The Alfvén speed and plasma beta in photospheric bright points observed by the Broadband Filter Imager ( BFI ) of the Solar Optical Telescope ( SOT ) on board the Hinode satellite , are estimated seismologically .
The diagnostics is based on the theory of slow magnetoacoustic waves in a non-isothermally stratified photosphere with a uniform vertical magnetic field .
We identify and track bright points in a G-band movie by using the 3D region growing method , and align them with blue continuum images to derive their brightness temperatures .
From the Fourier power spectra of 118 continuum light curves made in the bright points , we find that light curves of 91 bright points have oscillations with properties which are significantly different from oscillation in quiet regions , with the periods ranging 2.2–16.2 min .
We find that the model gives a moderate value of the plasma beta when \gamma lies at around 5/3 .
The calculated Alfvén speed is 9.68 \pm 2.02 km s ^ { -1 } , ranging in 6.3–17.4 km s ^ { -1 } .
The plasma beta is estimated to be of 0.93 \pm 0.36 , ranging in 0.2–1.9 .