Interferometric radius and limb darkening of the asteroseismic red giant<i>η</i> Serpentis with the CHARA Array

Mérand, A.; Kervella, P.; Barban, C.; Josselin, E.; Brummelaar, Theo A. ten; McAlister, Harold A.; Foresto, V. Coudé du; Ridgway, Stephen T.; Turner, N.; Sturmann, J.; Sturmann, L.; Goldfinger, P. J.; Farrington, C.

doi:10.1051/0004-6361/200912103

Cited by 13 publications

(9 citation statements)

References 20 publications

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“…9). For comparison, the power law exponent α = 0.23 ± 0.05 found by Mérand et al (2010) in the K band for the red subgiant η Ser (K0III-IV) is higher than the power law exponent we find for α Cen B in the H band. η Ser is cooler than α Cen B and its effective gravity is significantly lower (T eff = 4955 K, log g = 3.2; Hekker & Meléndez 2007).…”

Section: Comparison With Literature Models and The Suncontrasting

confidence: 76%

The radii and limb darkenings of α Centauri A and B

Kervella

Bigot

Gallenne

et al. 2017

A&A

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The photospheric radius is one of the fundamental parameters governing the radiative equilibrium of a star. We report new observations of the nearest solar-type stars α Centauri A (G2V) and B (K1V) with the VLTI/PIONIER optical interferometer. The combination of four configurations of the VLTI enable us to measure simultaneously the limb darkened angular diameter θ LD and the limb darkening parameters of the two solar-type stars in the near-infrared H band (λ = 1.65 µm). We obtain photospheric angular diameters of θ LD (A) = 8.502 ± 0.038 mas (0.43%) and θ LD (B) = 5.999 ± 0.025 mas (0.42%), through the adjustment of a power law limb darkening model. We find H band power law exponents of α(A) = 0.1404 ± 0.0050 (3.6%) and α(B) = 0.1545 ± 0.0044 (2.8%), which closely bracket the observed solar value (α = 0.15027). Combined with the parallax π = 747.17 ± 0.61 mas previously determined, we derive linear radii of R A = 1.2234 ± 0.0053 R (0.43%) and R B = 0.8632 ± 0.0037 R (0.43%). The power law exponents that we derive for the two stars indicate a significantly weaker limb darkening than predicted by both 1D and 3D stellar atmosphere models. As this discrepancy is also observed on near-infrared limb darkening profile of the Sun, an improvement of the calibration of stellar atmosphere models is clearly needed. The reported PIONIER visibility measurements of α Cen A and B provide a robust basis to validate the future evolutions of these models.

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Section: Comparison With Literature Models and The Suncontrasting

confidence: 76%

The radii and limb darkenings of α Centauri A and B

Kervella

Bigot

Gallenne

et al. 2017

A&A

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“…Moreover, the model dependence on the diameter determination has also an impact on the reliability of the existing catalogs of calibrator stars for interferometry that are based on red giants with similar parameters to those studied in this work. In fact, the formal high accuracy reached on diameter determination (a fraction of 1%, Mérand et al 2010) is based only on 1D models, while we show that the correction reported in Table 3 can have a sizeable impact.…”

Section: Estimation Of Diameter Correction: 1d Versus 3d Modelsmentioning

confidence: 68%

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

Chiavassa¹,

Collet²,

Casagrande³

et al. 2010

A&A

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Context. Theoretical predictions from models of red giant branch stars are a valuable tool for various applications in astrophysics ranging from galactic chemical evolution to studies of exoplanetary systems. Aims. We use the radiative transfer code Optim3D and realistic 3D radiative-hydrodynamical (RHD) surface convection simulations of red giants to explore the impact of granulation on interferometric observables. We assess how 3D simulations of surface convection can be validated against observations. Methods. We computed intensity maps for the 3D simulation snapshots in two filters, the optical at 5000 ± 300 Å and the K band 2.14±0.26 μm FLUOR filter, corresponding to the wavelength-range of instruments mounted on the CHARA interferometer. From the intensity maps, we constructed images of the stellar disks and account for center-to-limb variations. We then derived interferometric visibility amplitudes and phases. We study their behavior with position angle and wavelength, and compare them with CHARA observations of the red giant star HD 214868. Results. We provide average limb darkening coefficients for different metallicities and wavelengths ranges. We explain prospects for detecting and characterizing granulation and center-to-limb variations of red giant stars with today's interferometers. Regarding interferometric observables, we find that the effect of convective-related surface structures depends on metallicity and surface gravity. We provide theoretical closure-phases that should be incorporated into the analysis of red giant planet companion closure phase signals. We estimate 3D−1D corrections to stellar radii determination: 3D models are ∼3.5% smaller to ∼1% larger in the optical than 1D, and roughly 0.5 to 1.5% smaller in the infrared. Even if these corrections are small, they are needed to properly set the zero point of effective temperature scale derived by interferometry and to strengthen the confidence of existing red giant catalogs of calibrating stars for interferometry. Finally, we show that our RHD simulations provide an excellent fit to the red giant HD 214868 even though more observations are needed at higher spatial frequencies and shorter wavelength.

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“…This measurement is challenging, and in some cases, such as the Kepler-138 system, the required precision is unattainable by current instrumentation. Alternatively, a direct measurement of the radius can be obtained from interferometry (Ligi et al 2016), although a slight dependence with the limb-darkening exists if the star is not completely resolved (Mérand et al 2010). This technique is not accessible for Kepler targets, but will be determinant for TESS and PLATO targets.…”

Section: Discussionmentioning

confidence: 99%

Absolute densities in exoplanetary systems: photodynamical modelling of Kepler-138

Almenara

Díaz

Dorn

et al. 2018

Monthly Notices of the Royal Astronomical Society

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In favourable conditions, the density of transiting planets in multiple systems can be determined from photometry data alone. Dynamical information can be extracted from light curves, providing modelling is done self-consistently, i.e. using a photodynamical model, which simulates the individual photometric observations instead of the more generally used transit times. We apply this methodology to the Kepler-138 planetary system. The derived planetary bulk densities are a factor of 2 more precise than previous determinations, and we find a discrepancy in the stellar bulk density with respect to a previous study. This leads, in turn, to a discrepancy in the determination of masses and radii of the star and the planets. In particular, we find that interior planet, Kepler-138b, has a size in between Mars and the Earth. Given our mass and density estimates, we characterize the planetary interiors using a generalized Bayesian inference model. This model allows us to quantify for interior degeneracy and calculate confidence regions of interior parameters such as thicknesses of the core, the mantle, and ocean and gas layers. We find that Kepler-138b and Kepler-138d have significantly thick volatile layers, and that the gas layer of Kepler-138b is likely enriched. On the other hand, Kepler-138c can be purely rocky.

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Interferometric radius and limb darkening of the asteroseismic red giantη Serpentis with the CHARA Array

Cited by 13 publications

References 20 publications

The radii and limb darkenings of α Centauri A and B

The radii and limb darkenings of α Centauri A and B

Three-dimensional hydrodynamical simulations of red giant stars: semi-global models for interpreting interferometric observations

Absolute densities in exoplanetary systems: photodynamical modelling of Kepler-138

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