Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2009-04-08
Astrophys.J.698:1165-1173,2009
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
10 pages, 3 figures, accepted for publication by ApJ
Scientific paper
10.1088/0004-637X/698/2/1165
We have used the Very Large Array (VLA) at 7 mm wavelength to image five rotational transitions (J=1-0) from three SiO isotopologues towards Orion BN/KL: 28SiO v=0,1,2; and 29SiO and 30SiO v=0. For the first time, we have mapped the 29SiO and 30SiO J=1-0 emission, established the maser nature of the emission, and confirmed association with the deeply embedded high-mass young stellar object commonly denoted radio Source I. The 28SiO v=0 maser emission shows a bipolar structure that extends over ~700 AU along a northeast-southwest axis, and we propose that it traces a bipolar outflow driven by Source I. The high-brightness isotopic SiO maser emission imaged with a ~0.2 arcsec resolution has a more compact distribution, generally similar to that of the 28SiO v=1,2 emission, and it probably traces bulk gas flows in a region of diameter <100 AU centered on Source I. On small scales of <10 AU, however, compact 29SiO/30SiO v=0 and 28SiO v=1,2 emission features may be offset from one another in position and line-of-sight velocity. From a radiative transfer analysis based on a large velocity gradient (LVG) pumping model, we derive similar temperatures and densities for the optimum excitation of both 29SiO/30SiO v=0 and 28SiO v=1,2 masers, significantly higher than required for 28SiO v=0 maser excitation. In order to account for the small-scale differences among the isotopologues (v=0) and the main species (v=1,2), follow-up radiative transfer modeling that incorporates non-local line overlap among transitions of all SiO isotopic species may be required.
Chandler Claire J.
Goddi Ciriaco
Gray Malcolm D.
Greenhill Lincoln J.
Humphreys E. M. L.
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