OXYGEN ABUNDANCES IN HALO GIANTS .6. M10, A GLOBULAR-CLUSTER WITH METALLICITY SIMILAR TO M3 AND M13

We have obtained high resolution echelle spectra of 15 bright giants of the intermediate metallicity globular cluster M10, in order to compare the oxygen and sodium abundance variations of this cluster with those of similar metallicity clusters M3 and M13. M10, like M13, has a color-magnitude diagram with an extremely blue horizontal branch and, relative to M3, exhibits the "second parameter effect." As in earlier papers of this series we have first determined abundances of the Fe-peak and α element groups. These element abundances reveal no surprises. For iron, 〈[Fe/H]〉=-1.52±0.02, with little star-to-star scatter (σ=0.07). The α elements are enhanced by typical factors for metal-poor stars, [〈Si,Ca,Ti〉/Fe]=+0.26±0.04. The Fe-peak elements track Fe quite closely, [〈Sc,V,Ni〉/Fe]=-0.08 ±0.07. As in all other intermediate and low metallicity globular clusters, the sodium and oxygen abundances of M10 giants are anticorrelated. While the general form of the O vs Na anticorrelation trend for M10 is indistinguishable from that defined by M3 and M13, the extent of the O and Na abundance excursions indicates that M10 is an intermediate case between the other two clusters. No M10 giants display the extreme O depletions exhibited by the M13 red giant tip stars, but the average O abundance of M10 is lower than that of M3, and the average Na abundance is higher. This suggests that the variations of O and Na in globular clusters do not by themselves tightly constrain the variations in horizontal branch morphologies of the clusters. © 1995 American Astronomical Society.