Investigating ChaMPlane X-ray sources in the Galactic Bulge with Magellan LDSS2 spectra

Abstract

We have carried out optical and X-ray spectral analyses on a sample of 136 candidate optical counterparts of X-ray sources found in five Galactic-bulge fields included in our Chandra Multi-wavelength Plane Survey. We use a combination of optical spectral fitting and quantile X-ray analysis to obtain the hydrogen column density towards each object, and a three-dimensional dust model of the Galaxy to estimate the most probable distance in each case. We present the discovery of a population of stellar coronal emission sources, likely consisting of pre-main sequence, young main sequence and main sequence stars, as well as a component of active binaries of RS CVn or BY Dra type. We identify one candidate quiescent low-mass X-ray binary with a sub-giant companion; we note that this object may also be an RS CVn system. We report the discovery of three new X-ray detected cataclysmic variables (CVs) in the direction of the Galactic Center (at distances ~2kpc). This number is in excess of predictions made with a simple CV model based on a local CV space density of <~ 10^-5 pc^-3, and a scale height ~200pc. We discuss several possible reasons for this observed excess.

41 pages, 11 figures. Accepted for publication in Astrophysical Journal, September 10 edition

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• The X-ray source content of the XMM-Newton Galactic Plane Survey
• Discovery of a Significant Magnetic CV Population in the Limiting Window
• The Chandra ACIS Timing Survey Project: glimpsing a sample of faint X-ray pulsators
• The XMM-Newton SSC survey of the Galactic Plane
• ChaMPlane Deep Galactic Bulge Survey. I. Faint accretion-driven binaries in the Limiting Window
• DRAFTS: A Deep, Rapid Archival Flare Transient Search in the Galactic Bulge
• The ChaMPlane bright X-ray sources - Galactic longitudes l = 2-358 deg
• Spectroscopic Follow-up of X-ray Sources in the ChaMPlane Survey: Identification of a New Cataclysmic Variable
• The Galactic Plane at faint X-ray fluxes - I: Properties and characteristics of the X-ray source population