A search for dormant binaries with degenerate components in ω Centauri and NGC 6397
Abstract
Aims: We report on the first spectroscopic search for quiescent degenerate binaries in globular clusters.
Methods: Our survey is based on a sample of short-period optical variables that are likely optical counterparts of the quiescent X-ray sources in ω Centauri (NGC 5139) and NGC 6397.
Results: The studied candidates have nearly sinusoidal light curves with amplitudes of 0.05-0.12 mag in V (0.35 mag in one case) and periods of 0.1-1.3 days. This type of variability, most probably from the ellipsoidal effect, has been observed in X-ray novae when they settled into quiescence after an outburst.
Conclusions: We find that two of the surveyed systems harbor dim components with masses in excess of 1 M_⊙, making them attractive targets for future investigations. We also suggest that there are two subpopulations of blue stragglers in ω Centauri, differing in either mass-transfer history or helium content, or even in both at once.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 2010
- DOI:
- 10.1051/0004-6361/201015295
- arXiv:
- arXiv:1006.5607
- Bibcode:
- 2010A&A...524A..78R
- Keywords:
-
- stars: general;
- binaries: close;
- blue stragglers;
- subdwarfs;
- globular clusters: individual: NGC 5139 (ω Centauri);
- globular clusters: individual: NGC 6397;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted by A&