Fumi Yoshida

We report on the first polarimetric study of (3200) Phaethon, the target of JAXA’s DESTINY+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. We conducted observations at low phase angles (Sun-target-observer angle, α = 8.8–32.4°) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree Pmin = −1.3 ± 0.1  per cent, a polarimetric slope h = 0.22 ± 0.02  per cent deg−1, and an inversion angle α0 = 19.9 ± 0.3°. The derived geometric albedo is pV = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.

We present an analysis of survey observations of the trailing L5 Jupiter Trojan swarm using the wide-field Hyper Suprime-Cam CCD camera on the 8.2 m Subaru Telescope. We detected 189 L5 Trojans from our survey that covered about 15 deg2 of sky with a detection limit of m r = 24.1 mag, and selected an unbiased sample consisting of 87 objects with absolute magnitude 14 ≲ H r ≤ 17 corresponding to diameter 2 km ≲ D ≲ 10 km for analysis of size distribution. We fit their differential magnitude distribution to a single-slope power law with an index α = 0.37 ± 0.01, which corresponds to a cumulative size distribution with an index of b = 1.85 ± 0.05. Combining our results with data for known asteroids, we obtained the size distribution of L5 Jupiter Trojans over the entire size range for 9 ≲ H V ≤ 17, and found that the size distributions of the L4 and L5 swarms agree well with each other for a wide range of sizes. This is consistent with the scenario that asteroids in the two swarms orig...

Context. The close approach of the near-Earth asteroid (99942) Apophis to Earth in 2029 will provide a unique opportunity to examine how the physical properties of the asteroid could be changed due to the Earth’s gravitational perturbation. As a result, the Republic of Korea is planning a rendezvous mission to Apophis. Aims. Our aim was to use photometric data from the apparitions in 2020−2021 to refine the shape model and spin state of Apophis. Methods. Using thirty-six 1- to 2-meter-class ground-based telescopes and the Transiting Exoplanet Survey Satellite, we carried out a photometric observation campaign throughout the 2020−2021 apparition. The convex shape model and spin state were refined using the light-curve inversion method. Results. According to our best-fit model, Apophis is rotating in a short-axis mode with rotation and precession periods of 264.178 h and 27.38547 h, respectively. The angular momentum vector orientation of Apophis was found to be (275°, −85°) in the ec...

DESTINY (Demonstration and Experiment of Space Technology for INterplanetary voYage, Phaethon fLy-by and dUst Science) is a mission proposed for JAXA/ISAS Epsilon class small program, currently in the pre-project phase (Phase-A) with a launch targeted for 2022. DESTINY is a joint mission of technology demonstration and scientific observation. The science mission objectives are (1) to measure physical and chemical properties of cosmic dusts around 1 au and (2) to conduct geological observation of Phaethon upon flyby and analyze dusts nearby Phaethon. Phaethon is known as a parent body of the Geminid meteor shower, the size of which is approximately 6 km in diameter. Phaethon is important as a known source for cosmic dust delivered to the Earth. During the flyby of Phaethon spatially resolved images of Phaethon will be taken by two onboard cameras, the Telescopic CAmera for Phaethon (TCAP) and the Multiband CAmera for Phaethon (MCAP). The relative flyby speed is as high as 33 km/s and...

Jason Rhodes (Jet Propulsion Laboratory, California Institute of Technology; Jason.d.rhodes@jpl.nasa.gov), Takahiro Sumi (Osaka University), David Bennett (NASA/GSFC), Peter Capak (IPAC/Caltech), Olivier Doré (JPL), A. Fukui (NAOJ), Jeremy Kasdin (Princeton University), Bryan Holler (STScI), Takayuki Kodama (Tohoku), Yusei Koyama (NAOJ), Noriyuki Matsunaga (The University of Tokyo), Stefanie Milam (NASA/GSFC), Hironao Miyatake (Nagoya), Shogo Nishiyama (Miyagi University of Education), Masami Ouchi (University of Tokyo), James Rhoads (NASA/GSFC), Dan Scolnic (Duke University), Daisuke Suzuki (JAXA), Nao Suzuki (IPMU), Masaomi Tanaka (Tohoku University), Motohide Tamura (U. Tokyo and Astrobiology Center), Tsuyoshi Terai (NAOJ), David Weinberg (Ohio State), Ben Williams (University of Washington), Toru Yamada (JAXA), Fumi Yoshida (PERC/Chitech)

We observed a stellar occultation by (3200) Phaethon, which occurred in western Japan on 2021 October 3 (UTC). This observation was requested by the DESTINY+ mission team, which plans to conduct a flyby of asteroid Phaethon in 2028. Overall, this research effort contributes towards a large-scale observation campaign with a total of 72 observers observing from western Japan to southern Korea. 36 stations were established, and stellar occultation by the asteroid Phaethon was detected in 18 of them. This is the first time that this many multiple chord observations have been made for such a small asteroid (it has a diameter of 5–6 km). Observational reductions show that the apparent cross-section of Phaethon at the time of the occultation could be approximated using an ellipse with a major diameter of 6.12 ± 0.07 km and a minor diameter of 4.14 ± 0.07 km, and a position angle of 117.°4 ± 1.°5. As can be seen from the small error bars of the fitted ellipse, we have succeeded in estimatin...

Japanese asteroid explorer Hayabusa2 arrived at C-type asteroid 162173 Ryugu in June 2018. Laser altimeter (LIDAR) onboard Hayabusa2 measured its own transmitted laser pulse intensity and returned pulse intensity from the surface of Ryugu until November 2019. Because the Ryugu surface is extremely rough, topography dominates material property in the conventional derivation of normal albedo. We develop a method to derive the albedo from the rough surface of the C-type asteroid at the LIDAR laser wavelength of 1.064 μm. Using the intensity data obtained before the conjunction of the spacecraft with the Sun, the albedo map covering an equatorial band between – 40˚ and + 20˚ in the latitude is created with 2˚ by 2˚ resolution. The average of the albedo is 0.0406 [[EQUATION]] 0.0031, while about half of them are in the range between 0.04 and 0.045. The low and uniform albedo feature is common to other remote-sensing observations of Ryugu by visible and near-infrared cameras onboard the H...

CCD photometric observations of the asteroid were performed by the author over two nights on 2019 January 28 and 30. A total of 13 hours 10 minutes of observation resulted in 235 data points for analysis. The rotation period was found to be 3.846 ± 0.002 h with a lightcurve amplitude of 0.15 ± 0.02 mag. A search of the asteroid lightcurve database (LCDB, Warner et al., 2009) indicates no previously reported rotation period for this asteroid.

NAMIKI, Noriyuki 1∗ ; MIZUNO, Takahide ; SENSHU, Hiroki 1 ; YAMADA, Ryuhei ; NODA, Hirotomo ; SHIZUGAMI, Makoto ; HIRATA, Naru ; IKEDA, Hitoshi ; ABE, Shinsuke ; MATSUMOTO, Koji ; OSHIGAMI, Shoko ; YOSHIDA, Fumi ; HIRATA, Naoyuki ; MIYAMOTO, Hideaki ; SASAKI, Sho ; ARAKI, Hiroshi ; TAZAWA, Seiichi ; ISHIHARA, Yoshiaki ; KOBAYASHI, Masanori 1 ; WADA, Koji 1 ; DEMURA, Hirohide ; KIMURA, Jun ; HAYAKAWA, Masahiko ; KOBAYASHI, Naoki ; MITA, Makoto ; KAWAHARA, Kousuke ; KUNIMORI, Hiroo

Using the high-cadence lightcurves collected from the FOSSIL survey, rotation periods of 17 small (diameter 1 km < D < 3 km) Hilda asteroids (hereinafter Hildas) were obtained. Combined with the previously measured rotation periods of Hildas, a spin-rate limit appears at around 3 hr. Assuming rubble-pile structures for the Hildas, a bulk density of ∼1.5 g cm−3 is required to withstand this spin-rate limit. This value is similar to that of the C-type asteroids (1.33 g cm−3) and higher than the ∼1 g cm−3 bulk density of the Jupiter Trojans. This suggests that the Hildas population may contain more C-type asteroids than expected, and the limit at 3 hr simply reflects the spin-rate limit for C-type asteroids. In addition, a Hilda superfast rotator was found, which has a rotation period of 1.633 hr and an estimated diameter of 0.7 km. This object is unlikely to be explained by a rubble-pile or monolithic structure.

<p>The Tomo-e Gozen project conducts optical wide-field survey programs with a wide-field CMOS camera, Tomo-e Gozen, attached on the 105-cm Schmidt telescope at the Kiso Observatory, the University of Tokyo, Japan. Tomo-e Gozen is the world's first wide-field CMOS camera which covers 20 square degrees with 84 chips of 35 mm full HD CMOS image sensors. A wide-field and high-cadence survey in the optical wavelengths began in 2018 with the Tomo-e Gozen (hereafter referred to as the Tomo-e Gozen transient survey). The main purpose of this survey is to detect young supernovae. However, the survey simultaneously detects a large number of moving objects in their images. As one of the by-products of the survey, here we show our preliminary result about production of phase curves (solar phase angles versus absolute magnitude) of more than 44,000 small solar system bodies including main-belt asteroids, near-Earth asteroids, Jupiter Trojans, Centaurs, and Transneptunian objects (this number is as of April 11, 2020). Combining the moving object catalogue derived from the survey and the output ephemeris that the Horizons/JPL system provides, we are now able to obtain phase curves of these objects almost automatically. As the Kiso moving object catalogue is updated and being expanded on a daily basis, the number of the objects (small bodies) that we deal with goes up as well. Our result, when completed, will make a fair complement as well as a significant keystone to what is already published such as from the Pan-STARRS systematic survey on the knowledge of the surface characteristics of the small solar system bodies.</p>

Simultaneous photometric and polarimetric observations of asteroid 3 Juno have been carried out with a low-resolution spectropolarimeter HBS at Okayama Astrophysical Observatory from 2000 August 4 to 8. The amplitude of the light curve was 0.14 mag with almost the same brightness maxima and 0.10 mag different minima. Polarimetric data showed one maximum and minimum in the absolute values of polarization degree |Pr |, and the difference attained 0.149% in the V band. The minimum of |Pr | appeared around the second minimum of the light curve, which means that a bright area exists on the surface of 3 Juno. We found that the values of |Pr | tend to increase 0.1%-0.2% with wavelength, and this result is consistent with the general tendency of S-type asteroids. In addition, we might find that the increase rate of |Pr | is steeper in wavelengths longer than 7000 A. From the variation of polarization degree with the rotation of 3 Juno, we estimated the albedo of the bright area with a simple model and obtained a range of 0.19-0.41.

ONBOARD THE DESTINY+ SPACECRAFT. K. Ishibashi1, P. Hong1, T. Okamoto2, T. Ishimaru2, S. Sato2, M. Yamada1, O. Okudaira1, T. Arai1, F. Yoshida1, S. Kameda3, M. Kagitani4, T. Iwata2, T. Okada2, and T. Takashima2, 1Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino-shi, Chiba 275-0016, Japan, 2Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan, 3Rikkyo University, 3-341 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan, 4Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan.

The Karin family is a very young asteroid family created by an asteroid breakup 5.8 Myr ago. Since the members of this family probably have not experienced significant orbital or collisional evolution yet, it is possible that they still preserve properties of the original family-forming event in terms of their spin state. As we carried out a series of photometric observations of the Karin family asteroids, here we report an analysis result of lightcurves including the rotation period of eleven members. The mean rotation rate of the Karin family members turned out to be much lower than those of NEAs or smaller MBAs (diameter D<12 km), and even lower than that of larger MBAs (D>130 km). We investigated a correlation between the peak-to-peak variation magnitude reduced to zero solar phase angle and the rotation period of the eleven Karin family asteroids, and found a possible trend that elongated members have lower spin rate, and less elongated members have higher spin rate. Howe...

Context. The object 2012 DA14 is a near-Earth asteroid with a size of several tens of meters. It had approached closely the Earth on 15 February, 2013 UT, providing an opportunity for precise measurements of this tiny asteroid. Aims. The solar phase angle of 2012 DA14 had varied widely around its closest approach but was almost constant during the following night. We performed time-series photometric observations on those two nights to determine the rotational properties and phase effect. Methods. The observations were carried out using the 0.55-m telescope at Saitama University, Japan. The R-band images were obtained continuously over a 2 hr period at the closest approach and for about 5 hr on the next night. Results. The lightcurve data from the second night indicates a rotational period of 11.0 +1.8/-0.6 hr and a peak-to-peak amplitude of 1.59 +/- 0.02 mag. The brightness variation before and after the closest approach was separated into two components that are derived from the r...

Time-series multi-band photometry and spectrometry were performed in Nov.-Dec. 2017 to investigate the homogeneity of the surface of asteroid (3200) Phaethon. We found that Phaethon is a B-type asteroid, in agreement with previous studies, and that it shows no evidence for rotational color variation. The sub-solar latitude during our observation period was approximately 55 degree S, which corresponded to the southern hemisphere of Phaethon. Thus, we found that the southern hemisphere of Phaethon has a homogeneous surface. We compared our spectra with existing spectral data to examine the latitudinal surface properties of Phaethon. The result showed that it doesn't have a latitudinal color variation. To explain this observation, we investigated the solar-radiation heating effect on Phaethon, and the result suggested that Phaethon underwent a uniform thermal metamorphism regardless of latitude, which was consistent with our observations. Based on this result, we discuss the homoge...

Additional file 1: Table S1. Fully normalized spherical harmonic coefficients of the gravity field model of Ryugu up to degree and order 10 obtained from the shape model SHAPE_SPC_3M_v20181109 based on the assumption of the globally constant density.

We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V=8.3 mag, K=7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a T_ eff =6509^+50_-49 K, a mass of M_* = 1.460^+0.055_-0.059M_, radius of R_* = 1.506±0.022R_, and an age of 0.78^+0.61_-0.42 Gyr. Its planetary companion (KELT-24 b) has a radius of R_ P = 1.272±0.021R_ J, a mass of M_ P = 5.18^+0.21_-0.22M_ J, and from Doppler tomographic observations, we find that the planet's orbit is well-aligned to its host star's projected spin axis (λ = 2.6^+5.1_-3.6). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migra...

We examined the size distributions of small L4 and L5 Jovian Trojan asteroids detected in the Subaru main belt asteroid survey (SMBAS). This was the first attempt to make a comparison of the size distribution between the L4 and L5 Trojans for sizes ranging from 1 km to 10 km, using the results of systematic surveys. We detected 51 L4 Trojans and 62 L5 Trojans ranging from 0.7 km to 13 km in diameter (D) (assuming an albedo of 0.04). We found that there is a difference of the cumulative size distribution between the L4 and L5 populations. The slopes of the cumulative size distribution of the L4 population with 2 km<D< 5 km and 5 km<D< 10 km were 1.3˙0.1 and 2.4 ˙0.1, respectively; meanwhile, that of the L5 population with 2 km<D< 5 km was 2:1 ˙ 0:3. For both populations, we also give composite size distributions covering a range of 5 km<D< 100 km, whose mean slopes are found to be 2.2˙0.1 for L4 and 2.1˙0.1 for L5. Key words: minor planets, asteroids — solar s...

We examined the size distributions of small L4 and L5 Jovian Trojan asteroids detected in the Subaru main belt asteroid survey (SMBAS). This was the first attempt to make a comparison of the size distribution between the L4 and L5 Trojans for sizes ranging from 1 km to 10 km, using the results of systematic surveys. We detected 51 L4 Trojans and 62 L5 Trojans ranging from 0.7 km to 13 km in diameter (D) (assuming an albedo of 0.04). We found that there is a difference of the cumulative size distribution between the L4 and L5 populations. The slopes of the cumulative size distribution of the L4 population with 2 km<D< 5 km and 5 km<D< 10 km were 1.3˙0.1 and 2.4 ˙0.1, respectively; meanwhile, that of the L5 population with 2 km<D< 5 km was 2:1 ˙ 0:3. For both populations, we also give composite size distributions covering a range of 5 km<D< 100 km, whose mean slopes are found to be 2.2˙0.1 for L4 and 2.1˙0.1 for L5. Key words: minor planets, asteroids — solar s...

ABSTRACT Hayabusa-2 is the second asteroid mission of Japan to be launched between 2014 and 2015. LIDAR is one of five instruments onboard Hayabusa-2, and measures altitudes of the spacecraft from a surface of the asteroid, 1999JU3, by taking a time of flight of laser pulse. LIDAR is a part of attitude and orbit control subsystem and is designed for navigation of the spacecraft, in particular, during touch-down phase. Also the LIDAR data are scientifically important for analysis of the shape, mass, and surface properties of the asteroid. Hayabusa-2 LIDAR is an improved version of LIDAR onboard Hayabusa. We adopt Nd:YAG laser of which wavelength is 1.064 micro-m, and passive Q-switch. The size is 240 x 240 x 230 mm, and weighs 3.7 kg. To elucidate the nature and history of accretion and destruction of rubble pile body, we determine shape and mass of the asteroid 1999JU3. The model is developed basically from ONC images and LIDAR range data. Non dimensional shape is estimated using images taken from various configurations, and LIDAR range data determines its length scale. Mass is also essential for geodetic study of C-type asteroid. Because carbonaceous chondrites show wide variation of microscopic porosity, it is difficult to distinguish rubble pile and monolithic structures from either observation or theoretical analysis. Direct observation of mass and shape of C-type asteroid together with average density measurement of returned sample is necessary. We plan to let the spacecraft descent toward 1999JU3 from 20-km to 1-km altitude without orbital maneuvers, and also let the spacecraft ascend freely as well. Such experiments will be conducted 2 to 6 times depending on fuel left in the spacecraft. An accuracy of gravity estimate is improved as a number of free fall/rise experiments increases. LIDAR is an active sensor unlike other instruments on Hayabusa-2. Ratio of transmitting and receiving powers can be directly translated to geometric albedo at the surface of 1999JU3. In case of Hayabusa-1, the power meter could not measure both transmitting and receiving power at the same time. Then a design of Hayabusa-2 LIDAR is modified so that both transmitting and receiving powers can be measured simultaneously.

We present the results of photometric observations for the asteroid 4 Vesta in the B, Rc, and z’ band at the minimum phase angle 0.1 deg has been performed at four small telescopes. The magnitude reduced to unit distance and phase angle: M B(1, 1, 0) = 3.85 +0.05 mag, MRc = 2.71+-0.04 mag, and M z’(1, 1, 0) = 2.98 +0.03 were obtained in this study. The absolute magnitude under the IAU H-G function are about0.1 mag darker than the magnitude at the phase angle of 0deg based on the Shevchenko function model and the Hapke model. Porosity of the optically active regolith on Vesta are estimated with the Hapke model yielding rho = 0.4–0.7. We found that the opposition effect for Vesta is made a contribution to not only the shadow-hiding effect but also the coherent backscattering effect which appears from around 1deg. The amplitude of the coherent backscatter opposition effect of Vesta increases as the reflectance is brightening. We suggested that multiple-scattering in optically active sc...

Sho Sasaki, sho@miz.nao.ac.jp National Astronomical Observatory of Japan, Iwate, Japan Masaki Fujimoto, fujimoto@stp.isas.jaxa.jp Japan Aerospace Exploration Agency, Kanagawa, Japan Hajime Yano, yano.hajime@jaxa.jp JAXA/ISAS & JSPEC, Kanagawa, Japan Takeshi Takashima, ttakeshi@stp.isas.jaxa.jp ISAS/JAXA, Sagamihara, Japan Yasumasa Kasaba, kasaba@pat.gp.tohoku.ac.jp Tohoku University, Sendai, Japan Ryu Funase, funase.ryu@jaxa.jp JAXA, Japan Yuichi Tsuda, tsuda.yuichi@jaxa.jp JAXA/JSPEC, Japan Junichiro Kawaguchi, kawaguchi.junichiro@jaxa.jp Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan Yasuhiro Kawakatsu, kawakatsu.yasuhiro@jaxa.jp JAXA/ISAS & JSPEC, Japan Osamu Mori, mori.osamu@jaxa.jp JAXA/JSPEC, Sagamihara, Japan Mutsuko Morimoto, morimoto.mutsuko@jaxa.jp JAXA/JSPEC, Japan Fumi Yoshida, fumi.yoshida@nao.ac.jp National Astronomical Observatory of Japan, Japan Naruhisa Takato National Astronomical Observatory of Japan, Japan

1 , S. Miyasaka 2 , N. Tokimasa 3 , A. Sogame 4 , M. A. Ibrahimov 5 , F. Yoshida 6 , M. Abe 1 , and D. Kuroda 7 , 1 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara-shi, Kanagawa, 229-8510 Japan (hasehase@isas.jaxa.jp, abe@planeta.sci.isas.jaxa.jp), 2 Tokyo Metropolitan Government, Tokyo, Japan (seidai@toybox.gr.jp), 3 Nishi-Harima Astronomical Observatory, Hyogo, Japan (tokimasa@nhao.go.jp), 4 Tokai Univ., Kanagawa, Japan (akito.sogame@nifty.ne.jp), 5 Ulugh Beg Astronomical Institute, Tashkent, Uzbekistan (mansur@astrin.uzsci.net), 6 National Astronomical Observatory of Japan, Tokyo, Japan (fumi.yoshida@nao.ac.jp), 7 Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Okayama, Japan (dai.kuroda@nao.ac.jp).