Jets and disk scattering - Spatially resolved optical and FUV observations of AA Taudac
Abstract
Planets form during the time, when the central star accretes material from the surrounding circumstellar disk and the final system architecture depends on the poorly known accretion and ejection history. Accretion tracers are particularly prominent in the UV so that the HST legacy program ULLYSES was conceived to obtain a UV atlas of accreting, young stars. In the UV, however, extinction is a severe issue and already moderate amounts of dust can completely extinguish any (accretion) signal. Accretion and extinction decline with age so that it is imperative to understand how well UV observations actually trace genuine accretion emission for higher absorption column densities or if rather other processes, namely jet emission or light scattered towards the observer by the upper disk layers, mimic accretion in spatially unresolved data such as the ULLYSES COS observations.
Our target, the classical T Tauri star AA Tau, currently experiences a long-lasting dimming event, presumably caused by inner disk dust, i.e., the star is currently hidden behind a "natural coronograph" and the direct emission is greatly reduced. Spatially unresolved HST COS data suggest that jet emission and scattering dominate the integrated FUV light during the dimming event. We propose to utilize this situation to detect UV scattering for the first time and to measure the jet's contribution to the FUV light through spatially resolving the emission with a series of STIS long-slit spectra. This experiment, right in time for ULLYSES, will uncover what fundamentally limits UV accretion studies, lack of signal due to absorption or "contaminating" emission spoiling the interpretation of the signals.- Publication:
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HST Proposal
- Pub Date:
- May 2020
- Bibcode:
- 2020hst..prop16233S