SIMBAD references

2005ApJ...618L.129K - Astrophys. J., 618, L129-L132 (2005/January-2)

The dearth of massive, helium-rich white dwarfs in young open star clusters.

KALIRAI J.S., RICHER H.B., HANSEN B.M.S., REITZEL D. and RICH R.M.

Abstract (from CDS):

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 M–about 0.2 Mlarger than the mean seen among field WDs. A surprising result is that all of the NGC 2099 WDs have hydrogen-rich atmospheres (DAs); 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.

Abstract Copyright:

Journal keyword(s): Galaxy: Open Clusters and Associations: Individual: NGC Number: NGC 2099 - Stars: White Dwarfs

Simbad objects: 16

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2020.09.25-03:57:51

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