Spectroscopic data in the visual region is described for the peculiar emission-line objects with IR-excess HD 45677, HD 87643, and GG Car. A model consisting of a central star surrounded by an equatorial disc and a dust shell is suggested.

An outline is given of the observing programme of peculiar radio stars with combination spectrum at the Asiago Observatory.

When X-ray sources in the galaxy were discovered in 1962 (Giacconi et al., 1962) it was only possible to speculate on their nature, which centered on supernova and cosmic-ray phenomena since these were the only very energetic events known. In particular, the discovery of an X-ray source associated with the Crab Nebula led to the idea that the emission might be the thermal radiation from the surface of a hot, neutron star. However, it was soon demonstrated (Bowyer et al., 1964) that a neutron star could not be responsible for the bulk of the X-radiation from the Crab, and it was not possible to exclude highly pathological conditions in otherwise ordinary stellar systems as being responsible for the X-ray sources (cf. Hayakawa and Matsuoka, 1964).

The analysis of photometric observations of the X-ray source Sco X-1 leads to the conclusion of the existence of a periodic component in the light variations of this source. For 1966–74, the results can be presented as

The photoelectric observations of some authors are shown in Figure 1, using the period. Figure 2 shows the mean light-curve of Sco X-1. The amplitude ΔB is about .

Two problems of X-ray astronomy are discussed: (1) Optical identifications of X-ray sources, and (2) Optical and X-ray observations of U Geminorum.

The optical component of the pulsating binary X-ray source Cen X-3 is identified with a faint, <V > = 13.35, heavily reddened variable star lying slightly outside the 3rd Uhuru Catalogue error box. It shows a double peaked light curve with an amplitude of about 0.12 mag. which agrees both in period and phase with the X-ray data. The shallower minimum coincides in time with the X-ray pulsar eclipse. Interpretation of the light curve leads to the conclusion that the contribution from gravity darkening dominates to a large extent the reflection effect. The estimated distance to Cen X-3 is about 8 kpc.

At the Special Astrophysical Observatory of the U.S.S.R., an experiment to detect super-rapid variability of brightness and polarization in a number of peculiar objects is being carried out. This includes the optical stars identified with X-ray sources, specifically Cyg X-1, Her X-1 and Sco X-1, as well as the so-called DC-dwarfs and some BL Lac-type objects (that is optical objects possessing a continuous spectrum). The time range of measurements varies for different objects; however as a rule, it lies within 10−5 to 10 s.

At the time of our observations no rapid and super-rapid fluctuations of radiation exceeding in amplitude 10% have been detected.

An attempt is made to detect polarization from Cyg X-1, Sco X-1 and 3C273.

Our observations of the X-ray binary V 1357 Cyg suggest that a small circular polarization increasing towards the longer wavelength exists in the light of the star.

Rapid variations with small amplitudes were detected in the light of the white dwarf EG 159 = G 29–38, a 13th magnitude star.

Multicolour linear polarization of optical radiation of the X-ray sources Sco X-1, Cyg X-2, Cyg X-1 and Her X-1 was measured at the Crimean Astrophysical Observatory in 1970–1973. These observations indicate that polarization of Sco X-1 in the ultraviolet, blue and red spectral regions appears to be variable. No statistically significant variations of polarization were found for the other three sources observed.

A model for the double system with the X-ray source Her X-1 is considered. It is supposed that the central star has a sufficiently strong magnetic field for the outflow of the matter to occur in jets. When the neutron star is in the jet the optical depth τx attributable to the X-ray emission due to Compton scattering is greater than unity and the solid angle of the emitted X-radiation is broad, ∼ 180°. In the opposite case, τx < 1, there is a narrow angle of emission and the radiation falls on to the star and is not observed on the Earth. The motion of the neutron star relative to the jet is due to nonsynchronization between the orbital motion and rotation of the central star. If the duration of the whole orbit around the central star is 35 days and the dimension of the jet is about 1/3 of the orbit, then such a model explains features connected with the 35-day cycle.

This note discusses the properties of the Crab pulsar assuming that it is moving in the gravitational field of the second component.

In order to find out the physical nature of galactic X-ray sources, data on the variability of 24 sources during 1964–1971 have been investigated. The fluxes of 9 sources are found to be increasing to the maximum value (for several months) and then slowly decreasing (for 3 years). These 9 sources have been related by us to the class of X-ray Novae. The X-ray Nova synthetic light curve has been drawn from data of the fluxes of 9 discovered Novae. Assumptions have been made on the physical nature of the X-ray Novae. Between the flares the X-ray Novae may be weak X-ray sources with a luminosity of about 1034 erg s−1. During the flares the luminosity increases to about 1038 erg s−1. The number of X-ray sources in the Galaxy is about 103–104. The object of the optical identification may be a dwarf star of no earlier spectral class than F.

RR Lyrae stars: Normalized period-frequency diagrams are discussed, see Table I and Figure 1. Two ‘standard’ period-frequency relations were derived: one for − 1.17 and the other for − 1.72. The peculiarity of the diagrams for some clusters is pointed out. Various metallicity criteria are discussed together with other features of globular clusters. Some unexplained anomalies are found.

W Virginis stars: Properties of these stars are discussed. They too seem not to form a homogeneous group. The lack of accurate observations is stressed.

The present state of knowledge of the red variables in the halo and globular clusters is summarized. Techniques for their discovery are described. The correlations between their properties and those of the globular clusters to which they belong are discussed. The evolutionary state of the variables is considered and stars are assigned tentatively to the first or second ascent of the giant branch or to the excursions from the asymptotic giant branch resulting from instabilities in the He-burning shell.

The assumption that a recognizable type of variable represents a unique type of star leads to the conclusions that the bulk of the stars in the central bulge of the Galaxy are more metal-rich than 47 Tuc and that the Large Magellanic Cloud contains an old, moderately metal-deficient population similar to that represented by clusters such as 47 Tuc in the Galaxy while the Small Magellanic Cloud does not.

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

The dependence of the period changes of RR Lyrae stars, especially in globular clusters, on the evolutionary track through the instability strip has still found no explanation. The present paper is an attempt to give a review of the observed phenomena.

Observations of some RR Lyrae stars with varying periods and shapes of the light curves were discussed. These are:

TU Com (Ureche, V., 1965)

WY Dra (Chis, D., Chis, G. H., and Mihoc, I. (1974))

SW Psc (Ureche, V. (1971a, b))

Spectra of over 100 stars classed as type II Cepheids of short period (BL Her-type) or long period (W Vir-type) or RV Tauri stars have been obtained. A range of metallic line strength and hence presumably metal abundance is present at all periods, those having weak lines being found especially in the globular clusters and the central bulge of the Galaxy. Stars which have enhanced Carbon molecular features (CH, CN and sometimes C2) occur at all periods but are probably distributed differently in space from the other stars.