GRAVITY: getting to the event horizon of Sgr A*

We present the second-generation VLTI instrument GRAVITY, which currently is in the preliminary design phase. GRAVITY is specifically designed to observe highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at center of the Milky Way. We have identified the key design features needed to achieve this goal and present the resulting instrument concept. It includes an integrated optics, 4-telescope, dual feed beam combiner operated in a cryogenic vessel; near infrared wavefront sensing adaptive optics; fringe tracking on secondary sources within the field of view of the VLTI and a novel metrology concept. Simulations show that the planned design matches the scientific needs; in particular that 10 microarcsecond astrometry is feasible for a source with a magnitude of K=15 like Sgr A*, given the availability of suitable phase reference sources.Comment: 13 pages, 11 figures, to appear in the conference proceedings of SPIE Astronomical Instrumentation, 23-28 June 2008, Marseille, Franc

ARGOS: the laser guide star system for the LBT

ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.12 page(s

HPLC-Analyse von Fettreif

Bloom was isolated from stored chocolate products for the separation of its triglycerides via high performance liquid chromatography and for the estimation of melting curves by means of thermal analysis. Different types of bloom show specific triglyceride distributions. Bloom on plain chocolate consists of cocoa butter fractions with increased concentrations of POP, POS and SOS, while nut products reveal bloom with high triolein contents. With respect to these results the accelerating effect of nut or almond oils as well as the retarding effect of milk fat may be explained

When are chocolates really finished?

Unfinished crystallisation in freshly produced chocolates is one of the major reasons for fat bloom, especially for filled products. Chocolate shells, if insufficiently crystallised, show reduced resistance to oil-migration of fillings. The influence of two production parameters, cooling tunnel time and storage temperature, on the finished state of chocolates is investigated. It is found that the crystallisation in the chocolates is not finished when the products leave the cooling tunnel

Kinetik der Fettmigration in Schokoladenprodukten. Teil 1. Grundlagen und Analytik

Nougat filled milk chocolates were stored at different temperatures. Changes of the triglycerides compositions within chocolate coating and nougat filling were measured by means of HPLC analysis. The well-known diffusion equations could be applied to describe kinetics of migration of triolein from nougat into the chocolate layer. These kinetics may explain some practical experience and may be used in quality control of multilayer or coated chocolate products

ARGOS wavefront sensing: from detection to correction

Argos is the ground-layer adaptive optics system for the Large Binocular Telescope. In order to perform its wide-field correction, Argos uses three laser guide stars which sample the atmospheric turbulence. To perform the correction, Argos has at disposal three different wavefront sensing measurements : its three laser guide stars, a NGS tip-tilt, and a third wavefront sensor. We present the wavefront sensing architecture and its individual components, in particular: the finalized Argos pnCCD camera detecting the 3 laser guide stars at 1kHz, high quantum efficiency and 4e- noise; the Argos tip-tilt sensor based on a quad-cell avalanche photo-diodes; and the Argos wavefront computer. Being in the middle of the commissioning, we present the first wavefront sensing configurations and operations performed at LBT, and discuss further improvements in the measurements of the 3 laser guide star slopes as detected by the pnCCD