An independent determination of Fomalhaut b's orbit and the dynamical effects on the outer dust belt

The nearby star Fomalhaut harbours a cold, moderately eccentric dust belt with a sharp inner edge near 133 au. A low-mass, common proper motion companion (Fom b), was discovered near the inner edge and was identified as a planet candidate that could account for the belt morphology. However, the most recent orbit determination based on four epochs of astrometry over eight years reveals a highly eccentric orbit that appears to cross the belt in the sky plane projection. We perform here a full orbital determination based on the available astrometric data to independently validate the orbit estimates previously presented. Adopting our values for the orbital elements and their associated uncertainties, we then study the dynamical interaction between the planet and the dust ring, to check whether the proposed disk sculpting scenario by Fom b is plausible. We used a dedicated MCMC code to derive the statistical distributions of the orbital elements of Fom b. Then we used symplectic N-body integration to investigate the dynamics of the dust belt, as perturbed by a single planet. Different attempts were made assuming different masses for Fom b. We also performed a semi-analytical study to explain our results. Our results are in good agreement with others regarding the orbit of Fom b. We find that the orbit is highly eccentric, is close to apsidally aligned with the belt, and has a moderate mutual inclination relative to the belt plane of. If coplanar, this orbit crosses the disk. Our dynamical study then reveals that the observed planet could sculpt a transient belt configuration with a similar eccentricity to what is observed, but it would not be simultaneously apsidally aligned with the planet. This transient configuration only occurs a short time after the planet is placed on such an orbit (assuming an initially circular disk), a time that is inversely proportional to the planet's mass, and that is in any case much less than the 440 Myr age of the star. We constrain how long the observed dust belt could have survived with Fom b on its current orbit, as a function of its possible mass. This analysis leads us to conclude that Fom b is likely to have low mass, that it is unlikely to be responsible for the sculpting of the belt, and that it supports the hypothesis of a more massive, less eccentric planet companion Fom c.Comment: 17 pages, 15 figures, accepted for publication in Astronomy \& Astrophysic

Développement d'un outil informatique opérationnel d'aide à la décision et de modélisation des pollutions en Méditerranée

National audienc

Coronary angioplasty is associated with a better neurological outcome in the era of modern management of out-of-hospital cardiac arrest.: Angioplasty and neurologic outcome of cardiac arrest

International audienc

Développement d'un outil informatique opérationnel d'aide à la décision et de modélisation des pollutions en Méditerranée

National audienc

INFLUENCE OF HCV GENOTYPE 1 SUBTYPES ON THE VIRUS RESPONSE TO PEG INTERFERON ALPHA-2a PLUS RIBAVIRIN THERAPY

International audienceNew factors that influence the viral response in HCV non-genotype 2/3 patients must be identified in order to optimize anti-HCV treatment. This multicenter prospective study evaluates the influence of HCV variability and pharmacological parameters on the virological response of these patients to pegylated interferon α2a (peg-IFN-α2a: 180 µg/week) and ribavirin (800-1200 mg/day) for 48 weeks. HCV subtypes were identified by sequencing the NS5B region. Serum ribavirin and peg-IFN-α2a concentrations were measured at weeks 4 and 12. The 115 patients (67 men; median age=49, range [31-76]) included 64 who had never been treated and 27 co-infected with HIV. The mean baseline HCV RNA was 6.30 ± 0.06 log IU/mL and the HCV genotypes were: G1 (n=93) with 1a (n=37) and 1b (n=50), G4 (n=20) and G5 (n=2). Most patients (79/108; 73%) had an early virological response. Independent predictors of an early virological response were interferon naive patients (OR=2.98 [1.15; 7.72]) and ribavirin of > 2,200 ng/mL at week 12 (OR=3.41 [1.31; 8.90]). Forty of 104 patients (38%) had a sustained virological response. The only independent predictors of a sustained virological response were subtype 1b (OR=6.82 [1.7; 26.8]), and HCV RNA 2,200 ng/mL was associated with an early virological response and patients infected with HCV subtype 1b had a better chance of a sustained virological response than did those infected with subtype 1a

Marine ecosystems’ responses to climatic and anthropogenic forcings in the Mediterranean

International audienceThe semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a “hotspot” for climate change, is therefore expected to experience environmental impacts that are considerably greater than those in many other places around the world. These natural pressures interact with the increasing demographic and economic developments occurring heterogeneously in the coastal zone, making the Mediterranean even more sensitive. This review paper aims to provide a review of the state of current functioning and responses of Mediterranean marine biogeochemical cycles and ecosystems with respect to key natural and anthropogenic drivers and to consider the ecosystems’ responses to likely changes in physical, chemical and socio-economical forcings induced by global change and by growing anthropogenic pressure at the regional scale. The current knowledge on and expected changes due to single forcing (hydrodynamics, solar radiation, temperature and acidification, chemical contaminants) and combined forcing (nutrient sources and stoichiometry, extreme events) affecting the biogeochemical fluxes and ecosystem functioning are explored. Expected changes in biodiversity resulting from the combined action of the different forcings are proposed. Finally, modeling capabilities and necessity for modeling are presented. A synthesis of our current knowledge of expected changes is proposed, highlighting relevant questions for the future of the Mediterranean ecosystems that are current research priorities for the scientific community. Finally, we discuss how these priorities can be approached by national and international multi-disciplinary research, which should be implemented on several levels, including observational studies and modeling at different temporal and spatial scales

Theia: Faint objects in motion or the new astrometry frontier

In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 $\%$ of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision