Rotation lightcurves of small jovian Trojan asteroids (original) (raw)

Rotational properties of outer belt asteroids

Icarus, 1989

We present new photometric observations of 13 asteroids (153, 190, 225,279, 334, 420, 483, 528, 588, 692, 721, 940, 1583) orbiting in the outer part of the belt, beyond the Hecuba gap at 3.3 AU from the Sun. The resulting periods and amplitudes are then used to compare the properties of a main-belt asteroid sample and an outer-belt sample at similar sizes. The outer-belt sample includes objects which are likely to have been affected less by collisional evolution and to have retained a better record of their "primordial" features. The distributions of rotational periods are not different at a statistically significant level; however, the outer-belt sample does not include the "population" of slow rotators which make the main-belt distribution markedly non-MaxweHian. As already pointed out by L. M. French (1987 Icarus 72, 325) and W. K. Hartmann and coworkers (1988, Icarus 73, 487) for Trojans and Hildas, amplitudes in the outer belt are clearly higher than in the main belt. We suggest that elongated shapes might have been frequent among planetesimals in the outer belt, as a consequence of smaller impact velocities and lower densities than for the present main-belt asteroids.

A Troop of Trojans: Photometry of 24 Jovian Trojan Asteroids

Because of their greater distance from the Sun, the Jovian Trojans have been less studied than main belt asteroids. Although they are numerous (nearly 6000 have well determined orbits as of July 2013), the Trojans remain mysterious in many ways. Their spectra are unlike those of any meteorites in terrestrial collections. The spectra and the low albedos of Trojans, however, bear a strong resemblance to those of cometary nuclei (Abell et al. 2005; Fornasier et al. 2007; Emery et al. 2011). The Nice Model (Morbidelli et al. 2005; 2009) predicts that the Trojans may well be objects that originated with today's Kuiper Belt Objects. The rotation of asteroids larger than ~50 km in diameter seems to be determined largely by collisions, while that of smaller bodies is shaped primarily by YORP forces and torques (Pravec et al. 2008). We are surveying the rotation properties of Trojans to see whether similar trends are present. We find an abundance of slow rotators, including the first doc...

Photometry and Spin Rate Distribution of Small-Sized Main Belt Asteroids

2008

Photometry results of 32 asteroids are reported from only seven observing nights on only seven fields, consisting of 34.11 cumulative hours of observations. The data were obtained with a wide-field CCD (40.5'x27.3') mounted on a small, 46-cm telescope at the Wise Observatory. The fields are located within ±1.5 0 from the ecliptic plane and include a region within the main asteroid belt.

Rotation periods for small main-belt asteroids

Astronomy and Astrophysics, 2004

The results of new CCD observations are presented as part of the campaign we are performing in Brazil to measure rotational periods for small asteroids. The observations presented here have been acquired at the Pico dos Dias Observatory between 1997 and 2002 and result in 48 single night lightcurves for 20 asteroids, most of them Main-Belt objects with D < 40 km. We present the rotation periods -ranging from about 3 to 18 hr -along with the composite lightcurve obtained for each observed object.

Angular momentum of binary asteroids: Implications for their possible origin

Icarus, 2008

We describe in this work a thorough study of the physical and orbital characteristics of extensively observed main-belt and Trojan binaries, mainly taken from the LAOSA (Large Adaptive Optics Survey of Asteroids, Marchis et al., 2006c) database, along with a selection of bifurcated objects. Dimensionless quantities, such as the specific angular momentum and the scaled primary spin rate, are computed and discussed for each system. They suggest that these asteroidal systems might be the outcome of rotational fission or mass shedding of a parent body presumably subjected to an external torque. One of the most striking features of separated binaries composed of a large primary (R p > 100 km) with a much smaller secondary (R s < 20 km) is that they all have total angular momentum of ~0.27. This value is quite close to the Maclaurin-Jacobi bifurcation (0.308) of a spinning fluid body. Alternatively, contact binaries and tidally locked double asteroids, made of components of similar size, have an angular momentum larger than 0.48. They compare successfully with the fission equilibrium sequence of a rotating fluid mass. In conclusion, we find that total angular momentum is a useful proxy to assess the internal structure of such systems.

Rotation Rates of Recently Discovered Small Near-Earth Asteroids

Advanced Maui Optical and Space Surveillance Technologies Conference, 2009

As part of an effort to obtain astrometric data on newly discovered Near-Earth Asteroids (NEAs) using the Magdalena Ridge Observatory's (MRO) 2.4-meter telescope, a program has also been implemented to obtain physical characterization information on some of the smallest objects in the asteroid population. Characterization studies that determine physical properties such as spin rates and orientations, shapes, material type and internal structure/strength are important for properly addressing and mitigating any potential threats from dangerous Earthcrossing objects. The rotation rate of an object can imply essential information about its internal composition (via deduction of strength boundary limits) and degree of fracture, and thereby its collisional history. In particular, the discovery of asteroids having sub-hour rotation periods is highly indicative of a non-negligible tensile strength. Previously, extensive work had been done to acquire rotation rates for asteroids greater than 200 meters in diameter, and although progress has been made extending this database to the less than 200 meter size-range, the data are still lacking. Therefore, our research has been focused toward collecting lightcurves of objects primarily smaller than 200 meters which have allowed the determination of rotation rates. Rotation rates derived from the lightcurves collected to date indicate that the asteroids studied in this small size regime exhibit both slow (hours) and fast (minutes) rotation periods. With respect to superfast rotators, one object in our database of special note is asteroid 2009 BF2 (approximately 27 meters in diameter) which is the second fastest rotator yet discovered, with a rotation period of about 58 seconds (2008 HJ is the fastest rotator at 42.7 seconds). Additionally, this survey has collected three lightcurves for objects with absolute magnitudes H > 22 that have been observed to be rotating more slowly (greater than 7 hours) than the presumed strengthless body limit. In particular, asteroid 2008 UP100 exhibits an amplitude of ~1.2 magnitudes or greater even after correcting to zero phase. Recent modeling of rubble pile structures indicates that this borders on or exceeds the elongation limit of a slowly rotating strengthless object, implying the possible existence of tensile strength.

Physical study of outer belt asteroids

Advances in Space Research, 1991

Located in the proximity of Jovian resonances, the outer belt asteroids are kept from interacting with other asteroids and are likely to represent a population of primitive bodies. The systematic investigation of the physical properties of these objects and the subsequent understanding of their nature and origin, will have a direct implication for any theoretical study on the evolution of the solar system. In the last decade the information on the spectral and photometric properties of distant asteroids has strongly increased, leading to the formulation of specific questions, the answer to which will enable a comprehensive picture of this class of bodies. Since 1988 our group is carrying out a program devoted to the physical study of the Trojans and outer belt asteroids (Hilda and Cybele groups) to characterize their rotational properties, composition and shapes. During several observing campaigns, carried out at different observatories, reliable rotational periods and light curve amplitudes have been determined for eight distant asteroids using both CCD and photoelectric photometry. We will here present some preliminary results of our campaigns.