Asteroseismic inferences on red giants in open clusters NGC 6791, NGC 6819, and NGC 6811 using<i>Kepler</i>

Hekker, S.; Basu, Sarbani; Stello, Dennis; Kallinger, T.; Grundahl, F.; Mathur, S.; García, R. A.; Mosser, B.; Huber, Daniel; Bedding, Timothy R.; Szabo, Robert M.; Ridder, J. De; Chaplin, W. J.; Elsworth, Y.; Hale, Steven J.; Christensen‐Dalsgaard, J.; Gilliland, Ronald L.; Still, M.; McCauliff, Sean; Quintana, Elisa V.

doi:10.1051/0004-6361/201016303

Cited by 67 publications

(68 citation statements)

References 56 publications

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“…The peak in the mass distribution for NGC 6819 in Fig. 2 in Hekker et al (2011a) is also located at a mass close to 1.5 M . This is significantly less than the mass 1.68 ± 0.03 M derived for RG stars in NGC 6819 by Basu et al (2011) using asteroseismic grid modelling with Kepler light curves.…”

Section: Discussionmentioning

confidence: 93%

KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

Frandsen

Lehmann

Hekker

et al. 2013

A&A

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119

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Context. Detached eclipsing binaries (dEBs) are ideal targets for accurately measuring the masses and radii of their component stars. If at least one of the stars has evolved off the main sequence (MS), the masses and radii give a strict constraint on the age of the stars. Several dEBs containing a bright K giant and a fainter MS star have been discovered by the Kepler satellite. The mass and radius of a red giant (RG) star can also be derived from its asteroseismic signal. The parameters determined in this way depend on stellar models and may contain systematic errors. It is important to validate the asteroseismically determined mass and radius with independent methods. This can be done when stars are members of stellar clusters or members of dEBs. Aims. This paper presents an analysis of the dEB system KIC 8410637, which consists of an RG and an MS star. The aim is to derive accurate masses and radii for both components and provide the foundation for a strong test of the asteroseismic method and the accuracy of the deduced mass, radius, and age. Methods. We analysed high-resolution, high-signal-to-noise spectra from three different spectrographs. We also calculated a fit to the Kepler light curve and used ground-based photometry to determine the flux ratios between the component stars in the BVRI passbands. Results. We measured the masses and radii of the stars in the dEB, and the classical parameters T eff , log g, and [Fe/H] from the spectra and ground-based photometry. The RG component of KIC 8410637 is most likely in the core helium-burning red clump phase of evolution and has an age and composition that are very similar to the stars in the open cluster NGC 6819. The mass of the RG in KIC 8410637 should therefore be similar to the mass of RGs in NGC 6819, thus lending support to the latest version of the asteroseismic scaling relations. This is the first direct measurement of both mass and radius for an RG to be compared with values for RGs from asteroseismic scaling relations thereby providing an accurate comparison. We find excellent agreement between log g values derived from the binary analysis and asteroseismic scaling relations. Conclusions. We have determined the masses and radii of the two stars in the binary accurately. A detailed asteroseismic analysis will be presented in a forthcoming paper, allowing an informative comparison between the parameters determined for the dEB and from asteroseismology.

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Section: Discussionmentioning

confidence: 93%

KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

Frandsen

Lehmann

Hekker

et al. 2013

A&A

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119

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“…This involves exploiting the correlation between the asteroseismic observables and apparent magnitude for stars with very similar mass and effective temperature. The asteroseismology of seven stars (one early AGB and six red clump) have been discussed by different authors (Stello et al 2011a,b;Hekker et al 2011;Corsaro et al 2012), but we have redone the asteroseismic analysis of the nine NGC 6811 candidates using all available long-cadence data from Kepler (starting with either quarters 0 or 1 and reaching quarter 17) in Data Release 23. The longer time baseline compared to previous studies has allowed us to reduce the previously determined uncertainties on the asteroseismic parameters ∆ν and ν max by almost a factor of 1.5 − 2 relative to Corsaro et al (2012).…”

Section: Red Clump Stars and Asteroseismologymentioning

confidence: 99%

“…The brightest stars of the open cluster NGC 6811 comprise a rich set of objects with astrophysical information that has not yet been fully exploited. On the cool side, there are a group of helium-burning red clump and asymptotic giant stars with solar-like oscillations previously detected with the Kepler spacecraft (Stello et al 2011a,b;Hekker et al 2011;Corsaro et al 2012). On the hot side, the bright end of the main sequence fits neatly within the instability strip, and δ Scuti (Sct) and γ Doradus (Dor) pulsating stars have been previously identified (van Cauteren et al 2005;Luo et al 2009;Debosscher et al 2011;Uytterhoeven et al 2011).…”

Section: Introductionmentioning

confidence: 99%

THE AGE AND DISTANCE OF THE KEPLER OPEN CLUSTER NGC 6811 FROM AN ECLIPSING BINARY, TURNOFF STAR PULSATION, AND GIANT ASTEROSEISMOLOGY^∗

Sandquist

Jessen-Hansen

Shetrone³

et al. 2016

ApJ

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We present the analysis of an eccentric, partially eclipsing long-period (P = 19.23 d) binary system KIC 9777062 that contains main sequence stars near the turnoff of the intermediate age open cluster NGC 6811. The primary is a metal-lined Am star with a possible convective blueshift to its radial velocities, and one star (probably the secondary) is likely to be a γ Dor pulsator. The component masses are 1.603 ± 0.006(stat.)±0.016(sys.) and 1.419 ± 0.003 ± 0.008M , and the radii are 1.744 ± 0.004 ± 0.002 and 1.544 ± 0.002 ± 0.002R . The isochrone ages of the stars are mildly inconsistent: the age from the mass-radius combination for the primary (1.05±0.05±0.09 Gyr, where the last quote was systematic uncertainty from models and metallicity) is smaller than that from the secondary (1.21 ± 0.05 ± 0.15 Gyr) and is consistent with the inference from the color-magnitude diagram (1.00 ± 0.05 Gyr). We have improved the measurements of the asteroseismic parameters ∆ν and ν max for helium-burning stars in the cluster. The masses of the stars appear to be larger (or alternately, the radii appear to be smaller) than predicted from isochrones using the ages derived from the eclipsing stars. The majority of stars near the cluster turnoff are pulsating stars: we identify a sample of 28 δ Sct, 15 γ Dor, and 5 hybrid types. We used the period-luminosity relation for high-amplitude δ Sct stars to fit the ensemble of the strongest frequencies for the cluster members, finding (m − M ) V = 10.37 ± 0.03. This is larger than most previous determinations, but smaller than values derived from the eclipsing binary (10.47 ± 0.05).

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“…This has the potential to strengthen the procedure followed in this paper. Furthermore, NGC 6791 is in the Field-OfView of the NASA Kepler mission (Borucki et al 2010), which will not only allow many more detached eclipsing binaries to be found and measured, but also complementary model constraints from asteroseismology of the giant stars in the cluster Hekker et al 2011;Pablo et al 2011;Stello et al 2011;Corsaro et al 2012;Miglio et al 2012). All our acceptable model fits give a mass on the RGB at the V-magnitude of the RC in the range 1.15 ± 0.02 M which will be an important consistency check, along with the age and helium content, for future detailed asteroseismic modelling of the cluster giants.…”

Section: Summary Conclusion and Outlookmentioning

confidence: 99%

Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members

Brogaard

VandenBerg

Bruntt

et al. 2012

A&A

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Context. Models of stellar structure and evolution can be constrained by measuring accurate parameters of detached eclipsing binaries in open clusters. Multiple binary stars provide the means to determine helium abundances in these old stellar systems, and in turn, to improve estimates of their age. Aims. In the first paper of this series, we demonstrated how measurements of multiple eclipsing binaries in the old open cluster NGC 6791 sets tighter constraints on the properties of stellar models than has previously been possible, thereby potentially improving both the accuracy and precision of the cluster age. Here we add additional constraints and perform an extensive model comparison to determine the best estimates of the cluster age and helium content, employing as many observational constraints as possible. Methods. We improve our photometry and correct empirically for differential reddening effects. We then perform an extensive comparison of the new colour-magnitude diagrams (CMDs) and eclipsing binary measurements to Victoria and DSEP isochrones in order to estimate cluster parameters. We also reanalyse a spectrum of the star 2-17 to improve [Fe/H] constraints. Results. We find a best estimate of the age of ∼8.3 Gyr for NGC 6791 while demonstrating that remaining age uncertainty is dominated by uncertainties in the CNO abundances. The helium mass fraction is well constrained at Y = 0.30 ± 0.01 resulting in ΔY/ΔZ ∼ 1.4 assuming that such a relation exists. During the analysis we firmly identify blue straggler stars, including the star 2-17, and find indications for the presence of their evolved counterparts. Our analysis supports the RGB mass-loss found from asteroseismology and we determine precisely the absolute mass of stars on the lower RGB, M RGB = 1.15 ± 0.02 M . This will be an important consistency check for the detailed asteroseismology of cluster stars. Conclusions. Using multiple, detached eclipsing binaries for determining stellar cluster ages, it is now possible to constrain parameters of stellar models, notably the helium content, which were previously out of reach. By observing a suitable number of detached eclipsing binaries in several open clusters, it will be possible to calibrate the age-scale and the helium enrichment parameter Δ Y/Δ Z, and provide firm constraints that stellar models must reproduce.

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Asteroseismic inferences on red giants in open clusters NGC 6791, NGC 6819, and NGC 6811 usingKepler

Cited by 67 publications

References 56 publications

KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

THE AGE AND DISTANCE OF THE KEPLER OPEN CLUSTER NGC 6811 FROM AN ECLIPSING BINARY, TURNOFF STAR PULSATION, AND GIANT ASTEROSEISMOLOGY^∗

Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members

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Asteroseismic inferences on red giants in open clusters NGC 6791, NGC 6819, and NGC 6811 usingKepler

Cited by 67 publications

References 56 publications

KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

KIC 8410637: a 408-day period eclipsing binary containing a pulsating giant star

THE AGE AND DISTANCE OF THE KEPLER OPEN CLUSTER NGC 6811 FROM AN ECLIPSING BINARY, TURNOFF STAR PULSATION, AND GIANT ASTEROSEISMOLOGY∗

Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members

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THE AGE AND DISTANCE OF THE KEPLER OPEN CLUSTER NGC 6811 FROM AN ECLIPSING BINARY, TURNOFF STAR PULSATION, AND GIANT ASTEROSEISMOLOGY^∗