A considerable amount of observational interest in short timescale phenomena has developed in optical astronomy in recent years. This interest has stemmed primarily from search efforts directed towards optical pulsars and the study of rapid fluctuations in cataclysmic variable and flare stars. Such studies have been made feasible by the development of the necessary photon pulse-counting technology required for rapid data sampling.

The eighth magnitude star HD 101065 has an extremely peculiar spectrum dominated by very numerous lines of the rare earths (with only the one possible exception of ytterbium, whose lines are difficult to identify). Besides the rare earths only strontium, yttrium and zirconium could be found in substantial quantities, while calcium though present is highly underabundant. The most surprising feature of the star is the absence of iron peak elements in its spectrum.

The Schmidt camera is conceptually elegant and has a remarkable performance, but it suffers from several practical disadvantages. Two of these concern us here. First, there are very few craftsmen who are competent to make the aspheric correcting plate of the Schmidt camera compared with the number of those competent to make spherical surfaces of high quality.

On 1971 January 24 a 3B flare at 18° N., 49° W. was associated with the acceleration of protons to relativistic energies; it was one of the rare events recorded by ground-level neutron monitors. Excellent radio coverage was obtained with single-frequency radiometers in the range 1000-9400 MHz, and at Culgoora with the 8-8000 MHz spectrograph and the 80 MHz radioheliograph. At the Earth relativistic protons and electrons arrived very promptly from the flare, whose site was near the foot of the nominal interplanetary field line which connects to the Earth.

It is well known that the wings of the solar sodium D-lines cannot be predicted successfully using present line-broadening theories and elemental abundances derived from an equivalent-width analysis of the weak lines. By far the most important cause of broadening of the D-lines is collision broadening by neutral hydrogen.

Recent spectroscopic investigations of OB stars by Walborn (1970,1971a) have revealed the existence of OB stars with anomalous nitrogen and carbon spectra. In particular, two groups of stars were identified — those with strong nitrogen features and accompanying weak carbon-oxygen blends (called ON stars), and those with weak nitrogen features and strong carbon features (called OC stars). These groups bear a striking resemblance to the WN, WC dichotomy exhibited by the Wolf Rayet stars and is suggestive that a common process may be responsible for both phenomena.

Type I storms generally occur in association with large sun-spots and the radiation is usually circularly polarized. Statistically it has been found that the sense of polarization, right-hand (RH) or left-hand (LH), usually corresponds to the ordinary magneto-ionic mode in the field of the dominant spot of the active region; when a following spot dominates, the polarization tends to be determined by this spot rather than by the leading field. One-dimensional position measurements show that the type I sources are usually not radially above the active region but are displaced by a few minutes of arc. The source sizes are about l′.2 to 4′.5 at 169 MHz and the sources frequently contain double, multiple or bipolar structure at 80 and 160 MHz.

It is generally agreed that T-Tauri stars are very young stars of solar mass which are still engaged in the process of gravitational contraction toward the main sequence (Ambartzumian, Herbig).

In calculating models of stellar interiors convection is almost always treated by assuming that it is present if and only if the Schwarzschild criterion is satisfied. It seems possible that this oversimplifies the actual situation. In particular convective motions may overshoot beyond the formal boundary of the convective core, as given by the Schwarzschild criterion. The principal result of such overshooting would be the mixing of additional material into the core. This sort of additional mixing has been considered by Maeder (1974) and by Prather and Demarque (1974) in relation to the evolution of stars away from the main sequence in old open clusters.

Type I radio bursts, as distinct from the continuum component frequently associated with them in a solar storm, are short-lived (0.1-2 s), narrow-band (2-10 MHz) bursts with frequency drift rates from 0 to 20 MHz s−1. They come from coronal regions close to the corresponding plasma levels, i.e. the frequency of radiation ω is close to the local plasma frequency ωp. They occur more frequently at frequencies above ~100 MHz but at times extend to frequencies as low as 20 MHz. Their observed equivalent brightness temperatures are usually about 109 K but they can reach 1011 K or higher. Except for an average decrease in polarization towards the limb and except for initial stages of a storm, type I bursts are strongly circularly polarized (approaching 100 per cent) in the sense of the O-mode.

Several methods are available for sensitizing photographic plates, each with its own disadvantage. Pre-flashing greatly increases the plate background and is useful only for enhancing the plate’s response to light levels near the plate’s threshold. Baking and (or) evacuating enhance the plate’s response at all light levels and leave a slightly higher background. Unfortunately all of these methods produce plates with a short shelf life after sensitization.

The conditions for the equality of the line source functions associated with fine structure transitions in a multilevel atom have been examined by several authors. The equality or otherwise of the source functions depends largely on the value of the fine structure collision rate, equality occurring when this rate becomes infinitely large. The fact that the theoretical collision rates between fine structure levels of alkali atoms are so large suggests the possibility of simplifying complicated multilevel atom transfer problems by the consideration of the limit of an infinite fine structure collision rate.

In recent years there have been numerous investigations of the helium shell-burning evolution of low-mass stars, and it was in such studies that Schwarzschild and Härm and Weigert independently discovered the thermal instability phenomenon. In the case of stars with hydrogen-rich envelopes, its reality has been amply confirmed. On the other hand, studies have also been made of the shell-burning in pure helium stars (many for comparison with the nuclei of planetary nebulae), and here the situation is far less clear. Some investigators have found the instability, while others have not. Paczyński has drawn attention to the fact that in all cases where thermal pulses have been reported for pure helium stars, the helium shell-source was treated as an abundance discontinuity, while in all cases where a detailed abundance profile was used, there was no evidence of pulses. He suggests therefore that the shells in pure helium stars are stable. We wish to report a calculation for a 0.8 ɱ⊙ pure helium star, with a detailed shell abundance profile, in which a single thermal pulse was encountered at the end of the shell-burning evolution.

That the parent masses of white dwarf (WD) stars can exceed the Chandrasekhar limit of approximately 1.2 can be seen from star clusters that have turn-off points in excess of this mass and still contain WD. Auer and Woolf argued that WD in the Hyades and Pleiades is evidence that stars with masses larger than 2.5 can become WD. Sandage and Jones have used the luminosity function to compute the number of WD expected in several clusters. Jones estimated that the brighter of the two WD sequences arises from stars of mass greater than 1-9 Schwarzschild, for example, has stressed the importance of a knowledge of the resulting mass-loss. Deutsch has discussed mass-loss from red giants and Faulkner has summarized the relationship between the planetary nebulae and the WD. Nevertheless, the role of WD formation in the enrichment of the interstellar medium and the relationship between WD and their parent stars is unclear.

Important observations of X-ray sources and searches for the optical counterparts of X-ray and radio pulsars require a capability of detecting and analysing light variations with a time scale of milliseconds. X-ray sources in binary star systems are expected to be collapsed objects – neutron stars or black holes (Peterson 1973) – and are expected to produce light variations. In the case of a neutron star, pulses with the same period as the rotation period of the neutron star would be produced, and such have been observed from Cen X-3 (schreier et al. 1972) in the X-ray, and from Her X-1 (Middleditch and Nelson 1973) and the Crab Nebula pulsar (Cocke et al. 1969) in the X-ray optical.

On the basis of (R — I) colours it has been suggested that the N stars (the cool carbon stars) occupy a very restricted region in the Mb01 — log Te diagram (Te = 3300 to 3500 K) Mb01 ~ —3), falling on the normal giant sequence, but hotter than the M variables. This appeared somewhat puzzling in view of the variability of many of the carbon stars and their large range of periods, which suggested that the N stars ought perhaps to have similar temperatures to the variable M stars. In order to compare the continua of the M stars and N stars within the range of the R and I filters, and also to determine the continuum between the molecular bands, photometric observations were made of 20 M and N stars at carefully chosen wavelengths with 30Å resolution.

Recently E. M. Burbidge and P. A. Strittmatter1 have found that the DB-like star G61-29 has broad He emission lines suggesting a rapid rotation. The purpose of this paper is to suggest a further white dwarf candidate for rapid rotation.

Current evolutionary theory indicates that evolving stars in globular clusters arrive on the horizontal branch with ~30% less mass than they had on the main sequence. If, as seems likely, this mass loss results from the outflow of unprocessed material at the stellar surface during the giant stage, and if the ejected mass were retained within the cluster between successive sweeps through the galactic plane (~108 yr), sufficient hydrogen (100-2000 M⊙ should accumulate for detection. Radio searches, however, have failed to find evidence for either neutral or ionized gas. The hydrogen mass upper limits obtained by various workers are: Hills and Klein (1973) ionized H, 3.8 cm, <20-200 M⊙; Knapp, Rose and Kerr (1973) neutral H, 21 cm, <1-20 M⊙; Conklin and Kimble (1974) neutral H, 21 cm, <0.7-1.4 M⊙.

We have extended the search into the optical region and have also calculated time-independent gas flow models to try to resolve this anomaly.

Type I storms are the most frequently observed solar phenomena at metre and decimetre wavelengths. Since the first identification of the emission of this type with a large sunspot group a great many type I storms have been recorded with radio-spectrographs, polarimeters and interferometers (see, for example, Wild, Smerd and Weiss, Kundu, Wild). Nevertheless, we can offer no satisfactory answers to the most fundamental questions about type I storms: ‘What kind of disturbances supply energy to a localized coronal region to maintain the storm activity for up to several days?’; ‘What is the emission mechanism responsible for the peculiar features observed in type I storms?’.

One of the quantities usually required when solving the equation of radiative transfer is the intensity of radiation emerging from the surface of the medium under consideration. For multi-dimensional situations however, the methods presented to date have been numerical, and these first calculate the so-called source function Sv (r, Ω) as a function of position r, angle Ω and frequency v. This is generally the most difficult part of the exercise since an integro-difierential equation must be solved. The emergent intensity is then determined by solving a relatively simple first order differential equation by any of the well known numerical integration schemes. However, if the emergent intensity is required at a large number of angles, frequencies, and positions on the surface of the medium, and this is usually the case, the amount of computing needed may be considerable.