The helium chromosphere, coronal holes, and stellar X-rays.
Abstract
The solar chromosphere at the limb seen in D3 is an irregular bright band 1000 km thick with a dark band 1000 km thick beneath. The D3 chromosphere disappears in coronal holes. It is shown that the D3 emission, as well as the other He I and He II lines, can be explained quantitatively by photoionization by coronal back-radiation. A Chapman layer with N(He)H = 5 times 10 to the 17th power is formed near tau = 1 in the He I and He II continua. The chromospheric He emission or absorption is weak in coronal holes because there is no coronal back-radiation. Based on this model, the soft X-ray flux from stars with He 10830-A absorption lines is estimated as proportional to the 10830-A equivalent width and the apparent area.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1975
- DOI:
- 10.1086/181849
- Bibcode:
- 1975ApJ...199L..63Z
- Keywords:
-
- Chromosphere;
- Helium;
- Solar Corona;
- Stellar Radiation;
- X Ray Astronomy;
- Astronomical Models;
- D Lines;
- H Alpha Line;
- Solar Limb;
- Solar Spectra;
- Solar Physics