Uv and Halpha-Bright Stars in the Core of NGC 6752

Details Uv and Halpha-Bright Stars in the Core of NGC 6752 Uv and Halpha-Bright Stars in the Core of NGC 6752

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6823s&link_type=abstract

HST Proposal ID #6823

Physics

Hst Proposal Id #6823 Binaries And Star Fo

Scientific paper

The cores of globular clusters (GCs) are predicted to harbornumerous close, interacting binaries. HST's FOC has revealedthe presence of four UV-excess objects in the core of the GCthecluster. Photometric variability, expected if the starsare cataclysmic variables (CVs), has not been detected.Further, for two of the stars for which archival HST/PC R andHAlpha images exist, no HAlpha excess has been detected. Thelack of both variability and HAlpha excess, as well as thefact that none of the stars has been observed in outburst,suggests, but does not rule out, that they are not canonicalcataclysmic variables. We also have extracted post-COSTARobservations from the archive which reveal some two dozen newHAlpha-bright objects in the core, which might well be CVs. Wepropose to obtain red FOS spectra of the two brightest UVstars and two HAlpha excess stars to determine their naturefrom an examination of their spectral features. The detectionof flat continuua and/or emission lines, however weak, wouldlead to identifications as dwarf novae. If instead weak, broadhydrogen and/or helium absorption features are detected,possibly with emission reversals, the candidates would beidentified as novalike CVs. Finally, if narrower photosphericabsorption features are observed, model atmosphere analyses todetermine the stellar effective temperatures, surfacegravities, and helium abundances would be possible. Incombination with the known cluster distance modulus, thesewould in turn allow estimates of the stellar masses.

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