A study of the observations made on the development and, in some cases, even the decay of 15 large active regions is presented. It is shown that the mature spots results from the subphotospherically controlled attraction of several large fragments of 1-2 x 10 to the 21st Mx, which are themselves made of smaller elements. The fragments are more

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The question of efficiency of radiative energy losses in spectral lines is addressed. In a semi-infinite atmosphere with constant temperature, the total radiative energy loss (integrated over all depths) in a spectral line without continuum is infinite, in both LTE and non-LTE. Thus, only local energy balances may be considered with such models

High-resolution spectra of Alpha Cen B, Xi Boo A, 70 Oph A, and Epsilon Ind obtained using the Coude Echelle Spectrometer and the 1.4-m Coude Auxiliary Telescope of ESO are analyzed. Variations in the normalized fluxes for the four dwarfs are described. Position and intensity measurements of the Ca II H features are examined. The use of the spectra

This paper presents an automatic method for (1) digital estimation of the width of the atmospherical seeing in astronomical images of extended objects and (2) image restoration by using the constrained Jansson-Van Cittert deconvolution algorithm. The estimation of the seeing is achieved by computing the radial profile of the averaged log spectrum

Synthetic horizontal branches, constructed on the basis of Sweigart and Gross (1976) horizontal branch star models and of the recently revised theoretical instability strip (Stellingwerf, 1984) are presented for various chemical compositions appropriate for Population II systems, for various assumptions on the mass size of the helium core and for