Resolving the Controversy Over the Core Radius of 47 Tucanae (NGC 104)

Abstract

This paper investigates the discrepancy between recent measurements of the density profile of the globular cluster 47 Tuc that have used HST data sets. Guhathakurta et al. (1992) used pre-refurbishment WFPC1 V-band images to derive r_c = 23" +/- 2". Calzetti et al. (1993) suggested that the density profile is a superposition of two King profiles (r_c = 8" and r_c = 25") based on U-band FOC images. De Marchi et al. (1996) used deep WFPC1 U-band images to derive r_c = 12" +/- 2". Differences in the adopted cluster centers are not the cause of the discrepancy. Our independent analysis of the data used by De Marchi et al. reaches the following conclusions: (1) De Marchi et al.'s r_c ~ 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. (2) 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 r_c = 18". (3) Combining such a limiting magnitude with accurate photometry derived from PSF fitting, instead of the less accurate aperture photometry employed by De Marchi et al., results in a reliable measurement of the density profile which is well fit by r_c = 22" +/- 2". Archival WFPC2 data are used to derive a star list with a higher degree of completeness, greater photometric accuracy, and wider areal coverage than the WFPC1 and FOC data sets; the WFPC2-based density profile supports the above conclusions, yielding r_c = 24" +/- 1.9".

22 pages, 5 figures, 1 table; accepted for publication in PASP; see http://www.ucolick.org/~raja/hgg.tar.gz for full-resolution figures

References in corpus (2)

• Internal Dynamics of Globular Clusters
• Globular Cluster Photometry with the Hubble Space Telescope. V. WFPC2 Study of M15's Central Density Cusp

Cited by in corpus (36)

• High Resolution X-ray Imaging of a Globular Cluster Core: Compact Binaries in 47Tuc
• A Deep Chandra Survey of the Globular Cluster 47 Tucanae: Catalog of Point Sources
• Star formation histories of early-type galaxies. I: Higher order Balmer lines as age indicators
• HST Proper Motions and Stellar Dynamics in the Core of the Globular Cluster 47 Tucanae
• Detection of ionized gas in the globular cluster 47 Tucanae
• The Frequency of Binary Stars in the Core of 47 Tucanae
• A Library of Integrated Spectra of Galactic Globular Clusters
• Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate
• The contribution of primordial binaries to the blue straggler population in 47 Tucanae
• Chandra Study of a Complete Sample of Millisecond Pulsars in 47Tuc and NGC6397
• An Extensive Census of HST Counterparts to Chandra X-ray Sources in the Globular Cluster 47 Tucanae. I. Astrometry and Photometry
• Timing the millisecond pulsars in 47 Tucanae
• Discovery of another peculiar radial distribution of Blue Stragglers in Globular Clusters: The case of 47 Tuc
• Chandra Observation of the Globular Cluster NGC 6440 and the Nature of Cluster X-ray Luminosity Functions
• Globular Cluster Abundances from High-Resolution Integrated Light Spectra, I: 47 Tuc
• Monte Carlo Simulations of Star Clusters - VII. The globular cluster 47 Tuc
• X-ray Studies of Two Neutron Stars in 47 Tucanae: Toward Constraints on the Equation of State
• A Far-Ultraviolet Survey of 47 Tucanae. I. Imaging
• Population Synthesis in the Blue II. The Spectroscopic Age of 47 Tucanae
• Stellar Exotica in 47 Tucanae
• Testing Newtonian Gravity with AAOmega: Mass-To-Light Profiles and Metallicity Calibrations From 47 Tuc and M55
• New Cataclysmic Variables and other Exotic Binaries in the Globular Cluster 47 Tucanae
• Is Dust Forming on the Red Giant Branch in 47 Tuc?
• Population Synthesis in the Blue I. Synthesis of the Integrated Spectrum of 47 Tucanae from its Color-Magnitude Diagram
• Discovery and timing of pulsars in the globular cluster M13 with FAST
• Spectrum Syntheses of High Resolution Integrated Light Spectra of Galactic Globular Clusters
• Upper limits on the central black hole masses of 47Tuc and NGC6397
• The radio luminosity distribution of pulsars in 47 Tucanae
• Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6752
• Optimal Integrated Abundances for Chemical Tagging of Extragalactic Globular Clusters
• Tracing the Dynamical History of the Globular Cluster 47 Tucanae
• A Polarimetric Survey for Dust in 47 Tucanae (NGC 104)
• Quantum effects and stability of chameleon cosmology
• A new pulsar candidate in 47 Tucanae discovered with MeerKAT imaging
• Are there brown dwarfs in globular clusters?
• Far-Ultraviolet Surveys of Globular Clusters: Hunting for the Products of Stellar Collisions and Near Misses