Statistics – Computation
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...292..191s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 292, no. 1, p. 191-207
Statistics
Computation
39
Chromosphere, Computational Astrophysics, Dwarf Stars, Giant Stars, M Stars, Planetary Waves, Stellar Physics, Stellar Rotation, Calcium, Color-Color Diagram, Flux Density, Magnesium, Magnetic Fields, Stellar Color, Stellar Temperature
Scientific paper
Empirical arguments for using the Rossby number as a rotation measure of active stars are reviewed using the log activity - rotation period diagrams. It is shown that when giant stars are considered the scatter on such diagrams cannot be appreciably diminished by replacing rotation period with the Rossby number. The observed scatter is, however, substantially reduced in activity-rotation diagrams of the solar type stars, i.e. dwarfs with 0.5 less than or approximately = B-V less than or approximately = 0.8, when the rotation period is scaled with appropriate factors, in other words, when the Rossby number is used. In case of active dwarfs lying outside of this spectral range, the using of the Rossby number does not improve the scatter. It is shown that the empirical turnover times determined from the calcium emission flux, magnesium emission flux and X-ray flux are identical with one another apart from constant factors: after a rapid increase with increasing F and early G spectral type, the turnover time levels off for late G and K types. Numerical relations between the calcium emission flux, X-ray flux or the surface magnetic field of active dwarfs on one side with the stellar color index and the Rossby number on the other side are determined from the observational data. They indicate that the chromospheric losses are proportional to Teff2.9 times (the mean value of Bsurf)exp(0.6) whereas the coronal losses are more sensitive to the both parameters and are proportional to Teff8.3 times (the mean value of Bsurf)exp(1.9).
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