The luminosity of supernovae of type Ia from tip of the red-giant branch distances and the value of H₀

Department of Physics and Astronomy, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
e-mail: g-a.tammann@unibas.ch

Received: 24 May 2012
Accepted: 7 October 2012

Abstract

Distances from the tip of the red-giant branch (TRGB) in the halo population of galaxies – calibrated through RR Lyr stars as well as tied to Hipparcos parallaxes and further supported by stellar models – are used to determine the luminosity of six nearby type Ia supernovae (SN 2011fe, 2007sr, 1998bu, 1989B, 1972E, and 1937C). The result is ⟨ M^corr_V ⟩ = -19.41 ± 0.05. If this value is applied to 62 SNe Ia with 3000 < v < 20,000   km   s^-1 a large-scale value of the Hubble constant follows of H₀ = 64.0 ± 1.6 ± 2.0. The SN HST Project gave H₀ = 62.3 ± 1.3 ± 5.0 from ten Cepheid-calibrated SNe Ia. The near agreement of young Population I (Cepheids) and old, metal-poor Population II (TRGB) distance indicators is satisfactory. The combined weighted result is H₀ = 63.7 ± 2.3 (i.e.  ± 3.6%). The value will be helpful to constrain models of the early Universe.