Fundamental Stellar Parameters from the CHARA Array

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This award supports the Georgia State University's Center for High Angular ResolutionAstronomy (CHARA). The CHARA Array consists of six 1-m aperture telescopesoperating in the optical/near infrared and arranged in a Y configuration which provides15 baselines from 33 to 331 meters in length. In terms of the number and aperture size ofits telescopes and the length of its baselines, the CHARA Array is among the mostpowerful facilities of its type in the world.Built with funds provided by Georgia State University (GSU), the NSF, the W.M. KeckFoundation, and the David and Lucile Packard Foundation, the CHARA Array hasundertaken several extensive observational programs with a broad impact on stellarastrophysics. These include measuring the oblateness and other physical parameters(including gravity darkening) for the rapidly rotating stars Regulus, Alderamin, andVega; checking the Baade-Wesselink method for calibrating the Cepheid periodluminosityrelation; detecting the circumstellar envelopes of Delta Cephei and Polaris(two Cepheid variables) and showing that emission from these envelopes must bemodeled to avoid biases in the Baade-Wesselink method; discovering that solarmetallicity M dwarfs are larger than similar mass but lower metallicity M dwarfs whichimplies an additional opacity source not included in current models; and measuring theangular separation between the components of the binary star 12 Persei to an accuracy of0.05% their separation thereby improving the accuracy of their derived masses.During the award period, several science programs will be carried out which continue tocapitalize on CHARA's unique capabilities. These include the measurement of stellarangular diameters of brighter stars to better than 1% accuracy. This will allow the criticaltesting of stellar atmosphere codes (including effective temperatures and brightnessprofiles) at temperatures from M to B. Evolved stars will be included as well tocharacterize the scale heights of their atmospheres. Pulsations of more Cepheid variableswill be measured to further calibrate the Baade-Wesselink method. The properties ofdisks surrounding Be stars will also be characterized. With regard to binaries, CHARA'shigh angular resolution will be used to resolve spectroscopic binaries, which will in turnallow high quality measurements of stellar mass, luminosity, and radius for stars acrossthe Hertzsprung-Russell Diagram. Known extrasolar planetary systems will also beinspected to ensure face-on binaries are not contaminating the samples.The training of the next generation of scientific and technical experts in interferometrywill also continue. CHARA is enhancing scientific awareness through the incorporationof its results into the large undergraduate courses taught at Georgia State. Thousands ofpublic visitors to Mt. Wilson will also have the opportunity to interactively learn theprinciples of interferometry through a display at the CHARA Exhibit Hall on Mt. Wilson(which also houses the 20-foot Michelson Stellar Interferometer used at the 100-inchtelescope).