Bibcode
Sánchez-Andrade Nuño, B.; Bello González, N.; Blanco Rodríguez, J.; Kneer, F.; Puschmann, K. G.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 486, Issue 2, 2008, pp.577-587
Advertised on:
8
2008
Revista
Número de citas
12
Número de citas referidas
11
Descripción
Context: We study the chromosphere of an active region of the Sun in the
Hα line. Aims: The development of new instrumentation and
new methods of data analysis allows to scrutinize the dynamics of the
solar chromosphere with high spatial, spectral, and temporal resolution.
The observations we present shed light on some magneto-dynamic processes
occurring above an active region in the chromosphere. Methods: We
took a time series of 55 min in Hα from AR 10875 at
θ≈36°. We used the “Göttingen”
Fabry-Perot spectrometer at the Vacuum Tower Telescope, Observatorio del
Teide/Tenerife, to obtain two-dimensional spectrograms in Hα.
Adaptive optics and image reconstruction yielded a spatial resolution
better than 0.5 arcsec throughout the time sequence. From the wealth of
structures, we selected areas of interest to study further, in detail,
some ongoing processes. Results: A small straight surge developed
aside of a pore with upward phase speed of 100 km s-1 and
line-of-sight (LOS) velocity of 15 km s-1. The surge
retreated rapidly with LOS velocity of 45 km s-1 at its
mouth. It underwent a rebound and fell back again. Two sympathetic
mini-flares were observed that lasted only approximately 40 s, but
showed strong Hα emission. We found magnetoacoustic waves in long
fibrils as mainly short wave trains, short packets or pulses, i.e.,
solitary waves consisting of small (1´´-2´´)
blobs. They start at either end of the fibrils and travel with phase
speeds of 12-14 km s-1, i.e., close to the tube speed and
approximately the sound velocity for sufficiently large magnetic field
strengths. Some waves speed up to reach velocities of the order of 30 km
s-1. This is much lower than the expected Alfvén
velocity of ≥200 km s-1 for reasonable magnetic field
strengths and mass densities. We suggest that slow waves are not purely
longitudinal, but possess gas velocities perpendicular to the direction
of propagation of few km s-1. Also, fast waves travel along
sinuous lines suggesting entangled magnetic fields. They spread out
along the direction of propagation in the course of their evolution and
often vanish. We discuss the implications.
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