Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Effect of Porosity on X-ray Emission Line Profiles from Hot-Star
  Winds   We investigate the degree to which the nearly symmetric form of X-ray
emission lines seen in Chandra spectra of early-type supergiant stars could be
explained by a possibly porous nature of their spatially structured stellar
winds. Such porosity could effectively reduce the bound-free absorption of
X-rays emitted by embedded wind shocks, and thus allow a more similar
transmission of red- vs. blue-shifted emission from the back vs. front
hemispheres. For a medium consisting of clumps of size l and volume filling
factor f, in which the `porosity length' h=l/f increases with local radius as h
= h' r, we find that a substantial reduction in wind absorption requires a
quite large porosity scale factor h' > 1, implying large porosity lengths h >
r. The associated wind structure must thus have either a relatively large scale
l~ r, or a small volume filling factor f ~ l/r << 1, or some combination of
these. The relatively small-scale, moderate compressions generated by intrinsic
instabilities in line-driving seem unlikely to give such large porosity
lengths, leaving again the prospect of instead having to invoke a substantial
(ca. factor 5) downward revision in assumed mass-loss rates.

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The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics