Ingleby, Laura and Calvet, Nuria and Bergin, Edwin and Yerasi, Ashwin and Espaillat, Catherine and Herczeg, Gregory and Roueff, Evelyne and Abgrall, Hervé and Hernández, Jesus and Briceño, César and Pascucci, Ilaria and Miller, Jon and Fogel, Jeffrey and Hartmann, Lee and Meyer, Michael and Carpenter, John and Crockett, Nathan and McClure, Melissa (2009) Far-Ultraviolet H_2 Emission from Circumstellar Disks. Astrophysical Journal, 703 (2). L137-L141. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20091006-121502174
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We analyze the far-ultraviolet (FUV) spectra of 33 classical T Tauri stars (CTTS), including 20 new spectra obtained with the Advanced Camera for Surveys Solar Blind Channel (ACS/SBC) on the Hubble Space Telescope. Of the sources, 28 are in the ~1 Myr old Taurus-Auriga complex or Orion Molecular Cloud, 4 in the 8-10 Myr old Orion OB1a complex, and 1, TW Hya, in the 10 Myr old TW Hydrae Association. We also obtained FUV ACS/SBC spectra of 10 non-accreting sources surrounded by debris disks with ages between 10 and 125 Myr. We use a feature in the FUV spectra due mostly to electron impact excitation of H_2 to study the evolution of the gas in the inner disk. We find that the H_2 feature is absent in non-accreting sources, but is detected in the spectra of CTTS and correlates with accretion luminosity. Since all young stars have active chromospheres which produce strong X-ray and UV emission capable of exciting H_2 in the disk, the fact that the non-accreting sources show no H_2 emission implies that the H_2 gas in the inner disk has dissipated in the non-accreting sources, although dust (and possibly gas) remains at larger radii. Using the flux at 1600 Å, we estimate that the column density of H_2 left in the inner regions of the debris disks in our sample is less than ~3 × 10^(–6) g cm^(-2), 9 orders of magnitude below the surface density of the minimum mass solar nebula at 1 AU.
|Additional Information:||© 2009 American Astronomical Society. Print publication: Issue 2 (2009 October 1); received 2009 August 12; accepted for publication 2009 August 27; published 2009 September 14. We thank Al Glassgold for discussions clarifying the ionization mechanisms in the disk. This work was supported by NASA through grants GO-08317, GO-09081, GO-9374, GO- 10810, and GO-10840 from the Space Telescope Science Institute. This material is also based upon work supported by the National Science Foundation under Grant No. 0707777 to E.A.B.|
|Subject Keywords:||accretion, accretion disks; circumstellar matter; stars: pre-main sequence|
|Official Citation:||Far-Ultraviolet H2 Emission from Circumstellar Disks Laura Ingleby, Nuria Calvet, Edwin Bergin, Ashwin Yerasi, Catherine Espaillat, Gregory Herczeg, Evelyne Roueff, Hervé Abgrall, Jesus Hernández, César Briceño, Ilaria Pascucci, Jon Miller, Jeffrey Fogel, Lee Hartmann, Michael Meyer, John Carpenter, Nathan Crockett, and Melissa McClure 2009 ApJ 703 L137-L141 doi: 10.1088/0004-637X/703/2/L137|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||07 Oct 2009 15:00|
|Last Modified:||26 Dec 2012 11:26|
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