The recent years have seen a spectacular progress of angular resolution in optical astronomy, with increasingly long interferometric baselines becoming used at several sites. However, the limiting ...magnitudes have remained modest, in spite of the large apertures used at instruments such as the VLTI. Much cutting-edge science remains to be performed with the VLTI, but the time has come for a new generation of interferometer systems exploiting many apertures.
Stellar winds of hot stars Stee, Ph; Chesneau, O.
EAS publications series,
01/2014, Volume:
69-70
Journal Article
In this paper, we summarize the basic properties of radiative stellar winds from the theoretical and observational point of views. We illustrate two examples of a radiative code applied to stellar ...physics: the SIMECA code successfully used to constrain the physics of the circumstellar environment of the Be star α Arae constrained by VLTI-AMBER spectrally resolved measurements and the CMFGEN code applied to the BA supergiants Deneb and Rigel constrained by CHARA-VEGA measurements.
gamma Cas is thought to be the prototype of classical Be stars and is the most studied object among this group. The authors constrain the geometry and kinematics of its circumstellar disk from the ...highest spatial resolution ever achieved on this star. The authors present new observations in the near infrared and in the visible (VEGA) obtained with the CHARA interferometer. The VEGA instrument allows them to not only obtain a global disk geometry but also spectrally dispersed visibility modulus and phases within the H alpha emission line, which enables them to study the kinematics within gamma Cas's disk. For the first time they demonstrate that the rotation mapped by the emission in the H alpha line within the disk of gamma Cas and up to 10 R sub( lowast) is Keplerian. These observations have pushed the size of the disk to greater proportions. gamma Cas was also confirmed to be a nearly critical rotator.
Context.γ Cas is thought to be the prototype of classical Be stars and is the most studied object among this group. However, as for all Be stars, the origin and the physics of its circumstellar disk ...responsible for the observed near IR-excess, emission lines, and peculiar X-ray emission is still being debated. Aims. We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star. This investigation is a part of a large multi-technique observing campaign to obtain the most complete picture of γ Cas which emphasizes the relation of the circumstellar environment to the star’s X-ray flux. Methods. We present new observations in the near infrared (MIRC) and in the visible (VEGA) obtained with the CHARA interferometer. The VEGA instrument allows us to not only obtain a global disk geometry but also spectrally dispersed visibility modulus and phases within the Hα emission line, which enables us to study the kinematics within γ Cas’s disk. Results. We obtain a disk extension in the nearby Hα continuum of 1.72 stellar diameter and 1.86 stellar diameter in the H band at 1.65 μm assuming a Gaussian disk model but also compatible with an elliptical ring model with a minor internal diameter of 1.38 stellar diameter in H. For the first time we demonstrate that the rotation mapped by the emission in the Hα line within the disk of γ Cas and up to 10 R⋆ is Keplerian. Conclusions. These observations have pushed the size of the disk to greater proportions. γ Cas was also confirmed to be a nearly critical rotator. The disk imaging gives neither indication of a 1-arm spiral feature nor evidence of a secondary star reinforcing the interpretation that the secondary is certainly a low-mass and low-luminosity star or a degenerate companion.
We discuss and illustrate contributions that optical interferometry has made on our current understanding of cool evolved stars. We include red giant branch (RGB) stars, asymptotic giant branch (AGB) ...stars, and red supergiants (RSGs). Studies using optical interferometry from visual to mid-infrared wavelengths have greatly increased our knowledge of their atmospheres, extended molecular shells, dust formation, and winds. These processes and the morphology of the circumstellar environment are important for the further evolution of these stars toward planetary nebulae (PNe) and core-collapse supernovae (SNe), and for the return of material to the interstellar medium.
This is one of two chapters that describe the methods used to extract closure phase from CLIMB data and visibility amplitude from both the CLASSIC and CLIMB beam combiners. In this, the second ...chapter, I describe the pipeline software.
The very high spatial resolution provided by current interferometers (VLTI, CHARA, …) makes it possible to measure directly the change in angular diameter of more than thirty Cepheids over their ...pulsation cycle. When combined with radial velocity measurements, this allows us to measure precisely their distances in a quasi-geometrical way. This is an essential information to calibrate the Cepheid's Period-Luminosity law. On the other hand, a careful analysis of the dynamical structure of their atmosphere is required to avoid biases in their distance determination.
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