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White Dwarf Candidates in the Globular Cluster NGC 6752

Published online by Cambridge University Press:  12 April 2016

Harvey B. Richer
Harvey B. Richer*
Affiliation:
Department of Geophysics and Astronomy, University of British Columbia, Vancouver, Canada

Extract

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In a recent paper (Richer 1978, hereafter Paper I) the results of a search for faint blue objects in and around the globular cluster NGC 6752 were reported. The aim of the program was to isolate a sample of white dwarf candidates in this cluster which could then be studied in further detail. The plate material for this survey consisted of a set of deep UBV plates (only one in each color) obtained at the prime focus of the Cerro Tololo Interamerican Observatory 4-meter telescope. Limiting magnitudes reached by the plates were about U=22.4, B=23.0, V=22.0. A reanalysis of the photometry presented in Paper I (using a reduction program supplied by W. Harris [see Stetson and Harris 1977]) has now yielded a total of 68 candidate objects within 20′ of the cluster center having B≤22.7 and (U–B) ≤ –0.4. Although the accuracy of the photometry is low (about ±0.2 magnitudes), it seems clear that the preponderance of the objects do not have UBV colors typical of white dwarfs. Of the 68 candidate objects, 36 had a measurable V magnitude, and only 11 of these lay in the area of the color-color diagram known to be occupied by white dwarfs (Eggen and Greenstein 1965). The remaining 25 were generally well above the black body line in the two-color diagram and are probably QSO’s or peculiar blue stellar objects. Among these 11 good candidates, 7 are within 14’ of the cluster center and hence have a probability of greater than 50% of being cluster members according to the star counts of King et al (1968) assuming that white dwarfs have a radial distribution in NGC 6752 similar to other cluster members.

Type
Colloquium Session IV
Information
International Astronomical Union Colloquium , Volume 53: White Dwarfs and Variable Degenerate Stars , August 1979 , pp. 259 - 265
Copyright
Copyright © The University of Rochester 1979

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