A search for dormant binaries with degenerate components in omega Centauri and NGC 6397

作者：Rozyczka M^*; Kaluzny J; Pietrukowicz P; Pych W; Catelan M; Contreras C; Thompson I B

来源：Astronomy & Astrophysics, 2010, 524: A78.

DOI：10.1051/0004-6361/201015295

• stars: general
• binaries: close
• blue stragglers
• subdwarfs
• globular clusters: individual: NGC 5139 (omega Centauri)
• globular clusters: individual: NGC 6397

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 omega 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-circle dot, making them attractive targets for future investigations. We also suggest that there are two subpopulations of blue stragglers in omega Centauri, differing in either mass-transfer history or helium content, or even in both at once.

• 出版日期2010-12