The usually assumed identification of small-scale magnetic concentrations with bright facular or network points on the photosphere is observationally checked by using high spatial resolution spectra of Ca II K bright points very near the disk center. The detection of spatially unresolved magnetic structures is made via a new differential analysis

The low l solar acoustic spectrum has been measured with great accuracy for intermediate radial order modes, n = 11-34 (Jimenez et al., 1986; Grec et al., 1983; Palle et al., 1986). The measurement of the frequencies of modes of lower n, up to the fundamental one, are very important as they depart from asymptotic behavior and, therefore, put more

Simultaneous spectrometric and photometric observations have been performed on the red giant star Arcturus, in a search for radial velocity or luminosity variations related to global oscillations of the stellar structure. From a preliminary analysis of the spectrometric data, several frequencies have been discovered in the range from 1 to 50 micro

A summary of data collected during a sixty night international campaign devoted to cataclysmic variables is presented.

This paper presents high-resolution, high dynamic range narrow-band images of the extended narrow-line region (ENLR), as well as broad-band continuum images, of the type 1.5 Seyfert galaxy NGC 4151. An 'excitation map' is obtained by division of the calibrated O III forbidden 5007-A line image by the H-alpha image. This line-ratio map shows that

The possibility that radiative instabilities in stellar atmospheres are driven by transfer of energy processes between stellar gas and the radiation field is considered. Harmonic temperature fluctuations in gray radiative equilibrium atmospheres are introduced, and the linear response of the radiation field to the ensuing Planck-function and