Plot of log ϵ(Th) vs. [Fe/H] and log (Th/Eu) vs. [Fe/H]. Detected results from this work are in black, and the upper limits are in red. Results from other studies are in green. These filled symbols are the stars in common with previous works. See text for the definations of different subclasses. A dashed red line is plotted in the lower panel corresponding to the “zero-age” log (Th/Eu). Averaged error bars are given at the lower right corner.