J/A+A/708/A232 GJ 1137 RVs and activity indices (Stoeva+, 2026)
Long-period magnetic activity in the K dwarf GJ1137 and a new super Earth on a
9-day orbit.
A cautionary tale for Jovian-analogue detection from Doppler surveys.
Stoeva D., Stefanov A.K., Stefanov S.Y., Lafarga M., Bebekovska E.V.,
Filomeno S., Gonzalez-Hernandez J.I., Suarez-Mascareno A., Rebolo R.,
Nari N., Mestre J.M., Antonova D., Zaharieva E., Bozhilov V., Trifonov T.
<Astron. Astrophys. 708, A232 (2026)>
=2026A&A...708A.232S 2026A&A...708A.232S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Stars, K-type ; Exoplanets ;
Radial velocities ; Spectroscopy ; Optical
Keywords: techniques: radial velocities - planets and satellites: detection -
stars: activity
Abstract:
Detection and characterisation of Jovian analogues in precision radial
velocity (RV) measurements is gaining momentum due to the constantly
increasing observational baseline of Doppler surveys. The occurrence
rate of Jovian-mass exoplanets is crucial for understanding the
architecture of planetary systems. However, long-period RV signals in
Doppler surveys could also be induced by stellar magnetic cycles,
leading to misinterpretations of planetary candidates.
We investigate the long-term RV variability in the K-dwarf star GJ1137
(HD93083, HIP52521), a known Saturn-mass exoplanet host, and assess
the role of stellar activity in shaping the observed signals.
We analyse 13 years of archival high-precision spectroscopic
observations obtained with the High Accuracy Radial velocity Planet
Searcher spectrograph (HARPS). We performed an extensive spectroscopic
analysis of the stellar activity indicators and applied an RV
modelling approach, incorporating Keplerian fits, Gaussian process
regression as a proxy for stellar activity, and other stellar activity
diagnostics. Furthermore, we refined the orbital parameters and the
minimum mass of the known exoplanet GJ 1137 b and searched for
additional planetary candidates in the system.
We detect a long-period RV signal that, if interpreted as planetary,
would suggest the presence of a Jovian-analogue companion. However,
our spectroscopic activity analysis provides strong evidence that this
variability is induced by the star's long-term magnetic cycle
Pcyc=5870+480-350 days rather than by an orbiting planet. The
signal is detected in both the full width at half maximum (FWHM) of
the cross-correlation function and the chromospheric activity index
logR'_HK. We measure the stellar rotation period to
Prot=32.3+1.2-1.3 days and identify a significant short-period
RV signal, which we attribute to a Super Earth with a period of
9.6412+12-11 days and a minimum mass of 5.12+0.70-0.69 Earth
masses, making GJ 1137 a multiple-planet system.
Description:
Table A1 includes 141 RV measurements from the HARPS spectrograph and
its respective activity indices, for the GJ 1137 multi-planetary
system.
Objects:
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RA (2000) DE Designation(s)
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10 44 20.91 -33 34 37.28 GJ 1137 = HD 93083
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 211 140 HARPS Doppler measurements and activity index
measurements of GJ 1137 evaluated using SERVAL
and RACOON and their corresponding uncertainties
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.3 d BJD Barycentric Julian Date
13- 22 F10.6 m/s RVservalNZP Radial Velocity (SERVAL)
24- 31 F8.6 m/s e_RVservalNZP Error in Radial Velocity (SERVAL)
33- 41 F9.6 km/s RVracoon Radial Velocity (RACOON)
43- 50 F8.6 km/s e_RVracoon Error in Radial Velocity (RACOON)
52- 59 F8.6 --- Halpha H-alpha index
61- 68 F8.6 --- e_Halpha Error in H-alpha index
70- 75 F6.4 --- NaD1 Sodium D1 index
77- 82 F6.4 --- e_NaD1 Error in Sodium D1 index
84- 89 F6.4 --- NaD2 Sodium D2 index
91- 96 F6.4 --- e_NaD2 Error in Sodium D2 index
98-105 F8.4 --- CRX Chromatic index
107-113 F7.4 --- e_CRX Error in chromatic index
115-124 F10.6 m/s dLw Line width variation
126-133 F8.6 m/s e_dLw Error in line width variation
135-143 F9.7 --- RHKp R'HK chromospheric activity indicator
145-153 F9.7 --- e_RHKp Error in chromospheric activity indicator
155-162 F8.6 km/s FWHMracoon Full width at half maximum (RACOON)
164-171 F8.6 km/s e_FWHMracoon Error in FWHM (RACOON)
173-181 F9.6 % Contracoon Contrast (RACOON)
183-190 F8.6 % e_Contracoon Error in contrast (RACOON)
192-200 F9.6 km/s BISracoon Bisector span (RACOON)
202-209 F8.6 km/s e_BISracoon Error in bisector span (RACOON)
211 I1 --- IDset Observation set identifier
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Acknowledgements:
From Denitza Stoeva, dstoeva(at)phys.uni-sofia.bg
D.S., S.S, E.Z., D.A., V.B., and T.T. acknowledge support by the BNSF
program "VIHREN-2021" project No. KP-06-DV/5.
(End) Patricia Vannier [CDS] 02-Feb-2026