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Title: CO AND H{sub 2} ABSORPTION IN THE AA TAURI CIRCUMSTELLAR DISK

Abstract

The direct study of molecular gas in inner protoplanetary disks is complicated by uncertainties in the spatial distribution of the gas, the time variability of the source, and the comparison of observations across a wide range of wavelengths. Some of these challenges can be mitigated with far-ultraviolet spectroscopy. Using new observations obtained with the Hubble Space Telescope Cosmic Origins Spectrograph, we measure column densities and rovibrational temperatures for CO and H{sub 2} observed on the line of sight through the AA Tauri circumstellar disk. CO A - X absorption bands are observed against the far-UV continuum. The CO absorption is characterized by log{sub 10}(N({sup 12}CO)) = 17.5 {+-} 0.5 cm{sup -2} and T{sub rot}(CO) = 500{sup +500}{sub -200} K, although this rotational temperature may underestimate the local kinetic temperature of the CO-bearing gas. We also detect {sup 13}CO in absorption with an isotopic ratio of {approx}20. We do not observe H{sub 2} absorption against the continuum; however, hot H{sub 2} (v > 0) is detected in absorption against the Ly{alpha} emission line. We measure the column densities in eight individual rovibrational states, determining a total log{sub 10}(N(H{sub 2})) = 17.9{sup +0.6}{sub -0.3} cm{sup -2} with a thermal temperature of T(H{submore » 2}) = 2500{sup +800}{sub -700} K. The high temperature of the molecules, the relatively small H{sub 2} column density, and the high inclination of the AA Tauri disk suggest that the absorbing gas resides in an inner disk atmosphere. If the H{sub 2} and CO are cospatial within a molecular layer {approx}0.6 AU thick, this region is characterized by {approx} 10{sup 5} cm{sup -3} with an observed (CO/H{sub 2}) ratio of {approx}0.4. We also find evidence for a departure from a purely thermal H{sub 2} distribution, suggesting that excitation by continuum photons and H{sub 2} formation may be altering the level populations in the molecular gas.« less

Authors:
; ; ;  [1];  [2]; ;  [3]; ;  [4];  [5]
  1. Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States)
  2. Max-Planck-Institut fuer extraterrestriche Physik, Postfach 1312, D-85741 Garching (Germany)
  3. JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309 (United States)
  4. LUTH and UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, Place J. Janssen, F-92195 Meudon (France)
  5. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
22004355
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 744; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; FAR ULTRAVIOLET RADIATION; HYDROGEN; INCLINATION; ISOTOPE RATIO; PLANETARY ATMOSPHERES; PROTOPLANETS; SPATIAL DISTRIBUTION; SPECTROSCOPY; STARS; TELESCOPES

Citation Formats

France, Kevin, Burgh, Eric B., Schindhelm, Eric, Brown, Alexander, Herczeg, Gregory J., Yang, Hao, Linsky, Jeffrey L., Abgrall, Herve, Roueff, Evelyne, and Brown, Joanna M., E-mail: kevin.france@colorado.edu. CO AND H{sub 2} ABSORPTION IN THE AA TAURI CIRCUMSTELLAR DISK. United States: N. p., 2012. Web. doi:10.1088/0004-637X/744/1/22.
France, Kevin, Burgh, Eric B., Schindhelm, Eric, Brown, Alexander, Herczeg, Gregory J., Yang, Hao, Linsky, Jeffrey L., Abgrall, Herve, Roueff, Evelyne, & Brown, Joanna M., E-mail: kevin.france@colorado.edu. CO AND H{sub 2} ABSORPTION IN THE AA TAURI CIRCUMSTELLAR DISK. United States. doi:10.1088/0004-637X/744/1/22.
France, Kevin, Burgh, Eric B., Schindhelm, Eric, Brown, Alexander, Herczeg, Gregory J., Yang, Hao, Linsky, Jeffrey L., Abgrall, Herve, Roueff, Evelyne, and Brown, Joanna M., E-mail: kevin.france@colorado.edu. Sun . "CO AND H{sub 2} ABSORPTION IN THE AA TAURI CIRCUMSTELLAR DISK". United States. doi:10.1088/0004-637X/744/1/22.
@article{osti_22004355,
title = {CO AND H{sub 2} ABSORPTION IN THE AA TAURI CIRCUMSTELLAR DISK},
author = {France, Kevin and Burgh, Eric B. and Schindhelm, Eric and Brown, Alexander and Herczeg, Gregory J. and Yang, Hao and Linsky, Jeffrey L. and Abgrall, Herve and Roueff, Evelyne and Brown, Joanna M., E-mail: kevin.france@colorado.edu},
abstractNote = {The direct study of molecular gas in inner protoplanetary disks is complicated by uncertainties in the spatial distribution of the gas, the time variability of the source, and the comparison of observations across a wide range of wavelengths. Some of these challenges can be mitigated with far-ultraviolet spectroscopy. Using new observations obtained with the Hubble Space Telescope Cosmic Origins Spectrograph, we measure column densities and rovibrational temperatures for CO and H{sub 2} observed on the line of sight through the AA Tauri circumstellar disk. CO A - X absorption bands are observed against the far-UV continuum. The CO absorption is characterized by log{sub 10}(N({sup 12}CO)) = 17.5 {+-} 0.5 cm{sup -2} and T{sub rot}(CO) = 500{sup +500}{sub -200} K, although this rotational temperature may underestimate the local kinetic temperature of the CO-bearing gas. We also detect {sup 13}CO in absorption with an isotopic ratio of {approx}20. We do not observe H{sub 2} absorption against the continuum; however, hot H{sub 2} (v > 0) is detected in absorption against the Ly{alpha} emission line. We measure the column densities in eight individual rovibrational states, determining a total log{sub 10}(N(H{sub 2})) = 17.9{sup +0.6}{sub -0.3} cm{sup -2} with a thermal temperature of T(H{sub 2}) = 2500{sup +800}{sub -700} K. The high temperature of the molecules, the relatively small H{sub 2} column density, and the high inclination of the AA Tauri disk suggest that the absorbing gas resides in an inner disk atmosphere. If the H{sub 2} and CO are cospatial within a molecular layer {approx}0.6 AU thick, this region is characterized by {approx} 10{sup 5} cm{sup -3} with an observed (CO/H{sub 2}) ratio of {approx}0.4. We also find evidence for a departure from a purely thermal H{sub 2} distribution, suggesting that excitation by continuum photons and H{sub 2} formation may be altering the level populations in the molecular gas.},
doi = {10.1088/0004-637X/744/1/22},
journal = {Astrophysical Journal},
number = 1,
volume = 744,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2012},
month = {Sun Jan 01 00:00:00 EST 2012}
}