Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The white dwarf cooling sequence of the Galactic bulge   We collected F606W- and F814W-band time-series data of the Sagittarius
low-reddening window in the Galactic bulge with the Advanced Camera far Surveys
mounted on the Hubble Space Telescope. We sampled the region approximately
every two weeks for one year, with the principal aim to detect a hidden
population of isolated black holes and neutron stars in the Galactic disk
through astrometric microlensing. We present preliminary results here based on
a photometric catalog including ~3*10^5 stars down to F606W ~ 31 mag. Proper
motions were also measured, with an accuracy of better than ~ 0.5 mas/yr at
F606W ~ 28 mag in both coordinates. We were then able to separate disk and
bulge stars and to obtain a clean bulge color-magnitude diagram. Together with
a dozen candidate extreme horizontal branch stars we were able to identify for
the first time a clearly defined white dwarf (WD) cooling sequence in the
bulge. The comparison between theory and observations shows that a substantial
fraction of the WDs (~40%) is systematically redder than the canonical cooling
tracks for CO-core DA WDs. This evidence would suggest the presence of a
significant number of He-core WDs in the bulge, formed in close binaries, as
has been found in some Galactic globular and open clusters. The presence of
close binaries in the bulge population is further supported by the finding of a
candidate dwarf nova in outburst and a few candidate cataclysmic variables in
quiescence in the same field.

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The categories of this paper are: supr-con
1
The categories of this paper are: cs
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
2
The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph