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Title:
The activity cycle of Sigma Draconis
Authors:
Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff, Brian A.
Affiliation:
AA(Western Ontario Univ., London, Canada), AB(Harvard-Smithsonian Center for Astrophysics, Cambridge, MA), AC(Lowell Observatory, Flagstaff, AZ), AD(Lowell Observatory, Flagstaff, AZ)
Publication:
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 400, no. 2, p. 681-691. (ApJ Homepage)
Publication Date:
12/1992
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Dwarf Stars, Line Spectra, Stellar Activity, Stellar Spectrophotometry, Stellar Temperature, Metallicity, Solar Cycles, Solar Granulation
DOI:
10.1086/172030
Bibliographic Code:
1992ApJ...400..681G

Abstract

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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