Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microstructure of the Local Interstellar Cloud and the Identification of
  the Hyades Cloud   We analyze high-resolution UV spectra of the Mg II h and k lines for 18
members of the Hyades Cluster to study inhomogeneity along these proximate
lines of sight. The observations were taken by the Space Telescope Imaging
Spectrograph (STIS) instrument on board the Hubble Space Telescope (HST). Three
distinct velocity components are observed. All 18 lines of sight show
absorption by the Local Interstellar Cloud (LIC), ten stars show absorption by
an additional cloud, which we name the Hyades Cloud, and one star exhibits a
third absorption component. The LIC absorption is observed at a lower radial
velocity than predicted by the LIC velocity vector derived by Lallement &
Bertin (1992) and Lallement et al. (1995), (v(predicted LIC) - v(observed LIC)
= 2.9 +/- 0.7 km/s), which may indicate a compression or deceleration at the
leading edge of the LIC. We propose an extention of the Hyades Cloud boundary
based on previous HST observations of other stars in the general vicinity of
the Hyades, as well as ground-based Ca II observations. We present our fits of
the interstellar parameters for each absorption component. The availability of
18 similar lines of sight provides an excellent opportunity to study the
inhomogeneity of the warm, partially ionized local interstellar medium (LISM).
We find that these structures are roughly homogeneous. The measured Mg II
column densities do not vary by more than a factor of 2 for angular separations
of < 8 degrees, which at the outer edge of the LIC correspond to physical
separations of < 0.6 pc.

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The categories of this paper are: hep-ph
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat