[en] High-resolution spectroscopic data are presented on the rapidly rotating late-type stars AB Dor (HD 36705) and PZ Tel (HD 174429). Both stars show chromospheric activity, with strong Ca II K emission and a filled-in H α line, as noted previously by other workers. No apparent relationship holds between the level of H α filling and rotation phase for either star. In one observing run of a few days there was a clear anticorrelation between the strength of Ca II K emission and the photometric wave for AB Dor. There is some indication, although the data are sparse, that this also occurred in an earlier observing run. For PZ Tel, lack of data prevents any conclusion about a possible relationship between the strength of Ca II K emission and the photometric wave. The radial velocity data strongly suggest that both stars are single. (author)

[en] The Star Procyon (α CMi) was observed for 2 weeks using the Birmingham double magneto-optical filter spectrometer on the 1.9 m reflector of the South African Astronomical Observatory in 1988 January. Our analysis of these velocity data shows that the noise level in the power spectrum of the combined nightly runs is approximately 12 m² s^-2. These data were searched for the presence of small scale oscillations, but none were obviously present. On one night the surface integrated magnetic field of Procyon was measured using a rotating quarter wave plate to select alternatively opposite senses of circularly polarised light

[en] The space velocities U, V, W, for the rapidly rotating late-type stars AB Dor (HD 36705) and PZ Tel (HD 174429) are shown to be identical within the observational uncertainties with those of the Pleiades moving group (Local Association). It is suggested that these two stars are members of this group, and hence stars in the final stages of their approach to the main sequence. (author)

[en] A relation is found between peak radio luminosities measured at 8 GHz and the rotational velocity of 51 late-type F, G, and K stars (including the sun). The sample includes both single stars and active components of close binary systems, with equatorial surface velocities ranging from 1 to 100 km/s. A gyrosynchrotron source model originally developed to explain solar microwave bursts could explain the relation. The main parameter depending on rotation rate is the filling factor, i.e., the fraction of the stellar surface and corona occupied by intense magnetic fields. As the rotation speed increases, the scale size of the coronal structures emitting microwave gyrosynchrotron radiation increases, and there is a corresponding increase in the area of the surface covered by intense starspot magnetic fields. However, the peak magnetic field of the starspots probably does not increase significantly above observed sunspot values. 47 references

[en] Broadband photoelectric light curves for the RS CVn type star PZ Telescopium are presented. The photometric period is about 0.943 days. The V light curve shows radical changes in form and range over a few months and may be continuously variable. In 1982 no (B-V) change with phase was detected. However, in the first part of the 1983 observing season a change of around 0.02 magnitude was found. Also at this time, maximum light was some 0.05 magnitude above that measured previously. Preliminary spectroscopic data indicate that P2 Tel is a double lined binary whose components are of approximately equal luminosities. It is suggested that the photometric variations are due to the presence of large cooler starspots on the photosphere of one or both components

[en] High-quality radial-velocity observations of Procyon A (α CMi, F5 IV) have been obtained with the Birmingham magneto-optical filter spectrometers using the 1.9-m telescopes at SAAO (1988, 1989 and 1990) and Mt Stromlo (1989 only). These data were searched for the presence of an acoustic p-mode spectrum of oscillations. The power spectra were also studied for possible periodicities due to the presence of equifrequency spaced modes of comparable power to the background noise. While some periodicities were seen they were not reproducible in all three data sets, and thus are probably not of stellar origin. (author)

[en] We present a photometric study of the rapidly rotating star PZ Tel (HD 174429). Our analysis suggests that although the light curves show a large range in shape and amplitude, the overall variation can be interpreted with a qualitative model of just three large starspots. The lifetimes of the spots are of the order of two years or more. It is suggested that the decay of one spot resulted in the formation of a short-lived bright area on the star. Two separate interpretations of the light curves in terms of starspots are given. Both have two spots of essentially the same rotation periods on opposite hemispheres of the star, similar to the situation found on the comparable star AB Dor. The first interpretation also requires a long-lived third spot with a substantially different rotation period, indicating the presence of differential rotation on PZ Tel. (author)

[en] New photometric results are presented on the rapidly rotating late-type active star AB Dor. The rapid changes in the shape and range of the light curve noted previously by other workers are also seen in our data. Combining our observations with previously published material gives 18 light curves spanning late 1978 to early 1987. Our qualitative analysis of these data suggests that over this time AB Dor had two large, long-lived starspots. One spot was present in late 1979, and decayed almost completely over about three years. The other was present in late 1978, decayed and reappeared in late 1981. It then intensified to dominate the light curve in early 1984. The most recent light curve from 1987 January indicates a redevelopment of both spots. (author)

[en] The results are reported of a survey of 153 active-chromosphere stars made with the Parkes 64-m telescope at 5.0/8.4 GHz from 1981 to 1987. Most of the stars were observed on at least 10 separate days in order to better establish flare rate and luminosity. The sample included RS CVn and Algol-type binaries, CaII emitters with as yet unknown stellar content and AM-Her type cataclysmic variables. For some of the strongest stellar flares we measured the circular polarization at 8.4 GHz and obtained crude radio spectra involving frequencies in the range 0.843 < υ < 22 GHz. Microwave emission was detected from 70 stars on at least one occasion, with the highest detection rate of 68 per cent from the RS CVn group. The CaII stars and Algol-type binaries yielded detection rates of 44 and 30 per cent respectively. Two of the four observed AM-Her-type binaries were detected. (author)