Short-period giant planets ($P$\,lesssim \,10 days p J $) are frequently found to be solitary compared to other classes of exoplanets. Small inner companions to giant planets with $P$\,lesssim \,15 days are known only in five compact systems: WASP-47, Kepler-730, WASP-132, TOI-1130, and TOI-2000. Here, we report the confirmation of TOI-5398, the youngest known compact multi-planet system composed of a hot sub-Neptune (TOI-5398 c c $\,=\,4.77271 days) orbiting interior to a short-period Saturn (TOI-5398 b b $\,=\,10.590547 days) planet, both transiting around a 650\,pm \,150 Myr G-type star. As part of the Global Architecture of Planetary Systems (GAPS) Young Object project, we confirmed and characterised this compact system, measuring the radius and mass of both planets, thus constraining their bulk composition. Using multi-dimensional Gaussian processes, we simultaneously modelled stellar activity and planetary signals from the Transiting Exoplanet Survey Satellite ( TESS ) Sector 48 light curve and our High Accuracy Radial velocity Planet Searcher (HARPS-N) radial velocity (RV) time series. We confirmed the planetary nature of both planets, TOI-5398 b and TOI-5398 c, and obtained a precise estimation of their stellar parameters. Through the use of astrometric, photometric, and spectroscopic observations, our findings indicate that TOI-5398 is a young, active G dwarf star (650\,pm \,150 Myr) with a rotational period of rot $\,=\,7.34 days. The transit photometry and RV measurements enabled us to measure both the radius and mass of planets b, $R_b$\,=\,10.30pm 0.40 oplus $, $M_b$\,=\,58.7pm 5.7 oplus $, and c, $R_c$\,=\,3.52\,pm \,0.19 oplus $, $M_c$\,=\,11.8pm 4.8 oplus TESS observed TOI-5398 during sector 48 and no further observations are planned in the current Extended Mission, making our ground-based light curves crucial for improvement of the ephemeris. With a transmission spectroscopy metric (TSM) value of around 300, TOI-5398 b is the most amenable warm giant (10\,<\,$P$\,<\,100 days) for JWST atmospheric characterisation.

pdf/the-gaps-programme-at-tng-xlix-toi-5398-the-youngest-compact-2u160cyg17.pdf

The GAPS programme at TNG. XLIX. TOI-5398, the youngest compact multi-planet system composed of an inner sub-Neptune and an outer warm Saturn

We report the discovery and characterization of three giant exoplanets orbiting solar-analog stars, detected by the TESS space mission and confirmed through ground-based photometry and radial velocity measurements taken at La Silla observatory with FEROS. TOI-2373 b is a warm Jupiter orbiting its host star every ∼13.3 days, and is one of the most massive known exoplanet with a precisely determined mass and radius around a star similar to the Sun, with an estimated mass of m p = 9.3−0.2+0.2Mjup and a radius of r p = 0.93−0.2+0.2Rjup . With a mean density of ρ=14.4−1.0+0.9gcm−3 , TOI-2373 b is among the densest planets discovered so far. TOI-2416 b orbits its host star on a moderately eccentric orbit with a period of ∼8.3 days and an eccentricity of e = 0.32−0.02+0.02 . TOI-2416 b is more massive than Jupiter with m p = 3.0−0.09+0.10Mjup , however is significantly smaller with a radius of r p = 0.88−0.02+0.02,Rjup , leading to a high mean density of ρ=5.4−0.3+0.3gcm−3 . TOI-2524 b is a warm Jupiter near the hot Jupiter transition region, orbiting its star every ∼7.2 days on a circular orbit. It is less massive than Jupiter with a mass of m p = 0.64−0.04+0.04Mjup , and is consistent with an inflated radius of r p = 1.00−0.03+0.02Rjup , leading to a low mean density of ρ=0.79−0.08+0.08gcm−3 . The newly discovered exoplanets TOI-2373 b, TOI-2416 b, and TOI-2524 b have estimated equilibrium temperatures of 860−10+10 K, 1080−10+10 K, and 1100−20+20 K, respectively, placing them in the sparsely populated transition zone between hot and warm Jupiters.

pdf/three-warm-jupiters-around-solar-analog-stars-detected-with-42yhavatby.pdf

Three Warm Jupiters around Solar-analog Stars Detected with TESS

We report the discovery and characterization of a small planet, TOI-1408 c, on a 2.2-day orbit located interior to a previously known hot Jupiter, TOI-1408 b ($P=4.42$ d, $M=1.86\pm0.02\,M_\mathrm{Jup}$, $R=2.4\pm0.5\,R_\mathrm{Jup}$) that exhibits grazing transits. The two planets are near 2:1 period commensurability, resulting in significant transit timing variations (TTVs) for both planets and transit duration variations (TDVs) for the inner planet. The TTV amplitude for TOI-1408 c is 15% of the planet's orbital period, marking the largest TTV amplitude relative to the orbital period measured to date. Photodynamical modeling of ground-based radial velocity (RV) observations and transit light curves obtained with the Transiting Exoplanet Survey Satellite (TESS) and ground-based facilities leads to an inner planet radius of $2.22\pm0.06\,R_\oplus$ and mass of $7.6\pm0.2\,M_\oplus$ that locates the planet into the Sub-Neptune regime. The proximity to the 2:1 period commensurability leads to the libration of the resonant argument of the inner planet. The RV measurements support the existence of a third body with an orbital period of several thousand days. This discovery places the system among the rare systems featuring a hot Jupiter accompanied by an inner low-mass planet.

TOI-1408: Discovery and Photodynamical Modeling of a Small Inner Companion to a Hot Jupiter Revealed by TTVs

Abstract Multiple analytical, semi-analytical, and empirical stability criteria have been derived in the literature for two-planet systems. But, the dependence of the stability limit on the initial mutual inclination between the inner and outer orbits is not well modeled by previous stability criteria. Here, we derive a semi-analytical stability criteria for two-planet systems, at arbitrary inclinations, in which the inner planet is a test particle. Using perturbation theory we calculate the characteristic fractional change in the semimajor axis of the inner binary β = δ a 1 / a 1 caused by perturbations from the companion. Stability criteria can be derived by setting a threshold on β. Focusing initially on circular orbits, we derive an analytical expression for β for coplanar prograde and retrograde orbits. For noncoplanar configurations, we evaluate a semi-analytical expression. We then generalize to orbits with arbitrary eccentricities and account for the secular effects. Our analytical and semi-analytical results are in excellent agreement with direct N -body simulations. In addition, we show that contours of β ∼ 0.01 can serve as criteria for stability. More specifically, we show that (1) retrograde orbits are generally more stable than prograde ones; (2) systems with intermediate mutual inclination are less stable due to von Ziepel–Lidov–Kozai (vZLK) dynamics; and (3) mean motion resonances (MMRs) can stabilize intermediate inclination secularly unstable regions in phase space, by quenching vZLK secular processes (4) MMRs can destabilize some of the dynamically stable regions. We also point out that these stability criteria can be used to constrain the orbital properties of observed systems and their age. 

Dynamical and Secular Stability of Mutually Inclined Planetary Systems

The star HD 118203, classified as a K0 subgiant, was known to harbour a transiting hot Jupiter planet on a 6.1-day eccentric orbit. Previous studies also revealed a linear trend in the radial velocity (RV) domain, indicative of a companion on a wide orbit. Such a hierarchical orbital architecture could be helpful in studies of the origins of hot Jupiters. We acquired precise RV measurements over 17 years using the 9.2 m Hobby-Eberly Telescope and the 3.6 m Telescopio Nazionale Galileo . Combining these observations with space-born photometric time series from the Transiting Exoplanet Survey Satellite, we constructed a two-planetary model for the system. Astrometric observations from Hipparcos and Gaia were used to constrain the orbital inclination of the wide-orbit companion and its mass. Numerical simulations were used to investigate the dynamics of the system. The photometric data were searched for additional transit-like flux drops. We found that the additional companion is an 11-Jupiter mass planet orbiting HD 118203 on a 14-year moderately eccentric orbit, constituting a hierarchical planetary system with the hot Jupiter. Both planets were found to be dynamically decoupled mainly due to the general relativistic apsidal precession of the inner planet, marginalising secular interactions. The orbits of both planets might have a relatively low mutual inclination unless the longitudes of the ascending node differ substantially. This configuration favours the coplanar high-eccentricity migration as a path to the present-day orbital configuration. No other transiting planets with radii down to 2 Earth radii and orbital periods less than 100 days were found in the system. 

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. VIII. A wide-orbit planetary companion in the hot-Jupiter system HD 118203


 Hot jupiters (P < 10 d, M > 60 M⊕) are almost always found alone around their stars, but four out of hundreds known have inner companion planets. These rare companions allow us to constrain the hot jupiter’s formation history by ruling out high-eccentricity tidal migration. Less is known about inner companions to hot Saturn-mass planets. We report here the discovery of the TOI-2000 system, which features a hot Saturn-mass planet with a smaller inner companion. The mini-neptune TOI-2000 b (2.70 ± 0.15 R⊕, 11.0 ± 2.4 M⊕) is in a 3.10-d orbit, and the hot saturn TOI-2000 c ($8.14_{-0.30}^{+0.31}$ R⊕ , $81.7_{-4.6}^{+4.7}$ M⊕) is in a 9.13-d orbit. Both planets transit their host star TOI-2000 (TIC 371188886, V = 10.98, TESS magnitude = 10.36), a metal-rich ([Fe/H] = 0.439 $_{-0.043}^{+0.041}$) G dwarf  173 pc away. TESS observed the two planets in sectors 9–11 and 36–38, and we followed up with ground-based photometry, spectroscopy, and speckle imaging. Radial velocities from CHIRON, FEROS, and HARPS allowed us to confirm both planets by direct mass measurement. In addition, we demonstrate constraining planetary and stellar parameters with MIST stellar evolutionary tracks through Hamiltonian Monte Carlo under the PyMC framework, achieving higher sampling efficiency and shorter run time compared to traditional Markov chain Monte Carlo. Having the brightest host star in the V band among similar systems, TOI-2000 b and c are superb candidates for atmospheric characterization by the JWST, which can potentially distinguish whether they formed together or TOI-2000 c swept along material during migration to form TOI-2000 b.

/pdf/tess-spots-a-mini-interior-to-a-hot-saturn-in-the-toi-2000-3eoxni2o.pdf

TESS spots a mini- interior to a hot saturn in the TOI-2000 system

We report the discovery of a super-Jovian 2:1 mean-motion resonance (MMR) pair around the G-type star TIC 279401253, whose dynamical architecture is a prospective benchmark for planet formation and orbital evolution analysis. The system was discovered thanks to a single-transit event recorded by the Transiting Exoplanet Survey Satellite mission, which pointed to a Jupiter-sized companion with poorly constrained orbital parameters. We began ground-based precise radial velocity (RV) monitoring with HARPS and FEROS within the Warm gIaNts with tEss survey to constrain the transiting body’s period, mass, and eccentricity. The RV measurements revealed not one but two massive planets with periods of 76.80−0.06+0.06 and 155.3−0.7+0.7 days, respectively. A combined analysis of transit and RV data yields an inner transiting planet with a mass of 6.14−0.42+0.39 M Jup and a radius of 1.00−0.04+0.04 R Jup, and an outer planet with a minimum mass of 8.02−0.18+0.18 M Jup, indicating a massive giant pair. A detailed dynamical analysis of the system reveals that the planets are locked in a strong first-order, eccentricity-type 2:1 MMR, which makes TIC 279401253 one of the rare examples of truly resonant architectures supporting disk-induced planet migration. The bright host star, V ≈ 11.9 mag, the relatively short orbital period (P b = 76.80−0.06+0.06 days), and pronounced eccentricity (e = 0.448 −0.029+0.028 ) make the transiting planet a valuable target for atmospheric investigation with the James Webb Space Telescope and ground-based extremely large telescopes.

https://iopscience.iop.org/article/10.3847/2041-8213/acbd4f/pdf

A 2:1 Mean-motion Resonance Super-Jovian Pair Revealed by TESS, FEROS, and HARPS

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TESS spots a mini- interior to a hot saturn in the TOI-2000 system

A 2:1 Mean-motion Resonance Super-Jovian Pair Revealed by TESS, FEROS, and HARPS