Photometric properties of the gas shell around Pleione during 1971-76

To explain the UBV observations of Pleione during 1971-76 a two-component model has been used. It consists of a constant source (the star) and a variable source (shell), which changes its brightness but not its color. The color indices of the shell, with interstellar reddening subtracted, were found to be (U - B)0 = -1m.25 and (b - V)0 = -0m.26. They correspond well to the following parameters for the star and gas: Teff = 11,500-12,000 degree K, Te = 10,000 degree K, Ne = 2·1010 cm-3, dilution factor W ∼ (1-2)·10-2, and escape probability β12 ∼ (1-2)·10-5 for an Lα photon. The behavior of the color indices and V magnitude of the star during 1976-82 indicates an enhancement of a selective factor that acts only in the ultraviolet and appears to be due to the blocking influence of the absorption lines of the shell. As a result of subsequent dissipation of the shell, the color indices of the star returned in 1986 to the values they had before the ejection of the shell in 1970-71