Tests of stellar model atmospheres by optical interferometry IV: VINCI interferometry and UVES spectroscopy of Menkar

摘要

We present K-band interferometric and optical spectroscopic observations ofMenkar obtained with the instruments VINCI and UVES at Paranal Observatory.Spherically symmetric PHOENIX stellar model atmospheres are constrained bycomparison to our interferometric and spectroscopic data, and high-precisionfundamental parameters of Menkar are obtained. Our high-precision VLTI/VINCIobservations in the first and second lobes of the visibility function directlyprobe the model-predicted strength of the limb darkening effect in the K-bandand the stellar angular diameter. The high spectral resolution of UVES allowsus to confront observed and model-predicted profiles of atomic lines andmolecular bands. We show that our derived PHOENIX model atmosphere for Menkaris consistent with both the measured strength of the limb-darkening in thenear-infrared K-band and the profiles of spectral bands around selected atomiclines and TiO bandheads. At the detailed level of our high spectral resolution,however, noticeable discrepancies between observed and synthetic spectra exist.We obtain a Rosseland angular diameter of Theta_Ross=12.20 mas pm 0.04 mas.Together with the Hipparcos parallax, it corresponds to R_Ross=89 pm 5 R_sun,and together with the bolometric flux to T_eff=3795 K pm 70 K.Our approachillustrates the power of combining interferometry and high-resolutionspectroscopy to constrain and calibrate stellar model atmospheres. Thesimultaneous agreement of the model atmosphere with our interferometric andspectroscopic data increases confidence in the reliability of the modelling ofthis star, while discrepancies at the detailed level of the high resolutionspectra can be used to further improve the underlying model.