X-RAY SOURCES AND THEIR OPTICAL COUNTERPARTS IN THE GALACTIC GLOBULAR CLUSTER M12 (NGC 6218)
- Institute of Astronomy and Department of Physics, National Tsing Hua University, Taiwan (China)
- SRON, Netherlands Institute for Space Research Sorbonnelaan 2, 3584 CA, Utrecht (Netherlands)
- Astronomical Institute, Utrecht University, P.O. Box 80000, 3508 TA, Utrecht (Netherlands)
- Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
- Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
- Astronomy Department, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States)
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 (2.'16) of which two are inside the core radius (0.'72) of the cluster. If we assume that these sources are all associated with globular cluster M12, the luminosity L {sub X} among these sources between 0.3 and 7.0 keV varies roughly from 10{sup 30} to 10{sup 32} erg s{sup -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.
- OSTI ID:
- 21378410
- Journal Information:
- Astrophysical Journal, Vol. 705, Issue 1; Other Information: DOI: 10.1088/0004-637X/705/1/175; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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