An Eclipsing White Dwarf-M Dwarf system comoving with an M Dwarf

  Marco Lam [1, 3]  ,  Paul Ross McWhirter [2, 3]  
[1] [1] Tel Aviv University
[2] [2] Instituto de Astrofísica de Canarias
[3] [3] Liverpool John Moores University

Post-Common Envelope Binary (PCEB) are short-period binary systems consisting of a white dwarf (WD) and a main sequence (MS) star, the end product of common envelope evolution. A PCEB system loses angular momentum via magnetic braking and gravitational waves and will eventually begin mass-transfer, resulting in a cataclysmic variable (CV). Thus, they are the progenitor system of CVs. The MS stars tend to have high metallicity, which is hypothesised to come from the accretion during the process of common envelope evolution. However, there are few systems that we can study in detail, namely, the ones with eclipse(s) and measurable radial velocities from which we can extract the full set of stellar and orbital parameters. Current evidence shows that we have discovered such a system containing a mid-M dwarf and, potentially, the lowest mass WD in an eclipsing PCEB to date. This system is coincidentally comoving with another approximately equal-mass, equal-distance mid-M dwarf at a projected distance of 500AU (5′′ on sky). Given that coeval system that should all have the same metal content at birth, they give us an excellent opportunity to measure the extent of metallicity enrichment in the CE phase.