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Toward A New Calibration of the Hubble Constant

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I will present new results from the Carnegie-Chicago Hubble Program (CCHP), a decade-long project to independently measure a value of the Hubble constant to very high precision and accuracy. This program leverages and combines the resolution of the Hubble Space Telescope, the long-wavelength reach of Spitzer, the light-gathering capabilities of ground-based telescopes having a range of aperture sizes and operating with multi-wavelength detectors, including dedicated robotic follow-up telescopes, to provide new and independent data for the measurement of extragalactic distances. The CCHP  was initiated in anticipation of the launch of ESA ’s Gaia satellite. The goal of the program is to identify, reduce and provide external cross-checks on systematic errors in the distance scale. A robust determination of the overall systematic uncertainties in Ho can only be achieved using independent methods of equal precision. This program includes classical Cepheids, RR Lyrae variables, red giant branch stars, and Type Ia supernovae, the latter being part of the Carnegie Supernova Project (CSP). By building an entirely new data set from the ground up,  we have calibrated and applied two independent methods to the derivation of Ho. The two determinations, using Cepheids and red giant branch stars, respectively, are demonstrably of high precision and equally high systematic accuracy.

This talk is part of the Institute of Astronomy Colloquia series.

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