Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Interstellar Matter and the Boundary Conditions of the Heliosphere   The interstellar cloud surrounding the solar system regulates the galactic
environment of the Sun, and determines the boundary conditions of the
heliosphere. Both the Sun and interstellar clouds move through space, so these
boundary conditions change with time. Data and theoretical models now support
densities in the cloud surrounding the solar system of n(HI)=0.22+/-0.06 cm^-3,
and n(e-)~0.1 cm-3, with larger values allowed for n(HI) by radiative transfer
considerations. Ulysses and Extreme Ultraviolet Explorer satellite HeI data
yield a cloud temperature of 6,400 K. Nearby interstellar gas appears to be
structured and inhomogeneous. The interstellar gas in the Local Fluff cloud
complex exhibits elemental abundance patterns in which refractory elements are
enhanced over the depleted abundances found in cold disk gas. Within a few
parsecs of the Sun, inconclusive evidence for factors of 2--5 variation in MgII
and FeII gas phase abundances is found, providing evidence for variable grain
destruction. Observations of the hydrogen pile-up at the nose of the
heliosphere are consistent with a barely subsonic motion of the heliosphere
with respect to the surrounding interstellar cloud. Uncertainties on the
velocity vector of the cloud that surrounds the solar system indicate that it
is uncertain as to whether the Sun and alpha Cen are or are not immersed in the
same interstellar cloud.

28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th