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2000PASP..112.1200H - Publ. Astron. Soc. Pac., 112, 1200-1211 (2000/September-0)
Resolving the controversy over the core radius of 47 Tucanae (NGC 104).
HOWELL J.H., GUHATHAKURTA P. and GILLILAND R.L.
Abstract (from CDS):
De Marchi et al.'s rcore∼12'' value is spuriously low, a result of radially varying bias in the star counts in a magnitude-limited sample; photometric errors and a steeply rising stellar luminosity function cause more stars to scatter across the limiting magnitude into the sample than out of it, especially near the cluster center, where crowding effects are most severe.
Changing the limiting magnitude to the main-sequence turnoff, away from the steep part of the luminosity function, partially alleviates the problem and results in rcore=18''.
Combining such a limiting magnitude with accurate photometry derived from point-spread function fitting, instead of the less accurate aperture photometry employed by De Marchi et al., results in a reliable measurement of the density profile that is well fitted by rcore=22''±2''.
The Calzetti et al. FOC-based density profile measurement is also likely to have been biased by a poor choice of limiting magnitude and large radially varying photometric errors associated with aperture photometry. Archival Wide Field Planetary Camera 2 (WFPC2) data are used to derive a star list with a higher degree of completeness, greater photometric accuracy, and wider area coverage than the WFPC1 and FOC data sets; the WFPC2-based density profile supports the above conclusions, yielding rcore=24".0±1".9.
Abstract Copyright: ∼
Journal keyword(s): globular clusters: individual (47 Tucanae, NGC 104) - Galaxy: Globular Clusters: General - Methods: Data Analysis - Techniques: Photometric
Simbad objects: 1
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