The phase-polarization curve of asteroid (3200) Phaethon†

Abstract

A multi-colour phase-polarization curve of asteroid (3200)~Phaethon has been\nobtained during the December 2017 apparition by merging measurements taken at\nthe observing station of Calern (France) and at the Rhozen observatory\n(Bulgaria). All the observations were obtained in the positive polarization\nbranch, the phase angle ranging from 36$^\\circ$ to 116$^\\circ$. The measured\nvalues of linear polarization are among the highest ever observed for a Solar\nsystem body. The covered interval of phase angle was not sufficiently extended\nto derive a firm determination of the $P_{\\rm max}$ parameter, but this appears\nto occur at a phase angle around 130$^\\circ$ and reaches more than 45\\% of\nlinear polarization. Phaethon is the parent body of the Geminid meteor shower,\nand the real physical nature of this object (asteroid or comet) has been a\nlong-debated subject. Our polarimetric measurements seem to support the\nasteroid hypothesis with a phase-polarization curve similar to the asteroid\n(2)~Pallas, but further observations at smaller phase angles are needed to draw\ndefinitive conclusions.\n