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Three years of HARPS-N high-resolution spectroscopy and precise radial velocity data for the Sun

Published version
Peer-reviewed

Type

Article

Change log

Authors

Dumusque, X 
Cretignier, M 
Sosnowska, D 
Buchschacher, N 
Lovis, C 

Abstract

jats:pjats:italicContext.</jats:italic> The solar telescope connected to HARPS-N has been observing the Sun since the summer of 2015. Such a high-cadence, long-baseline data set is crucial for understanding spurious radial-velocity signals induced by our Sun and by the instrument. On the instrumental side, this data set allowed us to detect sub- m sjats:sup−1</jats:sup> systematics that needed to be corrected for.</jats:p> jats:pjats:italicAims.</jats:italic> The goals of this manuscript are to (i) present a new data reduction software for HARPS-N, (ii) demonstrate the improvement brought by this new software during the first three years of the HARPS-N solar data set, and (iii) release all the obtained solar products, from extracted spectra to precise radial velocities.</jats:p> jats:pjats:italicMethods.</jats:italic> To correct for the instrumental systematics observed in the data reduced with the current version of the HARPS-N data reduction software (DRS version 3.7), we adapted the newly available ESPRESSO DRS (version 2.2.3) to HARPS-N and developed new optimised recipes for the spectrograph. We then compared the first three years of HARPS-N solar data reduced with the current and new DRS.</jats:p> jats:pjats:italicResults.</jats:italic> The most significant improvement brought by the new DRS is a strong decrease in the day-to-day radial-velocity scatter, from 1.27 to 1.07 m sjats:sup−1</jats:sup>; this is thanks to a more robust method to derive wavelength solutions, but also to the use of calibrations closer in time. The newly derived solar radial-velocities are also better correlated with the chromospheric activity level of the Sun in the long term, with a Pearson correlation coefficient of 0.93 compared to 0.77 before, which is expected from our understanding of stellar signals. Finally, we also discuss how HARPS-N spectral ghosts contaminate the measurement of the calcium activity index, and we present an efficient technique to derive an index free of instrumental systematics.</jats:p> jats:pjats:italicConclusions.</jats:italic> This paper presents a new data reduction software for HARPS-N and demonstrates its improvements, mainly in terms of radial-velocity precision, when applied to the first three years of the HARPS-N solar data set. Those newly reduced solar data, representing an unprecedented time series of 34 550 high-resolution spectra and precise radial velocities, are released alongside this paper. Those data are crucial to understand stellar activity signals in solar-type stars further and develop the mitigating techniques that will allow us to detect other Earths.</jats:p>

Description

Keywords

Sun: activity, techniques: radial velocities, methods: data analysis, instrumentation: spectrographs, astronomical databases: miscellaneous, planets and satellites: detection

Journal Title

Astronomy and Astrophysics

Conference Name

Journal ISSN

0004-6361
1432-0746

Volume Title

648

Publisher

EDP Sciences