Dr. James Neff (College of Charleston, South Carolina) and Dr. Douglas O'Neal (Keystone College, Pennsylvania) will lead an effort to understand the physical conditions in starspots. Analogous to spots on the Sun, starspots are regions in the atmospheres of other stars that are cooler than the rest of the stellar surface. The goals of this project are to use recent advances in atmospheric modeling codes to determine starspot properties, re-analyze extensive databases of existing spectra using the new techniques, expand observational surveys to include cooler stars, and combine various techniques to yield a better understanding of the observational signatures of starspots.
Magnetic activity on the Sun is perhaps the most dramatic way in which astronomy impacts our daily lives. By measuring the properties and distribution of starspots on a wide range of active stars, it might be possible to uncover the fundamental nature of the solar dynamo. Photometric light curve modeling, Doppler imaging, and the spectroscopic properties of molecular bands (which are formed only in starspots, not in the warmer unspotted atmosphere) all yield important information about the distribution, temperature, and fractional coverage of starspots.
Since graduate school, the P. I. (Douglas O'Neal) has used molecular bands of the titanium oxide (TiO) molecule to measure starspot area and temperature on magnetically active stars. This has been done using proxy stars to compare to the spotted and unspotted regions of the active stars. This grant covered the extension of this to two other techniques: using model atmospheres and synthetic spectra instead of proxy stars; and comparing the results using these methods to those found from Doppler imaging. One major result was that results using synthetic spectra find a somewhat higher spot filling factor and somewhat lower temperature than those using proxy stars. Another was that results from Doppler imaging are consistent in ratio with those using proxy stars and synthetic spectra, but find only a fraction of the spot coverage. This (finding low spot filling factors) has long been known as a feature of Doppler imaging methods. Two observing runs at McDonald Observatory were undertaken for this project, and the P.I. attended two American Astronomical Society meetings (one accompanied by an undergraduate student). Four published papers resulted from these investigations. Also, a fruitful collaboration with Volkan Senavci of Ankara University, Turkey and Gaitee Hussain of the European Southern Observatory, Garching, Germany was achieved.