Probing Planck Cold Clump Sightlines through HST STIS UV Spectroscopy

The Planck Catalogue of Galactic Cold Clumps (PGCC) has provided a wealth of information about the cold, dusty ISM across the entire sky, identifying regions ranging from relatively diffuse cold clouds to pre-stellar cores in giant molecular clouds. This catalogue uses sub-millimeter emission arising from cold dust to determine the physical properties, morphology, and temperature of these regions. Combining this information with the diagnostic capabilities of UV absorption line spectroscopy allows us to better characterize the interstellar gas associated with these dusty regions. We have identified numerous target stars with STIS high-resolution UV spectra in the Hubble Space Telescope data archive whose sightlines lie in the sky vicinity of PGCC objects. By analyzing select interstellar absorption lines along these target sightlines, we can investigate several important cloud properties. Here we investigate the gas thermal pressure using C I fine structure excitation, and find a similar distribution to previous studies of the broader diffuse ISM. We also investigate the potential destruction of dust grains by shock processing by determining abundance ratios of heavily depleted elements to those that are typically lightly depleted.