Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hubble Space Telescope observations of the Kepler-field cluster NGC
  6819. I. The bottom of the white dwarf cooling sequence   We use Hubble Space Telescope (HST) to reach the end of the white dwarf (WD)
cooling sequence (CS) in the solar-metallicity open cluster NGC 6819. Our
photometry and completeness tests show a sharp drop in the number of WDs along
the CS at magnitudes fainter than mF606W = 26.050+/- 0.075. This implies an age
of 2.25+/-0.20 Gyr, consistent with the age of 2.25+/-0.30 Gyr obtained from
fits to the main-sequence turn-off. The use of different WD cooling models and
initial-final-mass relations have a minor impact the WD age estimate, at the
level of ~0.1 Gyr. As an important by-product of this investigation we also
release, in electronic format, both the catalogue of all the detected sources
and the atlases of the region (in two filters). Indeed, this patch of sky
studied by HST (of size ~70 arcmin sq.) is entirely within the main
Kepler-mission field, so the high-resolution images and deep catalogues will be
particularly useful.

2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an
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The categories of this paper are: cond-mat
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
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The categories of this paper are: cs