Details

Autor(en) / Beteiligte

• Cho, I.-H.
• Cho, K.-S.
• Bong, S.-C.
• Moon, Y.-J.
• Nakariakov, V. M.
• Park, J.
• Baek, J.-H.
• Choi, S.
• Kim, Y.-H.
• Lee, J.

Titel

Determination of the Alfvén Speed and Plasma-beta Using the Seismology of Sunspot Umbra

Ist Teil von

• Astrophysical journal. Letters, 2017-03, Vol.837 (1), p.L11-L11

Ort / Verlag

United States: The American Astronomical Society

Erscheinungsjahr

2017

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• For 478 centrally located sunspots observed in the optical continuum with Solar Dynamics Observatory/Helioseismic Magnetic Imager, we perform seismological diagnostics of the physical parameters of umbral photospheres. The new technique is based on the theory of slow magnetoacoustic waves in a non-isothermally stratified photosphere with a uniform vertical magnetic field. We construct a map of the weighted frequency of three-minute oscillations inside the umbra and use it for the estimation of the Alfvén speed, plasma-beta, and mass density within the umbra. We find the umbral mean Alfvén speed ranges between 10.5 and 7.5 km s−1 and is negatively correlated with magnetic field strength. The umbral mean plasma-beta is found to range approximately between 0.65 and 1.15 and does not vary significantly from pores to mature sunspots. The mean density ranges between (1-6) × 10−4 kg m−3 and shows a strong positive correlation with magnetic field strength.