Variability of Hot Post-AGB Star IRAS 19336-0400 in the Early Phase of   its Planetary Nebula Ionization
  We present photoelectric and spectral observations of a hot candidate proto-planetary nebula - early B-type supergiant with emission lines in spectrum - IRAS 19336-0400. The light and color curves display fast irregular brightness variations with maximum amplitudes dV=0.30 mag, dB=0.35 mag, dU=0.40 mag and color-brightness correlations. By the variability characteristics IRAS 19336-0400 appears similar to other hot proto-planetary nebulae. Based on low-resolution spectra in the range lambda 4000-7500 A we have derived absolute intensities of the emission lines H_alpha, H_beta, H_gamma, [SII], [NII], physical conditions in gaseous nebula: n_e=10^4 cm^{-3}, T_e=7000 \pm 1000 K. The emission line H_alpha, H_beta equivalent widths are found to be considerably variable and related to light changes. By UBV-photometry and spectroscopy the color excess has been estimated: E(B-V)=0.50-0.54. Joint photometric and spectral data analysis allows us to assume that the star variability is caused by stellar wind variations. 
V. P. Arkhipova, M. A. Burlak, V. F. Esipov, N. P. Ikonnikova, G. V.   Komissarova
astro-ph.SR