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The Dearth of Massive, Helium-Rich White Dwarfs in Young Open Star Clusters | Jasonjot Singh Kalirai
; Harvey B. Richer
; Brad M. S. Hansen
; David Reitzel
; R. Michael Rich
; | Date: |
7 Sep 2004 | Journal: | Astrophys.J. 618 (2004) L129-L132 | Subject: | astro-ph | Affiliation: | UBC), Harvey B. Richer (UBC), Brad M. S. Hansen (UCLA), David Reitzel (UCLA), and R. Michael Rich (UCLA | Abstract: | Spectra have been obtained of 21 white dwarfs (WDs) in the direction of the young, rich open star cluster NGC 2099. This represents an appreciable fraction (>30%) of the cluster’s total WD population. The mean derived mass of the sample is 0.8 Msun - about 0.2 Msun larger than the mean seen among field WDs. A surprising result is that all of the NGC 2099 WDs have hydrogen-rich atmospheres (DAs) and none exhibit helium-rich ones (DBs), or any other spectral class. The number ratio in the field at the temperatures of the NGC 2099 WDs is DA/DB ~ 3.5. While the probability of seeing no DB WDs in NGC 2099 solely by chance is ~2%, if we include WDs in other open clusters of similar age it then becomes highly unlikely that the dearth of DB WDs in young open clusters is just a statistical fluctuation. We explore possible reasons for the lack of DBs in these clusters and conclude that the most promising scenario for the DA/DB number ratio discrepancy in young clusters is that hot, high-mass WDs do not develop large enough helium convection zones to allow helium to be brought to the surface and turn a hydrogen-rich WD into a helium-rich one. | Source: | arXiv, astro-ph/0409172 | Services: | Forum | Review | PDF | Favorites |
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