The Impact of Evolutionary Envelope Masses on the Evolution of White Dwarfs

Abstract

Whether white dwarf (WD) models should have “thin” or “thick” envelopes of H and He has been a matter of debate for several years. It is well known that the WD evolution depends sensitively on this question (see e.g. Wood 1995). Evolutionary calculations (e.g. Paczynksi 1971) show that at the tip of the Asymptotic Giant Branch (AGB) the envelope masses are tightly correlated with the mass of the hydrogen exhausted core (≈ total mass). Accordingly the masses of hydrogen, M _H, and helium, M _He, on top of the degenerate C/O interiors decrease by orders of magnitudes with increasing stellar mass. In contrast, many applications of WD calculations consider only single values of q _H,_He = log (M _H,He/M _*) asuming either “thick” or “thin” envelopes.