Volume 522, November 2010
|Number of page(s)||8|
|Section||Interstellar and circumstellar matter|
|Published online||29 October 2010|
The near-infrared reflected spectrum of source I in Orion-KL⋆
ESO, Karl Schwarzschild str. 2,
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
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.