A comprehensive Gaia view of ellipsoidal and rotational red giant binaries

TL;DR

This study utilizes Gaia data to analyze a large sample of red giant binaries, revealing their physical, orbital, and chemical properties, and identifying potential Type Ia supernova progenitors.

Contribution

It provides the largest chemo-dynamical and physical characterization of red giant binaries, including new insights into their evolutionary states and potential supernova progenitors.

Findings

Ellipsoidal variables are low to intermediate-mass stars with radii near Roche lobe.

Eccentricities decrease with smaller radii, indicating tidal circularization.

At least 14 binaries are compatible with Type Ia supernova progenitor models.

Abstract

The latest Gaia Focused Product Release (FPR) provided variability information for $\sim$1000 long-period red giant binaries, the largest sample to date of this binary type having both photometric and spectroscopic time series observations. We cross-matched the Gaia DR3 measurements with the catalogue of long-period red giant candidates from the Gaia FPR, having photometric and radial velocity variability information. Combined with the photo-geometric distances, the extinction, bolometric magnitude, luminosity, spectroscopic radius and mass were estimated. ELL variables are characterized to be low to intermediate-mass stars, with radii as large as the Roche lobe radius of the binary. Eccentricities tend to be lower for primary stars with smaller radii, as the expected result of tidal circularization. Combined with the orbital properties, estimates for the minimum mass of the companion agree with the scenario of a low-mass compact object as the secondary star. There are at least 14 ELL binaries with orbital periods and masses compatible with model predictions for Type Ia SN progenitors. For the rotational variables, their orbital periods, enhanced chromospheric activity, smaller radii and low mass point to a different type of binaries than the original ELL sample. The velocity dispersion is much higher in ELL than in rotational binaries, probably indicating older/younger dynamical ages. The enhanced [$\alpha$/Fe] abundances for some of the ELL binaries resemble the population of young $\alpha$-rich binaries in the thick disk. An episode of mass transfer in those systems may have produced the enhanced $\alpha$ abundances, and the enhanced [Ce/Fe] abundances reported in a few ELL binaries. Luminosities, radii and masses were derived for 243 ELL and 39 rotational binary candidates, the largest Galactic sample of these variables, having chemo-dynamical and physical parameterization.