Investigations of the temperature and granulation of Sigma Draconis (HR 7462, HD 185144, K0 V) are discussed. Temperature is monitored using a line-depth ratio, and temperature variations of about 5 K are seen. Intermediate-band photometry and Ca II H and K-line emission mimic the temperature changes: a monotonic decline from the 1984 season, a smooth minimum around 1988, followed by a rise back to the 1984 values at the current time. The temperature variations are physically compatible with the photometric ones, implying a constant radius over the activity cycle. Granulation is invariant during this portion of the activity cycle, at least to the level of about +/- 3 m/s, or about +/- 5 percent. The temperature variations by themselves can also be interpreted as rotational modulation with a 20.3-d period, but no evidence of this period is seen in the photometry, the H and K emission, or the line asymmetries, and it is argued to be a chance occurrence.
No takes yet. Share an insight, caveat, or question.
Gray et al. (1992) studied this question.