The GAPS programme with HARPS-N at TNG

VII. Putting exoplanets in the stellar context: magnetic activity and asteroseismology of τ Bootis A^⋆,⋆⋆

¹ INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
e-mail: francesco.borsa@brera.inaf.it
² INAF–Osservatorio Astrofisico di Catania, via S.Sofia 78, 95123 Catania, Italy
³ INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁴ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
⁵ INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁶ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁸ Instituto de Astrofísica de Canarias, C/Via Láctea S/N, 38200 La Laguna, Tenerife, Spain
⁹ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
¹⁰ Department of Physics, University of Atacama, 485 Copayapu, Copiapo, Chile
¹¹ Fundación Galileo Galilei–INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹² INAF–Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹³ Landessternwarte Königstuhl, Zentrum für Astronomie der Universitat Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁴ INAF–IASF Milano, via Bassini 15, 20133 Milano, Italy
¹⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁶ Dip. di Fisica e Astronomia Galileo Galilei – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹⁷ Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001, USA
¹⁸ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK

Received: 26 January 2015
Accepted: 24 March 2015

Abstract

Aims. We observed the τ Boo system with the HARPS-N spectrograph to test a new observational strategy aimed at jointly studying asteroseismology, the planetary orbit, and star-planet magnetic interaction.

Methods. We collected high-cadence observations on 11 nearly consecutive nights and for each night averaged the raw FITS files using a dedicated software. In this way we obtained spectra with a high signal-to-noise ratio, used to study the variation of the Ca ii H&K lines and to have radial velocity values free from stellar oscillations, without losing the oscillations information. We developed a dedicated software to build a new custom mask that we used to refine the radial velocity determination with the HARPS-N pipeline and perform the spectroscopic analysis.

Results. We updated the planetary ephemeris and showed the acceleration caused by the stellar binary companion. Our results on the stellar activity variation suggest the presence of a high-latitude plage during the time span of our observations. The correlation between the chromospheric activity and the planetary orbital phase remains unclear. Solar-like oscillations are detected in the radial velocity time series: we estimated asteroseismic quantities and found that they agree well with theoretical predictions. Our stellar model yields an age of 0.9 ± 0.5 Gyr for τ Boo and further constrains the value of the stellar mass to 1.38 ± 0.05 M_⊙.