Measurements of Starspot Area and Temperature on II Pegasi

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Session 15 -- Flare and Active Stars
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[15.05] Measurements of Starspot Area and Temperature on II Pegasi

Douglas O'Neal (Penn State), James E. Neff (Penn State), Steven H. Saar (CfA)

We are developing an empirical technique that yields independent measurements of starspot area and starspot temperature on active stars. Our technique involves fitting observed spectra near TiO absorption bands with synthetic spectra derived for various combinations of starspot and non-spot temperatures and starspot filling factors. Our comparison grid is generated from observed spectra of inactive G and K stars and of M dwarfs and giants. The absolute depth of the TiO bands in the spectra of active stars is a measure of the starspot filling factor, while the relative strength of different bands constrains the starspot temperature. We have analyzed a series of spectra of the single-lined spectroscopic binary system II Pegasi (HD~224085), K2 IV-V, P=6.7d. We find that cool starspots ($T_{eff} \approx 3400K$) are always visible, covering from 35\% to 50\% as the star rotates. However, the absolute and relative depths of TiO bands are not by themselves sufficient to establish the temperature of the non-spot photosphere. When coupled with a temperature difference provided by multi-color photometry, this technique will enable us to uniquely determine temperatures and relative filling factors of both the spot and non-spot components of spotted stars.

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