M-dwarf's Chromosphere, Corona and Wind Connection via the Nonlinear Alfvén Wave |
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Takahito Sakaue Submitted: 2021-06-25 12:13
M dwarf's atmosphere is expected to be highly magnetized. The magnetic energy can be responsible for heating the stellar chromosphere and corona, and driving the stellar wind. The nonlinear propagation of Alfvén wave is the promising mechanism for both heating stellar atmosphere and driving stellar wind. Based on this Alfvén wave scenario, we carried out the one-dimensional compressive magnetohydrodynamic (MHD) simulation to reproduce the stellar atmospheres and winds of TRAPPIST-1, Proxima Centauri, YZ CMi, AD Leo, AX Mic, as well as the Sun. The nonlinear propagation of Alfvén wave from the stellar photosphere to chromosphere, corona, and interplanetary space is directly resolved in our study. The simulation result particularly shows that the slow shock generated through the nonlinear mode coupling of Alfvén wave is crucially involved in both dynamics of stellar chromosphere (stellar spicule) and stellar wind acceleration. Our parameter survey further revealed the following general trends of physical quantities of stellar atmosphere and wind. (1) The M dwarfs' coronae tend to be cooler and denser than solar corona. (2) M dwarfs' stellar winds can be characterized with relatively faster velocity and much smaller mass-loss rate compared to those of solar wind. The physical mechanisms behind these tendencies are clarified in this paper, where the stronger stratification of M dwarf's atmosphere and relatively smaller Alfvén wave energy input from the M dwarf's photosphere are remarkable.
Authors: Takahito Sakaue and Kazunari Shibata
Projects: None
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Publication Status: accepted for publication in The Astrophysical Journal
Last Modified: 2021-06-26 06:05
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Observational Study on the Fine Structure and Dynamics of a Solar Jet. I. Energy Build-Up Process around a Satellite Spot. |
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Takahito Sakaue Submitted: 2017-07-09 13:09
We report a solar jet phenomenon associated with successive flares on November 10th 2014. These explosive events were involved with the satellite spots' emergence around a delta-type sunspot in the decaying active region NOAA 12205. The data of this jet was provided by Solar Dynamic Observatory (SDO), X-Ray Telescope (XRT) aboard Hinode, Interface Region Imaging Spectrograph (IRIS) and Domeless Solar Telescope (DST) at Hida Observatory, Kyoto University. These plentiful data enabled us to present this series of papers to discuss the entire processes of the observed phenomena including the energy storage, event trigger, and energy release. In this paper, we focus on the energy build-up and trigger phases, by analyzing the photospheric horizontal flow field around the active region with an optical flow method. The analysis reveals the following three. (i) The observed explosive phenomena involved three satellite spots, the magnetic fluxes of which successively reconnected with their pre-existing ambient fields. (ii) All of these satellite spots emerged in the moat region of a pivotal delta-type sunspot, especially near its convergent boundary with the neighboring supergranules or moat regions of adjacent sunspots. (iii) Around the jet ejection site, the positive polarities of satellite spot and adjacent emerging flux encountered the global magnetic field with negative polarity in the moat region of the pivotal delta-type sunspot, and thus the polarity inversion line was formed along the convergent boundary of the photospheric horizontal flow channels.
Authors: Takahito SAKAUE, Akiko TEI, Ayumi ASAI, Satoru UENO, Kiyoshi ICHIMOTO, Kazunari SHIBATA
Projects: None
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Publication Status: accepted for publication in PASJ
Last Modified: 2017-07-11 11:22
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