J/A+A/707/A197 TOI-5789.01 planet candidate HARPS-N RVs (Bonomo+, 2026)
The GAPS programme at TNG LXXI. A sub-Neptune suitable for atmospheric
characterization in a multiplanet and mutually inclined system orbiting the
bright K dwarf TOI-5789 (HIP 99452).
Bonomo A.S., Naponiello L., Sozzetti A., Benatti S., Carleo I., Biazzo K.,
Cubillos P.E., Damasso M., Di Maio C., Dorn C., Hara N., Polychroni D.,
Steinmeyer M.-L., Collins K.A., Desidera S., Dumusque X., Lanza A.F.,
Safonov B.S., Stockdale C., Turrini D., Ziegler C., Affer L., D'Arpa M.,
Fardella V., Harutyunyan A., Lorenzi V., Malavolta L., Mancini L.,
Mantovan G., Micela G., Murgas F., Nardiello D., Pagano I., Palle E.,
Pedani M., Pinamonti M., Rainer M., Scandariato G., Spinelli R.,
Zingales T.
<Astron. Astrophys. 707, A197 (2026)>
=2026A&A...707A.197B 2026A&A...707A.197B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Spectroscopy ; Optical ;
Radial velocities
Keywords: techniques: photometric - techniques: radial velocities -
planets and satellites: atmospheres -
planets and satellites: composition -
planets and satellites: detection -
planets and satellites: fundamental parameters
Abstract:
Sub-Neptunes with planetary radii of Rp≃2-4 R⊕ are the
most common planets around solar-type stars in short-period (P<100d)
orbits. It is still unclear, however, what their most likely
composition is, that is whether they are predominantly gas dwarfs or
water worlds. The sub-Neptunes orbiting bright host stars are very
valuable because they are suitable for atmospheric characterization,
which can break the well-known degeneracy in planet composition from
the planet bulk density, when combined with a precise and accurate
mass measurement. Here we report on the characterization of the
sub-Neptune TOI-5789 c, which transits in front of the bright
(V=7.3mag and Ks=5.35mag) and magnetically inactive K1V dwarf
HIP 99452 every 12.93 days, thanks to TESS photometry and 141
high-precision radial velocities obtained with the HARPS-N
spectrograph. We find that its radius, mass, and bulk density are
Rc=2.86+0.18-0.15R⊕, Mc=5.00±0.50M⊕, and
ρc=1.16±0.23gcm-3, and we show that TOI-5789c is a promising
target for atmospheric characterization with both JWST and, in the
future, Ariel. By analyzing the HARPS-N radial velocities with
different tools, we also detect three additional non-transiting
planets, namely TOI-5789b, d, and e, with orbital periods and minimum
masses of Pb=2.76 d, Mbsini=2.12±0.28, Pd=29.6d,
Mdsini=4.29±0.68M⊕, and Pe=63.0d,
Mesini=11.61±0.97M⊕. TOI-5789 is a mutually inclined
system as the difference between the orbital inclinations of planets b
and c must be higher than ∼4deg. Nevertheless, from sensitivity
studies based on both the HARPS-N and archival HIRES radial-velocity
measurements, we can exclude that these relatively high mutual
inclinations are due to the perturbation by an outer gaseous giant
planet.
Description:
In study, we gather 141 HARPS-N RVs to confirm the planeta candidate
TOI-5789.01, now designated as TOI-5789 c, which transits the bright
and old K1 V star HIP 99452 every 12.93 d. As described in
section stellar parameters and elemental abundances, we derived
atmospheric and chromospheric parameters. The HARPS-N pipeline also
provides activity indicators that can be useful to check for possible
stellar activity signals in our RV time series such as BIS, FWHM,
contrast and the chromospheric CaII H&K S-index and logRHK' (i.e all
these parameters are based on the Cross-Correlation Function as
mentionned in section HARPS-N radial velocities). All informations are
presented in table1.dat for the 141 spectroscopic HARPS-N RVs of
TOI-5789.
Objects:
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RA (2000) DE Designation(s)
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20 11 06.07 +16 11 16.7 TOI-5789 = 2MASS J20110609+1611162
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 94 141 HARPS-N measurements of radial velocity and
activity indicators of TOI-5789
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See also:
J/A+A/693/A7 : BD+00 444 (TOI-2443) RV curves (Naponiello+, 2025)
J/A+A/677/A33 : 38 Kepler and K2 systems RVs (Bonomo+, 2023)
J/A+A/657/A7 : Stellar and substellar companions from Gaia EDR3
(Kervella+, 2022)
J/A+A/573/A101 : Generalised Lomb-Scargle periodogram code
(Mortier+, 2015)
J/A+A/562/A71 : Chemical abundances of solar neighbourhood dwarfs
(Bensby+, 2014)
J/A+A/388/632 : Radial-velocity of HD 108147 and HD 168746 (Pepe+, 2002)
J/ApJ/809/77 : Transiting Exoplanet Survey Satellite (TESS)
(Sullivan+, 2015)
J/ApJ/790/146 : Planets in Kepler's multi-transiting systems
(Fabrycky+, 2014)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+,2014)
J/ApJ/687/1264 : Age estimation for solar-type dwarfs (Mamajek+, 2008)
J/MNRAS/472/1618 : Kepler study of starspot lifetimes (Giles+, 2017)
J/MNRAS/459/3890 : ExoMol line lists for SO2 (Underwood+, 2016)
J/ApJS/254/39 : Exoplanet candidates from TESS first 2yr obs
(Guerrero+, 2021)
J/ApJS/254/42 : Hipparcos-Gaia (EDR3) Catalog of Accelerations
(Brandt, 2021)
J/AJ/159/19 : SOAR TESS survey. I. (Ziegler+, 2020)
J/AJ/157/52 : Radial velocity observations in super-Earth systems
(Bryan+, 2019)
J/AJ/156/102 : The TESS Input Catalog and Candidate Target List
(Stassun+, 2018)
J/AJ/154/109 : California-Kepler Survey (CKS). III. Planet radii
(Fulton+, 2017)
J/AJ/147/20 : Spectroscopy of 447 nearby M dwarfs (Newton+, 2014)
J/AZh/97/733 : Binary Star Pop. with Common Proper Motion
(Sapozhnikov+, 2020)
IV/38 : TESS Input Catalog - v8.0 (TIC-8) (Stassun+, 2019)
II/336 : AAVSO Photometric All Sky Survey (APASS) DR9
(Henden+, 2016)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
I/348 : Orbital parameters in Milky-Way-like potentials
(Mackereth+, 2018)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
J/other/ExA/51.109 : Transit KELT-11b observed by CHEOPS (Benz+, 2021)
J/other/Sci/377.1211 : RV and LC of 8 M dwarf stars with planets (Luque+, 2022)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Epochs of measurements TDB (BJD-2450000)
16- 25 F10.3 m/s RV Radial velocity
27- 31 F5.3 m/s e_RV 1-sigma uncertainty of the radial velocity
33- 39 F7.2 m/s FWHM Full with at half maximum of the cross
correlation function
41- 44 F4.2 m/s e_FWHM 1-sigma uncertainty of the full with at half
maximum
46- 51 F6.2 m/s BIS Bisector span of the cross correlation
function
53- 56 F4.2 m/s e_BIS 1-sigma uncertainty of the bisector span
58- 63 F6.3 % C Contrast of the cross correlation function
65- 69 F5.3 % e_C 1-sigma uncertainty of the contrast
71- 75 F5.3 --- SMW CaII H&K Mount Wilson S-index
77- 81 F5.3 --- e_SMW 1-sigma uncertainty of the S-index
83- 88 F6.3 [-] log(R'HK) Logarithm of the R'HK activity index
90- 94 F5.3 [-] e_log(R'HK) 1-sigma uncertainty of the logarithm of the
R'HK activity index
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Acknowledgements:
Aldo S. Bonomo, aldo.bonomo(at)inaf.it
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(End) Luc Trabelsi [CDS] 26-Jan-2026