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Session 66 - Galaxies.
Display session, Thursday, June 11
The HST Key Project on the Determination of the Extragalactic Distance Scale rests fundamentally on accurate distances to approximately 20 carefully selected galaxies in the 3 - 20 Mpc range obtained by using the Cepheid period-luminosity relation. In this paper, we report the results based on 26 Cepheid variables in the Virgo Cluster galaxy NGC 4548. A comparison is made with the Cepheid distances of 6 other spiral galaxies in the Virgo Cluster. For all, except NGC 4639, there is very good agreement, suggesting (cf. Jacoby, Ciardullo amp; Ford 1990, ApJ, 356, 332) that the core of the Virgo Cluster may be quite well defined and thus suited to the calibration of secondary distance indicators. The Cepheid distances all rest on an assumed LMC distance modulus of 18.5 mag. This value is consistent with the distances obtained by a number of different methods (e.g. Westerlund 1996 in The Magellanic Clouds (CUP)). The recent upward revision proposed by Feast amp; Catchpole (1997, MNRAS, 286, L1) has been discussed by Madore amp; Freedman (1998, ApJ, 492, 110) who concluded that any change in the above base value, with its effect on Cepheid distances, is still premature because of significant measuring uncertainties.
Program listing for Thursday