Improving the Distance Scale: NICMOS and ACS/HRC observations of Cepheids in the Maser Galaxy NGC 4258

Details Improving the Distance Scale: NICMOS and ACS/HRC observations of Cepheids in the Maser Galaxy NGC 4258 Improving the Distance Scale: NICMOS and ACS/HRC observations of Cepheids in the Maser Galaxy NGC 4258

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20910207m&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #102.07; Bulletin of the American Astronomical Society,

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We present results from HST NICMOS and ACS/HRC observations of a subset of 300 Cepheids in the maser-host galaxy NGC 4258 that we discovered with HST ACS/WFC on Cycle 12 (Macri et al., ApJ 653, 2006).
NGC 4258 is a key galaxy for the Extragalactic Distance Scale because of its accurate and precise geometric distance, which will soon be known to 3% (Humphreys et al, in preparation). The distance measurement is obtained through VLBI observations of water maser emission originating from a sub-parsec annular region within a nearly edge-on, warped accretion disk, bound by a supermassive black hole in the nucleus of the galaxy.
We present H-band Cepheid Period-Luminosity relations for 21 variables located in our inner field (solar metallicity) and 14 variables located in our outer field (LMC metallicity). Additionally, we present Vand I-band blending statistics for the Cepheids that were imaged with both ACS/WFC and HRC. We discuss the additional constraints that the H-band P-L relations and the blending corrections impose on the relative distance modulus between the LMC and NGC 4258 and its implications for the Hubble Constant.
Funding for this program was provided by NASA through STScI, as part of HST GO programs 9810 and 10399.

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