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Session 40 - The Interstellar Medium.
Display session, Tuesday, June 09
Atlas Ballroom,
Spectra of nearly three dozen stars in each of the globular clusters M15 and M92 obtained with the Hydra Fiber Positioner on the 3.5-m WIYN telescope allow examination of the distribution of matter in the intervening cold interstellar clouds on sub-parsec scales. The spectra were obtained for the purpose of determining stellar abundances, but the resolution and wavelength region selected also allow measurement of the interstellar Na I D lines at 5890 and 5896 Å\ . Stars were selected in both clusters to sample a range of luminosities on the giant branch, and the stars in both clusters have temperatures in the range 4000-5000K. Although the clusters are metal poor, metallic line contamination of the interstellar features must still be considered. The stellar Na I lines in both cases are shifted more than 100 km s^-1 to the blue of their nominal wavelength, and away from the interstellar components as well. Due to the velocity of the clusters, the intermediate velocity interstellar features may be affected by either Ni I \lambda5893 Å\ or Ti I \lambda5899 Å\ . The selected stars are found scattered across the face of each cluster, but generally lie within a 10' radius around cluster center.
