The detection and analysis of line emission of the CaII, H(396.8nm) and K(393.3nm) have confirmed the chromospheric activity of some single and binaries stars. This activity is associated to the presence of magnetic fields which in turn are produced by internal convective flows along with stellar rotation producing a long-term photometric cycle length related to the apparition and vanishing of superficial stellar spots. We present a photometric study of stars of the type RS CVn, Rotationally variable Star and BY Dra, that have shown evidence of chromospheric activity. The analysis of these measurements has allowed us to delimit periods of rotation. In addition, we have detected and measured the cycle length in some cases. It allows us to complement previous investigations and in some cases to determine for the first time the presence of a long photometric cycle, contributing to complement the link between rotation and magnetic cycles.

There is ample evidence for the presence of strong magnetic fields in the envelopes of (post-)Asymptotic Giant Branch (AGB) stars as well as supergiant stars. The origin and role of these fields are still unclear. This paper updates the current status of magnetic field observations around AGB and post-AGB stars, and describes their possible role during these stages of evolution. The discovery of magnetically aligned dust around a supergiant star is also highlighted. In our search for the origin of the magnetic fields, recent observations show the signatures of possible magnetic activity and rotation, indicating that the magnetic fields might be intrinsic to the AGB stars.

New observations of Kepler δ Scuti stars show that our understanding of pulsation in these stars is incomplete. A large fraction of A and B stars exhibit rotational modulation in light, suggesting that spots exist in stars with radiative envelopes. Flares are seen in some A stars, as may be expected if starspots are present. Differential rotation shear increases from M to F but decreases for A stars; it reaches a maximum among the γ Doradus variables. Current views of stars with radiative envelopes may need to be reviewed in the light of these observations.

If a star hosts a planet in an orbit such that it eclipses the star periodically, can be estimated the rotation profile of this star. If planets in multiplanetary system occult different stellar areas, spots in more than one latitude of the stellar disc can be detected. The monitored study of theses starspots in different latitudes allow us to infer the rotation profile of the star. We use the model described in Silva (2003) to characterize the starspots of Kepler-210, an active star with two planets. Kepler-210 is a late K star with an estimated age of 350 ± 50 Myrs, average rotation period of 12.33 days, mass of 0.63 M⊙ and radius of 0.69 R⊙. The planets that eclipses this star have radii of 0.0498 Rs and 0.0635 Rs with orbital periods of 2.4532 ± 0.0007 days and 7.9725 ± 0.0014 days, respectively, where Rs is the star radius.

The current photometric datasets, that span decades, allow for studying long-term cycles on active stars. Complementary Ca H&K observations give information also on the cycles of normal solar-like stars, which have significantly smaller, and less easily detectable, spots. In the recent years, high precision space-based observations, for example from the Kepler satellite, have allowed also to study the sunspot-like spot sizes in other stars. Here I review what is known about the properties of the cyclic stellar activity in other stars than our Sun.

The joint variability of chromospheric emission with the integrated flux in the Kepler visible band for the Sun as a star is examined. No correlation between our Ca II K line parameter and the Kepler passband is seen, suggesting that visible-band variability in solar-like stars is mostly independent of solar-like chromospheric activity. However, the K-line parameter time series and the total solar flux in the infrared K band appear weakly correlated, reflecting the wavelength dependence of the relationship between magnetic activity and broadband variability. We then apply a schematic, three-component model as a framework for the discussion of stellar photometric variability as observed by Kepler. The model confirms that spots tend to dominate stellar photometric variability in the visible though interesting cases do emerge where the facular disk coverage may become important in determining the amplitude of broadband variability.

Late-type stars exhibit cool regions on their surface, the stellar equivalent of sunspots. These dark starspots can also mimic the radial velocity variations caused by orbiting planets, making it at times difficult to distinguish between planets and activity signatures. The amount of spots on the Sun and other cool stars changes cyclically during an activity cycle, which has length varying from about a year to longer than the solar 11 years. In this work we investigate the influence of varying amount of starspots on the sparsely sampled radial velocity observations - which are the norm in the radial velocity studies searching for exoplanets on wide orbits. We study two simulated cases: one with a random spot configuration, and one where the spot occurrence is concentrated. In addition we use Doppler images of young solar analogue V889 Her as a high activity case.

Stellar magnetic activity manifests itself in a variety of ways including starspots–cool, dark regions on the stellar surface. Starspots can cause variations (‘jitter’) in spectral line-profiles which can mimic the radial velocity (RV) variations caused by an orbiting planet, or create RV noise that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?

Stars are usually faint point sources and investigating their surfaces and interiors observationally is very demanding. Here I give a review on the state-of-the-art observing techniques and recent results on studying interiors and surface features of active stars.

Our recent studies of late B-type stars with HgMn peculiarity revealed for the first time the presence of fast dynamical evolution of chemical spots on their surfaces. These observations suggest a hitherto unknown physical process operating in the stars with radiative outer envelopes. Furthermore, we have also discovered existence of magnetic fields on these stars that have up to now been thought to be non-magnetic. Here we will discuss the dynamical spot evolution on HD 11753 and our new results on magnetic fields on AR Aur.

I review basic observational features in Population I stars which strongly implicate rotation as a mixing agent; these include dispersion at fixed temperature in coeval populations and main sequence lithium depletion for a range of masses at a rate which decays with time. New developments related to the possible suppression of mixing at late ages, close binary mergers and their lithium signature, and an alternate origin for dispersion in young cool stars tied to radius anomalies observed in active young stars are discussed. I highlight uncertainties in models of Population II lithium depletion and dispersion related to the treatment of angular momentum loss. Finally, the origins of rotation are tied to conditions in the pre-main sequence, and there is thus some evidence that environment and planet formation could impact stellar rotational properties. This may be related to recent observational evidence for cluster to cluster variations in lithium depletion and a connection between the presence of planets and stellar lithium depletion.

Solar-type variability is enhanced in short period close binaries with increased dynamo driven activity. This activity is studied in our analysis of recent light curves taken of the newly discovered eclipsing binaries GSC 2764 1417 (And), GSC 3355 0394 (Per) and GSC 2537 0775 (CVn).

We have obtained high resolution, high S/N spectra of the RS CVn binary IM Peg using UVES spectrograph at Kueyen 8.2m telescope of ESO VLT. We use Doppler imaging techniques to obtain stellar surface temperature maps from the UVES data. The TempMap code allows us to use surface differential rotation as an input parameter and thus to try to construct the rotation pattern on the stellar surface as part of the inversion process. The UVES observations are combined with spectroscopic observations from another time period obtained at the STELLA observatory. We obtain stellar surface temperature maps also from these spectra. These Doppler images are used to study the magnetic activity and surface differential rotation on IM Peg.