Georgia State University's Center for High Angular Resolution Astronomy (CHARA) operates an interferometric array on Mt. Wilson, California. The CHARA Array consists of six 1-m aperture telescopes arranged in a Y configuration providing 15 baselines from 33 to 331 meters in length. The Array operates in the visible and near-infrared spectral regions with limiting resolutions of 1.6 and 0.4 milli-arcseconds at the K and V bands. 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 is poised to undertake extensive observational programs having a broad impact on stellar astrophysics. This award will support these programs primarily by maintaining an adequate scientific, technical and operational staff at the Array site. The core CHARA team has also developed a number of collaborations to more fully exploit the Array's scientific capability.
Because of its very high angular resolution and its good sensitivity and UV-plane coverage, the CHARA Array will have unprecedented access to stellar diameter measures for main sequence stars of all temperatures as well as for evolved stars. Accurate low-visibility measurements will characterize atmospheric limb darkening in stars. The sizes and shapes of young stellar objects will be mapped. Pulsations of Cepheid variables and their limb darkening will be measured to directly calibrate this important rung in the cosmic distance ladder. Continuum and molecular band observations will characterize scale heights in the atmospheres of evolved stars. Disks surrounding Be stars and massive outflows from luminous blue variable stars, Wolf-Rayet stars and interacting binaries will be detected and characterized. In the area of binary star studies, the Array will eliminate the classical problem of non-overlapping selection effects among the various techniques for discovering binary stars and measuring their orbital motions. It will resolve the majority of the spectroscopic binaries accessible to it, providing measurements of stellar mass, luminosity and radius for stars broadly distributed throughout the HR diagram. The emphasis will be on accuracy of mass determination, not just more masses of mediocre quality, to observationally detect the influence of age and metallicity on stellar evolution. Low-mass, unseen companions will be sought in wider binary systems. Known extrasolar planetary systems will be inspected to ensure that face-on binaries are not contaminating the sample even at a low level.
Broader impact beyond the scientific and intellectual goals exists in three areas. First, CHARA is actively training the next generation of scientific and technical experts in the field of interferometry. A significant fraction of GSU astronomy graduate students are pursuing their PhD research with the Array. CHARA staff have participated in all of the NASA/JPL Michelson Summer Schools. Second, CHARA will enhance science awareness in the large and diverse undergraduate community at GSU by incorporating Array imagery (real-time in some cases) in undergraduate astronomy courses, which enroll approximately 700 students per semester. Several undergraduates will be recruited to participate in remote observations and data processing. Third, a CHARA Exhibit Hall on Mt. Wilson dramatically displays the historic 20-ft Michelson Stellar Interferometer, used at the 100-inch telescope in the 1920s. Thousands of visitors to the observatory grounds each year will have a unique opportunity to interactively learn how interferometry can probe stars to reveal their surfaces and fundamental properties. ***
