Addendum: ``X-Ray Sources and Their Optical Counterparts in the Globular Cluster M4'' (ApJ, 609, 755 [2004])
Abstract
Luigi Bedin and Ivan King have informed us that the X-ray source CX 2 is in fact the candidate quasi-stellar object (QSO) identified by L.-R. Bedin et al. (ApJ, 609, 755 [2004]). The figure below shows a finding chart of the area around the X-ray position of CX 2 and allows for a direct comparison with the finding chart (Fig. 5) of Bedin et al. (2003).
From the location of the proposed optical counterpart to CX 2 in the color-magnitude diagram (Fig. 4), together with the X-ray-to-optical flux ratio (Fig. 6), we concluded that this X-ray source is a probable cataclysmic variable (CV). That it now turns out to be probably an extragalactic source underlines the difficulties in securely classifying X-ray sources in globular clusters. After removal of CX 2, the number of CVs in M4 is one (CX 1) or possibly two (CX 4). This does not change the conclusions made in § 5, as we only compared the core radii of M4 and 47 Tuc, while CX 2 is at nearly 3 core-radii. We also note that in Table 1, CX 9w is a misprint for CX 9.- Publication:
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The Astrophysical Journal
- Pub Date:
- February 2005
- DOI:
- 10.1086/426683
- Bibcode:
- 2005ApJ...619.1189B
- Keywords:
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- Errata;
- Addenda