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

Abstract

We report on the first spectroscopic search for quiescent degenerate binaries in globular clusters. Our survey is based on a sample of short-period optical variables which are likely optical counterparts of quiescent X-ray sources in omega Centauri (NGC 5139) and NGC 6397. All of the studied candidates have nearly sinusoidal light curves with amplitudes of 0.1--0.35~mag in $V$ and periods of 0.1--1.3~days. This type of variability, most probably originating from the ellipsoidal effect, has been observed in several X-ray novae when they settled into quiescence after an outburst. We find that two of the surveyed systems harbor dim components with masses in excess of one solar masss, making them attractive targets for future investigations. We also suggest that there are two subpopulations of blue stragglers in omega Centauri, differing in mass-transfer history and/or helium content.

Accepted by A&A, 8 pages, 6 figures, discussion expanded following the suggestions of the referee

References in corpus (14)

• X-ray Properties of Black-Hole Binaries
• The Dartmouth Stellar Evolution Database
• Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
• A Binary Origin for Blue Stragglers in Globular Clusters
• Deep ACS Imaging in the Globular Cluster NGC 6397: The Cluster Color Magnitude Diagram and Luminosity Function
• Radio observations of NGC 2808 and other globular clusters: constraints on intermediate mass black holes
• Chandra X-ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)
• A Deep Wide-Field Variable Star Catalog of Omega Centauri
• The Clusters AgeS Experiment (CASE). II. The Eclipsing Blue Straggler OGLEGC-228 in the Globular Cluster 47 Tuc
• Is a binary fraction-age relation responsible for the lack of EHB binaries in globular clusters?
• X-ray Spectral Identification of Three Candidate Quiescent Low-Mass X-ray Binaries in the Globular Cluster NGC 6304
• Millisecond pulsars around intermediate-mass black holes in globular clusters
• The Clusters AgeS Experiment (CASE). III. Analysis of the Eccentric Eclipsing Binary V32 in the Globular Cluster NGC 6397
• Hot subdwarf binaries - Masses and nature of their heavy compact companions

Cited by in corpus (1)

• Metal-Rich SX Phe stars in the Kepler Field