Oscillatory Thermal Instabilities at the Onset of Helium Shell Burning.

Abstract

view Abstract Citations (28) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Oscillatory Thermal Instabilities at the Onset of Helium Shell Burning. Härm, R. ; Schwarzschild, M. Abstract The onset of thermal instability has been investigated in detail for globular-cluster stars in the evolutionary phase during which the helium-burning shell is just forming. The investigation shows that (a) the main unstable phase ("second red-giant phase" or "asymptotic branch") is preceded by a short and inconsequential preliminary unstable phase during which the instability is weak and of an oscillatory character, (b) the main unstable phase generally commences not with a simple exponential instability (real eigenvalue), but with an oscillatory instability (complex eigenvalue), (c) this oscillatory instability appears to be caused by an interaction between the driving layer containing the helium shell source and a reacting layer below the driving layer, and (d) the oscillatory instability gives way (after a quite limited time span) to a simple exponential instability which causes the repetitive helium-shell flashes described in earlier investigations. Publication: The Astrophysical Journal Pub Date: March 1972 DOI: 10.1086/151360 Bibcode: 1972ApJ...172..403H full text sources ADS |