Related papers: LO Peg: surface differential rotation, flares, and…
In recent years it has been claimed that the length of stellar activity cycles is determined by the stellar rotation rate. It is observed that the cycle period increases with rotation period along the so-called active and inactive…
Spectral signatures of surface spots were recently discovered from high cadence observations of the A star Vega. We aim at constraining the surface distribution of these photospheric inhomogeneities, and investigating a possible short term…
We analyze various tracers of magnetic activity for 23 solar twins which are characterized by significant scatter of lithium abundance in their atmospheres. A level of coronal and chromospheric activity has been studied from available X-ray…
Photometric I band light curves of 21 ultra cool M and L dwarfs are presented. Variability with amplitudes of 0.01 to 0.055 magnitudes (RMS) with typical timescales of an hour to several hours are discovered in half of these objects.…
Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotations with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations on the emergence…
We have analysed K2 light curves for more than 3,000 low mass stars in the $\sim$8 Myr old Upper Sco association, the $\sim$125 Myr age Pleiades open cluster and the $\sim$700 Myr old Hyades and Praesepe open clusters to determine stellar…
Stellar rotation is crucial for studying stellar evolution since it provides information about age, angular momentum transfer, and magnetic fields of stars. In the case of the Sun, due to its proximity, detailed observation of sunspots at…
HD 208472 is among the most active RS~CVn binaries with cool starspots. Decade-long photometry has shown that the spots seem to change their longitudinal appearance with a period of about six years, coherent with brightness variations. Our…
On the Sun, the rotation periods of individual sunspots not only trace the latitude dependence of the surface rotation rate, but also provide clues as to the amount of subsurface fluid shear. In this paper we present the first measurements…
Using K2 data, we have identified 23 very low mass members of the $\rho$ Oph and Upper Scorpius star-forming region as having periodic photometric variability not easily explained by well-established physical mechanisms such as star spots,…
We publish 16 Doppler imaging temperature maps for the years 1994-2002 of the active RS CVn star II Peg. The six maps from 1999-2002 are based on previously unpublished observations. Through Doppler imaging we want to study the spot…
The light curves of old G-dwarfs obtained in the visible and near-infrared wavelength ranges are highly irregular. This significantly complicates the detectability of the rotation periods of stars similar to the Sun in large photometric…
Using a recent census of flare stars from the Kepler survey, we have explored how flare activity evolves across stellar main sequence lifetimes. We utilize a sample of 347 stars with robust flare activity detections, and which have rotation…
We present BV(RI)_C photometric measurements of the dM4-type V374 Peg covering ~430 days. The star has a mass of ~0.28M_Sun, so it is supposed to be fully convective. Previous observations detected almost-rigid-body rotation and stable,…
Measuring surface differential rotation (DR) on different types of stars is important when characterizing the underlying stellar dynamo. It has been suggested that anti-solar DR laws can occur when strong meridional flows exist. We aim to…
We study the chromosphere and corona of the ultra-fast rotator AB Dor A at high temporal and spectral resolution using simultaneous observations with XMM-Newton in the X-rays, VLT/UVES in the optical, and the ATCA in the radio. Our optical…
We have studied the photometric variability of ten SMC Be/X-ray pulsars using MACHO and OGLE-II data. For some of these systems we have found periodic behavior, including orbital outbursts and/or nonradial pulsations (NRP) of the Be star.…
Recent studies suggest that the angular momentum evolution of late-M and brown dwarfs differs from the well-known spin-down evolution of hotter stars. Characterizing the distribution of rotation periods of these objects in the solar…
The present study is an attempt to investigate the long term variations in coronal rotation by analyzing the time series of the solar radio emission data at 2.8 GHz frequency for the period 1947 - 2009. Here, daily adjusted radio flux…
We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high latitude spots located at the sub-white dwarf longitude region. By tracking the…