From: LARRY KLAES (ljk4_at_msn.com)
Date: Mon Dec 26 2005 - 11:05:47 PST
Paper: astro-ph/0512584
Date: Fri, 23 Dec 2005 02:59:43 GMT (270kb)
Title: The Ups and Downs of the Hubble Constant
Authors: G.A. Tammann (Astr. Inst. Univ. Basel)
Comments: 30 pages, 12 figures, 2 tables. 79th Annual Scientific Meeting of the
Astronomische Gesellschaft 2005, Karl-Schwarzschild-Lecture, to appear in
Reviews in Modern Astronomy, 19, 1
\\
A brief history of the determination of the Hubble constant H_0 is given.
Early attempts following Lemaitre (1927) gave much too high values due to
errors of the magnitude scale, Malmquist bias and calibration problems. By 1962
most authors agreed that 75< H_0 <130. After 1975 a dichotomy arose with values
near 100 and others around 55. The former came from apparent-magnitude-limited
samples and were affected by Malmquist bias. New distance indicators were
introduced; they were sometimes claimed to yield high values of H_0, but the
most recent data lead to H_0 in the 60's, yet with remaining difficulties as to
the zero-point of the respective distance indicators. SNe Ia with their large
range and very small luminosity dispersion (avoiding Malmquist bias) offer a
unique opportunity to determine the large-scale value of H_0. Their maximum
luminosity can be well calibrated from 10 SNe Ia in local parent galaxies whose
Cepheids have been observed with HST. An unforeseen difficulty - affecting all
Cepheid distances - is that their P-L relation varies from galaxy to galaxy,
presumably in function of metallicity. A proposed solution is summarized here.
The conclusion is that H_0 = 63.2 +/- 1.3 (random) +/- 5.3 (systematic) on all
scales. The expansion age becomes then (with Omega_m=0.3, Omega_Lambda=0.7)
15.1 Gyr.
\\ ( http://arXiv.org/abs/astro-ph/0512584 , 270kb)
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