Jennifer L. van Saders, Marc H. Pinsonneault
We report on the discovery of an instability in low mass stars just above the
threshold ($\sim 0.35 \textrm{M}_{\odot}$) where they are expected to be fully
convective on the main sequence. Non-equilibrium He3 burning creates a
convective core, which is separated from a deep convective envelope by a small
radiative zone. The steady increase in central He3 causes the core to grow
until it touches the surface convection zone, which triggers fully convective
episodes in what we call the "convective kissing instability". These episodes
lower the central abundance and cause the star to return to a state in which is
has a separate convective core and envelope. These periodic events eventually
cease when the He3 abundance throughout the star is sufficiently high that the
star is fully convective, and remains so for the rest of its main sequence
lifetime. The episodes correspond to few percent changes in radius and
luminosity, over Myr to Gyr timescales. We discuss the physics of the
instability, as well as prospects for detecting its signatures in open clusters
and wide binaries. Secondary stars in cataclysmic variables (CVs) will pass
through this mass range, and this instability could be related to the observed
paucity of such systems for periods between two and three hours. We demonstrate
that the instability can be generated for CV secondaries with mass-loss rates
of interest for such systems, and discuss potential implications.
View original:
http://arxiv.org/abs/1201.5381
No comments:
Post a Comment