Accession Number : ADA543637


Title :   Organic Molecules and Water in the Inner Disks of T Tauri Stars


Descriptive Note : Journal article


Corporate Author : NAVAL RESEARCH LAB WASHINGTON DC


Personal Author(s) : Carr, John S ; Najita, Joan R


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a543637.pdf


Report Date : 11 May 2011


Pagination or Media Count : 20


Abstract : 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 H2O and OH and rovibrational bands of simple organic molecules (CO2, HCN, C2H2) 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 H2O emission appears to form under a limited range of excitation conditions, as demonstrated by the similarity in relative strengths of H2O 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/H2O flux ratio shows a relatively small scatter. We interpret these results as evidence for OH production via FUV photodissociation of H2O 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/H2O 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.


Descriptors :   *STARS , REPRINTS , DENSITY , WATER , FLUX(RATE) , SPECTROGRAPHS , ORGANIC COMPOUNDS , DISKS , MOLECULAR PROPERTIES , EMISSION , SIGNAL TO NOISE RATIO


Subject Categories : Astronomy


Distribution Statement : APPROVED FOR PUBLIC RELEASE