Problems of Beta Cephei variables and of related pulsating B stars are discussed. In particular, various excitation mechanisms of both radial and nonradial oscillations so far suggested are critically examined. The present state of theory for these variables is found unsatisfactory.

Only a decade ago, this talk could have concerned only the β Cephei stars which however populate a much more precisely defined strip in the Hertzsprung-Russel diagram (MED). But recent reconnaissance surveys (Smith 1977; Smith and Penrod 1984; Waelkens and Rufener 1985; Baade, in preparation) show that perhaps only one, if any, sizeable region of the upper HRD is devoid of nonradially pulsating stars. The identification of the driving mechanism is still pending (cf. the parallel talk by Osaki), and apparently our knowledge about the internal structure of OB stars is incomplete. But, turning that argument around, it also is indicative of how much may be learned about OB stars from and through the solution of that fundamental problem. This seismologial potential, the ubiquity of the phenomenon, and the effect, as suggested by recent observations of some stars, of the pulsations on the mass loss of OB stars make the oscillations of OB stars one of the most important problems of current astrophysics. On the observational side, rotationally broadened spectral lines, large amplitudes, comparatively long periods, and high luminosities permit information to be gathered which otherwise is accessible only for the sun.

Be stars are B stars in which emission has been observed in at least one hydrogen line on at least one occasion. Some Be stars are pre-main-sequence stars, mass-transfer binaries, or supergiant stars with extended atmospheres. The majority, however, are classical Be stars: single stars on or near the main sequence. An important characteristic of these stars seems to be their rapid rotation – close to but not at the “critical” velocity at which the effective gravity vanishes at the equator.

The two subjects of the variability of WR stars and of supergiants are still in their infancy and are certainly promised to a great development in coming years. The physics and pulsation properties of WR stars and supergiants, although both kinds of stars result from massive star evolution, are indeed very different and will be discussed separately.

Solar five-minute oscillations provide a means of testing theoretical models of the sun. By judiciously combining data from low-degree modes, properties of the central and surface regions of the sun can be inferred separately. In principle, it should be possible to draw similar inferences from other stars, once adequate data are available. Recent solar rotational splitting data imply that in the equatorial regions much of the radiative envelope of the sun is rotating more slowly than the photosphere.

This paper reviews the three major cosmic microwave background radiation (CMBR) spectrum measurement programs conducted and published since the last (XVII) IAU General Assembly. The results are consistent with a Planckian spectrum with temperature 2.72 ± 0.03 K spanning a wavelength range of 0.1 to 12 cm. Limits on possible distortions and implications are outlined. Ongoing and future measurements are discussed.

Crucial cosmological information is provided by the observed angular distribution (isotropy) of the cosmic microwave background radiation. This report treats the current status of searches for anisotroples in this radiation on all angular scales from 180° (the dipole component) to 6″. With the exception of the dipole component, only upper limits (at ~ 10-4 in ΔT/T) are available, yet these upper limits have played an important role in refining models of the early Universe and of the origin of structure within it.

Recent data taken with the 40-m telescope of the Owens Valley Radio Observatory at 20 GHz have confirmed the detections of the Sunyaev-Zel’dovich effect towards three clusters of galaxies, 0016+16, Abell 665 and Abell 2218. Rough measurements of the angular scale of the effect have also been made, and a comparison of these with the X-ray observations supports an isothermal model for the cluster gas.

Microwave background astronomy has arrived. Largely because of improvements in receivers, the last three years have seen the emergence of agreement concerning important measurements of the microwave background radiation (MBR):

– hard evidence that the MBR has a black-body spectrum (see Smoot in these proceedings);

– the unambiguous detection of the Sunyaev-Zeldovich decrement in clusters of galaxies (Birkinshaw et al 1984), and indeed profiles of the decrement across clusters (Birkinshaw in these proceedings);

– the lack of anisotropy in the MBR temperature T on scales of a few arcmin down to ΔT/T˜5×10-5 (Uson & Wilkinson 1984; Readhead, private communication) and the consequent elimination of simple theories of adiabatic primordial fluctuations.

The search for neutral hydrogen 21 cm emission from collapsing protoclusters at redshifts of 3-20 is an important technique for establishing the history of galaxy formation. Observations already place strong constraints on the largest mass scales. Future measurements should reach sensitivities adequate to detect individual massive galaxies.

Here I would like to report on the HI intergalactic cloud in the Leo group of galaxies, which was first announced in 1983 by Schneider, Helou, Salpeter and Terzian (1983). This unexpected discovery was made accidentally by S. Schneider while calibrating the Arecibo λ21 cm system by looking at a part of the sky where no HI emission was expected at high velocities. These observations were made during a project of studying the HI distribution in binary galaxies and in small galaxy groups.

Radio, optical and infrared data are combined to study the nature of mJy-sources found in the 5C12 aperture-synthesis survey. The optical counterparts are QSOs, giant elliptical galaxies of the 3CR type, and blue galaxies. We find that the blue galaxies are a mixed group; the suggestion of a new blue population of evolving spirals at mJy levels is not supported by our data.

During the last decade several deep surveys have been made with various aperture synthesis radio telescopes. At milliJansky levels important contributions were made with the WSRT 3 km array and the Cambridge One Mile Telescope. At sub-milliJansky levels surveys have been done with the VLA and the WSRT down to rms noise values of ~10 μJy.

We have made a new deep 6 cm survey with the VLA in order to extend the radio source count to a lower flux density and to decrease the limits on the small scale fluctuations in the microwave background. The survey region covers ~10-5 ster and is nearly coincident with the survey previously reported by Fomalont et al. 1984a and 1984b. Both the observing time and bandwidth were increased by a factor of two over the previous survey to give a factor of two improvement in sensitivity.

Apart from the well known evolution in the space density of powerful radio sources, the maximum linear sizes and the spectral indices of extended radio sources could also evolve with epoch and it is important to investigate their epoch-dependence in order to understand the cosmological evolution of radio sources. Evidence for size evolution (in the sense that sources were smaller at earlier epochs) has been presented both from the angular size – redshift relation (θ – z) for quasars and from the angular size – flux density relation (θ – S) for all radio sources. Doubts have sometimes been expressed, however, mainly because it has been difficult to investigate the epoch dependence independent of a possible dependence on radio luminosity. Reasonably reliable estimates of the distances of radio sources have generally been limited to a relatively small range in flux density (S), so that high redshift sources are also of high luminosity. An inverse correlation between linear size (l) and radio luminosity (P) is therefore hard to distinguish from a genuine evolution with epoch. A similar situation appears to hold for the spectral indices (α) of extended radio sources, which have generally been assumed to get steeper at higher radio luminosities (eg. Laing and Peacock 1980) but a dependence on epoch cannot at present be ruled out (Katgert-Merkelijn et al. 1980).

The determinations of the primordial abundances of D, 3He, 4He and 7Li play a major role in building up models of Big Bang nucleosynthesis. Much progress has been made recently in that respect but there are still large uncertainties on these determinations. Although canonical Big Bang models predicting a cosmological baryonic parameter ΩB ~ 0.10 consistent with the dynamics of small groups of galaxies and three different families of neutrinos seem to be the most appropriate in accounting for these abundances, the simplest models of galactic evolution lead to discrepant comparisons concerning D and 4He. The relatively small abundance of 4He might challenge the canonical Big Bang models unless specific models of galactic evolution are invoked.

Recent discoveries have shown that magnetic activity is typical of cool stars with deep convective zones and magnetic cycles are found in slowly rotating stars like the sun. The current state of hydromagnetic dynamo theory is reviewed, and simplified models are used in an attempt to isolate the dominant nonlinear processes in stellar dynamos.

The main features of solar and stellar activity cycles are summarized, followed by a discussion of some outstanding observational problems for the future.

New observations of large scale convection on the Sun challenge the currently accepted dynamo theory of the generation of stellar magnetic field. The available evidence of the correlation between stellar activity and rotation teaches us something about the interaction of rotation with large scale convection. The question of what parameter to use to describe this correlation is discussed.

Evidence is given for convection controlling dynamo activity and the rotation of some stars.