Oxygen abundances in halo giants. II - Giants in the globular clusters M13 and M3 and the intermediately metal-poor halo field

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Abstract

Oxygen, sodium, iron, vanadium, and scandium abundances are derived for giants in the intermediately metal-poor globular clusters M3 and M13 and for giants of comparable metallicity in the local halo field. For M13, (Fe/H) of -1.51 +/-0.01 is derived from 13 giants with a range of 500 K in effective temperature. For M3, Fe/H of -1.47 +/-0.01 is found from seven stars with a range of 300 K in effective temperature. M13 stars divide into three apparently discrete oxygen abundance groups: four with 'high' oxygen, seven with 'low' oxygen, and two with 'super-low' oxygen. Fifty-nine giants with (Fe/H) in the range of -3 to -1.3 are found. The O-rich/O-poor dichotomy persists in M92, and most of the field halo giants (25 out of 27) belong to the O-rich group. (O/Fe) is essentially the same in O-rich giants of M3, M13, and the halo field, and a plot of (O/Fe) vs (Fe/H) is essentially flat for O-rich stars.

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