Infrared Imaging of Capella with the IOTA Closure Phase Interferometer
The Astronomical Journal
American Astronomical Society
© 2005. The American Astronomical Society. All rights reserved.
We present infrared aperture synthesis maps produced with the upgraded Infrared Optical Telescope Array interferometer. Michelson interferograms on the close binary system Capella (α Aur) were obtained in the H band between 2002 November 12 and 16 using the IONIC3 beam combiner. With baselines of 15 m ≤ B ≤ 38 m, we were able to determine the relative position of the binary components with milliarcsecond precision and to track their movement along the ≈14° arc covered by our observation run. We briefly describe the algorithms used for visibility and closure phase estimation. Three different hybrid mapping and bispectrum fitting techniques were implemented within one software framework and used to reconstruct the source brightness distribution. By dividing our data into subsets, the system could be mapped at three epochs, revealing the motion of the stars. The precise position of the binary components was also determined with model fits, which in addition revealed IAa/IAb = 1.49 ± 0.10 and apparent stellar uniform-disk diameters of ΘAa = 8.9 ± 0.6 mas and ΘAb = 5.8 ± 0.8 mas. To improve the (u,v)-plane coverage, we compensated this orbital motion by applying a rotation-compensating coordinate transformation. The resulting model-independent map with a beam size of 5.4 mas × 2.6 mas allows the resolution of the stellar surfaces of the Capella giants themselves.
S. K. was supported by NSF grant AST-0138303 and the International Max Planck Research School for Radio and Infrared Astronomy at the University of Bonn. We would like to thank Karl-Heinz Hofmann for useful discussions and the anonymous referee for his constructive comments on the paper.
This is the author accepted manuscript. The final version is available from the American Astronomical Society via the DOI in this record.
The Astronomical Journal, 2005, Vol. 130, Number 1, pp. 246-255