170 research outputs found
Tests of stellar model atmospheres by optical interferometry IV. VINCI Interferometry and UVES spectroscopy of Menkar
No full textAims. We present coordinated near-infrared K-band interferometric and optical spectroscopic observations of the M l .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 = 80000-110 000 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 ΘRoss = 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 RRoss = 89 ± 5R⊙, and together with the bolometric flux based on available spectrophotometry, to an effective temperature of Teff = 3795 K ±70 K. The luminosity based on these values is L = 1460 L ⊙ ± 300 L⊙. Relying on stellar evolutionary tracks, these values correspond to a mass M = 2.3 M ⊙ ± 0.2 M⊙ 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. © ESO 2006
Spectroscopic and Interferometric Tests of Stellar Atmosphere Models: UVES and VINCI Measurements of the M-giant α Cet
No full textWe present VLT/UVES spectroscopic and VLTI/VINCI interferometric observations of the cool giant α Cet (M2 III). Spherically symmetric PHOENIXstellar atmosphere models are tested by comparison with our spectroscopic and interferometric observations. The high spectral resolution of UVES allows us to constrain the effective temperature and the surface gravity of the star by comparing observed and model predicted bands that are temperature and gravity indicators. High angular resolution and high precision VLTI/VINCI observations directly measure the strength of the limb darkening effect of α Cet in the K-band. We derive fundamental stellar parameters, namely a Rosseland diameter of 12.08±0.18 mas corresponding to a Rosseland linear radius of 88±6 R☉, and an effective temperature of 3805+95 -109 K, using the Hipparcos parallax and the bolometric flux
Jordan blocks in a one-dimensional Markov map
No full textAbstractA simple one-dimensional chaotic map, whose spectral decomposition of the Frobenius-Perron operator in the space of polynomials has Jordan block structure is given and analyzed. The Jordan block structure implies that some correlation functions have exponential decay modified by coefficients, which are polynomials in t. Such a correlation is given for this system and a numerical simulation, which agrees with the theoretical prediction is presented
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Density evolution in systems with slow approach to equilibrium
No full texttextThis dissertation investigates the evolution of probability densities under the
Frobenius-Perron operator U in
chaotic
iterated-map systems that are slow to reach
equilibrium. It first
concentrates on one-dimensional maps that are slow to reach equilibrium
because they feature intermittent
chaos due to the presence of a marginal fixed
point. Using the method of shift states and
coherent states under U,
certain results
are obtained
concerning the spectrum of U in various functional spaces, using as the
main example the
cusp map f (x) = 1
- √ |1 - 2x |. Those results are applied to obtain
corrections to the well-known leading 1/t form of the x-x auto
correlation function
C(t). The symbolic
dynamics of one-dimensional maps are then investigated, with particular emphasis on the implications of the existence of intermittent
chaos and with
applications to topological
conjugation. Next, the statistics of extreme values in one dimensional
maps are investigated. Fn(x) is defined as the probability that a point
chosen from an initial probability distribution and its first n- 1 iterates under a particular map are all less than x; the properties of Fn(x) are derived analytically for a
wide variety of one-dimensional maps, and the
on
conclusions are
confirmed numerically.
Finally, higher-dimensional area-preserving maps are investigated. The technique of local spectral decomposition for U, in which approximate right and left eigenstates for U
are
constructed localized on unstable periodic
points, is used to study density evolution
and
correlation of observables over time.Physic
Resident Extracapsular Cataract Surgery: Results and a Comparison of Automated and Manual Techniques
No full text
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