There continues to be disagreement in the literature on whether or not low mass Helium-core stars experience thermal flashes as they evolve towards the white dwarf track. The presence or absence of thermal flashes can greatly alter the amount of time it takes such a star to evolve from a red giant into a white dwarf. Since these stars are the progenitors of the companions to binary millisecond pulsars, it is important to have an accurate estimate of their ages, as a constraint on the age and birth properties of the binary system. There is no such problem for stars with more massive cores, such as CO white dwarves or stars on the asymtotic giant branch. In these heavier stars, the presence of a thin burning region has made analysis straightforward, and there is a long-standing agreement between observation and theory. The analysis which leads to thermal flash stability criteria for high core mass stars is not applicable to lower mass stars, as the assumption of a thin burning region breaks down. For the low mass stars, a slightly different and more computationally intensive analysis is required to determine whether a thermal flash will occur. The problem of thermal stability of shell burning in low mass white dwarves is solved by normal mode analysis. We determine the region of instability and time scale of linear growth of the flash. Results are compared to previous work in the field and applied to the problem of the ages of PSR J1012+5307 and its white dwarf companion, which are discrepant by over an order of magnitude.
American Astronomical Society Meeting Abstracts #189
- Pub Date:
- January 1997