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Published January 10, 2014 | Published + Submitted
Journal Article Open

Direct Measurement of Interstellar Extinction toward Young Stars Using Atomic Hydrogen Lyα Absorption


Interstellar reddening corrections are necessary to reconstruct the intrinsic spectral energy distributions (SEDs) of accreting protostellar systems. The stellar SED determines the heating and chemical processes that can occur in circumstellar disks. Measurement of neutral hydrogen absorption against broad Lyα emission profiles in young stars can be used to obtain the total H i column density (N(H i)) along the line of sight. We measure N(H i) with new and archival ultraviolet observations from the Hubble Space Telescope (HST) of 31 classical T Tauri and Herbig Ae/Be stars. The H i column densities range from log_10(N(H i)) ≈19.6–21.1, with corresponding visual extinctions of A_V =0.02–0.72 mag, assuming an RV of 3.1. We find that the majority of the H i absorption along the line of sight likely comes from interstellar rather than circumstellar material. Extinctions derived from new HST blue-optical spectral analyses, previous IR and optical measurements, and new X-ray column densities on average overestimate the interstellar extinction toward young stars compared to the N(H i) values by ~0.6 mag. We discuss possible explanations for this discrepancy in the context of a protoplanetary disk geometry.

Additional Information

© 2014 American Astronomical Society. Received 2013 September 10; accepted 2013 November 29; published 2013 December 19. We thank Evelyne Roueff for helpful discussions pertinent to this work. G.J.H. appreciates a conversation with Sean Andrews and Sylvie Cabrit long ago on the reliability of inclination measurements. This work made use of data from HST guest observing program 11616 and was supported by NASA grant NNX08AC146 to the University of Colorado at Boulder.

Attached Files

Published - 0004-637X_780_2_150.pdf

Submitted - 1312.1650v1.pdf


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