Astronomy and Astrophysics – Astrophysics
Scientific paper
1996-03-15
Astronomy and Astrophysics
Astrophysics
12 pages, LaTeX using shst2.sty (enclosed), two embedded ps figures. To be published in Proc. "Science with the HST - II"
Scientific paper
HST has so far provided Cepheid distances to nine galaxies. Although not sufficient yet to determine the distance of the extended Virgo cluster, they are decisive for the distance scale in two ways. (1) Seven of the galaxies contribute to a much improved calibration of the Tully-Fisher relation. Applying this to a complete sample of Virgo spirals one obtains a cluster distance of (m-M)=31.79 +/- 0.09. Other distance indicators support this value. The adopted linear distance of 22.0 +/- 0.8 Mpc combined with the cluster velocity of 1178 +/- 32 km s^-1 (in the CMB frame) gives H_0=54 +/- 2 (internal error). (2) Six of the galaxies have been the site of seven SNe Ia with well observed maxima. Their resulting calibration in absolute magnitudes gives M_B(max)=-19.53 +/- 0.07 and M_V(max)=-19.49 +/- 0.07 with negligible intrinsic scatter. If this calibration is used to determine the distances of all distant SNe Ia with known maxima and with 1100 < v < 30'000 km s^-1, H_0 becomes 56 +/- 3 (internal error). Systematic errors tend to make this an upper limit; in particular the case H_0 >= 70 can be excluded. The conclusion is that the large-scale value of the Hubble constant is H_0=55 +/- 10 (external error).
Federspiel Martin
Labhardt Lukas
Macchetto Ferdinando D.
Panagia Nino
Saha Avishek
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