The Structure of the Solar Chromosphere. I. a Picture Based on Extreme Ultraviolet, Millimeter, and λ 10830 Data.
Abstract
We consider the stringent limits placed on a chromospheric model by optical, radio, infrared, and ultraviolet data. These observations appear to favor a picture in which (1) the chromospheric density falls off rapidly to coronal values by 150() 2000 km, at which height the temperature has risen to 7000 , before a very sharp transition to coronal temperatures takes place, and (2) all the high-excitation emission, including all the helium lines, arises in spicules. In between the spicules is the corona. The optical observations of the flash spectrum show that low-excitation lines fall off very sharply with height, whereas helium and hydrogen lines show a much lower gradient. Observations of the 10830 line of He I show that it jumps from an optical depth around 0.1 just inside the limb to a depth of about 3 just above the limb. This indicates that the spicules cover just a fraction of the surface but, above the limb, show their intrinsic optical depth. The radio data for wavelengths below 3 cm is introduced to show that the boundary temperature of the chromosphere is about 7000 and that the amount of overlying material at a higher temperature is very small. The surface must either have a very steep density gradient or be rough. The limb brightening is due to spicules. The extreme ultraviolet spectrum is discussed in detail. The Lyman continuum observations indicate an origin at a temperature of 7000 and again set a limit on any overlying hot layer. The lines of intermediate ions, such as C ii-iv and 0 ii-v, are shown to originate in a very small volume, corresponding to that occupied by spicules. Temperatures are derived for these ions from line ratios; the temperatures range from 30 to 80 thousand degrees.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1963
- DOI:
- 10.1086/147677
- Bibcode:
- 1963ApJ...138..664Z