Volume 534, October 2011
|Number of page(s)||70|
|Section||Catalogs and data|
|Published online||19 October 2011|
The Kepler characterization of the variability among A- and F-type stars
I. General overview
Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot; CEA, IRFU, SAp, Centre de Saclay,
2 Kiepenheuer-Institut für Sonnenphysik, Schöneckstraße 6, 79104 Freiburg im Breisgau, Germany
3 Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain ; Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
4 Laboratorio de Astrofísica Estelar y Exoplanetas, LAEX-CAB (INTA-CSIC), PO BOX 78, 28691 Villanueva de la Cañada, Madrid, Spain
5 Centro de Astrofísica, Faculdade de Ciências, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
6 Los Alamos National Laboratory, XTD-2, Los Alamos, NM 87545-2345, USA
7 Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
8 LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 92195 Meudon, France
9 Valentian International University, Prolongación C/ José Pradas Gallen, s/n 12006 Castellón de la Plana, Spain
10 Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
11 Institut für Astronomie, Türkenschanzstraße 17, 1180 Wien, Austria
12 Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
13 South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
14 Instytut Astronomiczny, Uniwersytet Wrocławski, Kopernika 11, 51-622 Wrocław, Poland
15 Observatorio Astronómico Nacional, Instituto de Astronomía, UNAM, Ensenada B.C., Apdo. Postal 877, Mexico
16 CISAS, Padova University, via Venezia 15, 35131 Padova, Italy
17 INAF - Astronomical Observatory of Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
18 UMR 6525 H. Fizeau, UNS, CNRS, OCA, Campus Valrose, 06108 Nice Cedex 2, France
19 Instituut voor Sterrenkunde, K.U.Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
20 Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest PO Box 67, Hungary
21 INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
22 Lab. d’Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 57 avenue d’Azereix, 65000 Tarbes, France
23 Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany
24 Department of Astronomy, New Mexico State University, Las Cruces, NM 88001, USA
25 Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
26 University of Birmingham, School of Physics and Astronomy, Edgbaston, Birmingham B15 2TT, UK
27 Department of Astronomy and Physics, Saint Marys University, Halifax, NS B3H 3C3, Canada
28 Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
29 Los Alamos National Laboratory, XCP-6, MS T-087, Los Alamos, NM 87545-2345, USA
30 Jeremiah Horrocks Institute of Astrophysics, University of Central Lancashire, Preston PR1 2HE, UK
31 Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
32 Department of Physics and Astronomy, University of Aarhus, bygn. 1520, Ny Munkegade, 8000 Aarhus C., Denmark
33 Department of Astronomy, University of Texas, Austin, TX 78712, USA
34 Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW, 2006, Australia
35 Bay Area Environmental Research Inst./NASA Ames Research Center, Moffett Field, CA 94035, USA
36 SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035, USA
Received: 30 May 2011
Accepted: 29 June 2011
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” and “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, log g)-diagram has been extended. We investigate two newly constructed variables, “efficiency” and “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.
Key words: stars: oscillations / stars: fundamental parameters / binaries: general / asteroseismology / stars: variables:δScuti / stars: statistics
© ESO, 2011
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