| Popis: |
It has only been recently that vidicon systems have gained sufficient sensitivity as to allow their use in ground-based infrared studies of the solar corona. This paper reports on the use of a silicon vidicon spectrometer for ground-based eclipse studies of infrared coronal lines. Two forbidden spectral emission lines in the ground state of Fe xiii in the near infrared at 10,747 A ( 3 P 1 → 3 P 0 ) and 10,798 A ( 3 P 2 → 3 P 1 ) are the strongest coronal lines in line-to-continuum ratio accessible to ground-based observers. It has been shown that the ratio of the intensity of these lines is insensitive to temperature and provides a good measure of the electron density in corona since one level is radiatively and the other collisionally populated. Simultaneous observations of the 10,747 A and 10,798 A lines therefore provide a sensitive probe of coronal electron density. Both coronagraphic and eclipse observations of these lines have been made but all observations have been severely handicapped by the fact that the lines lie beyond the effective limit of most photographic film and on the upper end of the wavelength limit of the S-1 photocathode of the most commonly employed image tube. At the total solar eclipse of June 30, 1973 in Kenya, we observed the spectral region that included the two lines with a Tektronix J20/7J20 rapid scanning silicon vidicon spectrometer. We scanned the corona in height from 1.1 to 2.0 R⊙. We report here on the observations and their reduction, as well as describe the instrumentation and the theory of the [Fe xiii ] lines. |
