1. THE ATOMIC AND MOLECULAR CONTENT OF DISKS AROUND VERY LOW-MASS STARS AND BROWN DWARFS.
- Author
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Pascucci, I., Herczeg, G., Carr, J. S., and Bruderer, S.
- Subjects
STELLAR mass ,DWARF stars ,T Tauri stars ,BROWN dwarf stars ,PLANETS - Abstract
There is growing observational evidence that disk evolution is stellar-mass-dependent. Here, we show that these dependencies extend to the atomic and molecular content of disk atmospheres. We analyze a unique dataset of high-resolution Spitzer/IRS spectra from eight very low mass star and brown dwarf disks. We report the first detections of Ne
+ , H2 , CO2 , and tentative detections of H2 O toward these faint and low-mass disks. Two of our [Ne II] 12.81 μm emission lines likely trace the hot (⩾5000 K) disk surface irradiated by X-ray photons from the central stellar/sub-stellar object. The H2 S(2) and S(1) fluxes are consistent with arising below the fully or partially ionized surface traced by the [Ne II] emission in gas at ∼600 K. We confirm the higher C2 H2 /HCN flux and column density ratio in brown dwarf disks previously noted from low-resolution IRS spectra. Our high-resolution spectra also show that the HCN/H2 O fluxes of brown dwarf disks are on average higher than those of T Tauri disks. Our LTE modeling hints that this difference extends to column density ratios if H2 O lines trace warm ⩾600 K disk gas. These trends suggest that the inner regions of brown dwarf disks have a lower O/C ratio than those of T Tauri disks, which may result from a more efficient formation of non-migrating icy planetesimals. An O/C = 1, as inferred from our analysis, would have profound implications on the bulk composition of rocky planets that can form around very low mass stars and brown dwarfs. [ABSTRACT FROM AUTHOR]- Published
- 2013
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