Cometary Polarimetry

Abstract

AbstractComets are known to have a high (2-10 percent) polarization, caused mainly due to dust scattering and resonance fluorescence emission. Since near earth comets are generally bright (integrated visual magnitudes of 10 or even brighter) and as they show high polarization near earth-sun location, one can try to perform imaging polarimetry of such objects with small (40 cm or even smaller) telescopes. By using a dichroic polaroid sheet either in front of the telescope tube or before the imaging detector at the Cassegrain plane, one can record cometary images with a good signal to noise ratio. By rotating the dichroic sheet in three discrete steps and then reducing the corresponding three comet images to a single image, one can determine the linear polarization value at each pixel location on the image. The error in polarization will typically be the inverse of the ‘signal to noise ratio’. Such polarization images of a comet help us to determine its dust properties and also to look for possible dust jet activities. This type of work is possible with small telescopes and minor instruments.