Far-Ultraviolet Luminosity Functions for M3 and M13

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Session 74 -- Globular Clusters
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[74.10] Far-Ultraviolet Luminosity Functions for M3 and M13

J.H. Whitney, R.W. O'Connell, R.T. Rood (UVa), R.C. Bohlin (STScI), K.P. Cheng (GSFC), P.M.N. Hintzen (GSFC), W.B. Landsman (Hughes STX), M.S. Roberts (NRAO), A.M. Smith, E.P. Smith, and T.P. Stecher (GSFC)

Far-ultraviolet exposures (centroid 1620 \AA; bandwidth 225 \AA; field of view 40\'{ } diameter; exposure times 199 and 46 seconds) were obtained of the globular clusters M3 (NGC 5272) and M13 (NGC 6205) with the Ultraviolet Imaging Telescope during the Astro-1 mission. In addition to the previously known Post-Asymptotic Giant Branch stars vZ1128 and Barnard 29, we detect many less luminous hot stars in each cluster. The M3 photometry extends to a far-ultraviolet (FUV) magnitude of 16.1. This is a faint enough limit to detect many of the cluster's blue horizontal branch (HB) stars as well as a number of hot stars above the HB. Approximately 70 sources are detected, of which one fifth are above the HB. The M13 photometry extends to an FUV magnitude of 14.0. This is significantly brighter than the expected FUV magnitude of the zero-age HB; therefore, we interpret the detected sources as evolved hot stars above the HB. We find approximately twice as many hot stars above the HB of M13 as compared with M3, consistent with the bluer HB of M13. We compare our luminosity functions with theoretical HB models to determine the evolutionary status of the hot populations of these clusters.

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