quiescent black hole + normal star binaries. We investigate one population of black hole candidate binaries highlighted in the data release: sources near the main sequence in the color-magnitude diagram (CMD) with dynamically-inferred companion masses 𝑀 2 larger than the CMD-inferred mass of the luminous star. We model light curves, spectral energy distributions, and archival spectra of the 14 such objects in DR3 with high-significance orbital solutions and inferred 𝑀 2 > 3 𝑀 . We find that 100% of these sources are mass-transfer binaries containing a highly stripped lower giant donor (0.2 𝑀/𝑀 0.4) and much more massive (2 𝑀/𝑀 2.5) main-sequence accretor. The Gaia orbital solutions are for the donors, which contribute about half the light in the Gaia RVS bandpass but only 20% in the 𝑔−band. The accretors' broad spectral features likely prevented the sources from being classified as double-lined. The donors are all close to Roche lobe-filling (𝑅/𝑅 Roche lobe > 0.8), but modeling suggests that a majority are detached (𝑅/𝑅 Roche lobe < 1). Binary evolution models predict that these systems will soon become detached helium white dwarf + main sequence "EL CVn" binaries. Our investigation highlights both the power of Gaia data for selecting interesting sub-populations of binaries and the ways in which binary evolution can bamboozle standard CMD-based stellar mass estimates.

A Sample of Neutron Star and Black Hole Binaries Detected through Gaia DR3 Astrometry

“…To select our sample, we start with the catalog of 134,598 binaries in the DR3 catalog of non-single stars that are detected using astrometry only (Gaia Collaboration et al 2022). We focus on these binaries, avoiding spectroscopic and photometric binaries, as these have been discussed elsewhere (El-Badry & Rix 2022;Gomel et al 2022;Mazeh et al 2022). For each of these binaries, we calculate the angular orbital separation of the luminous star, a 0 , from the Thiele-Innes parameters, A, B, F , and G, provided in the non-single star catalog following the formula provided by Halbwachs et al (2022):…”