Abstract
SPIRou is the newest spectropolarimeter and high-precision velocimeter that has recently been installed at the Canada-France-Hawaii Telescope on Maunakea, Hawaii. It operates in the near-infrared and simultaneously covers the 0.98–2.35 μm domain at high spectral resolution. SPIRou is optimized for exoplanet search and characterization with the radial-velocity technique, and for polarization measurements in stellar lines and subsequent magnetic field studies. The host of the transiting hot Jupiter HD 189733 b has been observed during early science runs. We present the first near-infrared spectropolarimetric observations of the planet-hosting star as well as the stellar radial velocities as measured by SPIRou throughout the planetary orbit and two transit sequences. The planetary orbit and Rossiter-McLaughlin anomaly are both investigated and modeled. The orbital parameters and obliquity are all compatible with the values found in the optical. The obtained radial-velocity precision is compatible with about twice the photon-noise estimates for a K2 star under these conditions. The additional scatter around the orbit, of about 8 m s−1, agrees with previous results that showed that the activity-induced scatter is the dominant factor. We analyzed the polarimetric signal, Zeeman broadening, and chromospheric activity tracers such as the 1083nm HeI and the 1282nm Paβ lines to investigate stellar activity. First estimates of the average unsigned magnetic flux from the Zeeman broadening of the FeI lines give a magnetic flux of 290 ± 58 G, and the large-scale longitudinal field shows typical values of a few Gauss. These observations illustrate the potential of SPIRou for exoplanet characterization and magnetic and stellar activity studies.
Highlights
The study and characterization of exoplanet systems has greatly benefited from the instrumental developments in high-resolution optical spectroscopy since the pioneer work by Walker et al (1995), Mayor & Queloz (1995), and Marcy & Butler (1992) and in particular, from the improvement of simultaneous wavelength calibrations (Baranne et al 1996) in the advent of precise radialvelocity (RV) measurements
Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated from the summit of Maunakea by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii
SPIRou data allowed the recovery of the orbital signature and spectropolarimetric features in agreement with previous work done at optical wavelengths
Summary
The study and characterization of exoplanet systems has greatly benefited from the instrumental developments in high-resolution optical spectroscopy since the pioneer work by Walker et al (1995), Mayor & Queloz (1995), and Marcy & Butler (1992) and in particular, from the improvement of simultaneous wavelength calibrations (Baranne et al 1996) in the advent of precise radialvelocity (RV) measurements. A last set of masks was created from ATLAS9 stellar models (Castelli & Kurucz 2003) and the VALD database, the model corresponding to an effective temperature of 5000 K and log g of 5.0 This mask contained 6102 atomic lines in the SPIRou domain; when most opaque atmospheric bands at [1335–1490] and [1790–1994] were removed, 4121 lines remained. The pipeline estimates the RV uncertainty of each individual exposure using the optimal weight method on the spectrum, as introduced by Connes (1985) and Bouchy et al (2001) Because this is performed on the extracted spectrum rather than the CCF, this RV uncertainty indicator does not depend on the mask and underestimates the real value because telluric lines are still included. Worse seeing conditions in turn do not lead to significantly higher dispersion values in this limited data set
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