Catch me if you can: looking for time-variable ionization in the DQ Tau disk

Sierk van Terwisga

Thursday, Dec. 8th, 16:40CET

The ionizing radiation environment of young stars is a key part of the evolution of their protoplanetary disks. Disk ionization not only governs accretion onto the star, but also influences the chemistry of the molecular gas in the disk, most directly through the abundances of molecular ions. However, it is also clear that ionization is a highly variable parameter, over many orders of magnitude in time and flux, due to for example X-ray flares or accretion rate changes. While Cleeves et al. 2017 have shown that H13CO+ in IM Lup is variable, most likely due to an X-ray flare, the stochastic nature of X-ray variability in young stellar objects has made it very difficult to test models of the impact of variable ionization on molecular ion chemistry in the disk with direct observations. In this talk, we introduce the DQ Tau system as a unique laboratory for the impact of ionization on disk chemistry, both at long and short timescales. DQ Tau is an eccentric spectroscopic binary, which is unique for its predictable X-ray flares and increased accretion during periastron. We discuss the first results from a multi-wavelength observing campaign, with ALMA, Chandra, and optical monitoring of the system. Using time-dependent models, we investigate the DQ Tau disk as a nearby example of a disk experiencing a high ionization environment over Myr timescales, as well as short-term variability, and compare model and observational results.