Near-infrared CCD observations of umbral dots |
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| Authors: | Malcolm W Ewell Jr |
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| Institution: | (1) Big Bear Solar Observatory, California Institute of Technology, 91125 Pasadena, CA, U.S.A. |
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| Abstract: | Umbral fine structures have been observed at 8500 Å using a new CCD detector. Four frames with diffraction-limited seeing were obtained. Between 68 and 91 umbral dots with a brightness contrast greater than 2% were found in each frame, although no dots were found in the darkest part of the umbra. The intrinsic flux of the umbral dots varies widely, indicating that their intrinsic brightness does as well. The mean dot lifetime is estimated as 15 min, although some dots were observed to live more than 2 h. Some of the umbral dots are flowing into the umbra at speeds up to 0.5 km s-1. These dots have higher than average contrast and are associated with penumbral grains. |
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