Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...328..682s&link_type=abstract
Astronomy and Astrophysics, v.328, p.682-688 (1997)
Astronomy and Astrophysics
Astrophysics
52
Sun: Sunspots, Physical Data And Processes: Convection, Techniques: Image Processing
Scientific paper
The analysis of a 4 1/2 hour series of high resolution white light observations of the umbra in a medium-size sunspot (NOAA 7519, observed on 5 June 1993 at the Swedish Vacuum Solar Telescope, La Palma) is described. An automatic identification and tracking algorithm was applied to umbral dots (UDs) observed in a destretched movie of 360 frames. In total, 662 UDs were tracked and their filling factor, sizes, and lifetimes were measured. It was found that large (diameter > 0farcs 4) and long-lived (lifetime > 10 minutes) UDs appear mostly in regions with enhanced umbral diffuse background intensity. UDs do not have a ``typical'' size. Their number rapidly increases with decreasing diameter down to the resolution limit. Similarly, UDs do not have a ``typical'' lifetime, and their number rapidly increases with decreasing lifetime. UDs with lifetimes below 10 minutes represent about 2/3 of the population; the median lifetime is 5.9 minutes.
Brandt Peter N.
Simon George W.
Sobotka Michal
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