Sulfur and zinc are chemically volatile elements , which play significant roles as depletion-free tracers in studying galactic chemical evolution .
However , regarding red giants having evolved off the main sequence , reliable abundance determinations of S and Zn seem to be difficult despite that a few studies have been reported so far .
Given this situation , we tried to establish the abundances of these elements for an extensive sample of 239 field GK giants ( -0.8 \ltsim [ Fe/H ] \ltsim + 0.2 ) , by applying the spectrum-fitting technique to S i 8694–5 , S i 6757 , and Zn i 6362 lines and by taking into account the non-LTE effect .
Besides , similar abundance analysis was done for 160 FGK dwarfs to be used for comparison .
The non-LTE corrections for the S and Zn abundances derived from these lines turned out \ltsim 0.1 ( –0.2 ) dex for most cases and not very significant .
It revealed that the S i 6757 feature is more reliable as an abundance indicator than S i 8694–5 for the case of red giants , because the latter suffers blending of unidentified lines .
The finally resulting [ S/Fe ] – [ Fe/H ] and [ Zn/Fe ] – [ Fe/H ] relations for GK giants were confirmed to be in good agreement with those for FGK dwarfs , indicating that S and Zn abundances of red giants are reliably determinable from the S i 6757 and Zn 6362 lines .
Accordingly , not only main-sequence stars but also evolved red giant stars are usable for tracing the chemical evolution history of S and Zn in the regime of disk metallicity by using these lines .