Open AccessThe mass ratio distribution of short‐period double degenerate stars
Author(s) -
Maxted P. F. L.,
Marsh T. R.,
Moran C. K. J.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05368.x
Subject(s) - white dwarf , physics , mass ratio , astrophysics , stars , binary number , degenerate energy levels , binary star , mass distribution , stellar evolution , star (game theory) , astronomy , galaxy , arithmetic , mathematics , quantum mechanics
Short‐period double degenerates (DDs) are close white dwarf–white dwarf binary stars which are the result of the evolution of interacting binary stars. We present the first definitive measurements of the mass ratio for two DDs, WD 0136+768 and WD 1204+450, and an improved measurement of the mass ratio for WD 0957−666. We compare the properties of the six known DDs with measured mass ratios to the predictions of various theoretical models. We confirm the result that standard models for the formation of DDs do not predict sufficient DDs with mass ratios close to 1. We also show that the observed difference in cooling ages between white dwarfs in DDs is a useful constraint on the initial mass ratio of the binary. A more careful analysis of the properties of the white dwarf pair WD 1704+481.2 leads us to conclude that the brighter white dwarf is older than its fainter companion. This is the opposite of the usual case for DDs and is caused by the more massive white dwarf being smaller and cooling faster. The mass ratio in the sense (mass of younger star)/(mass of older star) is then 1.43±0.06 rather than the value of 0.70±0.03 given previously.