Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.2202x&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #22.02; Bulletin of the American Astronomical Society, Vol. 24, p.1156
Astronomy and Astrophysics
Astronomy
Scientific paper
The clumpiness of material in molecular clouds has never been considered in evaluating the uncertainties in the determination of (13) CO column density.\quad We take the effect of the clumpiness into account to examine the uncertainties in N((13) CO) owing to the use of the LTE approximation. \quad The clumpy cloud model proposed by Kwan and Sanders (1986, ApJ, 309, 783) is used to solve the radiative transfer problem in molecular clouds.\quad The model combines physically meaningful velocity fields and clumpy structures.\quad We select more parameters so that a wide range of clumpy structures is covered by our model calculations.\quad The (13) CO column densities are determined from the emergent (12) CO and (13) CO intensities under the LTE assumptions.\quad By assuming a (13) CO/H_2 abundance ratio, the H_2 column densities are estimated from the LTE (13) CO column densities.\quad The differences between the LTE H_2 column densities and the true H_2 column densities used in the model calculations measure the uncertainties originating from the LTE method.\quad Comparisons are made among various clumpy structures and temperature distributions in order to examine the extent to which the LTE method is valid.\quad The dependences of individual properties such as average optical depth and excitation temperature on the clumpiness are evaluated.
Kwan John
Xie Shuding
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