Picturing the faces of stars: limb-darkening models vs. interferometer measurements

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This award is made to study hundreds of stars with optical interferometry and spectroscopy. Interferometry combines light waves from different telescopes and produces very high angular resolution images. This allows astronomers to record the brightness variations across a stellar disk. The center shows deeper and warmer layers of a star, whereas the edges show shallower and cooler material. This effect is called limb-darkening. The group will also record optical spectra, which measure light emitted or absorbed by individual chemical elements. This enables derivation of fundamental parameters of the stars not already provided by interferometry, such as overall stellar luminosity, and chemical composition. All the data will be used to determine stellar diameters and temperature profiles and to test stellar astrophysics models. The data and modeling codes will be released to a public database. Two graduate students will be trained in both interferometric and modeling techniques.The team will use the NPOI (Naval Prototype Optical Interferometer) and CHARA (Center for High Angular Resolution Array) interferometers to obtain sub-milliarcsecond resolution images. They will collect moderate-resolution optical spectroscopy with Apache Point Observatory and Georgia State University telescopes. They will use several atmospheric models to explore three-dimensional effects and non-local thermodynamic equilibrium (NLTE) effects. The project will run precise model grids for a hundred stars and at least three different models. The stellar atmosphere model code SATLAS will be made fully open-source with updated microphysics and NLTE refinements. This code and the 3D radiative hydrodynamic STAGGER will be accelerated by Graphic Processor Units through partnerships with industry collaborators.