The spectral and photometric characteristics of the Hubble-Sandage objects (HSO) are similar to those of the η Car and S Dor variables. They are actually referred to as S Dor-type in the General Catalogue of Variable Stars. Their light variations differ from star to star.

The aim of the present paper is to discuss a possible periodicity in HSOs in M 31. We used phtometry from Hubble(1929), Sharov(1973, 1981), Rosino and Bianchini(1973), and added some observations taken during 1980-87. The latter were obtained with the 2-m Ritchey-Chretien-Coude and 0.5-m Schmidt telescopes of the Bulgarian National Astronomical Observatory – Rozhen.

η Car is one of the brightest stars in our Galaxy. For its luminosity, huge mass loss, large variability can be considered as an ideal laboratory to study the LBV phenomenon, and to give constraints on possible models of LBVs. We propose that η Car is a – possibly binary – F-type hypergiant whose wind is heated by dissipation of mechanical energy.

Emission lines are often observed in high luminosity stars and provide evidence of the presence of extended stellar envelopes. Ha is the most frequently observed across the H-R diagram, but lines of Hel or Fell are also found in emission in these stars. They could be used as diagnostics of the structure of their outer atmospheres and winds. High resolution (1/dl ~ 105) high S/N profiles of Ha and Hel 5876 in the galactic LBVs η Car, AG and HR Car, and in the LMC star S22 have been obtained with the ESO CAT-CES during 1984-87, and are described in Figs.1-5. We find that these stars show a large variety of profiles with narrow and broad emissions, wide or multiple blue-shifted absorptions. The profiles are largely variable. Once, a kind of inverse P Cyg profile was observed in HR Car (Fig.4). These results indicate the presence of large scale phenomena and high velocity fields which are dramatically variable in time. Continuous HIRES monitoring of these stars is urgently needed.

Emission and absorption lines of Fell frequently dominate the optical and UV spectra of LBVs. Many luminous blue stars possess a rich optical Fell emission line spectrum, which can be used as diagnostic of their extended atmospheres (Viotti 1976a). Since the launch of IUE several LBVs were observed in UV, and in many cases (n Car, AG Car, P Cyg, Hubble Sandage variables, etc.) their spectra were found dominated by a large amount of Fell absorptions, presumably formed in cooler envelopes. Often these absorptions are so strong as to seriously affect the UV energy distribution. In order to study line formation outside LTE of such a complex ion, the Fell line intensities in luminous stars were analyzed using the Self Absorption Curve (SAC) method by Friedjung and Muratorio (1987). The fitting of the emission line fluxes in different multiplets to theoretical SACs obtained with different wind models, leads to the determination of the relative upper and also relative lower level populations. The overlapping of the individual multiplet curves gives the observational SAC which provides an estimate of the wind parameters (column density, acceleration parameter a, mass loss rate). This method of analysis was applied to the optical and UV high resolution spectra of several luminous stars. For instance we found that in AG Car the relative population of the Fell levels from 1.6 to 8.6 eV can be fitted to the same Boltzmann distribution with an excitation temperature of Tex«=7200+/-350K, whereas for the W Cep star KQ Pup the linearity extends from 0 to about 9 eV with Tex=6700 K (Viotti et al. 1988).

The optical spectra of Luminous Blue Variables (LBV’s) are characterized by strong Balraer emission lines. In many cases, the narrow emission component (FWHM ≤ 300 km/sec) shows extended emission wings reaching up to -1000 km/sec. These wings are generally attributed to electron scattering of line photons in the dense stellar wind (Bernat and Lambert 1978). In this paper we discuss an alternative mechanism which may partly contribute to the observed line wings.

We study the relation between photospheric and wind parameters of LBV’s on the basis of self-consistent atmospheric models. Our theoretical model consists of a spherically extended, dynamical NLTE atmosphere for the radiative transfer and a modified CAK code for the hydrodynamics. These codes are combined in an iterative scheme to achieve self-consistency.

In the atmospheres of the most extreme luminous stars, close to the Humphreys-Davidson limit, the inward gravitational acceleration is for a great part compensated by outward accelerations due to radiation pressure, turbulent pressure and dynamic pressure of the stellar winds. As a result the effective acceleration is very small, resulting in blown-up atmospheres that can no longer be considered plane-parallel or in hydrostatic equilibrium.

The LMC star R84 (-HDE 269227 -BR 18) belongs to the group of Ofpe/WN stars believed to be closely related to the Luminous Blue Variables. Support for such a relation comes from the spectral resemblance of these stars to AG Car during visual minimum, and from the observed outburst of the Ofpe/WN star R127.

The spectral analysis of R84 presented here is based on model calculations with the NLTE comoving-frame code described by Wessolowski et al. (1988) and references therein. The helium model atom was represented by 28 levels and hydrogen by 9 levels. The free model parameters were varied until the observed line profiles and the absolutely calibrated and dereddened continuum flux were reproduced. The comparison of the theoretical continuum flux distribution with the observed one yields a reddening of EB-V =0.1.

One type of variability that is ubiquitous among luminous blue stars is that associated with their massive stellar winds. Ultraviolet spectral lines show variable narrow absorption components that may arise from dense shells or clumps in the wind; the observed soft X-ray and non-thermal radio emission from these stars may be produced in embedded wind shocks associated with these shells. The line-driving of such winds is known to be strongly unstable, and recent numerical simulations of the dynamical, nonlinear evolution of such instabilities indicate that such shocks and dense shells do indeed form (Owocki, Castor, and Rybicki 1988; hereafter OCR). However, the structure computed in these dynamical simulations is quite different, and in some sense opposite, what was anticipated in earlier heuristic shock models (e.g. Lucy 1984, Krolik and Raymond 1985, Abbott 1988); the highest speed material is very rarefied, not dense, and the strongest shocks that form are of the reverse, not forward, type. In subsequent simulations we have found that the detailed character of this structure can depend on many variables, but this tendency always to form high speed rarefied waves and reverse shocks is quite robust. It is thus important that we have a clear understanding of the reasons for this tendency, and it is on this point that we focus our comments here.

A survey of the infrared properties of late-type supergiant stars, using the IRAS database, reveals that about 25% of the stars possess resolved, extended circumstellar shells. These shells are typically several arc minutes in apparent size and therefore on the scale of parsecs at the source. Furthermore, among the resolved sources, there is an inverse correlation between physical size of the infrared shell and B-V color, suggesting that these shells are formed while the objects are red supergiants, but continue to expand ballistically, while the star evolves blueward from that extreme. These shells may be the material swept up into ring nebulae when the central star develops a fast wind.

We studied the luminous emission-line star S 111 in the LMC with high-dispersion spectroscopy and classified it as a new member of the class of B[e] sup ergi ants.

Of/WN, or as we will call them here, “slash ‘/’” stars were first described by Walborn (1977; 1982a; 1982b) as hot luminous stars that have spectroscopic properties of both O and low-ionization WN spectral classes. Walborn called attention to Sk -67° 22, an 03IP7WN6-A star that had strong O-type absorption lines, but also a broad emission feature at Hell λ4686Å. The ‘/’ symbol was used to indicate that there was difficulty in assigning either the Of or the WN type unambiguously. He labled other LMC stars as Ofpe/WN9 not only because of a similar ambiguity in the classification but also the presence of narrow “nebular” emission lines associated with the star. Conti and Garmany (1983) pointed out the similarity of Sk -71° 34 to Sk -67° 22. A total of ten stars with Ofpe/WN9 character have now been identified in the LMC (Bohannan and Walborn 1989) : HDE 269927C, 269445, 269582, 269687, 269858, 269227; Sk -66 040, -67 266, -69 297; BE 381.

Concentrations of material have been observed to propagate in the winds of many W-R stars. These are short-lived, stochastic features of unknown origin.

Optical and IR spectroscopy of two galactic objects previously considered to be extreme late WN stars (van der Hucht et al., 1984), LSS4005 (formerly tentatively listed as WR85a) and NaStl (WR122), show both objects not to be WR stars, but Ofpe/WN- or B[e]-like objects.