HIGH-PRECISION C{sup 17}O, C{sup 18}O, AND C{sup 16}O MEASUREMENTS IN YOUNG STELLAR OBJECTS: ANALOGUES FOR CO SELF-SHIELDING IN THE EARLY SOLAR SYSTEM

Journal Article · Mon Aug 10 00:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/701/1/163; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21313701

Smith, Rachel L; Young, Edward D ^[1]; Pontoppidan, Klaus M ^[2]; Morris, Mark R ^[3]

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1. Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles E. Young Drive East, Geology Building, Los Angeles, CA 90095-1567, USA. (United States)
2. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. (United States)
3. Division of Astronomy and Astrophysics, Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA. (United States)

Using very high resolution ({lambda}/{delta}{lambda} {approx} 95 000) 4.7 {mu}m fundamental and 2.3 {mu}m overtone rovibrational CO absorption spectra obtained with the Cryogenic Infrared Echelle Spectrograph infrared spectrometer on the Very Large Telescope (VLT), we report detections of four CO isotopologues-C{sup 16}O, {sup 13}CO, C{sup 18}O, and the rare species, C{sup 17}O-in the circumstellar environment of two young protostars: VV CrA, a binary T Tauri star in the Corona Australis molecular cloud, and Reipurth 50, an intermediate-mass FU Ori star in the Orion Molecular Cloud. We argue that the observed CO absorption lines probe a protoplanetary disk in VV CrA, and a protostellar envelope in Reipurth 50. All CO line profiles are spectrally resolved, with intrinsic line widths of {approx}3-4 km s{sup -1} (FWHM), permitting direct calculation of CO oxygen isotopologue ratios with 5%-10% accuracy. The rovibrational level populations for all species can be reproduced by assuming that CO absorption arises in two temperature regimes. In the higher temperature regime, in which the column densities are best determined, the derived oxygen isotope ratios in VV CrA are: [C{sup 16}O]/[C{sup 18}O] =690 {+-} 30; [C{sup 16}O]/[C{sup 17}O] =2800 {+-} 300, and [C{sup 18}O]/[C{sup 17}O]=4.1 {+-} 0.4. For Reipurth 50, we find [C{sup 16}O]/[C{sup 18}O] =490 {+-} 30; [C{sup 16}O]/[C{sup 17}O] =2200 {+-} 150, [C{sup 18}O]/[C{sup 17}O] = 4.4 {+-} 0.2. For both objects, {sup 12}C/{sup 13}C are on the order of 100, nearly twice the expected interstellar medium (ISM) ratio. The derived oxygen abundance ratios for the VV CrA disk show a significant mass-independent deficit of C{sup 17}O and C{sup 18}O relative to C{sup 16}O compared to ISM baseline abundances. The Reipurth 50 envelope shows no clear differences in oxygen CO isotopologue ratios compared with the local ISM. A mass-independent fractionation can be interpreted as being due to selective photodissociation of CO in the disk surface due to self-shielding. The deficits in C{sup 17} O and C{sup 18} O in the VV CrA protoplanetary disk are consistent with an analogous origin of the {sup 16}O variability in the solar system by isotope selective photodissociation, confirmation of which may be obtained via study of additional sources. The higher fractionation observed for the VV CrA disk compared with the Reipurth 50 envelope is likely due to a combination of disk geometry, grain growth, and vertical mixing processes.

• OSTI ID: 21313701
• Journal Information: Astrophysical Journal, Vol. 701, Issue 1; Other Information: DOI: 10.1088/0004-637X/701/1/163; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
ABSORPTION
ABSORPTION SPECTRA
ABUNDANCE
CARBON 12
CARBON 13
CARBON 17
CARBON 18
CARBON MONOXIDE
FRACTIONATION
GRAIN GROWTH
INFRARED SPECTROMETERS
MASS
OXYGEN 16
PHOTOLYSIS
PROTOPLANETS
PROTOSTARS
SELF-SHIELDING
SOLAR SYSTEM
T TAURI STARS
TELESCOPES