Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA study of asteroid pole-latitude distribution based on an extended set of shape models derived by the lightcurve inversion method
100
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
With the adaptive optics (AO) system on the 10 m Keck-II telescope, we acquired a high quality set of 84 images at 14 epochs of asteroid (52) Europa on 2005 January 20. The epochs covered its rotation period and, by following its changing shape and orientation on the plane of sky, we obtained its triaxial ellipsoid dimensions and spin pole location. An independent determination from images at three epochs obtained in 2007 is in good agreement with these results. By combining these two data sets, along with a single epoch data set obtained in 2003, we have derived a global fit for (52) Europa of diameters (379x330x249) +/- (16x8x10) km, yielding a volume-equivalent spherical-diameter of 315 +/- 7 km, and a rotational pole within 7 deg of [RA; Dec] = [257,+12] in an Equatorial J2000 reference frame (ECJ2000: 255,+35). Using the average of all mass determinations available forEuropa, we derive a density of 1.5 +/- 0.4, typical of C-type asteroids. Comparing our images with the shape model of Michalowski et al. (A&A 416, 2004), derived from optical lightcurves, illustrates excellent agreement, although several edge features visible in the images are not rendered by the model. We therefore derived a complete 3-D description of Europas shape using the KOALA algorithm by combining our imaging epochs with 4 stellar occultations and 49 lightcurves. We use this 3-D shape model to assess these departures from ellipsoidal shape. Flat facets (possible giant craters) appear to be less distinct on (52) Europa than on other C-types that have been imaged in detail. We show that fewer giant craters, or smaller craters, is consistent with its expected impact history. Overall, asteroid (52) Europa is still well modeled as a smooth triaxial ellipsoid with dimensions constrained by observations obtained over several apparitions.
Gaia Data Release 2 includes observational data for 14,099 pre-selected asteroids. From the sparsely sampled G band photometry, we derive lower-limit lightcurve amplitudes for 11,665 main belt asteroids in order to provide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for each asteroid, defined through the axial aspect ratios a > b and b=c, we find an average b/a=0.80+-0.04 for the ensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties from the literature, we investigate possible correlations of the aspect ratio with size, semi-major axis, geometric albedo, and intrinsic color. Based on our model simulations, we find that main belt asteroids greater than 50 km in diameter on average have higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences in the shape distribution of main belt asteroids as a function of the other properties that do not affect the average aspect ratios. We conclude that a more detailed investigation of shape distribution correlations requires a larger data sample than is provided in Gaia Data Release 2.
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.
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.
The study of meteorite craters on Earth provides information about the dynamic evolution of bodies within the Solar System. Bosumtwi crater is a well studied, 10.5 km in diameter, ca. 1.07 Ma old impact structure located in Ghana. The impactor was $sim$ 1 km in diameter, an ordinary chondrite and struck the Earth with an angle between 30$^circ$ and 45$^circ$ from the horizontal. We have used a two phase backward integration to constrain the most probable parent region of the impactor. We find that the most likely source region is a high inclination object from the Middle Main Belt.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
