Stellar Activity and the Planet-Star Connection

A major unanswered question in exoplanet science is the pathway for planetary formation and evolution. One approach to this problem is to accurately infer the histories of planets by comparing the demographics of late-age planetary systems to those of young systems. But, in contrast to the wealth of exoplanet discoveries at late ages, there are currently only a handful of confirmed planets at early ages (<10 Myr), and only one confirmed hot Jupiter (CI Tau b) orbiting a Classical T Tauri Star (CTTS). The severe deficit of young planets drives the motivation to find more of them. Doing so would provide concrete evidence for or against migration as well as timestamp the state of their atmospheric evolution. However, variability of CTTS is strong and occurs over a range of timescales, which can hinder the transit and RV detectability of young close-in planets. Intense magnetic activity in CTTS occurs in the form of long-lived cold spots and accretion hot spots which can mimic planetary signatures or drown them out entirely. Additionally, the high rate of energetic events generated by accretion shocks and flares is likely to affect the properties of the circumstellar disk and orbiting planets. The effects of CTTS’s stellar activity therefore offer incentive to characterize these sources of variability to (1) tease out the observational signatures of newly-formed planets and (2) understand the impact that high-energy magnetic events have on the evolution of planets and protoplanetary disks. Using CI Tau b as an example, I present a novel method for detecting close-in planets around CTTS based on the planet’s interaction with the circumstellar disk, driving pulsed accretion onto the star over the timescale of the planet’s orbit. I discuss how this method can be used to detect more young close-in planets like CI Tau b. I also provide a diagnosis of the astrophysical contributions to the total photometric variability of CTTS through both an observational and computational lens.