X-ray Sources and their Optical Counterparts in the Galactic Globular Cluster M12 (NGC 6218)
We study a Chandra X-ray Observatory ACIS-S observation of the Galactic globular cluster M12. With a 26 ks exposure time, we detect six X-ray sources inside the half-mass radius (216) of which two are inside the core radius (072) of the cluster. If we assume that these sources are all associated wit...
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Published in | The Astrophysical journal Vol. 705; no. 1; pp. 175 - 183 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Bristol
IOP Publishing
01.11.2009
IOP |
Subjects | |
Online Access | Get full text |
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Summary: | We study a Chandra X-ray Observatory ACIS-S observation of the Galactic globular cluster M12. With a 26 ks exposure time, we detect six X-ray sources inside the half-mass radius (216) of which two are inside the core radius (072) of the cluster. If we assume that these sources are all associated with globular cluster M12, the luminosity L X among these sources between 0.3 and 7.0 keV varies roughly from 1030 to 1032 erg s-1. For identification, we also analyzed the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and Wide Field and Planetary Camera 2 (WFPC2) data and identified the optical counterparts to five X-ray sources inside the HST ACS field of view. According to the X-ray and optical features, we found 2-5 candidate active binaries (ABs) or cataclysmic variables (CVs) and 0-3 background galaxies within the HST ACS field of view. Based on the assumption that the number of X-ray sources scales with the encounter rate and the mass of the globular cluster, we expect two X-ray sources inside M12, and the expectation is consistent with our observational results. Therefore, the existence of identified X-ray sources (possible CVs or ABs) in M12 suggests the primordial origin of X-ray sources in globular clusters which is in agreement with previous studies. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 0004-637X 1538-4357 |
DOI: | 10.1088/0004-637X/705/1/175 |