Dr Fraser Clarke

Abstract:

We present the SWIFT image slicer and its novel de-magnifying design. It is based on the MPE-3D and SPIFFI image slicers, uses plane mirrors to slice the input field, but achieves a considerable de-magnification through the use of a mosaic of spherical lenses. As only plane and spherical surfaces are used in the design, classical polishing techniques can be applied to achieve very high surface accuracy and quality. This reduces aberrations and scattered light, mandatory for an image slicer working at optical wavelengths and behind an adaptive optics system. Except for the lens mosaic, the SWIFT slicer is built entirely from Zerodur and is assembled using optical contacting. We present a detailed description of the design as well as results of the early stages of its fabrication.

Abstract:

White dwarfs are excellent targets for direct imaging searches for extra-solar planets, since they are up to 104 times fainter than their main sequence progenitors, providing a huge gain in the contrast problem. In addition, the orbits of planetary companions that lie beyond the maximum extent of the Red Giant envelope are expected to widen considerably, improving resolution and further encouraging direct detection. We discuss current searches for planetary companions to white dwarfs, including our own "DODO" programme. At the time of writing, no planetary companion to a white dwarf has been detected. The most sensitive searches have been capable of detecting companions ≳5MJup, and their non-detection is consistent with the conclusions of McCarthy & Zuckerman (2004), that no more than 3% of stars harbour 5-10MJup planets at orbits between 75-300AU. Extremely Large Telescopes are required to enable deeper searches sensitive to lower mass planets, and to provide larger target samples including more distant and older white dwarfs. ELTs will also enable spectroscopic follow-up for any resolved planets, and follow-up of any planetary companions discovered astrometrically by GAIA and SIM. © 2006 International Astronomical Union.

Abstract:

We report the results of observations designed to investigate the spectroscopic signatures of dust clouds on the L2 brown dwarf Kelu-1. Time-resolved medium-resolution spectra show no significant evidence of variability in the dust-sensitive TiO, CrH and FeH bandheads on a time-scale of 1-24 h. We do, however, report periodic variability in the pseudo-equivalent width of Hα consistent with the 1.8-h rotation period previously reported for this object. Near-contemporaneous I-band photometry shows evidence for non-periodic variability at the level of 2 per cent.