Prof Patrick Roche

Abstract:

Linear polarimetry in the mid-infrared can be used to obtain magnetic field directions in astronomical sources. However, since the polarization can arise from emission and/or absorption from aligned grains, care is needed to plan observations so that enough information is obtained to identify and separate the components of polarization. Procedures for doing this from spectropolarimetry, and from polarimetric imaging at a minimum of two wavebands and making an appropriate filter choice, are presented here, together with an example.

Abstract:

The mid-infrared instruments, operating in the 10 and 20 mum atmospheric windows, on the Gemini 8-m telescopes are described. The advantages and disadvantages of ground-based telescopes compared to satellite observatories are briefly discussed. On Gemini-N, Michelle, a cryogenic imager and grating and echelle spectrometer built at the UK Astronomy Technology Centre in Edinburgh offers imaging, long-slit spectroscopy and polarimetry. Spectral resolving powers between 200 and 20,000 are available by selecting one of five interchangeable gratings held in the cold grating drum. The Thermal Region Camera-Spectrometer (TReCS) is undergoing final tests at the University of Florida before delivery to Gemini-S. It offers imaging and low or moderate resolving power (R < 1000) spectroscopy. Even with the excellent image quality and low-emissivity of the Gemini telescopes, the thermal background from the sky, telescope and instrument windows are many orders of magnitude greater than the mid-infrared background emission in space. The main advantages of the Gemini instruments are the high spatial resolution available from large aperture ground-based telescopes (FWHM similar to lambda/D = 0.3 arcsec at 12 mum), the versatile instrumentation and the high spectral resolution, which coupled with the 50 m(2) collecting area, gives good spectroscopic performance. Some initial performance figures and results are given. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.