• DOI:10.1088/0004-637X/702/2/1530
• Corpus ID: 2015110

HOT HORIZONTAL BRANCH STARS IN ω CENTAURI: CLUES ABOUT THEIR ORIGIN FROM THE CLUSTER COLOR MAGNITUDE DIAGRAM

@article{Cassisi2009HOTHB,
  title={HOT HORIZONTAL BRANCH STARS IN $\omega$ CENTAURI: CLUES ABOUT THEIR ORIGIN FROM THE CLUSTER COLOR MAGNITUDE DIAGRAM},
  author={Santi Cassisi and Maurizio Salaris and Jay Anderson and Giampaolo Piotto and Adriano Pietrinferni and Antonino P. Milone and Andrea Bellini and Luigi R. Bedin},
  journal={The Astrophysical Journal},
  year={2009},
  volume={702},
  pages={1530 - 1535}
}

• S. Cassisi, M. Salaris, +5 authors L. Bedin
• Published 21 July 2009
• Physics
• The Astrophysical Journal

We investigate a peculiar feature at the hottest, blue end of the horizontal branch of Galactic globular cluster ω Centauri, using the high-precision and nearly complete catalog that has been constructed from a survey taken with the Advanced Camera for Survey on board the Hubble Space Telescope, that covers the inner 10 × 10 arcmin. It is a densely populated clump of stars with an almost vertical structure in the F435W-(F435W−F625W) plane, that we termed “blue clump.” A comparison with theoretical models leads to the conclusion that this feature must necessarily harbor either hot flasher stars or canonical He-rich stars—progeny of the blue main sequence (MS) subpopulation observed in this cluster—or a mixture of both types, plus possibly a component from the normal-He population hosted by the cluster. A strong constraint coming from theory is that the mass of the objects in the “blue clump” has to be very finely tuned, with a spread of at most only ∼0.03 M☉. By comparing observed and theoretical star counts along both the H- and He-burning stages we find that at least 15% of the expected He-rich horizontal branch stars are missing from the color–magnitude diagram. This missing population could be the progeny of red giants that failed to ignite central He-burning and have produced He-core white dwarfs (WDs). Our conclusion supports the scenario recently suggested by Calamida et al. for explaining the observed ratio of WDs to MS stars in ω Centauri.