Bipolar nebulae and jets from young stars: Contributions from calar alto

The topic is reviewed with emphasis on observations in the optical and near infrared spectral range.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.     

Radiation-hydrodynamic waves and global solar oscillations

We investigate nonadiabatic hydrodynamic waves in a nongrey, radiating, thermally conducting, homogeneous atmosphere in LTE with a finite mean free path of photons. Avoiding the Eddington approximation the remaining simplifications in the basic equations are discussed, the generalized dispersion relation is analysed, and some wave properties in a grey model are studied. The properties of waves in a stratified atmosphere are analysed as well. In connection with the predicted properties of the nonadiabatic waves we discuss observations ofp-modes by measuring brightness fluctuations.     

Signature of differential rotation in solar disk‐integrated chromospheric line emission

UARS SOLSTICE data have been subjected to Fourier and wavelet analyses in order to search for the signature of the solar rotation law in the disk‐integrated irradiance of UV lines. Lyman‐α, Mg II, and Ca II data show a different behaviour. In the SOLSTICE data there are significant temporal variations of the rotation rate of the UV tracers over 5—6 years. Often several distinct rotation periods appear almost simultaneously. Beside the basic period around 27 days there are signals at 32—35 days corresponding to the rotation rate at very high latitudes. For more than 5 years during another period of the solar cycle the rotational behaviour is quite different; there is an indication of differential rotation of active regions in these Ca II ground‐based data. The data contain a wealth of information about the solar differential rotation, but it proves difficult to disentangle the effects of the different emitting sources.     

About the Influence of a Magnetic Field on the Model Atmosphere of a Magnetic Star

A quasi-static magnetic field similar to that of a large single sunspot is assumed to be embedded in a photospheric model of an Ao star. The differences of the model atmosphere within the magnetic spot relative to the photosphere are calculated by means of the equations of hydromagnetics. The differences are small for τ ≧ I but increase towards smaller τ. The spot model is more transparent in its high layers. In equal geometrical depth the thermodynamic parameters are reduced by the magnetic field. While a small spot is darker than its photospheric surroundings, a large spot appears brighter; the wavelength dependence of its excess in brightness coincides with observations. Compared with the photosphere, the Balmer lines show narrower and deeper cores in the large spot, these differences increase towards larger quantum numbers. Also these features are qualitatively confirmed by observations. An outline is given how to extend and generalize the present model calculations.     

On the interpretation of some peculiarities observed in zeeman-split line contours in sunspots

Measurements of the H line intensity in a large active prominence indicate that , the fraction of length in the line of sight which contains emitting material, is less or equal to 0.1.