The Final SHOE; Completing a Rich Cepheid Field in NGC 1309

The Cycle 15 SHOES program {GO 10802} is a large HST program allocated 186 orbits to rebuild the distance ladder using NGC 4258 as a new anchor, a set of 6 recent, ideal type Ia supernovae and Cepheids in their hosts, and NICMOS as a single, homogeneous photometer of long period Cepheids. These tools provide the means to achieve a 4% measurement of the Hubble constant, an invaluable constraint for cosmic concordance fits to dark energy models. Unfortunately, the SHOES NICMOS integrations of long period Cepheids in the last and most recent nearby type Ia supernova host, NGC 1309, are too short because the preliminary estimate of its distance, 30 Mpc, was too low. Our refined estimate now based on the full reduction of both our Cycle 14 and 15 ACS data is 36 Mpc, or 0.4 mag farther. Fortunately, Nature was extremely kind providing a single rich NIC2 field in which we can fully make up for the shortfall due to its abundance of Cepheids. We are expensing our final 4 orbits on this field of a dozen P>30 day Cepheids and seek an additional 5 orbits to reach the depth for measuring the mean F160W magnitudes of the long-period Cepheids with the necessary signal-to-noise ratios of better than 10.