Volume 620, December 2018
|Number of page(s)||20|
|Section||Numerical methods and codes|
|Published online||29 November 2018|
Measuring precise radial velocities on individual spectral lines
Observatoire astronomique de l’Université de Genève, 51 ch. des Maillettes Garching bei München 1290 Versoix, Switzerland
Accepted: 5 September 2018
Context. Stellar activity is the main limitation to the detection of an Earth-twin using the radial-velocity (RV) technique. Despite many efforts in trying to mitigate the effect of stellar activity using empirical and statistical techniques, it seems that we are facing an obstacle that will be extremely difficult to overcome using current techniques.
Aims. In this paper, we investigate a novel approach to derive precise RVs considering the wealth of information present in high-resolution spectra.
Methods. This new method consists of building a master spectrum from all available observations and measure the RVs of each individual spectral line in a spectrum relative to this master. When analysing several spectra, the final product of this approach is the RVs of each individual line as a function of time.
Results. We demonstrate on three stars intensively observed with HARPS that our new method gives RVs that are extremely similar to the one derived from the HARPS data reduction software. Our new approach to derive RVs demonstrates that the non-stability of daily HARPS wavelength solution induces night-to-night RV offsets with an standard deviation of 0.4 m s−1, and we propose a solution to correct for this systematic. Finally, and this is probably the most astrophysically relevant result of this paper, we demonstrate that some spectral lines are strongly affected by stellar activity while others are not. By measuring the RVs on two carefully selected subsample of spectral lines, we demonstrate that we can boost by a factor of two or mitigate by a factor of 1.6 the red noise induced by stellar activity in the 2010 RV measurements of α Cen B.
Conclusions. By measuring the RVs of each spectral line, we are able to reach the same RV precision as other approved techniques. In addition, this new approach allows us to demonstrate that each spectral line is differently affected by stellar activity. Preliminary results show that studying in details the behaviour of each spectral line is probably the key to overcome the obstacle of stellar activity.
Key words: techniques: radial velocities / techniques: spectroscopic / stars: activity / stars: individual: HD10700 / stars: individual: HD128621 / stars: individual: HD10180
Based on observations made with the HARPS instrument on the ESO 3.6m telescope at La Silla Observatory under the GTO programme 072.C-0488 and Large programme 193.C-0972/193.C-1005/.
RV data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/620/A47
© ESO 2018
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