An experiment aimed at diffraction-limited imaging of astronomical sources in the 2-5-micron range is presented. It is based on a rotation shearing interferometer that produces fringes in the pupil plane that can be scanned through the zero optical path difference. The two-dimensional interferograms are recorded with an infrared camera looking at

From published catalogs, basic physical properties including diameters, masses, and neutral hydrogen contents of spiral galaxies have been studied as a function of the arm class. The results indicate that galaxies with well-defined arms have longer scale-lengths (a difference comparable in the red to that in the blue) and are more massive (in both

ABSTRACT: B, V, R, and I CCD frames were obtained for the Southern Galaxies NGC 5757, and IC 1091. The frames were analysed to derive standard photometric and geometric parameters such as integrated magnitudes and colors, dimensions and inclination. Radial luminosity profiles along several directions were calculated and combined to give one mean

Spectrophotometric data of giant H II regions covering the spectral range from λ3600 to 9700 Å in the spiral galaxies M101 and M51 have been analyzed in order to determine reliable chemical abundances and radial gradients. The behaviour of the S/O ratio with metallicity is also explored. The data are consistent, within the errors, with a constant S

We report four colour CCD photometry and photoelectric photometry of 3C 345 taken in the spring of 1990. After an initial partial recovery from the minimum observed in 1989 which was, at that time, the deepest ever recorded, a very fast decline to even fainter levels was seen over ten days in May 1990, which was then followed by a further partial

The mechanism proposed by Kormendy (1984) for the formation of counterrotating cores in elliptical galaxies is investigated using self-consistent numerical simulations of mergers between a high- and a low-luminosity elliptical galaxies. The conditions for a counterrotation to appear are determined, observational properties of the remnants are