Variability of Hot Supergiant IRAS 19336-0400 in the Early Phase of its Planetary Nebula Ionization

TL;DR

This study investigates the variability and physical conditions of the hot proto-planetary nebula IRAS 19336-0400 during its early ionization phase, revealing irregular brightness changes and stellar wind influences.

Contribution

It provides new observational data on IRAS 19336-0400's brightness variations, spectral line intensities, and nebular conditions, highlighting the role of stellar wind variations in its variability.

Findings

Irregular brightness variations with amplitudes up to 0.40 mag.

Derived nebular electron density of 10^4 cm^{-3} and temperature of 7000 K.

Variability linked to stellar wind changes.

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 Delta V=0.30 mag, Delta B=0.35 mag, Delta U=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.