title: A Calibration System for a Rayleigh Laser Guide Star Constellation & a Planet around a Giant Star
creator: Schwab, Christian
subject: ddc-520
subject: 520 Astronomy and allied sciences
description: My thesis consists of two parts. In Part I, I describe my contributions to the laser guide star adaptive optics facility at the Large Binocular Telescope, the Advanced Rayleigh guided Ground layer adaptive Optics System , ARGOS. I investigate the effect of scattered light from propagating the laser light across the aperture, and find that contamination is not a concern for the science instruments. I present a study of reflective laser launch telescopes based on commercial optics, and compare this to the refractive design chosen as baseline for ARGOS. The discussed options present an interesting alternative with only small additional light loss at substantially reduced cost and procurement risk. I develop a calibration scheme for the full adaptive optics system, based on artificial light sources that illuminate the deformable mirror, imitating the laser guide star beacons. This enables the interaction between deformable mirror and wavefront sensor to be calibrated at any time, greatly enhancing the possibilities and time available for engineering on the installed system. The light source has to be placed in the prime fcous, as ARGOS uses the adaptive secondary mirrors of LBT. The optical design of the calibration light source is not trivial as the guide star constellation comprises of three beacons forming an equilateral triangle on a circle with a radius of 2 arcminutes. The images of the beacons that have to be reproduced suffer from strong aberrations caused by the large off-axis distance. To match the wavefront of the beacons' images to the desired precision of 50 nanometres rms, I designed a custom objective, incorporating a computer generated hologram to shape the wavefronts of three optical fibres forming the light sources. The elliptical front surface of the objective is used in reflection to generate a central, diffraction limited spot serving as an alignment aid and truth sensor for the measurements. A thorough tolerance analysis including the assembly and the alignment at the telescope ensures that the design specifications can be met during operation. The second part of the thesis concerns the search for planets around a sample of nearby giant stars with the Doppler technique carried out at Lick Observatory's CAT telescope. I analyse new data from the previous three years, which together with the existing data from our survey form a database covering 11 years. The radial velocity measurements reveal the presence of a planetary companion around one of our target stars, which was previously unknown. This is the lightest planet found around a giant star to date with a minimum mass of 1.92 Jupiter masses in a 785 day orbit.
date: 2010
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/11042/1/Schwab_Thesis.pdf
identifier: DOI:10.11588/heidok.00011042
identifier: urn:nbn:de:bsz:16-opus-110424
identifier:   Schwab, Christian  (2010) A Calibration System for a Rayleigh Laser Guide Star Constellation & a Planet around a Giant Star.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/11042/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng