A three-component model for the formation of the chromospheric Caii K line

A recent two-component model for the formation of the Caii K line in the solar chromosphere put forward by Beebe and Johnson is discussed. Although this model is a great advance on existing one-component models, it is pointed out that observations require a minimum of three components in order to understand the formation of the K₂ peaks.In order to make some progress in the study of multicomponent models an adaptation of the empirical (or analytic) approach is suggested. This relates the line source function directly to observations and places a secondary importance (at this stage) on the synthetic approach to the problem. A model is obtained which is in adequate agreement with observed mean profiles and its features are briefly discussed.     

Center-limb observations of inhomogeneities in the solar atmosphere

Center-limb observations of line-center intensity and velocity fluctuations in the Magnesium b lines are described. Autocorrelation and power spectral analyses indicate small scale brightness structures having periodicities of 3000 km and 8000 km and large scale structures of 22000 km. Corresponding velocity structures are 6000 km and 30000 km.The relative rms fluctuation amplitude for the small scale bright features is found to be of order 12% and for the large scale features 8%. The variation of these rms values with heliocentric angle is also shown.At disk center some weak correlation is found between bright features and downward velocities in the large scale structures. Towards the limb there is a strong correlation in all three lines between line of sight motions and bright features. This indicates that the large scale bright features are closely associated with the supergranule motions.By inspecting the actual brightness and velocity fluctuation tracings it can be seen that, in some regions, the small scale structures show a significant negative correlation over a range of about 25000 km. Beyond this characteristic length, however, the correlation may decrease abruptly or even become positive for a similar distance. There is some evidence which suggests that this behaviour may also be related to the supergranule motions.     

Venus I. Carbon monoxide distribution and molecular-line searches

An observational program to study variations of the vertical distribution of CO in the Venus atmosphere is presented. Measurements of the J = 0 → 1 absorption line at 2.6 mm wavelength are reported for two phase angles in 1977, one near eastern elongation (Feb.) and the other near inferior conjunction (Apr.). The two spectra are significantly different, with the April absorption line being narrower and deeper. The results of numerical inversion calculations show that the CO mixing ratio increases a factor of ～ 100 between 78 and 100 km and that the CO abundance above ～ 100 km is greatest on the night-side hemisphere. These conclusions are in qualitative agreement with theoretical models. In addition to the CO observations, a search for other molecules was made to provide further information on the composition of the Venus middle atmosphere. The J = 0 → 1 transition of ¹³CO was detected and upper limits were derived for nine other molecules.     

Protogalactic explosions and intracluster chemical enrichment

Using a hydrodynamic model of protogalactic evolution, we explain the amount of iron in rich clusters, deduced from X-ray observations. In fact, our calculations show that a strong shock wave originates in the first violent collapse phase and leaves the protogalaxy, carrying out a substantial fraction of its mass, with roughly solar metallicity and high temperature (10⁷–10⁸ K). We also show that hot material ejected from proto-cD galaxies can probably explain the observed X-ray emission in clusters.     

On the properties of umbral dots

On the basis of a three-dimensional radiative transfer analysis of several models it is shown that bright structures in sunspot umbrae which have horizontal diameters of 300 km or less cannot extend more than 300 km down into the umbra. Thus, such models are inconsistent with the hypothesis that the bright features are due to convection from the deep regions of the umbra. No such restrictions can be applied if the surface diameter is of order 500 km, but a model of this type is shown to be inconsistent with the available data. Thus a convective explanation of these bright features appears to be ruled out.A model having a diameter of 200 km is shown to be consistent with the available observations but these are not sufficiently precise to warrant any strong claim for the validity of this model. The features of this model are described and it is shown that near the limb the apparent brightness of these features compared to the umbral background should increase. However, order-of-magnitude calculations show that there is some doubt whether joule heating can account for the non-radiative energy requirements of this model.