STELLAR OCCULTATION OBSERVATIONS OF ASTEROID (3200) PHAETHON FOR THE DESTINY+FLYBY. T. Arai1, F. Yoshida1, P. Hong1, T. Okamoto2, H. Noda3, M. Soma3, J. Watanabe3, S. Abe4, I. Sato4,
R. Yamada5, K. Arimatsu6, T. Horaguchi7, M.-Y. Yamamoto8, T. Hayamizu9,10, K. Nishiyama2, T. Takashima2, D.
W. Dunham11,12, S. Preston11, S. Marshall13, M. W. Buie14 and the DESTINY+ Occultation Team. 1Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, Japan (tomoko.arai@it-chiba.ac.jp), 2ISAS, JAXA,Japan, 3National Astronomical Observatory of Japan, Japan, 4Nihon University, Japan, 5Aizu University, Japan,6Kyoto University, Japan, 7National Museum of Nature and Science, Tokyo, Japan, 8Kochi University of Technology, Japan, 9Saga Hoshizora Astronomical Center, Japan, 10Japan Occultation Information Network (JOIN), Japan.
11International Occultation Timing Association (IOTA), USA, 12KinetX Aerospace, USA, 13Arecibo Observatory &University of Central Florida, USA, 14Southwest Research Institute, Boulder, CO, USA.
Introduction: DESTINY+ (Demonstration and Experiment of Space Technology for INterplanetary
voYage, Phaethon fLyby and dUst Science) is a joint
mission of technology demonstration and scientificobservation, which was selected in 2017 for
JAXA/ISAS small-class program [1]. It will test highperformance electric propelled vehicle technology andhigh-speed (33km/sec) flyby imaging of asteroid(3200) Phaethon and possibly asteroid 2005UD, whicha break-up body from Phaethon as an extended mission[1]. Phaethon is a parent body of Geminid meteor
shower [3, 4], and still actively ejects dust upon every
perihelion passage [5-8]. Phaethon passed 0.07 au fromthe Earth on December 16, 2017, which is the closestapproach since 1974 and until 2093. Durin this apparition, global astronomical observation campaign of
Phaethon was conducted [10], including optical, spectroscopic, polarimetric and radar observation withground and space-based telescopes [11-24]. There arelarge differences in the size estimate between twodimensional delay-Doppler radar images of Arecibo (6km, dia.) [14] and thermophysical modelling results ofobservations from NEOWISE mission (4.6 km, dia.)[23]. The variable size estimates yield a range of albedo estimate of 0.09-0.16 [14, 24]. To determine thesize of Phaethon independently, observations of stellar
occulation were conducted in 2019. Here, we reportresults of stellar occultation, mainly for events in Japan.
Occultation prediction: Total 17 events of stellar
occultation by Phaethon were predicted by I. Sato, H.
Noda, M. Soma and IOTA (Table 1). All predictions
were made based on the new Gaia DR2 catalog [25,26]. Thanks to the results from the Gaia mission, farmore precise orbit for Phaethon and star positions thanbefore were obtained, resulting in successful observation of stellar occultation by an asteroid of <10 km dia.
Observation equipments: Due to faint stars andshort duration for occultation in most events, large
telescopes of 20-30 cm coupled with GPS video-rate
recording. QHY174M-GPS cameras with CMOS detector and integrated GPS receiver for accurate time
tagging of images were used. The readout time wasnegligible.
Results: All results reported to IOTA were summarized [27]. Here are presented two events in Japan.

2019 August 21 occultation: Sixteen stations weredeployed in southern Hokkaido of Japan across thepredicted path at 1-km intervals (Fig. 1a). The observation was not successful due to cloudy weather.
2019 October 15 occultation: Ten stations were deployed in Yamagata and Miyagi of Japan across thepredicted path at about 1-km intervals (Fig. 1b). Theoccultation was recorded at two stations by M. Ida andby H. Tomioka et al. (Fig. 1b). Another station farther
south had no positive occultation. Observations at other stations failed due to clouds and fog. A preliminary
reduction profile and light curve are shown in Fig. 2.
Size determination: The best size information camefrom the July 29 event [27]. The size data from the US
event and from Oct. 15 Japan even are broadly consistent with the previous data [14,24], not yet sufficient.
Effort of size and shape determination continues with
3D shape model based on light curve and radar observatioin combined with future occultation observation.
Acknowledgements: Onservation in Japan was fundedby ISAS/JAXA and Chiba Inst. of Tech. The huge
success of observation in US was due to the incredible
support from IOTA and NASA.
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Table 1. List of predicted observation opportunities, modifided from IOTA website.
http://iota.jhuapl.edu/2019Phaethon.htm Observations of #1, 2, 5, 10, 11 and 14 were reported to IOTA.

(a)

(b)

Fig 1. Predicted occultation paths and the observation locations in Japan. (a) August 21, 2019 event and(b) October 15, 2019 event.

(a)

(b)

Fig 2. (a) Light curve obtained by M. Ida and (a) a preliminary reduction profile generated by T. Hirose(dashed lines are for the stations which were set up, but failed due to clouds or fog).