Henri Boffin – Science - Know your partner

The mass-ratio distribution of spectroscopic binaries

Binarity is now a well-established quality affecting a large fraction of stars and recent studies have shown that the fraction of binaries is a function of the spectral type of the primary star, with most massive stars being member of a close binary system. Knowing the masses of the components of binary systems is very useful for constraining the possible scenarios that could lead to their existence. While it is sometimes possible to determine the mass of the primary star, it is challenging to obtain good mass estimates of the secondary of a single-line spectroscopic binary. If the sample of such binaries is large enough, however, it is possible to use statistical methods to determine the mass-ratio distribution, and thus, the mass distribution of the secondary.

With my former colleagues Nicolas Cerf and Guy Paulus, we have developed a method based on the Richardson-Lucy deconvolution to derive the mass ratio distribution of single-lined spectroscopic binaries, for which the mass ratio is not directly attainable. This is described in this article and in this one, where there is also a first analysis of a sample of orbits with red giant primaries, obtained by Prof. Roger Griffin. A most recent work on a much larger sample is presented in the paper, My companion is bigger than your companion!, that I wrote with Virginia Trimble for the February 2020 issue of The Observatory.
A paper about the various methods is also available here or here.

I have recently applied the method to study the mass-ratio distribution along the main sequence, using first TGAS and then Gaia DR2 and cross-matching with the SB9 database:

Here is the PDF of the poster at the IAU Symp. 330, Astrometry and Astrophysics in the GAIA sky, held in Nice, April 24-28, 2017, in low or in full resolution.

A first, different attempt at deriving the mass ratio distribution along the main sequence was done in Pourbaix et al. (2004).

I also applied this to other kind of stars:


I have moreover collaborated on a different method, that can be seen here.