## Scientific Publications

On this page you will find a list of all peer reviewed KASC publications that have been published in a scientific journal.

### Kepler Observations of the Asteroseismic Binary HD 176465

T. R. White, O. Benomar, V. Silva Aguirre, W. H. Ball, T. R. Bedding, W. J. Chaplin, J. Christensen-Dalsgaard, R. A. Garcia, L. Gizon, D. Stello, S. Aigrain, H. M. Antia, T. Appourchaux, M. Bazot, T. L. Campante, O. L. Creevey, G. R. Davies and 17 coauthors.
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Binary star systems are important for understanding stellar structure and evolution, and are especially useful when oscillations can be detected and analysed with asteroseismology. However, only four systems are known in which solar-like oscillations are detected in both components. Here, we analyse the fifth such system, HD 176465, which was observed by Kepler. We carefully analysed the system's power spectrum to measure individual mode frequencies, adapting our methods where necessary to accommodate the fact that both stars oscillate in a similar frequency range. We also modelled the two stars independently by fitting stellar models to the frequencies and complementary spectroscopic parameters. We are able to cleanly separate the oscillation modes in both systems. The stellar models produce compatible ages and initial compositions for the stars, as is expected from their common and contemporaneous origin. Combining the individual ages, the system is about $3.0\pm0.5\,\mathrm{Gyr}$ old. The two components of HD 176465 are young physically-similar oscillating solar analogues, the first such system to be found, and provide important constraints for stellar evolution and asteroseismology.

### Convective-core overshoot and suppression of oscillations: Constraints from red giants in NGC 6811

T. Arentoft, K. Brogaard, J. Jessen-Hansen, V. Silva Aguirre, H. Kjeldsen, J. R. Mosumgaard, E. L. Sandquist.
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Using data from the NASA spacecraft Kepler, we study solar-like oscillations in red-giant stars in the open cluster NGC 6811. We determine oscillation frequencies, frequency separations, period spacings of mixed modes and mode visibilities for eight cluster giants. The oscillation parameters show that these stars are helium-core-burning red giants. The eight stars form two groups with very different oscillation power spectra; the four stars with lowest $\Delta\nu$-values display rich sets of mixed $l=1$ modes, while this is not the case for the four stars with higher $\Delta\nu$. For the four stars with lowest $\Delta\nu$, we determine the asymptotic period spacing of the mixed modes, $\Delta$P, which together with the masses we derive for all eight stars suggest that they belong to the so-called secondary clump. Based on the global oscillation parameters, we present initial theoretical stellar modeling which indicate that we can constrain convective-core overshoot on the main sequence and in the helium-burning phase for these $\sim$2 M$_{\odot}$ stars. Finally, our results indicate less mode suppression than predicted by recent theories for magnetic suppression of certain oscillation modes in red giants.

### Kepler sheds new and unprecedented light on the variability of a blue supergiant: gravity waves in the O9.5Iab star HD188209

Conny Aerts, Sergio Simon-Diaz, S. Bloemen, J. Debosscher, P. I. Pápics, S. Bryson, M. Still, E. Moravveji, M. H. Williamson, F. Grundahl, M. Fredslund Andersen, V. Antoci, P. L. Pallé, J. Christensen-Dalsgaard, T. M. Rogers.
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Context. Stellar evolution models are most uncertain for evolved massive stars. Asteroseismology based on high-precision uninterrupted space photometry has become a new way to test the outcome of stellar evolution theory and was recently applied to a multitude of stars, but not yet to massive evolved supergiants.
Aims. Our aim is to detect, analyse and interpret the photospheric and wind variability of the O9.5 Iab star HD188209 from Kepler space photometry and long-term high-resolution spectroscopy.
Methods. We used Kepler scattered-light photometry obtained by the nominal mission during 1460 d to deduce the photometric variability of this O-type supergiant. In addition, we assembled and analysed high-resolution high signal-to-noise spectroscopy taken with four spectrographs during some 1800 d to interpret the temporal spectroscopic variability of the star.
Results. The variability of this blue supergiant derived from the scattered-light space photometry is fully in agreement with the one found in the ground-based spectroscopy.We find significant low-frequency variability that is consistently detected in all spectral lines of HD188209. The photospheric variability propagates into the wind, where it has similar frequencies but slightly higher amplitudes.
Conclusions. The morphology of the frequency spectra derived from the long-term photometry and spectroscopy points towards a spectrum of travelling waves with frequency values in the range expected for an evolved O-type star. Convectively-driven internal gravity waves excited in the stellar interior offer the most plausible explanation of the detected variability.

### Hybrid Î³ Doradus-Î´ Scuti Pulsators: New Insights into the Physics of the Oscillations from Kepler Observations

A. GrigahcÃ¨ne, V. Antoci, L. Balona, G. Catanzaro, J. DaszyÅ„ska-Daszkiewicz, J. A. Guzik, G. Handler, G. Houdek, D. W. Kurtz, M. Marconi, M. J. P. F. G. Monteiro, A. Moya, V. Ripepi, J.-C. SuÃ¡rez, K. Uytterhoeven, W. J. Borucki, T. M. Brown and 25 coauthors.
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