[Previous] | [Session 52] | [Next]
D. R. Alves (Columbia), K. H. Cook, E. Wishnow (LLNL)
M3 and M13 are Galactic globular clusters that have nearly identical metallicity, but their horizontal branch (HB) stars have different colors. M13 has a blue HB and M3 has a mostly red HB. The so-called 2nd parameter besides metallicity that controls HB color is either mass loss or cluster age, and if it is age this has implications for how the Galaxy formed. If it is mass loss, more stars near the tip of the red giant branch (RGB) in M13 should have circumstellar dust that emits in the infrared than do the comparable stars in M3. In 3 nights using the Keck I telescope and the Long Wavelength Spectrometer (LWS) we observed the brightest 7 RGB stars in M3 and 9 similar stars in M13 in order to test the mass loss hypothesis. Our flux-calibrated N-band photometry derived from the LWS data reveals which stars have excess emission at 11.7 microns over expected photospheric levels. 3 out of 7 of the observed RGB stars in M3 have significant N-band flux excesses, while 9 out of 9 of the observed RGB stars in M13 have significant excesses. The probability that the M13 sample has M3-like mass loss properties as traced by warm dust is 0.05%. Hence mass loss is implicated as the 2nd parameter.
Data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.
[Previous] | [Session 52] | [Next]
Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.