SOPHIE+: First results of an octagonal-section fiber for high-precision radial velocity measurements

¹ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis Bd Arago, 75014 Paris, France
e-mail: bouchy@iap.fr
² Observatoire de Haute-Provence, CNRS/OAMP, 04870 St Michel l’Observatoire, France
³ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
⁴ UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble, UMR 5274, 38041 Grenoble, France
⁵ Aix-Marseille Université, CNRS, Laboratoire d’Astrophysique de Marseille, UMR 7326, 13388 Marseille, France

Received: 10 July 2012
Accepted: 30 October 2012

Abstract

High-precision spectrographs play a key role in exoplanet searches and Doppler asteroseismology using the radial velocity technique. The 1  m s^-1level of precision requires very high stability and uniformity of the illumination of the spectrograph. In fiber-fed spectrographs such as SOPHIE, the fiber-link scrambling properties are one of the main conditions for high precision. To significantly improve the radial velocity precision of the SOPHIE spectrograph, which was limited to 5–6  m s^-1, we implemented a piece of octagonal-section fiber in the fiber link. We present here the scientific validation of the upgrade of this instrument, demonstrating a real improvement. The upgraded instrument, renamed SOPHIE+, reaches radial velocity precision in the range of 1–2  m s^-1. It is now fully efficient for the detection of low-mass exoplanets down to 5–10 M_⊕ and for the identification of acoustic modes down to a few tens of  cm s^-1.