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SPIRou : specific software development

Par Jean-Francois Donati - 11/09/2008


SPIRou : data processing

As for all instruments, we of course need to set-up an automatic reduction pipeline capable of turning series of raw spectropolarimetric frames into wavelength-calibrated polarised echelle spectra. We will mostly adapt Libre_ESpRIT - the automatic reduction pipeline of ESPaDOnS & NARVAL - to the specific purpose of SPIRou; in particular, and following the HARPS & Sophie experience, we will incorporate all operations needed to match the 1 m/s precision in RV.

We will also implement a new tool aimed at subtracting telluring lines as accurately as possible. This is not crucial for reaching the expected performance of SPIRou; simply dropping all wavelength regions where telluric features are deeper than 2% to compute RVs ensures that the 'telluric jitter' is lower than 0.5 m/s while leaving at least 50% of YJHK bands useable (thanks to the very good nIR transparency of MaunaKea). Subtracting telluric lines may however help in further improving the efficiency of SPIRou, by widening significantly the spectral range available for RV measurements. We will also have a similar tool for removing OH airglow lines from the sky background.

Finally, we will also develop and implement a new tool aimed at correcting RV measurements from the intrinsic activity jitter of M dwarfs. The activity jitter from the majority of (weakly-active) M dwarfs is expected to be of a few m/s only in the nIR, and will therefore not compromise the main goals of SPIRou. Correcting from this jitter will however further increase the performances of SPIRou. Spectropolarimetric results on mid M dwarfs obtained with ESPaDOnS (eg Morin et al 2008, arXiv:0808.1423; Donati et al 2008, arXiv:0809.0269) indicate that RV fluctuations correlate with the magnetic topologies; by working out in detail how activity jitters relate to the magnetic topologies (derived from the Zeeman spectropolarimetric signatures simultaneously collected with SPIRou), we will thus be able to model activity jitters (from the observed magnetic topology) and remove them (to some extent) from the RV data. This technique should thus further extend the range of SPIRou to both smaller planets and more active dwarfs.



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