Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109..639s&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 109, no. 2, p. 639-649
Astronomy and Astrophysics
Astronomy
25
Color-Magnitude Diagram, Density Distribution, Globular Clusters, Position (Location), Blue Stars, Faint Object Camera, Hubble Space Telescope, Maximum Likelihood Estimates, X Rays
Scientific paper
We have used the Faint Object Camera (FOC) on the Hubble Space Telescope (HST) to observe three fields near the center of the post-collapse globular cluster NGC 6624 in B and V. We use individual stellar positions and a maximum-likelihood technique to measure a position for the cluster center. We then transfer this position and the position of the x-ray source 4U 1820-30 to right ascension and declination, and correct an error of 1.8 sec in an earlier paper. From star counts, we obtain a density profile, with a power-law cusp of slope -0.84 +/- 0.16. No flat core is evident. We construct color-magnitude diagrams down to the main-sequence turnoff near the cluster center, and more than three magnitudes below the turnoff in the outermost field at r = 28 sec. The former diagram reveals a central population of blue stragglers, which has not previously been observed in this cluster. These blue stragglers are quite similar in specific frequency to those recently observed by HST in the core of 47 Tuc, and their presence adds to the growing evidence of stellar interactions in dense globular-cluster cores.
King Ivan R.
Sosin Craig
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