Cool, late-type stars have proven problematic when determining accurate age estimates for young open clusters due to inaccuracies in stellar evolution models. Starspots have been suggested as an explanation for discrepancies between stellar model predictions and observed properties of cool stars. By applying a flexible starspot model to stellar evolution isochrones and comparing to photometric data from the Pleiades and Praesepe, we determine which starspot properties are required to bring stellar evolution isochrones into agreement with the observed data. The starspot model allows us to estimate starspot surface coverages and temperature contrasts for possible starspot formation mechanisms. Preliminary results suggest that starspots form in deeper, more opaque layers and not in stars’ superadiabatic layers. We find two families of starspot models are consistent with the photometric data. Models in which the star restructures to redistribute flux as compensation for the spot, and models assuming that spots exist for a small duration of time, causing only a brief decrease in luminosity, provide accurate fits for the data. Both models are consistent with expected temperature contrast values, and provide similar surface coverage, with the inflationary model generally requiring lower surface coverage. Although we cannot yet discriminate between these two families of models, efforts to do so will provide an important clue as to how starspots form and how they affect stellar structure and evolution.

Research funded by the University of North Georgia