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

By K. Uytterhoeven, A. Moya, A. Grigahcène, J. Guzik, J. Gutiérrez-Soto, B. Smalley, G. Handler, L. Balona, E. Niemczura, L. Machado and 31 more. 2011

280 citations recorded by the source corpus.

Context. The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. Aims. 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, and observationally investigate the relation between γ Doradus (γ Dor), δ Scuti (δ Sct), and hybrid stars. Methods. We compile a database of physical parameters for the sample stars from the literature and new ground-based observations. We analyse the Kepler light curve of each star and extract the pulsational frequencies using different frequency analysis methods. We construct two new observables, “energy ”a nd “efficiency”, related to the driving energy of the pulsation mode and the convective efficiency of the outer convective zone, respectively. Results. We propose three main groups to describe the observed variety in pulsating A-F type stars: γ Dor, δ 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 higher 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 γ Dor and δ Sct range, also between 5 and 10 d −1 , which is a challenge for the current models. We find indications for the existence of δ Sct and γ Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the δ Sct and γ Dor instability strips and beyond. Non-variable stars seem to exist within the instability strips. The location of γ Dor and δ Sct classes in the (Teff ,l ogg)-diagram has been extended. We investigate two newly constructed variables, “efficiency ”a nd “energy”, as a means to explore the relation between γ Dor and δ Sct stars. Conclusions. Our results suggest a revision of the current observational instability strips of δ Sct and γ Dor stars and imply an investigation of pulsation mechanisms to supplement the κ mechanism and convective blocking effect to drive hybrid pulsations. Accurate physical parameters for all stars are needed to confirm these findings.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/7b506133e0eb4717fbfbc5cc9042d93dcea354dc

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In Astronomy and Astrophysics

1. D. Huber
2. E. Gaidos
3. W. Chaplin
4. A. Mann
5. D. Stello
6. D. Charbonneau
7. A. Serenelli
8. T. Bedding

In Instrumentation

1. D. Huber
2. W. Chaplin
3. D. Stello
4. E. Gaidos
5. T. Bedding
6. A. Mann
7. S. Hekker
8. B. Mosser

In Statistical and Nonlinear Physics

1. A. Serenelli
2. W. Chaplin
3. D. Huber
4. E. Gaidos
5. B. Demory
6. S. Basu
7. D. Fabrycky
8. F. Bastien

Citations in the corpus

• Planet Hunters IX. KIC 8462852-where's the flux? (2015, background): “The position of KIC 8462852 is within the Gamma Doradus (γ Dor) region of the instability strip, where pulsations are observed at <5 cycles d−1 (e.g. Uytterhoeven et al. 2011).”
• Asteroseismic measurement of surface-to-core rotation in a main-sequence A star, KIC 11145123 (2014, background): “The best candidates for this are stars known as δ Sct – γ Dor hybrids, of which there are several hundred amongst the 190 000 stars observed by Kepler during its four-yea mission (Uytterhoeven et al. 2011).”
• K2 Variable Catalogue: Variable Stars and Eclipsing Binaries in K2 Campaigns 1 and 0 (2015, methodology): “Catalogues were made available using a variety of techniques (Debosscher et al. 2011; Uytterhoeven et al. 2011).”
• Rotation, differential rotation, and gyrochronology of active Kepler stars (2015, background): “To reduce the number of false positives, i.e., periodic variability not related to stellar rotation, we discarded 17 eclipsing binaries2, 878 planetary candidates3, 2 RR Lyrae stars (Kolenberg et al. 2010; Szabó et al. 2010; Benkő et al. 2010; Guggenberger et al. 2012; Nemec et al. 2011; Moskalik ”
• REVISED STELLAR PROPERTIES OF KEPLER TARGETS FOR THE QUARTER 1–16 TRANSIT DETECTION RUN (2013, background): “K dwarfs, Muirhead et al. (2012a) for M dwarfs, and Uytterhoeven et al. (2011) for A–”
• Rotation and differential rotation of active Kepler stars (2013, methodology): “Attempts were made to group the whole Kepler sample into known classes of variability like defined pulsation classes (e.g. RR Lyrae, δ Scuti, etc.), rotation induced variability, binarity, and other groups (Debosscher et al. 2011; Uytterhoeven et al. 2011).”