167 research outputs found
A new catalogue of observations of the eight major satellites of Saturn (1874-2007)
The original publication in Astronomy & Astrophysics is available at www.aanda.org.International audienceContext : The lastest catalogue of observations includes about 51 000 observations (over 3500 nights) of Saturn's satellites from 1874 to 1989. Since 1989, many observations have been published, often in different formats, based on the publication. Aims : Our new catalogue of observations of the eight major satellites of Saturn includes the observations of the previous catalogues, newly published data and also old observations left out of the previous catalogue. The observations are tabulated in a consistent format. Methods : We give, for each observation, the corrections applied for reduction such as refraction, aberration or phase effects. Furthermore, when it was possible, the instrument and catalogue are also indicated. Results : The new catalogue presents more than 130 000 observations (over 6000 nights) of the eight major satellites of Saturn from 1874 to 2007
Somatocrinin receptor coupled with cAMP-dependent protein kinase on anterior pituitary granules.
Estimating the accuracy of satellite ephemerides using the bootstrap method
International audienceContext: The accuracy of predicted orbital positions depends on the quality of the theorical model and of the observations used to fit the model. During the period of observations, this accuracy can be estimated through comparison with observations. Outside this period, the estimation remains difficult. Many methods have been developed for asteroid ephemerides in order to evaluate this accuracy. Aims: This paper introduces a new method to estimate the accuracy of predicted positions at any time, in particular outside the observation period. Methods: This new method is based upon a bootstrap resampling and allows this estimation with minimal assumptions. Results: The method was applied to two of the main Saturnian satellites, Mimas and Titan, and compared with other methods used previously for asteroids. The bootstrap resampling is a robust and practical method for estimating the accuracy of predicted positions
Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations
The prediction of stellar occultations by Transneptunian objects and Centaurs
is a difficult challenge that requires accuracy both in the occulted star
position as for the object ephemeris. Until now, the most used method of
prediction involving tens of TNOs/Centaurs was to consider a constant offset
for the right ascension and for the declination with respect to a reference
ephemeris. This offset is determined as the difference between the most recent
observations of the TNO and the reference ephemeris. This method can be
successfully applied when the offset remains constant with time. This paper
presents an alternative method of prediction based on a new accurate orbit
determination procedure, which uses all the available positions of the TNO from
the Minor Planet Center database plus sets of new astrometric positions from
unpublished observations. The orbit determination is performed through a
numerical integration procedure (NIMA), in which we develop a specific
weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs.
For this purpose, we have performed about 2900 new observations during
2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10
TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL
ephemerides, we highlighted the variation of the offset between them with time.
Giving examples, we show that the constant offset method could not accurately
predict 6 out of the 13 observed positive occultations successfully predicted
by NIMA. The results indicate that NIMA is capable of efficiently refine the
orbits of these bodies. Finally, we show that the astrometric positions given
by positive occultations can help to further refine the orbit of the TNO and
consequently the future predictions. We also provide the unpublished
observations of the 51 selected TNOs and their ephemeris in a usable format by
the SPICE library.Comment: 12 pages, 9 figures, accepted in A&
Statistical and numerical study of asteroid orbital uncertainty
Context. The knowledge of the orbit or the ephemeris uncertainty of asteroid presents a particular interest for various purposes. These quantities are for instance useful for recovering asteroids, for identifying lost asteroids or for planning stellar occultation campaigns. They are also needed to estimate the close approach of Near-Earth asteroids, and subsequent risk of collision. Ephemeris accuracy can also be used for instrument calibration purposes or for scientific applications. Aims. Asteroid databases provide information about the uncertainty of the orbits allowing the measure of the quality of an orbit. The aims of this paper is to analyse these different uncertainty parameters and to estimate the impact of the different measurements on the uncertainty of orbits. Methods. We particularly deal with two main databases ASTORB and MPCORB providing uncertainty parameters for asteroid orbits. Statistical methods are used in order to estimate orbital uncertainty and compare with parameters from databases. Simulations are also generated to deal with specific measurements such as future Gaia or present radar measurements. Results. Relations between the uncertainty parameter and the characteristics of the asteroid (orbital arc, absolute magnitude,...) are highlighted. Moreover, a review of the different measuments are compiled and the impact of these measures on the accuracy of the orbit is also estimated. Key words. Minor planets, asteroids: general â Ephemerides â Astrometry 1
Enabling discovery of solar system objects in large alert data streams
With the advent of large-scale astronomical surveys such as the Zwicky
Transient Facility (ZTF), the number of alerts generated by transient, variable
and moving astronomical objects is growing rapidly, reaching millions per
night. Concerning solar system minor planets, their identification requires
linking the alerts of many observations over a potentially large time, leading
to a very large combinatorial number. This work aims to identify new candidates
for solar system objects from massive alert data streams produced by
large-scale surveys, such as the ZTF and the Vera C. Rubin Observatory's Legacy
Survey of Space and Time. Our analysis used the Fink alert broker capabilities
to reduce the 111,275,131 processed alerts from ZTF between November 2019 and
December 2022 to only 389,530 new solar system alert candidates over the same
period. We then implemented a linking algorithm, Fink-FAT, to create real-time
trajectory candidates from alert data and extract orbital parameters. The
analysis was validated on ZTF alert packets linked to confirmed solar system
objects from the Minor Planet Center database. Finally, the results were
confronted against follow-up observations. Between November 2019 and December
2022, Fink-FAT extracted 327 new orbits from solar system object candidates at
the time of the observations, over which 65 were still unreported in the MPC
database as of March 2023. After two late follow-up observation campaigns of
six orbit candidates, four were associated with known solar system minor
planets, and two remain unknown. Fink-FAT is deployed in the Fink broker and
successfully analyzes in real time the alert data from the ZTF survey by
regularly extracting new candidates for solar system objects. Our scalability
tests also show that Fink-FAT can handle the even larger volume of alert data
that the Rubin Observatory will send.Comment: submitted to A&
Astrometric positions for 18 irregular satellites of giant planets from 23 years of observations
The irregular satellites of the giant planets are believed to have been
captured during the evolution of the solar system. Knowing their physical
parameters, such as size, density, and albedo is important for constraining
where they came from and how they were captured. The best way to obtain these
parameters are observations in situ by spacecrafts or from stellar occultations
by the objects. Both techniques demand that the orbits are well known. We aimed
to obtain good astrometric positions of irregular satellites to improve their
orbits and ephemeris. We identified and reduced observations of several
irregular satellites from three databases containing more than 8000 images
obtained between 1992 and 2014 at three sites (Observat\'orio do Pico dos Dias,
Observatoire de Haute-Provence, and European Southern Observatory - La Silla).
We used the software PRAIA (Platform for Reduction of Astronomical Images
Automatically) to make the astrometric reduction of the CCD frames. The UCAC4
catalog represented the International Celestial Reference System in the
reductions. Identification of the satellites in the frames was done through
their ephemerides as determined from the SPICE/NAIF kernels. Some procedures
were followed to overcome missing or incomplete information (coordinates,
date), mostly for the older images. We managed to obtain more than 6000
positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus
(Sycorax), and 1 of Neptune (Nereid). For some satellites the number of
obtained positions is more than 50\% of what was used in earlier orbital
numerical integrations. Comparison of our positions with recent JPL ephemeris
suggests there are systematic errors in the orbits for some of the irregular
satellites. The most evident case was an error in the inclination of Carme.Comment: 9 pages, with 3 being online materia
Strong tidal dissipation in Saturn and constraints on Enceladus' thermal state from astrometry
Tidal interactions between Saturn and its satellites play a crucial role in
both the orbital migration of the satellites and the heating of their
interiors. Therefore constraining the tidal dissipation of Saturn (here the
ratio k2/Q) opens the door to the past evolution of the whole system. If
Saturn's tidal ratio can be determined at different frequencies, it may also be
possible to constrain the giant planet's interior structure, which is still
uncertain. Here, we try to determine Saturn's tidal ratio through its current
effect on the orbits of the main moons, using astrometric data spanning more
than a century. We find an intense tidal dissipation (k2/Q= (2.3 \pm 0.7)
\times 10-4), which is about ten times higher than the usual value estimated
from theoretical arguments. As a consequence, eccentricity equilibrium for
Enceladus can now account for the huge heat emitted from Enceladus' south pole.
Moreover, the measured k2/Q is found to be poorly sensitive to the tidal
frequency, on the short frequency interval considered. This suggests that
Saturn's dissipation may not be controlled by turbulent friction in the fluid
envelope as commonly believed. If correct, the large tidal expansion of the
moon orbits due to this strong Saturnian dissipation would be inconsistent with
the moon formations 4.5 Byr ago above the synchronous orbit in the Saturnian
subnebulae. But it would be compatible with a new model of satellite formation
in which the Saturnian satellites formed possibly over longer time scale at the
outer edge of the main rings. In an attempt to take into account for possible
significant torques exerted by the rings on Mimas, we fitted a constant rate
da/dt on Mimas semi-major axis, also. We obtained an unexpected large
acceleration related to a negative value of da/dt= -(15.7 \pm 4.4) \times 10-15
au/day
Cassini ISS astrometry of the Saturnian satellites: Tethys, Dione, Rhea, Iapetus, and Phoebe 2004-2012
This work was mainly funded by European Communityâs
Seventh Framework Program (FP7/2007-2013) under grant agreement 263466
for the FP7-ESPaCE, and partially by UPMC-EMERGENCE (contract number
EME0911), for which R.T. and V.L. are grateful. R.T. was also supported
by the Cassini mission. In addition, this work was supported by the Science
and Technology Facilites Council (Grant No. ST/F007566/1) and C.D.M. and
N.J.C. are grateful to them for financial assistance. C.D.M. is also grateful to
the Leverhulme Trust for the award of a Research Fellowship
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