科研之友
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摘要
We report on the discovery of an instability in low-mass stars just above the threshold (similar to 0.35 M-circle dot) where they are expected to be fully convective on the main sequence (MS). Non-equilibrium He-3 burning creates a convective core, which is separated from a deep convective envelope by a small radiative zone. The steady increase in central He-3 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 it has a separate convective core and envelope. These periodic events eventually cease when the He-3 abundance throughout the star is sufficiently high that the star is fully convective, and remains so for the rest of its MS 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.
- 出版日期2012-6-1
