Open AccessOn the late spectral types of cataclysmic variable secondaries
Author(s) -
Baraffe I.,
Kolb U.
Publication year - 2000
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.1365-8711.2000.03628.x
Subject(s) - physics , astrophysics , stellar classification , stars , mass transfer , population , variable star , range (aeronautics) , spectral line , low mass , stellar mass , astronomy , star formation , thermodynamics , demography , materials science , sociology , composite material
We investigate why the spectral type of most cataclysmic variable (CV) secondaries is significantly later than that of a zero‐age main‐sequence (ZAMS) star with the same mean density. Using improved stellar input physics, tested against observations of low‐mass stars at the bottom of the main sequence, we calculate the secular evolution of CVs with low‐mass donors. We consider sequences with different mass transfer rates and with a different degree of nuclear evolution of the donor prior to mass transfer. Systems near the upper edge of the gap ( P ∼3–6 h) can be reproduced by models with a wide range of mass transfer rates from 1.5×10 −9 M ⊙ yr −1 to 10 −8 M ⊙ yr −1 . Evolutionary sequences with a small transfer rate and donors that are substantially evolved off the ZAMS (central hydrogen content 0.05–0.5) reproduce CVs with late spectral types above P ≳6 h. Systems with the most discrepant (late) spectral type should have the smallest donor mass at any given P . Consistency with the period gap suggests that the mass transfer rate increases with decreasing donor mass for evolved sequences above the period gap. In this case, a single‐parameter family of sequences with varying X c and increasing mass transfer rate reproduces the full range of observed spectral types. This would imply that CVs with such evolved secondaries dominate the CV population.