We investigate the giant planet-metallicity correlation for a homogeneous, unbiased set of 217 hot Jupiters taken from nearly 15 years of wide-field ground-based surveys. We compare the host star ...metallicity to that of field stars using the Besançon Galaxy model, allowing for a metallicity measurement offset between the two sets. We find that hot Jupiters preferentially orbit metal rich stars. However, we find the correlation consistent, though marginally weaker, for hot Jupiters (\(\beta=0.71^{+0.56}_{-0.34}\)) than it is for other longer period gas giant planets from radial velocity surveys. This suggests that the population of hot Jupiters probably formed in a similar process to other gas giant planets, and differ only in their migration histories.
One of the leading mechanisms invoked to explain the existence of the radius
valley is atmospheric mass loss driven by X-ray and extreme-ultraviolet
irradiation, with this process stripping the ...primordial envelopes of young,
small planets to produce the observed bimodal distribution. We present an
investigation into the TOI-431 and $\nu^2$ Lupi planetary systems, both of
which host planets either side of the radius valley, to determine if their
architectures are consistent with evolution by the XUV mechanism. With
$\textit{XMM-Newton}$, we measure the current X-ray flux of each star, and see
evidence for a stellar flare in the TOI-431 observations. We then simulate the
evolution of all of the transiting planets across the two systems in response
to the high-energy irradiation over their lifetimes. We use the measured X-ray
fluxes as an anchor point for the XUV time evolution in our simulations, and
employ several different models of estimating mass loss rates. While the
simulations for TOI-431b encountered a problem with the initial calculated
radii, we estimate a likely short ($\sim$ Myr) timespan for primordial envelope
removal using reasonable assumptions for the initial planet. $\nu^2$ Lupi b is
likely harder to strip, but is achieved in a moderate fraction of our
simulations. None of our simulations stripped any of the lower density planets
of their envelope, in line with prediction. We conclude that both systems are
consistent with expectations for generation of the radius valley through XUV
photoevaporation.
Discovering transiting exoplanets with long orbital periods allows us to study warm and cool planetary systems with temperatures similar to the planets in our own Solar system. The TESS mission has ...photometrically surveyed the entire Southern Ecliptic Hemisphere in Cycle 1 (August 2018 - July 2019), Cycle 3 (July 2020 - June 2021) and Cycle 5 (September 2022 - September 2023). We use the observations from Cycle 1 and Cycle 3 to search for exoplanet systems that show a single transit event in each year - which we call duotransits. The periods of these planet candidates are typically in excess of 20 days, with the lower limit determined by the duration of individual TESS observations. We find 85 duotransit candidates, which span a range of host star brightnesses between 8 < \(T_{mag}\) < 14, transit depths between 0.1 per cent and 1.8 per cent, and transit durations between 2 and 10 hours with the upper limit determined by our normalisation function. Of these candidates, 25 are already known, and 60 are new. We present these candidates along with the status of photometric and spectroscopic follow-up.
The recent discoveries of Neptune-sized ultra-short period planets (USPs) challenge existing planet formation theories. It is unclear whether these residents of the Hot Neptune Desert have similar ...origins to smaller, rocky USPs, or if this discrete population is evidence of a different formation pathway altogether. We report the discovery of TOI-3261b, an ultra-hot Neptune with an orbital period \(P\) = 0.88 days. The host star is a \(V = 13.2\) magnitude, slightly super-solar metallicity (Fe/H \(\simeq\) 0.15), inactive K1.5 main sequence star at \(d = 300\) pc. Using data from the Transiting Exoplanet Survey Satellite and the Las Cumbres Observatory Global Telescope, we find that TOI-3261b has a radius of \(3.82_{-0.35}^{+0.42}\) \(R_{\oplus}\). Moreover, radial velocities from ESPRESSO and HARPS reveal a mass of \(30.3_{-2.4}^{+2.2}\) \(M_{\oplus}\), more than twice the median mass of Neptune-sized planets on longer orbits. We investigate multiple mechanisms of mass loss that can reproduce the current-day properties of TOI-3261b, simulating the evolution of the planet via tidal stripping and photoevaporation. Thermal evolution models suggest that TOI-3261b should retain an envelope potentially enriched with volatiles constituting \(\sim\)5% of its total mass. This is the second highest envelope mass fraction among ultra-hot Neptunes discovered to date, making TOI-3261b an ideal candidate for atmospheric follow-up observations.
Discovering transiting exoplanets with relatively long orbital periods (\(>\)10 days) is crucial to facilitate the study of cool exoplanet atmospheres (\(T_{\rm eq} < 700 K\)) and to understand ...exoplanet formation and inward migration further out than typical transiting exoplanets. In order to discover these longer period transiting exoplanets, long-term photometric and radial velocity campaigns are required. We report the discovery of TOI-2447 b (\(=\) NGTS-29b), a Saturn-mass transiting exoplanet orbiting a bright (T=10.0) Solar-type star (T\(_{\rm eff}\)=5730 K). TOI-2447 b was identified as a transiting exoplanet candidate from a single transit event of 1.3% depth and 7.29 h duration in \(TESS\) Sector 31 and a prior transit event from 2017 in NGTS data. Four further transit events were observed with NGTS photometry which revealed an orbital period of P=69.34 days. The transit events establish a radius for TOI-2447 b of \(0.865 \pm 0.010\rm R_{\rm J}\), while radial velocity measurements give a mass of \(0.386 \pm 0.025 \rm M_{\rm J}\). The equilibrium temperature of the planet is \(414\) K, making it much cooler than the majority of \(TESS\) planet discoveries. We also detect a transit signal in NGTS data not caused by TOI-2447 b, along with transit timing variations and evidence for a \(\sim\)150 day signal in radial velocity measurements. It is likely that the system hosts additional planets, but further photometry and radial velocity campaigns will be needed to determine their parameters with confidence. TOI-2447 b/NGTS-29b joins a small but growing population of cool giants that will provide crucial insights into giant planet composition and formation mechanisms.
We report the discovery of two exoplanets orbiting around HD 212729 (TOI\,1052, TIC 317060587), a \(T_{\rm eff}=6146\)K star with V=9.51 observed by TESS in Sectors 1 and 13. One exoplanet, ...TOI-1052b, is Neptune-mass and transits the star, and an additional planet TOI-1052c is observed in radial velocities but not seen to transit. We confirm the planetary nature of TOI-1052b using precise radial velocity observations from HARPS and determined its parameters in a joint RV and photometry analysis. TOI-1052b has a radius of \(2.87^{+0.29}_{-0.24}\) R\(_{\oplus}\), a mass of \(16.9\pm 1.7\) M\(_{\oplus}\), and an orbital period of 9.14 days. TOI-1052c does not show any transits in the TESS data, and has a minimum mass of \(34.3^{+4.1}_{-3.7}\) M\(_{\oplus}\) and an orbital period of 35.8 days, placing it just interior to the 4:1 mean motion resonance. Both planets are best fit by relatively high but only marginally significant eccentricities of \(0.18^{+0.09}_{-0.07}\) for planet b and \(0.24^{+0.09}_{-0.08}\) for planet c. We perform a dynamical analysis and internal structure model of the planets as well as deriving stellar parameters and chemical abundances. The mean density of TOI-1052b is \(3.9^{+1.7}_{-1.3}\) g cm\(^{-3}\) consistent with an internal structure similar to Neptune. A nearby star is observed in Gaia DR3 with the same distance and proper motion as TOI-1052, at a sky projected separation of ~1500AU, making this a potential wide binary star system.
We present the discovery of an exoplanet transiting TOI-908 (TIC-350153977) using data from TESS sectors 1, 12, 13, 27, 28 and 39. TOI-908 is a T = 10.7 mag G-dwarf (\(T_{eff}\) = 5626 \(\pm\) 61 K) ...solar-like star with a mass of 0.950 \(\pm\) 0.010 \(M_{\odot}\) and a radius of 1.028 \(\pm\) 0.030 \(R_{\odot}\). The planet, TOI-908 b, is a 3.18 \(\pm\) 0.16 \(R_{\oplus}\) planet in a 3.18 day orbit. Radial velocity measurements from HARPS reveal TOI-908 b has a mass of approximately 16.1 \(\pm\) 4.1 \(M_{\oplus}\) , resulting in a bulk planetary density of 2.7+0.2-0.4 g cm-3. TOI-908 b lies in a sparsely-populated region of parameter space known as the Neptune desert. The planet likely began its life as a sub-Saturn planet before it experienced significant photoevaporation due to X-rays and extreme ultraviolet radiation from its host star, and is likely to continue evaporating, losing a significant fraction of its residual envelope mass.
To date, thousands of planets have been discovered, but there are regions of the orbital parameter space that are still bare. An example is the short period and intermediate mass/radius space known ...as the Neptunian desert, where planets should be easy to find but discoveries remain few. This suggests unusual formation and evolution processes are responsible for the planets residing here. We present the discovery of TOI-332 b, a planet with an ultra-short period of \(0.78\) d that sits firmly within the desert. It orbits a K0 dwarf with an effective temperature of \(5251 \pm 71\) K. TOI-332 b has a radius of \(3.20^{+0.16}_{-0.12}\) R\(_{\oplus}\), smaller than that of Neptune, but an unusually large mass of \(57.2 \pm 1.6\) M\(_{\oplus}\). It has one of the highest densities of any Neptune-sized planet discovered thus far at \(9.6^{+1.1}_{-1.3}\) gcm\(^{-3}\). A 4-layer internal structure model indicates it likely has a negligible hydrogen-helium envelope, something only found for a small handful of planets this massive, and so TOI-332 b presents an interesting challenge to planetary formation theories. We find that photoevaporation cannot account for the mass loss required to strip this planet of the Jupiter-like envelope it would have been expected to accrete. We need to look towards other scenarios, such as high-eccentricity migration, giant impacts, or gap opening in the protoplanetary disc, to try and explain this unusual discovery.
We report the discovery and characterization of a nearby (~ 85 pc), older (27 +/- 3 Myr), distributed stellar population near Lower-Centaurus-Crux (LCC), initially identified by searching for stars ...co-moving with a candidate transiting planet from TESS (HD 109833; TOI 1097). We determine the association membership using Gaia kinematics, color-magnitude information, and rotation periods of candidate members. We measure it's age using isochrones, gyrochronology, and Li depletion. While the association is near known populations of LCC, we find that it is older than any previously found LCC sub-group (10-16 Myr), and distinct in both position and velocity. In addition to the candidate planets around HD 109833 the association contains four directly-imaged planetary-mass companions around 3 stars, YSES-1, YSES-2, and HD 95086, all of which were previously assigned membership in the younger LCC. Using the Notch pipeline, we identify a second candidate transiting planet around HD 109833. We use a suite of ground-based follow-up observations to validate the two transit signals as planetary in nature. HD 109833 b and c join the small but growing population of <100 Myr transiting planets from TESS. HD 109833 has a rotation period and Li abundance indicative of a young age (< 100 Myr), but a position and velocity on the outskirts of the new population, lower Li levels than similar members, and a CMD position below model predictions for 27 Myr. So, we cannot reject the possibility that HD 109833 is a young field star coincidentally nearby the population.
We present the discovery and confirmation of a transiting hot, bloated Super-Neptune using photometry from TESS and LCOGT and radial velocity measurements from HARPS. The host star TOI-2498 is a V = ...11.2, G-type (T\(_{eff}\) = 5905 \(\pm\) 12K) solar-like star with a mass of 1.12 \(\pm\) 0.02 M\(_{\odot}\) and a radius of 1.26 \(\pm\) 0.04 R\(_{\odot}\). The planet, TOI-2498 b, orbits the star with a period of 3.7 days, has a radius of 6.1 \(\pm\) 0.3 R\(_{\oplus}\), and a mass of 35 \(\pm\) 4 M\(_{\oplus}\). This results in a density of 0.86 \(\pm\) 0.25 g cm\(^{-3}\). TOI-2498 b resides on the edge of the Neptune desert; a region of mass-period parameter space in which there appears to be a dearth of planets. Therefore TOI-2498 b is an interesting case to study to further understand the origins and boundaries of the Neptune desert. Through modelling the evaporation history, we determine that over its \(\sim\)3.6 Gyr lifespan, TOI-2498 b has likely reduced from a Saturn sized planet to its current radius through photoevaporation. Moreover, TOI-2498 b is a potential candidate for future atmospheric studies searching for species like water or sodium in the optical using high-resolution, and for carbon based molecules in the infra-red using JWST.
