Keywords:Asteroids, (3200) Phaethon, (155140) 2005UD
(3200) Phaethon is the flyby target and (155140) 2005UD is a second flyby candidate of the DESTINY+ mission. Each asteroid approached to the Earth and became bright in 2017-2018. We utilize this opportunity and organized an observation campaign for both asteroids with international collaborators. The following people participated to the observational campaign : F. Yoshida, R. Ishimaru, K. Ishibashi, P. Hong, T. Arai (PERC/ChiTech), R. Okazaki, T. Sekiguchi, H. Naito, M. Imai, T. Ono (Hokkaido University of Education), S. Urakawa (Japan Spaceguard Association, Bisei Spaceguard Center), Y. Shinnaka (Kyoto Sanyo Univ.), T. Tanigawa (Sumoto high school), T. Yanagisawa, H. Kurosaki (JAXA), S. Abe, R. Kato (Nihon Univ.), N. Natira, T. Nishiumi (Univ. of Tokyo), M. Ishiguro (Seoul National University), M.-J. Kim, Y.-J. Choi, H.-K. Moon (KASI), D.-H. Kim, H.-J. Lee, S.-M. Lee (Chungbuk National University), Zhong-Yi Lin (Institute of Astronomy, National Central University), Xiaobin Wang (Yunnan Observatories, CAS), A. Serebryanskiy, M. Krugov, I. Reva (Fesenkov Astrophysical Institute), O. Burkhonov, E. Kamoliddin (UBAI), A. Peyrot, J-P. Teng (Les Makes Observatory), Y. Krugly (Institute of Astronomy of V.N. Karazin Kharkiv National University), I. M. Volkov (SAI MSU, INASAN), I. V. Nikolenko, S. I. Barabanov (INASAN), M. Kaplan, O. Erece (Akdeniz university), A. Sonka, S. Anghel (Astronomical Institute of Romanian Academy, Bucharest University), M. Birlan, F. Vachier, J. Berthier (Observatoire de Paris, IMCCE, CNRS), A. Klotz (CNRS-OMP-IRAP), P. Thierry (Auragne Observatory), O. Ivanova, M. Husarik (Astronomical Institute of the Slovak Academy of Sciences), E. Kuznetsov, D. Glamazda, G. Kaiser, E. Koren, V. Krushinsky, A. Popov, A. Shagabutdinov, Y. Vibe (Ural Federal University), M. Lazzarin, V. Petropoulou, I. Bertini, F. La Forgia (University of Padova), E. Palomba, E. D'aversa, A. Migliorini (INAF-IAPS), J. Vaubaillon (Observatoire de Paris), T. G. Wilson (University College London, Isaac Newton Group), O. Vaduvescu (Isaac Newton Group, Instituto de Astrofísica de Canarias), M. Popescu, Julia de Leon (Instituto de Astrofísica de Canarias), V. Lorenzi (Fundación Galileo Galilei - INAF, Instituto de Astrofísica de Canarias), M. Granvik (University of Helsinki / Luleå University of Technology), A. Penttilä (University of Helsinki), K. O. Muinonen (University of Helsinki / National Land Survey of Finland), T. Kareta, V. Reddy, D. S. Lauretta, B. Sharkey, C. Hergenrother (LPL, University of Arizona), J. A. Sanchez (PSI), T. Linder (Astronomical Research Institute), O. Kuhn, A. Conrad (Large Binocular Telescope Observatory), N. Moskovitz (Lowell Observatory), J. Masiero, A. Mainzer, L. Benner, M. Brozovic, S. Naidu, J. Giorgini (NASA JPL), E.L. Wright, D. Jewitt (UCLA), P. Taylor, E. Rivera-Valentin, S. Bhiravarasu, B. Aponte-Hernandez (Lunar and Planetary Institute), S. Marshall, F. Venditti, A. Virkki, L. Zambrano-Marin (Arecibo Observatory & University of Central Florida), C. R. Sanchez-Vahamonde (University of Western Ontario) (in the order from east to west in Fig.1).
Most of results obtained from the campaign were presented in IDP2019, which was held at Tokyo Skytree Town Campus of CIT, Japan, on February 12-14, 2019 (Fig. 2). So far, for both asteroids, rotation period, average colors, absolute magnitudes, spectra (0.4-2.5μm) were obtained by photometry and spectroscopy during this observation campaign. Radar observation were done for Phaethon, and polarimetric observations were done for both asteroids. As preliminary results, the following properties were reported. Rotation periods: 5.2 hr (or 7.85 hr) for 2005UD, 3.6hr for Phaethon. Average colors : B-V=0.71, V-R=0.37, V-I=0.32 for 2005UD, B-V=0.73, V-R=0.36 for Phaethon. Absolute magnitude is 17.25 mag for 2005UD. No significant variation of rotationally resolved VIS-NIR spectra were seen for both asteroids. However, a slight variation of visual spectra of Phaethon taken in 2017 was reported. Both asteroids are in C-complex. Interestingly, in the NIR spectra, both asteroids show totally different spectra each other: concave-up and blue for Phaethon, linear and red for 2005UD. The results from polarimetric observation show both asteroids are very similar. As for Phaethon, rotational variation in polarization was reported. Lightcurve observations revealed Phethon has top shape. Radar observation estimated the Phaethon's diameter is about 6km, and revealed no coma, no satellite. Possible craters (D>1km below 30 deg latitude, D=1.5km near equator), 600m wide dark spot (likely a flattened region) were discovered.