The Kepler characterization of the variability among A- and F-type stars I. General overview

Uytterhoeven, K. and Moya, A. and Grigahcene, A. and Guzik, J. A. and Gutierrez-Soto, J. and Smalley, B. and Handler, G. and Balona, L. A. and Niemczura, E. and Fox Machado, L. and Benatti, S. and Chapellier, E. and Tkachenko, A. and Szabo, R. and Suarez, J. C. and Ripepi, V. and Pascual, J. and Mathias, P. and Martin-Ruiz, S. and Lehmann, H. and Jackiewicz, J. and Hekker, S. and Gruberbauer, M. and Garcia, R. A. and Dumusque, X. and Diaz-Fraile, D. and Bradley, P. and Antoci, V. and Roth, M. and Leroy, B. and Murphy, S. J. and De Cat, P. and Cuypers, J. and Kjeldsen, H. and Christensen-Dalsgaard, J. and Breger, M. and Pigulski, A. and Kiss, L. L. and Still, M. and Thompson, S. E. and Van Cleve, J. (2011) The Kepler characterization of the variability among A- and F-type stars I. General overview. Astronomy & Astrophysics, 534:A125. ISSN 0004-6361

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The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 c/d, which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips, and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (Teff,logg)-diagram has been extended. We investigate two newly constructed variables 'efficiency' and 'energy' as a means to explore the relation between gamma Dor and delta Sct stars. Our results suggest a revision of the current observational instability strips, and imply an investigation of other pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: File reproduced in accordance with the copyright policy of the publisher/author.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 26 Apr 2022 05:51
Last Modified: 06 May 2022 02:35
Uncontrolled Keywords: stars: oscillations, stars: fundamental parameters, binaries: general, asteroseismology, stars: variables: δ Scuti, stars: statistics, Astrophysics - Solar and Stellar Astrophysics
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
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