Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2S025

Time variation in the molecular infrared spectrum of IRS 46

Lahuis, Fred (SRON Netherlands Institute for Space Research & Leiden Observatory, Leiden University)
Kamp, Inga (Kapteyn Astronomical Institute)
Thi, Wing-Fai (Universite Joseph Fourier Grenoble-1, IPAG)
van Dishoeck, Ewine (Leiden Observatory, Leiden University & Max-Planck-Institut für extraterrestrische Physikwine)
Harsono, Daniel (Leiden Observatory, Leiden University & SRON Netherlands Institute for Space Research)
Woitke, Peter (School of Physics & Astronomy, University of St. Andrews)

Early Spitzer-IRS observations of the young star IRS 46 revealed strong absorption bands of gas-phase C2H2, HCN and CO2. These provided the first observational test of chemical models in the planet-forming zone of a circumstellar disk as well as a direct measure of the temperature and density. Subsequently, the same molecules have been observed in absorption toward the young star GV Tau and in emission (together with hot abundant H2O and OH) toward a number of T Tauri stars. However, follow-up Spitzer-IRS observations of IRS 46 at 5 epochs taken during 2008 and 2009 show dramatic changes of the mid-IR properties. The mid-IR continuum and the strength of hot water emission lines (previously not identified) have increased while the absorption features have strongly decreased in strength. At the same time no significant changes are observed in the molecular spectrum of GV Tau. Starting with the parameters of the SED model as presented in the original paper by Lahuis et al. 2006, we use the proptoplanetary disk model ProDiMo to model the chemical composition of the inner few AU of the IRS 46 disk. In addition ProDiMo is used to investigate the nature of the changes observed in the mid-IR spectra of IRS 46 and to test if an outburst event (akin EX Lupi) can explain the observed changes.

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