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Register a new userShape and Rotational Motion Models for Tumbling and Monolithic Asteroid 2012 $mathrm{TC_4}$:High Time Resolution Lightcurve with the Tomo-e Gozen Camera
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We present visible and near-infrared observations of a near-Earth object (NEO), 2012 $mathrm{TC_4}$. The NEO 2012 $mathrm{TC_4}$ approached close to the Earth at a distance of about 50,000 km in October 2017. This close approach provided a practical exercise for planetary defense. This apparition was also an appropriate opportunity to investigate 2012 $mathrm{TC_4}$, which is a monolithic asteroid citep{Polishook13}. We conducted the observation campaign of 2012 $mathrm{TC_4}$ using six small- and medium-sized telescopes. The multiband photometry analysis showed that the taxonomic class of 2012 $mathrm{TC_4}$ to be an X-type. In particular, we successfully obtained the high time resolution lightcurve of 2012 $mathrm{TC_4}$ with the Tomo-e Gozen camera, which is the worlds first wide-field CMOS camera, mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The shape and rotational motion models of 2012 $mathrm{TC_4}$ were derived from the lightcurve. When 2012 $mathrm{TC_4}$ was assumed to be a triaxial ellipsoid, the rotational and precession periods were 8.47 $pm$ 0.01 min and 12.25 $pm$ 0.01 min, respectively, with the long axis mode. This indicates that 2012 $mathrm{TC_4}$ is a tumbling and monolithic asteroid. The shape models showed that the plausible axial lengths to be 6.2 $times$ 8.0 $times$ 14.9~m or 3.3 $times$ 8.0 $times$ 14.3~m. The flattened and elongated shape indicates that 2012 $mathrm{TC_4}$ is a fragment produced by a impact event. We also estimated the excitation timescale, which implied that the impact event happened within $sim$3 $times$ 10$^{5}$ yr and 2012 $mathrm{TC_4}$ has a fresh surface.
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Lightcurve of the asteroid 3634 Iwan observed at the Bulgarian National Astronomical Observatory Rozhen in 2017 is presented. The asteroid was observed only one night, on 22 March 2017 accidentally in the field of view in which our target for shape modeling asteroid 289 Nenetta was positioned. The Asteroid Lightcurve Database (LCDB; Warner et al. 2009) did not contain any previously reported results for 3634 Iwan. If we accept that the ligtcurve of the asteroid is typical with two maxima and minima, a single night observations covers the whole rotational cycle. The lightcurve plotted by MPO Canopus provides a best fit to synodic period of $4.72pm 0.06$ h with amplitude of $0.15pm 0.02$ mag. Our assessment is that for the uniqueness of the period solution we need longer observational span which will reveal the number of extrema of the lightcurve and confirm the quality code U=3.
The discovery of 1I/2017 U1 (Oumuamua) has provided the first glimpse of a planetesimal born in another planetary system. This interloper exhibits a variable colour within a range that is broadly consistent with local small bodies such as the P/D type asteroids, Jupiter Trojans, and dynamically excited Kuiper Belt Objects. 1I/Oumuamua appears unusually elongated in shape, with an axial ratio exceeding 5:1. Rotation period estimates are inconsistent and varied, with reported values between 6.9 and 8.3 hours. Here we analyse all available optical photometry reported to date. No single rotation period can explain the exhibited brightness variations. Rather, 1I/Oumuamua appears to be in an excited rotational state undergoing Non-Principal Axis (NPA) rotation, or tumbling. A satisfactory solution has apparent lightcurve frequencies of 0.135 and 0.126 hr-1 and implies a longest-to-shortest axis ratio of 5:1, though the available data are insufficient to uniquely constrain the true frequencies and shape. Assuming a body that responds to NPA rotation in a similar manner to Solar System asteroids and comets, the timescale to damp 1I/Oumuamuas tumbling is at least a billion years. 1I/Oumuamua was likely set tumbling within its parent planetary system, and will remain tumbling well after it has left ours.
Imaging observations of faint meteors were carried out on April 11 and 14, 2016 with a wide-field CMOS mosaic camera, Tomo-e PM, mounted on the 105-cm Schmidt telescope at Kiso Observatory, the University of Tokyo. Tomo-e PM, which is a prototype model of Tomo-e Gozen, can monitor a sky of ${sim}1.98,mathrm{deg^2}$ at 2,Hz. The numbers of detected meteors are 1514 and 706 on April 11 and 14, respectively. The detected meteors are attributed to sporadic meteors. Their absolute magnitudes range from $+4$ to $+10,mathrm{mag}$ in the $V$-band, corresponding to about $8.3{times}10^{-2}$ to $3.3{times}10^{-4},mathrm{g}$ in mass. The present magnitude distributions we obtained are well explained by a single power-law luminosity function with a slope parameter $r = 3.1{pm}0.4$ and a meteor rate $log_{10}N_0 = -5.5{pm}0.5$. The results demonstrate a high performance of telescopic observations with a wide-field video camera to constrain the luminosity function of faint meteors. The performance of Tomo-e Gozen is about two times higher than that of Tomo-e PM. A survey with Tomo-e Gozen will provide a more robust measurement of the luminosity function.
Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population. We use sparse photometry from selected observatories from the AstDyS database, either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. The addition of new models increases the total number of models derived by the lightcurve inversion method to ~200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D < 30 km) is clustered towards ecliptic poles and can be explained by the YORP thermal effect while the latitude distribution of larger asteroids (D > 60 km) exhibits an evident excess of prograde rotators, probably of primordial origin.
We have observed the lightcurves of 13 V-type asteroids ((1933) Tinchen, (2011) Veteraniya, (2508) Alupka, (3657) Ermolova, (3900) Knezevic, (4005) Dyagilev, (4383) Suruga, (4434) Nikulin, (4796) Lewis, (6331) 1992 $mathrm{FZ_{1}}$, (8645) 1998 TN, (10285) Renemichelsen, and (10320) Reiland). Using these observations we determined the rotational rates of the asteroids, with the exception of Nikulin and Renemichelsen. The distribution of rotational rates of 59 V-type asteroids in the inner main belt, including 29 members of the Vesta family that are regarded as ejecta from the asteroid (4) Vesta, is inconsistent with the best-fit Maxwellian distribution. This inconsistency may be due to the effect of thermal radiation Yarkovsky--OKeefe--Radzievskii--Paddack (YORP) torques, and implies that the collision event that formed V-type asteroids is sub-billion to several billion years in age.
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