Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...18110804c&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #108.04D; Bulletin of the American Astronomical Society, Vol. 24, p.1294
Astronomy and Astrophysics
Astronomy
Scientific paper
Cataclysmic variable stars (CVs) are common and well studied objects in the field, characterized by Balmer emission lines on a blue continuum, and understood to be white dwarfs accreting from low mass companions. It has been thought for some time, and recent theoretical modeling of stellar collisions confirm, that CVs should also be present in significant numbers in at least the high mass and/or compact core globular clusters. Yet only one CV is currently known to be a cluster member; two historical novae are also believed to be cluster CVs, but their quiescent counterparts have not been found. It has been suggested that the low luminosity (L_x <= 10(34.5) ergs) compact x-ray sources in globulars, are CVs (Hertz and Grindlay 1983), although previous attempts at optical identification of these sources have failed to produce any CV-type counterparts. The overall aim of this work is to find CVs in globulars; alternatively we will set limits on their numbers which should usefully constrain current models of cluster stellar populations and dynamics. Unlike most previous work, this study focuses mainly on cluster cores, as recent modeling suggests that \about 80% of CVs should reside within just 2 core radii of the cluster centers. We attempt to circumvent as much as possible the major difficulties facing CV searches with the following tactics: focus exclusively on nearby globular clusters, to maximize CV flux and minimize effective crowding; supplement ground-based observations with HST images of the cluster centers where even 1'' seeing is woefully inadequate; and use ROSAT to look for new low luminosity sources, whose optical identification should be eased by the proximity of their hosts and the high spatial resolution of the HRI instrument. This work focuses on three nearby globulars: NGC6397, NGC6752, and 47-Tuc. The data consist of ground-based photometry in Hα and R on all three clusters; HST PC photometry of the centers of N6397 and N6752, also in Hα and R; and deep ROSAT HRI exposures of N6397 and N6752. We have also analyzed archival HST FOC data in UV filters of N6397. We describe our results to date, which include the
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