科研之友
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摘要
Emission in the centres of the Ca II H and K lines has become a much-employed tracer of chromospheric activity among late-type dwarf stars. Building upon the Mount Wilson HK project, standardized measurements of R'(HK), the ratio of flux in the chromospheric emission component of the H and K lines to the bolometric flux, have been made by a number of large observing programmes, sometimes as a by-product of searches for extra-solar planetary systems. By using the results of those programmes, values of log R'(HK) have been compiled from the literature for over 2600 dwarfs. The majority of the stars have colours in the range 0(m.)4 <= (B - V) <= I(m.)0, masses of 0.8 M-circle dot to 1.5 M-circle dot, and metallicities in the range -0.8 <= [Fe/H] <= +0.3. The spread in emission among typical dwarfs is -5.2 <= log R'(HK) <= -4.2 regardless of colour. Two trends formerly noted in the literature are confirmed with this larger data set: the minimum log R'(HK) shows a modest decrease with increasing [Fe/H], and with increasing luminosity above the Zero-Age Main Sequence. For dwarfs with (B - V) colours similar to the Sun and -4.7 <= R'(HK) <= -4.2, there is a correlation between emission and rotation speed that is approximately of the form R'(HK) proportional to (upsilon sin i)(1/2), albeit with notable scatter. The behaviour of log R'(HK) versus v sin i varies with (B - V) colour in a manner that is qualitatively consistent with an anticorrelation between the intensity of emission and the Rossby number.
- 出版日期2011-2
