TheHubble Space TelescopeKey Project on the Extragalactic Distance Scale. XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant

A Cepheid-based calibration is derived for four distance indicators thatutilize stars in the old stellar populations: the tip of the red giant branch(TRGB), the planetary nebula luminosity function (PNLF), the globular clusterluminosity function (GCLF) and the surface brightness fluctuation method (SBF).The calibration is largely based on the Cepheid distances to 18 spiral galaxieswithin cz =1500 km/s obtained as part of the HST Key Project on theExtragalactic Distance Scale, but relies also on Cepheid distances fromseparate HST and ground-based efforts. The newly derived calibration of the SBFmethod is applied to obtain distances to four Abell clusters in the velocityrange between 3800 and 5000 km/s, observed by Lauer et al. (1998) using theHST/WFPC2. Combined with cluster velocities corrected for a cosmological flowmodel, these distances imply a value of the Hubble constant of H0 = 69 +/- 4(random) +/- 6 (systematic) km/s/Mpc. This result assumes that the Cepheid PLrelation is independent of the metallicity of the variable stars; adopting ametallicity correction as in Kennicutt et al. (1998), would produce a (5 +/-3)% decrease in H0. Finally, the newly derived calibration allows us toinvestigate systematics in the Cepheid, PNLF, SBF, GCLF and TRGB distancescales.