MEASUREMENTS OF STARSPOT AREA AND TEMPERATURE ON 5 ACTIVE, EVOLVED STARS

We present results from a study of starspot areas and temperatures on active stars using the 7055 and 8860 Angstrom bands of the titanium ox ide molecule. Because the two bands have different temperature sensiti vities, the ratio of their strengths provides a measure of the spot te mperature, while their absolute strengths are a function of total star spot area. We have analyzed the TiO bands of four active, evolved, sin gle-lined spectroscopic binaries (EI Eridani, sigma Geminorum, V1762 C ygni, and II Pegasi) and of the FK Comae star V1794 Cygni. Where possi ble, we compare our results with contemporaneous photometry, which is used to refine our estimate of the nonspotted photospheric temperature . We find that, over multiple epochs of observation, the spot filling factor ranges from below our detection threshold (approximate to 8%) t o just under 60%. In some cases, we find that significant starspot cov erage was likely present at historical light maxima. Our results sugge st a possible correlation between increasing surface gravity and the t emperature difference between the spotted and nonspotted photosphere. This might result from smaller starspot magnetic field strengths on ac tive stars of lower gravity and the corresponding decrease in the pres sure and temperature contrast between the photosphere and the umbra.