Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Dearth of Massive, Helium-Rich White Dwarfs in Young Open Star
  Clusters   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.

25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex