11institutetext:  Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France 22institutetext: Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland 33institutetext: Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey, RH5 6NT, UK 44institutetext: Department of Physics, University of Warwick, Coventry, UK 55institutetext: Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, Santiago, Chile 66institutetext: Millennium Institute for Astrophysics (MAS), Santiago, Chile 77institutetext: Data Observatory Foundation, Chile 88institutetext: Institut d’astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France 99institutetext: Laboratório Nacional de Astrofísica, Rua Estados Unidos 154, 37504-364, Itajubá - MG, Brazil 1010institutetext: CFisUC, Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal 1111institutetext: IMCCE, UMR8028 CNRS, Observatoire de Paris, PSL University, Sorbonne Univ., 77 av. Denfert-Rochereau, 75014 Paris, France 1212institutetext: Departamento de Matemática y Física Aplicadas, Universidad Católica de la Santísima Concepción, Alonso de Rivera 2850, Concepción, Chile 1313institutetext: Université de Montréal, Département de Physique & Institut Trottier de Recherche sur les Exoplanètes, Montréal, QC H3C 3J7, Canada 1414institutetext: Canada-France-Hawaii Telescope (CFHT) Corporation, CNRS UAR2208, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743, USA 1515institutetext: Department of Astrophysical Sciences, Princeton University, NJ 08544, USA 1616institutetext: Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal 1717institutetext: Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua Campo Alegre ,4169-007 Porto, Portugal 1818institutetext: Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA 1919institutetext: NASA Exoplanet Science Institute – Caltech/IPAC, 1200 E. California Blvd, Pasadena, CA 91125 USA 2020institutetext: Department of Physics & Astronomy, McMaster University, 1280 Main St W, Hamilton, ON, L8S 4L8, Canada 2121institutetext: Department of Physics, McGill University, 3600 rue University, Montréal, Québec, H3A 2T8, Canada 2222institutetext: Department of Earth and Planetary Sciences, McGill University, 3450 rue University, Montréal, Québec, H3A 0E8, Canada 2323institutetext: Univ. Federal do Rio G. do Norte, UFRN, Dep. de Física, CP 1641, 59072-970, Natal, RN, Brazil 2424institutetext: Université de Toulouse, CNRS, IRAP, 14 avenue Belin, 31400 Toulouse, France 2525institutetext: Dept. of Earth Sciences, University of Hawai’i at Mänoa, Honolulu, HI 96822 USA 2626institutetext: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA 2727institutetext: Wesleyan University, Middletown, CT 06459, USA 2828institutetext: Max Planck Institute for Astronomy, Königstuhl 17, 69117 - Heidelberg, Germany 2929institutetext: NASA Ames Research Center, Moffett Field, CA 94035, USA 3030institutetext: LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France 3131institutetext: NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA 3232institutetext: SETI Institute, 189 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA 3333institutetext: Physics & Astrophysics Group, Dept. of Physical & Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada 3434institutetext: David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto. 50 St. George Street, Toronto, Ontario, M5S 3H4, Canada 3535institutetext: Department of Physics, University of Toronto, 60 St George Street, Toronto, Ontario, M5S 1A7, Canada 3636institutetext: Instituto de Astrofísica de Canarias (IAC), E-38200 La Laguna, Tenerife, Spain 3737institutetext: Dept. Astrofísica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain 3838institutetext: Department of Physics and Astronomy, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA 3939institutetext: Research Institute for Advanced Computer Science, Universities Space Research Association, Washington, DC 20024, USA 4040institutetext: European Southern Observatory, Alonso de Córdova 3107, Vitacura, Región Metropolitana, Chile 4141institutetext: Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan

# TOI-4860 b, a short-period giant planet transiting an M3.5 dwarf

J.M. Almenara TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarf X. Bonfils TOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarf E. M. Bryant TOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf A.
Jordán TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf G. Hébrard TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf E. Martioli TOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarf A. C. M. Correia
TOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a
short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period
giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf N. Astudillo-Defru TOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf C. Cadieux TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf L. Arnold TOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf É.
Artigau TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf G.Á.
Bakos TOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarf S.C.C. Barros TOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf D. Bayliss TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf F. Bouchy TOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf G.
Boué TOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarf R. Brahm TOI-4860 b, a
short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period
giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf A.
Carmona TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf D.
Charbonneau TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf D.R.
Ciardi TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf R.
Cloutier TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf M.
Cointepas TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarf N.J. Cook TOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarf N.B. Cowan TOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf X.
Delfosse TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf J. Dias
do Nascimento TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarf J.-F. Donati TOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarf R. Doyon TOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf T. Forveille TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf P. Fouqué TOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf E.
Gaidos TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf E.A.
Gilbert TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf J. Gomes
da Silva TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf J.D.
Hartman TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf K. Hesse
TOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a
short-period giant planet transiting an M3.5 dwarf M.J. Hobson TOI-4860 b, a
short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period
giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf J.M. Jenkins TOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf F.
Kiefer TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf V.B.
Kostov TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarf J. Laskar TOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarf M. Lendl TOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf A. L’Heureux TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf J.H.C. Martins TOI-4860 b, a short-period giant planet transiting
an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf
K. Menou TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf C. Moutou TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarf F. Murgas TOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860
b, a short-period giant planet transiting an M3.5 dwarf A.S. Polanski TOI-4860
b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-
period giant planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant
planet transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet
transiting an M3.5 dwarf D. Rapetti TOI-4860 b, a short-period giant planet
transiting an M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an
M3.5 dwarfTOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf E.
Sedaghati TOI-4860 b, a short-period giant planet transiting an M3.5
dwarfTOI-4860 b, a short-period giant planet transiting an M3.5 dwarf H. Shang
TOI-4860 b, a short-period giant planet transiting an M3.5 dwarfTOI-4860 b, a
short-period giant planet transiting an M3.5 dwarf

(Received ; Accepted)

We report the discovery and characterisation of a giant transiting planet
orbiting around a nearby M3.5V dwarf (d = 80.4 pc, $G$ = 15.1 mag, $K$=11.2
mag, $R_{\star}=0.354\pm 0.011$ $R_{\odot}$, $M_{\star}=0.3400\pm 0.0086$
$M_{\odot}$). Using the photometric time series from the Transiting Exoplanet
Survey Satellite (TESS) sectors 10, 36, 46, and 63, and near-infrared
spectrophotometry from ExTrA, we measured a planetary radius of $0.766\pm
0.026\leavevmode\nobreak\ \hbox{$\mathrm{R}_{\rm J}$}$ and an orbital period
of 1.52 days. With high-resolution spectroscopy taken by the CFHT/SPIRou and
ESO/ESPRESSO spectrographs, we refined the host star parameters
($\rm[Fe/H]=0.27\pm 0.12$) and measured the mass of the planet ($0.2729\pm
0.0058$ $\mathrm{M}_{\rm J}$). Based on these measurements, TOI-4860 b joins
the small set of massive planets found around mid-to-late M dwarfs ($<0.4$
$R_{\odot}$), providing both an interesting challenge to planet formation
theory and a favourable target for further atmospheric studies with
transmission spectroscopy. We identify an additional signal in the radial
velocity data that we attribute to an eccentric ($e=0.657\pm 0.089$) planet
candidate with an orbital period of $426.9\pm 7.4$ days and a minimum mass of
$1.66\pm 0.26$ $\mathrm{M}_{\rm J}$.

###### Key Words.:

stars: individual: TOI-4860 – stars: low-mass – (stars:) planetary systems –
techniques: photometric – techniques: radial velocities

##  1 Introduction

Twenty-five years ago, the discovery of GJ 876 b, a planet with twice the mass
of Jupiter, marked an important milestone in exoplanet research (Marcy et al.
1998; Delfosse et al. 1998). It was the first planet detected around an M
dwarf, and only the ninth exoplanet found around a main-sequence star at that
time. The discovery of GJ 876 b soon after the detection of 51 Pegasi b around
a solar-type star (Mayor & Queloz 1995), suggested that giant planets could
form just as easily around late-type stars. The pace of planet detections
around M dwarfs, however, remained much behind that around FGK stars, and,
instead, giant planets appear to have a decreasing occurrence rate with
decreasing stellar mass (Endl et al. 2006; Johnson et al. 2007; Bonfils et al.
2005).

Probing the whole sky for transiting planets, the Transiting Exoplanet Survey
Satellite (TESS, Ricker et al. 2015) survey vastly expands the target list and
therefore gains sensitivity to rare outcomes of planet formation. A new planet
population emerged: giant planets around very-low-mass stars (e.g., TOI-519 b,
Kagetani et al. 2023; TOI-3714 b, Cañas et al. 2022; TOI-3757 b, Kanodia et
al. 2022; TOI-5205 b, Kanodia et al. 2023; TOI-3235 b, Hobson et al. 2023).
These planets are massive in comparison to expectations for protoplanetary
disk masses around M dwarfs (Andrews et al. 2013; Gaidos 2017), and therefore
are interesting for the investigation of planetary formation.

Recently, Bryant et al. (2023) performed a systematic search for giant planets
transiting M dwarfs in the TESS photometry and measured an occurrence rate of
$0.194\pm 0.072\%$ giant planets with periods below 10 days per M dwarf
(0.08$-$0.71 $M_{\odot}$), and $0.134\pm 0.069\%$ for stellar masses between
0.088 and 0.4 $M_{\odot}$. Gan et al. (2023), also using the TESS data,
measured a hot Jupiters occurrence rate around early-type M dwarfs
(0.45$-$0.65 $M_{\odot}$) of $0.27\pm 0.09\%$. For comparison, the hot
Jupiters occurrence rate around G-type stars is $0.55\pm 0.14\%$ (Beleznay &
Kunimoto 2022). Further characterisation of these planets masses, orbits, and
general architecture is now key to understanding how they form.

We report here the validation and mass measurement of TOI-4860 b. Ground-based
photometry confirms that the transits around TOI-4860, initially identified by
TESS photometry, are produced by a giant planet. Doppler spectroscopy measures
its mass and helps characterise the host star. This new planet detection adds
to a small set of giant planets detected around stars with $M_{\star}<0.4$
$M_{\odot}$, a stellar mass regime where standard core accretion models are
not able to form giants (e.g., Burn et al. 2021), and therefore provides a
challenge to the hypothesis underlying these models. Additionally, TOI-4860 b
is an interesting target for atmospheric characterisation with transmission
spectroscopy.

In Sect. 2 we describe the data used to detect and characterise TOI-4860 b. In
Sect. 3 we characterise its host star, and in Sect. 4 we model the radial
velocity (RV) and transit data. Finally, in Sect. 5 we discuss the results of
our work.

##  2 Observations

###  2.1 TESS photometry

TOI-4860 was observed in four TESS sectors: one sector during the primary
mission (sector 10, March/April 2019), two sectors during the first extended
mission (sector 36, March/April 2021; sector 46, December 2021), and one
sector in the second extended mission (sector 63, March/April 2023). Only Full
Frame Image (FFI) data were collected for sectors 10, 36, and 46, at
respectively 30 min, 10 min, and 10 min cadence. For sector 63, data were
obtained as both postage stamps at a 2-min cadence and 200-s FFIs.

A transit signature with a 1.52-day period and 6% depth was first identified
from the FFIs by the Faint Star Search (Kunimoto et al. 2022) using data
products from the Quick-Look Pipeline (QLP, Huang et al. 2020a, b; Kunimoto et
al. 2021). The TESS Science Processing Operations Center (SPOC; Jenkins et al.
2016; Caldwell et al. 2020) at NASA Ames Research Center conducted a transit
search of Sector 36 on 5 May 2021 on an FFI 10-minute cadence observation with
an adaptive, noise-compensating matched filter (Jenkins 2002; Jenkins et al.
2010, 2020), producing a Threshold Crossing Event (TCE) for which an initial
limb-darkened transit model was fitted (Li et al. 2019) and a suite of
diagnostic tests were conducted to help make or break the planetary nature of
the signal (Twicken et al. 2018). The signature and associated diagnostics
were reviewed by the TESS Science Office and TOI-4860.01 was alerted as a TESS
Object of Interest (TOI) on 21 December 2021 (Guerrero et al. 2021). The
signal was repeatedly recovered as additional observations were made in
Sectors 46 and 63, and the transit signature passed all the diagnostic tests
presented in the Data Validation reports. The difference image centroiding
analyses constrain the location of the host star to within $3.5\pm 2.5\arcsec$
of the source of the transit signal.

For the analysis in Sect. 4, we used the Pre-search Data Conditioning Simple
Aperture Photometry (PDCSAP; Smith et al. 2012, Stumpe et al. 2012, 2014,
Caldwell et al. 2020) light curve of TOI-4860 (Fig. 1), produced by the SPOC,
which is corrected for dilution in the TESS aperture by known contaminating
sources. This is critical to ensure that no visually close-by targets that
could affect the depth of the transit are present in the 21″ TESS pixel and to
check for a contaminating eclipsing binary. Figure 2 shows a plot of the
target pixel file (TPF) from sector 10 and the aperture mask that is used for
the simple aperture photometry (SAP). We can see that no star overlaps the
TESS aperture down to 6 magnitude fainter than TOI-4860.

Figure 1: TESS PDCSAP photometry time series (sectors 10, 36, 46, and 63,
green dots), with the transits of TOI-4860 b highlighted in orange. The
sampling is 30 min for sector 10, 10 min for sectors 36 and 46, and 2 min for
sector 63. Figure 2: TESS target pixel file image of TOI-4860 in Sector 10
(created with tpfplotter, Aller et al. 2020). The electron counts are color-
coded. The red bordered pixels are used in the simple aperture photometry. The
size of the red circles indicates the Gaia DR2 magnitudes of all nearby stars
(Gaia Collaboration et al. 2018).

###  2.2 Inspection for contaminants

####  2.2.1 Proper motion

TOI-4860 has a proper motion of 177 mas/yr (Gaia Collaboration et al. 2023),
and therefore has moved by 6.7 arcsec from its position on the Palomar
Observatory Sky Survey (POSS, Minkowski & Abell 1963; Lasker et al. 1996) I
red plate taken in 1984. This offset is large enough to check for background
stars at the current position of TOI-4860, and we see none (Fig. 3).

Figure 3: Images extracted from POSS (retrieved from
https://archive.eso.org/dss/dss) and Pan-STARS (Chambers et al. 2016) surveys.
From left to right, the epochs are years 1984, 1991, and 2011, respectively.
The open red circle marks the position of the star determined by Gaia (Gaia
Collaboration et al. 2023). There is no background star at the current
position of TOI-4860.

####  2.2.2 Gaia assessment

In addition to proper motion, we used Gaia (Gaia Collaboration et al. 2016,
2023) to identify any wide stellar companions that may be bound members of the
system. Typically, these stars are already in the TESS Input Catalog (Stassun
et al. 2019) and their flux dilution to the transit has already been accounted
for in the transit fits and associated derived parameters. There are no
additional widely separated companions identified by Gaia that have the same
distance and proper motion as TOI-4860 (see also Mugrauer & Michel 2020,
2021).

The Gaia DR3 astrometry provides additional information on the possibility of
inner companions that may have gone undetected by either Gaia or high-
resolution imaging. The Gaia Renormalized Unit Weight Error (RUWE) is a metric
similar to a reduced chi-square, and values $\lesssim 1.4$ indicate that the
Gaia astrometric solution is consistent with the star being single whereas
RUWE values $\gtrsim 1.4$ indicate excess astrometric noise, which is often
caused by an unseen companion (e.g., Ziegler et al. 2020). TOI-4860 has a Gaia
DR3 RUWE value of 1.04 and therefore appears single. Additionally, TOI-4860
does not appear in the Gaia DR3 binary table; as such, the Gaia astrometric
fit is fully consistent with a single-star model.

####  2.2.3 High-resolution imaging

As part of our standard process for validating transiting exoplanets to assess
the possible contamination of bound or unbound companions on the derived
planetary radii (Ciardi et al. 2015), we also observed TOI-4860 with high-
resolution near-infrared adaptive optics (AO) imaging at Keck Observatory. The
observations were made with the NIRC2 instrument on Keck-II behind the natural
guide star AO system (Wizinowich et al. 2000) on 10 June 2023 UT in the
standard 3-point dither pattern that is used with NIRC2 to avoid the left
lower quadrant of the detector which is typically noisier than the other three
quadrants. The dither pattern step size was $3\arcsec$ and was repeated twice,
with each dither offset from the previous dither by $0.5\arcsec$. NIRC2 was
used in the narrow-angle mode with a full field of view of $\sim 10\arcsec$
and a pixel scale of approximately $0.0099442\arcsec$ per pixel. The Keck
observations were made in both the $Ks$ filter
$(\lambda_{o}=2.146;\Delta\lambda=0.311\leavevmode\nobreak\ \mu$m) and $J$
$(\lambda_{o}=1.248;\Delta\lambda=0.163\leavevmode\nobreak\ \mu$m) with an
integration time in each filter of 20 and 40 seconds for a total of 180 and
360 seconds, respectively. Flat fields were generated from a median average of
dark subtracted dome flats. Sky frames were generated from the median average
of the 9 dithered science frames; each science image was then sky-subtracted
and flat-fielded. The reduced science frames were combined into a single
combined image using a intra-pixel interpolation that conserves flux, shifts
the individual dithered frames by the appropriate fractional pixels; the final
resolution of the combined dithers was determined from the full-width half-
maximum of the point spread function; 0.101″ and 0.114″ for the two filters,
respectively. To within the limits of the AO observations, no stellar
companions were detected. The final $5\sigma$ limit at each separation was
determined from the average of all of the determined limits at that separation
and the uncertainty on the limit was set by the root mean square (RMS)
dispersion of the azimuthal slices at a given radial distance (Figure 4).

Figure 4: Companion sensitivity for the near-infrared adaptive optics imaging.
The black points represent the 5$\sigma$ limits and are separated in steps of
one full-width at half-maximum; the purple represents the azimuthal dispersion
(1$\sigma$) of the contrast determinations (see text). The inset image is of
the primary target showing no additional close-in companions.

###  2.3 Ground-based photometry with ExTrA

ExTrA (Bonfils et al. 2015) is a near-infrared (0.85 to 1.55 $\mu$m) multi-
object low-resolution spectrograph fed by three 60-cm telescopes located at La
Silla Observatory in Chile. One partial and six full transits were observed
using two or three of the ExTrA telescopes. The first of those transits
happened to be partial due to the then uncertain ephemeris, and helped refine
the ephemeris for the following observations.

We used 8$\arcsec$ aperture fibres and the lowest-resolution mode
($R$$\sim$20) of the spectrograph, a combination that is optimal for the
target’s magnitude, with an exposure time of 60 seconds. Five fibres are
positioned in the focal plane of each telescope to select light from the
target and four comparison stars. We chose comparison stars1112MASS
J12145957-1303121, 2MASS J12154216-1243286, 2MASS J12130766-1243315, and 2MASS
J12123143-1255153. with 2MASS $J$-magnitudes (Skrutskie et al. 2006a) and
effective temperatures (Gaia Collaboration et al. 2018) similar to the target.
The resulting ExTrA data were analysed using a custom data reduction software,
described in more detail in Cointepas et al. (2021).

###  2.4 Radial velocities

####  2.4.1 SPIRou

The SPIRou instrument is a near-infrared high-resolution (980–2450 nm;
$R=70,000$) high-stability ($\sim$1 m s-1) velocimeter and spectropolarimeter
installed at the Cassegrain focus of the 3.6 m CFHT at Mauna Kea (Donati et
al. 2020). TOI-4860 was observed between March 2022 and July 2023 with SPIRou
as part of the large program SPIRou Legacy Survey (SLS; ID P42, PI: Jean-
François Donati). It was observed at 28 observing epochs with four
polarimetric exposures per epoch, except on 4 July 2023 when the sequence was
interrupted after the first exposure. In total, 109 spectra were acquired with
integration time changing from 184 s for the first 8 exposures to 602 s for
the rest of the sequence. The median signal-to-noise ratio (S/N) per pixel
measured in the middle of $H$ band for the two exposure times were 9 and 28
respectively.

To process the raw data obtained with SPIRou, we employed A PipelinE to Reduce
Observations (APERO, Cook et al. 2022) version 0.7.275. The APERO software
initially corrects detector effects, removes constant background thermal
components, and detects bad pixels and cosmic-ray impacts. Subsequently, it
calculates the position of echelle spectral orders and optimally extracts
spectra from fibres A, B, and C into 2D order-separated e2ds and 1D order-
merged s1d spectra. A blaze function is derived from flat-field exposures. The
wavelengths of the spectra are determined from a set of nightly calibrations
following Hobson et al. (2021). An absolute calibration of wavelengths with
respect to the Solar System barycentric rest frame is also performed using the
current Barycentric Earth Radial Velocity (BERV) and the Barycentric Julian
Date (BJD) of each exposure with the barycorrpy code (Kanodia & Wright 2018;
Wright & Eastman 2014). Finally, APERO applies a three-step telluric
correction that we summarise here with a complete description to come (Artigau
et al. in prep.). First, the extracted spectrum is pre-cleaned by fitting a
TAPAS (Bertaux et al. 2014) atmospheric model. Second, an empirical removal of
residuals left after step one is performed using observations of fast-rotating
hot stars observed with SPIRou at varying conditions (e.g., airmass, water
column). Third, finite resolution artefacts from telluric modelling (Wang et
al. 2022) are mitigated, leaving final residuals at the level of the Principal
Component Analysis (PCA) method of Artigau et al. (2014).

The line-by-line (LBL) method of Artigau et al. (2022) was then applied on the
telluric-corrected spectra of TOI-4860 to measure its RVs. Several other TESS
exoplanets were characterised with SPIRou using the LBL method in recent
years: TOI-1759 b (Martioli et al. 2022), TOI-2136 b, (Gan et al. 2022),
TOI-1452 b (Cadieux et al. 2022), TOI-1695 b (Kiefer et al. 2023). The LBL
method is a statistical framework where the RV is obtained from the weighted
average of thousands of independent velocity measurements on individual
spectral lines over the full wavelength domain. Velocities are derived from
the difference between the observations and a high-S/N template spectrum of
the star (Bouchy et al. 2001 formalism). In practice, one can use the template
of any similar spectral type star in the LBL calculation. Since TOI-4860 is
relatively faint, we chose to use instead the template of Gl 905, a bright M5V
star observed in the SLS over three years. The final RVs are presented in
Table 5 and have median uncertainties of respectively 34.3 m s-1 and 16.2 m
s-1 for the 184 s and 602 s exposures.

The TOI-4860 SPIRou observations were performed in circular polarisation mode
(Stokes V), where each visit consists of a set of four exposures that provide
a polarimetric spectrum. We use previously-described methods (Donati et al.
1997; Martioli et al. 2020, 2022; Cook et al. 2022), implemented in the APERO
pipeline, to calculate the polarimetric spectra of TOI-4860 and analyse the
Stokes V spectra using Least Squares Deconvolution (LSD) technique as in
Donati et al. (1997). With a typical S/N of only 30 to 40, and even using LSD
analysis, we obtained a mean polarimetric RMS per visit of $\sigma_{V}=0.2\pm
0.1$%. Such precision is sensitive to a disk-integrated longitudinal magnetic
field on the stellar surface on the order of $B_{\ell}>20$ G. Non-detections
suggest that TOI-4860 is not extremely active, but moderate magnetic activity
cannot be completely ruled out.

####  2.4.2 ESPRESSO

We obtained seven spectra of TOI-4860 with the Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations (ESPRESSO; Pepe et al. 2021)
at the 8.2 m ESO Very Large Telescope (VLT) array, at the Paranal Observatory
in Chile. The observations were obtained from January to February 2023 in
Program ID: 0110.C-4069 (PI: Jordán) as part of a long-running campaign to
obtain mass measurements for giant planets transiting low-mass host stars.
Initially, candidates for this campaign were drawn from the HAT-South survey
(Bakos et al. 2013), and more recently from the TOI list (Guerrero et al.
2021) and our own dedicated search of the TESS FFI data (Bryant et al. 2023).

We observed TOI-4860 in the single UT, HR mode (1′′ fibre, R$\sim$140,000)
over a spectral range from $\sim$380 to $\sim$780 nm. The spectrograph is
contained in a temperature and pressure-controlled vacuum vessel to avoid
spectral drifts, and records cross-dispersed echelle spectra on two detectors.
They were read out in the 2x1 binned mode, which presents a reduced level of
continuum noise as compared to the unbinned readout mode. The calibration
fibre (fibre B) was placed on sky in order to monitor and remove any possible
contamination from the moon, as well as any sky emission lines.

The recorded spectra have a median S/N value of $\sim$ 8 at 550 nm, with this
value rising to $\sim$ 25 towards the red end of the spectrum. The spectra
were reduced with the updated version of the dedicated Data Reduction Software
(DRS; v. 3.0.0), which among other improvements, mitigates the bug in the
exposure meter data tables affecting the flux-weighted mid-exposure time
calculation. The reduction includes all the standard steps, whereby the
pipeline provides radial velocity measurements by fitting a Gaussian function
to the measured cross-correlation function (CCF; Baranne et al. 1996; Pepe et
al. 2002). This CCF is calculated using a stellar template matching closest
the spectral type of the star (M4 in this case). The measured RVs are given in
Table 5.

##  3 Stellar parameters

TOI-4860 is an M-type star located at a distance of $80.42\pm 0.22$ pc (Gaia
Collaboration et al. 2016, 2023; Lindegren et al. 2021). The astrometry,
photometry, and stellar parameters are reported in Table 1.

We derived the mass and radius of TOI-4860 from empirical relations based on
luminosity. We used the Gaia-corrected (Gaia Collaboration et al. 2016, 2023;
Lindegren et al. 2021) parallax determination ($12.434\pm 0.034$ mas) to
compute the distance and an absolute magnitude of $M_{K_{s}}=6.648\pm 0.027$.
We then used the empirical relations of Mann et al. (2019) and Mann et al.
(2015) to derive a mass of $M_{\star}=0.3400\pm 0.0086$ $M_{\odot}$ and a
radius of $R_{\star}=0.354\pm 0.011$ $R_{\odot}$, respectively. We derived an
alternate stellar radius from the spectral energy distribution (SED) that we
constructed using the magnitudes from Gaia (Riello et al. 2021), the 2-Micron
All-Sky Survey (2MASS; Skrutskie et al. 2006b; Cutri et al. 2003), and the
Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010; Cutri & et al.
2013). Those measurements are listed in Table 1. We modelled these magnitude
measurements using the procedure described in Díaz et al. (2014), with the
PHOENIX/BT-Settl (Allard et al. 2012) stellar atmosphere models. We used
informative priors for the effective temperature ($T_{\mathrm{eff}}=3191\pm
70$ K), and metallicity ($[\rm{Fe/H}]=0.27\pm 0.12$ dex) derived from the co-
added ESPRESSO spectra (which we analysed with SpecMatch-Emp; Yee et al.
2017), and for the distance from Gaia. We used uniform priors for the rest of
the parameters. We used an additive jitter (Gregory 2005) for each set of
photometric bands (Gaia, 2MASS, and WISE). The parameters, priors, and
posteriors are listed in Table 4. The maximum a posteriori (MAP) model is
shown in Fig 5. The derived SED radius ($R_{\star}=0.371\pm 0.010$
$R_{\odot}$) is compatible ($1.5\sigma$) with the radius computed above using
an empirical radius-luminosity relation. The derived SED
$T_{\mathrm{eff}}=3255\pm 49$ K, which corresponds to an M3.5V spectral type
(Pecaut & Mamajek 2013), is our adopted value.

Table 1: Stellar parameters for TOI-4860 (TIC 335590096, UCAC4 385-060574,
2MASS J12141555-1310290, WISE J121415.40-131029.3, Gaia DR3
3571038605366263424).

Parameter | Value | Refs
---|---|---
Astrometry |  |
Right ascension (J2016), $\alpha$ | 12h14m15.34s | 1
Declination (J2016), $\delta$ |  $-$13o10’29.43” | 1
Parallax, $\pi$ [mas] | $12.434\pm 0.034$ | 1,2
Distance, d [pc] | $80.42\pm 0.22$ | 1,2
Proper motion RA [mas/year] | $-177.238\pm 0.039$ | 1
Proper motion D [mas/year] | $-5.430\pm 0.033$ | 1
Photometry |  |
V [mag] | $16.47\pm 0.02$ | 3
Gaia-BP [mag] | 16.7328 $\pm$ 0.0074 | 1
Gaia-G [mag] | $15.0774\pm 0.0030$ | 1
Gaia-RP [mag] | 13.8435 $\pm$ 0.0033 | 1
TESS magnitude [mag] | $13.7726\pm 0.0079$ | 3
J [mag] | $12.056\pm 0.022$ | 4
H [mag] | $11.431\pm 0.026$ | 4
$K_{s}$ [mag] | $11.175\pm 0.026$ | 4
WISE-W1 [mag] | 11.016 $\pm$ 0.023 | 5
WISE-W2 [mag] | 10.886 $\pm$ 0.020 | 5
WISE-W3 [mag] | 10.96 $\pm$ 0.14 | 5
Stellar parameters |  |
Spectral type | M3.5 | 6
$M_{K_{s}}$ [mag] | $6.648\pm 0.027$ | 1,2,4,7
Stellar radius, $R_{\star}$ [$R_{\odot}$ ] | $0.354\pm 0.011$ | 7,8
Stellar mass, $M_{\star}$ [$M_{\odot}$ ] | $0.3400\pm 0.0086$ | 7,9
Effective temperature, $T_{\rm eff}$ [K] | $3255\pm 49$ | 7, SED
Surface gravity, log g [cgs] | $4.872\pm 0.029$ |  $R_{\star}$, $M_{\star}$
Metallicity, [Fe/H] [dex] | $0.27\pm 0.12$ | 7,10
$\log R^{\prime}_{HK}$ | $-5.65\pm 0.12$ | 7

  * •

References : 1) Gaia Collaboration et al. (2023), 2) Lindegren et al. (2021),
3) Stassun et al. (2019), 4) Cutri et al. (2003), 5) Cutri & et al. (2013), 6)
Pecaut & Mamajek (2013), 7) This work, 8) Mann et al. (2015), 9) Mann et al.
(2019), 10) Yee et al. (2017).

Figure 5: Spectral energy distribution of TOI-4860. The solid line is the MAP
PHOENIX/BT-Settl interpolated synthetic spectrum, red circles are the absolute
photometric observations (the jitter has been added quadratically to the data
error bars) and gray open circles are the result of integrating the synthetic
spectrum in the observed band passes.

The flux around the calcium lines is low but using the co-added ESPRESSO
spectra, we were able to measure the value of $\log R^{\prime}_{HK}=-5.65\pm
0.12$, derived from the calcium doublet. This translates to an estimated
stellar rotation period of P${}_{\rm rot}=114\pm 22$ days using the activity-
rotation relation of Astudillo-Defru et al. (2017). Such a rotation period
falls within the distribution of the “slow-rotator” population among mid-M-
type dwarfs in the field (Newton et al. 2017; Kiman et al. 2021; Popinchalk et
al. 2021), and thus the star is likely in the Skumanich-like spin-down phase
where the braking law is strongly rotation-dependent and period is a predictor
of age. The effective temperature of TOI-4860 (3255K) is at the poorly
constrained cool end of the 4 Gyr gyrochonology calibration based on rotation
periods of M67 M dwarf cluster members (Dungee et al. 2022; Gaidos et al.
2023), but adopting this yields an age of $\sim$2.2 Gyr. The star could be
older if it has gained angular momentum from the close-in planet via tides and
more rapidly rotating and active as a result (Ilic et al. 2022).

##  4 Analysis and modelling

We used the software package juliet (Espinoza et al. 2019) to model the
photometric and radial-velocity data. The algorithm is built on many publicly
available tools for the modelling of transits (batman, Kreidberg 2015), RVs
(radvel, Fulton et al. 2018), and Gaussian processes (GPs) (george,
Ambikasaran et al. 2015; celerite, Foreman-Mackey et al. 2017). In order to
compare different models, juliet efficiently computes the Bayesian evidence
($\mathcal{Z}$) using dynesty (Speagle 2020), a python package to estimate
Bayesian posteriors and evidence using nested sampling methods. Instead of
starting with an initial parameter vector centred on a likelihood maximum
discovered through optimisation techniques, nested sampling algorithms sample
directly from the given priors.

###  4.1 Transit chromaticity with TESS and ExTrA photometry

A wavelength-dependent transit depth would suggest a false positive scenario
involving an eclipsing binary. We, therefore, performed a joint fit of both
TESS and ExTrA photometry. To push further the chromatic analysis, in addition
to ExTrA’s full wavelength range (0.85 to 1.55 $\mu$m) light curve, we
synthesised from the ExTrA spectrophotometry photometry in the UKIRT-WFCAM
filters,222Retrieved from the SVO Filter Profile Service
(http://svo2.cab.inta-csic.es/theory/fps/, Rodrigo et al. 2012; Rodrigo &
Solano 2020) to produce four additional light curves: a truncated Z band (Z∗),
a $Y$, a $J$, and a truncated H band (H∗), shown in Fig. 11. The analysis is
similar to that presented in Sect. 4.4 except that radial velocities are not
used and the eccentricity is fixed to zero. All planetary parameters except
for the planet-to-star radius ratio ($R_{p}/R_{\star}$) are common to all data
sets, to allow for a different transit depth at each band, whose posteriors
median, and 68.3% credible interval (CI) are listed in Table 2. As shown in
Fig. 6 the photometry for all of these bandpasses is consistently modelled
with a similar $R_{p}/R_{\star}$. No chromaticity is seen, lending confidence
in the planet detection rather than a scenario with a blended binary333An
equivalent analysis was done with just the first full ExTrA transit and the
first two TESS sectors prior to the acquisition of radial velocity
observations..

Table 2: Inferred $R_{p}/R_{\star}$ in different bands.

Band |  $\lambda_{\rm pivot}$ [nm] | Prior | Median and 68.3% CI
---|---|---|---
TESS | 769.8 | $U(0.1,0.3)$ | $0.2202^{+0.0027}_{-0.0030}$
ExTrA | 1165.4 | $U(0.1,0.3)$ | $0.2204^{+0.0025}_{-0.0028}$
ExTrA $Z^{*}$ | 889.8 | $U(0.1,0.3)$ | $0.2174^{+0.0034}_{-0.0036}$
ExTrA $Y$ | 1030.5 | $U(0.1,0.3)$ | $0.2190^{+0.0029}_{-0.0031}$
ExTrA $J$ | 1248.3 | $U(0.1,0.3)$ | $0.2192^{+0.0027}_{-0.0029}$
ExTrA $H{*}$ | 1526.4 | $U(0.1,0.3)$ | $0.2220^{+0.0041}_{-0.0042}$
444The table lists: band, $\lambda_{\rm pivot}$ (Koornneef et al. 1986),
prior, posterior median, and 68.3% CI. $U(a,b)$: A uniform distribution
defined between a lower $a$ and an upper $b$ limit.

Figure 6: Posterior distribution comparison for $R_{p}/R_{\star}$ (error bars)
computed for different bands (shown and labeled with different colors). TESS,
ExTrA (0.85 to 1.55 $\mu$m), Z∗, Y, J, and H∗ data are fitted jointly with a
different $R_{p}/R_{\star}$ parameter for each of the data sets. The
horizontal solid and dotted grey lines represent the posterior median and
68.3% CI of $R_{p}/R_{\star}$ inferred in Sect. 4.4.

###  4.2 Transit timing variations

Transit timing variations (TTVs) would indicate the presence of additional
planets (Agol et al. 2005; Holman & Murray 2005) or orbital decay (Patra et
al. 2017). We analysed the TESS and ExTrA transit photometry with two models:
one with a linear ephemeris, and a second allowing for the time of individual
transits to vary (with uniform priors of $\pm$10 minutes width around the
linear ephemeris of the first model). The resulting TTVs are shown in Fig. 12.
A model comparison strongly favours (Kass & Raftery 1995) the model with a
linear ephemeris (P, T0) over the one with TTVs (log-Bayes factor
$\mathcal{Z}_{\rm P,T_{0}}/\mathcal{Z}_{\rm TTVs}$ of $92.54\pm 0.75$).

###  4.3 Radial velocity

The RVs are listed in Table 5. One ESPRESSO and six SPIRou observations were
taken during transit. The $\log R^{\prime}_{HK}$ is indicative of a slow
rotator, which would imply a Rossiter–McLaughlin effect (Rossiter 1924;
McLaughlin 1924) semi-amplitude of just $\sim$5 m s-1 (based on Prot,
estimated from the $\log R^{\prime}_{HK}$, we computed a $v$ sin $i_{\star}$
of $\sim$160 m s-1). Due to the difference in precision, we use only the
SPIRou in-transit observations. For the SPIRou data, we used the nightly
weighted average (we excluded the spectra on BJD 2460096.806090 because it is
an outlier, and BJD 2460064.896367 and 2460064.903591 because of low S/N of
about 2.5 in the middle of $H$ band). To choose the model for the RVs in the
global fit, we first analyse the radial velocity alone.

Fig. 13 shows the periodogram of SPIRou radial velocities, whose highest peak
corresponds to the period of TOI-4860 b. The residuals after removing the
signal of TOI-4860 b show additional signals at longer periods. This finding
is also supported by the ESPRESSO data, for which a model with a circular
planet (with priors on ephemeris from the transit observations) and a drift in
radial velocity are strongly favoured relative to the same model without drift
(log-Bayes factor of $3.88\pm 0.30$). We conducted a joint modelling of the
SPIRou and ESPRESSO data to search for a second planet. We assumed a circular
orbit for the transiting planet, and added a Keplerian with a period range
between 10 and 1000 days. The marginal posterior distribution of the trial
period shows a peak at 427 days (see Fig. 13). The log-Bayes factor for this
model with respect to the one-planet model is $12.28\pm 0.35$, which can be
interpreted as very strong evidence in favour of a second planet in the system
(planet c candidate). We therefore used a model with two Keplerians for the
joint fit of transit photometry and RVs. To confirm whether the additional
signal in the RVs corresponds to a second planet in the system, more data is
needed. The current time-span of 480 days is too close to the proposed period,
and there is poor phase coverage.

The posterior of the SPIRou jitter in the two-planet modelling is $27\pm
6\leavevmode\nobreak\ \hbox{m\,s${}^{-1}$}$, doubling the SPIRou
uncertainties. This jitter is probably inherent to the SPIRou data since the
ESPRESSO data do not support it.

###  4.4 Joint fit of all data

We modelled the TESS (extracting data spanning three transit durations around
the centre of each transit) and ExTrA (only the full wavelength range, 0.85 to
1.55 $\mu$m) transit photometry, and the SPIRou and ESPRESSO RVs. For the
transit photometry, a GP was used to model the residuals, with the approximate
Matern kernel, with different kernel hyperparameters for each transit
observation, except for the TESS data, for which we used common kernel
hyperparameters within each sector. For TESS sectors 10, 36, and 46 we
oversampled the model in time and accounted for the integration time of the
observations through binning (Kipping 2010). The RV model consists of two
Keplerians. We sampled from the posterior with dynesty (Speagle 2020). In
Table 3 we list the prior, the median, and the 68% CI of the marginal
distributions of the inferred system parameters. We used the stellar mass and
radius derived in Sect. 3 to compute the planetary mass and the radius of
TOI-4860 b. Figures 7 and 8 show the data sets and the model from this
analysis. The posterior of the stellar density ($11.70\pm
0.84\leavevmode\nobreak\ \mathrm{g\;cm^{-3}}$) is consistent with the value
derived from the stellar mass and radius in Sect. 3 ($10.8\pm
1.1\leavevmode\nobreak\ \mathrm{g\;cm^{-3}}$).

Table 3: Inferred system parameters.

Parameter | Units | Prior | Median and 68.3% CI
---|---|---|---
_Star_ |  |  |
Mean density, $\rho_{\star}$ |  [$\mathrm{g\;cm^{-3}}$] | $U(5,20)$ | $11.70\pm 0.84$
$q_{1}$ TESS |  | $U(0,1)$ | $0.34^{+0.26}_{-0.16}$
$q_{2}$ TESS |  | $U(0,1)$ | $0.29^{+0.30}_{-0.17}$
$q_{1}$ ExTrA |  | $U(0,1)$ | $0.136^{+0.21}_{-0.085}$
$q_{2}$ ExTrA |  | $U(0,1)$ |  $0.26^{+0.39}_{-0.19}$
_Planet b_ |  |  |
Semi-major axis, $a$ | [au] |  | $0.01808\pm 0.00015$
Eccentricity, $e$ |  |  |  ¡ 0.035(a), ($0.0077^{+0.013}_{-0.0056}$)
Argument of pericentre, $\omega$ | [°] |  | $240\pm 130$
Inclination, $i_{p}$ | [°] |  | $88.51^{+0.58}_{-0.36}$
Radius ratio, $R_{\mathrm{p}}/R_{\star}$ |  |  | $0.2228^{+0.0028}_{-0.0040}$
Scaled semi-major axis, $a/R_{\star}$ |  |  | $10.98\pm 0.36$
Impact parameter, $b$ |  |  | $0.294^{+0.064}_{-0.11}$
Transit duration, $T_{14}$ | [h] |  | $1.231\pm 0.011$
T0 \- 2 460 000 |  [BJDTDB] | $U(36.6907,36.6918)$ | $36.69124\pm 0.00010$
Orbital period, $P$ | [d] | $U(1.522757,1.522761)$ | $1.52275906\pm 3.1\times 10^{-7}$
RV semi-amplitude, K |  [m s-1] |  $U$(90, 110) | $98.9\pm 1.3$
Radius, $R_{\mathrm{p}}$ |  [$\mathcal{R}^{\rm N}_{e\rm E}$] |  | $8.58\pm 0.30$
|  [$\mathcal{R}^{\rm N}_{e\rm J}$] |  | $0.766\pm 0.026$
Mass, $M_{\mathrm{p}}$ |  [$\mathrm{M_{E}}$ ] |  | $86.7\pm 1.9$
|  [$\mathrm{M}_{\rm J}$] |  | $0.2729\pm 0.0058$
Mean density, $\rho_{\mathrm{p}}$ |  [$\mathrm{g\;cm^{-3}}$] |  | $0.754\pm 0.085$
Surface gravity, $\log$ $g_{\mathrm{p}}$ | [cgs] |  | $3.062\pm 0.032$
Equilibrium temperature, Teq | [K] |  | $694\pm 15$
Insolation flux |  [FE] |  | $42.5\pm 1.9$
$r_{1}$ |  | $U(0,1)$ | $0.529^{+0.043}_{-0.074}$
$r_{2}$ |  | $U(0.20,0.24)$ | $0.2228^{+0.0028}_{-0.0040}$
$\sqrt{e}\cos{\omega}$ |  | $U(-1,1)$ | $-0.021\pm 0.060$
$\sqrt{e}\sin{\omega}$ |  | $U(-1,1)$ |  $-0.017\pm 0.097$
_Planet c_ |  |  |
Semi-major axis, $a$ | [au] |  | $0.776\pm 0.011$
Eccentricity, $e$ |  |  | $0.657\pm 0.089$
Argument of pericentre, $\omega$ | [°] |  | $222\pm 14$
Scaled semi-major axis, $a/R_{\star}$ |  |  | $471\pm 17$
T0 \- 2 460 000 |  [BJDTDB] | $U(-200,350)$ | $92\pm 19$
Orbital period, $P$ | [d] | $U(350,550)$ | $426.9\pm 7.4$
RV semi-amplitude, K |  [m s-1] |  $U$(0, 250) | $121\pm 27$
Minimum mass, $M_{\mathrm{p}}\sin{i}$ |  [$\mathrm{M}_{\rm J}$] |  | $1.66\pm 0.26$
Equilibrium temperature, Teq | [K] |  | $106.0\pm 2.5$
Insolation flux |  [FE] |  | $0.0230\pm 0.0012$
$\sqrt{e}\cos{\omega}$ |  | $U(-1,1)$ | $-0.595^{+0.14}_{-0.094}$
$\sqrt{e}\sin{\omega}$ |  | $U(-1,1)$ |  $-0.54\pm 0.18$
_RV_ |  |  |
SPIRou jitter |  [m s-1] | $J(0.01,80)$ | $26.9\pm 5.4$
SPIRou offset |  [m s-1] | $U(20500,20800)$ | $20662\pm 16$
ESPRESSO jitter |  [m s-1] | $J(0.01,10)$ | $0.14^{+0.73}_{-0.12}$
ESPRESSO offset |  [m s-1] | $U(20400,20650)$ |  $20571.1\pm 9.1$
_Photometry_ |  |  |
Offset relative flux | [Relative flux] | $N(0,0.01)$ | (b)
Additive jitter | [ppm] | $J(1,1000)$ | (b)
Amplitude of the GP | [Relative flux] | $J(10^{-6},0.1)$ | (b)
Timescale of the GP | [days] | $J(0.001,10)$ | (b)
555The table lists: prior, posterior median, and 68.3% CI. Parameters without
prior are derived parameters. (a) Upper limit, 95% confidence. (b) The
parameters listed for the photometry are different for each TESS sector and
for each individual transit observed with each of the telescopes of ExTrA. The
parameters $q_{1}$ and $q_{2}$ are the quadratic limb-darkening coefficients
parameterised using Kipping (2013). The parameters $r_{1}$ and $r_{2}$ are the
impact parameter and transit depth parameterised using Espinoza (2018). The
planetary equilibrium temperature is computed for zero albedo and full
day/night heat redistribution. IAU 2012: au = 149 597 870 700 m . IAU 2015:
$\mathcal{R}^{\rm N}_{\odot}$= 6.957$\;\times 10^{8}$ m, $\mathcal{R}^{\rm
N}_{e\rm E}$ = 6.378 1$\;\times 10^{6}$ m, $\mathcal{(GM)}^{\rm N}_{\odot}$=
1.327 124 4$\;\times 10^{20}$ $\rm{m^{3}\;s^{-2}}$, $\mathcal{(GM)}^{\rm
N}_{\rm E}$= 3.986 004$\;\times 10^{14}$ $\rm{m^{3}\;s^{-2}}$,
$\mathcal{R}^{\rm N}_{e\rm J}$ = 7.149 2$\;\times 10^{7}$ m,
$\mathcal{(GM)}^{\rm N}_{\rm J}$= 1.266 865 3$\;\times 10^{17}$
$\rm{m^{3}\;s^{-2}}$. $M_{\odot}$ = $\mathcal{(GM)}^{\rm
N}_{\odot}$/$\mathcal{G}$, $\mathrm{M_{E}}$ = $\mathcal{(GM)}^{\rm N}_{\rm
E}$/$\mathcal{G}$, $\mathrm{M}_{\rm J}$= $\mathcal{(GM)}^{\rm N}_{\rm
J}$/$\mathcal{G}$. CODATA 2018: $\mathcal{G}$ = 6.674 30$\;\times 10^{-11}$
$\rm{m^{3}\;kg^{-1}\;s^{-2}}$. $U(a,b)$: A uniform distribution defined
between a lower $a$ and an upper $b$ limit. $J(a,b)$: Jeffreys (or log-
uniform) distribution defined between a lower $a$ and upper $b$ limit.
$N(\mu,\sigma)$: Normal distribution prior with mean $\mu$, and standard
deviation $\sigma$.

Figure 7: Modelling of transit photometry and RVs of TOI-4860. Top panel:
ExTrA transit photometry observations of TOI-4860 b. Each column corresponds
to a night (labelled with format YYYY-MM-DD) and each line to an ExTrA
telescope (labelled T1, T2, and T3) that is offset vertically for clarity. For
each transit, the median model (black line), and 68% CI (grey band, barely
visible) computed from 1000 random posterior samples are shown. Middle panel:
TESS (separated by sector) and ExTrA transits detrended with the MAP model
(whose transit component is shown as a grey line) and phase-folded. TESS
sector 10 looks more V-shaped due to the 30-min sampling. Bottom panel: SPIRou
RVs (main panel on the left, red error bars), median model (black line), and
68% CI (grey band). Residuals to the median model (bottom left). Idem for
ESPRESSO RVs (right panels, blue error bars). The time span of the ESPRESSO
panel is highlighted as a blue band in the SPIRou panel.

Figure 8: Phased RVs. Top panel: SPIRou (red error bars) and ESPRESSO (blue
error bars) RVs corrected for the MAP Keplerian orbit of planet c and phase-
folded to the period of planet b (the MAP jitter has been added quadratically
to the data error bars). The black line is the best-fit Keplerian model from
the joint fit. Bottom panel: Idem for planet c candidate.

##  5 Results and discussion

In this paper, we present the discovery and characterisation of a giant
planet, TOI-4860 b, transiting an M3.5 dwarf, with a period of 1.52 days. The
exoplanet was detected by the TESS mission, then characterised from ground-
based photometric follow-up using ExTrA and from precise RV measurements using
both SPIRou and ESPRESSO.

The giant planet is very close to its host star, at only 1.8 times the Roche
limit. Therefore, we expect that the system undergoes strong tidal
interactions, which distort the planet and lead to orbital decay. Adopting a
radial fluid Love number identical to that of Jupiter, $h_{f}=1.5$, we
estimate a difference between the longest and the shortest radius of the
planet of about 3% (Correia 2014). In addition, since the planet’s mean radius
is about 22% of the stellar radius, we expect $\sim 60$ ppm discrepancies with
respect to a spherical planet during transit ingress and egress (see Fig. 9).
These variations are similar to those observed for WASP-103 b (Akinsanmi et
al. 2019; Barros et al. 2022), and can thus be used to probe the interior
structure of the planet using the transit light curves (Ragozzine & Wolf 2009;
Correia 2014). The tidal dissipation of M-dwarf stars is unknown, but often
believed to be similar to that of other convective stars (e.g. Mathis 2015).
Assuming a tidal quality factor of $Q_{*}^{\prime}=10^{5}$, we estimate a
variation in the orbital period of about $\dot{P}\sim 10^{-9}$ day/yr
(Maciejewski et al. 2018). This rate is not detectable with current
instrumentation, but a direct estimation of $\dot{P}$ can still be used to put
a lower limit in the tidal $Q-$factor of the star (e.g. Barros et al. 2022).

Figure 9: Difference between the transit light curves of an ellipsoidal and a
spherical planet for TOI-4860 b, obtained with stellar uniform flux.

A long-standing prediction from core accretion planet formation is that giant
planets would not form around low-mass stars (Laughlin et al. 2004). In
particular, the models of Burn et al. (2021) are unable to form giant planets
around stars with masses $M_{*}\lesssim 0.4M_{\odot}$. The lack of such
systems from the first ground-based transit surveys, such as WASP (Pollacco et
al. 2006; Gaidos et al. 2014) and HATNet (Bakos et al. 2004), seemed to
confirm this prediction, although the magnitude range of these surveys meant
very few low mass stars were monitored to the precision needed to find
transiting exoplanets. A new generation of ground-based transit surveys, with
increased telescope apertures (e.g., HATSouth and NGTS; Bakos et al. 2013;
Bayliss et al. 2018), began to find transiting gas giant planets around lower
mass stars (Hartman et al. 2015; Bayliss et al. 2018; Bakos et al. 2020;
Jordán et al. 2022) but still not below the mass where core-accretion models
have trouble forming giants. The TESS mission, with its near all-sky coverage
and red wavelength sensitivity, is very well placed to detect giant planets
transiting low-mass stars. This has allowed the discovery of transiting giants
hosted by stars with masses $M_{\star}\lesssim 0.4$ $M_{\odot}$ (TOI-5205,
Kanodia et al. 2023; TOI-3235, Hobson et al. 2023; TOI-519, Parviainen et al.
2021; Kagetani et al. 2023). The TOI-4860 system joins this short list of
discoveries, being an M3.5V star hosting a giant planet with a radius of
$0.766\pm 0.026$ $\mathrm{R}_{\rm J}$ and a mass of $0.2729\pm 0.0058$
$\mathrm{M}_{\rm J}$ (Fig. 10), at the border of the hot Neptune desert (e.g.,
Lecavelier Des Etangs 2007). With a mass of $0.3400\pm 0.0086$ $M_{\odot}$ and
a radius of $0.354\pm 0.011$ $R_{\odot}$ its host star is well within the mass
range that challenges core accretion.

These recent discoveries have allowed for the occurrence rates of giant
planets around low-mass stars to be calculated, at least for short orbital
period systems. The results from Gan et al. (2023) and Bryant et al. (2023)
suggest that short-period giant planets occur around early-type M dwarfs at
approximately half the frequency they do around solar-mass stars, and about a
quarter the frequency when comparing mid to late M-dwarf host (0.088$-$0.4
$M_{\odot}$, like TOI-4860) to solar-mass stars. These results will become
more concrete as more systems such as TOI-4680 are confirmed.

TOI-4860 appears to be metal-rich ($\rm[Fe/H]=0.27\pm 0.12$) like other M
dwarfs hosting giant planets (see Fig. 3 of Kagetani et al. 2023). This
suggests, like for FGK stars (Fischer & Valenti 2005), a correlation between
the metallicity of a star and the likelihood of its hosting giant planets.

TOI-4860 b has a high transmission spectroscopy metric (TSM, Kempton et al.
2018) of $180\pm 13$, among the highest for its planet size. Moreover, based
on the host star’s $\log R^{\prime}_{HK}$ ($-5.65\pm 0.12$), the lack of
flares in the TESS light curve, and the small ESPRESSO RV jitter (¡ 1.9 m s-1
at 95% CI), we conclude that TOI-4860 currently exhibits low levels of
activity. The planet’s atmosphere composition can reveal insights into its
formation and evolution history and is a key constraint for models of the
planetary interior. Another constraint that can be placed upon the formation
history could be the spin-orbit angle. The expected semi-amplitude of the
Rossiter–McLaughlin effect (Rossiter 1924; McLaughlin 1924) for TOI-4860 b is
$\sim$5 m s-1. The one ESPRESSO observation obtained during transit does not
seem compatible with an aligned orbit (Fig. 14), but this will have to be
confirmed with further observations.

The RVs show evidence of an eccentric ($e=0.657\pm 0.089$) planet candidate
with a period of $426.9\pm 7.4$ days and a minimum mass of $1.66\pm 0.26$
$\mathrm{M}_{\rm J}$. This raises the possibility that TOI-4860 b ended up in
its small-periapsis orbit through planet-planet scattering or Kozai resonance
with the outer planet, and then became circularised by tides.

Figure 10: Comparison of TOI-4860 b with known exoplanets. Left: Mass-Radius
diagram of known exoplanets. Grey dots are transiting planets listed in the
NASA Exoplanet Archive (https://exoplanetarchive.ipac.caltech.edu/ with
planetary radius and mass uncertainty below 20%. TOI-519, TOI-3235, and
TOI-5205 are shown (from left to right) as red dots. The blue open circle with
error bars marks the position of TOI-4860 b. Center: Idem for planetary versus
stellar radii (restricted to planets with planetary radius uncertainty below
20%). Right: Idem for planetary radii versus orbital period.

###### Acknowledgements.

We are grateful to the ESO/La Silla staff for their continuous support. We
acknowledge funding from the European Research Council under the ERC Grant
Agreement n. 337591-ExTrA. This paper includes data collected by the TESS
mission. Funding for the TESS mission is provided by the NASA Explorer
Program. We acknowledge the use of public TESS data from the pipelines at the
TESS Science Office and at the TESS Science Processing Operations Center.
Resources supporting this work were provided by the NASA High-End Computing
(HEC) program through the NASA Advanced Supercomputing (NAS) Division at Ames
Research Center for the production of the SPOC data products. Based on
observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is
operated from the summit of Maunakea by the National Research Council of
Canada, the Institut National des Sciences de l’Univers of the Centre National
de la Recherche Scientifique of France, and the University of Hawaii. The
observations at the Canada-France-Hawaii Telescope were performed with care
and respect from the summit of Maunakea which is a significant cultural and
historic site. Based on observations obtained with SPIRou, an international
project led by Institut de Recherche en Astrophysique et Planétologie,
Toulouse, France. We thank the Swiss National Science Foundation (SNSF) and
the Geneva University for their continuous support to our planet search
programs. This work has been carried out within the framework of the National
Centre of Competence in Research PlanetS supported by the Swiss National
Science Foundation under grants 51NF40_182901 and 51NF40_205606. The authors
acknowledge the financial support of the SNSF. A.J., R.B., and M.H.
acknowledge support from ANID – Millennium Science Initiative – ICN12_009.
A.J. acknowledges additional support from FONDECYT project 1210718. R.B.
acknowledges support from FONDECYT Project 11200751. E.M. acknowledges funding
from FAPEMIG under project number APQ-02493-22 and research productivity grant
number 309829/2022-4 awarded by the CNPq, Brazil. X.B., G.H., E.M., A.C.,
X.D., J.-F.D, T.F., P.F. and C.M. acknowledge funding from the French ANR
under contract number ANR18CE310019 (SPlaSH). X.D., X.B., T.F., and A.C.
acknowledge funding from the French National Research Agency in the framework
of the Investissements d’Avenir program (ANR-15-IDEX-02), through the funding
of the “Origin of Life” project of the Grenoble-Alpes University. E.G.
acknowledges funding from NASA Award 80NSSC20K0957 (Exoplanets Research
Program). This work made use of tpfplotter by J. Lillo-Box (publicly available
in www.github.com/jlillo/tpfplotter), which also made use of the python
packages astropy, lightkurve, matplotlib and numpy. This research was carried
out in part at the Jet Propulsion Laboratory, California Institute of
Technology, under a contract with the National Aeronautics and Space
Administration (NASA). DR was supported by NASA under award number NNA16BD14C
for NASA Academic Mission Services. This work has made use of data from the
European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia),
processed by the Gaia Data Processing and Analysis Consortium (DPAC,
https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has
been provided by national institutions, in particular, the institutions
participating in the Gaia Multilateral Agreement. AC acknowledges support from
CFisUC (UIDB/04564/2020 and UIDP/04564/2020), GRAVITY (PTDC/FIS-
AST/7002/2020), and ENGAGE SKA (POCI-01-0145-FEDER-022217), funded by COMPETE
2020 and FCT, Portugal. JFD acknowledges funding from the European Research
Council (ERC) under the H2020 research & innovation program (grant agreement
#740651 NewWorlds). J.H.C.M. is supported in the form of a work contract
funded by Fundação para a Ciência e Tecnologia (FCT) with the reference DL
57/2016/CP1364/CT0007; and also supported from by FCT - Fundação para a
Ciência e a Tecnologia through national funds and by FEDER through COMPETE2020
- Programa Operacional Competitividade e Internacionalização by these grants:
UIDB/04434/2020; UIDP/04434/2020. J.H.C.M. also acknowledges funding by the
European Union (ERC, FIERCE, 101052347). Views and opinions expressed are
however those of the author(s) only and do not necessarily reflect those of
the European Union or the European Research Council. Neither the European
Union nor the granting authority can be held responsible for them. This
research has made use of the Spanish Virtual Observatory
(https://svo.cab.inta-csic.es) project funded by
MCIN/AEI/10.13039/501100011033/ through grant PID2020-112949GB-I00. The Pan-
STARRS1 Surveys (PS1) and the PS1 public science archive have been made
possible through contributions by the Institute for Astronomy, the University
of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its
participating institutes, the Max Planck Institute for Astronomy, Heidelberg
and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns
Hopkins University, Durham University, the University of Edinburgh, the
Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics,
the Las Cumbres Observatory Global Telescope Network Incorporated, the
National Central University of Taiwan, the Space Telescope Science Institute,
the National Aeronautics and Space Administration under Grant No. NNX08AR22G
issued through the Planetary Science Division of the NASA Science Mission
Directorate, the National Science Foundation Grant No. AST-1238877, the
University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos
National Laboratory, and the Gordon and Betty Moore Foundation. This research
was carried out in part at the Jet Propulsion Laboratory, California Institute
of Technology, under a contract with the National Aeronautics and Space
Administration (80NM0018D0004).

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##  Appendix A Additional figures and tables

Table 4: Modelling of the SED.

Parameter |  | Prior | Posterior median
---|---|---|---
|  |  | and 68.3% CI
Effective temperature, $T_{\mathrm{eff}}$ | [K] |  $N$(3191, 70) |  3255$\pm 49$
Surface gravity, $\log g$ | [cgs] |  $U$(-0.5, 6.0) |  5.39${}^{+0.45}_{-0.70}$
Metallicity, $[\rm{Fe/H}]$ | [dex] |  $N$(0.27, 0.12) | $0.25\pm 0.12$
Distance | [pc] |  $N$(80.42, 0.22) | $80.42\pm 0.22$
$E_{\mathrm{(B-V)}}$ | [mag] |  $U$(0, 3) |  0.039${}^{+0.051}_{-0.029}$
Jitter Gaia | [mag] |  $U$(0, 1) |  0.164${}^{+0.21}_{-0.079}$
Jitter 2MASS | [mag] |  $U$(0, 1) |  0.027${}^{+0.057}_{-0.020}$
Jitter WISE | [mag] |  $U$(0, 1) |  0.089${}^{+0.19}_{-0.068}$
Radius, $R_{\star}$ |  [$R_{\odot}$ ] |  $U$(0, 100) |  0.371$\pm 0.010$
Luminosity |  [L⊙] |  |  0.01388$\pm$ 0.00059
666$N$($\mu$,$\sigma$): Normal distribution prior with mean $\mu$, and
standard deviation $\sigma$. $U$(l,u): Uniform distribution prior in the range
[l, u].

Figure 11: ExTrA transit photometry observations of TOI-4860 b in Z*, Y, J,
and H* bands (error bars). Each line corresponds to a night (with format YYYY-
MM-DD) and ExTrA telescope (labelled T1, T2, and T3) observation that are
offset vertically for clarity. For each transit the median model (black line),
and 68% CI (grey band, barely visible) computed from 1000 random posterior
samples are shown. Figure 12: TTVs from TESS (green error bars), ExTrA (red
error bars), and a transit observed simultaneously by TESS and ExTrA (black
error bar).

Figure 13: Periodogram of SPIRou data. Top panel: Generalised Lomb–Scargle
periodogram (GLS, Zechmeister & Kürster 2009) of the nightly averaged SPIRou
velocities for TOI-4860 (red line). The horizontal lines represents 10, 1, and
0.1% false-alarm levels, from bottom to top, respectively. The vertical dotted
green line mark the period of the transiting planet. Bottom panel: Idem after
subtracting the Keplerian orbit of planet b. The blue line in the graph
represents the marginal posterior distribution of the period of a second
planet search with SPIRou and ESPRESSO (the vertial scale is arbitrary). Table
5: Radial velocity measurements.

Time | RV | $\pm 1\leavevmode\nobreak\ \sigma$ | Exposure | Instrument
---|---|---|---|---
$[{\rm BJD_{TDB}}]$ |  [m s-1] |  [m s-1] | time [s] |
2459651.014632aa$a$Flagged by the telluric correction algorithm. | 20672.79 | 35.56 | 184 | SPIRou
2459651.017018aa$a$Flagged by the telluric correction algorithm. | 20728.73 | 38.07 | 184 | SPIRou
2459651.019405aa$a$Flagged by the telluric correction algorithm. | 20727.25 | 38.52 | 184 | SPIRou
2459651.021792aa$a$Flagged by the telluric correction algorithm. | 20783.75 | 41.44 | 184 | SPIRou
2459652.016441 | 20635.91 | 31.35 | 184 | SPIRou
2459652.018828 | 20655.03 | 32.13 | 184 | SPIRou
2459652.021215 | 20594.47 | 32.59 | 184 | SPIRou
2459652.023602 | 20609.83 | 33.11 | 184 | SPIRou
2459682.962344 | 20667.94 | 15.51 | 602 | SPIRou
2459682.969568 | 20689.38 | 15.49 | 602 | SPIRou
2459682.976857 | 20672.99 | 15.11 | 602 | SPIRou
2459682.984081 | 20675.06 | 15.54 | 602 | SPIRou
2459683.975195 | 20438.47 | 15.71 | 602 | SPIRou
2459683.982484 | 20553.25 | 15.54 | 602 | SPIRou
2459683.989773 | 20480.31 | 16.34 | 602 | SPIRou
2459683.996998 | 20506.34 | 17.13 | 602 | SPIRou
2459688.978921 | 20589.02 | 14.55 | 602 | SPIRou
2459688.986145 | 20617.96 | 15.26 | 602 | SPIRou
2459688.993370 | 20667.28 | 15.46 | 602 | SPIRou
2459689.000595 | 20677.68 | 15.52 | 602 | SPIRou
2459689.971959 | 20475.41 | 15.64 | 602 | SPIRou
2459689.979248 | 20550.51 | 15.97 | 602 | SPIRou
2459689.986473 | 20536.16 | 16.77 | 602 | SPIRou
2459689.993697 | 20539.39 | 16.53 | 602 | SPIRou
2459690.966227 | 20586.54 | 15.28 | 602 | SPIRou
2459690.973517 | 20577.52 | 15.71 | 602 | SPIRou
2459690.980745 | 20631.14 | 16.52 | 602 | SPIRou
2459690.988031 | 20561.25 | 16.73 | 602 | SPIRou
2459711.923333 | 20627.61 | 16.30 | 602 | SPIRou
2459711.930622 | 20583.55 | 17.47 | 602 | SPIRou
2459711.937910 | 20631.63 | 17.86 | 602 | SPIRou
2459711.945134 | 20662.24 | 17.92 | 602 | SPIRou
2459712.898086 | 20302.36 | 15.85 | 602 | SPIRou
2459712.905375 | 20438.74 | 18.02 | 602 | SPIRou
2459712.912599 | 20394.84 | 16.58 | 602 | SPIRou
2459712.919823 | 20455.80 | 17.72 | 602 | SPIRou
2459714.871905 | 20549.95 | 16.01 | 602 | SPIRou
2459714.879195 | 20642.84 | 16.56 | 602 | SPIRou
2459714.886419 | 20591.96 | 17.63 | 602 | SPIRou
2459714.893708 | 20547.20 | 18.88 | 602 | SPIRou
2459715.894581 | 20418.06 | 15.11 | 602 | SPIRou
2459715.901869 | 20457.61 | 15.26 | 602 | SPIRou
2459715.909158 | 20434.95 | 15.93 | 602 | SPIRou
2459715.916382 | 20499.60 | 17.42 | 602 | SPIRou
2459716.903709bb$b$Observation during transit. | 20550.12 | 13.69 | 602 | SPIRou
2459716.910997bb$b$Observation during transit. | 20534.58 | 14.51 | 602 | SPIRou
2459716.918222bb$b$Observation during transit. | 20486.82 | 14.86 | 602 | SPIRou
2459716.925446bb$b$Observation during transit. | 20534.29 | 15.74 | 602 | SPIRou
2459717.904838 | 20430.67 | 21.65 | 602 | SPIRou
2459717.912126 | 20535.44 | 25.12 | 602 | SPIRou
2459717.919415 | 20558.42 | 24.88 | 602 | SPIRou
2459717.926639 | 20623.72 | 27.34 | 602 | SPIRou
2459719.919542 | 20453.45 | 16.00 | 602 | SPIRou
2459719.926830 | 20539.12 | 17.01 | 602 | SPIRou
2459719.934054bb$b$Observation during transit. | 20542.62 | 27.27 | 602 | SPIRou
2459719.941278bb$b$Observation during transit. | 20477.03 | 23.83 | 602 | SPIRou
2459737.775387 | 20649.42 | 15.23 | 602 | SPIRou
2459737.782675 | 20682.05 | 15.45 | 602 | SPIRou

Time | RV | $\pm 1\leavevmode\nobreak\ \sigma$ | Exposure | Instrument
---|---|---|---|---
$[{\rm BJD_{TDB}}]$ |  [m s-1] |  [m s-1] | time [s] |
2459737.789964 | 20635.10 | 16.42 | 602 | SPIRou
2459737.797252 | 20656.47 | 15.27 | 602 | SPIRou
2459741.833491 | 20510.06 | 14.71 | 602 | SPIRou
2459741.840779 | 20569.59 | 14.97 | 602 | SPIRou
2459741.848004 | 20518.22 | 15.84 | 602 | SPIRou
2459741.855228 | 20521.80 | 16.34 | 602 | SPIRou
2459974.822807 | 20519.66 | 1.18 | 2400 | ESPRESSO
2459975.790100b,cb,cfootnotemark: $b,c$ | 20592.20 | 1.62 | 2400 | ESPRESSO
2459990.710841 | 20676.61 | 1.40 | 2400 | ESPRESSO
2459994.713548 | 20542.96 | 1.73 | 2400 | ESPRESSO
2459995.728387 | 20524.94 | 1.39 | 2400 | ESPRESSO
2459996.704515 | 20681.57 | 1.13 | 2400 | ESPRESSO
2459998.681241 | 20556.29 | 1.78 | 2400 | ESPRESSO
2460034.973275 | 20747.20 | 16.20 | 602 | SPIRou
2460034.980499 | 20691.66 | 15.74 | 602 | SPIRou
2460034.987723 | 20728.46 | 16.72 | 602 | SPIRou
2460034.994948 | 20750.87 | 16.75 | 602 | SPIRou
2460064.881853 | 20636.17 | 20.74 | 602 | SPIRou
2460064.889078 | 20628.63 | 38.55 | 602 | SPIRou
2460064.896367a,ca,cfootnotemark: $a,c$ | 20688.17 | 50.19 | 602 | SPIRou
2460064.903591a,ca,cfootnotemark: $a,c$ | 20764.02 | 60.23 | 602 | SPIRou
2460069.886522 | 20717.37 | 13.70 | 602 | SPIRou
2460069.893810 | 20705.09 | 14.03 | 602 | SPIRou
2460069.901034 | 20715.34 | 14.51 | 602 | SPIRou
2460069.908259 | 20698.83 | 14.95 | 602 | SPIRou
2460075.860806 | 20730.24 | 14.42 | 602 | SPIRou
2460075.868095 | 20768.85 | 13.83 | 602 | SPIRou
2460075.875383 | 20695.31 | 13.50 | 602 | SPIRou
2460075.882608 | 20707.40 | 13.94 | 602 | SPIRou
2460076.879995 | 20502.99 | 14.82 | 602 | SPIRou
2460076.887283 | 20542.48 | 16.61 | 602 | SPIRou
2460076.894508 | 20505.84 | 15.54 | 602 | SPIRou
2460076.901732 | 20556.08 | 15.46 | 602 | SPIRou
2460096.784419 | 20513.62 | 17.24 | 602 | SPIRou
2460096.791645 | 20606.75 | 16.41 | 602 | SPIRou
2460096.798874 | 20581.53 | 17.00 | 602 | SPIRou
2460096.806090a,ca,cfootnotemark: $a,c$ | 21324.07 | 73.70 | 602 | SPIRou
2460098.813093 | 20731.23 | 25.57 | 602 | SPIRou
2460098.820377 | 20615.90 | 21.33 | 602 | SPIRou
2460098.827671 | 20714.14 | 22.61 | 602 | SPIRou
2460098.834895 | 20749.88 | 23.10 | 602 | SPIRou
2460102.846326 | 20522.33 | 13.25 | 602 | SPIRou
2460102.853615 | 20553.68 | 13.26 | 602 | SPIRou
2460102.860903 | 20551.93 | 13.50 | 602 | SPIRou
2460102.868127 | 20566.81 | 13.76 | 602 | SPIRou
2460124.740016 | 20611.59 | 16.83 | 602 | SPIRou
2460124.747305 | 20601.19 | 16.32 | 602 | SPIRou
2460124.754594 | 20615.81 | 16.28 | 602 | SPIRou
2460124.761820 | 20651.56 | 16.51 | 602 | SPIRou
2460128.751561 | 20552.08 | 18.63 | 602 | SPIRou
2460128.758785 | 20557.96 | 17.93 | 602 | SPIRou
2460128.766009 | 20520.20 | 18.43 | 602 | SPIRou
2460128.773233 | 20519.43 | 21.04 | 602 | SPIRou
2460129.750056 | 20450.99 | 24.34 | 602 | SPIRou
2460130.751754 | 20668.27 | 13.81 | 602 | SPIRou
2460130.759042 | 20649.19 | 13.81 | 602 | SPIRou
2460130.766331 | 20659.68 | 14.01 | 602 | SPIRou
2460130.773555 | 20691.74 | 14.74 | 602 | SPIRou
777$c$$c$footnotetext: Not used in the analysis.

Figure 14: Idem Fig. 8 including the ESPRESSO observation during transit
(green error bar), with its phase coverage highlighted in green. The transit
center is marked with a vertical solid grey line, and the ingress and egress
are marked with dotted vertical grey lines. The green line is a model for the
RVs including the Rossiter–McLaughlin effect for an aligned system (computed
with the starry code, Luger et al. 2019), and the green open circle is the
integration of this model for the ESPRESSO observation during transit.