Volume 380, Number 2, December III 2001
|Page(s)||714 - 718|
|Section||Planets and planetary systems|
|Published online||15 December 2001|
Fine structure in sunspots
IV. Penumbral grains in speckle reconstructed images
Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic
2 Sterrenkundig Instituut Utrecht, Postbus 80 000, 3508 TA Utrecht, The Netherlands e-mail: P.Suetterlin@astro.uu.nl
Corresponding author: M. Sobotka, email@example.com
Accepted: 15 October 2001
The properties of penumbral grains (PGs) in a large regular sunspot are studied from a 70 min sequence of G-band images acquired on 20 September 1999 at the Dutch Open Telescope, La Palma. The frames were processed using the speckle masking algorithm, resulting in an almost diffraction-limited time series (30 s cadence), basically free of atmospheric distortions. Applying feature tracking to a movie of 140 frames yields proper motions, intensities, and lifetimes for a set of 1058 PGs with lifetimes longer than 10 min. About 54% of the PGs move toward the umbra and 46% toward the photosphere. The inward-moving PGs are located mostly in the inner penumbra (up to 0.6 of the distance from the umbra to the photosphere). Their average lifetime and median speed are 50 min and 0.52 km s-1. Most of the outward-moving PGs are observed in the outer penumbra and their average lifetime and median speed are 31 min and 0.75 km s-1. These measurements confirm the previous results published by Sobotka et al. ([CITE]).
Key words: Sun: sunspots
© ESO, 2001
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.