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Paper: The Discovery of Pulsating Hot Subdwarfs in NGC 2808
Volume: 481, 6th Meeting on Hot Subdwarf Stars and Related Objects
Page: 29
Authors: Brown, T.; Landsman, W.; Randall, S.; Sweigart, A.; Lanz, T.; Hubeny, I.
Abstract: We present preliminary results of a Hubble Space Telescope program to search for pulsating hot subdwarfs in the core of NGC 2808. These observations, obtained in March of 2013, were motivated by the recent discovery of such stars in the outskirts of ω Cen. Both ω Cen and NGC 2808 are massive globular clusters exhibiting complex stellar populations and large numbers of extreme horizontal branch stars. Our far-UV photometric monitoring of over 100 UV-bright stars has revealed at least six pulsating subdwarfs with periods ranging from 100 to 150 seconds. In the UV color-magnitude diagram of NGC 2808, all six of these stars lie immediately below the canonical horizontal branch, a region populated by the subluminous “blue hook” stars. Three of these six pulsators also have low-resolution far-UV spectroscopy that is sufficient to broadly constrain their atmospheric abundances and effective temperatures. Curiously, the spectroscopic and photometric data do not exhibit the uniformity one might expect from a well-defined instability strip.
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