arXiv subjects

S. Hippler

Publications and source records attributed to S. Hippler.

75 records · Page 5Linked to original sources

arXiv2000

Near-infrared adaptive optics observations of galaxy clusters: Abell 262 at z=0.0157, J1836.3CR at z=0.414, and PKS 0743-006 at z=0.994

We report on high angular resolution near-infrared (NIR) observations of three galaxy clusters at different redshifts using adaptive optics (AO). In the case of the barred spiral \object{UGC 1347} in Abell 262 we presented the first AO results obtained using a laser guide star. The observations have been carried out with the MPE/MPIA adaptive optics laser guide star system ALFA and the ESO AO system ADONIS combined with the SHARP II+ camera built at MPE. The three clusters are well suited for high resolution investigations since bright field stars for tip-tilt or wavefront sensing are located close to the line of sight to cluster galaxies. In summary our high angular resolution NIR data combined with other information clearly indicates star formation activity or interaction between cluster members at all three redshifts. The results and implications for future high angular resolution adaptive optics observations are discussed in the framework of current galaxy and cluster evolution models.

astro-ph↗

arXiv1999

The ALFA Laser: Beam Relay and Control System

The ALFA laser subsystem uses a 4 watt continuous wave laser beam to produce an artificial guide star in the mesospheric sodium layer as a reference for wavefront sensing. In this article we describe the system design, focusing on the layout of the beam relay system. It consists of seven mirrors, four of which are motor-controlled in closed loop operation accounting for turbulences inside the dome and flexure of the main telescope. The control system features several computers which are located close to analysis and control units. The distribution of the tasks and their interaction is presented, as well as the graphical user interface used to operate the complete system. This is followed by a discussion of the aircraft detection system ALIENS. This system shuts off the laser beam when an object passes close to the outgoing laser.

astro-ph↗

arXiv1998

First Observational Results from ALFA with Natural and Laser Guide Stars

The sodium laser guide star adaptive optics system ALFA, which is installed at the Calar Alto 3.5-m telescope, has been undergoing an intensive optimisation phase. Observations using natural guide stars that are presented in this paper, show that for bright stars (V~<8) it is now possible to reach K-band Strehl ratios in excess of 60% and to easily resolve binaries at the diffraction limit of the telescope. In more typical usage Strehl ratios in the range 10-15% can be achieved over a wide field (~2'); and the limiting magnitude is currently V~<12.5. We also present some of the first spectroscopy at diffraction limited scales, showing we are able to distinguish spectra of binary stars with a separation of only 0.26''. Our last set of results are on Abell galaxy clusters, including a correction on a galaxy using the laser guide star as the reference. There are still a number of difficulties associated with the laser, but our best result to date is of the galaxy UGC 1347 in Abell 262. Correcting tip-tilt on a star 41'' away and higher orders on the laser, we achieved in increase in peak intensity of 2.5, and a reduction in FWHM from 1.07'' to 0.40''. It is expected that further significant advances will be made in the next 6 months and beyond.

astro-ph↗