The activity cycle of Sigma Draconis

Details The activity cycle of Sigma Draconis The activity cycle of Sigma Draconis

Dec 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...400..681g&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 400, no. 2, p. 681-691.

Astronomy and Astrophysics

Astrophysics

33

Dwarf Stars, Line Spectra, Stellar Activity, Stellar Spectrophotometry, Stellar Temperature, Metallicity, Solar Cycles, Solar Granulation

Scientific paper

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.

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