Variability of Hot Post-AGB Star IRAS 19336-0400 in the Early Phase of its Planetary Nebula Ionization
Abstract
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 Halpha, Hbeta, Hgamma, [SII], [NII], physical conditions in gaseous nebula: ne=104 cm-3, Te=7000 1000 K. The emission line Halpha, Hbeta 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.