Metallicity and the Cepheid Distance Scale

Details Metallicity and the Cepheid Distance Scale Metallicity and the Cepheid Distance Scale

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7849f&link_type=abstract

HST Proposal ID #7849

Physics

Hst Proposal Id #7849 Clusters Of Galaxies And Cosmology

Scientific paper

The local distance scale to galaxies is largely based on the Cepheid period-luminosity relation. Motivated by the goal of measuring an accurate value of the Hubble constant, HST has been used successfully to discover scores of Cepheid variables in each of about 20 galaxies. However, several studies have recently suggested that a large systematic error remains in these distances, and that the distance scale based upon them is in doubt. The source of this error is metallicity, and estimates of its impact on the Hubble constant range from ~5 available for most Cepheids. Thus, independently correcting the Cepheids for both reddening and metallicity remains problematic, and is now very controversial. However, removal of each of these sources of systematic uncertainty can be achieved at infrared wavelengths where both atmospheric line blanketing and interstellar reddening are negligible effects. We are therefore proposing observations of the extragalactic Cepheids using the NICMOS camera at H = 1.6 Mum. The importance of these observations cannot be overstated: without the addition of H-band data, the influence of metallicity effects on the extragalactic distance scale will remain in dispute without any obvious resolution. In combination with the existing optical data from HST, H- band data will bring the systematic uncertainties in the Cepheid distances derived to a level below 5 determination of H_o to <10

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