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

Portable and modular electronic nose for olfactometric measurements

In this paper we describe an olfactometric measuring system, equipped with a measuring chamber for eight semiconductor gas sensors. The entire system is controlled by a PC/104-system. The measuring program controls the measurement data recording, as well as the process control and the data analysis. As test measurements for the olfactometer nuts with different roasting degrees were selected. A measurement cycle of about two minutes is possible. The main advantages of this device are the modular and portable system concept, the temperature transient operation methods and that most of the different sensortypes (for example semiconductor-, surface acoustic wave-, quartz micro balance- or interdigital capacitor gassensors) can be used

The ARGOS wavefront sensor pnCCD camera for an ELT: characteristics, limitations and applications

While a large visible fast low-noise detector for a Shack-Hartmann wavefront sensor (SH WFS) for an ELT does not exist yet, the current CCD technology pushed to its limits already provides several solutions for the ELT AO detector requirements. One of these devices is the new WFS pnCCD camera of ARGOS, the Ground-Layer Adaptive Optics system (GLAO) for LUCI at LBT. Indeed, with its 264×264 pixels, 48µm pixel size and 1kHz frame rate, this camera provides a technological solution to different needs of the AO systems for ELTs, such as "first-light" low-order SH but as well possibly higher order sensing using pyramid WFS. In this contribution, we present the newly developed WFS pnCCD camera of ARGOS and how it fulfills future detector needs of AO on ELTs