We present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant stars for which solarlike oscillations have been detected by either Kepler or CoRoT. By combining interferometric angular diameters, Hipparcos parallaxes, asteroseismic densities, bolometric fluxes, and high-resolution spectroscopy, we derive a full set of near-model-independent fundamental properties for the sample. We first use these properties to test asteroseismic scaling relations for the frequency of maximum power (ν max ) and the large frequency separation (Δν). We find excellent agreement within the observational uncertainties, and empirically show that simple estimates of asteroseismic radii for main-sequence stars are accurate to 4%. We furthermore find good agreement of our measured effective temperatures with spectroscopic and photometric estimates with mean deviations for stars between T eff = 4600-6200 K of −22 ± 32 K (with a scatter of 97 K) and −58 ± 31 K (with a scatter of 93 K), respectively. Finally, we present a first comparison with evolutionary models, and find differences between observed and theoretical properties for the metal-rich main-sequence star HD 173701. We conclude that the constraints presented in this study will have strong potential for testing stellar model physics, in particular when combined with detailed modeling of individual oscillation frequencies.
We present the results of long-baseline optical interferometry observations using the Precision Astronomical Visual Observations (PAVO) beam combiner at the Center for High Angular Resolution Astronomy (CHARA) Array to measure the angular sizes of three bright Kepler stars: θ Cygni, and both components of the binary system 16 Cygni. Supporting infrared observations were made with the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the CHARA Array. We find limb-darkened angular diameters of 0.753 ± 0.009 mas for θ Cyg, 0.539 ± 0.007 mas for 16 Cyg A and 0.490 ± 0.006 mas for 16 Cyg B. The Kepler Mission has observed these stars with outstanding photometric precision, revealing the presence of solar-like oscillations. Due to the brightness of these stars the oscillations have exceptional signal-to-noise, allowing for detailed study through asteroseismology, and are well constrained by other observations. We have combined our interferometric diameters with Hipparcos parallaxes, spectrophotometric bolometric fluxes and the asteroseismic large frequency separation to measure linear radii (θ Cyg: 1.48±0.02 R ⊙ , 16 Cyg A: 1.22±0.02 R ⊙ , 16 Cyg B: 1.12±0.02 R ⊙ ), effective temperatures (θ Cyg: 6749±44 K, 16 Cyg A: 5839±42 K, 16 Cyg B: 5809±39 K), and masses (θ Cyg: 1.37±0.04 M ⊙ , 16 Cyg A: 1.07±0.05 M ⊙ , 16 Cyg B: 1.05±0.04 M ⊙ ) for each star with very little model dependence. The measurements presented here will provide strong constraints for future stellar modelling efforts.
Optical and infrared interferometers definitively established that the photometric standard Vega (= α Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner (MIRC6) on the Center for High Angular Resolution Astronomy (CHARA) Array. With our greater angular resolution and dense (u,v)-coverage, we find Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and also consistent with the possible rotational period of ∼0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of 2.15 +0.10 −0.15 M ⊙ and an age 700 −75 +150 Myrs, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z = 0.006 +0.003 −0.002 ).
The Kepler satellite reveals details of the oscillations patterns of an evolved star in an exotic triple-star system.
We report here an analysis of the physical stellar parameters of the giant star HD 185351 using Kepler short-cadence photometry, optical and near infrared interferometry from CHARA, and high-resolution spectroscopy. Asteroseismic oscillations detected in the Kepler short-cadence photometry combined with an effective temperature calculated from the interferometric angular diameter and bolometric flux yield a mean density, ρ ⋆ = 0.0130 ± 0.0003 ρ ⊙ and surface gravity, log g = 3.280 ± 0.011. Combining the gravity and density we find R ⋆ = 5.35 ± 0.20 R ⊙ and M ⋆ = 1.99 ± 0.23 M ⊙ . The trigonometric parallax and CHARA angular diameter give a radius R ⋆ = 4.97 ± 0.07 R ⊙ . This smaller radius, when combined with the mean stellar density, corresponds to a stellar mass 1.60 ± 0.08 M ⊙ , which is smaller than the asteroseismic mass by 1.6-σ. We find that a larger mass is supported by the observation of mixed modes in our high-precision photometry, the spacing of which is consistent only for M ⋆ 1.8 M ⊙ . Our various and independent mass measurements can be compared to the mass measured from interpolating the spectroscopic parameters onto stellar evolution models, which yields a model-based mass M ⋆,model = 1.87 ± 0.07 M ⊙ . This mass agrees well with the asteroseismic value, but is 2.6-σ higher than the mass from the combination of asteroseismology and interferometry. The discrepancy motivates future studies with a larger sample of giant stars. However, all of our mass measurements are consistent with HD 185351 having a mass in excess of 1.5 M ⊙ . 10 In the analysis described later we make use of the BaSTI model grids. We have confirmed that using the BaSTI grids in our iterative SME analysis yields the same result as using the Y 2 grids.
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