Issue |
A&A
Volume 414, Number 1, January IV 2004
|
|
---|---|---|
Page(s) | 245 - 259 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20031580 | |
Published online | 12 January 2004 |
The peculiar circumstellar environment of NGC 2024 IRS2
1
Astronomical Institute “Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2
Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 3-72, 58090 Morelia, Mich. México
3
Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
4
Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada N6A 3K7
5
Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720, USA
Corresponding author: A. Lenorzer, lenorzer@science.uva.nl
Received:
20
March
2003
Accepted:
2
October
2003
We re-examine the nature of NGC 2024 IRS2 in light of the recent
discovery of the late O-type star, IRS2b, located 5´´ from
IRS2. Using L-band spectroscopy, we set a lower limit of AV = 27.0 mag
on the visual extinction towards IRS2. Arguments based on the
nature of the circumstellar material, favor an AV of 31.5 mag. IRS2
is associated with the UCHii region G206.543–16.347 and the infrared
source IRAS 05393–0156. We show that much of the mid-infrared
emission towards IRS2, as well as the far infrared emission peaking at
~100 , do not originate in the direct surroundings of IRS2,
but instead from an extended molecular cloud. Using new K-, L- and
L'-band spectroscopy and a comprehensive set of infrared and radio
continuum measurements from the literature, we apply diagnostics based
on the radio slope, the strength of the infrared hydrogen
recombination lines, and the presence of CO band-heads to constrain
the nature and spatial distribution of the circumstellar material of
IRS2. Using simple gaseous and/or dust models of prescribed geometry,
we find strong indications that the infrared flux originating in the
circumstellar material of IRS2 is dominated by emission from a dense
gaseous disk with a radius of about 0.6 AU. At radio wavelengths the
flux density distribution is best described by a stellar wind
recombining at a radius of about 100 AU. Although NGC 2024 IRS2 shares
many similarities with BN-like objects, we do not find evidence for
the presence of a dust shell surrounding this object. Therefore, IRS2
is likely more evolved.
Key words: stars: circumstellar matter / early-type / individual: NGC 2024 IRS2 / infrared: stars
© ESO, 2004
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