HARPS-N observes the Sun as a star
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Radial velocity (RV) perturbations induced by stellar surface inhomogeneities including spots, plages and granules currently limit the detection of Earth-twins using Doppler spectroscopy. Such stellar noise is poorly understood for stars other than the Sun because their surface is unresolved. In particular, the effects of stellar surface inhomogeneities on observed stellar radial velocities are extremely difficult to characterize, and thus developing optimal correction techniques to extract true stellar radial velocities is extremely challenging. In this paper, we present preliminary results of a solar telescope built to feed full-disk sunlight into the HARPS-N spectrograph, which is in turn calibrated with an astro-comb. This setup enables long-term observation of the Sun as a star with state-of-the-art sensitivity to RV changes. Over seven days of observing in 2014, we show an average 50 cm s‑1 RV rms over a few hours of observation. After correcting observed radial velocities for spot and plage perturbations using full-disk photometry of the Sun, we lower by a factor of two the weekly RV rms to 60 cm s‑1. The solar telescope is now entering routine operation, and will observe the Sun every clear day for several hours. We will use these radial velocities combined with data from solar satellites to improve our understanding of stellar noise and develop optimal correction methods. If successful, these new methods should enable the detection of Venus over the next two to three years, thus demonstrating the possibility of detecting Earth-twins around other solar-like stars using the RV technique.
Dumusque , X , Glenday , A , Phillips , D F , Buchschacher , N , Cameron , A C , Cecconi , M , Charbonneau , D , Cosentino , R , Ghedina , A , Latham , D W , Li , C-H , Lodi , M , Lovis , C , Molinari , E , Pepe , F , Udry , S , Sasselov , D , Szentgyorgyi , A & Walsworth , R 2015 , ' HARPS-N observes the Sun as a star ' Astrophysical Journal Letters , vol 814 , no. 2 . DOI: 10.1088/2041-8205/814/2/L21
Astrophysical Journal Letters
© 2015. The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at http://dx.doi.org/10.1088/2041-8205/814/2/L21
This work was performed with support from the Smithsonian Astrophysical Observatory, The Harvard Origins of Life Initiative, the National Science Foundation, NASA, and Progetto Premiale WOW of the Italian Research Ministry (for support of the astro-comb). X.D. thanks the Society in Science-Branco Weiss fellowship for its support, as well as NASA's Transiting Exoplanet Survey Satellite (TESS) mission for partial support via subaward 5710003554 from MIT to SAO. A.C.C. acknowledges support from STFC grant ST/M001296/1 during the course of this work. The research leading to these results received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 313014 (ETAEARTH). This publication was made possible through the support of a grant from the John Templeton Foundation.