Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observational Constraints on the Origin of Metals in Cool DA-type White
  Dwarfs   We present ISOCAM 7 micron and 15 micron observations of 12 nearby white
dwarfs, 6 of which have been found to have metals such as Ca, Mg and Fe in
their photospheres. Our purpose was to search for an excess of infrared
emission above the stellar photospheres. We find that none of the white dwarfs
other than G29-38 shows a detectable infrared excess and this places strong
constraints on the existence of a dusty disk around these stars. We conclude
that ongoing accretion of the interstellar medium seems an unlikely explanation
for the existence of metals in the photospheres of cool hydrogen atmosphere
white dwarfs.
  The excess associated with G29-38 is 3.8+/-1.0 mJy and 2.9+/-0.6 mJy at 7
micron and 15 micron respectively. The broadband spectrum of this star
strengthens the hypothesis that the infrared excess arises from a disk of
particulate matter surrounding the white dwarf rather than from a cool brown
dwarf companion.

19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
0
The categories of this paper are: hep-ph
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
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The categories of this paper are: math-ph
37
The categories of this paper are: supr-con