Volume 552, April 2013
|Number of page(s)||13|
|Section||Planets and planetary systems|
|Published online||13 March 2013|
A coordinated optical and X-ray spectroscopic campaign on HD 179949: searching for planet-induced chromospheric and coronal activity
1 INAF-Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
2 INAF-Osservatorio Astronomico di Palermo “G. S. Vaiana”, Piazza del Parlamento 1, 90134 Palermo, Italy
3 School of Physics and Astronomy, Univ. of St. Andrews, St Andrews, Scotland KY16 9SS, UK
4 Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ, 86001, USA
5 HIA/NRC, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
6 School of Mathematics and Physics, University of Tasmania, PB 37 GP0 Hobart, Tasmania 7001, Australia
7 IRAP-UMR 5277, CNRS & Univ. de Toulouse, 14 Av. E. Belin, 31400 Toulouse, France
8 Fundación Galileo Galilei – INAF, Rambla José Ana Fernández Pérez, 7, 38712 Breña Baja, TF, Spain
9 LAM-UMR 6110, CNRS & Univ. de Provence, 38 rue Fréderic Juliot-Curie, 13013 Marseille, France
Received: 22 June 2012
Accepted: 23 December 2012
Context. HD 179949 is an F8V star, orbited by a close-in giant planet with a period of ~3 days. Previous studies suggested that the planet enhances the magnetic activity of the parent star, producing a chromospheric hot spot which rotates in phase with the planet orbit. However, this phenomenon is intermittent since it was observed in several but not all seasons.
Aims. A long-term monitoring of the magnetic activity of HD 179949 is required to study the amplitude and time scales of star-planet interactions.
Methods. In 2009 we performed a simultaneous optical and X-ray spectroscopic campaign to monitor the magnetic activity of HD 179949 during ~5 orbital periods and ~2 stellar rotations. We analyzed the Ca ii H&K lines as a proxy for chromospheric activity, and we studied the X-ray emission in search of flux modulations and to determine basic properties of the coronal plasma.
Results. A detailed analysis of the flux in the cores of the Ca ii H&K lines and a similar study of the X-ray photometry shows evidence of source variability, including one flare. The analysis of the time series of chromospheric data indicates a modulation with a ~11 days period, compatible with the stellar rotation period at high latitudes. Instead, the X-ray light curve suggests a signal with a period of ~4 days, consistent with the presence of two active regions on opposite hemispheres.
Conclusions. The observed variability can be explained, most likely, as due to rotational modulation and to intrinsic evolution of chromospheric and coronal activity. There is no clear signature related to the orbital motion of the planet, but the possibility that just a fraction of the chromospheric and coronal variability is modulated with the orbital period of the planet, or the stellar-planet beat period, cannot be excluded. We conclude that any effect due to the presence of the planet is difficult to disentangle.
Key words: planet-star interactions / stars: activity / stars: magnetic field / stars: solar-type
© ESO, 2013
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