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We present spatially resolved spectra observed with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the upper chromosphere and dust envelope of Betelgeuse (α Orionis, M2 Iab). In the fall of 2002 a set of five high-resolution near-UV spectra was obtained by scanning at intensity peak-up position and four off-limb target positions up to one arcsecond, using a small aperture (200 by 63 mas), to investigate the thermal conditions and flow dynamics in the outer atmosphere of this important nearby cool supergiant star.Based on Mg ii h & k, Fe ii λ2716, C ii λ2327, and Al ii] λ2669 emission lines we provide the first evidence for the presence of warm chromospheric plasma at least 1 arcsecond away from the star at ∼40 R* (1 R*≃700 R⊙). The STIS spectra reveal that Betelgeuse's upper chromosphere extends far beyond the circumstellar Hα envelope of ∼5 R*, determined from previous ground-based imaging (Hebden et al. 1987).The flux in the broad and self-absorbed resonance lines of Mg ii decreases by a factor of ∼700 compared to the flux at chromospheric disk center. We observe strong asymmetry changes in the Mg ii h and Si i resonance line profiles when scanning off-limb, signaling the outward acceleration of gas outflow in the upper chromosphere.From the radial intensity distributions of Fe i and Fe ii emission lines we determine the radial non-LTE iron ionization balance. We compute that the local kinetic gas temperatures of the warm chromospheric gas component in the outer atmosphere exceed 2600 K, when assuming local gas densities of the cool gas component we determine from radiative transfer models that fit the 9.7 μm silicate dust emission feature. The spatially resolved STIS spectra directly demonstrate that warm chromospheric plasma co-exisists with cool gas in Betelgeuse's circumstellar dust envelope.

Betelgeuse is an example of a cool supergiant displaying brightness fluctuations and irregular surface structures. Simulations by Freytag, Steffen, & Dorch (2002) of the convective envelope of the star have shown that the fluctuations in the star's luminosity may be caused by giant cell convection. A related question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing detailed numerical simulations, I find that both linear kinematic and non-linear dynamo action are possible and that the non-linear magnetic field saturates at a value somewhat below equipartition: in the linear regime there are two modes of dynamo action.

A brief review of the observational properties of evolved massive stars is presented. In the pursuit of clues for their rotation, formidable difficulties are encountered. At the same time, common features emerge between B[e] supergiants, Luminous Blue Variables and Wolf-Rayet stars. Several indications of rapid rotation are found, mostly indirect ones, in each class. It is shown that fast rotation can probably survive the mass loss events which characterize the late evolution of massive stars.

The abundances of red giants will be reviewed, in particular those of carbon, nitrogen, oxygen and 12C:13C. The observed abundances are compared to predictions based on recent models with stellar rotation. Three topics will be emphasized: abundances in very metal-poor stars related to a previous generation of supernova; 12C:13C in red giants and rotation induced extra mixing; CNO abundances in yellow supergiants and their connection with models computed with rotation.

Observational v sin i line-width measurements for OBA stars are summarized, and the relationship of these measurements to ve sin i, the true projected equatorial rotation velocity, reviewed. In general, ve sin i ≥ v sin i for Be Stars, while ve sin i ≤ v sin i for O-type stars. The implications are that (i) it is probable that Be Stars are closer to their critical rotation velocities than is generally supposed (rendering plausible a range of new physical mechanisms for the Be phenomenon); and (ii) some non-rotational macroscopic line broadening (‘turbulence’) occurs in the atmospheres of O stars (and BA supergiants). Physical interpretations of this ‘turbulence’ are considered.

In this paper we review the development of the concept of the stellar rotation parameter commonly known as v sin i. We emphasize that the interpretation of the parameter in terms of physical characteristics of the star always depends on comparison with a model that is intended to represent the physical properties of the star. To that end we will trace the development of such models along with the observational means of determining the parameter. Emphasis will be place on the traditional methods involving stellar spectroscopy, but some attention will be place on indirect methods involving direct measurement of the rotation period and recent interferometric determination of stellar oblatness. In addition we will comment on recent techniques involving the simultaneous measurement of many spectral lines and synthetic spectra to improve the accuracy of rotational half-widths.The natural desire for simplicity of such models has often resulted in erroneous values for stellar parameters. This is particularly the case for the most rapidly rotating stars generally of early spectral type, but may also be present in some giants and supergiants where rapid rotation is difficult to detect. Finally, we will comment on the possibilities of improving the quality of both the measurement and interpretation of this important stellar rotation parameter.

Multifrequency spatially-resolved radio continuum observations of the M supergiants, α Ori (M2 Iab) and α Sco (M1.5 Iab + B2.5 V), have been obtained using the VLA A array and VLA+Pie Town configurations, to study changes in the extended (i.e. scale 1 − 10 stellar radii) atmospheres of these stars and to model the conditions in their wind acceleration regions. Strong modelling constraints on the atmospheric thermal properties are derived, because the radio emission is resolved at multiple wavelengths. Changes seen in the α Ori source flux density and radio visibility data occurring on several year timescales are described, based on observations obtained in 2002 February and April and in 1996 December. The need for multicomponent models of the plasma conditions in both the warm and cool gas around α Ori is discussed. The radio properties of the α Sco system, both of the M supergiant itself and in the H II region surrounding the B-type companion, provide important tools for estimating conditions within the M supergiant's wind.

The use of photospheric abundances in OB-type main-sequence stars and A and B-type supergiants as probes of rotation and evolutionary status is reviewed. The abundances of CNO and boron can be compared quantitatively with stellar evolutionary calculations. In particular the abundance ratios of N/O and N/C can be derived in blue supergiants to determine if they are consistent with the stars having gone through a red supergiant phase and dredge-up of core material to the surface. The results from several different studies are reviewed and compared. For blue supergiant stars in the mass-range 5-80 M⊙ the situation appears consistent — there is no evidence for stars of any mass having undergone blue-loops in the HR diagram. The stellar samples show significant signs of having N enriched atmospheres, and the quantitative values are consistent with stellar evolutionary calculations which invoke turbulent diffusive mixing while massive stars are on the main-sequence. Results on the interesting blue supergiant Sher 25 are presented, and linked to Sk-69°202; the B3Ia progenitor of SN 1987A. A spectacular ejection nebula surrounds Sher 25, much like that which was ejected by Sk–69°202 during its final stages of evolution. Both of these were thought to have been formed during a mass-loss event when the stars were in the red supergiant phase. The CNO abundances derived in Sher 25 suggest the nebula was ejected during the blue supergiant phase, and that rotation can explain the N-enrichment found in the stellar photosphere.

We report the discovery of a population of Wolf-Rayet stars in the young Galactic open cluster Westerlund 1. In an incomplete shallow spectroscopic survey, we find six nitrogen-rich (WN) and five carbon-rich (WC) WR stars. We also confirm the presence of a large population of yellow supergiants, some of which are candidate hypergiants. Given this population, Westerlund 1 is likely to be one of the most massive young clusters in the Local Group.

The mechanism responsible for driving the ubiquitous winds of cool giant and supergiant stars remains to be established. To this end, we are constructing semi-empirical models of the extended outer atmospheres (‘chromospheres’) and winds of selected red supergiants. These models are constrained by analyses of the UV line spectra of single stars, and of red supergiants in binaries that eclipse their main-sequence companions: the ζ Aur and VV Cep stars. These detached binaries are well-separated, with no evidence of mass transfer. The C II] 2325 Å line profiles of the binaries are similar to those of comparable single stars, suggesting that the chromospheres remain relatively unperturbed by binarity. However, it is unclear how much binarity disturbs the wind: binary observations suggest a gradual acceleration (β ∼ 3), but line profile analyses of single red supergiants imply a rapid acceleration (β < 1). To date, we have obtained extensive series of HST/GHRS and STIS observations of three eclipsing red supergiant binaries: ζ Aur, HR 2554 and VV Cep. In this paper, we focus on ζ Aur, and present observations and modelling results for this eclipsing binary.

Low and intermediate mass stars leave the Asymptotic Giant Branch (AGB) when the mass in their H-rich envelope is less than about 0.01 M⊙, and the high mass loss drops several orders of magnitude. The central star rapidly evolves to the left part of the HR diagram along a track of constant luminosity (e.g. Schönberner 1983). In principle the evolution of the central star to higher Teff and the expansion and cooling of the AGB remnant are easy to calculate. In practice several complicating factors arise which make it much more difficult to predict the morphology and properties of post-AGB stars, such as binarity, post-AGB mass loss and aspherical AGB mass loss. Binarity of post-AGB stars affects the morphology of the circumstellar environment, and it affects evolutionary timescales and surface chemical abundances of the components in the system. This review discusses some properties of binary post-AGB stars.

The Magellanic Clouds are unique in providing sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (~1 pc) all the way up to global scales. We present a sample of recent and current work using the MCELS dataset.

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.We compare our results with the abundances expected from studies of H II regions.

We are measuring Fe abundances of cool, luminous stars within 30 pc of the center of the Milky Way. Our sample contains both AGB stars and M supergiants. Low-resolution (λ/Δλ = 500) H and K band spectra are used to estimate temperatures and gravities. Stellar Fe abundances are determined from high-resolution (λ/Δλ = 40 000) K band spectra obtained on the IRTF using CSHELL. We find that Fe abundances of stars in the Galactic Center are consistent with the solar Fe abundance.

Among the mid-Teff (5000–7000 K) range stars, those on or near the main sequence are particularly important, because they provide much information on Galactic evolution and nucleosynthesis of the elements. This is due to the fact that these stars represent an age range from 0 to 15 Gyr, and a metallicity range from [Fe/H] ⋍ −4.0 to +0.3. Furthermore, it is likely that the present composition of elements in their atmospheres is similar to the composition of the interstellar gas from which they were formed, and that the present kinematics of the stars give information about their birthplaces. Hence, by observing selected samples of nearby F and G main sequence and subgiant stars one has the possibility to study the chemical and dynamical history of our Galaxy. Due to space limitation the present review is limited to these F and G stars. Supergiants are not discussed, but it should be emphasized, that their abundances are important for studies of advanced stellar evolutionary phases and determinations of the chemical composition of nearby galaxies. e.g. the Magellanic Clouds (Hill et al. 1995).

Stars close to the main sequence, if they rotate rapidly enough, show magnetic activity in the form of spots, active regions, and strong chromospheres. With the exception of the hybrid stars, stars cooler and more luminous than the so-called Linsky-Haisch dividing line, in contrast, are not known to have any of these phenomena. In fact, it is not clear such stars, even though rotating and convective, show any magnetic phenomena at all. We discuss (1) photometry used to search for spots in the hybrid stars, which we have not found, and (2) evidence for chromospheric variation in K supergiants that takes the form of enhanced winds, but which may be analogous to the activity of stars closer to the main sequence.

We have obtained the first direct image of the surface of a star with HST in March 1995. Our near-ultraviolet images of the M2 Iab supergiant-star Betelgeuse (Alpha Orionis) taken with the COSTAR-corrected Faint Object Camera show about 10 resolution elements over the stellar disk. With direct resolution of Betelgeuse the following discoveries resulted: 1) The apparent size of the disk in the UV (≃ λ 2550) is larger by a factor of ≃2.1 than in the optical, demonstrating the extent of the supergiant atmosphere. 2) An unresolved hot spot (higher temperature than the disk by a few thousand degrees) dominates the spatial structure of the atmosphere. 3) The atmosphere at 2550 å extends to 125 milliarcsec (FWHM 108 mas) with a limb-darkening coefficient of about 1.0.

The aim of this paper is to evaluate recent observational and theoretical results concerning the physics of chromospheric heating as inferred from IUE, HST-GHRS and ROSAT data. These results are discussed in conjunction with theoretical model calculations based on acoustic and magnetic heating to infer some conclusions about the magnetic and nonmagnetic surface structure of cool luminous stars. I find that most types of stars may exhibit both magnetic and nonmagnetic structures. Candidates for pure nonmagnetic surface structure include M-type giants and supergiants. M-type supergiants are also ideal candidates for identifying direct links between the appearance of hot spots on the stellar surface (perhaps caused by large convective bubbles) and temporarily increased chromospheric heating and emission.

High-mass X-ray binaries (HMXBs) represent an important stage in the evolution of massive binary systems. The compact object (in most cases an X-ray pulsar) not only provides information on the orbital and stellar parameters, but also probes the stellar wind of the massive companion, an OB supergiant or Be star. The X-ray luminosity directly depends on the density and the velocity of the wind at the orbit of the X-ray source. Important constraints on the stellar-wind structure can be set by studying the orbital modulation of UV P-Cygni profiles. In this paper different aspects of the interactive wind-accretion process are highlighted, such as the highly variable X-ray luminosity, the influence of the X-rays on the radiative acceleration of the wind inside the ionization zone, and the large-scale structures that trail the X-ray source in its orbit.

Firstly, a brief account is given on the recent progresses in model assumptions, which influence the evolution of surface abundances in massive stars. A concise overview of this chemical evolution is presented.We discuss in detail the surface chemistry of WN and WC stars, in particular, the effects of the initial metallicity Z and mass loss rates on the resulting abundances. The abundances in WN stars are not very sensitive to model assumptions and are mainly a test on nuclear cross sections. Conversely, the chemical abundances in WC stars are very much model dependent. Major differences in the composition of WC stars (and subtype distributions) are expected according to their initial metallicity. The various models proposed to explain the N/C enrichments in blue supergiants and the properties of the progenitor of SN 1987A are reviewed.

Observations of circular polarization of molecular masers associated with late type giant and supergiant stars can be used to estimate the magnetic field strength in the masing region. Magnetic field strengths of ~ 5 mG are deduced for OH masers in circumstellar envelopes at distances of ~ 1016 cm from the star, and magnetic field strengths of ~ 50 G are deduced for SiO masers that reside above the photosphere. Extrapolation to the stellar photosphere suggests that average surface magnetic fields are on the order of 103 G.

Although many of the nearest dim and cool stars (the red dwarfs) were catalogued in the early sixties, the majority of the astronomers did not realize that these objects provide almost nine tenths of all the stars in our Galaxy. In fact 90-95% of the stars in the solar vicinity (r ≤ 25 pc) are main sequence stars, and at least 80% of them are M dwarfs. Outside the main sequence (MS) one can find a few subdwarfs and somewhat more white dwarfs, but the contribution of this latter type is not known precisely. Estimates range between 4% and 8%. The relative frequency of giants and supergiants can not be determined from the census of the local star population because they are not represented in a statistically meaningful number. But investigations of much greater cosmic volumes demonstrate that luminosity classes Ia, Ib, II, III, and IV altogether contribute fewer than 1% of the stellar content of the Galaxy.

We present preliminary results of a long-term spectroscopic monitoring of a magnitude-limited (V < 7.5) sample of OB-supergiants (07.5-B9) aimed at establishing the incidence of co-rotating, large-scale wind structures. In the optical, this can be achieved by detecting rotationally modulated variability in Hα. Dramatic line-profile variations operating on a daily (and in some cases on a hourly) timescale are observed. Firm conclusions regarding the origin of the variability must, however, await a detailed period analysis. There is no clear evidence for a causal link between photospheric and wind activities.

We present CNO abundance determinations in 11 Magellanic Cloud O and early B supergiants based on physical parameters obtained from FUSE, HST/IUE and VLT spectroscopy, plus model atmospheres which allow for stellar winds and line blanketing. In all cases, nitrogen is substantially enhanced whilst carbon and generally oxygen are moderately depleted, indicative of rotationally induced mixing of unprocessed and CNO processed material at their stellar surfaces.

We present and discuss statistical relation between rotation and X-ray activity for giant and supergiant stars.”

The non-spherically symmetric winds of B[e] supergiants are investigated. An empirical density distribution is chosen that accounts for the density concentrations and ratios derived from observations, and our model winds are assumed to contain only H and He. We calculate the Strömgren radii and the more accurate ionization fractions for H and He and find that in equatorial direction the winds of B[e] supergiants can become neutral very near the stellar surface. A neutral disk therefore exists around these stars in which molecules and dust can form which are shielded from the photodissociating stellar radiation field.

We present the analysis of UV and optical spectra of M 33 early B-type supergiants. Stellar parameters, metal abundances (Si, Mg, O and N) and mass loss rates are derived from anlyses of optical spectra by means of non-LTE unblanketed unified model atmospheres (fastwind code, Santolaya-Rey, Puls & Herrero 1997). These analyses use wind terminal velocities previously derived from the analysis of UV P-Cygni profiles. Stellar radial gradients of Si, O and Mg are derived for the M 33 disk. Differential abundances of those elements with respect to Galactic counterparts are also presented, along with nitrogen. Finally, the wind momenta of M 33 stars is derived and compared with the one found for Galactic B-type supergiants.

We present preliminary results concerning the O4If+ star HD 15570. Of-type supergiants are believed to represent an evolved evolutionary stage of very high mass stars (Minit > 40 M⊙). Their low numbers and extreme peculiarity make each of these objects worth of continuous monitoring. HD 15570 dominates the very young open cluster IC 1805 and is thought to have had an initial mass ≥ 100 M⊙. Low-, intermediate- and high-resolution spectra were collected at the Loiano and San Pedro Mártir telescopes since 1992. The comparison of our high- and low-resolution spectra shows clear variability of a number of spectral features. It is worth noticing, that the variation of Hα seems to follow a repeated secular trend, increasing its equivalent width from ~ 3Å to more than 8 Å in a few years. At the same time, its profile is varying, from a shape quite similar to the theoretical one corresponding to the Klein & Castor (1978) model C, to a much more developed P-Cygni profile, with a deep blue absorption wing. The possibility of instrumental effects is ruled out by the remarkable constancy of the nearby diffuse interstellar band at 6613 Å and of the He ii 6683 Å absorption. The Hβ profile variability is evident from the comparison of the 1996 and 1998 high-resolution spectra. The emission component, which is clearly visible at all epochs, is absent in the 1996 spectrum when the line appears in pure absorption. No relevant line-profile variation seems to be present in the He ii and N iii lines contributing to the ‘feature f’, that looks remarkably constant, as well as Hγ, while their equivalent widths seem to show a modest amount of random variability.

We have searched for magnetic signatures in A-type supergiants. The obtained magnetic values for seven of these stars are presented here.

We present the spatial distribution of chemical species in M 31, as derived from intermediate resolution spectra of seven B-type supergiants, lying within four OB associations, covering a galactocentric distance of 5 – 12 kpc. We do not detect any systematic oxygen gradient across this galactocentric range. We find that the inner regions of M 31 are not, as previously thought, very ‘metal-rich’. Our abundances of C, N, O, Mg, Si, Al, S and Fe in the M 31 supergiants are very similar to those of massive stars in the solar neighbourhood.

The masses and the evolutionary states of the progenitors of core-collapse supernovae are not well constrained by direct observations. Stellar evolution theory generally predicts that massive stars with initial masses less than about 30M⊙ should undergo core-collapse when they are cool M-type supergiants. However the only two detections of a SN progenitor before explosion are SN1987A and SN1993J, and neither of these was an M-type supergiant. Attempting to identify the progenitors of supernovae is a difficult task, as precisely predicting the time of explosion of a massive star is impossible for obvious reasons. There are several different types of supernovae which have different spectral and photometric evolution, and how exactly these are related to the evolutionary states of the progenitor stars is not currently known. I will describe a novel project which may allow the direct identification of core-collapse supernovae progenitors on pre-explosion images of resolved, nearby galaxies. This project is now possible with the excellent image archives maintained by several facilities and will be enhanced by the new initiatives to create Virtual Observatories, the earliest of which (astrovirtel) is already producing results.

We describe FUSE time-series observations of stellar wind variability in Sk-67°166 (HDE 269698), a nitrogen-rich O4 supergiant in the LMC.

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Because of this, they form a very heterogeneous group. This group contains objects with different evolutionary stages. Lamers et al. (1998) have suggested a new designation with five sub-groups, which indicate the evolutionary stage. They are: supergiants, pre-main sequence or Herbig Ae/Be, compact planetary nebulae, symbiotic and unclassified. The unclassified group has many objects that need a better study to resolve their evolutionary status. Forbidden lines can be a useful tool to solve this problem. They can give informations about chemical composition, ionization and density of the circunstellar medium and probably the evolutionary phase of these objects. We analize spectra of some galactic objects, obtained with the feros and b&c spectrographs at the 1.52m telescope in ESO (La Silla-Chile), with a special focus on the forbidden lines. We have studied the spectra of five B[e] stars of uncertain evolutionary stage. We find that one of them is a pre-WN star, the other four are supergiant B[e] stars.

We present far-UV spectra (910-1190Å) of Sk 80, an 07 supergiant in the Small Magellanic Cloud, observed by the FUSE satellite during its In-Orbit Checkout phase. The spectra reveal many interstellar absorption lines, including H2, and O VI, and several key stellar wind features.

We report radial velocity studies of photospheric absorption lines from spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations with a quasi-period ∼ 2 days have been detected in high-resolution echelle spectra and most probably indicate that the supergiant is pulsating. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile have been observed. The fundamental parameters of the star have been derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, these last including the mass-loss rate. The binary nature of this star is not suggested either from Hipparcos photometry or from radial-velocity curves.

We present first results of our study of the interplay between the 106 K, 104 K, 102 K gas phases in the supergiant shell LMC 4.

Accurate radial velocities have been obtained with the CORAVEL photoelectric scanner at ESO, La Silla, for 36 F-M supergiants in the 30 Dor and Shapley II regions of the LMC (5h20m < RA(2000) < 5h50m, −70°09′ < Dec (2000) < −68°30′). On the basis of these data, we revisit the content and spatial extent of the four kinematical groups of F-M supergiants discovered in this area by Prévot et al. 1989. Each is the oldest part of a larger star forming region, recognized by young HII regions or CO clouds, and/or a surrounding Hα + [NII] superbubble. We discuss various gas tracers including the interstellar sodium and calcium lines.

We study here the influence of micro-turbulence in the synthesis of H and He lines, in order to quantify its effect on the determination of stellar parameters of O-type stars, in particular on the stellar He abundance. We find that only He I lines and He II λ 4686 are considerably affected, the effect being more relevant for models corresponding to supergiant stars. We also find that neglecting micro-turbulence in the analyses of O-type stars introduces deviations in the derived parameters that are within our standard error box. The He content is not or slightly reduced, thus micro-turbulence cannot be responsible for the He-discrepancy to all its extent.

LMC2 was one of the first supergiant shells in the Large Magellanic Cloud (LMC) to be identified, based on the detection of long, curved Hα filaments extending over 900 pc (Goudis & Meaburn 1978). LMC 2 is located to the east of the active star formation region south of 30 Doradus. LMC 2 is a spectacular supergiant shell in the LMC, having the most coherent filamentary structure and the highest X-ray surface brightness. As shown in Fig. 1, the diffuse X-ray emission from LMC 2 is bounded by the Hα filaments in the north and east. A bright X-ray arc is seen in the southwest quadrant, extending from N 158 and N 159.

About 10 X-ray binaries in our Galaxy and LMC/SMC are considered to contain black hole candidates (BHCs). Among these objects, Cyg X-1 was identified as the first BHC, and it has led BHCs for more than 25 years(Oda 1977, Liang and Nolan 1984). It is a binary system composed of normal blue supergiant star and the X-ray emitting compact object. The orbital kinematics derived from optical observations indicates that the compact object is heavier than ~ 4.8 M⊙ (Herrero 1995), which well exceeds the upper limit mass for a neutron star(Kalogora 1996), where we assume the system consists of only two bodies. This has been the basis for BHC of Cyg X-1.

A-type supergiants are just at the boundary between the early type supergiants, with strong stellar winds driven by radiation pressure and the cool supergiants in which the origin of mass loss is the dissipation of mechanical energy. The mechanisms involved in the mass loss processes in A supergiants as a whole, are still uncertain.

C2 and CN bands in the wavelength region λ 560 - 680 nm were used to obtain the carbon and nitrogen abundances in the supergiant star A7 of the young, metal-poor, globular cluster NGC 330 in the Small Magellanic Cloud (SMC).

A group of A-type stars in the field of the Small Magellanic Cloud (SMC) were noticed by Humphreys (1983) to have anomalously strong hydrogen (H) lines and a Balmer jump that are too strong for their luminosities. Their visual luminosities, based on membership in the SMC, are about two magnitudes brighter than one would expect from the appearance of the Balmer series. Humphreys also found that their colours are too red in U-B by 0.2 to 0.3 mag, but show little or no change in B-V relative to normal A-type supergiants; this is consistent with the strong Balmer jump in these stars' spectra. She also concluded that the objects do belong to the SMC.Earlier, Sanduleak (1972) had identified a group of stars with similar properties in the LMC, but, because of their strong hydrogen lines, rejected them as members. However, Fehrenbach and Duflot (1972) recognized about 30 stars with A and F type spectra with unusually strong H lines. They concluded that they were members of the Large Magellanic Cloud (LMC) because of their large negative radial velocities.

We have performed an abundance analysis of six Large Magellanic Cloud (LMC) F supergiants, based on infrared photometry and echelle spectra obtained from CTIO. We find a real dispersion in Fe/H values, indicating that the LMC is inhomogeneous. Oxygen abundances appear to be equal in all six stars, resulting in a steep O/Fe slope with Fe/H. Other element abundances appear near normal, although there is a hint of a small enhancement of second s-process peak elements. Iron abundances are probably affected by non-LTE; this does not change our conclusions concerning oxygen.

We present some results on the burst properties in star forming galaxies, using near infrared stellar features typical of red supergiants and Brackett nebular lines which trace the presence of luminous H II regions.

CCD imaging and BVRI photometry of 14 IRAS sources with far-IR colours similar to planetary nebulae and post-AGB stars are presented. Also results of optical and near-IR spectroscopy of 10 of these candidates are given. Based on the spectral energy distribution from 0.4 μm to 100 μm, the sample of program stars are put into two groups. The sources IRAS 08187-1905, IRAS 05238-0626 and IRAS 17086-2403 present similar flux distributions. These three sources have detached cold dust components with dust radii Rd ≈ 1000 R∗. The low infrared variability of theses sources suggests that the intense mass loss has been ceased. All three sources are at high galactic latitude (1>9°) suggesting that these are old low-mass evolved stars. In the IRAS colour-colour diagram of Likkel et al (1991) these sources fall in the region where most of the stars are evolved stars and PNe but without CO detection. This is consistent with at least one source IRAS 17086-2403, in which OH and CO molecular features are not detected. The far-IR excess, non-variability and high latitude of these objects suggest that these are post-AGB supergiants, slowly evolving towards planetary nebula phase.

An abundance analysis of the photosphere of the F-type Post-AGB candidate IRAS 05341-+0852 is presented. It shows that the star is metal-poor ([Fe/H]=–1.0) and carbon-rich (C/0≈2.2). Carbon, nitrogen, oxygen, silicon, and possibly lithium and aluminum are found to be over abundant. Most importantly this star has large overabundance of s-process elements which are as follows: [Y/Fe]= 1.80, [Ba/Fe]= 2.58, [La/Fe]= 2.86, [Ce/Fe]= 2.95, [Pr/Fe]= 2.27, [Nd/Fe]= 1.97, and [Sm/Fe]= 0.86. The overabundances of s-process elements and carbon in IRAS 05341+0852 is direct evidence for the association of s-process enhancements with shell-flashes and dredge-up. These are likely responsible for the increase in C/O. The possible overabundance of Li ([Li/Fe]≤2.5) and Al ([Al/Fe]≤ 1.1) in IRAS 05341+0852 could indicate that there was Hot Bottom Burning (HBB), where the base of the convective envelope is hot enough for nucleosynthesis to occur (Lattanzio 1993). HBB has been suggested as the mechanism responsible for the production of Li in the Li-rich AGB stars discovered by Smith and Lambert (1989). In fact these are bright AGB stars which are oxygen-rich rather than carbon-rich. Recent calculations by Sackmann and Boothroyd (1992) showed that Li-rich and O-rich AGB stars are the result of HBB. In the HBB models temperatures of the order of 0.5–1 × 108 K are encountered at the base of the convective envelope (Blöcker and Schönberner 1991). This is hot enough for the reaction 25Mg(p,γ) 26 Al resulting in the production of Al.

We develop the idea (Harris & Pudritz 1994, ApJ, 429, 177) that, like currently forming star clusters and associations, globular clusters (mean mass ≃3×105M⊙) were born in the ‘cores’ of much larger (∼108 – 109M⊙) star-forming complexes which we call ‘supergiant molecular clouds,’ or SGMCs. The number N(m) of protoclusters at mass m is then determined by a steady-state balance between their growth by core-core collisions, and their self-destruction via the side effects of star formation. This mass spectrum is ultimately passed on to the globular cluster system (GCS) itself, by virtue of the very high star-formation efficiency required to produce a bound stellar cluster from a gaseous core.

We argue that easily measured, reliable estimates of terminal velocities for early-type stars are provided (1) by the central velocity asymptotically approached by narrow absorption features in unsaturated UV P Cygni profiles, and (2) by the violet limit of zero residual intensity in saturated P Cygni profiles. We use these estimators and high resolution IUE data to determine terminal velocities, v∞, for 181 O stars, 70 early B supergiants, and 35 Wolf-Rayet stars. For OB stars our values are typically 15-20% smaller than the extreme violet edge velocities, vedge, while for WR stars v∞ = 0.76vedge on average. We give new mass-loss rates for WR stars which are thermal radio emitters, taking into account our new terminal velocities and recent revisions to estimates of distances and to the mean nuclear mass per electron. We examine the relationships between v∞, the surface escape velocities, and effective temperatures.

This review is restricted to the most recent studies of the structure of stars in the approximate range from 10 to 100 M⊙, during the core H- and He-burning phases. Other recent major reviews on this subject are by Dallaporta (1971), Massevich and Tutukov (1974) and Iben (1974). The lower limit was chosen to be just above the transition from degeneracy to non-degeneracy in the core at carbon ignition (Schwarzschild and Härm 1958). The upper limit is very uncertain. The canonical value of about 60 M⊙for Pop I composition was set by Schwarzschild and Harm (1959), using linear pulsation theory. More recent non-linear dynamical calculations lift the limit above 100 M⊙, and also show that mass loss by vibrational instability occurs at such a rate that stars in the range from 100 to 200 M⊙can survive for a time comparable to the total main sequence lifetime (Appenzeller 1970a, b, Ziebarth 1970, Talbot 1971a,b and Papaloizou and Taylor 1974).