Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-12-20
Astronomy and Astrophysics
Astrophysics
15 pages (9 figures, 3 tables). To appear in "A New Era in Cosmology" (ASP Conference Proceedings), eds. T. Shanks and N. Metc
Scientific paper
The local expansion field is mapped using Cepheids, a complete sample of TF distances, and nearby cluster distances. The large-scale field is mapped using Cepheid-calibrated blue SNeIa. These data give Ho(local)=59.2+/-1.4 [km/s Mpc^-1] and Ho(cosmic)=57.4+/-2.3. The intermediate expansion field (1200 < v < 10000km/s) is less well calibrated but fully consistent with Ho~60. Ho is therefore (nearly) scale-invariant (high-density regions excluded). -- The P-L relation of Cepheids is based on an improved zero point of (m-M)_{LMC}=18.56. The slope of the P-L relation for P>10days, as judged from OGLE data (Udalski et al. 1999) is flatter than anticipated, which tends to increase the above values of Ho by 3.4 units. No significant metallicity effect on the Cepheid distances seems to be indicated. For all practical purposes Ho=60 is recommended with a systematic error of probably less than 10%. -- The corresponding expansion age is T=15.7+/-1.5Gy (with Omega(Matter)=0.3, Omega(Lambda)=0.7), which compares well with the formation time of 15+/-2Gy for the apparently oldest globular cluster M107.
Reindl B.
Saha Avishek
Sandage Alan
Tammann Gustav A.
Thim Frank
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