Cepheid Astrophysics: Measuring the Fundamental Physical Properties of a 3.8-day Classical Cepheid Variable in the Eclipsing Binary System OGLE-LMC-CEP227

Details Cepheid Astrophysics: Measuring the Fundamental Physical Properties of a 3.8-day Classical Cepheid Variable in the Eclipsing Binary System OGLE-LMC-CEP227 Cepheid Astrophysics: Measuring the Fundamental Physical Properties of a 3.8-day Classical Cepheid Variable in the Eclipsing Binary System OGLE-LMC-CEP227

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011sptz.prop80021m&link_type=abstract

Spitzer Proposal ID #80021

Physics

Scientific paper

Using Spitzer, we have a unique opportunity to measure the zero point of the Cepheid Period-Luminosity relation and determine a direct distance to the Large Magellanic Cloud. We will map the surface brightness structure of a short-period, fundamental-mode Classical Cepheid variable in the LMC, measure its mean radius in two independent ways, and thereby determine its intrinsic luminosity and distance taking two physically based and independent paths to the same end goal. Located in the Large Magellanic Cloud, OGLE-LMC-CEP227 is a detached, eclipsing binary system, having an orbital period of 309 days. It is composed of a yellow supergiant (the secondary) and an equal-mass, but more luminous, Cepheid variable (the primary) having a radial pulsation period of 3.8 days. The mass and radius of each star is independently well determined from the eclipse timings and orbital-parameter solutions. By photometrically monitoring the ingress and egress of the Cepheid while passing behind and then again while passing in front of the physically larger but slightly cooler secondary star we will be able to map the surface-brightness structure (most notably the limb darkening) of each star in the mid-infrared. Out of eclipse we will use the Baade-Wesselink Method to again, but independently, determine the radius and luminosity of the Cepheid, this time from its observed pulsation properties. Comparing the orbital and pulsational solutions will provide a fundamental test of the input physics currently being used to calibrate the zero point of Cepheid Period-Luminosity relation using the Baade-Wesselink Method. An extremely well understood distance to the LMC (with a highly constrained uncertainty) will be an important end-product.

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