Abstract

Longitudinally asymmetric starspots modulate observed stellar flux as stars rotate, an assumption underpinning stellar age estimates from gyrochronology. Longitudinally symmetric starspots induce no lightcurve modulation, remaining largely unquantified owing to their lack of temporal variability. Growing evidence for circumpolar starspots suggests that the areal coverage fraction of starspots may be significantly underestimated at young ages, questioning the reliability of standard pre-main sequence evolutionary models and derived stellar masses and ages. I have extended the spectral inference framework Starfish to measure starspot properties with probabilistic spectral decomposition: the observed IGRINS spectrum arises from a mixture of starspot emission and ambient photosphere. The framework provides exceptional constraints on the total starspot coverage of a stellar hemisphere, consistent with lower limits from the large Kepler/K2/ASSASN variability amplitudes. I propose a path forward for evaluating starspot-induced biases in star cluster ages, eclipsing binary radii, exoplanet transit depths, and retrieved exoplanet transmission spectroscopy with JWST. I will also show applications of probabilistic spectral analysis to IGRINS/Keck spectra of brown dwarfs, evolved stars, and protostars.

Abstract