I have been asked to review the “observations” of winds in “early-type” stars. This normally means stars of spectral type OB and those of the Wolf-Rayet (WR) class. In this paper I will concentrate on the massive population I stars of these types, and primarily the O and WR classes on which most of the recent work has been done. The early B type supergiants share many of the wind properties of the O stars but the later supergiant types, Be stars, and main sequence stars may not. Stellar winds are a ubiquitous phenomenon among these early type stars (Snow and Morton 1976). We see evidence of their winds in the resonance line P Cygni profiles in the UV region, in the emission lines of Hα and λ4686 He II in the optical spectrum, and in the free-free emission from the ionized plasma as observed in the IR and radio regions of the spectrum.

We determined the dependence of mass loss on the stellar parameters for O and B stars of various luminosities. We used four homogenous sets of mass loss rates derived by different authors from the radioflux, the infrared excess, the UV lines and Hα emission. As the rates derived from the radio flux are the least dependent on model assumptions for the stellar wind, these will be adopted as our standards. The others sets of mass loss rates will be corrected for the differences in the adopted wind model, especially in the velocity law, by scaling the rates to those derived from radio data, using the stars which the different sets have in common.

The stellar winds of hot early-type stars are characterised spectroscopically by the presence of P-Cygni profiles, which are most marked for resonance transitions of common ions and generally occur in the UV, and typical resonance lines of SiIV, CIV, NV and OVI are well known P-Cygni signatures of stellar winds in luminous OB stars. Analyses of these profiles can lead to important information concerning the velocity, density and temperature structure of such winds. The WR stars have more developed stellar winds than OB stars, supporting higher particle densities at larger distances from the stellar “photosphere”. Recently Barlow, Smith & Willis, hereinafter BSW, (1980), have derived reliable mass loss rates for 21 WR stars. The mean value is 4x10-5 M0 /y and the rates are considerably larger than can be accomodated by soley radiative models. The, as yet unidentified, mechanism initiating the WR mass loss may also be important for Of stars ( Lamers 1980 ).

The emission lines in the optical and UV spectrum of the WC 9 star HD 164270 indicate a terminal velocity of its wind of v∞ ≈ 1400 km s-1. In the UV spectrum Fe III absorption lines appear from transitions with metastable lower levels. Because they are displayed over only 830 km s-1, it is suggested that they are formed in the decelerating part of the wind. A radius of 1.8 x 104 R⊙, is found for the circumstellar Fe III shell. This value is within the range of radii calculated by Cohen et al. (1975) for the dust shells of WC 9 stars.

In addition to certain manifestation of a stellar wind during steady states of WR-stars that we have heard here about I have two notes on their extremal stages of evolution which may be also connected to such a hydrodynamical event.

The first note. There is a pecular object, HM Sge that had brightened for several magnitudes during several months. It has a strong emission spectrum that is similar to a planetary nebula spectrum in general, and it was suggested that we register a planetary nebula birth. However, in Crimea we have found that a total width of H-alfa emission line is ~ 2000 Km/sec and a central part of its profile is asymmetric significantly. These features exclude a genetic, relationship between HM Sge and Planetary nebulae.

The 07 n star HD 217086 which provides the ionization of the H II region S 155 A and is the brightest member of the Cep OB 3 association, has been observed in the ultraviolet with IUE. From an analysis of the UV spectra we determine a terminal velocity of 3560 ± 100 km s-1 and a mass loss rate of . A comparison is made with the stars of similar spectral type.

From a high resolution spectrum taken with IUE, the central star of the planetary nebula IC 2149 is found to exibit a wind with edge velocity of 1440 ± 100 km s-1. Our preliminary evaluation of the associated mass loss rate gives 10-8 M0 yr-1. Other planetary nebulae nuclei are studied with low resolution IUE spectra and indications are found of mass loss rates consistent with the above value.

In this paper we report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types (Fig. 1).

37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined indipendently by various Authors for stars in common. Our data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity.

High resolution profiles of the Hα line are derived for about thirty Be stars and several bright stars by means of the anological television system. The profiles obtained with this method fairly agree with the theoretical ones (a Lyrae).

From the free-free excess at 10μ. Barlow and Cohen (1977) (hereafter referred to as BC) derived a mass loss rate of 6.9 10-7 M⊙ yr-1 for α Cyg. They predicted a 10 GHz radio flux of 2.2 mJy. On the other hand Praderie et al. (1980) derived a considerable lower mass loss rate of 1.1 10 -8 ≤Ṁ ≤ 7 10-8 M ⊙ yr-1 from a curve of growth analysis of the envelope ultraviolet Fell-lines of α Cyg. Radio observations are desirable to make a decision about these discrepant results. Therefore we observed α Cyg at 15 GHz with the 100 m telescope of the MPIfR at Effelsberg. The observations are discussed together with recent VLA data of Abbott et al. (1980).

Mass loss rates have been derived for twenty one WR stars encompassing most subtypes in the WN and WC sequences, from measurements of their infrared free-free fluxes. The resultant mass loss rates show a range of only a factor of four. WC stars generally have larger mass loss rates than WN stars, the mean rates being Ṁ(WC) = 4.1x10-5 M⊙y-1 and Ṁ(WN) = 2.7x10-5 M⊙y-1. Optical and ultraviolet data have been used to estimate bolometric luminosities for a range of WR spectral types, and it is shown that the derived mass loss rates are too large to be powered by radiation pressure. The total kinetic energy ejected into the interstellar medium through mass loss during the WR phase of a massive star is estimated to be 7x1050 ergs, comparable to that of a supernova event.

AG Car is a variable supergiant surrounded by a small ring nebula. Its ultraviolet and optical spectrum, and UV to IR energy distribution are similar to those of P Cyg with v∞ = -290 km s-1. Also the strength of the 2200 A band is the same and suggests E(B-V) = 0.55 for both stars. The possible variability of the infrared flux is discussed.

The evolutionary implications of mass loss from post-asymptotic giant branch stars is discussed, with reference to the UV observations of sdO's.

Contrary to the results of some investigators, the ratio of terminal to escape velocities (V∞/Vesc) observed for the winds in early-type stars is found to be linearly correlated with log Γ - Γ being the ratio of stellar to Eddington's luminosities.

Although the determination of terminal velocities for O-type main sequence stars from edge velocity information may be somewhat questionable (Lamers, 1980). The determined values for the β and γ fitting parameters for the observed profiles by Conti and Garmany (1980) are tipically on the order of one for these stars. Hence, from the grid of profiles by Castor and Lamers (1979), we estimate that at most a 10% error is introduced by adopting the edge velocities as representative values of the terminal velocities of main sequence O-type stars.

Observations mainly from the IUE Spectra of HD 152236 (Blla) have been used to provide support to the various aspects of the theory of stellar wind (SW) and its interaction with the interstellar medium (ISM). Lines arising from excited levels connected radiatively to the ground level tend to be more frequent and/or strong compared to those arising from radiatively forbidden levels of similar excitation as expected from radiatively driven wind. The outward velocity from shifts of Si III lines from different excited levels increases steeply with decreasing excitation energy in agreement with theories. Absorption lines (P-Cygni like) of C II, Al II, Si II and Mg II shifted shortward by about 300 km s-1 suggest an expanding shell around the star. As this velocity is smaller than the terminal velocity (880 km s-1) the circumstellar shell may have been formed as a result of interaction of SW with ISM.

The present observations are part of a search for spectral and radial velocity variations among central stars of planetary nebulae (Méndez 1980). The spectrograms were taken with the image-tube spectrographs of the 1-m and 4-m telescopes at the Cerro Tololo Inter-American Observatory (CTIO). The emulsion was always IIIa-J baked in “forming gas” (N2+H2). The “blue” spectrograms extend from 3600 to 5000 Å at 45 Å mm-1; the “red” ones extend from 5000 to 7000 Å, at 45 Å mm-1 (4-m plates) and 90 Å mm-1 (1-m plates). All plates were calibrated with a spot sensitometer. Seven “blue” and seven “red” spectrograms, all obtained with the 4-m telescope, were traced with the PDS microphotometer of the David Dunlap Observatory. The intensities from each plate were stored in computer memory and were later added together, in order to improve the signal-to-noise ratio. The resulting intensity tracings reveal more details than had previously been observed (Swings and Struve 1941, Aller and Wilson 1954, Andrillat 1957, Aller and Kaler 1964).

Recently obtained spectroscopic observations indicating mass loss in cool stars are reviewed with analogies to the solar atmosphere. Spectral diagnostics of mass loss are discussed with new theoretical calculations of chromospheric line profiles. A general picture of mass loss from cool stars is developed and related to chromospheric and coronal emissions measured by IUE and the HEAO-2 Observatory. These winds range in characteristics from the hot (106 K) and fast wind with low mass loss found in the dwarf stars to the warm ( ~ 105 K), moderate speed winds present in hybrid luminous supergiants, and the coolest massive winds emerging from the latest type supergiants exhibiting lowest thermal velocities and circumstellar shells. Evidence for stellar surface inhomogeneity and variability of outflow is briefly discussed.