7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Cosmic rays in star and disk formation processes

Kengo Tomida1, Shigeo Kimura1,2, Shinsuke Takasao3
1
Astronomical Institute, Tohoku University, 2 Frontier Research Institute for InterdisciplinarySciences, Tohoku University, 3 Department of Earth and Space Sciences, Osaka University
e-mail (speaker): tomida@astr.tohoku.ac.jp
As an AAPPS-DPP standard, we do not need to add your postal address.
Angular momentum transport by magnetic fields is oneof the key processes in star and disk formation, andnon-ideal Magnetohydrodynamic (MHD) effects
strongly affect the disk formation and evolution [1]. The
rates of the non-ideal MHD effects depend on theionization rate as well as dust properties, and theionization rate depends on many physical processes suchas cosmic rays, ionizing radiation, and decay ofradioactive nuclei. Therefore, it is of crucial importanceto understand how these ionization processes work instar formation processes.
Cosmic rays are one of the most important ionization
processes in star and disk formation processes. Whilecosmic rays from the interstellar space can propagate
into star forming clouds, shocks in jets and protostellar
flares driven by magnetic reconnection can internallyaccelerate cosmic rays within star forming clouds.
In this talk, I will discuss acceleration and propagationof cosmic rays in star forming clouds and their impact on
the disk formation and evolution. Based on MHD
simulations of star and disk interaction, we found that
giant protostellar flares are driven by magnetic
reconnection in the innermost region of a protoplanetary
disk [2]. These flares are very energetic and release up toa few 1038 erg every 20-30 orbital periods, producing hotejecta This is consistent with X-ray observations ofprotostellar flares.
Motivated by this work, we constructed a model of
non-thermal radiation from these flares [3]. We firstcalibrated the model based on solar flares and extended it
to the protostellar flare regime. We found that such flaresare good sites of cosmic-ray acceleration and produce
broad emissions from radio to gamma-ray. The emission
can be observed with the Cherenkov Telescope Array andother future observatories at various wavelengths.
References[1] K. Tomida, S. Okuzumi, M. N. Machida, “Radiation
Magnetohydrodynamic Simulations of Protostellar
Collapse: Nonideal Magnetohydrodynamic Effects andEarly Formation of Circumstellar Disks”, The
Astrophysical Journal, Volume 801, Issue 2, article id.
117, 20 pp. (2015)[2] S. Takasao, K. Tomida, K. Iwasaki, T. K. Suzuki,“Giant Protostellar Flares: Accretion-driven

Accumulation and Reconnection-driven Ejection ofMagnetic Flux in Protostars”, The Astrophysical Journal
Letters, Volume 878, Issue 1, article id. L10, 7 pp.
(2019).
[3] S. S. Kimura, S. Takasao, K. Tomida, “Modeling
Hadronic Gamma-Ray Emissions from Solar Flares andProspects for Detecting Nonthermal Signatures fromProtostars”, The Astrophysical Journal, Volume 944,
Issue 2, id.192, 14 pp.

Figure 1. Hot ejecta produced in a giant protostellar faredriven by magnetic reconnection in a protoplanetary disk[2]. Lines indicate magnetic field lines and the yellow towhite region is hot gas.

Figure 2. A schematic picture of acceleration of cosmic
rays and production of non-thermal emissions [3].
Note: Abstract should be in (full) double-columned one page.