Identification of Galactic Bulge Survey X-Ray Sources with Tycho-2 Stars

Robert I. Hynes, N. J. Wright, Thomas Maccarone, Peter G. Jonker, S. Greiss, D. Steeghs, M A.P. Torres, C. T. Britt, G. Nelemans

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Abstract

We identify 69 X-ray sources discovered by the Galactic Bulge Survey (GBS) that are coincident with or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-ray-to-optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also examine Two Micron All Sky Survey colors, variability information from the All-Sky Automated Survey, and X-ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very mixed selection, ranging in spectral class from O9 to M3. In some
Original languageEnglish
Pages (from-to)162
JournalAstrophysical Journal
StatePublished - Dec 2012

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Hynes, R. I., Wright, N. J., Maccarone, T., Jonker, P. G., Greiss, S., Steeghs, D., Torres, M. A. P., Britt, C. T., & Nelemans, G. (2012). Identification of Galactic Bulge Survey X-Ray Sources with Tycho-2 Stars. Astrophysical Journal, 162.