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Title: THE DISCOVERY OF PULSATING HOT SUBDWARFS IN NGC 2808

We present the results of a Hubble Space Telescope program to search for pulsating hot subdwarfs in the core of NGC 2808. These observations were motivated by the recent discovery of such stars in the outskirts of ω Cen. Both NGC 2808 and ω Cen are massive globular clusters exhibiting complex stellar populations and large numbers of extreme horizontal branch stars. Our far-UV photometric monitoring of over 100 hot evolved stars has revealed six pulsating subdwarfs with periods ranging from 85 to 149 s and UV amplitudes of 2.0%-6.8%. 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. For three of these six pulsators, we also have low-resolution far-UV spectroscopy that is sufficient to broadly constrain their atmospheric abundances and effective temperatures. Curiously, and in contrast to the ω Cen pulsators, the NGC 2808 pulsators do not exhibit the spectroscopic or photometric uniformity one might expect from a well-defined instability strip, although they all fall within a narrow band (0.2 mag) of far-UV luminosity.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  2. Adnet Systems, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  3. European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany)
  4. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  5. Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte dAzur, F-06304 Nice (France)
Publication Date:
OSTI Identifier:
22215380
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; DIAGRAMS; LUMINOSITY; OSCILLATIONS; SPACE; SPECTROSCOPY; STARS; TELESCOPES; ULTRAVIOLET RADIATION