Stellar and molecular radii of a Mira star: First observations with the Keck Interferometer grism

Creators: Eisner, J. A.; Graham, J. R.; Akeson, R. L.; Ligon, E. R.; Colavita, M. M.; Basri, G.; Summers, K.; Ragland, S.; Booth, A.

Abstract

Using a new grism at the Keck Interferometer, we obtained spectrally dispersed (R ~ 230) interferometric measurements of the Mira star R Vir. These data show that the measured radius of the emission varies substantially from 2.0 to 2.4 μm. Simple models can reproduce these wavelength-dependent variations using extended molecular layers, which absorb stellar radiation and reemit it at longer wavelengths. Because we observe spectral regions with and without substantial molecular opacity, we determine the stellar photospheric radius, uncontaminated by molecular emission. We infer that most of the molecular opacity arises at approximately twice the radius of the stellar photosphere.

Additional Information

© 2007 The American Astronomical Society. Received 2006 October 9; accepted 2006 November 8; published 2006 December 7. Data presented here were obtained at the W. M. Keck Observatory from telescope time allocated to NASA through the agency's scientific partnership with Caltech and the University of California. The Observatory was made possible by the generous support of the W. M. Keck Foundation. We thank the entire KI team for making these observations possible and acknowledge the role of MSC software in our data acquisition and analysis. We are indebted to P. Wizinowich, G. Vasisht, and L. Hillenbrand for helping to ensure the successful implementation of the grism, and to P. Hauschildt, J. Carr, and M. Ireland for providing models and molecular opacities used in our analysis.

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