A method to deconvolve mass ratio distribution from binary stars

TL;DR

This paper introduces a novel analytical method to deconvolve the mass ratio distribution of binary stars from observational data, enabling better understanding of binary star evolution and formation.

Contribution

It extends previous deconvolution techniques to directly obtain the cumulative distribution function of mass ratios, applicable to real datasets of binary stars.

Findings

Reproduced previous results for Am stars binary systems.

Discovered an excess of small mass ratio systems in massive binaries.

Method is robust and requires only a single step for deconvolution.

Abstract

To better understand the evolution of stars in binary systems as well as to constrain the formation of binary stars, it is important to know the binary mass-ratio distribution. However, in most cases, i.e. for single-lined spectroscopic binaries, the mass ratio cannot be measured directly but only derived as the convolution of a function that depends on the mass ratio and the unknown inclination angle of the orbit on the plane of the sky. We extend our previous method to deconvolve this inverse problem (Cure et al. 2014), i.e., we obtain as an integral the cumulative distribution function (CDF) for the mass ratio distribution. After a suitable transformation of variables it turns out that this problem is the same as the one for rotational velocities $v \sin i$, allowing a close analytic formulation for the CDF. We then apply our method to two real datasets: a sample of Am stars binary systems, and a sample of massive spectroscopic binaries in the Cyg OB2 Association.} {We are able to reproduce the previous results of Boffin (2010) for the sample of Am stars, while we show that the mass ratio distribution of massive stars shows an excess of small mass ratio systems, contrarily to what was claimed by Kobulnicky et al. (2014). Our method proves very robust and deconvolves the distribution from a sample in just a single step.