The<i>Hubble Space Telescope</i>Key Project on the Extragalactic Distance Scale. XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant

Abstract

A Cepheid-based calibration is derived for four distance indicators that\nutilize stars in the old stellar populations: the tip of the red giant branch\n(TRGB), the planetary nebula luminosity function (PNLF), the globular cluster\nluminosity function (GCLF) and the surface brightness fluctuation method (SBF).\nThe calibration is largely based on the Cepheid distances to 18 spiral galaxies\nwithin cz =1500 km/s obtained as part of the HST Key Project on the\nExtragalactic Distance Scale, but relies also on Cepheid distances from\nseparate HST and ground-based efforts. The newly derived calibration of the SBF\nmethod is applied to obtain distances to four Abell clusters in the velocity\nrange between 3800 and 5000 km/s, observed by Lauer et al. (1998) using the\nHST/WFPC2. Combined with cluster velocities corrected for a cosmological flow\nmodel, these distances imply a value of the Hubble constant of H0 = 69 +/- 4\n(random) +/- 6 (systematic) km/s/Mpc. This result assumes that the Cepheid PL\nrelation is independent of the metallicity of the variable stars; adopting a\nmetallicity correction as in Kennicutt et al. (1998), would produce a (5 +/-\n3)% decrease in H0. Finally, the newly derived calibration allows us to\ninvestigate systematics in the Cepheid, PNLF, SBF, GCLF and TRGB distance\nscales.\n