ABSTRACT
Ultra-short period planets (USPs) have orbital periods of less than 1 d. Since their masses and radii can be determined to a higher precision than long-period planets, they are the preferred ...targets to determine the density of planets which constrains their composition. The K2-106 system is particularly interesting because it contains two planets of nearly identical masses. One is a high-density USP, the other is a low-density planet that has an orbital period of 13 d. Combining the Gaia DR3 results with new ESPRESSO data allows us to determine the masses and radii of the two planets more precisely than before. We find that the USP K2-106 b has a density consistent with an Earth-like composition, and K2-106 c is a low-density planet that presumably has an extended atmosphere. We measure a radius of $\rm R_p=1.676_{-0.037}^{+0.037}$$\rm R_{{\oplus }}$, a mass of $\rm M_p=7.80_{-0.70}^{+0.71}$M⊕, and a density of $\rm \rho =9.09_{-0.98}^{+0.98}$$\rm g\, cm^{-3}$ for K2-106 b. For K2-106 c, we derive $R_p=2.84_{-0.08}^{+0.10}$$\rm R_{{\oplus }}$, $M_p=7.3_{-2.4}^{+2.5}$$\rm M_{{\oplus }}$, and a density of $\rm \rho = 1.72_{-0.58}^{+0.66}$$\rm g\, cm^{-3}$. We finally discuss the possible structures of the two planets with respect to other low-mass planets.
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.
ABSTRACT
We report on the precise radial velocity follow-up of TOI-544 (HD 290498), a bright K star (V = 10.8), which hosts a small transiting planet recently discovered by the Transiting Exoplanet ...Survey Satellite (TESS). We collected 122 high-resolution High Accuracy Radial velocity Planet Searcher (HARPS) and HARPS-N spectra to spectroscopically confirm the transiting planet and measure its mass. The nearly 3-yr baseline of our follow-up allowed us to unveil the presence of an additional, non-transiting, longer-period companion planet. We derived a radius and mass for the inner planet, TOI-544 b, of 2.018 ± 0.076 R⊕ and 2.89 ± 0.48 M⊕, respectively, which gives a bulk density of $1.93^{+0.30}_{-0.25}$ g cm−3. TOI-544 c has a minimum mass of 21.5 ± 2.0 M⊕ and orbital period of 50.1 ± 0.2 d. The low density of planet-b implies that it has either an Earth-like rocky core with a hydrogen atmosphere, or a composition which harbours a significant fraction of water. The composition interpretation is degenerate depending on the specific choice of planet interior models used. Additionally, TOI-544 b has an orbital period of 1.55 d and equilibrium temperature of 999 ± 14 K, placing it within the predicted location of the radius valley, where few planets are expected. TOI-544 b is a top target for future atmospheric observations, for example with JWST, which would enable better constraints of the planet composition.
ABSTRACT
We report new photometric and spectroscopic observations of the K2-99 planetary system. Asteroseismic analysis of the short-cadence light curve from K2’s Campaign 17 allows us to refine the ...stellar properties. We find K2-99 to be significantly smaller than previously thought, with R⋆ = 2.55 ± 0.02 R⊙. The new light curve also contains four transits of K2-99 b, which we use to improve our knowledge of the planetary properties. We find the planet to be a non-inflated warm Jupiter, with Rb = 1.06 ± 0.01 $\mathrm{R_{\rm Jup}}$. 60 new radial velocity measurements from HARPS, HARPS-N, and HIRES enable the determination of the orbital parameters of K2-99 c, which were previously poorly constrained. We find that this outer planet has a minimum mass Mcsin ic = 8.4 ± 0.2 $\mathrm{M_{\rm Jup}}$, and an eccentric orbit (ec = 0.210 ± 0.009) with a period of 522.2 ± 1.4 d. Upcoming TESS observations in 2022 have a good chance of detecting the transit of this planet, if the mutual inclination between the two planetary orbits is small.
ABSTRACT
We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an ...intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (∼500 Myr) active star with a rotational period of 12.08 ± 0.11 d, and a mass and radius of 0.73 ± 0.02 M⊙ and 0.65 ± 0.02 R⊙, respectively. HD 73583 b (Pb = $6.3980420 _{ - 0.0000062 } ^ { + 0.0000067 }$ d) has a mass and radius of $10.2 _{ - 3.1 } ^ { + 3.4 }$ M⊕ and 2.79 ± 0.10 R⊕, respectively, which gives a density of $2.58 _{ - 0.81 } ^ { + 0.95 }$ ${\rm g\, cm^{-3}}$. HD 73583 c (Pc = $18.87974 _{ - 0.00074 } ^ { + 0.00086 }$ d) has a mass and radius of $9.7 _{ - 1.7 } ^ { + 1.8 }$ M⊕ and $2.39 _{ - 0.09 } ^ { + 0.10 }$ R⊕, respectively, which translates to a density of $3.88 _{ - 0.80 } ^ { + 0.91 }$ ${\rm g\, cm^{-3}}$. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.
We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776,
J
= 8.5 mag,
M
= 0.54 ± 0.03
M
⊙
) detected during Sector 10 observations of the ...Transiting Exoplanet Survey Satellite (TESS). Combining the TESS photometry with HARPS radial velocities, as well as ground-based follow-up transit observations from the MEarth and LCOGT telescopes, for the inner planet, TOI-776 b, we measured a period of
P
b
= 8.25 d, a radius of
R
b
= 1.85 ± 0.13
R
⊕
, and a mass of
M
b
= 4.0 ± 0.9
M
⊕
; and for the outer planet, TOI-776 c, a period of
P
c
= 15.66 d, a radius of
R
c
= 2.02 ± 0.14
R
⊕
, and a mass of
M
c
= 5.3 ± 1.8
M
⊕
. The Doppler data shows one additional signal, with a period of ~34 d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776 b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54
M
⊙
. Due to the brightness of the star, the TOI-776 system is also an excellent target for the
James Webb
Space Telescope, providing a remarkable laboratory in which to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.
HD 191939 (TOI-1339) is a nearby (
d
= 54 pc), bright (
V
= 9 mag), and inactive Sun-like star (G9 V) known to host a multi-planet transiting system. Ground-based spectroscopic observations confirmed ...the planetary nature of the three transiting sub-Neptunes (HD 191939 b, c, and d) originally detected by TESS and were used to measure the masses for planets b and c with 3σ precision. These previous observations also reported the discovery of an additional Saturn-mass planet (HD 191939 e) and evidence for a further, very long-period companion (HD 191939 f). Here, we report the discovery of a new non-transiting planet in the system and a refined mass determination of HD 191939 d. The new planet, HD 191939 g, has a minimum mass of 13.5±2.0
M
⊕
and a period of about 280 days. This period places the planet within the conservative habitable zone of the host star, and near a 1:3 resonance with HD 191939 e. The compilation of 362 radial velocity measurements with a baseline of 677 days from four different high-resolution spectrographs also allowed us to refine the properties of the previously known planets, including a 4.6
σ
mass determination for planet d, for which only a 2
σ
upper limit had been set until now. We confirm the previously suspected low density of HD 191939 d, which makes it an attractive target for attempting atmospheric characterisation. Overall, the planetary system consists of three sub-Neptunes interior to a Saturn-mass and a Uranus-mass planet plus a high-mass long-period companion. This particular configuration has no counterpart in the literature and makes HD 191939 an exceptional multi-planet transiting system with an unusual planet demographic worthy of future observation.
Abstract
π
Men hosts a transiting planet detected by the Transiting Exoplanet Survey Satellite space mission and an outer planet in a 5.7 yr orbit discovered by radial velocity (RV) surveys. We ...studied this system using new RV measurements taken with the HARPS spectrograph on ESO’s 3.6 m telescope, as well as archival data. We constrain the stellar RV semiamplitude due to the transiting planet,
π
Men c, as
K
c
= 1.21 ± 0.12 m s
−1
, resulting in a planet mass of
M
c
= 3.63 ± 0.38
M
⊕
. A planet radius of
R
c
= 2.145 ± 0.015
R
⊕
yields a bulk density of
ρ
c
= 2.03 ± 0.22 g cm
−3
. The precisely determined density of this planet and the brightness of the host star make
π
Men c an excellent laboratory for internal structure and atmospheric characterization studies. Our HARPS RV measurements also reveal compelling evidence for a third body,
π
Men d, with a minimum mass
M
d
sin
i
d
= 13.38 ± 1.35
M
⊕
orbiting with a period of
P
orb,d
= 125 days on an eccentric orbit (
e
d
= 0.22). A simple dynamical analysis indicates that the orbit of
π
Men d is stable on timescales of at least 20 Myr. Given the mutual inclination between the outer gaseous giant and the inner rocky planet and the presence of a third body at 125 days,
π
Men is an important planetary system for dynamical and formation studies.
We report on the precise radial velocity follow-up of TOI-544 (HD 290498),ã bright K star ( V = 10.8), which hostsã small transiting planet recently disco v ered by the Trãnsiting Exoplanet Survey ...Satellite (TESS) . We collected 122 high-resolution High Accuracy Radial velocity Planet Searcher (HARPS)ãnd HARPS-N spectra to spectroscopically confirm the transiting planetãnd measure its mass. The nearly 3-yr baseline of our follow-upãllowed us to unveil the presence ofãnãdditional, non-transiting, longer-period companion planet. We derivedã radiusãnd mass for the inner planet, TOI-544 b, of 2.018 ±0.076 R⊙and 2.89 ±0.48 M⊙, respectively, which givesã bulk density of 1 . 93 + 0 . 30 -0 . 25 g cm -3 . TOI-544 c hasã minimum mass of 21.5 ±2.0 M⊙and orbital period of 50.1 ±0.2 d. The low density of planet-b implies that it has eitherãn Earth-like rocky core withã hydrogenãtmosphere, orã composition which harboursã significant fraction of water. The composition interpretation is degenerate depending on the specific choice of planet interior models used. Additionally, TOI-544 b hasãn orbital period of 1.55 dãnd equilibrium temperature of 999 ±14 K, placing it within the predicted location of the radius valley, where few planetsãre expected. TOI-544 b isã top target for futureãtmospheric observations, for example with JWST , which would enable better constraints of the planet composition.
Understanding planet formation is important in the context of the origin of planetary systems in general and of the Solar System in particular, as well as to predict the likelihood of finding ...Jupiter, Neptune, and Earth analogues around other stars. We aim to precisely determine the radii and dynamical masses of transiting planets orbiting the young M star AU\,Mic using public photometric and spectroscopic datasets. We performed a joint fit analysis of the TESS and CHEOPS light curves and more than 400 high-resolution spectra collected with several telescopes and instruments. We characterise the stellar activity and physical properties (radius, mass, density) of the transiting planets in the young AU\,Mic system through joint transit and radial velocity fits with Gaussian processes. We determine a radius of $R_ p b $=\,4.79\,pm \,0.29 R$_ a mass of p b $=\,9.0\,pm \,2.7 M$_ and a bulk density of $ p b $\,=\,0.49\,pm \,0.16 $ for the innermost transiting planet AU\,Mic\,b. For the second known transiting planet, AU\,Mic\,c, we infer a radius of p c $=\,2.79\,pm \,0.18 R$_ a mass of p c $=\,14.5\,pm \,3.4 M$_ and a bulk density of $ p c $\,=\,3.90\,pm \,1.17 $. According to theoretical models, AU\,Mic\,b may harbour an $ envelope larger than 5<!PCT!> by mass, with a fraction of rock and a fraction of water. AU\,Mic\,c could be made of rock and/or water and may have an $ atmosphere comprising at most 5<!PCT!> of its mass. AU\,Mic\,b has retained most of its atmosphere but might lose it over tens of millions of years due to the strong stellar radiation, while AU\,Mic\,c likely suffers much less photo-evaporation because it lies at a larger separation from its host. Using all the datasets in hand, we determine a 3sigma upper mass limit of p d i oplus $ for the AU\,Mic 'd' TTV-candidate. In addition, we do not confirm the recently proposed existence of the planet candidate AU\,Mic\,'e' with an orbital period of 33.4 days. We investigated the level of the radial velocity variations and show that it is lower at longer wavelength with smaller changes from one observational campaign to another.
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