Publications of the MPIfR
Optical & Infrared
Interferometry Group
Wittkowski, M.; Aufdenberg, J. P.;
Driebe, T.; Roccatagliata, V.; Szeifert, T.; Wolff, B.
Tests of stellar model atmospheres by optical
interferometry. IV. VINCI interferometry and UVES spectroscopy of Menkar
Astronomy and Astrophysics, Volume 460, Issue 3,
December IV 2006, pp.855-864
Abstract
Aims.We present coordinated near-infrared K-band interferometric
and
optical spectroscopic observations of the M 1.5 giant α Cet (Menkar)
obtained with the instruments VINCI and UVES at the Paranal
Observatory. Spherically symmetric PHOENIX stellar model atmospheres
are constrained by comparison to our interferometric and spectroscopic
data, and high-precision fundamental parameters of Menkar are obtained.
Methods: .Our high-precision VLTI/VINCI observations in the
first and
second lobes of the visibility function directly probe the
model-predicted strength of the limb darkening effect in the K-band and
the stellar angular diameter. The high spectral resolution of UVES of
R=80 000-110 000 allows us to confront in detail observed and
model-predicted profiles of atomic lines and molecular bands.
Results: .We show that our derived PHOENIX model atmosphere for
Menkar
is consistent with both the measured strength of the limb-darkening in
the near-infrared K-band and the profiles of spectral bands around
selected atomic lines and TiO bandheads from 370 nm to 1000 nm. At the
detailed level of our high spectral resolution, however, noticeable
discrepancies between observed and synthetic spectra exist. We obtain a
high-precision Rosseland angular diameter of Θ_Ross=12.20~mas±
0.04~mas. Together with the Hipparcos parallax of 14.82 mas ± 0.83 mas,
it corresponds to a Rosseland radius of R_Ross=89 ± 5 R_ȯ, and together
with the bolometric flux based on available spectrophotometry, to an
effective temperature of T_eff=3795~K ± 70 K. The luminosity based on
these values is L=1460~L_ȯ ± 300~L_ȯ. Relying on stellar evolutionary
tracks, these values correspond to a mass M= 2.3~M_ȯ~± 0.2~M_ȯ and a
surface gravity log g=0.9 ± 0.1 (cgs).
Conclusions: .Our approach illustrates the power of combining
interferometry and high-resolution spectroscopy to constrain and
calibrate stellar model atmospheres. The simultaneous agreement of the
model atmosphere with our interferometric and spectroscopic data
increases confidence in the reliability of the modelling of this star,
while discrepancies at the detailed level of the high resolution
spectra can be used to further improve the underlying model.
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