J/AJ/169/107 Radial velocity curves of Gaia-4 and Gaia-5 (Stefansson+, 2025)
Gaia-4b and 5b: Radial Velocity Confirmation of Gaia Astrometric Orbital
Solutions Reveal a Massive Planet and a Brown Dwarf Orbiting Low-mass Stars.
Stefansson G., Mahadevan S., Winn J.N., Marcussen M.L., Kanodia S.,
Albrecht S., Fitzmaurice E., Mikulskyte O., Canas C.I.,
Espinoza-Retamal J.I., Zwart Y., Krolikowski D.M., Hotnisky A.,
Robertson P., Alvarado-Montes J.A., Bender C.F., Blake C.H.,
Callingham J.R., Cochran W.D., Delamer M., Diddams S.A., Dong J.,
Fernandes R.B., Giovinazzi M.R., Halverson S., Libby-Roberts J.,
Logsdon S.E., McElwain M.W., Ninan J.P., Rajagopal J., Reji V., Roy A.,
Schwab C., Wright J.T.
<Astron. J., 169, 107 (2025)>
=2025AJ....169..107S 2025AJ....169..107S
ADC_Keywords: Radial velocities; Exoplanets; Stars, M-type; Stars, K-type;
Proper motions; Spectroscopy; Optical
Keywords: Astrometric exoplanet detection ; Exoplanet detection methods ;
Astrometry ; Radial velocity ; Exoplanets ; Exoplanet systems ;
Extrasolar gaseous planets ; Exoplanet formation ; Brown dwarfs
Abstract:
Gaia astrometry of nearby stars is precise enough to detect the tiny
displacements induced by substellar companions, but radial velocity
(RV) data are needed for definitive confirmation. Here we present RV
follow-up observations of 28 M and K stars with candidate astrometric
substellar companions, which led to the confirmation of two systems,
Gaia-4b and Gaia-5b, identification of five systems that are single
lined but require additional data to confirm as substellar companions,
and the refutation of 21 systems as stellar binaries. Gaia-4b is a
massive planet (M=11.8±0.7MJ) in a P=571.3±1.4d orbit with a
projected semimajor axis a0=0.312±0.040mas orbiting a
0.644±0.02M☉ star. Gaia-5b is a brown dwarf (M=20.9±0.5MJ)
in a P=358.62±0.20d eccentric e=0.6423±0.0026 orbit with a
projected angular semimajor axis of a0=0.947±0.038mas around a
0.34±0.03M☉ star. Gaia-4b is one of the first exoplanets
discovered via the astrometric technique, and is one of the most
massive planets known to orbit a low-mass star.
Description:
To detect potentially massive substellar companions around nearby M
and K stars being unveiled by Gaia, we conducted spectroscopic
observations of 28 northern hemisphere Gaia-ASOI candidates to
characterize them and rule out false positives. These 28 systems
constitute the northern M and K stars in the Gaia-ASOI list with a
decl. δ≥-20° and GBp-GRp>1.5. The DR3 (I/355) results were
based on 34 months of observations and about 40 scans per star, on
average.
The Habitable-zone Planet Finder (HPF) is a temperature-stabilized
fiber-fed near-infrared spectrograph on the 10m Hobby-Eberly
Telescope (HET) at McDonald Observatory in Texas covering the
wavelength range from 810 to 1280nm at a resolution of R∼55,000. For
Gaia-4 and Gaia-5, we obtained 11 and 18 observations with an average
SNR of 97 and 87 per extracted 1D pixel at 1um, respectively. All
exposures had an exposure time of 900s, except for one of the Gaia-4b
observations, which had an exposure time of 245s.
NEID is a temperature-stabilized fiber-fed red-optical spectrograph on
the WIYN 3.5m Telescope at Kitt Peak National Observatory in Arizona
covering a wavelength range from 380 to 930nm at a resolution of
R∼110,000. For Gaia-4 and Gaia-5, we obtained six and three
observations with a median SNR of 8.7 and 5.2 per extracted 1D pixel
at 550nm, respectively. All exposures had an exposure time of 900s,
except for one exposure of Gaia-4b, which had an exposure time of
600s.
We also employed the FIber-fed Echelle Spectrograph mounted to the
2.56m Nordic Optical Telescope (NOT), at the Roque de los Muchachos
Observatory on La Palma, Spain. We used FIES in high-resolution mode,
which provides a resolving power of R∼67,000 with a spectral range
of 3700-7300Å. We obtained spectra for Gaia-4 (G-ASOI-47), along
with G-ASOI-11 and G-ASOI-43. The exposure time used was 2000s. For
Gaia-4 we obtained five exposures.
Objects:
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RA (2000) DE Designation(s) (Period)
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13 58 01.62 +31 41 43.4 Gaia-4 = Gaia-4 (Per=571.3d)
20 08 09.65 +41 56 28.3 Gaia-5 = Gaia-5 (Per=358.62d)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 31 23 Radial velocities of Gaia-4
table6.dat 32 21 Radial velocities of Gaia-5
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See also:
II/328 : AllWISE Data Release (Cutri+ 2013)
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
J/ApJ/622/1102 : The planet-metallicity correlation. (Fischer+, 2005)
J/A+A/525/A95 : Search for brown-dwarf companions of stars (Sahlmann+, 2011)
J/A+A/547/A105 : D-burning in core accretion objects (Molliere+, 2012)
J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/ApJ/828/46 : ALMA survey of Lupus protoplanetary disks. I. (Ansdell+, 2016)
J/ApJ/831/125 : ALMA 887um obs. of ChaI star-forming region (Pascucci+, 2016)
J/A+A/603/A30 : Evidence for 2 distinct giant planet population (Santos+, 2017)
J/AJ/156/102 : The TESS Input Catalog & Candidate Target List (Stassun+, 2018)
J/A+A/624/A94 : The role of the host star's metallicity (Maldonado+, 2019)
J/other/Sci/365.1441 : GJ 3512 radial velocity & light curves (Morales+, 2019)
J/ApJ/892/31 : Teff and metallicities of M dwarfs in APOGEE DR14 (Birky+, 2020)
J/MNRAS/491/5216 : Rotation per. for 107 M dwarfs from APACHE (Giacobbe+, 2020)
J/AJ/159/100 : Flux & RVs of the dwarf G9-40 with K2 & HPF (Stefansson+, 2020)
J/AJ/160/192 : Photometry and RVs of K2-25b with HPF (Stefansson+, 2020)
J/A+A/649/A6 : Gaia Catalogue of Nearby Stars - GCNS (Gaia collaboration, 2021)
J/A+A/664/A65 : Early-M dwarfs occurrence rates (Pinamonti+, 2022)
J/A+A/663/A48 : Two Saturn-mass planets around M dwarfs (Quirrenbach+, 2022)
J/A+A/674/A114 : Southern extrasolar planets CORALIE surv. XIX (Barbato+, 2023)
J/A+A/674/A10 : Gaia DR3 systems with companions (Holl+, 2023)
J/AJ/165/120 : g and i'-band light curve of TOI-5205 with SDSS (Kanodia+, 2023)
J/AJ/166/11 : Stellar properties & RV variability for M-dwarfs (Pass+, 2023)
J/other/Sci/382.1031 : LHS 3154 RV and activity indicators (Stefansson+, 2023)
J/A+A/680/A16 : RV measurements for 12 stars (Unger+, 2023)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD [2460039/2460562] Barycentric Julian Date at TDB
16- 21 F6.1 m/s RVel [-393/222] Radial velocity
23- 26 F4.1 m/s e_RVel [5.8/26.4] Uncertainty in RVel
28- 31 A4 --- Inst Instrument used for RVel (1)
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Note (1): Instruments used as follows:
HPF = Habitable-zone Planet Finder, a fiber-fed, near-infrared
spectrograph on the 10m Hobby-Eberly Telescope at McDonald
Observatory in Texas, USA (10 occurrences)
NEID = fiber-fed, red-optical spectrograph on the WIYN 3.5m Telescope at
Kitt Peak National Observatory, Arizona, USA (8 occurrences)
FIES = FIber-fed Echelle Spectrograph, 2.56m Nordic Optical Telescope,
the Roque de los Muchachos Observatory on La Palma, Spain
(5 occurrences)
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD [2460069/2460600] Barycentric Julian date at TDB
16- 22 F7.1 m/s RVel [-1692/1176] Radial velocity
24- 27 F4.1 m/s e_RVel [10.5/39.1] Uncertainty in RVel
29- 32 A4 --- Inst Instrument used for RVel (1)
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Note (1): Instruments used as follows:
HPF = Habitable-zone Planet Finder, a fiber-fed, near-infrared
spectrograph on the 10m Hobby-Eberly Telescope at McDonald
Observatory in Texas, USA (18 occurrences)
NEID = fiber-fed, red-optical spectrograph on the WIYN 3.5m Telescope at
Kitt Peak National Observatory, Arizona, USA (3 occurrences)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 04-Dec-2025