2012ApJ...745...90B -
Astrophys. J., 745, 90 (2012/January-3)
EX Lupi from quiescence to outburst: exploring the LTE approach in modeling blended H2 O and OH mid-infrared emission.
BANZATTI A., MEYER M.R., BRUDERER S., GEERS V., PASCUCCI I., LAHUIS F., JUHASZ A., HENNING T. and ABRAHAM P.
Abstract (from CDS):
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 H2O lines, highly excited OH lines, and the Q branches of the organics C2H2, HCN, and CO2, similar to the emission observed toward several T Tauri systems. The outburst emission shows instead remarkable changes: H2 O and OH line fluxes increase, new OH, H2, 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 H2 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 H2 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 H2 O and OH emission suggests a key role for UV radiation in the disk surface chemistry.
Abstract Copyright:
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Journal keyword(s):
circumstellar matter - molecular processes - stars: activity - stars: individual: EX Lupi - stars: pre-main sequence - stars: variables: T Tauri, Herbig Ae/Be
Errata:
erratum vol. 751, art. 160 (2012)
Simbad objects:
3
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