TiO Photometry of Naked T Tauri Stars: V410 Tau

Guinan, McCook, and DeWarf, with Villanova senior M. Lesniak, began a study of the weak emission-line T Tauri (WTT) star, V410 Tauri (HD 283518; K4 V-IV; $< V >= +10.6$ mag; $< B-V >= +1.3$). This star has very large (nearly) periodic light variations ( $\Delta V\approx 0.4$ mag) and with a period of P $\sim 1.87$ days. Modeling of the light curves and Doppler imaging techniques indicate the light variations primarily arise from the rotational modulation by large dark starspot regions, distributed unevenly over its surface. Bright (warm) regions also appear to be present. The rapid rotation of the star (P = 1.87d; v sin i = 70 km/s), coupled with its expected deep convective zone ($\sim$ K4 V-IV spectral type), insure a vigorous magnetic dynamo that results in the observed large starspot coverage and related strong coronal X-ray and chromospheric emissions.

A TiO-index was formed from the photometry. This TiO-index, when calibrated with Wing standard stars, yielded a measure of the strength of the TiO absorption band at 719 nm relative to a continuum region at 754 nm. TiO absorption is very sensitive to $T_{\rm eff}$ for cool stars and is also present in cooler sunspot and starspot regions. TiO photometry, coupled with VRI photometry, was used to determine the properties of the surface features on V410 Tau. TiO photometry provides unambiguous measures of the fractional cool starspot coverage. Importantly, combining the TiO with the VRI photometry allows the discrimination of white-light faculae (= hot spots) and cool (TiO absorption) starspots. During 2003, there was a good correlation between the light variations and TiO-index in the sense that the TiO absorption is strongest when the star is faintest. They recently presented new TiO narrow, and VRI wide-band, photometry of V410 Tau, carried out with the recently refurbished photoelectric photometer attached to the 0.8 m FCAPT, at the 202$^{nd}$ meeting of the American Astronomical Society in Nashville, TN. This research is supported by NSF/RUI Grant AST-00 71260.