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 globular cluster NGC 2808 obtained with the Hubble Space Telescope. These data were first analyzed by Brown and coworkers, with an emphasis on the bright, blue horizontal- branch ( HB) stars in this cluster. Here, our focus is on the population of fainter FUV sources, which include white dwarfs ( WDs), blue stragglers ( BSs), and cataclysmic variables ( CVs). We have therefore constructed the deepest FUV - NUV color- magnitude diagram of NGC 2808 and searched for variability among our FUV sources. Overall, we have found approximate to 40 WD, approximate to 60 BS, and approximate to 60 CV candidates; three of the BSs and two of the CV candidates are variable. We have also recovered a known RR Lyrae star in the core of NGC 2808, which exhibits massive ( approximate to 4 mag) FUV variability. We have investigated the radial distribution and found that our CV and BS candidates are more centrally concentrated than the HB stars and WD candidates. This might be an effect of mass segregation but could as well be due to the preferential formation of such dynamically formed objects in the dense cluster core. For one of our CV candidates we found a counterpart in WFPC2 optical data published by Piotto and coworkers.