J/A+A/706/A231 HARPS-N 10yrs precise solar radial velocities (Dumusque+, 2026)
A decade of solar high-fidelity spectroscopy and precise radial velocities from
HARPS-N.
Dumusque X., Al Moulla K., Cretignier M., Buchschacher N., Segransan D.,
Phillips D.F., Affer L., Aigrain S., John A.A., Bonomo A.S., Bourrier V.,
Buchhave L.A., Collier Cameron A., Cegla H.M., Cortes-Zuleta P.,
Cosentino R., Costes J., Damasso M., de Beurs Z.L, Ehrenreich D.,
Ghedina A., Gonzales M., Haywood R.D., Klein B., Lakeland B.S.,
Langellier N., Latham D.W., Leleu A., Lodi M., Lopez-Morales M., Lovis C.,
Malavolta L., Maldonado J., Mantovan G., Matinez Fiorenzano A.F.,
Micela G., Milbourne T., Molinari E., Mortier A., Naponiello L.,
Nicholson B.A., O'Sullivan N.K., Pepe F., Pinamonti M., Piotto G.,
Rescigno F., Rice K., Dimitar S., Silva A.M., Sozzetti A., Stalport M.,
Tavella S., Udry S., Vanderburg A., Vissapragada S., Watson C.A.
<Astron. Astrophys. 706, A231 (2026)>
=2026A&A...706A.231D 2026A&A...706A.231D (SIMBAD/NED BibCode)
ADC_Keywords: Spectroscopy ; Sun ; Radial velocities ; Optical
Keywords: instrumentation: spectrographs - methods: data analysis -
techniques: radial velocities - astronomical data bases -
Sun: activity - planets and satellites: detection
Abstract:
The HARPS-N solar telescope has been observing the Sun every possible
day since the summer of 2015. We recently released 10 years of these
data, which are available online.The goal of this manuscript is to
present the different optimisations made to the ESPRESSO data
reduction software used to extract the published HARPS-N solar
spectra, to describe data curation, and to perform some analyses that
demonstrate the extreme RV precision of those data. By analysing all
the HARPS-N wavelength solutions over 13 years, we bring to light
instrumental systematics at the 1ms level. We mitigate those
systematics by curating the thorium line list used to derive the
wavelength solution, and by applying a correction to the drift of
thorium lines induced by the aging of thorium-argon hollow cathode
lamps. After optimisation, we demonstrate a peak-to-peak precision on
the HARPS-N wavelength solution better than 0.75ms over 13 years. We
then carefully curate the decade of HARPS-N re-reduced solar
observations by rejecting 30% of the data affected either by clouds,
bad atmospheric conditions or well-understood instrumental
systematics. Finally, we correct the curated data for spurious sub-\ms
RV effects caused by erroneous instrumental drift measurements and by
changes in the spectral blaze function over time. After curation and
correction, a total of 109466 HARPS-N solar spectra and respective RVs
over a decade are available. The median photon-noise precision of the
RV data is 0.28ms and, on daily timescales, the median RV rms is
0.49ms, similar to the level imposed by stellar granulation signals.
On 10-year timescales, the large RV rms of 2.95\ms results from the RV
signature of the Sun's magnetic cycle. When modeling this long-term
effect using the Bremen Composite Magnesium II activity index, we
demonstrate a long-term RV precision of 0.41ms. We also analysed
contemporaneous HARPS-N and NEID solar RVs and found the data from
both instruments to be of similar quality and precision. However, an
analysis of the RV difference between these two RV datasets over the
three available years gives a surprisingly large RV rms of 1.3ms. This
variation is dominated by an unexplained trend that could be caused by
a different sensitivity to stellar activity of the two datasets. Once
this trend is modeled, the overall RV rms for three years reaches
0.79ms, and the RV rms during the low activity phase decreases to
0.6ms, compatible with what is expected from supergranulation. This
decade of high-cadence HARPS-N solar observations with short- and
long-term precision below 1ms represents a crucial dataset for further
understanding stellar activity signals in solar-type stars and to
advance other science cases requiring such extreme precision.
Description:
tabled1.dat corresponds to a curated Thorium line list used for
deriving optimised HARPS-N wavelength solutions. This line list is
critical to obtain long-term precision radial-velocities with the
HARPS-N instrument.
harpnsun.dat corresponds to 10 years of precise solar
radial-velocities (RVs) gathered by the HARPS-N solar telescope. This
file contains observational conditions, the solar RVs, different
activity indicators (Log(R'hk), MgII, CCF BIS SPAN, CCF FWHM, CCF
CONTRAST) and correction for barycentric Earth RV and barycentric to
heliocentric RV.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tabled1.dat 29 2020 Thorium line list
harpnsun.dat 313 109466 HARPS-N solar data
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See also:
J/ApJS/211/4 : Thorium spectrum from 250nm to 5500nm (Redman+, 2014)
Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 0.1nm lambda Wavelength in vacuum (1)
12- 14 A3 --- El Element (TH1, TH2, TH3)
16- 17 I2 --- HARPS-Norder Order number for HARPS-N
19- 29 F11.6 --- HARPS-Npixel Pixel number for HARPS-N
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Note (1): Wavelengths are in the vacuum and are coming from Redman et al.
(2014ApJS..211....4R 2014ApJS..211....4R, Cat. J/ApJS/211/4).
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Byte-by-byte Description of file: harpnsun.dat
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Bytes Format Units Label Explanations
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1- 29 A29 --- Fileroot Filename identifier
31- 40 A10 "date" Night Day of observation
42- 53 F12.6 d BJD Barycentric Julian date
55- 56 I2 h RAh Right Ascension at BJD
58- 59 I2 min RAm Right Ascension at BJD
61- 67 F7.4 s RAs Right Ascension at BJD
69 A1 --- DE- Declination sign at BJD
70- 71 I2 deg DEd Declination at BJD
73- 74 I2 arcmin DEm Declination at BJD
76- 82 F7.4 arcsec DEs Declination at BJD
84- 88 F5.1 s Texp Exposure time
90- 94 F5.3 --- Airmass Airmass of the Sun
96-101 F6.4 --- Photocenter Flux barycentre of exposure
103-107 F5.1 --- sn-order-20 S/N in order 20
109-113 F5.1 --- sn-order-50 S/N in order 50
115-119 F5.1 --- sn-order-60 S/N in order 60
121-125 F5.3 --- obs-quality Quality flag (>0.9 = good)
127 I1 --- data-quality [1] Pipeline quality (1 = good)
129-136 F8.6 km/s RV-raw Raw solar radial velocity
138-146 F9.6 km/s RV Solar radial velocity (1)
148-155 F8.6 km/s e_RV Solar radial velocity error
157-163 F7.4 --- logRHK Log(R'hk) activity index
165-170 F6.4 --- e_logRHK Log(R'hk) error
172-178 F7.5 --- SMW Mount-Wilson S-index
180-186 F7.5 --- e_SMW Mount-Wilson S-index error
188-194 F7.5 --- Mg2 Magnesium II activity index
196-204 F9.6 km/s bis-span-raw Raw CCF bisector span
206-214 F9.6 km/s bis-span CCF bisector span
216-223 F8.6 km/s e_bis-span CCF bisector span error
225-232 F8.6 km/s FWHM-raw Raw CCF FWHM
234-241 F8.6 km/s FWHM CCF FWHM
243-250 F8.6 km/s e_FWHM CCF FWHM error
252-258 F7.4 % Contrast-raw Raw CCF contrast
260-266 F7.4 % Contrast CCF contrast
268-273 F6.4 % e_Contrast Raw CCF contrast error
275-283 F9.6 km/s BERV Barycentric Earth RV
285-293 F9.6 km/s BERV-B-to-H Barycentric to heliocenter RV
295-303 F9.6 km/s RV-diff-ext Differential extinction RV
305-313 F9.6 km/s RV-opt-corr Radial velocity optimised correction
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Note (1): Column "RV" is obtained by subtracting BERVBARYTO_HELIO,
RVDIFFEXTINCTION, RVOPTIMISEDCORR and constant 0.16759939657 to column
"RV-raw"
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Acknowledgements:
Xavier Dumusque, xavier.dumusque(at)unige.ch
Astronomy Department Geneva University, Switzerland
(End) X. Dumusque [Astron. Dep. Geneva Univ.], P. Vannier [CDS] 17-Dec-2025