Abschätzung von Quasarmassen

The masses of quasi-stellar objects having absorption lines with redshifts larger than the redshifts of the corresponding emission lines are attributed to gas clouds which are moving radially against the quasar. Other forces than the gravitational attraction of the quasars are neglected. The average of the mass of a quasi-stellar object is 5 ⋅ 10¹² 𝔐 ⊙.     

On the existence and the density of intergalactic dust

A relation between the redshift z of QSO's and their colour index (B–V)' corrected for line emission and galactic absorption is interpreted in terms of an intergalactic selective extinction. The observed amount of extinction corresponds to a density of intergalactic dust grains of about 10⁻³⁴ to 10⁻³³ g cm⁻³ at z = 0. The life-time of these particles are estimated to be longer than the Hubble -time at present. But at large z the life-time of the grains considerably depends on the flux density of cosmic rays. Some implications of the existence of intergalactic dust are discussed.     

Zum Dichteverhältnis zwischen interstellarem Staub und Gas

The density ratio between interstellar dust and gas is investigated using the colour excesses of the stars of Habing's list [17] and published 21 cm data. Generally there does not exist a correlation between the amount of neutral hydrogen in the line of sight and the interstellar extinction. In the contrary the scattering of the data is considerable. The influences falsifying the density ratio are discussed whereby the cooling of the interstellar clouds reaching large distances from the galactic plane was considered schematically. From the discussion of the results it follows that at present a reliable determination of the interstellar density ratio between dust and gas is impossible. The necessity of direct observations of the interstellar H₂ but also the determination of the kinetic temperature of the HI in separate regions are pointed out.     

The x-ray luminosity function of galaxy clusters

From published data on X-ray sources identified with clusters of galaxies the X-ray luminosity function of the clusters was derived to ϕ_x ˜ L_x^-0.8 in the range 10⁴³ ≦ L_x ≦ (2–3) · 10⁴⁵ ergs/s. For L_x > 3 · 10⁴⁵ ergs/s the function decreases abruptly.     

Missing Mass in Galactic Coronae?

The concept of massive galactic coronae proposed by EINASTO et al. is discussed. Only hot gas and under certain circumstances black holes have a good chance to be main constituents of the galactic coronae proposed by EINASTO et al.     

POLIS: A spectropolarimeter for the VTT and for GREGOR

The polarimetric Littrow Spectrograph POLIS is designed for vector polarimetry at high angular and spectral resolution. It measures the magnetic field simultaneously in the photosphere and the chromosphere of the sun. Both branches of the polarimetry unit are dual beam systems with a single rotating modulator for both wavelengths and polarizing beam splitters in front of each CCD camera. POLIS has been installed at the VTT on Tenerife and has seen First Light on 17 May 2002. A modified version of POLIS will be developed for the balloon mission Sunrise . That version will have UV capabilities down to 200 nm.     

X-ray emission – an ageing effect of galaxy clusters (Mitteilungen der Universitäts-Sternwarte zu Jena Nr. 145)

Die Röntgenleuchtkraft L_X und -temperatur T_X von Galaxienhaufen wurden zu dem dynamischen Entwicklungsparameter W in Beziehung gesetzt, den VON HOERNER (1976) eingeführt hat. Offensichtlich ist Röntgenstrahlung eine Alterserscheinung der Galaxienhaufen.