134 research outputs found
ADAM: a general method for using various data types in asteroid reconstruction
We introduce ADAM, the All-Data Asteroid Modelling algorithm. ADAM is simple
and universal since it handles all disk-resolved data types (adaptive optics or
other images, interferometry, and range-Doppler radar data) in a uniform manner
via the 2D Fourier transform, enabling fast convergence in model optimization.
The resolved data can be combined with disk-integrated data (photometry). In
the reconstruction process, the difference between each data type is only a few
code lines defining the particular generalized projection from 3D onto a 2D
image plane. Occultation timings can be included as sparse silhouettes, and
thermal infrared data are efficiently handled with an approximate algorithm
that is sufficient in practice due to the dominance of the high-contrast
(boundary) pixels over the low-contrast (interior) ones. This is of particular
importance to the raw ALMA data that can be directly handled by ADAM without
having to construct the standard image. We study the reliability of the
inversion by using the independent shape supports of function series and
control-point surfaces. When other data are lacking, one can carry out fast
nonconvex lightcurve-only inversion, but any shape models resulting from it
should only be taken as illustrative global-scale ones.Comment: 11 pages, submitted to A&
Asteroid models from the Lowell Photometric Database
We use the lightcurve inversion method to derive new shape models and spin
states of asteroids from the sparse-in-time photometry compiled in the Lowell
Photometric Database. To speed up the time-consuming process of scanning the
period parameter space through the use of convex shape models, we use the
distributed computing project Asteroids@home, running on the Berkeley Open
Infrastructure for Network Computing (BOINC) platform. This way, the
period-search interval is divided into hundreds of smaller intervals. These
intervals are scanned separately by different volunteers and then joined
together. We also use an alternative, faster, approach when searching the
best-fit period by using a model of triaxial ellipsoid. By this, we can
independently confirm periods found with convex models and also find rotation
periods for some of those asteroids for which the convex-model approach gives
too many solutions. From the analysis of Lowell photometric data of the first
100,000 numbered asteroids, we derived 328 new models. This almost doubles the
number of available models. We tested the reliability of our results by
comparing models that were derived from purely Lowell data with those based on
dense lightcurves, and we found that the rate of false-positive solutions is
very low. We also present updated plots of the distribution of spin obliquities
and pole ecliptic longitudes that confirm previous findings about a non-uniform
distribution of spin axes. However, the models reconstructed from noisy sparse
data are heavily biased towards more elongated bodies with high lightcurve
amplitudes
Asteroid Models from Multiple Data Sources
In the past decade, hundreds of asteroid shape models have been derived using
the lightcurve inversion method. At the same time, a new framework of 3-D shape
modeling based on the combined analysis of widely different data sources such
as optical lightcurves, disk-resolved images, stellar occultation timings,
mid-infrared thermal radiometry, optical interferometry, and radar
delay-Doppler data, has been developed. This multi-data approach allows the
determination of most of the physical and surface properties of asteroids in a
single, coherent inversion, with spectacular results. We review the main
results of asteroid lightcurve inversion and also recent advances in multi-data
modeling. We show that models based on remote sensing data were confirmed by
spacecraft encounters with asteroids, and we discuss how the multiplication of
highly detailed 3-D models will help to refine our general knowledge of the
asteroid population. The physical and surface properties of asteroids, i.e.,
their spin, 3-D shape, density, thermal inertia, surface roughness, are among
the least known of all asteroid properties. Apart for the albedo and diameter,
we have access to the whole picture for only a few hundreds of asteroids. These
quantities are nevertheless very important to understand as they affect the
non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth,
or the bulk composition and internal structure of asteroids.Comment: chapter that will appear in a Space Science Series book Asteroids I
The Thousand Asteroid Light Curve Survey
We present the results of our Thousand Asteroid Light Curve Survey (TALCS)
conducted with the Canada-France-Hawaii Telescope in September 2006. Our
untargeted survey detected 828 Main Belt asteroids to a limiting magnitude of
g'~22.5 corresponding to a diameter range of 0.4 km <= D <= 10 km. Of these,
278 objects had photometry of sufficient quality to perform rotation period
fits. We debiased the observations and light curve fitting process to determine
the true distribution of rotation periods and light curve amplitudes of Main
Belt asteroids. We confirm a previously reported excess in the fraction of fast
rotators but find a much larger excess of slow rotating asteroids (~15% of our
sample). A few percent of objects in the TALCS size range have large light
curve amplitudes of ~1 mag. Fits to the debiased distribution of light curve
amplitudes indicate that the distribution of triaxial ellipsoid asteroid shapes
is proportional to the square of the axis-ratio, (b/a)^2, and may be bi-modal.
Finally, we find six objects with rotation periods that may be less than 2
hours with diameters between 400 m and 1.5 km, well above the break-up limit
for a gravitationally-bound aggregate. Our debiased data indicate that this
population represents <4% of the Main Belt in the 1-10 km size range.Comment: Accepted to Icarus. Full tables to appear there in electronic format,
or contact autho
Reconstruction of asteroid spin states from Gaia DR3 photometry
Gaia Data Release 3 contains accurate photometric observations of more than
150,000 asteroids covering a time interval of 34 months. With a total of about
3,000,000 measurements, a typical number of observations per asteroid ranges
from a few to several tens. We aimed to reconstruct the spin states and shapes
of asteroids from this dataset. We computed the viewing and illumination
geometry for each individual observation and used the light curve inversion
method to find the best-fit asteroid model, which was parameterized by the
sidereal rotation period, the spin axis direction, and a low-resolution convex
shape. To find the best-fit model, we ran the inversion for tens of thousands
of trial periods on interval 2-10,000 h, with tens of initial pole directions.
To find the correct rotation period, we also used a triaxial ellipsoid model
for the shape approximation. In most cases the number of data points was
insufficient to uniquely determine the rotation period. However, for about 8600
asteroids we were able to determine the spin state uniquely together with a
low-resolution convex shape model. This large sample of new asteroid models
enables us to study the spin distribution in the asteroid population. The
distribution of spins confirms previous findings that (i) small asteroids have
poles clustered toward ecliptic poles, likely because of the YORP-induced spin
evolution, (ii) asteroid migration due to the Yarkovsky effect depends on the
spin orientation, and (iii) members of asteroid families have the sense of
rotation correlated with their proper semimajor axis: over the age of the
family, orbits of prograde rotators evolved, due to the Yarkovsky effect, to
larger semimajor axes, while those of retrograde rotators drifted in the
opposite direction
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