Starspots and Plages on the Active G8 IV-III Star Lambda Andromedae from Wing Near-IR TiO band Photometry

Details Starspots and Plages on the Active G8 IV-III Star Lambda Andromedae from Wing Near-IR TiO band Photometry Starspots and Plages on the Active G8 IV-III Star Lambda Andromedae from Wing Near-IR TiO band Photometry

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...198.9403m&link_type=abstract

American Astronomical Society, 198th AAS Meeting, #94.03; Bulletin of the American Astronomical Society, Vol. 33, p.1181

Astronomy and Astrophysics

Astronomy

Scientific paper

We present initial results of Wing near IR TiO and V-band photometry of the bright chromospherically-active star, λ And (G8 III-IV; V ~+3.82 d (Hip)=25.8 pc; P rot ~54.5 days). λ And is a long-period RS CVn star and has sinusoidal-like light variations with periods that range from 53--57 days. These light variations are relative large (Δ V ~ 0.10-0.25 mag) and are believed to arise from the uneven (and changing) distribution of large dark starpots on its differentially rotating surface. The photometry was conducted during 1996--2001 with small telescopes located in Zanjan, Iran and Allentown, PA. Also, over 20 years of nearly continuous intermediate-band Strömgren and UBV photometry was carried out at Villanova University Observatory. The Wing narrow-band 3 filter system (Wing, JAAVSO, 1992, 21,42) uses 3 filters centered on the TiO γ (0,0) bandhead at 719 nm, and two filters centered on essentially line-free spectral regions at 754 nm and 1040 nm, respectively. A photometric TiO-index (that measures the strength of the TiO molecular absorption) is formed from the observations. The index is calibrated with temperature (T eff) by observations of standard stars having spectral types that range from G0 to M9. The TiO photometry can provide measures of the fractional starspot coverage (fill-factor). Also as the star rotates, the variations in the TiO-index light curve can yield information on the distribution of starspots over the star's photosphere. Combining the TiO light curves with continuum 550 nm and the near-IR light curves makes it feasible to investigate contributions of white light plages and dark starspots to the continuum light curves. In the case of λ And, we find strong evidence that the observed light variations arise primarily from bright plage regions. This is contrary to the widely held view that the light variations of λ And and those of most RS CVn stars arise exclusively from the rotational modulation in brightness from dark (cool) starspots. We will discuss the preliminary results and future plans.

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