R&G Division Lunch Talk 
Friday, May 16, 12:30, M340 160 Concord Ave

Models of Starless Cores

Eric Keto, CFA

I will discuss the results of research on starless
cores done in collaboration with Avery Broderick,
Ramesh Narayan, and George Field of the Theory Division,
and Charles Lada of R&G, and Paola Caselli now
at Leeds. 

Starless cores, a class of small dark clouds
that includes Bok Globules and Lynds Nebulae, are 
significant in the interstellar medium as the future birthplaces 
of stars.  Following the suggestion of Lada et al (2003) 
that the internal motions in some starless cores may be 
sound waves, we model oscillations in the cores the same 
way as we do oscillations in stars thus introducing the study 
of nepho(cloud)-seismology. We find that oscillations 
of clouds in stable equilibrium are able to reproduce 
spectral line profiles similar to those seen in clouds during 
the subsonic phase of contraction that leads to star formation.
This complicates the interpretation of these spectral line 
observations. However, the two cases, stable and contracting,
can still be distinguished by other observations. 
Models of the cores that include the radiative equilibrium 
of the gas and dust and the chemical evolution of CO 
indicate that the gas and dust temperatures, gas densities, 
and CO excitation temperatures are quite different in
the two classes of cores.  Observational examples of both 
cases are easily found. The starless cores
are the simplest of all molecular clouds and relatively
simple physics are able to explain the variety of 
observable properties exhibited by these stellar incubators.