AAS 196th Meeting, June 2000
Session 40. High Resolution Spectroscopy at Visible and Ultraviolet Wavelengths
Topical Contributed Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

## [40.07] A High-Resolution Survey of Interstellar K I Absorption

D. E. Welty, L. M. Hobbs (U Chicago)

We discuss new high-resolution (FWHM ~ 0.4-1.8 km s-1), high-S/N spectra of interstellar \ion{K}{1} absorption toward 54 Galactic stars. These new \ion{K}{1} spectra reveal narrow, closely blended components (median FWHM and separation both \la 1.2 km s-1) in many lines of sight. If T is typically ~ 100 K, then at least half the individual components have subsonic internal turbulent velocities.

We also re-examine the relationships between the column densities of \ion{K}{1}, \ion{Na}{1}, \ion{C}{1}, \ion{Li}{1}, H\rm tot, H2, and CH. The four trace neutral species exhibit essentially linear relationships with each other over wide ranges in overall column density. If C is uniformly depleted by 0.4 dex, then Li, Na, and K are each typically depleted by 0.6-0.7 dex. The total line of sight values for N(\ion{K}{1}) and N(\ion{Na}{1}) show roughly quadratic dependences on N(H\rm tot), but the relationships for the ensemble of individual clouds could be significantly steeper. These general quadratic dependences appear to rule out significant contributions to the ionization from cosmic rays, X-rays, and/or charge exchange with \ion{C}{2} in most cases (Hobbs 1974, 1976).

Both N(CH) and N(H2) seem nearly linearly proportional to N(\ion{K}{1}) and N(\ion{Na}{1}) [except for 1015 cm-2 \la N(H2) \la 1019 cm-2, over which H2 makes the transition to the self-shielded regime]. Those relationships appear also to hold for many individual components and component groups, suggesting that high-resolution spectra of \ion{K}{1} and \ion{Na}{1} can be very useful for interpreting lower resolution molecular data.

The scatter about all these mean relationships is generally small (\la 0.1-0.2 dex), if certain consistently discrepant'' sightlines are excluded --- suggesting that both the relative depletions and the relative ionization of Li, C, Na, and K are generally within factors of 2 of their mean values. Differences noted for sightlines in Sco-Oph, in the Pleiades, near the Orion Trapezium, and in the LMC and SMC may be due to differences in the strength and/or shape of the ambient radiation fields.

This work has been supported by NASA LTSA grant NAG5-3228.