Theoretical evolutionary sequences have been generated with the YREC code for a 15 M⊙ star from the ZAMS to core helium exhaustion with a variety of physical assumptions, covering both rotating and non-rotating cases. The non-rotating models agree qualitatively with other models found in the literature. The addition of only rotational distortion has little effect on the models, while the full treatment of rotation results in additional mixing and theoretical tracks that are similar to models with small amounts of convective overshoot. Models which include only rotation have fair agreement with the observed main sequence surface rotation velocities, but rotate too rapidly during the post-main sequence phases. The addition of mass loss at the given rates helps this problem somewhat but does not appear to completely resolve it. Neither the non-rotating models nor the rotating models provide full agreement with the terminal-age main sequence band used by Maeder & Meynet (1987); this may be indicative that additional mixing processes are necessary or that a more recent TAMS, such as that of Stothers (1991), should be used.

Available observational data indicate that some kind of additional mixing is present in radiative envelopes of O and early B-type stars. Because of these stars are known to be the fastest rotators amongst all normal stars, the most probable candidate for the role of additional mixing in their interiors is rotationally induced turbulent diffusion discovered by Zahn (1983, 1992). Recently Denissenkov (1993a,b) calculated evolution of massive main sequence (MS) stars with turbulent diffusive mixing in order to explain atmospheric abundance peculiarities in OB-stars. This note summarizes the main results which have been obtained.

The way rotation influences the main sequence evolution of early type stars depends strongly on their internal angular momentum distribution. Their convective core mass is not always decreased as a consequence of a reduced “effective mass” due to rotation, since rotation laws close to uniform specific angular momentum may increase Δrad and thereby the convective core mass (Clement). In addition, rotationally induced mixing processes may redistribute angular momentum and chemical elements inside the stars (e.g. Endal & Sofia 1978).

Walborn (1970, 1971) observationally found that OB stars showed nitrogen and carbon abundance anomalies in their atmospheres. Schönberner et al. (1988) found that OBN stars had helium enriched atmospheres. Several different suggestions have been made so far to explain the abundance anomalies in these stars (Paczynski 1973; Walborn 1976; Bolton and Rogers 1978). Maeder (1987) and Weiss et al. (1988) call attention to some possible effects of rotation in mixing chemical elements in Wolf-Rayet stars and B-supergiant stars respectively. They suggested that rotational mixing could explain the high He/H ratios and the high N/C and N/O ratios in the progenitor of 1987A Supernova. Saio et al. (1988) in an attempt to explain the nitrogen and helium enhancement in the progenitor of SN 1987A invoked extensive mixing in their models. They pointed out that such an effective mixing may be produced by rapid rotation. Such observations and ideas were the motivation for the present study.

The double cluster h and x Persei is one of the richest clusters containing early-B stars, and therefore is important for observational and theoretical studies on the fundamental parameters of massive stars. The colour-magnitude diagram of the double cluster shows an important scatter (see Figure 1). It has long been known that h and x Persei are extremely rich in Be stars (Slettebak 1968). Our previous contention (Waelkens et al. 1990) that the large-amplitude variable stars we discovered are also Be stars, could be confirmed for a few objects. Rotation velocities for stars in h and x Persei are usually high, which is not surprising in view of the large fraction of Be stars.

Globally ordered magnetic fields are known to exist in non-degenerate stars with spectral types between approximately F0 and B2. Among the B stars, and in order of increasing effective temperature, these include the Bp Si stars, helium-weak stars, and the helium-strong stars. These rather remarkable objects present us with an excellent opportunity to quantitatively examine the possible effects of magnetic fields on the photospheres, winds, and circumstellar environments of hot stars. In this paper we review some of the observations of the magnetic fields and field geometries of magnetic B stars, and also briefly discuss the success of attempts to measure magnetic fields in hotter OB and Be stars. We point out some of the interesting observational similarities of the helium-weak and helium-strong stars to Be and other hot stars, including their spectroscopic and photometric variability, variable winds as demonstrated by the UV resonance lines of C IV and Si IV, and their non-thermal radio emission. Continuing work also suggests that a considerable fraction of the rapidly rotating magnetic helium-peculiar stars are in fact variable Be and Be shell stars.

HD 21699 is a He-weak star whose longitudinal magnetic field ranges from − 1.3 to +1.1 kG (Brown et al. 1985). Its effective temperature, Teff = 15900 K, and its gravity, log g = 4.0, were determined by Wolff (1990) from photometry of the Balmer discontinuity and from measurements of the Hγ line. HD 21699 was reported to exhibit remarkable variations in the C IV ultraviolet resonance lines at 1548 and 1551 Å (Shore et al. 1987). These variations occur with the same period, 2d49 (Percy 1985), as the magnetic variations and the photometric variations in the optical region. Similar UV line variations could be found only in two other He-weak stars, HD 5737 and HD 79158. They were interpreted as an evidence of the occurrence of outflowing winds controlled by the magnetic field. Furthermore, Shore et al. emphasized that no lines in IUE spectra other than C IV, and possibly Si IV, show any statistically significant variation. Recently, irregular brightening of a few hundredths of magnitude, superimposed over the periodic variations, were observed in the U photometric band (Vetö 1993); their origin is currently unknown.

HD 96446 is a B2p He-strong star, in which a large-scale organized magnetic field is present. From spectra recorded in both circular polarizations, various moments of this magnetic field have been repeatedly determined, among which the mean longitudinal magnetic field and the crossover. The mean longitudinal magnetic field 〈Hz〉 is the line-intensity weighted average over the visible stellar hemisphere of the line-of-sight component of the magnetic vector. The crossover, ve sin i 〈x Hz〉,is the product of the projected equatorial velocity, ve sini, and of the mean asymmetry of the longitudinal magnetic field, 〈x Hz〉. The latter is the line-intensity weighted first-order moment about the plane defined by the line of sight and the stellar rotation axis of the component of the magnetic field along the line of sight.

The light and spectrum of the magnetic, chemically peculiar Be star σ Orionis E (=HD 37479) vary with the rotational period of 1.19081 d because of the effects of inhomogeneities in the photosphere and circumstellar matter (Walborn and Hesser 1976, Landstreet and Borra 1978, Hunger 1974). In this paper, we describe a model for the distribution of the Hα emitting material in the magnetosphere based on analysis of 24 high quality spectra covering the entire rotation period and published data from other sources.

The strong magnetic fields found in the Ap and Bp stars are reviewed, with critical attention to the competing dynamo and fossil theories for their origin. A number of difficulties for the dynamo theory are identified. Whilst the fossil theory is not free of problems, they appear less severe. From the modulation of certain spectral lines, rather weaker fields are deduced to be present above the surface of Be stars. The question of whether observed spectral transients might arise from magnetic fluctuations is discussed.

Observational data of the last 10 years allow two main conclusions:

a) Main sequence stars can be separated in two classes: - magnetic (Bp) stars with surface strengths of a dipole or quadrupole magnetic field of Bs ≈ n · (102 − 103) G, n = 2,3,4…7, and - normal main sequence stars (F-O) with magnetic fields Bs ≈ 1 − 100 G (< 300 G);

b) Typical star formation takes place in interstellar molecular clouds with magnetic field strengths B ≈ 10-5 G (See Dudorov 1990).

We present results from a survey of X-ray emission properties of near main-sequence B stars, including several Be and β Cephei stars. The main conclusions of our survey are: 1) The X-rays are soft, probably because the shock velocity jumps are small since the terminal wind speeds are small. 2) A major fraction of the wind emission measure is hot, assuming wind theory estimates for the density distribution. A large fraction of the wind is not expected to be hot in current wind shock models. 3) A hard component is found to be present in τ Sco; possible causes are discussed. 4) For the Be stars, the X-rays emission is from a normal B-star wind that is coming from the poles as in the WCD model of Be stars. 5) None of the stars, including the β Cep stars, show noticeable variability in their X-rays. For the normal B stars we conclude from the lack of variability that the shocks are in the form of fragments in the wind instead of spherical shells. 6) Our observations suggest that all B stars are X-ray sources and that there is a basal amount of X-ray luminosity of about 10-8.5Lboi. The hot component in τ Sco and the high X-ray luminosity of B stars detected in the all-sky survey suggests that there is a source of X-ray emission in addition to wind shocks in some B stars.

Extensive stellar surveys with the Einstein Observatory (Chlebowski et al., 1989) and with ROSAT have clearly confirmed the presence of stellar X-ray emission over nearly the whole range of the HR diagram. In the ROSAT all-sky survey data approximately 20000 stellar X-ray sources were detected (Schmitt et al., 1992). Most of these stellar X-ray emitters are low mass late-type stars, the origin of their X-ray emission is thought to be coronal.

It is important to understand the ionization state of Be star winds for several reasons, including: (1) if known, mass loss rates can be determined from UV P Cygni profiles; (2) the radiation line driving force which accelerates the winds depends on the ionization distribution; and (3) analysis of line profiles, in conjunction with polarization data, can help assess the credibility of various hypotheses for the assymetric nature of Be star winds.

We present infrared spectra of 4 Be/X-ray binaries in the K band, and 4 spectra in the J, H and K bands of 2 more sources. The HI IR emission lines are useful determinators of the conditions in the inner regions of the circumstellar disk about the Be star, due to optical depth effects. These are preliminary results, and hope to be followed up by high resolution echelle spectra, where we wish to estimate the velocity field, temperature and density structure of the circumstellar material.

EXO2030+375 consists of a neutron star in an eccentric 46 day orbit around a 20th magnitude Be-star companion (Coe et al., 1988; Parmar et al., 1989; Stollberg et al., 1993). The Be-star is thought to be surrounded by a shell/disc of material which is responsible for the infrared excess and Balmer emission lines which are characteristic of Be-stars in general. At periastron, the neutron star passes through this circumstellar material, giving rise to enhanced accretion onto the neutron star surface. As a result of this, the X-ray emission (pulsed at the neutron star spin period of 41.8s) increases dramatically, so producing the transient, outburst behaviour which is commonly seen in Be-star / X-ray binaries.

The X-ray source 2S0114+65 was identified as a Be star from its optical spectrum. The X-ray spectrum is hard and spectral fits indicate the presence of a large amount of circumstellar matter around the X-ray source. The source also undergoes transient X-ray outbursts as well as flaring activity is present. 2S0114+65 was observed with the EXOSAT satellite on four occasions: on 1983 July 28, 1985 December 29, 1986 January 1 and 2. We have carried out an analysis of the X-ray data on this star.

The Be massive X-ray binary LSI+61°303 is a 26.5 days periodic radiosource (Taylor & Gregory, 1984), exhibiting radio outbursts maxima between phases 0.6–0.8. Evidence of a photometric period of similar value has also been reported (Paredes & Figueras, 1986; Mendelson & Mazeh, 1989). The previous spectroscopic radial velocity observations of Hutchings & Crampton (1981) are in agreement with the radio period, and give support to the presence of a companion. We present new optical and infrared photometric observations and high resolution Hα spectra of LSI+61°303.

Compared to several other Be/X-ray binaries, 4U1907+09 has been observed more frequently due to the fact that it is found in an ‘on’ state more often. It also has a short orbital period of ~ 8 days as compared to the long orbital periods commonly found in these binaries. But despite the attention it has received, the exact nature of the primary remains elusive. While some observers maintain it to be a Be/X-ray binary, others prefer to put it into the class of OB supergiants.

The first comprehensive linear polarization data on hot stars covering the spectral range from 1500 to 7600Å are presented. These results are based on recent observations made with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE), combined with ground-based observations from the Pine Bluff Observatory. Implications of the data for models of the circumstellar envelopes of hot stars are discussed, with particular emphasis on the surprising results found for the rapidly rotating Be stars. In particular, WUPPE discovered that the continuum polarization in Be stars decreases into the ultraviolet, which was not predicted by models prior to the observations. Time variability in the optical data is also discussed. Possible interpretations of these results are examined in the light of recent new models for Be star disks.