This paper presents a detailed description, analysis, and interpretation of the spectropolarimetric observations recently reported by Socas-Navarro, Trujillo Bueno, & Ruiz Cobo. These observations consist of time series of Stokes I and V profiles above a sunspot umbra. The spectral lines observed simultaneously are the Ca II chromospheric lines at

The importance of the study of Planetary Nebulae (PNe) in our Galaxy and in external galaxies is outlined, with the aim of highlighting how the combined study of galactic and extragalactic PNe can bring a substantial contribution to our understanding of the late stages of stellar evolution and of related astrophysical topics. We then illustrate the

We present improved visual and near-infrared empirical mass-luminosity relations for very low mass stars (M

We have obtained adaptive optics images and accurate radial velocities for 7 very low mass objects, In the course of a long term effort to determine accurate masses for very low mass stars (M

In this paper, we present meteorological and photometric studies of the Oukaimeden astronomical site in Morocco. The meteorological measurements were obtained over 537 days. The photometric data were measured by both FIP and GONG instruments over 1182 days. We have also analysed the weather parameters at the Observatorio del Roque de los Muchachos

We have used a flux-calibrated mosaiced CCD image of M33 in Hα emission to produce a catalogue of the positions and Hα luminosities of 9190 HII regions complete down to a limiting luminosity LHα of 1036 erg/s and constructed a luminosity function (LF) from this catalogue. In contrast to previously published M33 LFs we find the slope of the function