Exoplanets and Stellar Physics

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:

Abstract We present the first spatially resolved kinematic evidence for dust in the outflows of Active Galactic Nuclei (AGN). We utilise observations from JWST with NIRSpec IFU and MIRI MRS data of 10 local Seyferts and use Principal Component Analysis (PCA) tomography to extract the kinematics of Polycyclic Aromatic Hydrocarbon (PAH) features. PAHs comprise the smallest carbonaceous dust molecules in the Interstellar Medium (ISM), and produce emission features in the infrared providing the potential to measure kinematics. This is however challenging due to their broad shapes and variations in their intrinsic profile, prompting the need for techniques such as PCA tomography. We find that the velocity of the PAHs is similar to the molecular gas as traced by the rotational transitions of H2, where for NGC 5728 and NGC 7582, both disk and outflow are present. We detect the outflow in the kinematics of large and neutral PAHs, namely the 11.3 μm and 17 μm PAH features, where after subtracting the disk, the velocity field matches that of high-ionisation potential lines such as [NeVI] (7.65 μm, IP = 158 eV). Finally, we fail to detect kinematics of the 6.2 μm PAH due to an altered intrinsic profile while the the 3.3 μm PAH kinematics purely trace the circumnuclear disk. This suggests the PAHs in the outflow are more neutral and larger than in star-forming regions, consistent with PAH band ratios in previous studies of AGN.

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.