Context. Although many studies have been performed so far, there are still dozens of low-mass stars and brown dwarfs in the young σ Orionis open cluster without detailed spectroscopic characterisation. Aims: We look for unknown strong accretors and disc hosts that were undetected in previous surveys. Methods: We collected low-resolution

We report a study of the quiet sun's magnetic field based on high-resolution infrared spectropolarimetric observations (TIP/VTT). We find that in almost 50% of the pixels Stokes V and in 15% the Stokes Q and/or U profiles have a signal above 10-3. The statistical properties of the mainly intranetwork field sampled by these observations are

The characterization of the vertical turbulence distribution on an astronomical site should be based on statistical behaviour, as it is required for other parameters in site testing. We present the statistical results of the optical-turbulence profiles at the Roque de los Muchachos and Teide observatories at the Canary Islands (Spain). The data

We present results of our combined X-ray and optical study of NGC 2451, which actually consists of two different stellar clusters situated along the same line-of-sight at distances of 190 and 360 pc, respectively. Based on ROSAT X-ray observations and on our extensive optical CCD BVR-photometry we are able to identify 113 stars down to spectral

We present simultaneous two-dimensional spectroscopy of the circumnuclear region (12" x 9") of the galaxy NGC 7331, obtained with an optical fiber system coupled to the ISIS double spectrograph of the 4.2 m William Herschel Telescope. The system allows simultaneous observation of 125 regions of this galaxy in two spectral ranges: 4590--5400

We have conducted a systematic search for stellar disk truncations in disk--like galaxies at intermediate redshift (z