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

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK
e-mail: ast@arm.ac.uk; sba@arm.ac.uk
² Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT, UK
³ INAF–Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: tozzi@arcetri.inaf.it
⁴ Max-Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁵ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁶ Department of Physics, University of Helsinki, PO Box 64, Gustaf Hällströmin katu 2a, 00014 Helsinki, Finland
⁷ Finnish Geospatial Research Institute FGI, Geodeetinrinne 2, 02430 Masala, Finland
⁸ The Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, UK

Received: 4 November 2015
Accepted: 9 May 2016

Abstract

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).

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.

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.

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.