The spectrum of α Orionis is composite and consist of three components: 1) a photospheric spectrum characterized by symmetric absorption lines more or less typical of the spectrum of an M2 supergiant, except for their very great widths; 2) a shell spectrum consisting of P Cygnitype profiles of neutral and singly-ionized metallic lines of very low excitation potential; and 3) asymmetric absorption lines, including Hα Hβ , Fel lines of intermediate excitation potential and the infrared triplet of Ca+, which appear to be formed in a relatively warm layer, probably an extended chromosphere.

High dispersion spectrograms of α Ori are obtained. Several strong absorption lines which have circumstellar components are measured. Assuming the plane-parallel envelope and thermal equilibrium, the mass loss rate is estimated as 1x10-6 Mʘ/yr.

To obtain the mass loss rate of red giant stars is very important in connection with the study of the stellar evolution. Several authors have observed circumstellar lines and obtained mass loss rate using precise theories of radiation transfer. However, accuracy of the studies seems to depend not on the adopted theories but on the dispersion of spectrograms, since the structure of the circumstellar space is too complicated to be expressed by,e.g.,single expansion velocity. Because our spectrograms have higher dispersion, compared with others, our study is meaningful, though the assumed model is very simple.

The supergiant Rho Cas F8Ia has a very high luminosity. Astronomers have payed attention to this star in August 1946, when its by its brightness had dropped from 4.2 to 6.2. The systematic spectrographic observations of Rho Cas are beeing carried out at the Crimean Astrophysical Observatory since 1965. No large light variations were observed during that time.

Spectral lines of the ΔV=2 rotation vibration bands of CO are well suited for study of photospheric motions and the mass ejection process in cool stars. We have obtained high spectral resolution (1.8 km/sec) and high signal-to-noise (>102) line profiles for a selection of K and M giants. These profiles are being studied for evidence of gas motions in the photosphere and near circumstellar regions.

I assume that the purpose of this review of the theory of winds from early type stars is to summarize the way in which the mass loss rate of a star may be included in a calculation of stellar evolution. Let me summarize my conclusions. It is not possible. One can only use estimates of mass loss rates obtained from the observations. Even these give a large uncertainty. The observed mass loss rates for different stars of the same spectral type vary. Further the mass loss rates obtained by different methods for the same star differ. An extreme example of this is 9 Sgr. The mass loss rate derived from the radio observations is forty times greater than that derived from the U.V. and optical measurements (Abbott et al. 1980).

Customarily, one assumes that the internal structure of the star is not changed by a mass-flux from the atmosphere; thus one changes evolutionary calculations with mass-loss from those without it only by homologously decreasing the mass at each static evolutionary step. Furthermore, it is customary to assume that the mass-flux can be expressed in terms of only the thermal parameters (luminosity, Tepp) or (g, Teff). Sometimes rotation is introduced, but only as a modification of equatorial gravity, not of internal nonthermal structure. The phenomena of large-amplitude variability in times short compared with evolutionary ones, and of individuality (two stars of the same taxonomic class having different atmospheric distributions of Te and density) invalidate such static evolutionary calculations. We summarize the evidence for such large-amplitude variability in Be and la supergiant B stars. We also summarize the evidence for individuality as exhibited by observations: of OVI in OB stars; of x-ray luminosity across the HR diagram; of far-UV spectra of O stars; and of visual and far-UV spectra of Be stars. These observational results require nonthermal fluxes of mass and nonradiative energy to be imposed from below by the subatmosphere; which implies a nonthermal structure of subatmosphere and at least some part of the interior. Such nonthermal structure must then be included in evolutionary calculations. Thus current observations of nonthermal mass-flux from essentially all stars require including a nonthermal internal structure, not simply a mass-loss, in evolutionary calculations.

Cosmic rays (CR) are fast or relativistic protons and electrons (and nuclei), detected on the top of the terrestrial atmosphere. Except at the highest energies (>1017eV) the Larmor radii of the particles in the galactic magnetic field are much smaller than the scale height of the interstellar gas, and the arriving particles have completely lost memory of their sources. Therefore, their origin is unknown, at least directly. But recent advances in γ-ray astronomy, and in shock acceleration mechanisms, have shed a radically new light on a old problem.

We summarize the results of recent IUE observations of the spectra of α Cygni and discuss possible explanations for the Doppler-shifted pure absorption profiles in the resonance lines of the singly ionized metals. The results of detailed modeling for MgII λ 2795, 2802 are presented, and discussed in the context of observations of α Cyg in the radio, infrared, visible, ultraviolet and X-ray parts of the spectrum.

The main-sequence BO star Tau Sco has been studied previously by Lamers and Rogerson (1978). However, their line fit was restricted to the blue wings of the UV resonance lines because the line formation was calculated in Sobolev approximation. We now repeat this investigation by means of the comoving-frame (CMF) method, which we have extended to the treatment of overlapping doublets. From a systematic comparison (Hamann 1980b) we know that the results may deviate considerably from those of the Sobolev method. Our method has been applied previously to the other “prototype” of mass loosing early-type stars, the Of star Zeta Puppis (Hamann 1980a).

The mechanisms by which early type (0 and B) stars loose mass is investigated. The phenomena occuring close to the photosphere are crucial for the structure of the wind. It is shown that the effects of radiation are not sufficient to explain the observed winds. A general scheme for energy balance including a corona is proposed.

The processes of radiative acceleration of stellar winds in OB stars by single and multiple photon scattering are considered. Single scattering can be the dominant accelerating process for stars later than B2 (Teff < 2 x 104 K) and can account for terminal velocities up to 500 – 1000 km s-1 . Multiple scattering of photons in the approximate range 200 – 500 A provides additional wind acceleration for stars earlier than B2 to reach terminal velocities of up to 2000 – 4000 km s-1 A systematic increase of the terminal velocity as a function of the effective temperature is predicted. Observational data confirm this expectation quite well.

Eight O-type giants and supergiants, selected for being relatively isolated in the sky, have been observed at 5 GHz with 17 antennae of the partially completed VLA (NRAO, Socorro, New Mexico: The National Radio Astronomy Observatory is operated by Associated Universities under contract with the National Science Foundation) on October 7 and 8, 1979. The integration times ranged between 38 and 187 minutes. The results are displayed in Table 1. Most of the stars (6 out of 8) were not detected. The upper limits given in Table 1 for these stars correspond to the 3σ noise level. Possible detection has been achieved for the two supergiants HD 225160 and HD 30614 both with a flux density of 0.15 mJy. Although this flux is equal to the 3a noise level, the detections can be considered to be real because 1) Excellent positional coincidence is found between stars and the radio peaks (better than 1”) 2) The observed source pattern corresponds very well to the expected response to a point-like source.

The UV resonance lines of early type stars show narrow absorption components, with a width of the order of 300 km s-1, superimposed on the wider P Cygni profiles. Such narrow components have been detected in the Copernicus spectra of a few early type stars by Morton (1976) and Snow and Morton (1979). The variability of these components was studied by Snow (1977) who compared two scans of the UV line profiles of 15 stars taken about four years apart. He found that the narrow components do not change in velocity (except for the CIII λ 1175 line in ζ, Pup) but that the strength of the components can change drastically. In some stars the narrow components were present in only one of the two spectra. We studied the characteristics of these narrow components in the Copernicus spectra (Snow and Jenkins, 1977). The stars are listed in Table 1. Examples of these narrow components are shown in Figure 1.

Four basic mechanisms have been proposed to explain the acceleration of winds in late-type stars –– thermal pressure gradients, radiation pressure on circumstellar dust grains, momentum addition by Alfvén waves, and momentum addition by periodic shock waves. In this review I describe recent work in applying these mechanisms to stars, and consider whether these mechanisms can work even in principle and whether they are consistent with recent ultraviolet and X-ray data from the IUE and Einstein spacecraft. Thermally-driven winds are likely important for late-type dwarfs, where the mass loss rates are small, and perhaps also in G giants and supergiants, but they cannot operate alone in the K and M giants and supergiants. Radiatively-driven winds are probably unimportant for all cool stars, even the M supergiants with dusty circumstellar envelopes. In principle, Alfvén waves can accelerate winds to high speeds provided the field lines are initially open or forced open by some mechanism, but detailed calculations are needed. Magnetic reconnection is an interesting suggestion for an acceleration mechanism when the field lines are initially closed. For the Mras and semiregular variable supergiants, periodic shock waves provide a simple way of producing rapid mass loss. Thus we are making some progress in understanding mass loss mechanisms for the cool half of the H-R diagram.

If studied in detail, the mass flows from the stars appear to be variable. “Mere inspection of solar wind data reveals large variations on a time scale of several days” (Hundhausen, 1972). Also, “it is obvious that mass loss from hot stars is not a stationary phenomenon but that variations on short timescale occur” (de Jager et. al., 1979). And a cool supergiant has “a photosphere fluctuating in both brightness and radial velocity, (and) an expanding chromosphere … uncoupled from motions in the photosphere” (Goldberg, 1979).

In the past few years both growing observational evidence and theoretical understanding have shown that mass loss by stellar wind is a common occurrence in the evolutionary history of many types of star. Recent reviews on the subject may be found in Conti (1978), Cassinelli (1979), Conti and Mc Cray (1980), Hutchings (1980a), de Loore (1979, 1980) and Sreenivasan (1979).

Therefore, in this paper we will concentrate only on those observational and theoretical aspects of the problem that demand further investigation.

The distribution of the spectral types of the WR stars in our galaxy is different at different distances from the galactic center. This distribution is also different in all three galaxies, in our, in the LMC and in the SMC. These results have been interpreted as due to the dependence of the mass loss rate from the original chemical abundace which is known to be different in these objects.

On the other hand it has been proposed by Chiosi et al. (1974) and confirmed by Bisiacchi et al. (1978) that most of the 0 supergiants should be stars in the hydrogen burning phase. These authors also find evidence that the large relative number of supergiants among th 0 and early B type stars must be related to the longer time spent by the evolutionary tracks with mass loss at the low gravity region. Recently, a new empirical formula has been proposed by Chiosi (1980) for the mass loss rate as function of the luminosity and temperature of the stars.

Evolutionary tracks for a 30 Mʘ star with various mass loss rates (MLR) were evolved to core He exhaustion. The “overluminosity” of mass losing (ML) stars is explained in terms of the well known mass-luminosity (M-L) law. A critical ZAMS MLR above which mass loss leads to evolution to fainter luminosities is derived. Two tracks showed reversals in their direction of evolution across the HR diagram. These have been shown to be a consequence of mass loss dominating over the effects of the shell source. An analytic criterion for this condition has been derived.

It is shown that mass loss by stellar wind with rates observed in O, B-stars cannot change qualitatively their evolution in the core hydrogen-burning stage. The effects, that are usually attributed to the mass loss, can be explained by other causes: e.g., duplicity or enlarged chemically homogeneous stellar cores.

The significance of mass loss by stellar wind for the evolution of massive stars was studied extensively by numerous authors (see e.g. Chiosi et al. (1979) and references therein). However, the problem is unclear as yet. There does not exist any satisfactory theory of mass loss by stars. Therefore one is usually forced to assume that mass loss rate depends on some input parameters.

S22 is a peculiar supergiant in the Large Magellanic Cloud whose optical spectrum is characterized by numerous emission lines including Fell and [Fell] (Muratorio 1978). A detailed study performed by Friedjung and Muratorio (1980) led to two main conclusions: (a) A wind with a velocity of 70 km s-1 and a mass loss rate between 4x10-6 and 5x10-5 Mʘ yr-1 is suggested by the examination of the Balmer line P Cygni profiles, (b) The Fell and [Fell] emission lines come from a different region which is optically very thick in the permitted lines. Emission line curve-of-growth methods indicated that the region of line formation has a surface area perpendicular to the line of sight equal to that of a disk perpendicular to this direction with a radius between 3x1013 and 3x1014cm.