Publications
of the
MPIfR Optical & Infrared Interferometry Group

M. Eberhardt, H.C. Woodruff, T. Driebe, K.-H. Hofmann, M. Schöller, M. Scholz, G. Weigelt, M. Wittkowski

VINCI VLTI interferometry of Mira stars and determination of stellar parameters

In: Schielikke, R.E. (ed.): Short Contrib. Ann. Sci. Meeting Astron. Ges. Freiburg 2003. Astron. Nachr. 324, Suppl. Issue 3 (2003), p.136
"The Sun and Planetary Systems - Paradigms for the Universe"
Annual Scientific Meeting of the Astronomische Gesellschaft, Sep 15-20, 2003, Freiburg, Germany

Abstract

We present accurate K'-band visibility and angular diameter measurements of Mira stars, recently obtained at the Very Large Telescope Interferometer with the VINCI instrument (commissioning data). The data was obtained in the period between 2001 April and 2003 February. For several Mira variables the observed visibility functions (modulus of the Fourier transform of the intensity distribution of the object) change noticeably from one epoch to another. The observations were compared with Mira star models of Bessel, Scholz & Wood [A&A 307 (1996) 481, BSW] and Hofmann, Scholz & Wood [A&A 339 (1998) 846, HSW]. Angular stellar filter radii and Rosseland radii were derived from the measured visibilities by fitting theoretical center-to-limb intensity variations (CLVs) of different Mira star models (BSW, HSW). If available, HIPPARCOS parallaxes allow us to determine linear radii.

From the measured angular diameters and bolometric fluxes we calculated the effective temperatures. For instance, the measured visibility curves (within the baseline length range from 11 m to 16 m) of Omicron Ceti and the determined linear Rosseland radius of 328 Rsun agree well with the near-maximum fundamental mode P model of BSW and HSW. On the other hand, comparison of the data with the first-overtone pulsation modes suggest that these models do not represent well the behaviour of Omicron Ceti.