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The effects of uncertainties in the structure of the superficial layers of the Sun, such as the helium abundance, opacity and equation of state, on the p-mode frequencies are considered in terms of the phase function. The analysis is carried out by means of a linear relation between phase-function differences and equilibrium structure differences

The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory

MASSIVE compact objects in the Galactic halo, known as MACHOs, have been postulated as the origin of a substantial fraction of the 'dark matter' known to exist in the haloes of galaxies1,2. Paczyn acuteski3 has suggested that it might be possible to detect these low-luminosity objects by their potential to act as gravitational lenses, causing a

We have observed a number of the most luminous A and B supergiants in the galaxies M 31 and M 33 at intermediate dispersion obtaining both blue and red spectrograms. We have determined spectral types and luminosity classifications from these data, in a few cases revising previous evaluations. From comparison with galactic analogues we estimate

We present the spectral evolution, from about one to six months after optical maximum, of two type Ic supernovae, 1990U in NGC 7479 and 1991A in IC 2973 (UGC 6872). We analyze and compare the SN 1990U and SN 1991A spectral sequences. We looked for differences, at similar phases, between the more characteristic spectral features and their evolution