Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: H$_2$O and O$_2$ Absorption in the Coma of Comet
  67P/Churyumov-Gerasimenko Measured by the Alice Far-Ultraviolet Spectrograph
  on Rosetta   We have detected H$_2$O and O$_2$ absorption against the far-UV continuum of
stars located on lines of sight near the nucleus of Comet
67P/Churyumov-Gerasimenko using the Alice imaging spectrograph on Rosetta.
These stellar appulses occurred at impact parameters of $\rho=4$-20 km, and
heliocentric distances ranging from $R_h=-1.8$ to 2.3 AU (negative values
indicate pre-perihelion observations). The measured H$_2$O column densities
agree well with nearly contemporaneous values measured by VIRTIS-H. The clear
detection of O$_2$ independently confirms the initial detection by the ROSINA
mass spectrometer; however, the relative abundance of O$_2$/H$_2$O derived from
the stellar spectra (11%-68%, with a median value of 25%) is considerably
larger than published values found by ROSINA. The cause of this difference is
unclear, but potentially related to ROSINA measuring number density at the
spacecraft position while Alice measures column density along a line of sight
that passes near the nucleus.

33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph