Volume 550, February 2013
|Number of page(s)||7|
|Section||Stellar structure and evolution|
|Published online||21 January 2013|
Constraining magnetic-activity modulations in three solar-like stars observed by CoRoT and NARVAL
1 High Altitude Observatory, NCAR, PO Box 3000, Boulder, CO 80307, USA
2 Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot; IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France
3 CNRS, Institut de Recherche en Astrophysique et Planétologie, 14 avenue Edouard Belin, 31400 Toulouse, France
e-mail: email@example.com; firstname.lastname@example.org; email@example.com;
4 Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
5 Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
6 Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
7 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
8 LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, 92195 Meudon Cedex, France
Received: 18 August 2011
Accepted: 28 November 2011
Context. Stellar activity cycles are the manifestation of dynamo process running in the stellar interiors. They have been observed from years to decades thanks to the measurement of stellar magnetic proxies on the surface of the stars, such as the chromospheric and X-ray emissions, and to the measurement of the magnetic field with spectropolarimetry. However, all of these measurements rely on external features that cannot be visible during, for example, a Maunder-type minimum. With the advent of long observations provided by space asteroseismic missions, it has been possible to penetrate the stars and study their properties. Moreover, the acoustic-mode properties are also perturbed by the presence of these dynamos.
Aims. We track the temporal variations of the amplitudes and frequencies of acoustic modes allowing us to search for signature of magnetic activity cycles, as has already been done in the Sun and in the CoRoT target HD 49933.
Methods. We used asteroseimic tools and more classical spectroscopic measurements performed with the NARVAL spectropolarimeter to check that there are hints of any activity cycle in three solar-like stars observed continuously for more than 117 days by the CoRoT satellite: HD 49385, HD 181420, and HD 52265. To consider that we have found a hint of magnetic activity in a star we require finding a change in the amplitude of the p modes that should be anti-correlated with a change in their frequency shifts, as well as a change in the spectroscopic observations in the same direction as the asteroseismic data.
Results. Our analysis gives very small variation in the seismic parameters preventing us from detecting any magnetic modulation. However, we are able to provide a lower limit of any magnetic-activity change in the three stars that should be longer than 120 days, which is the length of the time series. Moreover we computed the upper limit for the line-of-sight magnetic field component being 1, 3, and 0.6 G for HD 49385, HD 181420, and HD 52265, respectively. More seismic and spectroscopic data would be required to have a firm detection in these stars.
Key words: asteroseismology / methods: data analysis / stars: solar-type / stars: activity / stars: general
© ESO, 2013
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