Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

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Table 15.2: Former PhD students of the SHERPA group. Name PhD thesis Current position Françoise Rosso 1994 teacher (classes préparatoires) Jonathan Ferreira 1994 assistant professor in the group Alexandre Marcowith 1996 CNRS position at CESR-Toulouse Pierre-Olivier Petrucci 1998 CNRS position in the group Nicolas Renaud 1999 teacher (classes préparatoires) Evy Kersalé 2000 postdoctoral position at Leeds-Cambridge Fabien Casse 2001 assistant professor at Paris VII Denis Gialis 2004 engineer at ONERA Ludovic Saugé 2004 postdoctoral position at IPN-Lyon • GLAST: the whole team is involved in the scientific support. With an overlap with the HESS window, this mission should provide invaluable clues on compact objects and GRBs. • ECLAIRS: G. Henri and G. Pelletier are involved in the scientific support of this instrument with the goal of studying the prompt emission of GRBs. • HESS: G. Henri, G. Pelletier, P.-O. Petrucci are deeply involved in the HESS collaboration where they provide a scientific support, especially for the interpretation of Blazar observations and multi-wavelength approaches. This Astroparticle experiment is very successful (cf. papers in Nature, Science...) and is opening a new window of astrophysics. 15.10 Doctoral formation and Schools The SHERPA team is heavily involved in teaching activities through the presence of 3 teachers (out of 6 permanent members), including 2 professors who have benefitted from a position at the prestigious Institut Universitaire de France. One of them, G. Henri, is the current director for the ”Master 2 Recherche Astrophysique et Milieux Dilués”, which is the pre-doctoral year before French thesis. The group has regularly formed PhD thesis students who found good academic or industrial positions for most of them (see Table 2). Members of the team have also organized schools for researchers. G. Henri, G. Pelletier and F. Ménard (FOST) organized a school on ”Accretion disks, jets and high-energy phenomena in astrophysics” in 2002 at Les Houches. A JETSET school on ”MHD jet models and constraints”, to be held January 2006, is organized by J. Ferreira and C. Dougados (FOST). 15.11 Scientific Highlights (2002-2005) • ”Transport of cosmic rays in chaotic magnetic fields”, Casse Fabien, Lemoine Martin, Pelletier Guy, 2002, Phys. Rev. D. The knowledge of the diffusion coefficients of cosmic rays is crucial for astrophysical applications and especially for astroparticle physics, both for mastering the cosmic ray propagation and the efficiency of Fermi acceleration. They have been computed with a Monte Carlo simulation as a function of the cosmic ray rigidity and the spectrum of the magnetic field (characterized by its index and its degree of irregularities). The Bohm scaling, often assumed in astroparticle physics in the strong turbulence regime, has been ruled out. The scalings derived for the pitch angle diffusion and for the parallel diffusion with the ”quasi-linear theory” are extended in an appropriate way in the strong turbulence regime. However the transverse diffusion coefficient follows a law which is nor Bohm nor quasi-linear, but a law that stems from the analysis of the spatial chaos of field lines. This result is important to estimate the confinement time of cosmic-rays in galaxies and in extragalactic jets. 158
• “Particle Transport in Tangled Magnetic Fields and Fermi Acceleration at Relativistic Shocks”, Lemoine Martin, Pelletier Guy, 2003, ApJ, 589L. In Monte Carlo simulations, test particle trajectories are followed in a magnetic scattering medium in which a plane is moving at subrelativistic or relativistic speed. The conditional probabilities for a particle to come back to the plane after crossing as a function of the pitch angles have been computed. Then the amplification of the particle energy at each Fermi cycle (downstream-upstream-downstream) across a shock is calculated for arbitrary value of the shock speed. Thus the formation of the cosmic ray spectrum at a relativistic shock is derived and the result displays that the first Fermi cycle produces a strong energy amplification by a factor on the order of the shock Lorentz factor to the square, whereas the other cycles amplify by a factor 2, as predicted by Achterberg and Gallant. The index is computed as a function of the shock Lorentz factor and the results are in excellent agreement with an analytical formula. A precise law for the acceleration time have also been obtained. • “Stationary Accretion Disks Launching Super-fast-magnetosonic Magnetohydrodynamic Jets”, Ferreira J., Casse F. 2004, ApJ, 601, L139 This is the last paper in the series on Magnetized Accretion-Ejection Structures (MAES), which represents the only available self-consistent model of a self-confined jet driven by an accretion disk (with the disk fully resolved), able to cross all three MHD critical points. Biases induced by the self-similarity contraints are discussed. • ”Physical interpretation of the NGC 7469 UV/X-ray variability”, Petrucci, P. O., Maraschi, L., Haardt, F., & Nandra, K. 2004, A&A, 413, 477 Data fits, with a detailed model of comptonized spectra obtained from simultaneous UV and X observations of a Seyfert galaxy. These fits not only reproduce the spectral shape, but the source variability as well. They allow us to show that the data are consistent with a model where all the accretion power is liberated in the corona (producing X-rays), while the UV emission comes from the reprocessing of the X-ray flow rather than from the energy dissipation in the disk. The observed variability is produced by a geometric modification of the corona. • “Astrocladistics: a phylogenetic analysis of galaxy evolution. I. Character evolutions and galaxy histories”, D. Fraix-Burnet, P. Choler, E. Douzery, A. Verhamme. 2005, accepted in Journal of Classification. This is a first paper in series; the method of astrocladistics is described. It should allow us to establish a galaxy classificatoin based on physical criteria besides the galaxy morphology. • “On the Relevance of Subcritical Turbulence to Accretion Disk Transport”, Lesur, G., and Longaretti, P.-Y. 2005, accepted in A&A This paper solves a riddle dating back to the seventies, and which has given rise to an important controversy in the last ten years. Namely, it is shown that a linearly stable, keplerian hydrodynamic flow is indeed turbulent through non linear mechanisms, but that this turbulence has a low efficiency in terms of angular momentum transport, with a Shakura-Sunyaev parameter α < 10 −5 . The discrepancy between numerical simulations and laboratory experiments is explained away. • ”The bulk Lorentz factor crisis of TeV Blazars: evidence for an inhomogeneous pile-up energy distribution”, Gilles Henri & Ludovic Saugé, 2005, accepted in ApJ It is shown that the Lorentz factors of Blazar jets, deduced from homogeneous SSC models, are contradicted by the source statisticsn which implies Lorentz factors of order 3, whereas homogeneous models require 50 or more. The only way out of this conundrum is to take the jet stratification into account, so that high energy photons are not produced in the same region as low energy ones. Observations then require mono-energetic distribution functions whereas most models make use of power-law distributions. In contradistinction with the dominant view, this work shows that (1) jets do not need to be highly relativistic, and (2) turbulence rather than shocks is at the origin of the production of high energy particles. 159
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LABORATOIRE D’ASTROPHYSIQUE DE GR
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III Team ASTROMOL 41 2 Presentation
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8.1.3 Graduate Students . . . . . .
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VI Team SHERPA 145 15 Results 147 1
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Part I Foreword: Presentation of th
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Part II Executive Summary A 18th ce
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of CNRS for technicians and enginee
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Figure 1.3: New LAOG organigram (20
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heart attack. Manuel went back to t
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Figure 1.6: PhD student repartition
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• LAOG researchers (and publishin
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and published 95 papers in four yea
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• National astronomy programs. 4
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1.5 From dreams to reality: Human r
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and accretion disks with heavy nume
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emphasis on the chemistry of planet
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Part III TEAM ASTROMOL Sub-arcsecon
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• we develop quantum and classica
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Table shows not only the volume of
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• Herschel-HIFI: Astromol is invo
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particular, we calculated a 9D H2O-
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• The hot corinos. More spectacul
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the massive deeply embedded protost
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tens of visual magnitudes, hence pr
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quantum VCC-IOS approximation may f
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Rate constant (cm 3 s -1 ) 1e-09 1e
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• One of us (PV) is strongly invo
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sublimation of water ice trapped ei
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If the chemistry in the first phase
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4.2.2 Molecular Physics The theoret
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Source Herschel Time Astromol Class
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several important studies that anti
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Chapter 5 Selected Publications •
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Part IV TEAM FOST The first image o
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393254 (5MJup at 55 AU) & AB Pic (1
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2.2 µ m 0.5" 11.7 µ m Figure 6.1:
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Figure 6.3: Contribution of heating
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such mid-term (several weeks) magne
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systems: HD 141569, HD 32297, HD 18
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C2D Spitzer/IRAC and MIPS data of s
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et al. 2002; 2003). We have found t
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Figure 6.8: Distribution of separat
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with only three known to date. Most
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300 objects, a size sufficient for
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therefore no surprise that vast eff
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data to verify the predictions we a
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Chapter 8 Appendices 8.1 Members of
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