Infrared photometry, bolometric magnitudes, and effective temperatures for giants in M3, M13, M92, and M67

Broad-band infrared J-, H-, and K-magnitudes and narrow-band CO and H2O indices are presented for a selection of giants reaching 3 mag below the red-giant tip in the globular clusters M3, M 13, and M92, and in the old open cluster M67. Comparison of these data with a calculated grid of model atmospheres gives the following results: (1) the models satisfactorily predict the broad-band colors; (2) V - K measurements accurate to +0.1 mag can be used to give effective temperatures to + 100 K independent of surface gravity or metal abundance for metal-poor stars; (3) there is disagreement with a previous (Teff, spectral type)-calibration based on DDO photometry. Empirical bolometric magnitudes are derived by integrating the observed energy distributions out to 2.2 m. The derived luminosities and effective temperatures are plotted in a H-R diagram and are compared with a set of evolutionary tracks for metal-poor stars due to Rood. The agreement is good. The CO index, which is sensitive primarily to luminosity and effective temperature for Population I giants, becomes sensitive to metal abundance for very metal-poor stars. The relative metal abundance of M3 and M 13 derived from CO is reversed from that derived by some other methods. Some possible explanations are considered. Because of the importance of Rayleigh scattering in these cluster stars, B - V depends on surface gravity. Gravities determined from B - V colors are used to derive crude masses for the stars. These masses ( 0.6 M0) are roughly consistent with estimates of the turnoff mass. The CNO abundances are suggested as the second parameter affecting the color-magnitude diagrams of globular clusters. Subject headings: clusters: globular - clusters: open - infrared: sources - stars: atmospheres - stars: late-type - stars: luminosities