J/AJ/169/182 Radial velocities of Gl 229 with HARPS (Deslieres+, 2025)
The Gl 229 system revisited with the line-by-line framework: Planetary signals
now appear as stellar activity ghosts.
Deslieres A., Cadieux C., Doyon R., Artigau E., Cook N.J., Fontanive C.,
Vandal T.
<Astron. J., 169, 182 (2025)>
=2025AJ....169..182D 2025AJ....169..182D
ADC_Keywords: Radial velocities; Exoplanets; Stars, brown dwarf; Stars, M-type;
Spectroscopy; Optical
Keywords: Stellar activity ; Brown dwarfs ; Exoplanet formation ;
Exoplanet evolution ; Exoplanet systems ; M dwarf stars ;
Radial velocity ; Planetary system formation
Abstract:
Gl 229 is a well-known system hosting the first confirmed brown dwarf
(BD), Gl 229 B, discovered in 1995. Subsequent radial velocity (RV)
follow-up of the star unveiled, in 2014, an exoplanet on a 471 days
orbit with a minimum mass of ∼32M⊕. In 2020, a second
exoplanet with a 122 days orbital period and a minimum mass of
approximately 7M⊕ was reported. With its BD, now a known
binary, and two exoplanets, Gl 229 has been deemed one of the most
diverse systems and has sparked discussions regarding the different
formation mechanisms that could have taken place around this star.
This work presents a new analysis of the publicly available Gl 229
High Accuracy Radial Velocity Planet Searcher data reduced with the
line-by-line precision RV algorithm resistant to spectral outliers. We
find strong evidence for stellar activity impacting RV measurements.
Stellar activity-induced RVs were modelled with a Gaussian process
trained on the activity indicator provided by the algorithm, revealing
the star's rotation period at 28.9±1.6d. We show that systematic
errors and stellar activity are the most likely cause of the
previously reported exoplanet signals. Our analysis provides a
3σ upper limit of 9.1M⊕ for a planet in the system's
habitable zone except for the periods close to the star's rotation
period, where stellar activity worsens the limit to around
15M⊕.
Description:
The publicly available data of Gl 229 A from the High Accuracy Radial
Velocity Planet Searcher (HARPS) were used in this work. HARPS is an
optical spectrograph covering wavelengths from 378 to 691nm installed
at the European Southern Observatory (ESO) La Silla 3.6m telescope in
Chile. The 201 available spectra ranged from 2003 December 13th to
2016 September 29th and were retrieved from the ESO science archive.
On 2015 May 29th, the optical fibers feeding HARPS were replaced,
resulting in significantly better measurements. This change divides data
points into two categories: the pre- and postfibers change.
The RVs used in this work were extracted using the line-by-line (LBL)
algorithm (Artigau+, 2022AJ....164...84A 2022AJ....164...84A) that measures RV using the
Bouchy+ (2001A&A...374..733B 2001A&A...374..733B) framework on individual spectral lines,
checks for statistical consistency between them to reject spectral
outliers, and averages all valid per-line velocities into a final RV
measurement.
The 201 measurements have a median uncertainty of 0.65m/s and 1.45m/s
for the RVs and FWHM, respectively. We applied a cut in
signal-to-noise ratio (SNR), calculated as an average of the entire
spectrum, and rejected 5 data points with significantly lower values
(SNR≤50) compared to the average of the dataset (SNR=140).
Objects:
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RA (2000) DE Designation(s) (Period)
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06 10 34.61 -21 51 52.6 Gl 229 = HD 42581 (Per=27.3d)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 34 196 Gl229 data obtained with the LBL method
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See also:
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/ApJ/704/975 : Rotational velocities for M dwarfs (Jenkins+, 2009)
J/ApJS/190/1 : A survey of stellar families (Raghavan+, 2010)
J/ApJ/807/45 : Potentially habitable planets orbit. M dwarfs (Dressing+, 2015)
J/AJ/152/8 : Impact of stell. multiplicity on planetary sys. I. (Kraus+, 2016)
J/A+A/600/A13 : HARPS M dwarf sample magnetic activity (Astudillo-Defru+, 2017)
J/MNRAS/474/2094 : Inferring probabilistic stellar rot. periods (Angus+, 2018)
J/A+A/612/A79 : Barnard 30 dark cloud IR and submm data (Barrado+, 2018)
J/other/Nat/563.365 : Barnard's star radial velocity curve (Ribas+, 2018)
J/A+A/621/A126 : CARMENES input cat. of M dwarfs. IV. (Diez Alonso+ 2019)
J/ApJS/246/11 : Search for nearby earth analogs. II. RV analysis. (Feng+, 2020)
J/AJ/162/61 : RV follow up of Barnard's star with HPF (Lubin+, 2021)
J/A+A/650/A201 : 10 parsec sample in the Gaia era first update (Reyle+, 2021)
J/AJ/164/96 : SPIRou and IRD radial velocity of TOI-1452 (Cadieux+, 2022)
J/ApJS/262/21 : 3-D selection of 167 sub-stellar companions (Feng+, 2022)
J/A+A/664/A64 : GJ 832 stellar activity (Gorrini+, 2022)
J/A+A/660/A86 : Detection and characterization of TOI-1759 b (Martioli+, 2022)
J/MNRAS/517/5050 : K2-18 HARPS time-series (Radica+, 2022)
J/AJ/166/62 : New HIRES radial velocity data for V1298 Tau (Blunt+, 2023)
https://archive.eso.org/cms.html : ESO Science Archive Facility
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 8 F8.2 d JD [52986/57661] Reduced Julian Date, JD-2,400,000
10- 16 F7.2 m/s RVel [4706/4724] Radial velocities extracted with LBL
algorithm (1)
18- 21 F4.2 m/s e_RVel [0.56/1.2] Uncertainty in RV
23- 29 F7.2 m/s FWHM [3194/3276] Full-width half-maximum extracted
with LBL algorithm (1)
31- 34 F4.2 m/s e_FWHM [1.2/2.8] Uncertainty in FWHM
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Note (1): The line-by-line algorithm (Artigau+, 2022AJ....164...84A 2022AJ....164...84A).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 09-Jan-2026