Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2B024

Probing Interstellar and Circumstellar Material on the Line of Sight to Protoplanetary Disks

McJunkin, Matthew (University of Colorado at Boulder)
France, Kevin (University of Colorado at Boulder)

Absorption line spectroscopy provides the most straightforward means of determining the composition and physical state of material along the line of sight towards protostars. Using observations of 31 gas-rich classical T Tauri stars (CTTSs) and Herbig Ae/Be stars obtained with the Hubble Space Telescope (HST), we present new measurements of the molecular disk properties and the interstellar dust attenuation towards these objects. The high-sensitivity of the HST-Cosmic Origins Spectrograph has enabled the first ultraviolet detections of carbon monoxide (CO) absorption through protoplanetary disks. We compare the data from six objects with strong CO absorption to spectral synthesis models to determine the column density and temperature of the CO gas. We find column densities in the range log(N(CO)) = 16 18 and temperatures of 300 700 K, assuming thermal equilibrium. Reddening due to interstellar grains is notoriously challenging to determine towards CTTSs owing to veiling of the photospheric emission by excess flux due to accretion shocks. We present a new approach to this problem by using accurate interstellar atomic hydrogen column densities to determine the selective reddening using the well-known relationship between these quantities. We present new values of the optical extinction (A_v) for the 31 CTTSs and Herbig stars. Our general result is that literature values for A_v typically overestimate the reddening on CTTS sightlines.

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