Context. The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9 main-sequence star called CoRoT-6 with a period of 8.886 days. Aims: We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction. Methods: We apply

We present period change rates (dP/dt) for 42 RR Lyrae variables in the globular cluster IC 4499. Despite clear evidence of these period increases or decreases, the observed period change rates are an order of magnitude larger than predicted from theoretical models of this cluster. We find that there is a preference for increasing periods, a

We observed the new X-ray transient, MAXI J0556-332 (ATel #3102, #3103, #3104, #3106, #3110, #3112) with the Faulkes Telescope South on 17 and 18 January 2011 (MJD 55578.4 and 55579.5). On each date, three 200-sec exposures were taken; one each in Bessel V, R, and I bands, totalling six images. The suggested optical counterpart (ATel #3103) was

We report on the discovery of a relation between the stellar mass M* of early-type galaxies (hereafter ETGs), their shape, as parameterized by the Sersic index n, and their stellar mass-to-light ratio M*/L. In a three-dimensional log space defined by these variables, the ETGs populate a plane surface with small scatter. This relation tells us that

We report new observations of the intermediate-frequency peaked BL Lacertae object 3C 66A with the MAGIC telescopes. The data sample we use were taken in 2009 December and 2010 January, and comprises 2.3 hr of good quality data in stereoscopic mode. In this period, we find a significant signal from the direction of the blazar 3C 66A. The new MAGIC

Most of the visible light coming from the Sun originates in the solar photosphere. Numerical simulations are a common tool to study the solar atmosphere starting from the basic laws of physics and few additional assumptions. This thesis presents results of three-dimensional radiative magnetohydrodynamic simulations of the quiet-sun, plage and