Improved observations of sunspot umbral dots.
Abstract
New observations have been obtained of the umbrae of 18 spots near the solar disk center using the CSIRO 30-cm refractor in its photospheric mode under seeing-monitor control (Bray and Loughhead, 1977). The telescope was programmed to take sequences of photographs with exposures ranging (for a large spot) up to 13 times that for the photosphere in order to capture the fine detail in all parts of each umbra. Under normal circumstances the level of scattered light (instrumental plus atmospheric) in the Culgoora Telescope has been found to be less than 0.9% (Bray and Loughhead, 1977). For the umbral observations it was further reduced by placing small diaphragms at the prime focus in the manner described by Bray and Loughhead, 1964). The umbral dot structure is discussed. The observations made show that umbral dots virtually cover the umbra, including the darkest regions of large spots, where the low contrast of the dot pattern has hitherto hindered its observations.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1979
- Bibcode:
- 1979A&A....79..128L
- Keywords:
-
- Astronomical Photography;
- Sunspots;
- Umbras;
- Photosphere;
- Resolution;
- Solar Granulation;
- Telescopes;
- Solar Physics;
- Sunspots:Umbrae