61 research outputs found
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
Selecting asteroids for a targeted spectroscopic survey
Asteroid spectroscopy reflects surface mineralogy. There are few thousand
asteroids whose surfaces have been observed spectrally. Determining the surface
properties of those objects is important for many practical and scientific
applications, such as for example developing impact deflection strategies or
studying history and evolution of the Solar System and planet formation.
The aim of this study is to develop a pre-selection method that can be
utilized in searching for asteroids of any taxonomic complex. The method could
then be utilized im multiple applications such as searching for the missing
V-types or looking for primitive asteroids.
We used the Bayes Naive Classifier combined with observations obtained in the
course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey
Explorer surveys as well as a database of asteroid phase curves for asteroids
with known taxonomic type. Using the new classification method we have selected
a number of possible V-type candidates. Some of the candidates were than
spectrally observed at the Nordic Optical Telescope and South African Large
Telescope.
We have developed and tested the new pre-selection method. We found three
asteroids in the mid/outer Main Belt that are likely of differentiated type.
Near-Infrared are still required to confirm this discovery. Similarly to other
studies we found that V-type candidates cluster around the Vesta family and are
rare in the mid/oter Main Belt.
The new method shows that even largely explored large databases combined
together could still be further exploited in for example solving the missing
dunite problem.Comment: accepted to A
Asteroids seen by JWST-MIRI: Radiometric Size, Distance and Orbit Constraints
Infrared measurements of asteroids are crucial for the determination of
physical and thermal properties of individual objects, and for the
understanding of the small-body populations in the solar system as a whole. But
standard radiometric methods can only be applied if the orbit of an object is
known, hence its position at the time of the observation. We present MIRI
observations of the outer-belt asteroid 10920 and an unknown object, detected
in all 9 MIRI bands in close proximity to 10920. We developed a new method
"STM-ORBIT" to interpret the multi-band measurements without knowing the
object's true location. The method leads to a confirmation of radiometric
size-albedo solution for 10920 and puts constraints on the asteroid's location
and orbit in agreement with its true orbit. Groundbased lightcurve observations
of 10920, combined with Gaia data, indicate a very elongated object (a/b >=
1.5), with a spin-pole at (l, b) = (178{\deg}, 81{\deg}), and a rotation period
of 4.861191 h. A thermophysical study leads to a size of 14.5 - 16.5 km, a
geometric albedo between 0.05 and 0.10, and a thermal inertia in the range 9 to
35 Jm-2s-0.5K-1. For the newly discovered MIRI object, the STM-ORBIT method
revealed a size of 100-230 m. The new asteroid must be on a very
low-inclination orbit and it was located in the inner main-belt region during
JWST observations. A beaming parameter {\eta} larger than 1.0 would push the
size even below 100 meter, a main-belt regime which escaped IR detections so
far. These kind of MIRI observations can therefore contribute to formation and
evolution studies via classical size-frequency studies which are currently
limited to objects larger than about one kilometer in size. We estimate that
MIRI frames with pointings close to the ecliptic and only short integration
times of a few seconds will always include a few asteroids, most of them will
be unknown objects.Comment: 17 pages, 10 figures, 4 tables, accepted for A&A publication on Nov
22, 202
Gaia Data Release 1 : Open cluster astrometry: performance, limitations, and future prospects
Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.Peer reviewe
Large halloween asteroid at lunar distance
The near-Earth asteroid (NEA) 2015 TB had a very close encounter with Earth at 1.3 lunar distances on October 31, 2015. We obtained 3-band mid-infrared observations of this asteroid with the ESO VLT-VISIR instrument covering approximately four hours in total. We also monitored the visual lightcurve during the close-encounter phase. The NEA has a (most likely) rotation period of 2.939 ± 0.005 h and the visual lightcurve shows a peak-to-peak amplitude of approximately 0.12 ± 0.02 mag. A second rotation period of 4.779 ± 0.012 h, with an amplitude of the Fourier fit of 0.10 ± 0.02 mag, also seems compatible with the available lightcurve measurements. We estimate a V-R colour of 0.56 ± 0.05 mag from different entries in the MPC database. A reliable determination of the object's absolute magnitude was not possible. Applying different phase relations to the available R-/V-band observations produced H = 18.6 mag (standard H-G calculations) or H = 19.2 mag and H = 19.8 mag (via the H-G procedure for sparse and low-quality data), with large uncertainties of approximately 1 mag. We performed a detailed thermophysical model analysis by using spherical and partially also ellipsoidal shape models. The thermal properties are best explained by an equator-on (± 30°) viewing geometry during our measurements with a thermal inertia in the range 250-700 J m s K (retrograde rotation) or above 500 J m s K (prograde rotation). We find that the NEA has a minimum size of approximately 625 m, a maximum size of just below 700 m, and a slightly elongated shape with a/b 1.1. The best match to all thermal measurements is found for: (i) thermal inertia Γ = 900 J m s K; D = 644 m, p = 5.5% (prograde rotation with 2.939 h); regolith grain sizes of 50-100 mm; (ii) thermal inertia Γ = 400 J m s K; D = 667 m, p = 5.1% (retrograde rotation with 2.939 h); regolith grain sizes of 10-20 mm. A near-Earth asteroid model (NEATM) confirms an object size well above 600 m (best NEATM solution at 690 m, beaming parameter η = 1.95), significantly larger than early estimates based on radar measurements. In general, a high-quality physical and thermal characterisation of a close-encounter object from two-week apparition data is not easily possible. We give recommendations for improved observing strategies for similar events in the future. © ESO, 2017.The research leading to these results has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378. Funding from Spanish grant AYA-2014-56637-C2-1-P is acknowledged. Hungarian funding from the NKFIH grant GINOP-2.3.2-15-2016-00003 is also acknowledged. R.D. acknowledges the support of MINECO for his Ramon y Cajal Contract.Peer Reviewe
Bayesian Linking of Geosynchronous Orbital Debris Tracks as seen by the Large Synoptic Survey Telescope
We describe a Bayesian sampling model for linking and constraining orbit
models from angular observations of "streaks" in optical telescope images. Our
algorithm is particularly suited to situations where the observation times are
small fractions of the orbital periods of the observed objects or when there is
significant confusion of objects in the observation field. We use Markov Chain
Monte Carlo to sample from the joint posterior distribution of the parameters
of multiple orbit models (up to the number of observed tracks) and parameters
describing which tracks are linked with which orbit models. Using this
algorithm, we forecast the constraints on geosynchronous (GEO) debris orbits
achievable with the planned Large Synoptic Survey Telescope (LSST). Because of
the short 15 second exposure times, preliminary orbit determinations of GEO
objects from LSST will have large and degenerate errors on the orbital
elements. Combined with the expected crowded fields of GEO debris it will be
challenging to reliably link orbital tracks in LSST observations given the
currently planned observing cadence.Comment: 12 pages, 6 figures. Accepted for publication in Advances in Space
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