EX Lupi FROM QUIESCENCE TO OUTBURST: EXPLORING THE LTE APPROACH IN MODELING BLENDED H{sub 2}O AND OH MID-INFRARED EMISSION
- ETH Zuerich, Institut fuer Astronomie, Wolfgang-Pauli-Strasse 27, CH-8093 Zuerich (Switzerland)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- SRON Netherlands Institute for Space Research, P.O. Box 800, NL 9700 AV Groningen (Netherlands)
- Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)
- Konkoly Observatory, Konkoly Thege Miklos 15-17, H-1121 Budapest (Hungary)
We present a comparison of archival Spitzer spectra of the strongly variable T Tauri EX Lupi, observed before and during its 2008 outburst. We analyze the mid-infrared emission from gas-phase molecules thought to originate in a circumstellar disk. In quiescence the emission shows a forest of H{sub 2}O lines, highly excited OH lines, and the Q branches of the organics C{sub 2}H{sub 2}, HCN, and CO{sub 2}, similar to the emission observed toward several T Tauri systems. The outburst emission shows instead remarkable changes: H{sub 2}O and OH line fluxes increase, new OH, H{sub 2}, and H I transitions are detected, and organics are no longer seen. We adopt a simple model of a single-temperature slab of gas in local thermal equilibrium, a common approach for molecular analyses of Spitzer spectra, and derive the excitation temperature, column density, and emitting area of H{sub 2}O and OH. We show how model results strongly depend on the selection of emission lines fitted and how this is likely to be attributed to a combination of non-thermal excitation and multiple emission components. Using H{sub 2}O lines that can be approximated as thermalized to a single temperature, our results are consistent with a column density decrease in outburst while the emitting area of warm gas increases. A rotation diagram analysis suggests that the OH emission can be explained with two temperature components, which remarkably increase in column density in outburst. The relative change of H{sub 2}O and OH emission suggests a key role for UV radiation in the disk surface chemistry.
- OSTI ID:
- 22011647
- Journal Information:
- Astrophysical Journal, Vol. 745, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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