322 research outputs found
The Origin of (90) Antiope From Component-Resolved Near-Infrared Spectroscopy
The origin of the similary-sized binary asteroid (90) Antiope remains an
unsolved puzzle. To constrain the origin of this unique double system, we
recorded individual spectra of the components using SPIFFI, a near-infrared
integral field spectrograph fed by SINFONI, an adaptive optics module available
on VLT-UT4. Using our previously published orbital model, we requested
telescope time when the separation of the components of (90) Antiope was larger
than 0.087", to minimize the contamination between components, during the
February 2009 opposition. Several multi-spectral data-cubes in J band (SNR=40)
and H+K band (SNR=100) were recorded in three epochs and revealed the two
components of (90) Antiope. After developing a specific photometric extraction
method and running an error analysis by Monte-Carlo simulations, we
successfully extracted reliable spectra of both components from 1.1 to 2.4 um
taken on the night of February 21, 2009. These spectra do not display any
significant absorption features due to mafic mineral, ices, or organics, and
their slopes are in agreement with both components being C- or Cb- type
asteroids. Their constant flux ratio indicates that both components' surface
reflectances are quite similar, with a 1-sigma variation of 7%. By comparison
with 2MASS J, H, K color distribution of observed Themis family members, we
conclude that both bodies were most likely formed at the same time and from the
same material. The similarly-sized system could indeed be the result of the
breakup of a rubble-pile proto-Antiope into two equal-sized bodies, but other
scenarios of formation implying a common origin should also be considered.Comment: 46 pages, 1 table, 11 figures accepted for publication to Icaru
Compositional characterisation of the Themis family
Context. It has recently been proposed that the surface composition of icy
main-belt asteroids (B-,C-,Cb-,Cg-,P-,and D-types) may be consistent with that
of chondritic porous interplanetary dust particles (CPIDPs). Aims. In the light
of this new association, we re-examine the surface composition of a sample of
asteroids belonging to the Themis family in order to place new constraints on
the formation and evolution of its parent body. Methods. We acquired NIR
spectral data for 15 members of the Themis family and complemented this dataset
with existing spectra in the visible and mid-infrared ranges to perform a
thorough analysis of the composition of the family. Assuming end-member
minerals and particle sizes (<2\mum) similar to those found in CPIDPs, we used
a radiative transfer code adapted for light scattering by small particles to
model the spectral properties of these asteroids. Results. Our best-matching
models indicate that most objects in our sample possess a surface composition
that is consistent with the composition of CP IDPs.We find ultra-fine grained
Fe-bearing olivine glasses to be among the dominant constituents. We further
detect the presence of minor fractions of Mg-rich crystalline silicates. The
few unsuccessfully matched asteroids may indicate the presence of interlopers
in the family or objects sampling a distinct compositional layer of the parent
body. Conclusions. The composition inferred for the Themis family members
suggests that the parent body accreted from a mixture of ice and anhydrous
silicates (mainly amorphous) and subsequently underwent limited heating. By
comparison with existing thermal models that assume a 400km diameter
progenitor, the accretion process of the Themis parent body must have occurred
relatively late (>4Myr after CAIs) so that only moderate internal heating
occurred in its interior, preventing aqueous alteration of the outer shell.Comment: 9 pages, 5 figures, accepted for publication in A&
Colors and taxonomy of Centaurs and Trans-Neptunian Objects
The study of the surface properties of Centaurs and Trans-Neptunian Objects
(TNOs) provides essential information about the early conditions and evolution
of the outer Solar System. Due to the faintness of most of these distant and
icy bodies, photometry currently constitutes the best technique to survey a
statistically significant number of them. Our aim is to investigate color
properties of a large sample of minor bodies of the outer Solar System, and set
their taxonomic classification. We carried out visible and near-infrared
photometry of Centaurs and TNOs, making use, respectively, of the FORS2 and
ISAAC instruments at the Very Large Telescope (European Southern Observatory).
Using G-mode analysis, we derived taxonomic classifications according to the
Barucci et al. (2005a) system. We report photometric observations of 31
objects, 10 of them have their colors reported for the first time ever. 28
Centaurs and TNOs have been assigned to a taxon. We combined the entire sample
of 38 objects taxonomically classified in the framework of our programme (28
objects from this work; 10 objects from DeMeo et al. 2009a) with previously
classified TNOs and Centaurs, looking for correlations between taxonomy and
dynamics. We compared our photometric results to literature data, finding hints
of heterogeneity for the surfaces of 4 objects.Comment: 7 pages, 4 figures. To be published in Astronomy and Astrophysic
Spectral and Spin Measurement of Two Small and Fast-Rotating Near-Earth Asteroids
In May 2012 two asteroids made near-miss "grazing" passes at distances of a
few Earth-radii: 2012 KP24 passed at nine Earth-radii and 2012 KT42 at only
three Earth-radii. The latter passed inside the orbital distance of
geosynchronous satellites. From spectral and imaging measurements using NASA's
3-m Infrared Telescope Facility (IRTF), we deduce taxonomic, rotational, and
physical properties. Their spectral characteristics are somewhat atypical among
near-Earth asteroids: C-complex for 2012 KP24 and B-type for 2012 KT42, from
which we interpret the albedos of both asteroids to be between 0.10 and 0.15
and effective diameters of 20+-2 and 6+-1 meters, respectively. Among B-type
asteroids, the spectrum of 2012 KT42 is most similar to 3200 Phaethon and 4015
Wilson-Harrington. Not only are these among the smallest asteroids spectrally
measured, we also find they are among the fastest-spinning: 2012 KP24 completes
a rotation in 2.5008+-0.0006 minutes and 2012 KT42 rotates in 3.634+-0.001
minutes.Comment: 4 pages, 3 figures, accepted for publication in Icaru
Chemical and physical properties of the variegated Pluto and Charon surfaces
International audienceWe present new photometric and spectroscopic observations of the Pluto-Charon system carried out at the VLT-ESO (Chile) with two 8-meter telescopes equipped with the FORS2, ISAAC and SINFONI instruments. The spectra were obtained in the 0.6-2.45μm range with a spectral resolution from 300 to 1500. The SINFONI data were obtained using Adaptive Optics, allowing a complete separation of the two bodies. We derive both objects' magnitudes in the near infrared and convert them into albedo values. These first near infrared photometric data allow to adjust the different parts of Pluto's spectrum, provided by the three instruments. We run spectral models in order to give chemical and physical constraints on the surface of Pluto and Charon. We discuss the dilution properties of the methane ice and its implications on Pluto's surface. The heterogeneities of the pure and diluted methane ice on Pluto's surface is also investigated. The high signal-to-noise level of the data and our analyses may support the presence of ethane ice on the surface of Pluto, which is one of the main products of the methane irradiation and photolysis. The analyses of the spectra of Charon suggest that the water ice is almost completely in its crystalline form and that the ammonia compound is hydrated on the surface of this satellite
Evolution from protoplanetary to debris discs: The transition disc around HD 166191
HD 166191 has been identified by several studies as hosting a rare and
extremely bright warm debris disc with an additional outer cool disc component.
However, an alternative interpretation is that the star hosts a disc that is
currently in transition between a full gas disc and a largely gas-free debris
disc. With the help of new optical to mid-IR spectra and Herschel imaging, we
argue that the latter interpretation is supported in several ways: i) we show
that HD 166191 is co-moving with the ~4 Myr-old Herbig Ae star HD 163296,
suggesting that the two have the same age, ii) the disc spectrum of HD 166191
is well matched by a standard radiative transfer model of a gaseous
protoplanetary disc with an inner hole, and iii) the HD 166191 mid-IR silicate
feature is more consistent with similarly primordial objects. We note some
potential issues with the debris disc interpretation that should be considered
for such extreme objects, whose lifetime at the current brightness is mush
shorter than the stellar age, or in the case of the outer component requires a
mass comparable to the solid component of the Solar nebula. These aspects
individually and collectively argue that HD 166191 is a 4-5 Myr old star that
hosts a gaseous transition disc. Though it does not argue in favour of either
scenario, we find strong evidence for 3-5 um disc variability. We place HD
166191 in context with discs at different evolutionary stages, showing that it
is a potentially important object for understanding the protoplanetary to
debris disc transition.Comment: accepted to MNRAS, fixed typos in abstract and axis labe
Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies
Although petrologic, chemical and isotopic studies of ordinary chondrites and
meteorites in general have largely helped establish a chronology of the
earliest events of planetesimal formation and their evolution, there are
several questions that cannot be resolved via laboratory measurements and/or
experiments only. Here we propose rationale for several new constraints on the
formation and evolution of ordinary chondrite parent bodies (and by extension
most planetesimals) from newly available spectral measurements and
mineralogical analysis of main belt S-type asteroids (83 objects) and
unequilibrated ordinary chondrite meteorites (53 samples). Based on the latter,
we suggest spectral data may be used to distinguish whether an ordinary
chondrite was formed near the surface or in the interior of its parent body. If
these constraints are correct, the suggested implications include that: i)
large groups of compositionally similar asteroids are a natural outcome of
planetesimal formation and, consequently, meteorites within a given class can
originate from multiple parent bodies; ii) the surfaces of large (up to ~200km)
S-type main-belt asteroids expose mostly the interiors of the primordial
bodies, a likely consequence of impacts by small asteroids (D<10km) in the
early solar system (Ciesla et al. 2013); iii) the duration of accretion of the
H chondrite parent bodies was likely short (instantaneous or in less then ~10^5
yr but certainly not as long as 1 Myr); iv) LL-like bodies formed closer to the
Sun than H-like bodies, a possible consequence of radial mixing and size
sorting of chondrules in the protoplanetary disk prior to accretion.Comment: Accepted for publication in Ap
Visible spectroscopy of the new ESO Large Program on trans-Neptunian objects and Centaurs: final results
A second large programme (LP) for the physical studies of TNOs and Centaurs,
started at ESO Cerro Paranal on October 2006 to obtain high-quality data, has
recently been concluded. In this paper we present the spectra of these pristine
bodies obtained in the visible range during the last two semesters of the LP.
We investigate the spectral behaviour of the TNOs and Centaurs observed, and we
analyse the spectral slopes distribution of the full data set coming from this
LP and from the literature. We computed the spectral slope for each observed
object, and searched for possible weak absorption features. A statistical
analysis was performed on a total sample of 73 TNOs and Centaurs to look for
possible correlations between dynamical classes, orbital parameters, and
spectral gradient. We obtained new spectra for 28 bodies, 15 of which were
observed for the first time. All the new presented spectra are featureless,
including 2003 AZ84, for which a faint and broad absorption band possibly
attributed to hydrated silicates on its surface has been reported. The data
confirm a wide variety of spectral behaviours, with neutral--grey to very red
gradients. An analysis of the spectral slopes available from this LP and in the
literature for a total sample of 73 Centaurs and TNOs shows that there is a
lack of very red objects in the classical population. We present the results of
the statistical analysis of the spectral slope distribution versus orbital
parameters. In particular, we confirm a strong anticorrelation between spectral
slope and orbital inclination for the classical population. A strong
correlation is also found between the spectral slope and orbital eccentricity
for resonant TNOs, with objects having higher spectral slope values with
increasing eccentricity.Comment: 11 pages, 9 figure
Dynamic model of wind energy conversion systems with variable speed synchronous generator and full-size power converter for large-scale power system stability studies
Se inscribe dentro de la lÃnea de investigación de Integración en red de sistemas eólicos. Se presenta un modelo informático en plataforma PSS/E para sistemas de generación eólica de velocidad variable del tipo SÃncrono con Convertidor de plena potencia, capaz de simular el comportamuiento dinámico de estos sistemas en estudios de estabilidad del sistema eléctric
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