We observed the L4 Jupiter Trojans (JTs) swarm using the Hyper Suprime-Cam attached to the 8.2 m Subaru Telescope on 2015 March 30 (UT). The survey covered ∼26 deg2 of sky area near the opposition ...and around the ecliptic plane with a 240 s exposure time in the r-band filter through the entire survey. We detected 631 L4 JTs in the survey field with a detection limit of mr = 24.4 mag. We selected 481 objects with absolute magnitude Hr < 17.4 mag and heliocentric distance r < 5.5 au as an unbiased sample and then used them to estimate the size distribution. Assuming a geometric albedo of 0.07, the size range of our unbiased sample is ∼2-20 km in diameter (D). We fit a single-slope power law to the cumulative size distribution and found that the best-fit index (b) is b = 1.84 0.05 in . The slope value ( ) of the corresponding absolute magnitude distribution ( ) is 0.37 0.01. This is consistent with that of the faint-end slope presented by Wong & Brown. The size distribution obtained from this survey is slightly different from the results of previous surveys with a similar size range, which reported broken power-law or double power-law slopes in their cumulative size distribution. Our results insist that the slope of b = 1.84 continues from H = 14.0 to at least H = 17.4. Since this work contains the largest L4 JT samples and is 1 mag deeper than the study by Wong & Brown, we believe that our study has obtained the most robust size distribution of small JTs so far. Combining the cataloged L4 JTs and our survey, we show the entire size distribution of L4 JTs up to Hr = 17.4 mag.
Abstract
From the first phase of the high-cadence Formation of the Outer Solar System: an Icy Legacy (FOSSIL) survey, we analyzed lightcurves, ranging from one to four nights in length, of 371 ...trans-Neptunian objects (TNOs) for periodicity. We found 29 TNOs with periodic lightcurves, one of which is a good candidate for a close/contact binary. Another of the periodic FOSSIL TNOs could potentially have the fastest of all known TNO spin rates, with a period of 1.3 hr. We do not have total confidence in the period and thus plan to obtain a more detailed lightcurve for confirmation. The periodic TNOs have an average rotation period of 11.2 hr, close to the value obtained by Alexandersen et al., which had similar cadence, but different from other surveys. In regards to contention in the literature about whether smaller TNOs are more irregular in shape and thus have larger lightcurve amplitudes, we found that there is a weak correlation between absolute magnitude and lightcurve amplitude in a subset of 194 FOSSIL TNOs, even when using the more appropriate brightest (minimum) absolute magnitude instead of the time-averaged value.
Context.
This paper extends our previous study of the early evolution of Jupiter and its two Trojan swarms by introducing the possible perturbations of a free-floating planet (FFP) invading the Solar ...System.
Aims.
In the framework of the invasion of a FFP, we aim to provide some new scenarios to explain the number asymmetry of the L4 and L5 Jupiter Trojans, as well as some other observed features (e.g. the resonant amplitude distribution).
Methods.
We investigate two different cases: (i) the indirect case, where Jupiter experiences a scattering encounter with the FFP and jumps outwards at a speed that is sufficiently high to make the L4 point temporarily disappear, resulting in a change in the numbers of the L4 (
N
4
) and L5 (
N
5
) Trojan swarms; (ii) the direct case, in which the FFP traverses the L5 region and affects the stability of the local Trojans.
Results.
In the indirect case, the outward migration of Jupiter can be fast enough to make the L4 islands disappear temporarily, inducing an increase in the resonant amplitude of local Trojans. After the migration is over, the L4 Trojans come back to the reappeared and enlarged islands. As for the L5 islands, they always exist but expand even more considerably. Since the L4 swarm suffers less excitation in the resonant amplitude than the L5 swarm, more L4 Trojans are stable and could survive to the end. In the direct case, the FFP could deplete a considerable fraction of the L5 Trojans, while the L4 Trojans at large distances are not affected and all of them could survive.
Conclusions.
Both the indirect and direct cases could result in a number ratio of
R
45
=
N
4
/
N
5
~ 1.6 that can potentially explain the current observations. The latter has the advantage of producing the observed resonant amplitude distribution. To achieve these results, we propose that the FFP should have a mass of at least of a few tens of Earth masses and its orbital inclination should be allowed to be as high as 40°.
Here, we report on results of statistical analyses on spin periods and shapes of main-belt asteroids (MBAs) smaller than
$\ \sim\ $
1 km in diameter, which were derived from lightcurve observations ...of a single night with the 8.2 m Subaru telescope. It is shown that, among our detected 68 MBAs giving reliable lightcurve periods, the fraction of fast-rotating asteroids (with spin periods of
$\lt\ \sim\ $
2.3 hr, candidates of monolithic bodies) is about 49%. In particular, statistical tests reveal with a high confidence level that, in terms of the shape (deduced from the light variation amplitude), the fast rotators belong to a population quite different from that for non fast-rotators; in other words, most of the fast-rotators show a strong trend that they are more spherical in shape than the non fast-rotator group. Consideration of several orbital and rotational evolution timescales for small asteroids in the main asteroid belt seems to indicate that the above-mentioned trend is not by coincidence, but primordial. Therefore, referring to the shape distributions of impact fragments produced in laboratory experiments, our discovered sphericity preference of small fast-rotating asteroids probably requires some spin deceleration mechanisms, which selectively worked on all elongated objects during their impact formation and/or subsequent evolution. We also note that our fast rotators are much more spherical compared to known small MBAs and near-Earth objects.
The opposition effect of the asteroid 4 Vesta Hasegawa, Sunao; Miyasaka, Seidai; Tokimasa, Noritaka ...
Publications of the Astronomical Society of Japan,
10/2014, Letnik:
66, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Abstract We present the results of photometric observations carried out with four small telescopes of the asteroid 4 Vesta in the B, RC, and z ′ bands at a minimum phase angle of 0$_{.}^{\circ}$1. ...The magnitudes, reduced to unit distance and zero phase angle, were MB(1, 1, 0) = 3.83 ± 0.01, $M_{R_{\rm C}}$(1, 1, 0) = 2.67 ± 0.01, and $M_{z^{\,\prime }}(1, 1, 0) = 3.03\,\pm \,0.01\:$mag. The absolute magnitude obtained from the IAU H − G function is ∼ 0.1 mag darker than the magnitude at a phase angle of 0° determined from the Shevchenko function and Hapke models with the coherent backscattering effect term. Our photometric measurements allowed us to derive geometric albedos of 0.35 in the B band, 0.41 in the RC band, and 0.31 in the z′ bands by using the Hapke model with the coherent backscattering effect term. Using the Hapke model, the porosity of the optically active regolith on Vesta was estimated to be ρ = 0.4–0.7, yielding a bulk density of 0.9–2.0 × 103 kg m−3. It is evident that the opposition effect for Vesta makes a contribution not only to the shadow-hiding effect, but also the coherent backscattering effect that appears from ∼ 1°. The amplitude of the coherent backscatter opposition effect for Vesta increases with a brightening of reflectance. By comparison with other solar system bodies, we suggest that multiple-scattering on an optically active scale may contribute to the amplitude of the coherent backscatter opposition effect (BC0).
Context.
More than 10 000 Jupiter Trojans have been detected so far. They are moving around the L4 and L5 triangular Lagrangian points of the Sun-Jupiter system and their distributions can provide ...important clues about the early evolution of the Solar System.
Aims.
The number asymmetry of the L4 and L5 Jupiter Trojans is a longstanding problem. We aim to test a new mechanism in order to explain this anomalous feature by invoking the jumping-Jupiter scenario.
Methods.
First, we introduce the orbital evolution of Jupiter caused by the giant planet instability in the early Solar System. In this scenario, Jupiter could undergo an outward migration at a very high speed. We then investigate how such a jump changes the numbers of the L4 (
N
4
) and L5 (
N
5
) Trojans.
Results.
The outward migration of Jupiter can distort the co-orbital orbits near the Lagrangian points, resulting in L4 Trojans being more stable than the L5 ones. We find that this mechanism could potentially explain the unbiased number asymmetry of
N
4
/
N
5
~ 1.6 for the known Jupiter Trojans. The uncertainties of the system parameters, such as Jupiter’s eccentricity and inclination as well as the inclination distribution of Jupiter Trojans, are also taken into account and our results about the L4/L5 asymmetry have been further validated. However, the resonant amplitudes of the simulated Trojans are excited to higher values compared to the current population. A possible solution is that collisions among the Trojans may reduce their resonant amplitudes.
We present current results of our long-term campaign to make photometric observations of the new-born Karin family asteroids, especially those of (832) Karin. Karin, an S-type main-belt asteroid, is ...the largest member of the Karin family. This asteroid is likely a large fragment of a disruption event in the main asteroid belt that occurred about 5.8 million years ago. We obtained multi-color photometric observations of this asteroid in 2003 and 2004. We have reported a potential surface color variation of this asteroid, which indicates the existence of both mature and fresh surfaces on it. However, as of 2004 September, this asteroid apparently does not show a strong surface color difference, which might give us some insight into its spin axis orientation and shape. This is quite an interesting result, but it has to be confirmed by future observations.
Abstract
We present an analysis of survey observations of the trailing L
5
Jupiter Trojan swarm using the wide-field Hyper Suprime-Cam CCD camera on the 8.2 m Subaru Telescope. We detected 189 L
5
...Trojans from our survey that covered about 15 deg
2
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 L
5
Jupiter Trojans over the entire size range for 9 ≲
H
V
≤ 17, and found that the size distributions of the L
4
and L
5
swarms agree well with each other for a wide range of sizes. This is consistent with the scenario that asteroids in the two swarms originated from the same primordial population. Based on the above results, the ratio of the total number of asteroids with
D
≥ 2 km in the two swarms is estimated to be
N
L4
/
N
L5
= 1.40 ± 0.15, and the total number of L
5
Jupiter Trojans with
D
≥ 1 km is estimated to be 1.1 × 10
5
by extrapolating the obtained distribution.
ABSTRACT
A consensus view on the formation of planetesimals is now exposed to a threat, since recent numerical studies on the mechanical properties of dust aggregates tend to dispute the conceptual ...picture that submicrometer-sized grains conglomerate into planetesimals in protoplanetary discs. With the advent of precise laboratory experiments and extensive computer simulations on the interaction between elastic spheres comprising dust aggregates, we revisit a model for the tensile strength of dust aggregates consisting of small elastic grains. In the framework of contact mechanics and fracture mechanics, we examine outcomes of computer simulations and laboratory experiments on the tensile strength of dust aggregates. We provide a novel analytical formula that explicitly incorporates the volume effect on the tensile strength, namely, the dependence of tensile strength on the volume of dust aggregates. We find that our model for the tensile strength of dust aggregates well reproduces results of computer simulations and laboratory experiments, if appropriate values are adopted for the elastic parameters used in the model. Moreover, the model with dust aggregates of submicrometer-sized grains is in good harmony with the tensile strength of cometary dust and meteoroids derived from astronomical observations. Therefore, we reaffirm the commonly believed idea that the formation of planetesimals begins with conglomeration of submicrometer-sized grains condensed in protoplanetary discs.
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