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Rotational variation of the linear polarization of the asteroid (3200) Phaethon as evidence for inhomogeneity in its surface properties
journal contributionposted on 2019-09-10, 13:40 authored by G Borisov, M Devogele, A Cellino, S Bagnulo, A Christou, P Bendjoya, J-P Rivet, L Abe, D Vernet, Z Donchev, Y Krugly, I Belskaya, T Bonev, D Steeghs, D Galloway, V Dhillon, P O'Brien, D Pollacco, S Poshyachinda, G Ramsay, E Thrane, K Ackley, E Rol, K Ulaczyk, R Cutter, M Dyer
Asteroid (3200) Phaethon is a Near-Earth Apollo asteroid with an unusual orbit that brings it closer to the Sun than any other known asteroid. Its last close approach to the Earth was in 2017 mid-December and the next one will be on 2026 October. Previous rotationally time-resolved spectroscopy of Phaethon showed that its spectral slope is slightly bluish, in agreement with its B/F taxonomic classification, but at some rotational phases, it changes to slightly reddish. Motivated by this result, we performed time-resolved imaging polarimetry of Phaethon during its recent close approach to the Earth. Phaethon has a spin period of 3.604 h, and we found a variation of the linear polarization with rotation. This seems to be a rare case in which such variation is unambiguously found, also a consequence of its fairly large amplitude. Combining this new information with the brightness and colour variation as well as previously reported results from Arecibo radar observations, we conclude that there is no variation of the mineralogy across the surface of Phaeton. However, the observed change in the linear polarization may be related to differences in the thickness of the surface regolith in different areas or local topographic features.
This work was supported via a grant (ST/M000834/1) from the UK Science and Technology Facilities Council. We gratefully acknowledge observing grant support from the Institute of Astronomy and Rozhen National Astronomical Observatory, Bulgarian Academy of Sciences. The Calern Asteroid Polarimetric Survey (CAPS), carried out at Calern in the framework of C2PU, is a collaboration between INAF –Torino Astrophysical Observatory and the Observatoire de la cote d’Azur. The GOTO Observatory is a collaboration between the University of Warwick and Monash University (as the Monash–Warwick Alliance), Armagh Observatory & Planetarium, the University of Sheffield, the University of Leicester, the National Astronomical Research Institute of Thailand (NARIT), the Instituto de Astrofsica de Canarias (IAC), the University of Turku, and Rene Breton (University of Manchester). TB acknowledges financial support by contract DN 18/13-12.12.2017 with the Bulgarian NSF. This research was made possible through the use of the AAVSO Photometric All-Sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Gran
CitationMonthly Notices of the Royal Astronomical Society, 2018, 480 (1), pp. L131-L135 (5)
Author affiliation/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy
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