Photospheric Variations of the Supergiant γ Cyg
Abstract
New high-resolution spectroscopic observations of the supergiant γ Cyg (F8 Iab) taken between 2000 and 2008 consistently show strongly reversed-C-shaped bisectors for all unblended spectral lines. Small-amplitude variations in radial velocity and line shapes occur in an irregular manner with time scales ~100 days and longer. The radial velocities occasionally show changes as large as 2 km s-1, but much smaller changes are going on continuously. Differential line bisectors show shape changes and Doppler displacement characteristic of radial expansion and contraction. These might arise from non-periodic radial pulsation-like motions or from the appearance of giant convection cells that occupy most of the visible hemisphere of the star. Line-depth ratios are correlated with the line shifts on a seasonal basis and indicate temperature changes ranging up to ~15 K, with larger temperature occurring during times of most rapid contraction.
- Publication:
-
The Astronomical Journal
- Pub Date:
- November 2010
- DOI:
- 10.1088/0004-6256/140/5/1329
- Bibcode:
- 2010AJ....140.1329G
- Keywords:
-
- convection;
- line: profiles;
- stars: atmospheres;
- techniques: radial velocities;
- techniques: spectroscopic