Aims. We have obtained high-resolution spectroscopy, optical interferometry, and long-term broad band photometry of the ellipsoidal primary of the RS CVn-type binary system ζ And. These observations are used to obtain fundamental stellar parameters and to study surface structures and their temporal evolution. Methods. Temperature maps of the stellar surface were obtained from high-resolution spectra with Doppler imaging techniques. These spectra were also used to investigate the chromospheric activity using the Hα line and to correlate it with the photospheric activity. The possible cyclicity in the spot activity was investigated from the long-term broad band photometry. Optical interferometry was obtained during the same time period as the high-resolution spectra. These observations were used to derive the size and fundamental parameters of ζ And. Results. Based on the optical interferometry the apparent limb darkened diameter of ζ And is 2.55 ± 0.09 mas using a uniform disk fit. The expected ∼4% maximum difference between the long and short axes of the ellipsoidal stellar surface cannot be confirmed from the current data which have 4% errors. The Hipparcos distance and the limb-darkened diameter obtained with a uniform disk fit give stellar radius of 15.9 ± 0.8 R� , and combined with bolometric luminosity, it implies an effective temperature of 4665 ± 140 K. The temperature maps obtained from Doppler imaging show a strong belt of equatorial spots and hints of a cool polar cap. The equatorial spots show a concentration around the phase 0.75, i.e., 0.25 in phase from the secondary, and another concentration spans the phases 0.0‐0.4. This spot configuration is reminiscent of the one seen in the earlier published temperature maps of ζ And. Investigation of the Hα line reveals both prominences and cool clouds in the chromosphere. These features do not seem to have a clearly preferred location in the binary reference frame, nor are they strongly associated with the cool photospheric spots. The investigation of the long-term photometry spanning 12 years shows hints of a spot activity cycle, which is also implied by the Doppler images, but the cycle length cannot be reliably determined from the current data.

In this study, we present simultaneous low-resolution longitudinal magnetic field measurements and high-resolution spectroscopic observations of the cool single giant FK Com. The variation of the magnetic field over the rotational period of 2.4 d is compared with the star-spot location obtained using Doppler imaging techniques, V-band photometry and V - I colours. The chromospheric activity is studied simultaneously with the photospheric activity using high-resolution observations of the H alpha, H beta and H gamma line profiles. Both the maximum (272 +/- 24 G) and minimum (60 +/- 17 G) in the mean longitudinal magnetic field, < B(z)>, are detected close to the phases where cool spots appear on the stellar surface. A possible explanation for such a behaviour is that the active regions at the two longitudes separated by 0.2 in phase have opposite polarities.

We present results from the 1996 Multi-Site Continuous Spectroscopy (MUSICOS) campaign on the T Tauri star SU Aurigae. We find a 2.7-d periodicity in the HeI (587.6 nm) line, and somewhat longer, less well-pronounced periodicities in the Balmer lines and in Na D. Our observations support the suggestion that the wind and infall signatures are out of phase on SU Aur. We present Doppler images of SU Aur that have been obtained from least-squares deconvolved profiles. Images taken about one rotation apart show only limited overlap, in particular at low latitudes. This is due in part to limitations in signal-to-noise ratio, and in part to line-profile deformations that arise from short-lived and/or non-surface features. The agreement at high latitudes is better and suggests that at least some longer-lived features are present. The analysis of Stokes V profiles yields a marginal magnetic field detection during one of the phases.

The question is answered whether dynamo-generated magnetic fields are able to produce such quadrupole terms in the gravity potential which can explain the observed cyclic orbital variation of RS CVn stars. We start with spherical dynamo models with outer convection zones but without any differential rotation, i.e. with alpha(2)-dynamos which are known as nonoscillating. With the known anisotropic alpha-tensor of rapidly rotating stars the magnetic modes with the lowest dynamo numbers are nonaxisymmetric with a slow azimuthal drift. We also find, however, stable (i.e. with the lowest dynamo number) axisymmetric oscillating modes but only for a very special, highly inhomogeneous alpha-tensor. The dynamo model is a linear one with an arbitrary field amplitude which can be scaled in order to reproduce the observations. The star proves to be as prolate during the maximum of the toroidal field energy and it proves to be as oblate during the maximum of the poloidal field energy. In the time average the influence of the toroidal field dominates and the star is slightly prolate. From the computed temporal variations of the gravitation quadrupole moment a magnetic field of more than 10(5) G is found in order to produce the period modulation of order 10(-5) which has been observed.

We study the dynamics of magnetic flux tubes in young stars with masses between 0.4 M-circle dot and 1.7 M-circle dot and for rotation rates between 0.25 Omega(circle dot) and 63 Omega(circle dot). The resulting latitudinal emergence patterns at the stellar surface are compared with observed distributions of starspots in stellar latitude. The stellar models considered cover the range of evolutionary stages from shortly after the Hayashi phase down to the ZAMS, i.e. from the classical and weak-line T Tauri stars to the alpha-Persei stars. We use numerical simulations to follow the evolution of magnetic flux tubes from their origin at the bottom of the convection zone up to near-surface layers. We find a strong increase of emergence latitude with increasing rotation rate, a moderate decrease with increasing stellar mass, and a stronger decrease with stellar age. At very early evolutionary stages, when the central radiative zone is still quite small, we find magnetic flux emergence both in low latitudes as well as in the polar areas. High-latitude emergence is predicted in slightly more evolved pre-main-sequence and young main-sequence stars, but truly polar spots on these stars require an additional transport mechanism acting after magnetic flux emergence at the surface, probably meridional circulation or poleward slip of the 'anchored' part of the erupted flux tubes. We discuss our findings in the light of the results obtained from Doppler-imaging studies.

We describe the University of Vienna twin automatic photoelectric telescope (APT) located at the new Fairborn Observatory at Washington Camp in southern Arizona. Not only are the telescopes fully automatic, also the observatory itself is automatic. A site-control computer monitors weather sensors and operates the roof while the telescope control computer operates the photometer and accepts input files from and provides nightly observations to the astronomer; no direct operating personnel is needed. Both telescopes have 0.75-m primary mirrors, a CCD finder camera, and an environmentally controlled single-channel photoelectric photometer with filter combinations optimized for use in the blue (Wolfgang) and in the red (Amadeus) wavelength for asteroseismology of non-radially pulsating variables, and for monitoring asymtotic-giant-branch stars. Some first results are presented.

We present the results from a spectroscopic Ca II HK 23% with strong emission, 36% with moderate emission, and 41% with weak emission. These spectra are used to determine absolute H&K emission-line fluxes, radial velocities, and equivalent widths of the luminosity-sensitive Sr II line at 4077 ˚ A. Red-wavelength spectroscopic and Stromgren y photometric follow-up obser- vations of the 371 stars with H&K emission are used to ad- ditionally determine the absolute H-core flux, the lithium abundance from the Li I 6708 ˚ A equivalent width, the rotational velocity v sin i, the radial velocity, and the light variations and its periodicity. The latter is interpreted as the stellar rotation period due to an inhomogeneous surface brightness distribu- tion. 156 stars were found with photometric periods between 0.29 and 64 days, 11 additional systems showed quasi-periodic variations possibly in excess of 50 days. Further 54 stars had variations but no unique period was found, and four stars were essentially constant. Altogether, 170 new variable stars were discovered. Additionally, we found 17 new SB1 (plus 16 new candidates) and 19 new SB2 systems, as well as one definite and two possible new SB3 systems. Finally, we present a list of 21 stars that we think are most suitable candidates for a detailed study with the Doppler-imaging technique.

S-lie present continuous multicolor photometry for 47, stars from October 1996 through June 1997. Altogether, 7073 V (RI)(c), UBV, and by data points, each the:average of three individual readings, were acquired with three automatic photoelectric telescopes (APTs) at Fairborn Observatory in southers Arizona. Most of our targets: are chromospherically active single and binary stars: of-spectral type G to K but there are also four pre-main-sequence objects and three pulsating stars in our sample. The light variability is generally due to rotational modulation of an asymmetrically spotted stellar surface and therefore precise rotational periods and their seasonal variations are determined from Fourier analysis. We also report on photometric variations of gamma CrB (A0V) with a period of 0.44534 days. All data are available in numerical form.

Since 1996 November we have monitored four weak-lined, classical T Tauri stars — RY Tau, SU Aur, V410 Tau, and TIDE 283572 — with the University of Vienna twin automatic photoelectric telescope (APT). Here we present the first long-term light curves of RY Tau and SU Aur for the 1996/1997 observing season. A description of the APT can be found in Strassmeier et al. (1997, PASP 109, 697); a survey with more photometric observations is described by Strassmeier et al. (1997, A&AS 125, 11). Further information is also available at http://www.ast.univie.ac.at/~kgs/APT.