A CRITICAL-APPRAISAL OF PUBLISHED VALUES OF [FE/H] FOR K-II-IV STARS

This paper presents "primary" [Fe/H] averages for 373 evolved K stars (see section 4). These stars are of luminosity classes II-IV, and their values of [Fe/H] lie between -0.9 and +0.21 dex. The contributing data are from 58 high-dispersion papers and three spectrum-synthesis papers. The data have been selected (and in many cases, corrected) to be as free as possible from systematic error. References are given with the averages to encourage users to cite original sources. For the stars considered, the data define a "consensus" zero point with a precision of +/- 0.018 dex. In addition, analysis yields rms errors per datum which are typically 0.08-0.16 dex. There is no dependable reduction in the sizes of these errors when sensitive detectors such as Reticons are used. The averaged values of [Fe/H] reflect the consensus zero point, and they are based on weights which follow from the rms errors. The primary data base makes recalibration possible for two large [Fe/H] catalogs. Temperature corrections are necessary for both catalogs, and, while the corrections are 0.12 dex or less for the data of Hansen & Kjaergaard, they are as large as 0.4 dex for a recent survey of Brown et al. The corrected data are included in a "secondary" data base for 669 stars without primary data. Smaller data sets from two additional papers are also included in this data base. Weighting for the secondary data is again based on rms errors. Also given in section 4 are a set of [Fe/H] standard stars and a new DDO calibration. The rms errors for the standard-star data are 0.07 dex or less. These data and the DDO calibration reflect the consensus zero point. For normal K giants, CN-based values of [Fe/H] turn out to be more precise than many high-dispersion results. Some zero-point errors in the latter are also found, and new examples of continuum-placement problems appear. It therefore appears that, at present, high-dispersion results are not invariably superior to photometric metallicities. In section 5 a review is given of high-dispersion and related work on supermetallicity in K III-IV stars. The super-metal-rich (SMR) status of one subgiant (31 Aql) is found to be well established. Despite some assertions in the literature, however, no decisive high-dispersion case can be made at present for the existence of SMR K giants. Such stars may exist, but deciding this question will require further work.