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The Keck aperture masking experiment: multiwavelength observations of six Mira variables

Woodruff, H. C. and Tuthill, P. G. and Monnier, J. D. and Ireland, M. J. and Bedding, T. R. and Lacour, S. and Danchi, W. C. and Scholz, M. (2008) The Keck aperture masking experiment: multiwavelength observations of six Mira variables. Astrophysical Journal, 673 (1). pp. 418-433. ISSN 0004-637X. doi:10.1086/523936.

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The angular diameters of six oxygen-rich Mira-type long-period variables have been measured at various NIR wavelengths using the aperture-masking technique in an extensive observing program from 1997 January to 2004 September. These data sets span many pulsation cycles of the observed objects and represent the largest study of multiwavelength, multiepoch interferometric angular diameter measurements on Mira stars to date. The calibrated visibility data of ο Cet, R Leo, R Cas, W Hya, χ Cyg, and R Hya are fitted using a uniform disk brightness distribution model to facilitate comparison between epochs, wavelengths, and with existing data and theoretical models. The variation of angular diameter as a function of wavelength and time is studied, and cyclic diameter variations are detected for all objects in our sample. These variations are believed to stem from time-dependent changes of density and temperature (and hence varying molecular opacities) in different layers of these stars. The similarities and differences in behavior between these objects are analyzed and discussed in the context of existing theoretical models. Furthermore, we present time-dependent 3.08 μm angular diameter measurements, probing for the first time these zones of probable dust formation, which show unforeseen sizes and are consistently out of phase with other NIR layers shown in this study. The S-type Mira χ Cyg exhibits significantly different behavior compared to the M-type Mira variables in this study, in both its NIR light curves and its diameter pulsation signature. Our data show that the NIR diameters predicted by current models are too small and need to incorporate additional and/or enhanced opacity mechanisms. Also, new tailored models are needed to explain the behavior of the S-type Mira χ Cyg.

Item Type:Article
Related URLs:
URLURL TypeDescription
Monnier, J. D.0000-0002-3380-3307
Ireland, M. J.0000-0002-6194-043X
Bedding, T. R.0000-0001-5222-4661
Lacour, S.0000-0002-6948-0263
Additional Information:© 2008 American Astronomical Society. Received 2007 July 30; accepted 2007 September 24. This work has been supported by grants from the National Science Foundation, the Australian Research Council, and the Deutsche Forschungsgemeinschaft (H. C. W., M. S.). 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 Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. We also thank Albert Jones and Peter Williams for the W Hya light-curve data.
Funding AgencyGrant Number
Australian Research CouncilUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
Subject Keywords:instrumentation : interferometers; stars : AGB and post-AGB; stars : fundamental parameters; stars : individual (Mira, R hya, Chi Cyg, W Hya, R Leo, R cas); stars : late-type; techniques : interferometric
Issue or Number:1
Record Number:CaltechAUTHORS:20090713-135552907
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14574
Deposited By: Tony Diaz
Deposited On:27 Jul 2009 18:17
Last Modified:08 Nov 2021 23:12

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