We present a study of the H II regions in the central area of the giant irregular galaxy NGC 4449 based on observations taken on the William Herschel Telescope at the Roque de los Muchachos observatory with the Taurus II Fabry-Perot interferometer in the emission lines of Hα and [O III] 5006.8. We show that the usual methods of determining sizes of

We present the first part of the first large and homogeneous CCD color-magnitude diagram (CMD) data base, comprising 52 nearby Galactic globular clusters (GGC) imaged in the V and I bands using only two telescopes (one for each hemisphere). The observed clusters represent 75% of the known Galactic globulars with (m-M)_V

We compute photoionization models for the giant extragalactic H II region NGC 2363, and compare them with optical observational data. We show that models computed with the observed metallicity of the cluster (Z=0.10 Zodot) do not reproduce the observed features of the spectrum, and that the disagreement can be overcome by allowing for spatial

We report on the detection of magnetic field strength and velocity oscillations in the photosphere of a sunspot umbra. Our analysis is based on the inversion of the full Stokes vector of three Fe I lines at 15650 Å, from which the stratification with optical depth of the different atmospheric parameters has been derived. This allows us to estimate

Optical imaging observations for 50 radio galaxies are presented. For each object isophotal contours, photometric profiles, structural parameters (position angle, ellipticity, Fourier coefficients), and total magnitudes are given. These observations, obtained in the Cousins R band, complement the data presented in a previous paper and are part of a

Chandra X-ray Observatory has unprecedented spatial resolution and sensitivity. Its 0.5 arcsec on-axis PSF provides for the first time an angular resolution comparable to ground based optical telescopes. Thus the serendipitous sources in each Chandra field constitute a rich collection of previously unknown X-ray sources with precise positions. The