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Session 12 - Cosmology, Large-Scale Structure and Distance Scales.
Display session, Monday, June 10
Great Hall,

[12.14] Primary and Secondary Distance Indicators in the Leo I group of Galaxies

J. A. Graham (DTM), R. L. Phelps, W. L. Freedman (OCIW), A. Saha (STScI), R. C. Kennicutt (U. Arizona), J. R. Mould (MSSO), L. Ferrarese, H. C. Ford (JHU), J. P. Huchra (Harvard, CfA), S. M. Hughes (RGO), M. Han, J. G. Hoessel (U. Wisconsin), G. D. Illingworth (UCSC), B. F. Madore, S. Sakai, N. Silbermann (IPAC), P. B. Stetson (DAO)

The primary aim of the HST Extragalactic Distance Scale Key Project is to combine HST observations of Cepheid variable stars in \approx 25 galaxies with observations of a number of secondary indicators to measure the Hubble parameter H_0 to an accuracy of 10%. The Leo I group of galaxies contains several bright members of diverse galactic types and is very suitable for co-relating the various secondary indicators to the primary Cepheid distance scale. As a step to establishing a Cepheid distance to the Leo I group, we have used the HST to identify and measure 49 probable Cepheids within the barred spriral galaxy NGC 3351 (M95) over the period range 10-43 days. Light curves and period-luminosity relations will be presented. These indicate a true modulus of 30.01 \pm 0.07 mag corresponding to a distance of 10.05 \pm 0.3 Mpc. This is somewhat less than the distance of 11.6 \pm 0.8 Mpc determined by Tanvir et al. (Nature 1995, 377, 277) for a smaller sample of Cepheids in the neighboring spiral galaxy NGC 3368 (M96). We will examine data already available for other members of the Leo I group to illustrate the way our final calibration of the extragalactic distance scale will proceed. We will show that there is especially good agreement between our new distance and those obtained for group galaxies with the Surface Brightness Fluctuation and Planetary Nebula Luminosity Function methods as calibrated by the Cepheids in M31.

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