High signal to noise spectra are required in chromospheric modelling because chromospheric emission lines are formed in a boundary layer under conditions of NLTE and in non-hydrostatic equilibrium, as well as in multiple magnetically-controlled streams, with horizontal structure on several scales, and vertical velocity fields. To obtain useable

Data obtained at Izaña (Tenerife) and Haleakala (Maui), using optical resonant scattering with a potassium vapour cell over the years 1980 - 84, are used to determine the frequencies of the low l p modes. Possible variation in these frequencies with the solar cycle are investigated.

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In the circumnuclear zones of the disks of some spirals there is an absence of neutral interstellar hydrogen. A model is devised in which gaseous outflow is sustained by the combined action of massive stars in these zones. The energy requirement, which implies driving out the gas against gravity, can be satisfied if 10 percent or more of the gas

Analysis of solar velocity data obtained at Izaña (Tenerife) over the years 1981 - 1985, has shown the existence of significant signals in the frequency range 25 - 125 μHz. Several ways of analyzing the data have been used in order to interpret these as solar internal gravity modes of degree l ≤ 3.