High resolution near-IR imaging with arrays

The availability of large format, low noise detector arrays has opened the 1 to 20 m region for sub-arcsecond imaging. Using recent results in the investigation of Galactic star forming regions, the Galactic center and external galaxies as examples, we discuss the various techniques that have been employed. These range from image selection and image sharpening, over speckle techniques and adaptive optics to lunar occultation. These examples demonstrate that sub-arcsecond imaging and spatial interferometry in the near- and mid-infrared has a great future potential.     

Pan-African high pressure granulites from SE-Kenya: Petrological and geothermobarometric evidence for a polycyclic evolution in the Mozambique belt

Two different Pan-African tectono-metamorphic events are recognised in the Taita Hill Tsavo East National Park/Galana river area, SE-Kenya (Mozambique belt) based on petrographic and geothermobarometric evidence. Structurally, this area can be subdivided into four units: (1) the easternmost part of the basement along the Galana river is characterized by subhorizontal slightly to the west and east dipping foliation planes. Migmatic paragneisses with intercalated marbles, calcsilicates and metapelites and bands of amphibolites are the dominant rock type. (2) The western part of the Galana river within the Tsavo East National Park is a ca. 25 km wide shear zone with subvertical foliation planes. The eastern part shows similar rocks as observed in unit 1, while towards west, metasedimentary units become rare and the main rock types are tonalitic gneisses with intercalated amphibolites. (3) A 10 km wide zone (Sagala Hills zone) between the strike slip zone (unit 2) and the Taita Hills (unit 4) is developed. This zone is characterized by elongated and folded felsic migmatic amphibole and garnet bearing orthogneiss bodies with intercalated bands of mafic rocks. (4) The Taita Hills are a slightly to the N dipping nappe stack. The main rock type in the Taita Hills are amphibole–biotite–plagioclase–quartz ± garnet ± clinopyroxene ± scapolite bearing migmatic gneisses with mafic bands. In the southern part, metapelites, marbles and some amphibolites are common.Although the geological structures are different in units 1 and 2, the calculated PT conditions are similar with peak PT of 760–820 °C and 7.5–9.5 kbar. Temperatures in unit 3 (Sagalla Hills zone) and unit 4 (Taita Hills) are slightly higher ca. 760–840 °C, but pressure is significantly higher, ranging from 10 to 12 kbar. Sillimanite growth around kyanite, garnet zonation pattern, mineral reaction textures, and PT calculations constrain a “clock-wise” PT-path with near isobaric cooling following the peak of metamorphism. The different PT conditions, tectonic setting, and a different age of metamorphism are evidence that units 1 and 2 (Galana river) belong to a different tectono-metamorphic event than unit 3 (Sagala Hills zone) and 4 (Taita Hills). The major shear zone (unit 2) marks a tectonic suture dividing the two different tectono-metamorphic domains. It is also likely that it played an important role during exhumation of the granulite facies rocks from units 3 and 4.     

Zur chemischen Variabilität regionalmetamorph gebildeter Plagioklase,Epidote und Granate

Plagioclases, Fe-rich epidotes and garnets coexisting in metamorphic rocks of basaltoid and granitoid substrata have been analyzed by standard microprobe techniques. The results presented are based on 34000 data on plagioclases, nearly 24400 on coexisting epidotes as well as of 5000 garnet data. The chemical variations within the singular plagioclase grain and in the range of a thin section are very comprehensive. Adjoining microfields (10–20 μm distance) exhibit differences in the An-contents between 30 and 80% rel. These observations are valid for nearly 78% of the examined plagioclases. Only in the higher amphibolite facies the An-variations are reduced to an average value of 32% rel. Merely the high temperature plagioclases with a compositional range of An 68-An 79 coexisting with clinopyroxene are largely homogeneous. Their variation is amounting to 6,5% An rel. The epidote chemisms reveal a dependance on both of the different substrata and their oxidation status. The maximum value of the Fe (III) substitution on the M₁ position in the epidote structure is reaching 97 molar per cent at the higher oxidized meta-granitoids and merely 87% at the metabasaltoids. The variations of the Fe/Al-proportions in the microfields are amounting to 5–20% as to the granitoid substrata and to 5–47% rel. as to the basaltoid substrata. In both of the substrata the garnets are very rich of almandine (40–70%). Besides variable amounts of grossularite and pyrope components they also contain 10–20% (basaltoids) and 1–20% (granitoids) spessartine. The most significant element variations are observed for the element Mn in garnets of granitoid origin. These variations attain 46% within the garnet grains. Only for the garnets of the basic substrata from the amphibolite facies one can state a homogenization. The reaction inertia in achieving metamorphic equilibrium is demonstrated by a selected metabasite sample of the amphibolite facies. It seems that only at temperature >600°C a homogenization of the plagioclases and garnets is initiated so that at low temperature a thermometry by means of An-contents in the plagioclases or Mn/Fe-relations in the garnets is not possible.     

I Zwicky 1: Decomposition and dynamics of the nearby QSO host

We address current theories of research on morphology, environment and evolution of active galaxies in the form of a detailed case study of the nearby QSO host I Zw 1. This study is based on sub-kpc resolution ¹²CO(1-0) observations with the BIMA mm-interferometer and on near-infrared imaging with ISAAC at the VLT. The ¹²CO(1-0) maps reveal a circumnuclear molecular gas ring with a radius of 0.9 kpc. The imaging data in the J-band are analyzed with respect to a disk-bulge decomposition. Together with a model of the gas rotation curve, the radial profile of the dynamical J-band mass-to-light ratio (M/L) is discussed. The J-band images give new evidence for an interaction between I Zw 1 and its nearby companion. First results from a sequence of N-body simulations for an extensive test of the parameter space of the interaction are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cyclotron Heating of the Solar Corona

A physical model of the solar transition region and corona is presented, in which plasma flows in rapidly-diverging coronal funnels and holes are described within the framework of a two-fluid model including wave-particle interactions. The ions are heated by wave dissipation and accelerated by the pressure gradient of high-frequency Alfvén waves, which are assumed to originate at the bottom of the magnetic network by small-scale reconnection. The heating is assumed to be due to cyclotron-resonant damping of the waves near the local ion gyrofrequency. The EUV emission lines observed by the SUMER spectrometer on SOHO show very strong broadenings, which seem to be ordered according to the ion charge-per-mass ratio and thus to indicate cyclotron-resonant heating by waves. Based on quasilinear theory, a closure scheme for anisotropic multi-component fluid equations is developed for the wave-particle interactions of the ions with Alfvén waves. The acceleration and heating rates are calculated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Novel photosensors for neutrino detectors and telescopes

The volume and the photosensitive area of next generation detectors of the numerous rarely occurring phenomena will greatly exceed the sizes of the current experiments. These phenomena include cosmic neutrinos, atmospheric neutrinos, long-baseline neutrino beams from accelerators, geo-neutrinos, geo-reactor neutrinos, and hypothetic proton decays. Similar requirements hold for a new type of a large scanning device for homeland security and nuclear proliferation control, and for the future widely accessible medical imaging devices. Photon detectors are the most important component of such detectors. Existing photosensors are based on vacuum tubes and dynode electron multipliers that are essentially hand-made, expensive and nearly impossible to produce in large enough quantities. Silicon detectors are too small for experiments requiring a very large photosensitive area. Our laboratory is developing novel detectors with a large photosensitive area that can be mass-produced, similar to large flat panel TV displays.     

Sharp images of young stellar objects

We present high resolution infrared images of the pre-main sequence star V536 Aql and polarization maps of the reflection nebula IRN Cha observed with the SHARP camera on the ESO NTT. Extended structures are observed near V536 Aql. The polarization pattern of IRN Cha is typical of a centrally illuminated source but with a central band of anomalously oriented polarization believed to occur in an optically thick disk.