J/AJ/170/154 L 98-59 f confirmed with TESS, HARPS, ESPRESSO (Cadieux+, 2025)
Detailed architecture of the L 98-59 system and confirmation of a fifth planet
in the Habitable Zone.
Cadieux C., L'Heureux A., Piaulet-Ghorayeb C., Doyon R., Artigau E.,
Cook N.J., Coulombe L.-P., Roy P.-A., Lafreniere D., Lamontagne P.,
Radica M., Benneke B., Ahrer E.-M., Weisserman D., Cloutier R.
<Astron. J., 170, 154 (2025)>
=2025AJ....170..154C 2025AJ....170..154C
ADC_Keywords: Exoplanets; Radial velocities; Photometry; Spectra, optical
Keywords: Exoplanets ; Super Earths ; M dwarf stars ; Planetary interior ;
Transit timing variation method ; Transit photometry ; Radial velocity
Abstract:
The L 98-59 system, identified by TESS in 2019, features three
transiting exoplanets in compact orbits of 2.253, 3.691, and 7.451days
around an M3V star, with an outer 12.83day nontransiting planet
confirmed in 2021 using ESPRESSO. The planets exhibit a diverse range
of sizes (0.8-1.6R⊕), masses (0.5-3M⊕), and likely
compositions (Earth-like to possibly water-rich), prompting
atmospheric characterization studies with Hubble Space Telescope and
JWST. Here, we analyze 16 new TESS sectors and improve radial velocity
(RV) precision of archival ESPRESSO and HARPS data using a
line-by-line framework, enabling stellar activity detrending via a
novel differential temperature indicator. We refine the radii of
L 98-59 b, c, and d to 0.837±0.019R⊕,
1.329±0.029R⊕, and 1.627±0.041R⊕, respectively.
Combining RVs with transit timing variations (TTVs) of L 98-59 c and d
from TESS and JWST provides unprecedented constraints on the masses
and eccentricities of the planets. We report updated masses of
0.46±0.11M⊕ for b, 2.00±0.13M⊕ for c, and
1.64±0.07M⊕ for d, and a minimum mass of
2.82±0.19M⊕ for e. We additionally confirm L 98-59 f, a
nontransiting super-Earth with a minimal mass of 2.80±0.30M⊕
on a 23.06day orbit inside the Habitable Zone. The TTVs of L 98-59 c
and d (<3min, PTTV=396days) constrain the eccentricities of all
planets to near-circular orbits (e≤0.04). An internal structure
analysis of the transiting planets reveals increasing water-mass
fractions (fH2O) with orbital distance, reaching fH2O∼0.16 for
L 98-59 d. We predict eccentricity-induced tidal heating in L 98-59 b
with heat fluxes comparable to those of Io, potentially driving
volcanic activity.
Description:
L 98-59 (TOI-175, T=9.412) is a near Southern Continuous Viewing Zone
star that was observed at a 2min cadence with TESS in 25 sectors
between 2018 August and 2025 April. We collected the PDCSAP light
curves produced by the TESS Science Processing Operations Center
(SPOC). This work adds 16 new TESS sectors compared to the analysis
presented in Demangeon+2021 (J/A+A/653/A41) and 22 from
Kostov+2019 (2019AJ....158...32K 2019AJ....158...32K).
We obtained publicly accessible ESPRESSO observations of L 98-59 from
the ESO archive. This data set, described in detail in
Demangeon+2021 (J/A+A/653/A41), contains 66 spectra taken between 2018
November and 2020 March. The Echelle SPectrograph for Rocky Exoplanet and
Stable Spectroscopic Observations (ESPRESSO), installed on the Very
Large Telescope Interferometer (VLTI) at ESO's Paranal Observatory in
Chile, covers a wavelength range of 380 to 788nm. The replacement of
the fiber-link of ESPRESSO in 2019 June produced an RV offset. During
the analysis, we consider the data taken before and after this upgrade
as two instruments labeled "ESPRESSOpre" and "ESPRESSOpost."
The HARPS data set presented in Cloutier+2019 (J/A+A/629/A111) and
Demangeon+2021 (J/A+A/653/A41) was reanalyzed and integrated in this
study. A total of 166 L 98-59 spectra were collected with HARPS
between 2018 October and 2019 April, overlapping with the ESPRESSOpre
campaign. The High-Accuracy Radial velocity Planetary Searcher (HARPS)
is a spectrograph mounted on the 3.6m optical telescope at La Silla
Observatory in Chile. At some epochs, two consecutive exposures with
HARPS were taken. We work with the per-night binned velocities and end
up with a time series of 106 RVs.
We combined precise transit timing measurements of L 98-59 c and
L 98-59 d from JWST to constrain a global RV and TTV model. We used
two consecutive transits of L 98-59 c observed with JWST/NIRSpec and
reported in Scarsdale+2024 (2024AJ....168..276S 2024AJ....168..276S), a single transit of
L 98-59 d observed with JWST/NIRSpec and reported in
Gressier+2024 (2024ApJ...975L..10G 2024ApJ...975L..10G), and three additional transit
times obtained with JWST/NIRISS and JWST/NIRSpec will be presented in
a forthcoming publication (Benneke+2025, in prep).
Objects:
-----------------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------------
08 18 07.62 -68 18 46.8 L 98-59 = TOI-175
-----------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 51 93 Transit timing of L 98-59 c and d from TESS
tableb1.dat 53 173 Radial velocity and dTemp measurements of L 98-59
with HARPS and ESPRESSO
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See also:
I/322A : UCAC4 Catalogue (Zacharias+, 2012)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJ/715/1050 : Predicted abundances for extrasolar planets. I. (Bond+, 2010)
J/ApJS/200/15 : HARPS-TERRA project. I. (Anglada-Escude+, 2012)
J/ApJ/771/L45 : 3D global climate models for exopl. around M-star (Yang+, 2013)
J/ApJ/804/64 : Empirical and model parameters of 183 M dwarfs (Mann+, 2015)
J/A+A/605/L11 : YZ Ceti radial velocity curve (Astudillo-Defru+, 2017)
J/AJ/154/109 : California-Kepler Surv (CKS). III. Planet radii (Fulton+, 2017)
J/AJ/156/82 : RV characterization of TESS planets (Cloutier+, 2018)
J/A+A/629/A111 : L 98-59 (TOI 175) HARPS observations (Cloutier+, 2019)
J/ApJ/871/63 : How to constrain your M dwarf. II. Nearby binaries (Mann+, 2019)
J/A+A/627/A49 : Teegarden's Star RV and Hα curves (Zechmeister+, 2019)
J/AJ/159/211 : Exoplanets parameters from Kepler and K2 (Cloutier+, 2020)
J/A+A/642/A121 : LHS1140 radial velocity data (Lillo-Box+, 2020)
J/MNRAS/491/5287 : Exoplanet evaporation in multitransiting syst. (Owen+, 2020)
J/A+A/653/A41 : L 98-59 (TOI-175) ESPRESSO observations (Demangeon+, 2021)
J/A+A/666/A196 : Proxima telluric-corrected ESPRESSO RV (Allart+, 2022)
J/AJ/164/96 : SPIRou and IRD radial velocity of TOI-1452 (Cadieux+, 2022)
J/MNRAS/517/5050 : K2-18 HARPS time-series (Radica+, 2022)
J/AJ/165/167 : HARPS-N radial velocities of TOI-1695 (Cherubim+, 2023)
J/AJ/165/168 : Terrestrial planets in the Venus zone (Ostberg+, 2023)
J/A+A/670/A5 : GJ1022 radial velocity & FWHM data (Suarez Mascareno+, 2023)
J/AJ/168/252 : SPIRou & HARPS obs. template star parameters (Artigau+, 2024)
J/A+A/690/A79 : Barnard's star RV curves (Gonzalez Hernandez+, 2024)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Epoch-c [-4/651] Transit epoch number for Planet c,
since the reference epoch, T0
5- 17 F13.5 d BJD-c [2458356/2460774] Barycentric Julian Date of
mid-transit, Planet c
19- 25 F7.5 d e_BJD-c [6e-4/2e-3] Uncertainty in BJD-c
27- 29 I3 --- Epoch-d [-1/323]? Transit epoch number for Planet d,
since the reference epoch, T0
31- 43 F13.5 d BJD-d ? Barycentric Julian Date of mid-transit,
Planet d
45- 51 F7.5 d e_BJD-d [1e-3/1.8e-3]? Uncertainty in BJD-d
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.5 d JD [58408/58931] Reduced Barycentric Julian date,
BJD-2,400,000.0
13- 21 F9.3 m/s RVel [-5907/-5784] Radial velocity
23- 27 F5.3 m/s e_RVel [0.18/2.46] Uncertainty in RVel
29- 34 F6.3 K dTemp [-0.9/2.1] Differential temperature indicator
from LBL
36- 40 F5.3 K e_dTemp [0.04/0.46] Uncertainty in dTemp
42- 53 A12 --- Inst Instrument used (1)
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Note (1): Instrument as follows:
ESPRESSOpost = Echelle SPectrograph for Rocky Exoplanet and Stable
Spectroscopic Observations (ESPRESSO) installed on the
Very Large Telescope Interferometer (VLTI) at ESO's Paranal
Observatory in Chile, post replacement of the fiber-link from
June 2019 (26 occurrences)
ESPRESSOpre = Echelle SPectrograph for Rocky Exoplanet and Stable
Spectroscopic Observations (ESPRESSO) installed on the
Very Large Telescope Interferometer (VLTI) at ESO's Paranal
Observatory in Chile, pre replacement of the fiber-link from
June 2019 (26 occurrences)
HARPS = High-Accuracy Radial velocity Planetary Searcher at the 3.6m
telescope at La Silla Observatory in Chile (106 occurrences)
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 01-Jul-2026