EX Lupi from quiescence to outburst: Exploring the LTE approach in modeling blended H2O and OH mid-infrared emission

A. Banzatti, M. R. Meyer, S. Bruderer, V. Geers, I. Pascucci, F. Lahuis, A. Juhász, T. Henning, P. Ábrahám

Research output: Article

27 Citations (Scopus)

Abstract

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 2O 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: H2O and OH line fluxes increase, new OH, H 2, and HI 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 2O 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 H2O 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 H2O and OH emission suggests a key role for UV radiation in the disk surface chemistry.

Original languageEnglish
Article number90
JournalAstrophysical Journal
Volume745
Issue number1
DOIs
Publication statusPublished - jan. 20 2012

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local thermodynamic equilibrium
outburst
modeling
temperature
gas
H lines
gases
excitation
slab
slabs
diagram
diagrams
chemistry
vapor phases
radiation

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics
  • Nuclear and High Energy Physics

Cite this

EX Lupi from quiescence to outburst : Exploring the LTE approach in modeling blended H2O and OH mid-infrared emission. / Banzatti, A.; Meyer, M. R.; Bruderer, S.; Geers, V.; Pascucci, I.; Lahuis, F.; Juhász, A.; Henning, T.; Ábrahám, P.

In: Astrophysical Journal, Vol. 745, No. 1, 90, 20.01.2012.

Research output: Article

Banzatti, A. ; Meyer, M. R. ; Bruderer, S. ; Geers, V. ; Pascucci, I. ; Lahuis, F. ; Juhász, A. ; Henning, T. ; Ábrahám, P. / EX Lupi from quiescence to outburst : Exploring the LTE approach in modeling blended H2O and OH mid-infrared emission. In: Astrophysical Journal. 2012 ; Vol. 745, No. 1.
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T2 - Exploring the LTE approach in modeling blended H2O and OH mid-infrared emission

AU - Banzatti, A.

AU - Meyer, M. R.

AU - Bruderer, S.

AU - Geers, V.

AU - Pascucci, I.

AU - Lahuis, F.

AU - Juhász, A.

AU - Henning, T.

AU - Ábrahám, P.

PY - 2012/1/20

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N2 - 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 2O 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: H2O and OH line fluxes increase, new OH, H 2, and HI 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 2O 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 H2O 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 H2O and OH emission suggests a key role for UV radiation in the disk surface chemistry.

AB - 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 2O 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: H2O and OH line fluxes increase, new OH, H 2, and HI 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 2O 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 H2O 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 H2O and OH emission suggests a key role for UV radiation in the disk surface chemistry.

KW - circumstellar matter

KW - molecular processes

KW - stars: activity

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KW - stars: pre-main sequence

KW - stars: variables: T Tauri, Herbig Ae/Be

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