Issue |
A&A
Volume 522, November 2010
|
|
---|---|---|
Article Number | A44 | |
Number of page(s) | 8 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/201014497 | |
Published online | 29 October 2010 |
The near-infrared reflected spectrum of source I in Orion-KL⋆
1
ESO, Karl Schwarzschild str. 2,
85748
Garching,
Germany
e-mail: ltesti@eso.org
2
INAF-Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
50125
Firenze,
Italy
3
Departments of Astronomy & Physics, University of
Florida, Gainesville,
FL
32611,
USA
Received: 24 March 2010
Accepted: 31 May 2010
Context. Source I in the Orion-KL nebula is believed to be the nearest example of a massive star still in the main accretion phase. It is thus one of the best cases for studying the properties of massive protostars to constrain high-mass star formation theories. Near-infrared radiation from source I escapes through the cavity opened by the OMC1 outflow and is scattered by dust towards our line of sight.
Aims. The reflected spectrum offers a unique possibility of observing the emission from the innermost regions of the system and probing the nature of source I and its immediate surroundings.
Methods. We obtained moderately high spectral-resolution (λ / Δλ ~ 9000) observations of the near infrared diffuse emission in several locations around source I/Orion-KL. We observed a widespread rich absorption line spectrum that we compare with cool stellar photospheres and protostellar accretion disk models.
Results. The spectrum is broadly similar to strongly veiled, cool, low-gravity stellar photospheres in the range Teff ~ 3500−4500 K, luminosity class I–III. An exact match explaining all features has not been found, and a plausible explanation is that a range of different temperatures contribute to the observed absorption spectrum. The 1D velocity dispersions implied by the absorption spectra, σ ~ 30 kms-1, can be explained by the emission from a disk around a massive, m∗ ~ 10 M⊙, protostar that is accreting at a high rate, .
Conclusions. Our observations suggest that the near-infrared reflection spectrum observed in the Orion-KL region is produced close to source I and scattered to our line of sight in the OMC1 outflow cavity. The spectrum allows us to exclude source I being a very large, massive protostar rotating at breakup speed. We suggest that the absorption spectrum is produced in a disk surrounding a ~10 M⊙ protostar, accreting from its disk at a high rate of a few × 10-3 M⊙/yr).
Key words: stars: formation / accretion, accretion disks / stars: protostars / stars: massive
© ESO, 2010
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