Mathieu Servillat, J. Grindlay, M. van den Berg, J. Hong, P. Zhao, B. Allen
We present a multi-object optical spectroscopy follow-up study of X-ray
sources in a field along the Galactic Plane (l=327.42 deg, b=2.26 deg) which is
part of the Chandra Multi-wavelength Plane survey (ChaMPlane). We obtained
spectra for 46 stars, including 15 likely counterparts to X-ray sources, and
sources showing an H-alpha color excess. This has led to the identification of
a new cataclysmic variable (CV), CXOPS J154305.5-522709, also named ChaMPlane
Bright Source 7 (CBS~7), and we identified 8 X-ray sources in the field as
active late-type stars. CBS~7 was previously studied in X-rays and showed a
hard spectrum and two periods: 1.22+/-0.08 h and 2.43+/-0.26 h. We present here
clear evidence that the source is a CV through the detection of H, HeI and HeII
emission lines in its optical spectrum. The hard X-ray spectrum and the
presence of the HeII 4686 in emission with a large equivalent width suggest a
magnetic CV. The near-infrared counterpart is significantly variable, and we
found a period consistent with the longest X-ray period at 2.39+/-0.05 h but
not the shortest X-ray period. If this period is the orbital period, this would
place the system in the CV period gap. The possible orbital period suggests a
dM4+/-1 companion star. The distance is then estimated to be ~1 kpc. The system
could be a relatively hard and X-ray luminous polar or an intermediate polar,
possibly nearly-synchronous.
View original:
http://arxiv.org/abs/1112.0606
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