ORGANIC MOLECULES AND WATER IN THE INNER DISKS OF T TAURI STARS

Journal Article · Wed Jun 01 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/733/2/102· OSTI ID:21576733

Carr, John S ^[1]

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1. Naval Research Laboratory, Code 7211, Washington, DC 20375 (United States)

We report high signal-to-noise Spitzer Infrared Spectrograph spectra of a sample of 11 classical T Tauri stars. Molecular emission from rotational transitions of H{sub 2}O and OH and rovibrational bands of simple organic molecules (CO{sub 2}, HCN, C{sub 2}H{sub 2}) is common among the sources in the sample. The emission shows a range in both flux and line-to-continuum ratio for each molecule and in the flux ratios of different molecular species. The gas temperatures (200-800 K) and emitting areas we derive are consistent with the emission originating in a warm disk atmosphere in the inner planet formation region at radii <2 AU. The H{sub 2}O emission appears to form under a limited range of excitation conditions, as demonstrated by the similarity in relative strengths of H{sub 2}O features from star to star and the narrow range in derived temperature and column density. Emission from highly excited rotational levels of OH is present in all stars; the OH emission flux increases with the stellar accretion rate, and the OH/H{sub 2}O flux ratio shows a relatively small scatter. We interpret these results as evidence for OH production via FUV photodissociation of H{sub 2}O in the disk surface layers. No obvious explanation is found for the observed range in the relative emission strengths of different organic molecules or in their strength with respect to water. We put forward the possibility that these variations reflect a diversity in organic abundances due to star-to-star differences in the C/O ratio of the inner disk gas. Stars with the largest HCN/H{sub 2}O flux ratios in our sample have the largest disk masses. While larger samples are required to confirm this, we speculate that such a trend could result if higher mass disks are more efficient at planetesimal formation and sequestration of water in the outer disk, leading to enhanced C/O ratios and abundances of organic molecules in the inner disk. A comparison of our derived HCN-to-H{sub 2}O column density ratio to comets, hot cores, and outer T Tauri star disks suggests that the inner disks are chemically active.

• OSTI ID: 21576733
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 733; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BINARY STARS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
DENSITY
DISSOCIATION
EMISSION
ERUPTIVE VARIABLE STARS
HYDROCYANIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC COMPOUNDS
MASS
MOLECULES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
STARS
T TAURI STARS
VARIABLE STARS
VARIATIONS
WATER