AAS 202nd Meeting, May 2003
Session 53 Star Formation, Interstellar Medium
Oral, Thursday, May 29, 2003, 10:00-11:30am, 209/210

## [53.01] Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations

K. Pan, S. R. Federman (U. Toledo)

Interstellar clouds that give birth to stars are subsequently affected by those stars. Through the action of stellar winds, ultraviolet radiation and supernova explosions, the surrounding interstellar cloud is dispersed. In order to understand details of cloud dispersal, interstellar material in three star-forming regions, \rho Oph, Cep OB2, and Cep OB3, was probed through a study of absorption lines against the continua of background stars. High-resolution spectra (at ~ 1.4--1.7 km s-1) of interstellar CN, CH, CH+, \ion{Ca}{1}, \ion{Ca}{2}, and \ion{K}{1} absorption lines in 29 lines of sight were obtained. Analysis of these spectra yield information on cloud structure in terms of gas density, temperture, radiative flux, and the distribution of chemical species.

Our study finds cloud structures in the star-forming regions on both large and small scales. Gas densities for individual velocity components are inferred from a chemical model. The variation in density from one sight line to another indicates the presence of structure. Generally our large scale structure is consistent with the one suggested by maps of CO radio emission. On small scales, our results show that densities could differ by a factor of ~ 10 over 0.1 pc.

Correlations between b-values and column densities among species for individual velocity components are examined in order to learn more about the distribution of species. This contrasts with previous studies where total columns along a line of sight were compared. The analysis also yields information on the depletion of species. We find CN traces dense cores while CH+ arises mainly from less dense gase. We are able to distinguish more clearly than before the differences between regions containing CN-like CH and CH+-like CH. Moreover, the depletion of species onto grains is tied to physical conditions: denser gas shows more Ca and K depletion.

This work was supported by NASA grants NAG5-4957, NAG5-8961 and NAG5-10305.