Lammer H.,Austrian Academy of Sciences |
Chassefiere E.,University Paris - Sud |
Karatekin O.,Royal Observatory of Belgium |
Morschhauser A.,German Aerospace Center |
And 12 more authors.
Space Science Reviews | Year: 2013
The evolution and escape of the martian atmosphere and the planet's water inventory can be separated into an early and late evolutionary epoch. The first epoch started from the planet's origin and lasted ∼500 Myr. Because of the high EUV flux of the young Sun and Mars' low gravity it was accompanied by hydrodynamic blow-off of hydrogen and strong thermal escape rates of dragged heavier species such as O and C atoms. After the main part of the protoatmosphere was lost, impact-related volatiles and mantle outgassing may have resulted in accumulation of a secondary CO2 atmosphere of a few tens to a few hundred mbar around ∼4-4.3 Gyr ago. The evolution of the atmospheric surface pressure and water inventory of such a secondary atmosphere during the second epoch which lasted from the end of the Noachian until today was most likely determined by a complex interplay of various nonthermal atmospheric escape processes, impacts, carbonate precipitation, and serpentinization during the Hesperian and Amazonian epochs which led to the present day surface pressure. © 2012 Springer Science+Business Media Dordrecht.
Czekaj M.,University of Barcelona |
Robin A.C.,Observatoire de Besancon |
Luri X.,University of Barcelona |
Figueras F.,University of Barcelona |
EAS Publications Series | Year: 2011
From the Gaia mission, kinematic and star count data, together with the physical parameters of the stars - ages and metallicities-, will allow to characterise our Galaxy populations and, from that, the overall Galactic gravitational potential. One of the promising procedures to reach such goal will be to optimise the present Population Synthesis models by fitting, through robust statistical techniques, the large and small scale structure and kinematics parameters that best will reproduce Gaia data. As a first step we present here the comparison between the data from the Tycho-2 catalogue and the Besançon Galaxy Model simulations, as well as our present and future work on the model optimization. © EAS, EDP Sciences 2011.
Guittet M.,University Paris Diderot |
Haywood M.,University Paris Diderot |
Schultheis M.,Observatoire de Besancon
EPJ Web of Conferences | Year: 2012
We investigate the characteristics of the thick disk in the Canada - France - Hawaii - Telescope Legacy Survey (CFHTLS) fields, complemented at bright magnitudes with Sloan Digital Sky Survey (SDSS) data. The ([Fe/H], Z) distributions are derived in the W1 and W3 fields, and compared with simulated maps produced using the Besançon model. It is shown that the thick disk, represented in star-count models by a distinct component, is not an adequate description of the observed ([Fe/H], Z) distributions in these fields. © Owned by the authors, published by EDP Sciences, 2012.
Bonifacio P.,University Paris Diderot |
Arenou F.,University Paris Diderot |
Babusiaux C.,University Paris Diderot |
Balkowski C.,University Paris Diderot |
And 29 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010
We present the scientific motivations for GYES: a high multiplex (of the order of several hundred), high resolution (about 20 000), spectrograph to be placed at the prime focus of the CFHT. The main purpose of such an instrument is to conduct a spectroscopic survey complementary to the Gaia mission. The final Gaia catalogue (expected around 2020) will provide accurate distances, proper motions and spectrophotometry for all the stars down to a magnitude of 20. The spectroscopic instrument on board the Gaia satellite will provide intermediate resolution (R=11 500) spectra for stars down to the 17th magnitude. For the fainter stars there will be no radial velocity information. For all the stars the chemical information will be limited to a few species. A multifibre spectrograph at the prime focus of the CFHT will be able to provide the high resolution spectra for stars fainter than 13th magnitude, needed to obtain both accurate radial velocities and detailed chemical abundances. The possible use of GYES will not be limited to Gaia complementary surveys and we here describe the potentialities of such an instrument. We describe here how the scientific drivers are translated into technical requirements. The results of our on-going feasibility study are described in an accompanying poster. © 2010 Copyright SPIE - The International Society for Optical Engineering.
Parker A.H.,University of Victoria |
Parker A.H.,Harvard - Smithsonian Center for Astrophysics |
Kavelaars J.J.,National Research Council Canada |
Petit J.-M.,Observatoire de Besancon |
And 3 more authors.
Astrophysical Journal | Year: 2011
The low-inclination component of the Classical Kuiper Belt is host to a population of extremely widely separated binaries. These systems are similar to other trans-Neptunian binaries (TNBs) in that the primary and secondary components of each system are of roughly equal size. We have performed an astrometric monitoring campaign of a sample of seven wide-separation, long-period TNBs and present the first-ever well-characterized mutual orbits for each system. The sample contains the most eccentric (2006 CH69, em = 0.9) and the most widely separated, weakly bound (2001 QW 322, a/RH ≃ 0.22) binary minor planets known, and also contains the system with lowest-measured mass of any TNB (2000 CF 105, M sys ≃ 1.85 × 1017kg). Four systems orbit in a prograde sense, and three in a retrograde sense. They have a different mutual inclination distribution compared to all other TNBs, preferring low mutual-inclination orbits. These systems have geometric r-band albedos in the range of 0.09-0.3, consistent with radiometric albedo estimates for larger solitary low-inclination Classical Kuiper Belt objects, and we limit the plausible distribution of albedos in this region of the Kuiper Belt. We find that gravitational collapse binary formation models produce an orbital distribution similar to that currently observed, which along with a confluence of other factors supports formation of the cold Classical Kuiper Belt in situ through relatively rapid gravitational collapse rather than slow hierarchical accretion. We show that these binary systems are sensitive to disruption via collisions, and their existence suggests that the size distribution of TNOs at small sizes remains relatively shallow. © 2011. The American Astronomical Society. All rights reserved.