Towards stellar seismology of massive pulsators with the CoRoT and Kepler satellites
Zusammenfassung der Projektergebnisse
We analysed the light curves based on survey phase data recorded by Kepler and CoRoT with time spans between 9 d and 322 d for their associated frequency spectra of 750 candidate A-F type stars and two stars observed by Kepler (KIC 6761539, KIC 6443122) for in-depth seismic studies. The analysis was carried out in search for a better understanding of the stellar structure and oscillation driving mechanisms acting in δ Sct, γ Dor, and hybrid pulsators. The main results are: • Observationally, we propose three main groups to describe the observed variety: γDor, δ Sct, and hybrid stars. The latter group includes both δ Sctdominated and γ Dor-dominated hybrid stars. About 63% of the sample are unambiguously assigned to one of the three groups. About 23% of the sample are hybrid candidates (171 stars, or 36% of the stars assigned to the three groups). This is in strong contrast with the number of hybrid candidates so far observed from the ground. • We presented a characterization of the stars in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes, which provides valuable feedback for models and instability studies. This is the first time that this kind of information is available for a substantial sample of stars. Up to 500 non-combination frequencies are detected in the Kepler time series of a single star. The highest pulsation amplitude measured is 58 000 ppm. The shortest detected δ Sct periods are about 18min.We find that hybrid stars show all kinds of periodicities within the γ Dor and δ Sct range. In particular, the majority of hybrid stars shows frequencies between 5 and 10 d^−1. From a theoretical point of view, this result presents a number of challenges, because the currently accepted over-stability mechanisms cannot explain the presence of pulsational modes in the wide frequency ranges observed with Kepler. • The fast rotation of the selected targets for in-depth seismic study was a “surprise”, which complicates the identification of modes. We found that longer ground-based data are needed to allow for a clear assignment of the spatial oscillation pattern on the stellar surface. Nevertheless first models with a simplified inclusion of stellar rotation have been created. Many more (candidate) δ Sct, γ Dor, and hybrid stars are expected to be among the stars observed by Kepler and CoRoT. Also, a considerable fraction of the host stars of the published Kepler planet candidates turn out to be A-F type stars. Hence, we have promising prospects in studying and understanding the A-F type star variable behaviour in detail, to characterise planet-hosting stars better.
Projektbezogene Publikationen (Auswahl)
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2011, The Kepler characterization of the variability among A- and F-type stars. I. General overview, Astron. Astrophys. 534, 125
Uytterhoeven, K.; Moya, A.; Grigahcène, A.; Guzik, J. A.; Gutiérrez-Soto, J.; Smalley, B.; Handler, G.; Balona, L. A.; Niemczura, E.; Fox Machado, L.; et al.
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2011, Variability of A- and F-stars from Kepler (Uytterhoeven+ 2011), VizieR On-line Data Catalog: J/A+A/534/A125. Data products published in: 2011A&A...534A.125U
Uytterhoeven, K.; Moya, A.; Grigahcene, A.; Guzik, J. A.; Gutierrez-Soto, J.; Smalley, B.; Handler, G.; Balona, L. A.; Niemczura, E.; Fox Machado, L.; et al.
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2012, A Uniform Asteroseismic Analysis of 22 Solar-type Stars Observed by Kepler, Astrophy. J. 749, 152
Mathur, S.; Metcalfe, T. S.; Woitaszek, M.; Bruntt, H.; Verner, G. A.; Christensen-Dalsgaard, J.; Creevey, O. L.; Dogan, G.; Basu, S.; Karoff, C.; et al.
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2012, Ground-based multi-color photometry of the gamma Doradus-delta Scuti hybrid star KIC 6761539, Astron. N. 333, 1077
Herzberg, W.; Uytterhoeven, K.; Roth, M.
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2012, Kappa-effect and brightness oscillations of stars, Astron. N. 333, 926
Zhugzhda, Y. D.; Roth, M.; Herzberg, W.
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2014, KIC 6761539, a fast rotating gamma Dor - delta Sct hybrid star, Published in “Precision Asteroseismology”, Proceedings of the International Astronomical Union, IAU Symposium, Volume 301, pp. 419-420
Herzberg, W.; Corre, D.; Uytterhoeven, K.; Roth, M.
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2014, Pysca - Automated frequency extraction from photometric time series, published in “Precision Asteroseismology”, Proceedings of the International Astronomical Union, IAU Symposium, Volume 301, pp. 421-422
Herzberg, W.; Glogowski, K.
