11 research outputs found
Shape and spin distributions of asteroid populations from brightness variation estimates and large databases
Context. Many databases on asteroid brightnesses (e.g. ALCDEF, WISE) are
potential sources for extensive asteroid shape and spin modelling. Individual
lightcurve inversion models require several apparitions and hundreds of data
points per target. However, we can analyse the coarse shape and spin
distributions over populations of at least thousands of targets even if there
are only a few points and one apparition per asteroid. This is done by
examining the distribution of the brightness variations observed within the
chosen population.
Aims. Brightness variation has been proposed as a population-scale rather
than individual-target observable in two studies so far. We aim to examine this
approach rigorously to establish its theoretical validity, degree of
ill-posedness, and practical applicability.
Methods. We model the observed brightness variation of a target population by
considering its cumulative distribution function (CDF) caused by the joint
distribution function of two fundamental shape and spin indicators. These are
the shape elongation and the spin latitude of a simple ellipsoidal model. The
main advantage of the model is that we can derive analytical basis functions
that yield the observed CDF as a function of the shape and spin distribution.
The inverse problem can be treated linearly. Even though the inaccuracy of the
model is considerable, databases of thousands of targets should yield some
information on the distribution.
Results. We establish the theoretical soundness and the typical accuracy
limits of the approach both analytically and numerically. Using simulations, we
derive a practical estimate of the model distribution in the (shape,
spin)-plane. We show that databases such as Wide-field Infrared Survey Explorer
(WISE) yield coarse but robust estimates of this distribution, and as an
example compare various asteroid families with each other.Comment: 16 pages, 21 figures, manuscript accepted in Astronomy &
Astrophysics, to be published in section 10. Planets and planetary system
Spin states of asteroids in the Eos collisional family
Eos family was created during a catastrophic impact about 1.3 Gyr ago.
Rotation states of individual family members contain information about the
history of the whole population. We aim to increase the number of asteroid
shape models and rotation states within the Eos collision family, as well as to
revise previously published shape models from the literature. Such results can
be used to constrain theoretical collisional and evolution models of the
family, or to estimate other physical parameters by a thermophysical modeling
of the thermal infrared data. We use all available disk-integrated optical data
(i.e., classical dense-in-time photometry obtained from public databases and
through a large collaboration network as well as sparse-in-time individual
measurements from a few sky surveys) as input for the convex inversion method,
and derive 3D shape models of asteroids together with their rotation periods
and orientations of rotation axes. We present updated shape models for 15
asteroids and new shape model determinations for 16 asteroids. Together with
the already published models from the publicly available DAMIT database, we
compiled a sample of 56 Eos family members with known shape models that we used
in our analysis of physical properties within the family. Rotation states of
asteroids smaller than ~20 km are heavily influenced by the YORP effect, whilst
the large objects more or less retained their rotation state properties since
the family creation. Moreover, we also present a shape model and bulk density
of asteroid (423) Diotima, an interloper in the Eos family, based on the
disk-resolved data obtained by the Near InfraRed Camera (Nirc2) mounted on the
W.M. Keck II telescope.Comment: Accepted for publication in ICARUS Special Issue - Asteroids: Origin,
Evolution & Characterizatio
Distribution of shape elongations of main belt asteroids derived from Pan-STARRS1 photometry
Context. A considerable amount of photometric data is produced by surveys such as Pan-STARRS, LONEOS, WISE, or Catalina. These data are a rich source of information about the physical properties of asteroids. There are several possible approaches for using these data. Light curve inversion is a typical method that works with individual asteroids. Our approach in focusing on large groups of asteroids, such as dynamical families and taxonomic classes, is statistical; the data are not sufficient for individual models.Aim. Our aim is to study the distributions of shape elongation b∕a and the spin axis latitude β for various subpopulations of asteroids and to compare our results, based on Pan-STARRS1 survey, with statistics previously carried out using various photometric databases, such as Lowell and WISE.Methods. We used the LEADER algorithm to compare the b∕a and β distributions for various subpopulations of asteroids. The algorithm creates a cumulative distributive function (CDF) of observed brightness variations, and computes the b∕a and β distributions with analytical basis functions that yield the observed CDF. A variant of LEADER is used to solve the joint distributions for synthetic populations to test the validity of the method.Results. When comparing distributions of shape elongation for groups of asteroids with different diameters D, we found that there are no differences for D < 25 km. We also constructed distributions for asteroids with different rotation periods and revealed that the fastest rotators with P = 0 − 4 h are more spheroidal than the population with P = 4−8 h