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Abstract:

Simulated PLATO light curves generated at the University of Oxford in 2025. The light curves were used to test light curve filtering and transit detection algorithms. The light curves were generated in python using the PLATO Solar-like Light curve Simulator (PSLS), PySpot, and PyTransit codes. The data are primarily stored in feather files, which in python can be read using the pandas and pyarrow packages. Detailed information on the included files and contents are provided in the README file.

Abstract:

We report the direct imaging discovery of a third exoplanet in the β Pictoris (β Pic) system. We detect β Pictoris d (β Pic d) in noncoronagraphic observations obtained with the Very Large Telescope (VLT) Enhanced Resolution Imager and Spectrograph (ERIS), as well as multi-epoch archival datasets from the JWST Near Infrared Camera (NIRCam) and VLT/SPHERE. Astrometric measurements over an 11 yr baseline demonstrate that it is consistent with a gravitationally bound source with orbital motion. Joint multi-planet orbit fits of all three planets in the system yield a semimajor axis of 26.0−6.1+2.2 au and inclination 89.0−0.6+0.7 deg for planet d. β Pic d has a larger orbital semimajor axis than the other known planets in the system, but is coplanar with the inner two planets, and its orbit is consistent with sculpting the inner edge of the debris disk. β Pic d has a contrast of ΔL′=12.11±0.15 mag, with colors and luminosity that closely match those of 51 Eri b, another exoplanet in the β Pic moving group. Its VLT/ERIS and JWST/NIRCam colors are distinct from those of free-floating planetary-mass objects of a similar age and temperature. Its red F410M − F444W color indicates strong CO2 absorption in its atmosphere and suggests significant enhancement in metals compared to free-floating objects. From the ATMO hot-start evolutionary models, we estimate an effective temperature of 600−60+45 K and mass of 2.4 ± 0.6 MJup, which also closely matches similar estimates for 51 Eri b. β Pic d is among the lowest-mass exoplanets imaged from the ground. This discovery highlights the deep sensitivity achievable with ground-based imaging in the mid-infrared and the discovery potential of future high-contrast observations with the Extremely Large Telescope.

Abstract:

Young planets offer a unique window into the early stages of planetary evolution. AU Mic is one of the nearest (9.8 pc) pre-main-sequence stars (∼20 Myr), hosting two transiting Neptune-sized planets and a debris disk. Previous studies have shown that the rotations of the central star, the debris disk, and the inner planet b are all aligned, suggesting that the system has not undergone violent evolution. Here we report new Rossiter–McLaughlin measurements for both AU Mic b and c, which happened to transit back-to-back on 2024 August 24 and 25, using the Magellan Planet Finder Spectrograph, together with contemporaneous photometry from LCOGT and CHEOPS. We confirm the aligned orbit of AU Mic b (λb = 1∘ ± 12∘) and find two possible solutions for AU Mic c: we slightly favor an aligned solution (λc = −10∘ ± 16∘) but cannot rule out a polar solution ( λc=87∘−29∘+36∘ ). Broader considerations, including dynamical stability and transit possibility, also support the mutually aligned scenario. An unexpected stellar signal during ingress and the poor transit-timing variation predictions of AU Mic c prevent a precise constraint on its obliquity, and various attempts using chromatic spectral analyses fail to outperform simple data exclusion in mitigating stellar contamination. Our observation highlights the importance of understanding stellar activity across multiple timescales and channels when characterizing young, active systems. A robust solution for the AU Mic architecture will require either a better understanding of stellar activity or future observations fortuitously free from strong stellar contamination.

Abstract:

Ultra-hot Jupiters (UHJs) present extreme atmospheric phenomena not found in the solar system. These planets’ daysides experience strong temperature inversions, molecular species (including H2) dissociate, and magnetism effects disrupt atmospheric circulation. On their nightsides, H2 can recombine and clouds may form. Spectroscopic phase curves allow us to measure these spatially inhomogeneous conditions, which can then be interpreted with three-dimensional (3D) models. In this work, we compare the JWST Near Infrared Imager and Slitless Spectrograph (or NIRISS) spectroscopic phase curve of the UHJ WASP-121 b to state-of-the-art 3D models with varying modeling assumptions, including the aforementioned physical phenomena. We demonstrate the importance of accurately accounting for the planet’s radius when comparing data and models, as it changes the implied overall planetary emission. We find that the 3D models predict planetary emission that is ∼12% higher than observed, contributing to the continued tension between measured and predicted hot Jupiter albedos. We identify multiple lines of evidence confirming a strong source of drag operating in this planet’s atmosphere. In addition, the nightside emission spectrum is devoid of strong absorption features, which may be best explained by nightside clouds. One feature of the dataset that is not reproduced by the 3D models is a trend toward increasingly eastward phase offsets at wavelengths shorter than ∼1.4 μm. This result is inconsistent with reflection from dayside clouds, nor can it be explained by removing atmospheric opacity sources. Our analysis highlights the complexities involved in generating 3D models and interpreting observations of UHJs in the JWST era.