Using classical model atmospheres and an LTE analysis , Mg isotope ratios ^ { 24 } Mg : ^ { 25 } Mg : ^ { 26 } Mg are measured in 32 Hyades dwarfs covering 4000K \leq T _ { eff } \leq 5000K .
We find no significant trend in any isotope ratio versus T _ { eff } and the mean isotope ratio is in excellent agreement with the solar value .
We determine stellar parameters and Fe abundances for 56 Hyades dwarfs covering 4000K \leq T _ { eff } \leq 6200K .
For stars warmer than 4700K , we derive a cluster mean value of [ Fe/H ] = 0.16 \pm 0.02 ~ { } ( \sigma = 0.1 ) , in good agreement with previous studies .
For stars cooler than 4700K , we find that the abundance of Fe from ionized lines exceeds the abundance of Fe from neutral lines .
At 4700K [ Fe/H ] _ { II } - [ Fe/H ] _ { I } \simeq 0.3 dex while at 4000K [ Fe/H ] _ { II } - [ Fe/H ] _ { I } \simeq 1.2 dex .
This discrepancy between the Fe abundance from neutral and ionized lines likely reflects inadequacies in the model atmospheres and the presence of Non-LTE or other effects .
Despite the inability of the models to reproduce ionization equilibrium for Fe , the Mg isotope ratios appear immune to these problems and remain a powerful tool for studying Galactic chemical evolution .