اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA few of Michel Henons contributions to dynamical astronomy
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This article reviews Michel Henons contributions to a diverse set of problems in astrophysical dynamics, including violent relaxation, Saturns rings, roundoff error in orbit integrations, and planet formation.
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In this contribution to the volume in memoriam of Michel Henon, we thought appropriate to look at his early scientific work devoted to the dynamics of large assemblies of interacting masses. He predicted in his PhD thesis that, in such a system, firs
t a collapse of mass occurs at the center and that later binaries stars are formed there. Henceforth, the negative energy of binding of pairs becomes a source of positive energy for the rest of the cluster which evaporate because of that. We examine under what conditions such a singularity can occur, and what could happen afterwards. We hope to show that this fascinating problem of evolution of self-gravitating clusters keeps its interest after the many years passed since Henon thesis, and is still worth discussing now.
Paper in honour of Michel Henon, based on a talk presented at Institut Henri Poincare, Paris, 5 Decembre 2013.
We compute the cross correlation of the intensity and polarisation from the 5-year WMAP data in different sky-regions with respect to template maps for synchrotron, dust, and free-free emission. We derive the frequency dependence and polarisation fra
ction for all three components in 48 different sky regions of HEALPix (Nside=2) pixelisation. The anomalous emission associated with dust is clearly detected in intensity over the entire sky at the K (23 GHz) and Ka (33 GHz) WMAP bands, and is found to be the dominant foreground at low Galactic latitude, between b=-40 and b=+10. The synchrotron spectral index obtained from the K and Ka WMAP bands from an all-sky analysis is -3.32pm 0.12 for intensity and -3.01pm0.03 for the polarised intensity. The polarisation fraction of the synchrotron is constant in frequency and increases with latitude from ~5% near the Galactic plane up to ~40% in some regions at high latitude; the average value for |b|<20 is 8.6pm1.7 (stat) pm0.5 (sys) % while for |b|>20 it is 19.3pm0.8 (stat) pm 0.5 (sys) %. Anomalous dust and free-free emission appear to be relatively unpolarised...[Abridged]...the average polarisation fraction of dust-correlated emission at K-band is 3.2pm0.9 (stat) pm 1.5 (sys) %, or less than 5% at 95% confidence. When comparing real data with simulations, 8 regions show a detected polarisation above the 99th percentile of the distribution from simulations with no input foreground polarisation, 6 of which are detected at above 2sigma and display polarisation fractions between 2.6% and 7.2%, except for one anomalous region, which has 32pm12%. The dust polarisation values are consistent with the expectation from spinning-dust emission, but polarised dust emission from magnetic-dipole radiation cannot be ruled out. Free-free emission was found to be unpolarised with an upper limit of 3.4% at 95% confidence.
Papers on neutrino astronomy (diffuse fluxes and point sources, prepared for the 35th International Cosmic Ray Conference (ICRC 2017, Busan, South Korea) by the ANTARES Collaboration
Employing the the stellar evolution code (Modules for Experiments in Stellar Astrophysics), we calculate yields of heavy elements from massive stars via stellar wind and core-collapse supernovae (CCSN) ejecta to interstellar medium (ISM). In our mode
ls, the initial masses ($M_{rm ini}$) of massive stars are taken from 13 to 80 $M_odot$, their initial rotational velocities (V) are 0, 300 and 500 km s$^{-1}$, and their metallicities are [Fe/H] = -3, -2, -1, and 0. The yields of heavy elements coming from stellar winds are mainly affected by the stellar rotation which changes the chemical abundances of stellar surfaces via chemically homogeneous evolution, and enhances mass-loss rate. We estimate that the stellar wind can produce heavy element yields of about $10^{-2}$ (for low metallicity models) to several $M_odot$ (for low metallicity and rapid rotation models) mass. The yields of heavy element produced by CCSN ejecta also depend on the remnant mass of massive mass which is mainly determined by the mass of CO-core. Our models calculate that the yields of heavy elements produced by CCSN ejecta can get up to several $M_odot$. Compared with stellar wind, CCSN ejecta has a greater contribution to the heavy elements in ISM. We also compare the $^{56}$Ni yields by calculated in this work with observational estimate. Our models only explain the $^{56}$Ni masses produced by faint SNe or normal SNe with progenitor mass lower than about 25 $M_odot$, and greatly underestimate the $^{56}$Ni masses produced by stars with masses higher than about 30 $M_odot$.
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