HST observations of Cataclysmic Variables in the Globular Cluster 47 Tucanae

Details HST observations of Cataclysmic Variables in the Globular Cluster 47 Tucanae HST observations of Cataclysmic Variables in the Globular Cluster 47 Tucanae

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...19310104e&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #101.04; Bulletin of the American Astronomical Society, Vol. 30, p.1399

Astronomy and Astrophysics

Astronomy

Scientific paper

We present analysis of Faint Object Spectrograph observations of three likely cataclysmic variables (CVs) in the massive globular cluster 47 Tucanae. Optical and UV spectra of AKO9, an eclipsing binary known to undergo dramatic UV outbursts, were obtained during eclipse. These spectra, when combined with HST photometry, show that AKO9 has a bright UV component, U band flickering and emission lines in the optical and UV, all characteristic CV properties. The period for this system of 1.1 days is longer than most CV periods, but is consistent with the subgiant secondary. The large disk expected for such a system may explain the bright UV component, but appears inconsistent with the rapid outburst observed by Minniti et al. Alternative explanations for the behavior of AKO9 are briefly discussed. We also analyze UV and optical spectra of the faint variables V2 (a probable dwarf nova) and V3. An optical spectrum of V2 is compared with the spectra of CVs in NGC 6397 to study the theory that magnetic CVs are overabundant in globular clusters. We also comment on plausible ranges for the X-ray to optical ratio for this CV. Finally, by accounting for aperture contamination by a blue straggler we show that V3 has a blue excess and emission lines. Overall, these results suggest that deeper HST photometry of the center of 47 Tuc combined with upcoming AXAF observations are likely to find many more compact binaries in this cluster, with signficant ramifications for dynamical and evolutionary studies of globular clusters.

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