NOAO >   Observing Info >   Approved Programs >   2014A-0410

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Proposal Information for 2014A-0410


PI: Lucas Macri, Texas A& M University, lmacri@tamu.edu
Address: Physics Department, 4242 TAMU, College Station, TX 77843-4242, USA

CoI: Wenlong Yuan, Texas A& M University
CoI: Adam G. Riess, Johns Hopkins University & STScI

Title: Towards a 2% measurement of H_0: Near-infrared light curves of Galactic Cepheids

Abstract: A precise and accurate measurement of the Hubble constant (H_0) via Cepheids and type Ia supernovae plays a critical role in modern cosmology. Ongoing and planned dark energy surveys (such as DES and LSST) can significantly improve their figure of merit by including a prior on H_0. Furthermore, the combination of CMB measurements and local determinations of H_0 can reveal ``new Physics'' through departures from the standard cosmological model. We are currently using the \it Hubble Space Telescope to determine H_0 with a total uncertainty of 2% by measuring the parallaxes of 19 Milky Way Cepheids and obtaining Cepheid distances to the hosts of 9 recent SNe Ia. We are also laying the groundwork for a future determination of H_0 to 1% by acquiring single-epoch \it HST near- infrared photometry for as many as 60 Galactic Cepheids that will have excellent parallax measurements from \it Gaia in a few years. We request 10 nights of time at the CTIO 1.3-m to obtain sparsely- sampled, high-quality light curves of these Cepheids in the H band. The observations are critical to correct the single-epoch HST observations to ``mean light'' and realize the full potential of the Cepheid Period-Luminosity relation at near-infrared wavelengths.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



NOAO >   Observing Info >   Approved Programs >   2014A-0410

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