Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The CHANDRA HETGS X-ray Grating Spectrum of Eta Car   Eta Car may be the most massive and luminous star in the Galaxy and is
suspected to be a massive, colliding wind binary system. The CHANDRA X-ray
observatory has obtained a calibrated, high-resolution X-ray spectrum of the
star uncontaminated by the nearby extended soft X-ray emisssion. Our 89 ksec
CHANDRA observation with the High Energy Transmission Grating Spectrometer
(HETGS) shows that the hot gas near the star is non-isothermal. The temperature
distribution may represent the emission on either side of the colliding wind
bow shock, effectively ``resolving'' the shock. If so, the pre-shock wind
velocities are ~ 700 and ~ 1800 km/s in our analysis, and these velocities may
be interpreted as the terminal velocities of the winds from Eta Car and from
the hidden companion star. The forbidden-to-intercombination (f/i) line ratios
for the He-like ions of S, Si and Fe are large, indicating that the line
forming region lies far from the stellar photosphere. The iron fluorescent line
at 1.93 Angstrom, first detected by ASCA, is clearly resolved from the thermal
iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in
our CHANDRA observation than in any of the ASCA spectra. The CHANDRA
observation also provides an uninterrupted high-time resolution lightcurve of
the stellar X-ray emission from Eta Car and suggests that there was no
significant, coherent variability during the CHANDRA observation. The Eta Car
CHANDRA grating spectrum is unlike recently published X-ray grating spectra of
single massive stars in significant ways and is generally consistent with
colliding wind emission in a massive binary.

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The categories of this paper are: stat
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an