Stellar model chromospheres. VII. Capella (G5 III+), Pollux (K0 III), and Aldebaran (K5 III).
Abstract
Data from high-resolution SEC vidicon spectroscopy with a ground-based telescope (for the Ca II K line) and from spectral scans made with the BUSS ultraviolet balloon spectrograph (for the Mg II h and k lines) are used to derive models of the chromospheres and upper photospheres of three G-K giants. The models are based on partial-redistribution analyses of the Ca II K line wings and cores and on the fluxes in the Mg II lines. The photospheres thus computed are hotter than predicted by radiative-equilibrium models. The minimum-to-effective temperature ratio is found to decrease with decreasing effective temperature, while the mass column density at the top of the chromosphere increases with decreasing stellar surface gravity. The computed pressure at the chromosphere top in the primary member of the Capella spectroscopic binary system is 70 times smaller than the transition-region pressure derived by Haisch and Linsky (1976), which suggests that additional terms must be included in the transition-region energy equations for giant stars. Estimates of the Ca II and hydrogen column densities are made for the circumstellar envelope of Aldebaran.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 1978
- DOI:
- 10.1086/155985
- Bibcode:
- 1978ApJ...220..962K
- Keywords:
-
- Astronomical Models;
- Chromosphere;
- G Stars;
- K Stars;
- Late Stars;
- Stellar Atmospheres;
- Stellar Envelopes;
- Stellar Spectra;
- Balloon-Borne Instruments;
- Binary Stars;
- Emission Spectra;
- Line Spectra;
- Stellar Temperature;
- Ultraviolet Spectroscopy;
- Astrophysics;
- Chromospheres:Late-Type Stars;
- Emission Lines:Late-Type Stars;
- Stellar Chromospheres: Models