Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hubble Space Telescope Expansion Parallaxes of the Planetary Nebulae NGC
  6578, NGC 6884, NGC 6891, and IC 2448   We have combined two epochs of Hubble Space Telescope WFPC2 imaging data with
ground-based expansion velocities to determine distances to three planetary
nebulae (NGC 6578, NGC 6884, and IC 2448). We used two variants of the
expansion parallax technique--a gradient method and a magnification method--to
determine the distances. The results from the two methods agree to within the
errors. A fourth nebula was included in the study (NGC 6891), but the expansion
was too small to determine the distance, and only a lower limit was obtained.
This is the first paper in a series which will examine at least 24 nebulae in
total.

18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat