The most widely used indicator of the stellar magnetic activity is the flux in the CaII K-line core (K-index) (Baliunas and Vaughan, 1985). The K-index data have also been used for measuring the rotation of stars. But using the method for the Sun gives different results (Keil and Worden, 1984; Singh and Livingston, 1987). The reason for the observed differences, besides those indicated by Singh and Livingston, may be the character of the distribution of active regions. This study is based on observations made at Tashkent Astronomical Observatory and the data published in SGD for solar cycle 21. We study the longitudional distribution of sunspots and plages. Some intervals of active longitudes (IAL) were selected and the evolution of them was studied. Active regions were found to concentrate in certain longitude intervals which are in nearly rigid rotation. Fig. 1 shows the longitudinal distribution of sunspots areas for 1983-84, as an example.

We study a new indirect index of solar activity – the Intensity of Luminescence of Cave Flowstone Microzones. This index correlates directly with the solar activity. Using a time series of the index with resolution 4-5 pixels/year we study some of the statistical properties of the solar activity cycle during 28 prolonged minima and 21 prolonged maxima.

During September 24-29, 1987, the longitudinal magnetic fields of a decaying active region (AR 4855) were observed almost continuously at Big Bear and Huairou Solar Observatories. The target consisted of an αp sunspot and surrounding enhanced network. We achieved a 75-hour coverage with 4 night-time gaps of six to eight hours. The images were then combined to made a continuous movie.

The BBSO Videomagnetograph (VMG) System was originally developed by Leighton and Smithson and has been improved in recent years (Zirin, 1985). This system has made it possible to study very weak photospheric magnetic structures.

In this contribution, preliminary results of the main component analysis of Bartels diagram of time series of daily values of sunspot group numbers for solar cycles 18, 19 and 20 are presented. The results obtained suggest that the most significant feature in the longitudinal distribution of sunspot activity is the existence of preferred solar hemispheres alternating with a mean period of 2.5 Bartels rotations.

In order to test the validity of the usual neglect of pressure line shifts in investigations of Fe I line asymmetries and shifts, we calculated synthetic line bisectors and shifts of 96 moderate and weak photospheric lines, taking into account both hydrogen- and electron-impact shifts and neglecting the velocity fields. Absolute pressure line shifts obtained are less than or appr. equal to 50 m/s and the largest relative shifts along the bisectors are about 40 m/s. We found pronounced dependences of both shifts and bisectors on the energy of the upper level in transitions and on the transition array.

The rotation of large scale solar magnetic field patterns was studied using quiescent filaments and low temperature regions observed at 37 GHz as tracers.

A large set of observations of the Sun at 37 GHz is analysed. An association of 99% is found between the regions of brightness temperature depression and the magnetic field inversion lines. Observations indicate a possible existence of “giant cells” with duration of 1-2 years and a longitudinal extension up to 90°.

We are now at both the maximum of the solar activity cycle and at the most populated part of the saros. I discuss the solar corona over the recent saros and its changes with the solar activity cycle. We consider the scientific value of eclipse studies and how they relate to other ongoing coronal studies on the sun and other stars.

The rotation period of the Sun after it reached ZAMS is estimated from the present rotation rate, average X-ray emission flux and average calcium emission flux. Taking into account all existing uncertainties it is concluded that this initial period was within the range 1–9 days, with the most probable value 2–3 days. Possible influence of the solar activity on evolution of life on the Earth is briefly discussed.

We present a sequence of three Doppler images of the spotted RS CVn star UX Arietis obtained over a 5-month interval from August 1986 through January 1987. The spot distribution was quite complex and consisted of a large stable polar spot, a spot near the equator, and several other spots at intermediate positive and negative latitudes. The time intervals between successive images were small enough that we were able to reliably track the evolution of the spot distribution, measuring accurate longitudes, latitudes, and areas of the major spots, as well as their drift rates in longitude and latitude. The longitudinal drifts of spot features at equatorial, intermediate, and high latitudes yielded an accurate measurement of differential rotation. We find that the spotted primary of UX Arietis is indeed rotating differentially and in the sense opposite to that of the Sun, i.e. the poles rotate faster than the equator. The equator is synchronized to the orbital angular velocity, and the angular velocity increases towards either pole. The angular velocity distribution can be expressed as Ω(°/day) = −55.91 + 1.09(±0.09) sin2∅, where ∅ is the latitude. The amount of differential rotation, parameterized as the ratio of the difference between the equatorial and polar angular velocities to the equatorial angular velocity, is then α = −0.020(±0.002), as compared to a value of α = +0.2 for the Sun.

We intend to analyze the reliability of surface imaging of stars based on high resolution spectroscopy and the technique of inverse problem solution. Both astrophysical and mathematical aspects including different regularization methods are reviewed. The influence of the different factors on the resulting map is discussed and it is shown that the simultaneous use of different kinds of observational data (spectroscopy, photometry, polarimetry etc.) is very useful in providing additional constraints for the solution. The recent results in the surface imaging of Cp- and late-type stars show the way for further progress: the use of more adequate mathematical description of the stellar atmosphere and the simultaneous consideration of various surface inhomogeneities.

We present maps of the temperature distribution on the spotted RS CVn-type binary EI Eri (HD 26337), obtained by means of the surface imaging technique described in the Colloquium (Piskunov, 1991). Images were calculated for two separate lines for two epochs of observation. For one epoch we also calculated an image using a blend of several lines. The reliability of the maps is confirmed by comparing the simultaneous photometric observations with the light curves calculated from the temperature maps.

We present the first magnetic detections using Zeeman-Doppler Imaging (ZDI) in the two bright rapidly rotating RS CVn systems HR 1099 and σ2CrB, and discuss their compatibility with various recent results on magnetic activity in cool stars.

Several groups at this meeting are presenting maps of the spatial distribution of either brightness or effective temperature in the photospheres of rapidly-rotating, late-type stars. It is generally believed that structure seen in these maps traces the magnetic topology, in analogy with the Sun. We expect the structure of the outer atmospheres (i.e., chromosphere and corona) of these stars to be even more directly tied to the magnetic topology; the magnetic structure is three-dimensional. In order to probe the radial dimension of stellar atmospheres, we need to combine maps of the spatial distribution of emission from chromospheres and coronae with these detailed photospheric maps.

Along with collaborators at Armagh, Catania, Boulder, Paris, Helsinki, and Stony Brook, I have been obtaining high-dispersion ultraviolet spectra of several rapidly-rotating, late-type stars using the IUE spacecraft. I discuss results for two stars, El Eridani and HD 199178, for which photospheric maps are presented elsewhere at this conference.

The presence of photometric anomalies in broad band colours produced by chromospheric activity was first suggested by Campbell (1984). He defined the colour anomaly δ(B–V)V–K as the deviation from the mean relation (B–V)–(V–K) for Hyades dwarfs, and found this anomaly correlated well with several activity indicators.

Since the work of Campbell, several authors have discussed the relation between activity and colour anomalies, obtaining diverging results. This discussion is relevant because long baseline photometric colours are the most reliable temperature indicators, and the presence of such anomalies implies that no consistent temperature scales can be obtained for stars with different activity levels. These topics have been recently reviewed by Soderblom (1989).

Evolved stars tell us a great deal about dynamos. The granulation boundary shows us where solar-type convection begins. Since activity indicators also start at this boundary, it is a good bet that solar-type convection is an integral part of dynamo activity for all stars. The rotation boundary tells us where the magnetic fields of dynamos become effective in dissipating angular momentum, and rotation beyond the boundary tells us the limiting value needed for a dynamo to function. The observed uniqueness of rotation rates after the rotation boundary is crossed can be understood through the rotostat hypothesis. Quite apart from the reason for the unique rotation rate, its existence can be used to show that magnetic activity of giants is concentrated to the equatorial latitudes, as it is in the solar case. The coronal boundary in the H-R diagram is probably nothing more than a map of where rotation becomes too low to sustain dynamo activity.

The boundary between Ap-type magnetic fields and the magnetic fields of solar-type stars occurs near Te ~ 7000K, about where deep envelope convection develops in main sequence stars. This seems natural for solar-type stars, in which the field is generated by the convection zone. However, among magnetic Ap stars the frequency of occurrence declines from about 10% of all A stars near A0 to about 1% near F0. It is not clear what produces this decline in frequency, but the convection zone is probably not responsible. In fact, it seems likely that if global fossil fields occur in main sequence F stars, such fields should be detectable even if the stars having them are not chemically peculiar.

A code for Doppler mapping of the distribution of chemical elements on stellar surfaces (Goncharskij et al., 1977, 1982) has been used during the past decade to make maps for several CP-stars. The code is based on Tikhonov’s method of solution of so-called ill-posed inverse problems and on an analytical expression of local line profiles in the form of the Milne-Eddington solution of the radiative transfer equation. This code takes into account the atmospheric model of the star through an assumed central depth of very strong and saturated lines, and through limb-darkening coefficients. As a solution one gets local line profiles and hence local equivalent widths.

A hot region with an increase of effective temperature of 700 K was found on the surface of Si-star CU Vir, based on the analysis of the available photometric and spectroscopic observations. This hot region is located near the phase of negative magnetic extremum and can explain both hydrogen line and infrared light variations.

Spottedness, as evidenced by photometric variability in 277 late-type binary and single stars, is found to occur when the Rossby number is less than about 2/3. This holds true when the convective turnover time versus B–V relation of Gilliland is used for dwarfs and also for subgiants and giants if their turnover times are twice and four times longer, respectively, than for dwarfs. Differential rotation is found correlated with rotation period (rapidly rotating stars approaching solid-body rotation) and also with lobe-filling factor (the differential rotation coefficient k is 2.5 times larger for F = 0 than F = 1). Also reviewed are latitude extent of spottedness, latitude drift during a solar-type cycle, sector structure and preferential longitudes, starspot lifetimes, and the many observational manifestations of magnetic cycles.