Shine Bright like a Protostar: Flare Driven Chemistry in Protoplanetary Disks

Abygail Renee Waggoner

Young, active stars and their planet-forming disks are dynamic environments. Recent work suggests that stellar activity plays a major role in shaping disk chemical and physical composition. For example, pre-main sequence solar mass stars commonly undergo X-ray flaring events, which temporarily (hours to days) increases X-ray ionization rates anywhere from a few factors to several hundred factors. We present an observational and theoretical investigation of X-ray flare driven chemistry in planet forming disks. Chemical disk models suggest that gas-phase cations, such as HCO+ and N2H+, trace X-ray flaring events. We present tentative evidence of flare driven variability in HCO+ spectra, likely in response to a flaring event, in five disks observed as a part of the MAPS large ALMA program. The low level of observed variability is consistent with modeled statistics, thus supporting the X-ray flare theory. While individual flares are expected to drive ‘short-term’ variability in disk chemistry, our modeling also suggests that the cumulative impact of thousands of flares over hundreds of years may drive disk chemistry to a new ‘steady state.’ For example, chemical disk models suggest that X-ray flares may aid in the production of O2 and organosulphides, effectively aiding the formation of more complex chemical species