Volume 575, March 2015
|Number of page(s)||24|
|Section||Planets and planetary systems|
|Published online||05 March 2015|
The GAPS programme with HARPS-N at TNG
1 INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
2 Osservatorio Astronomico della Regione Autonoma Valle d’Aosta, Fraz. Lignan 39, 11020, Nus (Aosta), Italy
3 INAF–Osservatorio Astrofisico di Catania, via S.Sofia 78, 95123 Catania, Italy
4 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
5 Dip. di Fisica e Astronomia Galileo Galilei – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
6 Instituto de Astrofísica de Canarias, C/via Láctea S/N, 38200 La Laguna, Tenerife, Spain
7 Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
8 Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF – Spain
9 Obs. Astronomique de l’Univ. de Geneve, 51 ch. des Maillettes – Sauverny, 1290 Versoix, Switzerland
10 INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
11 Landessternwarte Königstuhl, Zentrum für Astronomie der Universitat Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
12 Inst. de Ciencies de l’Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, 08193 Bellaterra, Spain
13 Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
14 Centro deAstrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
15 Departamento de Física e Astronomia, Faculdade de Ciências, Univ. do Porto, Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal
16 INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
17 Dept. of Physics, University of Perugia, via A. Pascoli, 06123 Perugia, Italy
18 INAF–Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
19 Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano, Italy
20 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
21 INAF–IASF Milano, via Bassini 15, 20133 Milano, Italy
22 INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
23 Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
Received: 13 November 2014
Accepted: 23 December 2014
Aims. XO-2 is the first confirmed wide stellar binary system where the almost twin components XO-2N and XO-2S have planets, and it is a peculiar laboratory in which to investigate the diversity of planetary systems. This stimulated a detailed characterization study of the stellar and planetary components based on new observations.
Methods. We collected high-resolution spectra with the HARPS-N spectrograph and multi-band light curves. Spectral analysis led to an accurate determination of the stellar atmospheric parameters and characterization of the stellar activity, and high-precision radial velocities of XO-2N were measured. We collected 14 transit light curves of XO-2Nb used to improve the transit parameters. Photometry provided accurate magnitude differences between the stars and a measure of their rotation periods.
Results. The iron abundance of XO-2N was found to be +0.054 dex greater, within more than 3σ, than that of XO-2S. The existence of a long-term variation in the radial velocities of XO-2N is confirmed, and we detected a turnover with respect to previous measurements. We suggest the presence of a second massive companion in an outer orbit or the stellar activity cycle as possible causes of the observed acceleration. The latter explanation seems more plausible with the present dataset. We obtained an accurate value of the projected spin-orbit angle for the XO-2N system (λ = 7° ± 11°), and estimated the real 3D spin-orbit angle ( degrees). We measured the XO-2 rotation periods, and found a value of P = 41.6 ± 1.1 days in the case of XO-2N, in excellent agreement with the predictions. The period of XO-2S appears shorter, with an ambiguity between 26 and 34.5 days that we cannot solve with the present dataset alone. The analysis of the stellar activity shows that XO-2N appears to be more active than the companion, perhaps because we sampled different phases of their activity cycle, or because of an interaction between XO-2N and its hot Jupiter that we could not confirm.
Key words: stars: individual: XO-2 / stars: fundamental parameters / stars: abundances / planetary systems / techniques: radial velocities / techniques: photometric
Based on observations made (i) with the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the INAF – Fundacion Galileo Galilei (Spanish Observatory of Roque de los Muchachos of the IAC); (ii) with the Copernico and Schmidt telescopes (INAF – Osservatorio Astrofisico di Padova, Asiago, Italy); (iii) with the IAC-80 telescope at the Teide Observatory (Instituto de Astrofísica de Canarias, IAC); (iv) at the Serra la Nave “M.G. Fracastoro” Astronomical Observatory (INAF – Osservatorio Astrofisico di Catania); (v) at the Astronomical Observatory of the Autonomous Region of the Aosta Valley (OAVdA).
RV data (including Table 7) and photometry data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/575/A111
© ESO, 2015
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