The Earth atmospheric pressure fluctuations in the 5-min range of periods are analysed and their influence on observations of solar 5-min oscillations are briefly discussed. New series of observations confirmed the oscillations of the Sun with period of 160.010 min.

The earlier attempts to detect the lines of heavy elements (Pb, U, Th and others) in the spectra of Ap-stars from the ground-based observations are briefly discussed. UV observations of Ap-stars with the ultraviolet telescope aboard ASTRON space station are described. The reduction of these data is considered. Three spectral regions containing the lines PbIIλ2203.53, UIIλ2556.19 and ThIIλ2368.05 were analyzed by the method of synthetic spectra. It has been shown that relatively cool Ap-star 73 Dra (Teff = 8l50 K) has a great overabundance (≥ 103ε⊙) of heavy elements U, Th, Pb and W.

Observations of the far-UV spectrum (1300–1800 å) of the sky background at different galactic latitudes are presented. The measurements were made in deep space, at distances up to 2 × 105 km from the Earth with the photoelectric spectrometer (“Galaktika”) on board the “Prognoz-6” satellite. The highly elongated orbit of the satellite permitted corrections for scattered Lα-light. The contribution of stars was eliminated using fluxes measured in the TD-I and OAO-2 experiments.

All evidence of the solar origin of 160-min period oscillations is collected, and the present state of observations of this oscillation in optical and radio-ranges is considered. The main results are summarized: (a) the 160-min oscillation was observed in 1981 as well as before, (b) an attempt to find a nonradial component with l = 2 has failed, (c) the intensity and circular polarization of radioemission show with statistical significance the presence of this 160-min periodicity.

Numerical solutions of the general time-dependent gas-dynamical equations in linear adiabatic approximation are given for initial conditions imitating: (a) a central perturbation, (b) a boundary perturbation (in the convective envelope), and (c) a ‘shrinking’ of the Sun as a whole. For a variety of models of the Sun it is found that at the surface the radial component vr of velocity is much greater than the tangential component vt, and that the period T of stationary oscillations does not exceed 131m. The appearance at the surface of a g mode with period 160m is found to be improbable.

With the initial conditions adopted, a propagating wave is produced which is reflected successively from the centre to the periphery and back, producing 5-min oscillations at the surface of the Sun. Expansion of this wave into separate modes leads to a power spectrum qualitatively similar to that observed.

Oscillations of the Sun with the period of 160m first observed in Crimea in 1974 and described in a set of papers by Kotov, Severny and Tsap (Severny et al. 1976, 1978; Kotov et al. 1978) were observed also by Brookes et al. (1976) and have been afterwards observed during the last three years in Stanford (Scherrer et al. 1979) and Kitt Peak (Snider et al. 1978). This fact excludes possible instrumental origin of the effect. Moreover, the phase coherence (after elimination of integer number of 160m-periods) between these four observatories makes the assumption of Earth atmospheric origin of the oscillations (Fossat and Grec 1978) very unlikely. Besides that, (1) the dependence of amplitude of oscillations on the phase of solar rotation and (2) slow, synchronous (at Crimea and Stanford) drift of the phase of maximum from year to year, pointing to a true period slightly higher 160m (160m 0.1), make the “telluric hypothesis” of the effect completely inconsistent.

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

It is observed that the change of the net magnetic flux associated with flares can exceed 1017 Mx/s, which corresponds according to Maxwell's equation to the e.m.f. ∼ 109 V which is specific for the high energy protons generated in flares. It is shown that this value of e.m.f. can hardly be compensated by e.m.f. of inductance which should appear due to the actually measured motions in a flare generating active region. The values of electric field strength thus found, together with measured values of electric current density (from rotH), leads to an electric conductivity which is 103 times smaller than usually adopted.

The simultaneous measurements of longitudinal magnetic fields in lines λ5250 and λ6103, the line of sight velocities and intensities in these lines at some fixed point (area 2″.3 × 4″.5) within the moderately strong (∼ 100 G) areas of solar magnetic fields were examined to find the possible fluctuations of m.f. with time. No fluctuations were found which cannot be correlated with the simultaneously measured seeing conditions such as contrast, image excursions and scintillations for characteristic periods less than 5m. The possibility of ∼ 5m oscillations of magnetic fields correlated with the well known sight-line velocity oscillations is pointed out.

During the period of strong flare activity of the active center McMath No. 9740, from October 25 to November 2, 1968, 32 magnetograph records of longitudinal H∥ and 20 of transverse fields, H⊥, were obtained for this center with the Crimean magnetograph. Sometimes 5–7 daily records were made. Hα and K spectroheliograms, Hα cine film and routine determinations of sunspot magnetic fields were also obtained frequently. However the most important point is that all these optical observations were accompanied by simultaneous and continuous measurements of intensity and polarization of radio emission from this active center at a wavelength of 3 cm, recorded with the aid of the big 22-m radiotelescope of the Crimean Observatory (the resolution is 8′ for this wavelength), (Erushev and Zvetkov, 1970).

In an attempt to summarize the present knowledge on the general magnetic field (gmf) of the Sun we pointed out the fine structure and the statistical nature of the gmf as one of its most important properties. The dipole-like behaviour of the mean polar field strengths is combined sometimes (since 1964) with a bias of the S-polarity flux for both poles. Highly uneven distribution of gmf with latitude and longitude, the disappearance of gmf at the South pole for months, and short period, almost synchronous at both poles, variations in the sign of gmf are pointed out. The fluctuations with time of the mean magnetic field of the Sun seen as a star (as well as mf at different latitudes) shows periodicity connected with the rotation of the Sun and very close agreement with the fluctuations of the interplanetary field (sector structure). The effect of faster rotation of N-polarities as compared with S-polarities as well as the bias of mean solar as well as interplanetary S-polarity fields are also pointed out. The possibility of short time-scale (hours) intrinsic changes in the local pattern of gmf is demonstrated.

1. (1) The minimum measured brightness of the night sky (in the visual region) is about 100 stars of the 10th magnitude per square degree near the galactic poles.

2. (2) The ratio of fluxes in the ultraviolet (2300–3000 Å) and visual regions is approximately in agreement with expected theoretical data based on the models of stellar atmospheres for spectral classes B0 to G5 and on the distribution of stars of the different spectral classes over the sky.

3. (3) The nature of possible deviations (theory minus observation) is discussed.

As measured from space, the contribution of one moderate flare to the emission spectrum of the Sun in the far-ultraviolet (304 Å, Lyman continuum, etc.) is comparable with the emission of the whole undisturbed solar disc.

Up to the present time the technical possibilities of space research were not quite adequate for obtaining the ultraviolet spectrum of flares that occupy only a small portion (less than 10″ of arc) of the solar disk. Up to now all observations have been made in integrated sunlight. The importance of the knowledge of UV spectrum of flares is hardly necessary to emphasize. For example we just could mention that if ultraviolet spectra were available for a flare say from 850 Å up to 2000 Å, we would be able to estimate such extremely important parameters as the number of hydrogen atoms N1 in the first quantum state (by using L-α, L-β, etc.), electronic temperature and density (from Lyman continuum) and other physical parameters of a flare which at the present time we try to derive by different indirect and inadequate methods. Several resonance (ultimate) lines are concentrated in this spectral interval and their careful examination in flares can bring additional important information about conditions prevailing in flares and in the underlying chromosphere. The same applies of course to the whole UV spectrum below 800 Å, and in particular to the resonance lines of HeI (λ 512 Å) and HeII (λ 304 Å), as well as to a number of lines of highly ionized atoms.

The difference between abundances of such elements as Li, Be, B in active regions on the Sun and in the undisturbed atmosphere, if it exists at all, could be considered a very important indication on the possible nuclear reaction in active regions and on the rate of diffusion of elements inside magnetic fields of sunspots. One of the authors from the considerations of λ6707 Å has an estimated (Dubov, 1955) Li abundance in the undisturbed solar atmosphere as log N(Li) = 0·93 (taking log N(H) = 12·0), which is close to the later results (Goldberg et al., 1960). In sunspots we can expect that the first doublet λ6103 of Li diffuse series appears. The preliminary consideration (Dubov, 1964) showed that Li abundance in sunspots could be several times larger than the above estimate for the undisturbed atmosphere. This result forced us to consider as carefully as possible the region of λ6103 in eight spectra of four sunspots taken with the aid of the echelle-grating spectrograph of the Crimean observatory with a dispersion of 1 Å/mm and measured resolving power 0·03 Å. The consideration of the Zeeman pattern of this line shows that at the field strengths we had in sunspots (2000–3000 gs) the line should be diffuse band with width ~0·23 Å, and taking into account the broadening of the line the halfwidth of the line has not to be smaller than 0·25 Å.

The new big 22-m radio-telescope of Crimean Observatory shown on Figure 1 appeared to be of very good quality: for radio emission at λ = 8 mm the antenna beam is 1′.6, the efficiency ≅0·4, and the error of automatic pointing (guiding) does not exceed ±20″. A Dicke type radiometer was used as receiver possessing a sensitivity ≃2°K at the time constant τ = 1 sec, and pass-band ~30 MHz. The error in the contrast determination does not exceed ±0·5% of the level nearly corresponding to that of the quiet Sun. The scanning of the solar image is made in right ascension with velocity 0·5 sec in sec of time, the distance between successive scans in δ being 1′.5. An example of a single scan is shown in Figure 2, where the scan through Jupiter (for the determination of antenna beam) is also presented (for description see Moiseev, 1968).

With the image of the Sun held fixed, time variations of solar magnetic field were recorded simultaneously in two lines (λ5250 and λ6103) with the aid of double magnetograph (for the description see Severny, 1966, examples of such records are on Figures 1 and 2). The resolution was 2″.5 × 4″.5. The records in both lines λ5250 and λ6103 covering a time interval of about 1 hour show oscillations with the period ∼7·4min and amplitudes 10–20 gauss for moderately active region (full lines on the top of Figure 2). The oscillations of the magnetic field at both levels (the heights of λ 5250 and λ6103 differ by 260 km) are sometimes synchronous but now and then phase shift appears. For quiet regions near the centre of the disk the oscillations with the period ∼ 9·0 min and amplitudes less than 5 gauss are recorded and presented in Figure 1 (full line). These 7–9 min oscillations are probably sometimes damped or interrupted by more short-period fluctuations (with the mean period 80s) of smaller amplitude, but these last oscillations could be due to the fluctuations of seeing.

The discovery of magnetic fields on the Sun made by George Ellery Hale in 1908 (1) is undoubtedly one of the most outstanding events in the astronomy of this century. It is well worth mentioning that the geomagnetic field was a unique example of cosmical magnetic fields before this discovery. But during the last two decades, it became known through Babcock’s work (2) that numerous stars have also magnetic fields amounting to several thousand gauss on the average over the star’s surface and thus considerably exceeding solar magnetic fields concentrated mainly in sunspots.