Complex Modulation of Rapidly Rotating Young M Dwarfs: Adding Pieces to the Puzzle

Kavli Affiliate: Saul Rappaport

| First 5 Authors: Maximilian N. G√ľnther, David A. Berardo, Elsa Ducrot, Catriona A. Murray, Keivan G. Stassun

| Summary:

New sets of young M dwarfs with complex, sharp-peaked, and strictly periodic
photometric modulations have recently been discovered with Kepler/K2 and TESS
data. All of these targets are part of young star-forming associations.
Suggested explanations range from accretion of dust disks to co-rotating clouds
of material to stellar spots getting periodically occulted by
spin-orbit-misaligned dust disks. Here we provide a comprehensive overview of
all aspects of these hypotheses, and add more observational constraints in an
effort to understand these objects with photometry from TESS and the SPECULOOS
Southern Observatory (SSO). We scrutinize the hypotheses from three different
angles: (1) we investigate the occurrence rates of these scenarios through
existing young star catalogs; (2) we study the longevity of these features
using over one year of combined photometry from TESS and SSO; and (3) we probe
the expected color dependency with multi-color photometry from SSO. In this
process, we also revisit the stellar parameters accounting for activity
effects, study stellar flares as activity indicators over year-long time
scales, and develop toy models to imitate typical morphologies. We identify
which parts of the hypotheses hold true or are challenged by these new
observations. So far, none of the hypotheses stand out as a definite answer,
and each come with limitations. While the mystery of these complex rotators
remains, we here add valuable observational pieces to the puzzle for all
studies going forward.

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