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Search Results: 1 - 10 of 461929 matches for " A. Mordasini "
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Mise en uvre des politiques publiques globales : les agences d’aide joignent-elles le geste à la parole ?
Michel Mordasini
International Development Policy/Revue Internationale de Politique de Développement , 2012, DOI: 10.4000/poldev.945
Abstract: Ces dernières années, au-delà des effets de rhétorique et des déclarations d’intention, la mise en uvre des politiques publiques globales est restée fragile. On observe un fossé béant entre les discours officiels et la réalité. Le présent article se concentre sur le r le, l’engagement et la performance des agences d’aide en leur qualité de fournisseurs modestes mais importants de biens publics mondiaux. Tout en relevant certains progrès allant dans la bonne direction (large reconnaissance internationale et amélioration de l’estimation des risques mondiaux, consensus sur la grande vulnérabilité des pays à bas revenu et l’urgence d’agir, engagements financiers substantiels), l’article évoque les résultats des évaluations et des examens d’efficacité disponibles pour avancer que le modèle de prestation de l’aide n’a en fait évolué que dans une faible mesure et que les pauvres n’ont encore que peu bénéficié de ces promesses. L’article défend l’avis selon lequel de profondes réformes institutionnelles, structurelles et opérationnelles sont devenues urgentes dans les agences d’aide et affirme que la communauté internationale doit s’attaquer avec sérieux aux risques de fragmentation et de prolifération qui pèsent sur l’architecture de l’aide afin de se donner les moyens de répondre de manière crédible aux défis globaux qu’affrontent les pays en développement.
Implementing Global Public Policies : Are the Aid Agencies Walking the Talk?
Michel Mordasini
International Development Policy/Revue Internationale de Politique de Développement , 2012, DOI: 10.4000/poldev.985
Abstract: Published by Palgrave MacmillanBeyond much rhetoric and stated ambition in recent years, the implementation of global public policies has been weak so far. There is a huge gap between the official discourse and the reality. This chapter focuses on the role, commitment and performance of aid agencies as ‘small’ but important suppliers of global public goods. While acknowledging some advances in the right direction (broad international recognition and improved costing of the global risks, consensus on the high vulnerability of the low-income countries and the need to act urgently, and substantial financing commitments) the author argues, based on available evidence from evaluations and effectiveness reviews, that only limited progress has been made in the aid delivery model and that the poor have not yet gained much from these undertakings. The chapter makes the case that significant institutional, organisational and operational reforms must take place urgently in aid agencies. The international community, moreover, must address the high fragmentation and proliferation of the aid architecture, in order to set the stage for a credible response to the global challenges facing developing countries.
Luminosity of young Jupiters revisited. Massive cores make hot planets
Christoph Mordasini
Physics , 2013, DOI: 10.1051/0004-6361/201321617
Abstract: The intrinsic luminosity of young Jupiters is of high interest for planet formation theory. It is an observable quantity that is determined by important physical mechanisms during formation, namely the accretion shock structure, and even more fundamentally, the basic formation mechanism (core accretion or gravitational instability). We study the impact of the core mass on the post-formation entropy and luminosity of young giant planets forming via core accretion with a supercritical shock (cold accretion). For this, we conduct self-consistently coupled formation and evolution calculations of giant planets with masses between 1 and 12 Jovian masses and core masses between 20 and 120 Earth masses. We find that the post-formation luminosity of massive giant planets is very sensitive to the core mass. An increase of the core mass by a factor 6 results in an increase of the post-formation luminosity of a 10 Jovian mass planet by a factor 120. Due to this dependency, there is no single well defined post-formation luminosity for core accretion, but a wide range. For massive cores (~100 Earth masses), the post-formation luminosities of core accretion planets become so high that they approach those in the hot start scenario that is often associated with gravitational instability. For the mechanism to work, it is necessary that the solids are accreted before or during gas runaway accretion, and that they sink deep into the planet. We make no claims whether or not such massive cores can actually form in giant planets. But if yes, it becomes difficult to rule out core accretion as formation mechanism based solely on luminosity for directly imaged planets that are more luminous than predicted for low core masses. Instead of invoking gravitational instability as the consequently necessary formation mode, the high luminosity could also be caused simply by a more massive core.
Grain opacity and the bulk composition of extrasolar planets. II. An analytical model for the grain opacity in protoplanetary atmospheres
C. Mordasini
Physics , 2014, DOI: 10.1051/0004-6361/201423702
Abstract: Context. We investigate the grain opacity k_gr in the atmosphere of protoplanets. This is important for the planetary mass-radius relation since k_gr affects the H/He envelope mass of low-mass planets and the critical core mass of giant planets. Aims. The goal of this study is to derive an analytical model for k_gr. Methods. Our model is based on the comparison of the timescales of microphysical processes like grain settling in the Stokes and Epstein regime, growth by Brownian motion coagulation and differential settling, grain evaporation, and grain advection due to envelope contraction. With these timescales we derive the grain size, abundance, and opacity. Results. We find that the main growth process is differential settling. In this regime, k_gr has a simple functional form and is given as 27 Q/8 H rho in the Epstein regime and as 2 Q/H rho for Stokes drag. Grain dynamics lead to a typical radial structure of k_gr with high ISM-like values in the top layers but a strong decrease in the deeper parts where the grain-free molecular opacities take over. Conclusions. In agreement with earlier results we find that k_gr is typically much lower than in the ISM. The equations also show that a higher dust input in the top layer does not strongly increase k_gr with two important implications. First, for a formation of giant planet cores via pebbles, there could be the issue that pebbles increase the grain input high in the atmosphere due to ablation. This could potentially increase k_gr hindering giant planet formation. Our study shows that this adverse effect should not occur. Second, it means that a higher stellar [Fe/H] which presumably leads to a higher surface density of planetesimals only favors giant planet formation without being detrimental to it due to an increased k_gr. This corroborates the result that core accretion explains the increase of the giant planet frequency with [Fe/H].
Theoretical models of planetary system formation: mass vs semi-major axis
Y. Alibert,F. Carron,A. Fortier,S. Pfyffer,W. Benz,C. Mordasini,D. Swoboda
Physics , 2013, DOI: 10.1051/0004-6361/201321690
Abstract: Planet formation models have been developed during the last years in order to try to reproduce the observations of both the solar system, and the extrasolar planets. Some of these models have partially succeeded, focussing however on massive planets, and for the sake of simplicity excluding planets belonging to planetary systems. However, more and more planets are now found in planetary systems. This tendency, which is a result of both radial velocity, transit and direct imaging surveys, seems to be even more pronounced for low mass planets. These new observations require the improvement of planet formation models, including new physics, and considering the formation of systems. In a recent series of papers, we have presented some improvements in the physics of our models, focussing in particular on the internal structure of forming planets, and on the computation of the excitation state of planetesimals, and their resulting accretion rate. In this paper, we focus on the concurrent effect of the formation of more than one planet in the same protoplanetary disc, and show the effect, in terms of global architecture and composition of this multiplicity. We use a N-body calculation including collision detection to compute the orbital evolution of a planetary system. Moreover, we describe the effect of competition for accretion of gas and solids, as well as the effect of gravitational interactions between planets. We show that the masses and semi-major axis of planets are modified by both the effect of competition and gravitational interactions. We also present the effect of the assumed number of forming planets in the same system (a free parameter of the model), as well as the effect of the inclination and eccentricity damping.
Deuterium burning in objects forming via the core accretion scenario - Brown dwarfs or planets?
Paul Mollière,Christoph Mordasini
Physics , 2012, DOI: 10.1051/0004-6361/201219844
Abstract: Aims. Our aim is to study deuterium burning in objects forming according to the core accretion scenario in the hot and cold start assumption and what minimum deuterium burning mass limit is found for these objects. We also study how the burning process influences the structure and luminosity of the objects. Furthermore we want to test and verify our results by comparing them to already existing hot start simulations which did not consider, however, the formation process. Methods. We present a new method to calculate deuterium burning of objects in a self-consistently coupled model of planet formation and evolution. We discuss which theory is used to describe the process of deuterium burning and how it was implemented. Results. We find that the objects forming according to a hot start scenario behave approximately in the same way as found in previous works of evolutionary calculations, which did not consider the formation. However, for cold start objects one finds that the objects expand during deuterium burning instead of being partially stabilized against contraction. In both cases, hot and cold start, the mass of the solid core has an influence on the minimum mass limit of deuterium burning. The general position of the mass limit, 13 MJ, stays however approximately the same. None of the investigated parameters was able to change this mass limit by more than 0.8 MJ. Due to deuterium burning, the luminosity of hot and cold start objects becomes comparable after ~ 200 Myrs.
The near-infrared spectral energy distribution of β Pictoris b
M. Bonnefoy,A. Boccaletti,A. -M. Lagrange,F. Allard,C. Mordasini,H. Beust,G. Chauvin,J. H. V. Girard,D. Homeier,D. Apai,S. Lacour,D. Rouan
Physics , 2013, DOI: 10.1051/0004-6361/201220838
Abstract: A gas giant planet has previously been directly seen orbiting at 8-10 AU within the debris disk of the ~12 Myr old star {\beta} Pictoris. The {\beta} Pictoris system offers the rare opportunity to study the physical and atmospheric properties of an exoplanet placed on a wide orbit and to establish its formation scenario. We obtained J (1.265 {\mu}m), H (1.66 {\mu}m), and M' (4.78 {\mu}m) band angular differential imaging of the system between 2011 and 2012. We detect the planetary companion in our four-epoch observations. We estimate J = 14.0 +- 0.3, H = 13.5 +- 0.2, and M' = 11.0 +- 0.3 mag. Our new astrometry consolidates previous semi-major axis (sma=8-10 AU) and excentricity (e <= 0.15) estimates of the planet. These constraints, and those derived from radial velocities of the star provides independent upper limits on the mass of {\beta} Pictoris b of 12 and 15.5 MJup for semi-major axis of 9 and 10 AU. The location of {\beta} Pictoris b in color-magnitude diagrams suggests it has spectroscopic properties similar to L0-L4 dwarfs. This enables to derive Log10(L/Lsun) = -3.87 +- 0.08 for the companion. The analysis with 7 PHOENIX-based atmospheric models reveals the planet has a dusty atmosphere with Teff = 1700 +- 100 K and log g = 4.0+- 0.5. "Hot-start" evolutionary models give a new mass of 10+3-2 MJup from Teff and 9+3-2 MJup from luminosity. Predictions of "cold-start" models are inconsistent with independent constraints on the planet mass. "Warm-start" models constrain the mass to M >= 6MJup and the initial entropies to values (Sinit >= 9.3Kb/baryon), intermediate between those considered for cold/hot-start models, but likely closer to those of hot-start models.
Orbital and physical properties of planets and their hosts: new insights on planet formation and evolution
V. Zh. Adibekyan,P. Figueira,N. C. Santos,A. Mortier,C. Mordasini,E. Delgado Mena,S. G. Sousa,A. C. M. Correia,G. Israelian,M. Oshagh
Physics , 2013, DOI: 10.1051/0004-6361/201322551
Abstract: We explore the relations between physical and orbital properties of planets and properties of their host stars to identify the main observable signatures of the formation and evolution processes of planetary systems. We use a large sample of FGK dwarf planet hosts with stellar parameters derived in a homogeneous way from the SWEET-Cat database to study the relation between stellar metallicity and position of planets in the period-mass diagram. In the second part we use all the RV-detected planets orbiting FGK stars to explore the role of planet-disk and planet-planet interaction on the evolution of orbital properties of planets with masses above 1MJup. We show that planets orbiting metal-poor stars have longer periods than those in metal-rich systems. This trend is valid for masses at least from 10MEarth to 4MJup. Earth-like planets orbiting metal-rich stars always show shorter periods (fewer than 20 days) than those orbiting metal-poor stars. We also found statistically significant evidence that very high mass giants have on average more eccentric orbits than giant planets with lower mass.Finally, we show that the eccentricity of planets with masses higher than 4MJup tends to be lower for planets with shorter periods. Our results suggest that the planets in the P-MP diagram are evolving differently because of a mechanism that operates over a wide range of planetary masses. This mechanism is stronger or weaker depending on the metallicity of the respective system. One possibility is that planets in metal-poor disks form farther out from their central star and/or they form later and do not have time to migrate as far as the planets in metal-rich systems. The trends and dependencies obtained for very high mass planetary systems suggest that planet-disk interaction is a very important and orbit-shaping mechanism for planets in the high-mass domain. Shortened.
From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio
V. Adibekyan,N. C. Santos,P. Figueira,C. Dorn,S. G. Sousa,E. Delgado-Mena,G. Israelian,A. A. Hakobyan,C. Mordasini
Physics , 2015, DOI: 10.1051/0004-6361/201527059
Abstract: The main goal of this work is to study element ratios that are important for the formation of planets of different masses. We study potential correlations between the existence of planetary companions and the relative elemental abundances of their host stars. We use a large sample of FGK-type dwarf stars for which precise Mg, Si, and Fe abundances have been derived using HARPS high-resolution and high-quality data. A first analysis of the data suggests that low-mass planet host stars show higher [Mg/Si] ratios, while giant planet hosts present [Mg/Si] that is lower than field stars. However, we found that the [Mg/Si] ratio significantly depends on metallicity through Galactic chemical evolution. After removing the Galactic evolution trend only the difference in the [Mg/Si] elemental ratio between low-mass planet hosts and non-hosts was present in a significant way. These results suggests that low-mass planets are more prevalent around stars with high [Mg/Si]. Our results demonstrate the importance of Galactic chemical evolution and indicate that it may play an important role in the planetary internal structure and composition.
HD45364, a pair of planets in a 3:2 mean motion resonance
A. C. M. Correia,S. Udry,M. Mayor,W. Benz,J. -L. Bertaux,F. Bouchy,J. Laskar,C. Lovis,C. Mordasini,F. Pepe,D. Queloz
Physics , 2009, DOI: 10.1051/0004-6361:200810774
Abstract: Precise radial-velocity measurements with the HARPS spectrograph reveal the presence of two planets orbiting the solar-type star HD45364. The companion masses are 0.187 Mjup and 0.658 Mjup, with semi-major axes of 0.681 AU and 0.897 AU, and eccentricities of 0.168 and 0.097, respectively. A dynamical analysis of the system further shows a 3:2 mean motion resonance between the two planets, which prevents close encounters and ensures the stability of the system over 5 Gyr. This is the first time that such a resonant configuration has been observed for extra-solar planets, although there is an analogue in our Solar System formed by Neptune and Pluto. This singular planetary system may provide important constraints on planetary formation and migration scenarios.
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