Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989a%26a...223..321f&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 223, no. 1-2, Oct. 1989, p. 321-325. Research supported by CAICYT.
Astronomy and Astrophysics
Astrophysics
12
Early Stars, Interstellar Masers, Molecular Clouds, Silicon Oxides, H Ii Regions, Molecular Rotation, Vibrational Spectra
Scientific paper
Since 1986, we have carried out a monitoring of the SiO maser emission in the J = 1-0 (ν = 1, 2, and 3) transitions toward the star forming region W51-IRS 2. Maser emission in the J = 1-0 rotational transition is only observed in the vibrationally excited state ν=2. From 1986 to 1988, the J=1-0(ν=2) line profile shows two peaks separated by 2 km s-1 (similar to the line profile in 1985), but their relative intensity has varied from epoch to epoch. In 1989, we have detected clearly one of this components and tentatively the other one. The central radial velocity of the two peaks, ˜42 km s-1, is much smaller than the radial velocity of the molecular cloud and the newly formed star, 62 km s-1. Contrary to the SiO maser in Orion, the radial velocities of both peaks have systematically increased by 1.4 km s ' in the last three years, approaching the radial velocity of the bulk molecular cloud. Model calculations which take into account IR pumping show that the characteristics of the SiO maser emission (non detection of the J = 1-0, ν = 1, and ν = 3 transitions) in this source is consistent with the emission arising in hot (1500 K) dense (probably 109 cm-3) spherical cloudlets with a size of ˜2 1014 cm and located at ˜1015 cm from an IR source. We propose a scenario to explain the anomalous radial velocity and the systematic changes of the SiO maser emission. In this scenario, the SiO maser emission arises in small cloudlets which have been accelerated to very high velocities by the stellar winds of the young stars and they decelerates when moving through the more diffuse surrounding medium. We briefly discussed the importance of these high velocity cloudlets in the high velocity molecular outflows.
Alcolea Javier
Barcia Alberto
Fuente Asuncion
Martín-Pintado Jesús
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