Laboratory evidence for an asymmetric accretion structure upon slanted matter impact in young stars^⋆

¹ LULI – CNRS, CEA, UPMC Univ Paris 06 : Sorbonne Université, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
e-mail: konstantin.burdonov@polytechnique.edu
² Sorbonne Université, Observatoire de Paris, PSL Research University, LERMA, CNRS UMR 8112, 75005 Paris, France
³ INAF, Osservatorio Astronomico di Palermo, Palermo, Italy
⁴ Department of Physics and Chemistry, University of Palermo, 90133 Palermo, Italy
⁵ LNCMI, UPR 3228, CNRS-UGA-UPS-INSA, 31400 Toulouse, France
⁶ Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, Germany
⁷ ELI-NP, “Horia Hulubei” National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, 077125 Bucharest-Magurele, Romania
⁸ Department of Physics, IUNAT, Universidad de Las Palmas de Gran Canaria, 35001 Las Palmas, Spain
⁹ JIHT, Russian Academy of Sciences, 125412 Moscow, Russia
¹⁰ IAP, Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia
¹¹ NRNU MEPhI, 115409 Moscow, Russia
¹² Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany

Received: 17 April 2020
Accepted: 18 July 2020

Abstract

Aims. Investigating the process of matter accretion onto forming stars through scaled experiments in the laboratory is important in order to better understand star and planetary system formation and evolution. Such experiments can indeed complement observations by providing access to the processes with spatial and temporal resolution. A previous investigation revealed the existence of a two-component stream: a hot shell surrounding a cooler inner stream. The shell was formed by matter laterally ejected upon impact and refocused by the local magnetic field. That laboratory investigation was limited to normal incidence impacts. However, in young stellar objects, the complex structure of magnetic fields causes variability of the incident angles of the accretion columns. This led us to undertake an investigation, using laboratory plasmas, of the consequence of having a slanted accretion impacting a young star.

Methods. Here, we used high power laser interactions and strong magnetic field generation in the laboratory, complemented by numerical simulations, to study the asymmetry induced upon accretion structures when columns of matter impact the surface of young stars with an oblique angle.

Results. Compared to the scenario where matter accretes perpendicularly to the star surface, we observe a strongly asymmetric plasma structure, strong lateral ejecta of matter, poor confinement of the accreted material, and reduced heating compared to the normal incidence case. Thus, slanted accretion is a configuration that seems to be capable of inducing perturbations of the chromosphere and hence possibly influencing the level of activity of the corona.