C18O abundance in the nearby globule Barnard 68

Details C18O abundance in the nearby globule Barnard 68 C18O abundance in the nearby globule Barnard 68

Aug 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...391..275h&link_type=abstract

Astronomy and Astrophysics, v.391, p.275-285 (2002)

Astronomy and Astrophysics

Astrophysics

23

Ism: Individual Objects: Barnard 68, Ism: Abundances, Ism: Molecules, Ism: Dust, Extinction

Scientific paper

We have studied the radial variation of the CO abundance in the nearby isolated globule Barnard 68 (B68). For this purpose, B68 was mapped in the three rotational lines 13CO(J=1-0), C18O(J=1-0) and C18O(J=2-1). Using the recent discovery of Alves et al. (\cite{alves_01}) that the density structure of B68 agrees with the prediction for a pressure bound distribution of isothermal gas in hydrostatic equilibrium (Bonnor-Ebert sphere), we show that the flat CO column density distribution can be explained by molecular depletion. By combining the physical model with the observed CO column density profile, it was found that the density dependence of the CO depletion factor fd can be well fitted with the law fd=1+const. n(H2), which is consistent with an equilibrium between the accretion and the desorption processes. In the cloud centre, between 0.5% and 5% of all CO molecules are in the gas phase. Our observations suggest a kinetic temperature of ~8 K. In combination with the assumption that B68 is a Bonnor-Ebert sphere, this leads to a distance of 80 pc. The cloud mass consistent with these values is 0.7 Msun, considerably less than previously estimated. We find in B68 no clear deviance of the near-infrared reddening efficiency of dust grains per unit H2 column density with respect to values derived in diffuse clouds. Based on observations made with the Swedish-ESO Submillimetre Telescope (SEST), Chile.

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