This award supports the Georgia State University's Center for High Angular Resolution Astronomy (CHARA). The CHARA Array consists of six 1-m aperture telescopes operating in the optical/near infrared and arranged in a Y configuration which provides 15 baselines from 33 to 331 meters in length. In terms of the number and aperture size of its telescopes and the length of its baselines, the CHARA Array is among the most powerful facilities of its type in the world.
Built with funds provided by Georgia State University (GSU), the NSF, the W.M. Keck Foundation, and the David and Lucile Packard Foundation, the CHARA Array has undertaken several extensive observational programs with a broad impact on stellar astrophysics. These include measuring the oblateness and other physical parameters (including gravity darkening) for the rapidly rotating stars Regulus, Alderamin, and Vega; checking the Baade-Wesselink method for calibrating the Cepheid periodluminosity relation; detecting the circumstellar envelopes of Delta Cephei and Polaris (two Cepheid variables) and showing that emission from these envelopes must be modeled to avoid biases in the Baade-Wesselink method; discovering that solar metallicity M dwarfs are larger than similar mass but lower metallicity M dwarfs which implies an additional opacity source not included in current models; and measuring the angular separation between the components of the binary star 12 Persei to an accuracy of 0.05% their separation thereby improving the accuracy of their derived masses.
During the award period, several science programs will be carried out which continue to capitalize on CHARA's unique capabilities. These include the measurement of stellar angular diameters of brighter stars to better than 1% accuracy. This will allow the critical testing of stellar atmosphere codes (including effective temperatures and brightness profiles) at temperatures from M to B. Evolved stars will be included as well to characterize the scale heights of their atmospheres. Pulsations of more Cepheid variables will be measured to further calibrate the Baade-Wesselink method. The properties of disks surrounding Be stars will also be characterized. With regard to binaries, CHARA's high angular resolution will be used to resolve spectroscopic binaries, which will in turn allow high quality measurements of stellar mass, luminosity, and radius for stars across the Hertzsprung-Russell Diagram. Known extrasolar planetary systems will also be inspected to ensure face-on binaries are not contaminating the samples.
The training of the next generation of scientific and technical experts in interferometry will also continue. CHARA is enhancing scientific awareness through the incorporation of its results into the large undergraduate courses taught at Georgia State. Thousands of public visitors to Mt. Wilson will also have the opportunity to interactively learn the principles 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-inch telescope).
