We present the discovery of a transiting mini-Neptune around TOI-1201, a relatively bright and moderately young early M dwarf (
J
≈ 9.5 mag, ~600–800 Myr) in an equal-mass ~8 arcsecond-wide binary ...system, using data from the Transiting Exoplanet Survey Satellite, along with follow-up transit observations. With an orbital period of 2.49 d, TOI-1201 b is a warm mini-Neptune with a radius of
R
b
= 2.415 ± 0.090
R
⊕
. This signal is also present in the precise radial velocity measurements from CARMENES, confirming the existence of the planet and providing a planetary mass of
M
b
= 6.28 ± 0.88
M
⊕
and, thus, an estimated bulk density of 2.45
−0.42
+0.48
g cm
−3
. The spectroscopic observations additionally show evidence of a signal with a period of 19 d and a long periodic variation of undetermined origin. In combination with ground-based photometric monitoring from WASP-South and ASAS-SN, we attribute the 19 d signal to the stellar rotation period (
P
rot
= 19–23 d), although we cannot rule out that the variation seen in photometry belongs to the visually close binary companion. We calculate precise stellar parameters for both TOI-1201 and its companion. The transiting planet is anexcellent target for atmosphere characterization (the transmission spectroscopy metric is 97
−16
+21
) with the upcoming
James Webb
Space Telescope. It is also feasible to measure its spin-orbit alignment via the Rossiter-McLaughlin effect using current state-of-the-art spectrographs with submeter per second radial velocity precision.
The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, a steady progress was ...made in achieving the mission’s primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, the TESS’s observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star TOI-125, a V = 11.0 K0 dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TOI-125b, TOI-125c, and TOI-125d. TOI-125b has an orbital period of 4.65 d, a radius of 2.726 ± 0.075 R(E), a mass of 9.50 ± 0.88 M(E), and is near the 2:1 mean motion resonance with TOI-125c at 9.15 d. TOI-125c has a similar radius of 2.759 ± 0.10 R(E) and a mass of 6.63 ± 0.99 M(E), being the puffiest of the three planets. TOI-125d has an orbital period of 19.98 d and a radius of 2.93 ± 0.17 R(E) and mass 13.6 ± 1.2 M(E). For TOI-125b and d, we find unusual high eccentricities of 0.19 ± 0.04 and 0.17(sup +0.08, sub −0.06), respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for TOI-125.04 (R(P) = 1.36 R(E), P = 0.53 d), we find a 2σ upper mass limit of 1.6 M(E), whereas TOI-125.05 (R(P) = 4.2(sup +2.4, sub −1.4 R(E), P = 13.28 d) is unlikely a viable planet candidate with an upper mass limit of 2.7 M(E). We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system.
We report the detection of a transiting Earth-size planet around GJ 357, a nearby M2.5 V star, using data from the Transiting Exoplanet Survey Satellite (TESS). GJ 357 b (TOI-562.01) is a transiting, ...hot, Earth-sized planet (Teq = 525 ± 11 K) with a radius of Rb = 1.217 ± 0.084 R⊕ and an orbital period of Pb = 3.93 d. Precise stellar radial velocities from CARMENES and PFS, as well as archival data from HIRES, UVES, and HARPS also display a 3.93-day periodicity, confirming the planetary nature and leading to a planetary mass of Mb = 1.84 ± 0.31 M⊕. In addition to the radial velocity signal for GJ 357 b, more periodicities are present in the data indicating the presence of two further planets in the system: GJ 357 c, with a minimum mass of Mc = 3.40 ± 0.46 M⊕ in a 9.12 d orbit, and GJ 357 d, with a minimum mass of Md = 6.1 ± 1.0 M⊕ in a 55.7 d orbit inside the habitable zone. The host is relatively inactive and exhibits a photometric rotation period of Prot = 78 ± 2 d. GJ 357 b isto date the second closest transiting planet to the Sun, making it a prime target for further investigations such as transmission spectroscopy. Therefore, GJ 357 b represents one of the best terrestrial planets suitable for atmospheric characterization with the upcoming JWST and ground-based ELTs.
Abstract
We present stellar parameter estimates for 939 457 southern FGK stars that are candidate targets for the Transiting Exoplanet Survey Satellite (TESS) mission. Using a data-driven method ...similar to the CANNON, we build a model of stellar colours as a function of stellar parameters. We then use these in combination with stellar evolution models to estimate the effective temperature, gravity, metallicity, mass, radius, and extinction for our selected targets. Our effective temperature estimates compare well with those from spectroscopic surveys and the addition of Gaia DR2 parallaxes allows us to identify subgiant interlopers into the TESS sample. We are able to estimate the radii of TESS targets with a typical uncertainty of 9.3 per cent. This catalogue can be used to screen exoplanet candidates from TESS and provides a homogeneous set of stellar parameters for statistical studies.
We report the discovery of GJ 3929 b, a hot Earth-sized planet orbiting the nearby M3.5 V dwarf star, GJ 3929 (G 180-18, TOI-2013). Joint modelling of photometric observations from TESS sectors 24 ...and 25 together with 73 spectroscopic observations from CARMENES and follow-up transit observations from SAINT-EX, LCOGT, and OSN yields a planet radius of
R
b
= 1.150 ± 0.040
R
⊕
, a mass of
M
b
= 1.21 ± 0.42
M
⊕
, and an orbital period of
P
b
= 2.6162745 ± 0.0000030
d
. The resulting density of
ρ
b
= 4.4 ± 1.6 g cm
−3
is compatible with the Earth’s mean density of about 5.5 g cm
−3
. Due to the apparent brightness of the host star (
J
= 8.7 mag) and its small size, GJ 3929 b is a promising target for atmospheric characterisation with the JWST. Additionally, the radial velocity data show evidence for another planet candidate with
P
c
= 14.303 ± 0.035 d, which is likely unrelated to the stellar rotation period,
P
rot
= 122 ± 13 d, which we determined from archival HATNet and ASAS-SN photometry combined with newly obtained TJO data.
Context.
The CARMENES instrument, installed at the 3.5 m telescope of the Calar Alto Observatory in Almería, Spain, was conceived to deliver high-accuracy radial velocity (RV) measurements with ...long-term stability to search for temperate rocky planets around a sample of nearby cool stars. Moreover, the broad wavelength coverage was designed to provide a range of stellar activity indicators to assess the nature of potential RV signals and to provide valuable spectral information to help characterise the stellar targets.
Aims.
We describe the CARMENES guaranteed time observations (GTO), spanning from 2016 to 2020, during which 19 633 spectra for a sample of 362 targets were collected. We present the CARMENES Data Release 1 (DR1), which makes public all observations obtained during the GTO of the CARMENES survey.
Methods.
The CARMENES survey target selection was aimed at minimising biases, and about 70% of all known M dwarfs within 10 pc and accessible from Calar Alto were included. The data were pipeline-processed, and high-level data products, including 18 642 precise RVs for 345 targets, were derived. Time series data of spectroscopic activity indicators were also obtained.
Results.
We discuss the characteristics of the CARMENES data, the statistical properties of the stellar sample, and the spectroscopic measurements. We show examples of the use of CARMENES data and provide a contextual view of the exoplanet population revealed by the survey, including 33 new planets, 17 re-analysed planets, and 26 confirmed planets from transiting candidate follow-up. A subsample of 238 targets was used to derive updated planet occurrence rates, yielding an overall average of 1.44 ± 0.20 planets with 1
M
⊕
<
M
pl
sin
i <
1000
M
⊕
and 1 day <
P
orb
< 1000 days per star, and indicating that nearly every M dwarf hosts at least one planet. All the DR1 raw data, pipeline-processed data, and high-level data products are publicly available online.
Conclusions.
CARMENES data have proven very useful for identifying and measuring planetary companions. They are also suitable for a variety of additional applications, such as the determination of stellar fundamental and atmospheric properties, the characterisation of stellar activity, and the study of exoplanet atmospheres.
We present the confirmation and characterisation of GJ 3473 b (G 50–16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal (
P
= 1.1980035 ± 0.0000018 d) was ...first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass,
M
b
= 1.86 ± 0.30
M
⊕
, and radius,
R
b
= 1.264 ± 0.050
R
⊕
. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass,
M
c
sin
i
= 7.41 ± 0.91
M
⊕
, and orbital period,
P
c
= 15.509 ± 0.033 d. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy.
We present the discovery of an Earth-mass planet (
M
b
sin
i
= 1.26 ± 0.21
M
⊕
) on a 15.6 d orbit of a relatively nearby (
d ~
9.6 pc) and low-mass (0.167 ± 0.011
M
⊙
) M5.0 V star, Wolf 1069. ...Sitting at a separation of 0.0672 ± 0.0014 au away from the host star puts Wolf 1069 b in the habitable zone (HZ), receiving an incident flux of
S
= 0.652 ± 0.029
S
⊕
. The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range of
P
rot
= 150–170 d, with a likely value at 169.3
−3.6
+3.7
. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the sixth closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061 d, Teegarden’s Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069 b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-m s
−1
RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.
Context.
Despite being a prominent subset of the exoplanet population discovered in the past three decades, the nature and provenance of sub-Neptune-sized planets is still one of the open questions ...in exoplanet science.
Aims.
For planets orbiting bright stars, precisely measuring the orbital and planet parameters of the system is the best approach to distinguish between competing theories regarding their formation and evolution.
Methods.
We obtained 69 new radial velocity observations of the mid-M dwarf G 9–40 with the CARMENES instrument to measure for the first time the mass of its transiting sub-Neptune planet, G 9–40 b, discovered in data from the K2 mission.
Results.
Combined with new observations from the TESS mission during Sectors 44, 45, and 46, we are able to measure the radius of the planet to an uncertainty of 3.4% (
R
b
= 1.900 ± 0.065
R
⊕
) and determine its mass with a precision of 16% (
M
b
= 4.00 ± 0.63
M
⊕
). The resulting bulk density of the planet is inconsistent with a terrestrial composition and suggests the presence of either a water-rich core or a significant hydrogen-rich envelope.
Conclusions.
G 9–40 b is referred to as a keystone planet due to its location in period-radius space within the radius valley. Several theories offer explanations for the origin and properties of this population and this planet is a valuable target for testing the dependence of those models on stellar host mass. By virtue of its brightness and small size of the host, it joins L 98-59 d as one of the two best warm (
T
eq
~ 400 K) sub-Neptunes for atmospheric characterization with JWST, which will probe cloud formation in sub-Neptune-sized planets and break the degeneracies of internal composition models.
We report the discovery of HN Lib b, a sub-Neptunian mass planet orbiting the nearby (
d
≈ = 6.25 pc) M4.0 V star HN Lib detected by our CARMENES radial-velocity (RV) survey. We determined a ...planetary minimum mass of
M
b
sin
i
= 5.46 ± 0.75
M
⊕
and an orbital period of
P
b
= 36.116 ± 0.029 d, using ~5 yr of CARMENES data, as well as archival RVs from HARPS and HIRES spanning more than 13 yr. The flux received by the planet equals half the instellation on Earth, which places it in the middle of the conservative habitable zone (HZ) of its host star. The RV data show evidence for another planet candidate with
M
c
sin
i
= 9.7 ± 1.9
M
⊕
and
P
c
= 113.46 ± 0.20 d. The long-term stability of the signal and the fact that the best model for our data is a two-planet model with an independent activity component stand as strong arguments for establishing a planetary origin. However, we cannot rule out stellar activity due to its proximity to the rotation period of HN Lib, which we measured using CARMENES activity indicators and photometric data from a ground-based multi-site campaign as well as archival data. The discovery adds HN Lib b to the shortlist of super-Earth planets in the habitable zone of M dwarfs, but HN Lib c probably cannot be inhabited because, if confirmed, it would most likely be an icy giant.
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