The polarization signature of extra-solar planets
J. Hough¹, P. W. Lucas¹, J. A Bailey^2
1 Centre for Astrophysics Research, University of Hertfordshire, Hatfield, AL10 9AB, England ² Earth & Planetary Sciences, Macquarie University, NSW 2109, Australia
To date most extra-solar planets have been detected by indirect means, mainly through radial velocity measurements of the central star or, far less frequently, through changes in brightness of the star as a planet transits. Very recently Spitzer detected the light from extasolar planets at thermal infrared wavelenths. There are clearly significant advantages in direct detections of the light from extra-solar planets, which at optical and near-infrared wavelengths will be light from the central star reflected off the planetary atmosphere. Such direct detections, particularly with colour information, can provide information about the planet's albedo, radius, and nature of the scatterers. The small changes in brightness, as the planet orbits the star, cannot be detected by ground-based instruments. On the other hand, polarimetry - being a differential technique that in principle is not affected by the Earth's atmosphere, is capable of very high sensitivity, is limited only by photon noise, and will be effective for any orbital inclination.

We describe a polarimeter that has achieved the fractional polarization sensitivity of 1 in a million required to detect hot-Jupiters, discuss the results to date, and look at possible developments for an ELT.

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On 18 Oct 2005, 18:45.