Resolving Surface Features on Young M Dwarfs that Host Transient Corotating Material

In the era of space-based, time-series photometry, stellar variability has provided an invaluable lens on the physics of stellar magnetism and the interaction between stars and their circumstellar environment. One of the more enigmatic classes of stellar variability to emerge from the Kepler K2 mission are complex periodic variables (CPVs). These stars exhibit narrow dimming events with variable morphologies and depths that are periodic with the stellar rotation. With more systems now discovered with TESS, the growing sample is predominantly young (< ~200 Myr), low-mass (M < 0.4 Solar masses), and rapidly rotating (P < 1 day). Without evidence for disk material, the most likely scenario is magnetically confined material orbiting in co-rotation with the star. To further investigate the source of this variability, we have monitored four CPVs in Upper Sco with moderate-cadence, high-resolution, near-infrared spectra from the IGRINS spectrograph (simultaneous H and K at R ~ 45,000). We find large rotational velocities (vsini > 150 km/s), consistent with near edge on orientations, and no significant radial-velocity variability. Reconstructed line profiles reveal evidence for large and evolving spot features, preferentially at polar latitudes. The results of our sparsely sampled data highlight CPVs as prime candidates for future Doppler tomographic studies to fully reconstruct the stellar surface, and to measure the orientation and size of the transiting material.

Theme(s): The Sun and Cool Stars in the Time Domain, Cool Stars as Stellar Systems