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| Paper: |
Mass Loss on the Red Giant Branch of NGC 6791: The Case for Helium Core White Dwarfs |
| Volume: |
372, 15th European Workshop on White Dwarfs |
| Page: |
91 |
| Authors: |
Kalirai, J.S. |
| Abstract: |
NGC 6791 is a unique stellar system; it is both one of the oldest and most metal-rich open clusters in our Galaxy. Recently, a deep Hubble Space Telescope (HST) imaging study of its white dwarf (WD) population has led to the puzzling conclusion that the cluster is only 2.4 Gyr old (the main-sequence turnoff age is >8 Gyr). To explain this discrepancy, it has been proposed that a fraction of the red giant branch stars in NGC 6791 may have lost enough mass during their ascent (due to the high metallicity, [Fe/H] ~ +0.4) to avoid the helium (He) flash. Therefore, a fraction of theWD population in this cluster may not be canonical Carbon-Oxygen (C-O) core stars and rather be undermassive He-core stars. To test this, we obtained Keck/LRIS spectroscopy of a dozen bright WDs in NGC 6791 and measured their masses from Balmer line fitting. Our results indicate that most of the bright WDs in NGC 6791 are in fact undermassive and therefore were likely formed from this unique evolutionary channel. |
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