%0 Journal Article
%T The role of cosmic rays on magnetic field diffusion and the formation of protostellar discs
%+ Laboratoire Univers et Particules de Montpellier (LUPM)
%+ INAF - Osservatorio Astrofisico di Arcetri (OAA)
%+ Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA)
%+ Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU)
%+ Centre de Recherche Astrophysique de Lyon (CRAL)
%A Padovani, M.
%A Galli, D.
%A Hennebelle, P.
%A Commerçon, B.
%A Joos, M.
%Z M.P. and P.H. acknowledge the financial support of the Agence National pour la Recherche (ANR) through the COSMIS project. M.P. and D.G. also acknowledge the support of the CNRS-INAF PICS project “Pulsar wind nebulae, supernova remnants and the origin of cosmic rays”. This work has been carried out thanks to the support of the OCEVU Labex (ANR-11- LABX-0060) and the A*MIDEX project (ANR-11-IDEX-0001-02) funded by the “Investissements d’Avenir” French government programme managed by the ANR. B.C. acknowledges the financial support of the ANR through the “Feedback ISM” project
%< avec comité de lecture
%@ 0004-6361
%J Astronomy and Astrophysics - A&A
%I EDP Sciences
%V 571
%P A33
%8 2014-11
%D 2014
%Z 1408.5901
%Z 2014A&A...571A..33P
%R 10.1051/0004-6361/201424035
%K ISM: clouds
%K ISM: magnetic fields
%K cosmic rays
%Z Physics [physics]/Astrophysics [astro-ph]Journal articles
%X Context. The formation of protostellar discs is severely hampered by magnetic braking, as long as magnetic fields remain frozen in the gas. The latter condition depends on the levels of ionisation that characterise the innermost regions of a collapsing cloud.Aims. The chemistry of dense cloud cores and, in particular, the ionisation fraction is largely controlled by cosmic rays. The aim of this paper is to evaluate whether the attenuation of the flux of cosmic rays expected in the regions around a forming protostar is sufficient to decouple the field from the gas, thereby influencing the formation of centrifugally supported disc.Methods. We adopted the method developed in a former study to compute the attenuation of the cosmic-ray flux as a function of the column density and the field strength in clouds threaded by poloidal and toroidal magnetic fields. We applied this formalism to models of low- and high-mass star formation extracted from numerical simulations of gravitational collapse that include rotation and turbulence.Results. For each model we determine the size of the magnetic decoupling zone, where collapse or rotation motion becomes unaffected by the local magnetic field. In general, we find that decoupling only occurs when the attenuation of cosmic rays is taken into account with respect to a calculation in which the cosmic-ray ionisation rate is kept constant. The extent of the decoupling zone also depends on the dust grain size distribution and is larger if large grains (of radius ~10-5 cm) are formed by compression and coagulation during cloud collapse. The decoupling region disappears for the high-mass case. This is due to magnetic field diffusion caused by turbulence that is not included in the low-mass models.Conclusions. We conclude that a realistic treatment of cosmic-ray propagation and attenuation during cloud collapse may lead to a value of the resistivity of the gas in the innermost few hundred AU around a forming protostar that is higher than generally assumed. Forthcoming self-consistent calculations should investigate whether this effect is strong enough to effectively decouple the gas from the field and to compute the amount of angular momentum lost by infalling fluid particles when they enter the decoupling zone.
%G English
%2 https://cea.hal.science/cea-01290008/document
%2 https://cea.hal.science/cea-01290008/file/aa24035-14.pdf
%L cea-01290008
%U https://cea.hal.science/cea-01290008
%~ IN2P3
%~ ENS-LYON
%~ OBSPM
%~ CEA
%~ INSU
%~ ENS-PARIS
%~ UPMC
%~ CNRS
%~ UNIV-LYON1
%~ UNIV-MONTP2
%~ UNIV-CERGY
%~ LERMA
%~ LUPM
%~ CRAL
%~ DSM-IRFU
%~ PSL
%~ UPMC_POLE_2
%~ MIPS
%~ UNIV-MONTPELLIER
%~ CEA-DRF
%~ SORBONNE-UNIVERSITE
%~ AMIDEX
%~ SU-SCIENCES
%~ UDL
%~ UNIV-LYON
%~ ENS-PSL
%~ OBSPM-PSL
%~ SU-TI
%~ ANR
%~ ALLIANCE-SU
%~ UM1-UM2