Polarimetry of comets 67P/Churyumov-Gerasimenko, 74P/Smirnova-Chernykh, and 152P/Helin-Lawrence

Abstract

<BR /> Aims: Polarimetric characteristics of comets at large heliocentric distances is a relatively unexplored area; we extend the idea by adding and analysing the data for three Jupiter family comets (JFCs). <BR /> Methods: With the FORS2 instrument of the ESO VLT, we performed quasi-simultaneous photometry and polarimetry of three active JFCs 67P/Churyumov-Gerasimenko, 74P/Smirnova-Chernykh, and 152P/Helin-Lawrence. <BR /> Results: We obtained in total 23 polarimetric measurements at different epochs, covering a phase-angle range ~1°-16° and heliocentric distances from 3 to 4.6 au. From our observations we obtained both colour and polarimetric maps to look for structures in the comae and tails of the comets. <BR /> Conclusions: 74P/Smirnova-Chernykh and 152P/Helin-Lawrence exhibit enough activity at large heliocentric distances to be detectable in polarimetric measurements. Polarimetric and colour maps indicate no evidence of dust particle evolution in the coma. From near-infrared spectra we find no evidence of water ice in the coma of comet 152P/Helin-Lawrence. <P />Based on observations collected at the European Southern Observatory, Chile, under Programme IDs:089.C-0619 (PI = Tozzi), and 384.C-0115 (PI = Boehnhardt).