On the Formation of Wide Binary sdB and sdO Stars
Abstract
We present a detailed analysis of the conditions required to form subdwarf stars in wide binaries via stable Roche Lobe overflow. Starting with an evolutionary grid of almost 4000 primordial binaries with component masses between approximately 1 to 8 Msun and initial orbital periods of 1 to 200 days, many of these binaries experience an Algol-like phase of evolution and a substantial fraction of those produce binaries containing subdwarfs with orbital periods of between 20 to 500 days. We conclude that: (1) the final period is largely dependent on the assumed physics of non-conservative mass transfer; (2) the donor star (subdwarf progenitor) typically has a mass of between about 3 and 6 solar masses; (3) there is a very natural evolution of subdwarfs from a long-lived sdB stage ( 100 Myr) to the sdO stage ( 30 Myr); and, (4) the range of masses and effective temperatures of sdB and sdO stars can overlap substantially depending on the properties of the primordial binary. Specifically we find that the masses can range from 0.4 to 0.8 Msun, and that sdBs have temperatures in the range of 15000 < Teff (K) < 45000 while the range for sdOs is about 25000 < Teff (K) < 100000. One example of a post-Algol binary that is evolving towards the subdwarf stage is MWC882 (Zhou et al. 2018). The observational implications of this channel are also discussed.
- Publication:
-
American Astronomical Society Meeting Abstracts #234
- Pub Date:
- June 2019
- Bibcode:
- 2019AAS...23421502N