Bibcode
Sobotka, M.; Puschmann, K. G.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 504, Issue 2, 2009, pp.575-581
Fecha de publicación:
9
2009
Revista
Número de citas
37
Número de citas referidas
34
Descripción
Context: Substructures - dark lanes and tails - of umbral dots (UDs)
were predicted by numerical simulations of magnetoconvection and have
been detected later in some observations. Aims: To provide
constraints for realistic theoretical models of sunspot umbrae, we
describe the observed properties and evolutionary characteristics of UDs
(including their substructure) and of other umbral structures. Methods: We analyse a 6 h 23 min time series of broadband images of a
large umbra in the active region NOAA 10634, acquired with the 1-m
Swedish Solar Telescope, in the wavelength band around 602 nm. A 43 min
part of this series was reconstructed with the MFBD method, reaching a
spatial resolution of 0.14 arcsec. With the help of image segmentation,
feature tracking, and local correlation tracking, we measured
brightness, size, lifetime, and horizontal velocities of various umbral
structures. Results: Large structures in the umbra - strong and
faint light bridges (LBs) and an extended penumbral filament - evolve on
time scales of hours. Most (90%) of UDs and bright point-like features
in faint LBs split and merge, and their median lifetimes are 3.5 or 5.7
min, depending on whether the split or merge event is considered as the
end of their life. Both UDs and features in faint LBs that do not split
or merge are clearly smaller (0.15 arcsec) than the average size (0.17
arcsec) of all features. Horizontal motions of umbral bright small-scale
features are directed either into the umbra or along faint LBs with mean
horizontal velocities of 0.34 km s-1. Features faster than
0.4 km s-1 appear mostly at the periphery of the umbra. The
motion of peripheral UDs (PUDs) seems to be the continuation of the
motion of penumbral grains (PGs). The intensity of dark lanes, measured
in four bright central UDs (CUDs), is by a factor 0.8 lower than the
peak intensity of CUDs. The width of dark lanes is probably less than
the resolution limit 0.14 arcsec. The characteristic time of
substructure changes of UDs is ~4 min. We observe narrow (0.14 arcsec)
bright and dark filaments connected with PUDs. The bright filaments are
0.06 I_ph brighter than the dark ones. Usually one dark and two bright
filaments form a 0.4 arcsec wide tail attached to one PUD, resembling a
short dark-cored penumbral filament. Conclusions: Our results
indicate the similarity between PUDs and PGs located at the tips of
bright penumbral filaments. The features seen in numerical MHD
simulations are consistent with our observations of dark lanes in CUDs
and tails attached to PUDs.
Proyectos relacionados
![Erupción de un filamento solar visto por AIA / SDO en el ultravioleta extremo. Imagen del Proyecto](/sites/default/files/styles/crop_square_2_2_to_320px/public/images/project/Imagen%20Tobias.jpg?itok=Ryks0yoA)
Magnestismo Solar y Estelar
Los campos magnéticos son uno de los ingredientes fundamentales en la formación de estrellas y su evolución. En el nacimiento de una estrella, los campos magnéticos llegan a frenar su rotación durante el colapso de la nube molecular, y en el fin de la vida de una estrella, el magnetismo puede ser clave en la forma en la que se pierden las capas
Tobías
Felipe García