High-eccentricity tidal migration is a possible way for giant planets to be emplaced in short-period orbits. If it commonly operates, one would expect to catch proto-Hot Jupiters on highly elliptical ...orbits that are undergoing high-eccentricity tidal migration. As of yet, few such systems have been discovered. Here, we introduce TOI-3362b (TIC-464300749b), an 18.1-day, 5 \(M_{\rm Jup}\) planet orbiting a main-sequence F-type star that is likely undergoing high-eccentricity tidal migration. The orbital eccentricity is 0.815\(^{+0.023}_{-0.032}\). With a semi-major axis of 0.153\(^{+0.002}_{-0.003}\) au, the planet's orbit is expected to shrink to a final orbital radius of 0.051\(^{+0.008}_{-0.006}\) au after complete tidal circularization. Several mechanisms could explain the extreme value of the planet's eccentricity, such as planet-planet scattering and secular interactions. Such hypotheses can be tested with follow-up observations of the system, e.g., measuring the stellar obliquity and searching for companions in the system with precise, long-term radial velocity observations. The variation in the planet's equilibrium temperature as it orbits the host star and the tidal heating at periapse make this planet an intriguing target for atmospheric modeling and observation. Because the planet's orbital period of 18.1 days is near the limit of TESS's period sensitivity, even a few such discoveries suggest that proto-Hot Jupiters may be quite common.
We present the bright (V\(_{mag} = 9.12\)), multi-planet system TOI-431, characterised with photometry and radial velocities. We estimate the stellar rotation period to be \(30.5 \pm 0.7\) days using ...archival photometry and radial velocities. TOI-431b is a super-Earth with a period of 0.49 days, a radius of 1.28 \(\pm\) 0.04 R\(_{\oplus}\), a mass of \(3.07 \pm 0.35\) M\(_{\oplus}\), and a density of \(8.0 \pm 1.0\) g cm\(^{-3}\); TOI-431d is a sub-Neptune with a period of 12.46 days, a radius of \(3.29 \pm 0.09\) R\(_{\oplus}\), a mass of \(9.90^{+1.53}_{-1.49}\) M\(_{\oplus}\), and a density of \(1.36 \pm 0.25\) g cm\(^{-3}\). We find a third planet, TOI-431c, in the HARPS radial velocity data, but it is not seen to transit in the TESS light curves. It has an \(M \sin i\) of \(2.83^{+0.41}_{-0.34}\) M\(_{\oplus}\), and a period of 4.85 days. TOI-431d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterisation, while the super-Earth TOI-431b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431b is a prime TESS discovery for the study of rocky planet phase curves.
The imminent launch of space telescopes designed to probe the atmospheres of exoplanets has prompted new efforts to prioritise the thousands of transiting planet candidates for follow-up ...characterisation. We report the detection and confirmation of TOI-1842b, a warm Saturn identified by TESS and confirmed with ground-based observations from Minerva-Australis, NRES, and the Las Cumbres Observatory Global Telescope. This planet has a radius of \(1.04^{+0.06}_{-0.05}\,R_{Jup}\), a mass of \(0.214^{+0.040}_{-0.038}\,M_{Jup}\), an orbital period of \(9.5739^{+0.0002}_{-0.0001}\) days, and an extremely low density (\(\rho\)=0.252\(\pm\)0.091 g cm\(^{-3}\)). TOI-1842b has among the best known combinations of large atmospheric scale height (893 km) and host-star brightness (\(J=8.747\) mag), making it an attractive target for atmospheric characterisation. As the host star is beginning to evolve off the main sequence, TOI-1842b presents an excellent opportunity to test models of gas giant re-inflation. The primary transit duration of only 4.3 hours also makes TOI-1842b an easily-schedulable target for further ground-based atmospheric characterisation.
We report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright (\(V=8.75\) mag, \(K=7.15\) mag) solar twin HD 183579, delivered by the Transiting ...Exoplanet Survey Satellite (TESS). The host star is located \(56.8\pm0.1\) pc away with a radius of \(R_{\ast}=0.97\pm0.02\ R_{\odot}\) and a mass of \(M_{\ast}=1.03\pm0.05\ M_{\odot}\). We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of \(R_{p}=3.53\pm0.13\ R_{\oplus}\) on a \(17.47\) day orbit with a mass of \(M_{p}=11.2\pm5.4\ M_{\oplus}\) (\(3\sigma\) mass upper limit of \(27.4\ M_{\oplus}\)). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion.
We present the confirmation of the eccentric warm giant planet TOI-201 b, first identified as a candidate in \textit{TESS} photometry (Sectors 1-8, 10-13, and 27-28) and confirmed using ground-based ...photometry from NGTS and radial velocities from FEROS, HARPS, CORALIE, and \textsc{Minerva}-Australis. TOI-201 b orbits a young (\(\mathrm{0.87^{+0.46}_{-0.49} \, Gyr}\)) and bright(V=9.07 mag) F-type star with a \(\mathrm{52.9781 \, d}\) period. The planet has a mass of \(\mathrm{0.42^{+0.05}_{-0.03}\, M_J}\), a radius of \(\mathrm{1.008^{+0.012}_{-0.015}\, R_J}\), and an orbital eccentricity of \(0.28^{+0.06}_{-0.09}\); it appears to still be undergoing fairly rapid cooling, as expected given the youth of the host star. The star also shows long-term variability in both the radial velocities and several activity indicators, which we attribute to stellar activity. The discovery and characterization of warm giant planets such as TOI-201 b is important for constraining formation and evolution theories for giant planets.
We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be ...of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of \(M_P=0.138\pm0.023\)\,\(\rm{M_J}\) (\(43.9\pm7.3\)\,\(M_{\rm \oplus}\)), a radius of \(R_P=0.639\pm0.013\)\,\(\rm{R_J}\) (\(7.16\pm0.15\)\,\(R_{\rm \oplus}\)), bulk density of \(0.65^{+0.12}_{-0.11}\) (cgs), and period \(18.38818^{+0.00085}_{-0.00084}\)\,\(\rm{days}\). TOI-257b orbits a bright (\(\mathrm{V}=7.612\)\,mag) somewhat evolved late F-type star with \(M_*=1.390\pm0.046\)\,\(\rm{M_{\odot}}\), \(R_*=1.888\pm0.033\)\,\(\rm{R_{\odot}}\), \(T_{\rm eff}=6075\pm90\)\,\(\rm{K}\), and \(v\sin{i}=11.3\pm0.5\)\,km\,s\(^{-1}\). Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a \(\sim71\)\,day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (\(\sim100\)) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.
We present the discovery and characterization of five hot and warm Jupiters -- TOI-628 b (TIC 281408474; HD 288842), TOI-640 b (TIC 147977348), TOI-1333 b (TIC 395171208, BD+47 3521A), TOI-1478 b ...(TIC 409794137), and TOI-1601 b (TIC 139375960) -- based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The five planets were identified from the full frame images and were confirmed through a series of photometric and spectroscopic follow-up observations by the \(TESS\) Follow-up Observing Program (TFOP) Working Group. The planets are all Jovian size (R\(_{\rm P}\) = 1.01-1.77 R\(_{\rm J}\)) and have masses that range from 0.85 to 6.33 M\(_{\rm J}\). The host stars of these systems have F and G spectral types (5595 \(\le\) T\(_{\rm eff}\) \(\le\) 6460 K) and are all relatively bright (9 \(<V<\) 10.8, 8.2 \(<K<\) 9.3) making them well-suited for future detailed characterization efforts. Three of the systems in our sample (TOI-640 b, TOI-1333 b, and TOI-1601 b) orbit subgiant host stars (log g\(_*\) \(<\)4.1). TOI-640 b is one of only three known hot Jupiters to have a highly inflated radius (R\(_{\rm P}\) > 1.7R\(_{\rm J}\), possibly a result of its host star's evolution) and resides on an orbit with a period longer than 5 days. TOI-628 b is the most massive hot Jupiter discovered to date by \(TESS\) with a measured mass of \(6.31^{+0.28}_{-0.30}\) M\(_{\rm J}\) and a statistically significant, non-zero orbital eccentricity of e = \(0.074^{+0.021}_{-0.022}\). This planet would not have had enough time to circularize through tidal forces from our analysis, suggesting that it might be remnant eccentricity from its migration. The longest period planet in this sample, TOI-1478 b (P = 10.18 days), is a warm Jupiter in a circular orbit around a near-Solar analogue. NASA's \(TESS\) mission is continuing to increase the sample of well-characterized hot and warm Jupiters, complementing its primary mission goals.
We report the discovery of two short-period Saturn-mass planets, one transiting the G subgiant TOI-954 (TIC 44792534, \( V = 10.343 \), \( T = 9.78 \)) observed in TESS sectors 4 and 5, and one ...transiting the G dwarf K2-329 (EPIC 246193072, \( V = 12.70 \), \( K = 10.67 \)) observed in K2 campaigns 12 and 19. We confirm and characterize these two planets with a variety of ground-based archival and follow-up observations, including photometry, reconnaissance spectroscopy, precise radial velocity, and high-resolution imaging. Combining all available data, we find that TOI-954 b has a radius of \(0.852_{-0.062}^{+0.053} \, R_{\mathrm{J}}\) and a mass of \(0.174_{-0.017}^{+0.018} \, M_{\mathrm{J}}\) and is in a 3.68 day orbit, while K2-329 b has a radius of \(0.774_{-0.024}^{+0.026} \, R_{\mathrm{J}}\) and a mass of \(0.260_{-0.022}^{+0.020} \, M_{\mathrm{J}}\) and is in a 12.46 day orbit. As TOI-954 b is 30 times more irradiated than K2-329 b but more or less the same size, these two planets provide an opportunity to test whether irradiation leads to inflation of Saturn-mass planets and contribute to future comparative studies that explore Saturn-mass planets at contrasting points in their lifetimes.
Main sequence low-mass stars are known to spin-down as a consequence of their magnetised stellar winds. However, estimating the precise rate of this spin-down is an open problem. The mass-loss rate, ...angular momentum-loss rate and the magnetic field properties of low-mass stars are fundamentally linked making this a challenging task. Of particular interest is the stellar magnetic field geometry. In this work, we consider whether non-dipolar field modes contribute significantly to the spin-down of low-mass stars. We do this using a sample of stars that have all been previously mapped with Zeeman-Doppler imaging. For a given star, as long as its mass-loss rate is below some critical mass-loss rate, only the dipolar fields contribute to its spin-down torque. However, if it has a larger mass-loss rate, higher order modes need to be considered. For each star, we calculate this critical mass-loss rate, which is a simple function of the field geometry. Additionally, we use two methods of estimating mass-loss rates for our sample of stars. In the majority of cases, we find that the estimated mass-loss rates do not exceed the critical mass-loss rate and hence, the dipolar magnetic field alone is sufficient to determine the spin-down torque. However, we find some evidence that, at large Rossby numbers, non-dipolar modes may start to contribute.
