UBV photometry of clusters in M31

A critical review is given of all published photoelectricUBV photometry of star clusters in the Andromeda Nebula. Observations by Sharovet al. are shown to exhibit rather large random errors, but no systematic deviations from theUBV system.     

Oscillator strengths for resonance lines of some silicon and sulfur ions

Oscillator strengths are calculated for resonance lines of some silicon and sulfur ions, which are present in the solar spectrum from about 160 Å to 380 Å. Spin-spin and spin-other orbit interactions are included. A comparison is made with Garstang's results for Six; agreement is good.     

Comparison of the thermal and nonthermal radiation characteristics of Jupiter at 6, 11, and 21 cm with model calculations

Four different data sets on Jupiter, one at 6, one at 11, and two at 21 cm, are compared to each other and with the synchrotron radiation model of the magnetosphere developed by I. de Pater (1981, J. Geophys. Res., 86, 3397–3422, 3423–3429). The model agrees with all these data sets, and hence was used to derive and interpret the characteristics of the thermal radiation component at all three wavelengths. The disk temperatures are 233 ± 17, 280 ±20, and 340 ± 26°K at 6, 11, and 21 cm, respectively. A comparison of the data with atmospheric model calculations strongly suggests that the disk is uniform at λ6 and λ11 cm near the center of the disk, where μ > 0.6?0.7. This may indicate a nonuniform distribution of ammonia at layers at and above the visible cloud layers.     

Clusters of galaxies compared withN-body simulations: Masses and mass segregation

With three virially stableN-body simulations of Wielen, we show that use of the expression for the total mass derived from averaged quantities (velocity dispersion and mean harmonic radius) yields an overestimate of the mass by as much as a factor of 2–3, and use of the heaviest mass sample gives an underestimate by a factor of 2–3. The estimate of the mass using mass weighted quantities (i.e., derived from the customary definition of kinetic and potential energies) yields a better value irrespective of mass sample as applied to late time intervals of the models (three two-body relaxation times). The uncertainty is at most 50%. This suggests that it is better to employ the mass weighted expression for the mass when determining cluster masses. The virial ratio, which is a ratio of the mass weighted/averaged expression for the potential energy, is found to vary between 1 and 2. We conclude that ratios for observed clusters 4–10 cannot be explained even by the imprecision of the expression for the mass using averaged quantities, and certainly implies the presence of unseen matter. Total masses via customary application of the virial theorem are calculated for 39 clusters, and total masses for 12 clusters are calculated by a variant of the usual application. The distribution of cluster masses is also presented and briefly discussed. Mass segregation in Wielen's models is studied in terms of the binding energy per unit mass of the heavy sample compared with the light sample. The general absence of mass segregation in relaxed clusters and the large virial discrepancies are attributed to a population of many low-mass objects that may constitute the bulk mass of clusters of galaxies.     

Globular clusters and galactic evolution (invited review)

Observations of the frequency with which globular clusters surround galaxies are reviewed. With a single exception the data do not favour the view that elliptical galaxies are formed from merging disc systems. Attention is also drawn to the unusually high frequency of globular clusters in central galaxies of rich clusters.