Chromospheric activity to age relationship among Sun-like stars

The emission reversal in the cores of the CaII H and K lines of late-type dwarfs is correlated with their age and is potentially an accurate age indicator. Recent measurements of stellar rotation periods in intermediate-age open clusters indicate that the rotation rates of Sun-like stars older than 1 Gyr decay as age^{0.49M-1.19} for stellar masses M included between 0.7 and 1.1 MSun. The corresponding evolution of the R'HK activity index inferred from rotation-activity relationships is steeper than the relationship R' HK ~ age^{-0.5} generally used. Such a steep decay of the chromospheric activity beyond the age of 1 Gyr is supported by measurements of the R'HK index distributions among nearby G and K main sequence stars with near solar metallicity