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Session 20 - Molecular Clouds, Dense Cores, and Protostars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[20.10] The Monoceros R2 Molecular Core: A Toroid around a Star Formation Region

M. Choi (ASIAA), N. J. Evans II (UT Austin), M. Tafalla (CfA), R. Bachiller (Centro Astronómico de Yebes)

Monoceros R2 dense core region was observed in molecular emission lines of CS, C^34S, H_2CO, HCN, H^13CN, HCO^+, H^13CO^+, and CH_3OH. We suggest that the main part of the dense core can be explained as a parsec-scale toroid around the H \sc ii region with its symmetry axis roughly parallel to the CO outflow axis and the magnetic field direction. The toroid is rotating around the symmetry axis but does not show noticeable contraction or expansion. The Ømega \propto r^-1 rotation profile and relatively small rotation energy indicate that rotation alone cannot supported the dense core. We modeled the toroid with a 2-dimensional non-LTE radiative transfer code. Our simple model with constant density can reproduce the observed CS J = 2\rightarrow1, 3\rightarrow2, and 5\rightarrow4 transitions very well. Observed CS J = 7\rightarrow6 line strength, however, implies some density gradient. Analysis of the H_2CO and HCO^+ lines suggests there are some density fluctuations in the toroid. We simulated models with clumpy structure and models with density gradient. The temperature estimate from the toroid model is higher than what is expected from a spherical cloud but consistent with estimates from the H_2CO line ratio.

Program listing for Monday