Far‐Ultraviolet Observations of the Globular Cluster NGC 2808 Revisited: Blue Stragglers, White Dwarfs, and Cataclysmic Variables

We present a reanalysis of far-ultraviolet (FUV) observations of the globularcluster NGC 2808 obtained with the Hubble Space Telescope. These data werefirst analyzed by Brown and coworkers, with an emphasis on the bright, bluehorizontal branch (HB) stars in this cluster. Here, our focus is on thepopulation of fainter FUV sources, which include white dwarfs (WDs), bluestragglers (BSs) and cataclysmic variables (CVs). We have therefore constructedthe deepest FUV-NUV colour-magnitude diagram of NGC 2808 and also searched forvariability among our FUV sources. Overall, we have found approx. 40 WD,approx. 60 BS and approx. 60 CV candidates; three of the BSs and two of the CVcandidates are variable. We have also recovered a known RR Lyrae star in thecore of NGC 2808, which exhibits massive (approx. 4 mag) FUV variability. Wehave investigated the radial distribution and found that our CV and BScandidates are more centrally concentrated than the HBs and WD candidates. Thismight be an effect of mass segregation, but could as well be due to thepreferential formation of such dynamically-formed objects in the dense clustercore. For one of our CV candidates we found a counterpart in WFPC2 optical datapublished by Piotto and coworkers.Comment: 27 pages, including 7 figures, accepted for publication in ApJ, minor corrections in Sect.3.1.6. and Fig.