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Peculiar Multimodality on the Horizontal Branch of the Globular Cluster NGC 2808*

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©1997. The American Astronomical Society. All rights reserved. Printed in U.S.A.
, , Citation Craig Sosin et al 1997 ApJ 480 L35 DOI 10.1086/310606

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Author affiliations

1 Department of Astronomy, University of California, Berkeley, CA 94720-3411

2 Laboratory for Astronomy and Solar Physics, Code 681, NASA Goddard Space Flight Center, Greenbelt, MD 20771; and Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903-0818

3 Astronomy Department, MS 105-24, California Institute of Technology, Pasadena, CA 91125

4 Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy

5 Department of Astronomy, Columbia University, Box 46, Pupin Hall, 538 West 120th Street, New York, NY 10027

6 Steward Observatory, University of Arizona, Tucson, AZ 85721

7 Theoretical Astrophysics, MS 130-33, California Institute of Technology, Pasadena, CA 91125

8 Dipartimento di Astronomia, Università di Bologna, Cp. 596, I-40100 Bologna, Italy

Dates

  1. Received 1997 January 13
  2. Accepted 1997 February 6
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1538-4357/480/1/L35

Abstract

We present distributions of colors of stars along the horizontal branch (HB) of the globular cluster NGC 2808, from Hubble Space Telescope Wide Field Planetary Camera 2 imaging in B, V, and an ultraviolet filter (F218W). This cluster's HB is already known to be strongly bimodal, with approximately equal-sized HB populations widely separated in the color-magnitude diagram. Our images reveal a long blue tail with two gaps, for a total of four nearly distinct HB groups. These gaps are very narrow, corresponding to envelope-mass differences of only ~0.01 M☉. This remarkable multimodality may be a signature of mass-loss processes, subtle composition variations, or dynamical effects; we briefly summarize the possibilities. The existence of narrow gaps between distinct clumps on the HB presents a challenge for models that attempt to explain HB bimodality or other peculiar HB structures.

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Footnotes

  • * 

    Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

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10.1086/310606