THE FAR-ULTRAVIOLET 'CONTINUUM' IN PROTOPLANETARY DISK SYSTEMS. II. CARBON MONOXIDE FOURTH POSITIVE EMISSION AND ABSORPTION
- Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309 (United States)
- Max-Planck-Institut fuer Extraterrestriche Physik, Postfach 1312, 85741 Garching (Germany)
- School of Physics, Trinity College, Dublin 2 (Ireland)
- JILA, University of Colorado and NIST, 440 UCB, Boulder, CO 80309 (United States)
- LUTH and UMR 8102 du CNRS, Observatoire de Paris, Section de Meudon, Place J. Janssen, 92195 Meudon (France)
- NASA Herschel Science Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
- Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States)
- California Institute of Technology, Department of Astrophysics, MC 249-17, Pasadena, CA 91125 (United States)
- ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Muenchen (Germany)
We exploit the high sensitivity and moderate spectral resolution of the Hubble Space Telescope Cosmic Origins Spectrograph to detect far-ultraviolet (UV) spectral features of carbon monoxide (CO) present in the inner regions of protoplanetary disks for the first time. We present spectra of the classical T Tauri stars HN Tau, RECX-11, and V4046 Sgr, representative of a range of CO radiative processes. HN Tau shows CO bands in absorption against the accretion continuum. The CO absorption most likely arises in warm inner disk gas. We measure a CO column density and rotational excitation temperature of N(CO) = (2 {+-} 1) x 10{sup 17} cm{sup -2} and T{sub rot}(CO) 500 {+-} 200 K for the absorbing gas. We also detect CO A-X band emission in RECX-11 and V4046 Sgr, excited by UV line photons, predominantly H I Ly{alpha}. All three objects show emission from CO bands at {lambda} > 1560 A, which may be excited by a combination of UV photons and collisions with non-thermal electrons. In previous observations these emission processes were not accounted for due to blending with emission from the accretion shock, collisionally excited H{sub 2}, and photo-excited H{sub 2}, all of which appeared as a 'continuum' whose components could not be separated. The CO emission spectrum is strongly dependent upon the shape of the incident stellar Ly{alpha} emission profile. We find CO parameters in the range: N(CO) {approx} 10{sup 18}-10{sup 19} cm{sup -2}, T{sub rot}(CO) {approx}> 300 K for the Ly{alpha}-pumped emission. We combine these results with recent work on photo-excited and collisionally excited H{sub 2} emission, concluding that the observations of UV-emitting CO and H{sub 2} are consistent with a common spatial origin. We suggest that the CO/H{sub 2} ratio ({identical_to} N(CO)/N(H{sub 2})) in the inner disk is {approx}1, a transition between the much lower interstellar value and the higher value observed in solar system comets today, a result that will require future observational and theoretical study to confirm.
- OSTI ID:
- 21576661
- Journal Information:
- Astrophysical Journal, Vol. 734, Issue 1; Other Information: DOI: 10.1088/0004-637X/734/1/31; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABSORPTION
CARBON MONOXIDE
EMISSION
FAR ULTRAVIOLET RADIATION
PROTOPLANETS
T TAURI STARS
BINARY STARS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
ELECTROMAGNETIC RADIATION
ERUPTIVE VARIABLE STARS
OXIDES
OXYGEN COMPOUNDS
RADIATIONS
SORPTION
STARS
ULTRAVIOLET RADIATION
VARIABLE STARS