Volume 489, Number 3, October III 2008
|Page(s)||1213 - 1224|
|Section||Stellar structure and evolution|
|Published online||08 August 2008|
I. Results from the ground-based campaign
INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
2 Instituto de Astrofísica de Canarias, Calle Via Láctea s/n, 38205 La Laguna, Spain e-mail: email@example.com
3 UMR 6525 H. Fizeau, UNS, CNRS, OCA, Campus Valrose, 06108 Nice Cedex 2, France
4 Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
5 Institute of Astronomy, KULeuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
6 Astronomical Institute of the Wroclaw University, ul. Kopernika 11, 51-622 Wroclaw, Poland
7 Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
8 Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
Accepted: 5 July 2008
Context. We present an extensive ground-based photometric and spectroscopic campaign of the γ Dor CoRoT target HD 49434. This campaign was a preparatory step of the CoRoT satellite observations, which occurred between October 2007 and March 2008.
Aims. With satellite data, detection of low-degree pulsation modes only is achievable, and, as no filters are available, with poor identification. Ground-based data promise eventually to identify additional modes and provide extra input for the identification: spectroscopic data allows the detection of high-degree modes and an estimate of the azimuthal number m. We attempt to detect and identify as many pulsation modes as possible from the ground-based dataset of the γ Dor star HD 49434, and anticipate the CoRoT results.
Methods. We searched for frequencies in the multi-colour variations, the pixel-to-pixel variations across the line profiles, and the moments variations in a large dataset, consisting of both multi-colour photometric and spectroscopic data from different observatories, using different frequency analysis methods. We performed a tentative mode identification of the spectroscopic frequencies using the Moment Method and the Intensity Period Search Method. We also completed an abundance analysis.
Results. The frequency analysis clearly indicates the presence of four frequencies in the 0.2-1.7 d-1 interval, as well as six frequencies in the 5-12 d-1 domain. The low frequencies are typical of γ Dor variables, while the high frequencies are common to δ Sct pulsators. We propose that the frequency 2.666 d-1 is the rotational frequency. All modes, for which an identification was possible, appear to be high-degree modes (3 ≤ ≤ 8). We did not find evidence for a possible binary nature of the star HD 49434. The element abundances that we derived are consistent with values obtained in previous analyses.
Conclusions. We classify the γ Dor star HD 49434 as a hybrid pulsator, which pulsates simultaneously in p- and g-modes. This implies that HD 49434 is an extremely interesting target for asteroseismic modelling.
Key words: stars: oscillations / stars: individual: HD 49434 / line: profiles / stars: variables: δ Sct
Based on observations made with ESO Telescopes at the La Silla Observatory under the ESO Large Programme: LP178.D-0361, and on data collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Also based on observations obtained at Observatorio de Sierra Nevada (Spain), at Observatorio Astronómico Nacional San Pedro Mártir (Mexico), at the Piszkéstetõ Mountain Station of Konkoly Observatory (Hungary), at Observatoire de Haute Provence (France) and at Mount John University Observatory (New Zealand).
© ESO, 2008
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