An ultraviolet study of B[e] stars: evidence for pulsations, luminous blue variable type variations and processes in envelopes

Abstract

Stars with B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including presence of Balmer lines in emission, forbidden lines, and strong infrared excess due to the dust. The observations of emission lines indicate the illumination by ultraviolet ionizing source, which is a key part to understand the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and its correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including the light absorption by the disk, pulsations, LBV-type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is not present only in the disk but also above its plane. The flux and line variability is consistent with a two-component model of circumstellar environment composed of the dense disk and ionized envelope. The observations of B[e] supergiants show that many of these stars have nearly the same luminosity of about 1.9 × 10 5 L ⊙ and similar effective temperature.

GG Carinae: orbital parameters and accretion indicators from phase-resolved spectroscopy and photometry

“…B[ e ]SGs are usually not significantly photometrically variable, except for binary induced variability (Zickgraf et al 1986;Lamers et al 1998). Krtičková & Krtička (2018) suggests that any long-term broad-band photometric variability in B[ e ]SGs is most…”

GG Carinae: discovery of orbital-phase-dependent 1.583-day periodicities in the B[e] supergiant binary

“…Pulsations have been observed in B[e] stars at a similar timescale to the one we observe in GG Car, though they are rare. Krtičková & Krtička (2018) detects a pulsation period of 1.194 ± 0.06 days in the unclassified B[e] star HD 50138 (V743 Mon). Pulsations with periods at this timescale are often observed in blue supergiants (e.g.…”

“…This led them to state that one of the GG Car components is a variable, but no further analysis was undertaken and this periodicity has been neglected since that publication. Krtičková & Krtička (2018) were unable to determine a clear UV lightcurve of GG Car over the orbital period, presumably due to variability in the system; they conclude that the binary component that is brightest in the UV is the variable, but do not find a period.…”

“…GG Carinae (GG Car, also known as HD 94878 and CPD-59 2855) is an enigmatic Galactic B[e]SG binary which has been studied for over a century due to its peculiar spectroscopic and photometric properties (Pickering & Fleming 1896;Kruytbosch 1930;Greenstein 1938). Lamers et al (1998) classified GG Car as a B[e]SG building on the work of McGregor et al (1988) and Lopes et al (1992), noting their observation of the B[e] phenomenon in the object; its high luminosity; indications of mass-loss through P Cygni line profiles; and its hosting of a hybrid spectrum of narrow emission lines and broad absorption features.…”

“…Early time-series photometry studies noticed that GG Car displays significant intra-night variability, separate from its variability over its ∼31 day orbital period (Kruytbosch 1930;Greenstein 1938). Gosset et al (1984), through Fourier analysis, found an indication of a periodicity at ∼1.6 days in the system's photometry.…”