AAS 201st Meeting, January, 2003
Session 34. ISM: Dust and Molecular Clouds
Oral, Monday, January 6, 2003, 2:00-3:30pm, 602-604

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[34.02] The Dynamical State of Barnard 68: A Thermally Supported, Pulsating Dark Cloud.

C.J. Lada, E.A. Bergin (SAO), J.F. Alves (ESO), T.L. Huard (SAO)

We report sensitve, high resolution molecular-line observations of the dark cloud Barnard 68 obtained with the IRAM 30-m telescope. We analyze spectral-line observations of C18O (1-0), C32S(2-1), and N2H+ (1-0) in order to investigate the kinematics of the cloud. We find extremely narrow linewidths consistent with thermally broadened profiles for the measured gas temperature of 10.5 K. We determine the thermal pressure to be at least 4-5 times greater than the non-thermal (turbulent) pressure in the central regions of the cloud, indicating that thermal pressure is the primary source of support against gravity in this cloud. The rotational kinetic energy is found to be only a few percent of the gravitational potential energy, indicating that the contribution of rotation to the overall stability of the cloud is insignificant.

We find that the C32S line is optically thick and self-reversed across nearly the entire projected surface of the cloud. The shapes of the self-reversed profiles are asymmetric with evidence for both inward and outward motions at different locations across the cloud. Moreover, these motions appear to be organized in a clear and systematic alternating spatial pattern which is suggestive of a small amplitude, non-radial mode oscillation or pulsation of the cloud's outer layers.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.