As a result of a major program of spectral observations using the CAT 1.4 m telescope and Coude Echelle Spectrograph at ESO, La Silla, 68 high resolution profiles of the 3968.5 A Ca H resonance line have been obtained for 16 late type stars (dwarfs and subgiants, including the sun) ranging from F9 to K5, selected to be representative of a wide span

High resolution, high signal to noise spectral profiles of the 8498 and 8542 A lines of the Ca II infrared triplet (IRT) have been obtained for a sample of late type dwarfs, with a wide range of levels of chromospheric activity, in the spectral range F9 to K4/5. These profiles, and the difference profiles for selected active and quiescent objects

This article shows how some recent developments in the observation and theoretical modeling of weak polarization signals in chromospheric spectral lines are facilitating fundamental new advances in our ability to investigate the magnetism of the solar outer atmosphere via spectropolarimetry.

The authors have used high resolution IUE spectra from their own studies and from the archive to examine the Mg II h and k chromospheric emission cores of a sample of late-type dwarfs and giants. Sharp photospheric absorptions were used to provide a velocity rest-frame with respect to each stellar photosphere with the IUE-limited precision of ±4 km

A representative set of profiles is presented for the Ca II H resonace line in Stokes V and I, for the quiet sun, plages, sunspot umbrae, and a flare, as well as one example of the Ca II K line in a sunspot penumbra. The degree of polarization is highest in the spots and zero in the quiet sun, within error limits. The V profile asymmetries are

We report broad-band imaging observations which reveal a circum-nuclear gas ring in NGC 4151. The ring is delineated by two arc-like features probably resulting from dust extinction of the background stellar continuum. These features are distributed along opposite quadrants of an elliptical ring which has a semi-major axis of length 1.8kpc and is