We present a gravitational lensing and X-ray analysis of a massive galaxy cluster and its surroundings. The core of MACS J0717.5+3745 (M(R

GT2318+620 is a variable radio source exhibiting a jet-like feature on both sides of an unresolved core (Taylor et al., Nature 351, 1991), and it is possibly associated with an UHURU X-ray source. A red 20th magnitude star coincident with the radio core was identified as the optical counterpart. Based on a neutral hydrogen absorption spectrum and

Context. Short- to mid-term magnetic phenomena on the stellar surface of M-type stars can resemble the effects of planets in radial velocity data, and may also hide them. Aims: We analyze 145 spectroscopic HARPS-N observations of GJ 3942 taken over the past five years and additional photometry in order to disentangle stellar activity effects from

A survey of 380 sq. deg. of the sky with the 1m Schmidt telescope at the Observatorio Nacional de Llano del Halo and the QUEST camera has found 498 RR Lyrae variables lying from 4 to 60 kpc from the Sun. We describe the halo substructure revealed by these data and the results of measuring some of the stars' radial velocities and metal abundances.

The second Hispano-Argentinian Meridian Catalogue (HAMC2) contains more than 12.500.000 positions and magnitudes of stars brighter than V=16.5 and with declinations between -30° and 0°. It has been computed from the CCD observations of the San Fernando Automatic Meridian Circle (CMASF) installed at present at the Carlos U. Cesco Observatory (CUC)

We have run high resolution N-body models simulating the encounter of a dwarf galaxy with a bright elliptical galaxy. The dwarf absorbs orbital angular momentum and shows counter-rotating features in the external regions of the galaxy. To explain the core-envelope kinematic decoupling observed in some dwarf galaxies in high-density environments