Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Shock emission in the bipolar post-AGB star IRAS 16594-4656   In this paper we study the near-infrared emission spectrum of IRAS
16594-4656, a bipolar post-AGB star with spectral type B7 and no observed
ionization. Using optical and near-infrared photometry we determined the total
extinction towards this object to be A_V=7.5 +/- 0.4 mag and derived a distance
of 2.2 +/- 0.4 kpc, assuming a luminosity of 10^4 L_sol. The near-infrared
spectrum shows strong H_2 emission lines and some typical metastable shock
excited lines such as [Fe II] 1.257 & 1.644 micron. We determined the
rotational and vibrational excitation temperatures, as well as the
ortho-to-para ratio of the molecular hydrogen. Based on these we argue that the
H_2 emission is mainly collisionally excited. Line ratios indicate that the H_2
emission originates in a +/- 25 km/s C-type shock. On the other hand, the
metastable lines, and especially the [Fe II] emission lines, indicate the
presence of a +/- 75 km/s J-type shock. Hence we postulate that the H_2
emission originates where the stellar wind (with an observed terminal velocity
of +/- 126 km/s) is funneled through an equatorial density enhancement,
impinging almost tangentially upon the circumstellar material. The [Fe II]
emission either occurs along the walls of the bipolar lobes where the
transverse shock velocity would be higher, or could originate much closer to
the central star in shocks in the post-AGB wind itself, or possibly even an
accretion disk. Further high resolution near-infrared spectra are currently
being obtained to confirm the proposed geometry and kinematics.

0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
32
The categories of this paper are: atom-ph