Measurements of Starspot Area and Temperature on Five Active, Evolved Stars

Details Measurements of Starspot Area and Temperature on Five Active, Evolved Stars Measurements of Starspot Area and Temperature on Five Active, Evolved Stars

Jun 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...463..766o&link_type=abstract

Astrophysical Journal v.463, p.766

Astronomy and Astrophysics

Astronomy

70

Stars: Activity, Stars: Atmospheres, Techniques: Spectroscopic, Stars: Late-Type, Stars: Magnetic Fields

Scientific paper

We resent results from a study of starspot areas and temperatures on active stars using the 7055 and 8860 Å bands of the titanium oxide molecule. Because the two bands have different temperature sensitivities, the ratio of their strengths provides a measure of the spot temperature, while their absolute strengths are a function of total starspot area. We have analyzed the TiO bands of four active, evolved, single-lined spectroscopic binaries (EI Eridani, σ Geminorum, V1762 Cygni, and II Pegasi) and of the FK Comae star V1794 Cygni. Where possible, 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 (≍8%) to just under 60%. In some cases, we find that significant starspot coverage was likely present at historical light maxima. Our results suggest a possible correlation between increasing surface gravity and the temperature difference between the spotted and nonspotted photosphere. This might result from smaller starspot magnetic field strengths on active stars of lower gravity and the corresponding decrease in the pressure and temperature contrast between the photosphere and the umbra.

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