Photometry of dust grains of comet 67P and connection with nucleus regions

¹ INAF-Astronomical Observatory of Padova, Vicolo dell’Osservatorio 5, 35131 Padova, Italy
e-mail: gabriele.cremonese@oapd.inaf.it
² Center of Studies and Activities for Space (CISAS) “G. Colombo”, University of Padova, via Venezia 15, 35131 Padova, Italy
³ Dipartimento di Fisica e Astronomia, University of Padova, Vic. Osservatorio 3, 35122 Padova, Italy
⁴ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁵ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, Univ. Paris Diderot, Sorbonne Paris Cité, UPMC Univ. Paris 06, 5 place J. Janssen, 92195 Meudon Pricipal Cedex, France
⁶ Aix-Marseille Université, CNRS LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
⁷ Centro de Astrobiologia, CSIC-INTA, 28850 Torrejon de Ardoz, Madrid, Spain
⁸ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁹ Scientific Support Office, European Space Research and Technology Centre/ESA, Keplerlaan 1, Postbus 299, 2201 AZ Noordwijk ZH, The Netherlands
¹⁰ Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
¹¹ PAS Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
¹² Institut für Geophysik und extraterrestrische Physik, TU Braunschweig, 38106 Braunschweig, Germany
¹³ University of Maryland, Department of Astronomy, College Park, MD 20742-2421, USA
¹⁴ LATMOS, CNRS/UVSQ/IPSL, 11 boulevard d’Alembert, 78280 Guyancourt, France
¹⁵ CNR-IFN UOS Padova LUXOR, via Trasea 7, 35131 Padova, Italy
¹⁶ University of Trento, via Sommarive 9, 38123 Trento, Italy
¹⁷ Department of Industrial Engineering, University of Padova, via Venezia 1, 35131 Padova, Italy
¹⁸ INAF Osservatorio Astronomico di Trieste, via Tiepolo 11, 34014 Trieste, Italy
¹⁹ Instituto de Astrofísica de Andalucía-CSIC, 18008 Granada, Spain
²⁰ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany
²¹ National Central University, Graduate Institute of Astronomy, 300 Chung-Da Rd, 32054 Chung-Li, Taiwan
²² Operations Department, European Space Astronomy Centre/ESA, PO Box 78, 28691 Villanueva de la Canada, Madrid, Spain
²³ Department of Information Engineering, University of Padova, via Gradenigo 6/B, 35131 Padova, Italy
²⁴ Physikalisches Institut der Universität Bern, Sidlerstr. 5, 3012 Bern, Switzerland

Received: 4 September 2015
Accepted: 19 January 2016

Abstract

Aims. Multiple pairs of high-resolution images of the dust coma of comet 67P/Churyumov-Gerasimenko have been collected by OSIRIS onboard Rosetta allowing extraction and analysis of dust grain tracks.

Methods. We developed a quasi automatic method to recognize and to extract dust tracks in the Osiris images providing size, FWHM and photometric data. The dust tracks characterized by a low signal-to-noise ratio were checked manually. We performed the photometric analysis of 70 dust grain tracks observed on two different Narrow Angle Camera images in the two filters F24 and F28, centered at λ = 480.7 nm and at λ = 743.7 nm, respectively, deriving the color and the reddening of each one. We then extracted several images of the nucleus observed with the same filters and with the same phase angle to be compared with the dust grain reddening.

Results. Most of the dust grain reddening is very similar to the nucleus values, confirming they come from the surface or subsurface layer. The histogram of the dust grain reddening has a secondary peak at negative values and shows some grains with values higher than the nucleus, suggesting a different composition from the surface grains. One hypothesis comes from the negative values point at the presence of hydrated minerals in the comet.