We present colour transformations for the conversion of Wide-Field Survey Explorer W1, W2, and W3 magnitudes to the Johnson-Cousins BVIc, Sloan Digital Sky Survey gri, and Two Micron All Sky Survey JHKs photometric systems, for red clump (RC) stars. RC stars were selected from the Third Radial Velocity Experiment Data Release. The apparent

The three-dimensional structure of an active region filament is studied using nonlinear force-free field extrapolations based on simultaneous observations at a photospheric and a chromospheric height. To that end, we used the Si I 10827 Å line and the He I 10830 Å triplet obtained with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope

We present a detailed analysis of two fields located 26 kpc (˜5 radial scalelengths) from the centre of M31 along the south-west semimajor axis of the disc. One field samples the major axis populations - the Outer Disc field - while the other is offset by ˜18 arcmin and samples the warp in the stellar disc - the warp field. The colour-magnitude

We have combined deep photometry in the B, V and I bands from CTIO/MOSAIC of the Sculptor dwarf spheroidal galaxy, going down to the oldest main sequence turn-offs, with spectroscopic metallicity distributions of red giant branch stars. This allows us to obtain the most detailed and complete star formation history to date, as well as an accurate

Aims: We looked for signatures of quasi-biennial periodicity (QBP) over different phases of solar cycle by means of acoustic modes of oscillation. Low-degree p-mode frequencies are shown to be sensitive to changes in magnetic activity due to the global dynamo. Recently there has been reported evidence of two-year variations in p-mode frequencies

Context. The optical counterpart of the neutron star X-ray binary and well known X-ray burster, 4U 1636-53 (=4U 1636-536 = V801 Ara) has been studied for three decades. However, no infrared studies have been reported to date. Aims: Our aims are to identify and investigate the near-infrared (NIR) counterpart of 4U 1636-53. Methods: We present deep