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Mid-infrared interferometry of dust around massive evolved stars

Rajagopal, Jayadev and Menut, Jean-Luc and Wallace, D. and Danchi, W. C. and Chesneau, O. and Lopez, B. and Monnier, J. D. and Ireland, M. J. and Tuthill, P. G. (2007) Mid-infrared interferometry of dust around massive evolved stars. Astrophysical Journal, 671 (2). pp. 2017-2027. ISSN 0004-637X.

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We report long-baseline interferometric measurements of circumstellar dust around massive evolved stars with the MIDI instrument on the Very Large Telescope Interferometer and provide spectrally dispersed visibilities in the 8-13 mu m wavelength band. We also present diffraction-limited observations at 10.7 mu m on the Keck Telescope with baselines up to 8.7 m, which explore larger scale structure. We have resolved the dust shells around the late-type WC stars WR 106 and WR 95 and the enigmatic NaSt1 ( formerly WR 122), suspected to have recently evolved from a luminous blue variable (LBV) stage. For AG Car, the prototypical LBV in our sample, we marginally resolve structure close to the star, distinct from the well-studied detached nebula. The dust shells around the two WC stars show fairly constant size in the 8-13 mu m MIDI band, with Gaussian half-widths of similar to 25 to 40 mas, and the Keck observations reveal an additional extended structure around WR 106. The visibility profiles for NaSt 1 obtained from two MIDI baselines indicate a compact source embedded in an extended structure. The compact dust we detect around NaSt 1 and AG Car favors recent or ongoing dust formation. Using the measured visibilities, we build spherically symmetric radiative transfer models of the WC dust shells, which enable detailed comparison with existing SED-based models. Our results indicate that the inner radii of the shells are within a few tens of AU from the stars. In addition, our models favor grain size distributions with large (similar to 1 mu m) dust grains. This proximity of the inner dust to the hot central star emphasizes the difficulty faced by current theories in forming dust in the hostile environment around WR stars. Although we detect no direct evidence for binarity for these objects, dust production in a colliding-wind interface in a binary system is a feasible mechanism in WR systems under these conditions.

Item Type:Article
Related URLs:
URLURL TypeDescription
Monnier, J. D.0000-0002-3380-3307
Ireland, M. J.0000-0002-6194-043X
Additional Information:© 2007 The American Astronomical Society. Received 2007 April 22; accepted 2007 August 15. This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for the National Aeronautics and Space Administration (NASA) by the California Institute of Technology. Some of 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 NASA. The observatory was made possible by 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. We acknowledge the VLTI consortium for both technical and software support. We thank the referee for comments that have significantly improved this article.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:stars: individual (AG Car, NaSt 1, WR 95, WR 106); techniques: interferometric
Issue or Number:2
Record Number:CaltechAUTHORS:RAJapj07
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12185
Deposited By: Tony Diaz
Deposited On:13 Nov 2008 04:36
Last Modified:13 Dec 2019 04:19

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