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Published June 10, 2011 | Published
Journal Article Open

Exozodiacal Dust Levels for Nearby Main-sequence Stars: A Survey with the Keck Interferometer Nuller


The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main-sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1-4 AU from the star. We find one significant detection (η Crv), two marginal detections (γ Oph and α Aql), and 22 clear non-detections. Using a model of our own solar system's zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are η Crv (1250 ± 260), γ Oph (200 ± 80), and α Aql (600 ± 200), where the uncertainties are 1σ. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1σ). These measurements represent the best limits to date on exozodi levels for a sample of nearby main-sequence stars. A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding η Crv and γ Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3σ upper limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.

Additional Information

© 2011 The American Astronomical Society. Received 2011 January 28; accepted 2011 April 7; published 2011 May 25. The Keck Interferometer is funded by the National Aeronautics and Space Administration as part of its Exoplanet Exploration Program. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work has made use of services produced by the NASA Exoplanet Science Institute at the California Institute of Technology. This research has made use of the Washington Double Star Catalog maintained at the U.S. Naval Observatory. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The authors wish to acknowledge invaluable contributions from the KI team at Keck Observatory, the Jet Propulsion Lab, and the NASA Exoplanet Science Institute. R.M.G. acknowledges fruitful discussions with J. D. Monnier. Facilities: Keck: Interferometer

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