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

C. J. Lada, E. A. Bergin, J. F. Alves, T. L. Huard

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.

External organisation(s)
European Southern Observatory (Germany), Harvard-Smithsonian Center for Astrophysics
The Astrophysical Journal
Publication date
Peer reviewed
Austrian Fields of Science 2012
103004 Astrophysics
Portal url