Institute of Astronomy

Toward A New Calibration of the Hubble Constant

SpeakerTalk DateTalk Series
Wendy Freedman (Chicago)31 May 2018Institute of Astronomy Colloquia


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.


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