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.     

On static spherical symmetric solutions of the Bach-Einstein gravitational field equations

For field equations of 4th order, follwing from a Lagrangian “Ricci scalar plus Weyl scalar”, it is shown (using methods of non-standard analysis) that in a neighbourhood of Minkowski space there do not exist regular static spherically symmetric solutions. With that (besides the known local expansions about r = o nad r = ∞ resp.) for the first time a global statement on the existence of such solutions is given. Finally, this result will be discussed in connection with Einstein's particle programme.     

Determination of a temporally and spatially resolved supernova rate from OB stars within 5 kpc

We spatially and temporally resolve the future Supernova (SN) rate in the Solar vicinity and the whole Galaxy by comparing observational parameters of massive stars with theoretical models for estimating age and mass and, hence, the remaining lifetime until the SN explosion. Our SN rate derived in time and space for the future (few Myr) should be the same as in the last few Myr by assuming a constant rate. From BVRIJHK photometry, parallax, spectral type, and luminosity class we compile a Hertzsprung‐Russell diagram (HRD) for 25027 massive stars and derive extinction, and luminosity, then mass, age, and remaining lifetime from evolutionary models. Within 600 pc our sample of SN progenitors and, hence, SN prediction, is complete, and all future SN events of our sample stars take place in 8 % of the area of the sky, whereas 90 % of the events take place in 7 % of the area of the sky. The current SN rate within 600 pc is increased by a factor of 5–6 compared with the Galactic rate. For a distance of 5 kpc our sample is incomplete, nevertheless 90 % of those SN events take place in only 12 % of the area of the projected sky. If the SN rate in the near future is the same as the recent past, there should be unknown young neutron stars concentrated in those areas. Our distribution can be used as input for constraints of gravitational waves detection and for neutron star searches. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zur Metallhäufigkeit in ω Centauri

Radiation pressure during the high-luminosity collapse phase of cluster evolution may, under certain circumstances, lead to the ejection of interstellar grains. For the most luminous clusters such ejection might produce significant depletion of heavy elements. It is suggested that the metal abundance dispersion that has recently been detected among the giant stars in ω Centauri (which is the brightest known galactic globular cluster) might be accounted for by such radiation pressure induced heavy element depletion.