Two images have been obtained, from observations made almost two years apart, of the H-alpha chromospheric envelope of Alpha Orionis at the diffraction limited resolution of the co-phased Multiple Mirror Telescope. Significant emission out to a distance of several stellar radii above the photosphere is observed.

The temperature stratifications and the emitted fluxes of Mira model photospheres based upon the extended density distribution of a pulsation model differ substantially from those of conventional model photospheres based upon a hydrostatic density distribution. Hence, the interpretation of Mira spectra by means of hydrostatic models is inadequate, and the spectral characteristics of Miras may deviate significantly from those of non-Miras.

Although the bands of H2O are strong in cool stars, water vapor opacity has generally not been accurately treated due both to the inadequacy of laboratory data and the difficulty of treating the millions of lines involved. We report a new treatment based upon a statistical representation of the water vapor spectrum derived from available laboratory data. The statistical spectrum of water follows an exponential distribution of line strengths and random positions of lines to reproduce the line spacings and mean opacities observed in the laboratory. This statistical spectrum is then randomly sampled in the spirit of opacity sampling. Significant improvements are made in both the opacities and in the thermal structure and emergent fluxes of the model atmospheres.

Optical observations of the solar radiation resonance scattering in the hydrogen and helium lines (λ1216Å and 584Å) provide a unique opportunity for determining numerous parameters of the local interstellar medium closest to the Sun (LISM). The distance exceeds 10 to 102 AU where the interstellar medium is no longer perturbed by the gravity field, and the hard and corpuscular radiation of the Sun.

Mass loss from hot stars was first established by Morton (1967). He observed 3 OB supergiants, δ, ε and ζ Orionis, with an ultraviolet spectrograph sent up with a rocket. In the wavelength range of 1200 A to 2000 A he observed 6 resonance lines of highly ionized atoms such as C III, C IV, N V and Si IV. These resonance lines showed a P Cygni type line profile with an absorption component displaced to the blue corresponding to a velocity away from the stars of 1400 km s−1. Since the escape velocity from these stars is about 800 km s−1 these observations indicated the loss of mass from the stars. With rather simple assumptions he deduced a mass loss from the stars of 1 to 3 10−6 M⊙ yr−1. In spite of many more refined satellite observations and interpretations, the accepted value for mass loss from these stars has not changed by more than a factor of 2 or 3.

Recent observations of S Dor variables and B[e]-supergiants are reviewed. These objects belong to the visually and bolometrically brightest stars in the universe. They have gained considerable interest for their exceptional stellar wind properties and represent rare cases of hot blue stars which form dust envelopes. S Dor variables are characterized by major outbursts. The ejecta have been spatially resolved in some cases. These luminous emission line stars are supposed to represent a short-lived phase in the evolution of the very massive stars prior to becoming WR stars.

A considerable amount of observational information has been gathered on the so-called Hubble-Sandage Variables or S Doradus variable stars, largely due to the efforts of the Heidelberg group (see Wolf, this volume for a review). It is believed that the star P Cygni also belongs to this category. This group of objects is now being referred to as Luminous Blue Variables because they are massive (>10 M⊙), evolved (spectral type B or later) objects showing variability of more than one kind, and evidence of nuclear processed material at the surface.

Using the CASPEC echelle spectrograph of the European Southern Observatory, La Silla, Chile, we obtained new high resolution spectrograms of the LMC S Dor variable R 127 in the blue and red spectral range.

The red spectrogram, which contains the [N II] 6548 and 6533 and the [S II] 6717 and 6731 lines shows the presence of a well resolved extended gaseous nebula around R 127 (see Figures 1 and 2). The nebula (which is also detected at the Balmer lines) shows blueshifted and redshifted emission (projected) on the position of the stellar continuum, and no wavelength-shift at the maximum (East-West) distance from the star. Hence, the nebulosity appears to be an expanding shell, reminiscent of the nebula around the galactic extreme supergiant AG Car. The angular diameter (or East-West extension) of the nebula around R 127 is of the order 4“, corresponding to ≈1 pc at the distance of the LMC. The expansion velocity of the R 127 nebula is found to be 28 km s−1 from our spectrograms. Hence, assuming a constant expansion velocity we derive a kinematic age of the R 127 nebula of ≈2 · 104 years. This corresponds closely to the expected lifetime of the S Dor evolutionary phase.

A more detailed description of our results will be published in the proceedings of the Workshop on “Instabilities in Luminous Early Type Stars” (C. de Loore, H. Lamers, eds.) Lunteren 1986.

The structure of a stellar wind and its associated mass loss can be derived from the analysis of ñ Cygni-like line profiles. These do better occur in the UV range and have been extensively observed with the Copernicus (900–1450 A) and IUE Satellites (1150–3200 A).

The multiple absorption components in the Balmer lines of P Cygni indicate that shells are ejected regularly with a period of about 200 days. The newly found multiple, flat-topped emission components are attributed to thin, spherical, expanding shells. Together with the absorptions they allow the derivation of a velocity law, illustrated in the following by a sequence of figures.

The star P Cygni (=HD 193237) is the proto-type of a class of stars with peculiar spectra, the so-called P-Cygni-stars (or Luminous Blue Variables). They are characterized by extreme mass-loss characteristics and wind densities surpassed only by the winds of Wolf-Rayet stars.

The early-type supergiants of the Magellanic Clouds (MC's) include a class of objects, the B[e] -supergiants, which are described in detail in Zickgraf et al. (1985, 1986) who suggested a two-component wind model consisting of a cool, dense and slowly expanding disk-like equatorial wind component and a hot line-driven fast polar wind. This model could explain many properties of most of the B[e] -supergiants as e. g. the occurrence of “shell” absorption lines. R 4 of the SMC, however, although well fitting to the general scheme of B[e) -supergiants exhibits several pecularities of its line spectrum, which make this particular star an exceptional case among the B[e] -supergiants of the MC's.

HD 37836 (= R 123; Feast et al., 1960) is one of the brightest slightly variable (V ≃ 10.5–10.7; Stahl et al., 1984) emission-line stars of the LMC. Since it is also likely to be a hot star (see below) it is also bolometrically very bright (Mbol ≤ −11).

Study of FeII emission lines in emission and absorption using both emission line self absorption curves and ultraviolet spectral synthetis, shows that line emission is produced in the case of certain luminous Magellanic Cloud stars, in a region not in front of the photosphere. This region is most easily understood as being a disk. Absorption lines of FeII are either produced by a wind, or if the disk inclination is small with respect to the line of sight, in layers associated with the disk. The presence of disks also helps one to explain the form of the continuous energy distribution.

The luminous O-type star BD +60°2522 is embedded in the extended H II region S 162. Part of S 162 is NGC 7635, the striking spherically symmetric bubble nebula surrounding BD +60°2522. This star itself is unique in that it is the only known O star apparently associated with warm dust.

The massive, early-type star HD 148937 (spectral type O6.5f?p) is surrounded by a unique set of nebulosities. A spherically symmetric Strömgren sphere (Radius ≃ 25 pc), an ellipsoidal filamentary nebulosity (semimajor axis ≃ 5 pc) interpreted as a stellar-wind-blown shell, and a bipolar nebular complex (semimajor axis ≃ 1 pc) with HD 148937 located in the apparent center of symmetry. Here we report on observations of these nebulosities (narrow-band CCD imaging, IDS spectrophotometry, high resolution (ΔV ≃ 7 km sec−1) spectroscopy) in an attempt to establish a consistent model of HD 148937 and its nebulosities.

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞ , where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞ ) for N V and C IV.

A dynamical model has been developed, describing the joint evolution of a stellar wind and an associated HII region during the main sequence life time of an OB-star. It is proposed that in case of spherical symmetry all dynamical features are obtained by dividing the flow into spatially homogenous regions separated by discontinuities (shock fronts, contact discontinuity and ionization front). Different phases in the dynamical evolution can be distinguished. The results show that the extension and structure of the HII region depends sensitively on the initial density of the ambient medium, the Lyman continuum photon rate and the mechanical wind power of the central star. This will be important for future high resolution observations.

In 1985 April, the WC7+abs star HD 193793 was observed, using UKIRT, to have brightened significantly in the infrared owing to the formation of a new dust shell. Examination of infrared photometry of this star since 1979 and previously published data indicates that the dust formation occurs at intervals of 7.9 years. Phasing the published radial velocities of the absorption line component with this period confirms that it is a member of an eccentric (e = 0.7−0.8) binary system having periastron passage shortly before dust formation. The X-ray spectrum also changed between 1984 and 1985 in becoming significantly “harder” while the non-thermal radio source disappeared, both changes indicating greater extinction. This suggests a model wherein the source of the non-thermal radio and X-ray emission moves deep into the Wolf-Rayet wind.

An infrared photometric survey of all 40 known galactic WC7-10 stars shows that around most of them hot amorphous carbon is condensing continuously at distances of about 8500 R⊙, well within the ionized stellar winds around these stars. Typical dust production rates are of the order of 10−7 M⊙/yr.