We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 \leq \lambda \leq 2360 Å wavelength range for two metal-poor stars , HD 108317 and HD 128279 .
We derive abundances of Cu ii , Zn ii , As i , Se i , Mo ii , and Cd ii , which have not been detected previously in either star .
Abundances derived for Ge i , Te i , Os ii , and Pt i confirm those derived from lines at longer wavelengths .
We also derive upper limits from the non-detection of W ii , Hg ii , Pb ii , and Bi i .
The mean [ As/Fe ] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range - 2.8 < [ Fe/H ] < - 0.6 , \langle [ As/Fe ] \rangle = + 0.28 \pm 0.14 ( \sigma = 0.36 dex ) .
The mean [ Se/Fe ] ratio derived from these two stars and six others in the literature is also constant , \langle [ Se/Fe ] \rangle = + 0.16 \pm 0.09 ( \sigma = 0.26 dex ) .
The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses , suggesting that this mass region ( 75 \leq A \leq 82 ) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium \alpha -rich freezeout of the iron peak . \langle [ Cu ii /Cu i ] \rangle = + 0.56 \pm 0.23 in HD 108317 ( catalog HD~108317 ) and HD 128279 ( catalog HD~128279 ) , and we infer that lines of Cu i may not be formed in local thermodynamic equilibrium in these stars .
The [ Zn/Fe ] , [ Mo/Fe ] , [ Cd/Fe ] , and [ Os/Fe ] ratios are also derived from neutral and ionized species , and each ratio pair agrees within the mutual uncertainties , which range from 0.15 to 0.52 dex .