EDP Sciences
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Volume 421, Number 2, July II 2004
Page(s) 703 - 714
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20035826

A&A 421, 703-714 (2004)
DOI: 10.1051/0004-6361:20035826

Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared

H. C. Woodruff1, M. Eberhardt1, T. Driebe1, K.-H. Hofmann1, K. Ohnaka1, A. Richichi2, D. Schertl1, M. Schöller3, M. Scholz4, 5, G. Weigelt1, M. Wittkowski2 and P. R. Wood6

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2  European Southern Observatory, Karl-Schwarzschildt-Str. 2, 85748 Garching, Germany
3  European Southern Observatory, Casilla 19001, Santiago 19, Chile
4  Institut für Theoretische Astrophysik, Universität Heidelberg, Tiergartenstr. 15, 69121 Heidelberg, Germany
5  Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia
6  Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek ACT 2611, Australia

(Received 9 December 2003 / Accepted 1 April 2004 )

We present K-band commissioning observations of the Mira star prototype  o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats. The observations were carried out between 2001 October and December, in 2002 January and December, and in 2003 January. Rosseland angular radii are derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of Mira star models (Bessell et al. 1996; Hofmann et al. 1998; Tej et al. 2003b). Using the derived Rosseland angular radii and the SEDs reconstructed from available photometric and spectrophotometric data, we find effective temperatures ranging from $T_{\rm eff}=3192 \pm 200$ K at phase  $\Phi=0.13$ to  $2918 \pm 183$ K at $\Phi=0.26$. Comparison of these Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that  o Cet is a fundamental mode pulsator. Furthermore, we investigated the variation of visibility function and diameter with phase. The Rosseland angular diameter of o Cet increased from  $28.9 \pm 0.3$ mas (corresponding to a Rosseland radius of $332 \pm 38~R_{\odot}$ for a distance of $D=107\pm12~{\rm pc}$) at  $\Phi=0.13$ to  $34.9 \pm 0.4$ mas ( $402 \pm 46~R_{\odot}$) at  $\Phi=0.4$. The error of the Rosseland linear radius almost entirely results from the error of the parallax, since the error of the angular diameter is only approximately 1%.

Key words: instrumentation: interferometers -- techniques: interferometric -- stars: late-type -- stars: AGB and post-AGB -- stars: fundamental parameters -- stars: individual: Mira

Offprint request: H. C. Woodruff, woodruff@mpifr-bonn.mpg.de

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