Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: HST WFPC2 Imaging of Shocks in Superbubbles   Bright X-ray emission has been detected in superbubbles in the Large
Magellanic Cloud (LMC), and it is suggested that supernova remnants (SNRs) near
the inner shell walls are responsible for this X-ray emission. To identify SNR
shocks in superbubble interiors, we have obtained HST WFPC2 emission-line
images of the X-ray-bright superbubbles DEM L 152 and DEM L 192 and the
X-ray-dim superbubble DEM L 106. We use these images to examine the shell
morphology and [S II]/H-alpha ratio variations in detail.
  Of these three superbubbles, DEM L 152 has the highest X-ray surface
brightness, the most filamentary nebular morphology, the largest expansion
velocity, and the highest [S II]/H-alpha ratio. Its [S II]/H-alpha ratio
increases outwards and peaks in sharp filaments along the periphery. DEM L 192
has a moderate X-ray surface brightness, a complex but not filamentary
morphology, a moderate expansion velocity, and a low [S II]/H-alpha ratio. DEM
L 106 is not detected in X-rays. Its shell structure is amorphous and has
embedded dusty features; its expansion velocity is low.
  None of the three superbubbles show morphological features in the shell
interior that can be identified as directly associated with SNR shocks,
indicating that the SNR shocks have not encountered very dense material. We
find that the [S II]/H-alpha ratios of X-ray-bright superbubbles are strongly
dependent on the UV radiation field of the encompassed OB associations.
Therefore, a tight correlation between [S II]/H-alpha ratio and X-ray surface
brightness in superbubbles should not exist. We also find that the filamentary
morphologies of superbubbles are associated with large expansion velocities and
bright X-ray emission.

11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics