VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters

Abstract

The main goal of this research is to determine the angular size and the atmospheric structures of cool giant stars and to compare them with hydrostatic stellar model atmospheres, to estimate the fundamental parameters, and to obtain a better understanding of the circumstellar environment. We conducted spectro-interferometric observations of epsilon Oct, beta Peg, NU Pav, and psi Peg in the near-infrared K band (2.13-2.47 microm), and gamma Hya (1.9-2.47 microm) with the VLTI/AMBER instrument at medium spectral resolution. To obtain the fundamental parameters, we compared our data with hydrostatic atmosphere models (PHOENIX). We estimated the Rosseland angular diameters of epsilon Oct, beta Peg, NU Pav, psi Peg, and gamma Hya. Together with distances and bolometric fluxes, we estimated radii, effective temperatures, and luminosities of our targets. In the beta Peg visibility, we observed a molecular layer of CO with a size similar to that modeled with PHOENIX. However, there is an additional slope in absorption starting around 2.3 microm. This slope is possibly due to a shell of water that is not modeled with PHOENIX. The visibility of psi Peg shows a low increase in the CO bands, compatible with the modeling of the PHOENIX model. The visibility data of the other sources show no increase in molecular bands. The spectra and visibilities predicted by the PHOENIX atmospheres agree with the spectra and the visibilities observed in our stars (except for beta Peg). This indicates that the opacity of the molecular bands is adequately included in the model, and the atmospheres of our targets have an extension similar to the modeled atmospheres. The atmosphere of beta Peg is more extended than that predicted by the model. The targets are located close to the red limits of the evolutionary tracks of the STAREVOL model.

arXiv commentAccepted for publication in A&A

References in corpus (27)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Spectral Irradiance Calibration in the Infrared. XIV: the Absolute Calibration of 2MASS
• The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought
• Basic physical parameters of a selected sample of evolved stars
• The NextGen Model Atmosphere grid: II. Spherically symmetric model atmospheres for giant stars with effective temperatures between 3000 and 6800~K
• Interferometric data reduction with AMBER/VLTI.Principle,estimators and illustration
• Thermohaline instability and rotation-induced mixing. III - Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars at various metallicities
• Imaging the dynamical atmosphere of the red supergiant Betelgeuse in the CO first overtone lines with VLTI/AMBER
• Interferometric observations of the supergiant stars alpha Orionis and alpha Herculis with FLUOR at IOTA
• Tests of stellar model atmospheres by optical interferometry: VLTI/VINCI limb-darkening measurements of the M4 giant psi phe
• The Mira variable S Ori: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
• Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry
• New insights into the dust formation of oxygen-rich AGB stars
• Near-IR Spectra of Red Supergiants and Giants. I- Models with Solar and with Mixing-Induced Surface Abundance Ratios
• VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere
• High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument
• J, H, K spectro-interferometry of the Mira variable S Orionis
• Cool luminous stars: the hybrid nature of their infrared spectra -- Carbon, oxygen, and their isotopic abundances in 23 K - M giant stars
• The atmospheric structure and fundamental parameters of the red supergiants AH Sco, UY Sct and KW Sgr
• Supergiant Temperatures and Linear Radii from Near-Infrared Interferometry
• Inhomogeneities in molecular layers of Mira atmospheres
• Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER
• Temporal variations of the outer atmosphere and the dust shell of the carbon-rich Mira variable V Oph probed with VLTI/MIDI
• Mid-infrared interferometric monitoring of evolved stars - The dust shell around the Mira variable RR Aql at 13 epochs
• AMBER observations of the AGB star RS Cap: extended atmosphere and comparison with stellar models
• AMBER/VLTI observations of 5 giant stars

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