Context. Gaps in circumstellar disks can signal the existence of planetary perturbers, making such systems preferred targets for direct imaging observations of exoplanets. Aims. Being one of the brightest and closest stars to the Sun, the photometric standard star Vega hosts a two-belt debris disk structure. Together with the fact that its planetary system is being viewed nearly face-on, Vega has been one of the prime targets for planet imaging efforts. Methods. Using the vector vortex coronagraph on Keck/NIRC2 in the M-s band at 4.67 mu m, we report the planet detection limits from 1 au to 22 au for Vega with an on-target time of 1.8 h. Results. We reach a 3 M-Jupiter limit outward of 12 au, which is nearly an order of magnitude deeper than for other existing studies. Combining our observations with existing radial velocity studies, we can confidently rule out the existence of companions more than similar to 8 M-Jupiter from 22 au down to 0.1 au for Vega. Interior and exterior to similar to 4 au, this combined approach reaches planet detection limits down to similar to 2-3 M-Jupiter using radial velocity and direct imaging, respectively. Conclusions. By reaching multi-Jupiter mass detection limits, our results are expected to be complemented by the planet imaging of Vega in the upcoming observations using the James Webb Space Telescope to obtain a more holistic understanding of the planetary system configuration around Vega.

Giant planets around young stars serve as a clue to unveiling their formation history and orbital evolution. CI Tau is a 2 Myr-old classical T Tauri star hosting an eccentric hot Jupiter, CI Tau b. The standard formation scenario of a hot Jupiter predicts that planets formed further out and migrated inward. A high eccentricity of CI Tau b may be suggestive of high-e migration due to secular gravitational perturbations by an outer companion. Also, the Atacama Large Millimeter/submillimeter Array 1.3 mm-continuum observations show that CI Tau has at least three annular gaps in which unseen planets may exist. We present high-contrast imaging around CI Tau taken from the Keck/NIRC2 -band filter and vortex coronagraph that allows us to search for an outer companion. We did not detect any outer companion around CI Tau from angular differential imaging (ADI) using two deep imaging data sets. The detection limits from ADI-reduced images rule out the existence of an outer companion beyond similar to 30 au that can cause the Kozai-Lidov migration of CI Tau b. Our results suggest that CI Tau b may have experienced type II migration from ?2 au in megayears. We also confirm that no planets with >= 2-4 M-Jup are hidden in two outer gaps.

Planet formation imprints signatures on the physical structures of disks. In this paper, we present high-resolution (similar to 50 mas, 8 au) Atacama Large Millimeter/submillimeter Array observations of 1.3 mm dust continuum and CO line emission toward the disk around the M3.5 star 2MASSJ04124068+2438157. The dust disk consists of only two narrow rings at radial distances of 0 47 and 0 78 (similar to 70 and 116 au), with Gaussian sigma widths of 5.6 and 8.5 au, respectively. The width of the outer ring is smaller than the estimated pressure scale height by similar to 25%, suggesting dust trapping in a radial pressure bump. The dust disk size, set by the location of the outermost ring, is significantly larger (by 3 sigma) than other disks with similar millimeter luminosity, which can be explained by an early formation of local pressure bump to stop radial drift of millimeter dust grains. After considering the disk's physical structure and accretion properties, we prefer planet-disk interaction over dead zone or photoevaporation models to explain the observed dust disk morphology. We carry out high-contrast imaging at the L' band using Keck/NIRC2 to search for potential young planets, but do not identify any source above 5 sigma. Within the dust gap between the two rings, we reach a contrast level of similar to 7 mag, constraining the possible planet below similar to 2-4M(Jup). Analyses of the gap/ring properties suggest that an approximately Saturn-mass planet at similar to 90 au is likely responsible for the formation of the outer ring, which can potentially be revealed with JWST.

Context. The diverse morphology among protoplanetary disks may result from planet-disk interactions, suggesting the presence of planets undergoing formation. The characterization of disks can provide information on the formation environments of planets. To date, most imaging campaigns have probed the polarized light from disks, which is only a fraction of the total scattered light and not very sensitive to planetary emission.Aims. We aim to observe and characterize protoplanetary disk systems in the near-infrared in both polarized and total intensity light to carry out an unprecedented study of the dust scattering properties of disks, as well as of any possible planetary companions.Methods. Using the star-hopping mode of the SPHERE instrument at the Very Large Telescope, we observed 29 young stars hosting protoplanetary disks and their reference stars in the K-s-band polarized light. We extracted disk signals in total intensity by removing stellar light using the corresponding reference star observations, by adopting the data imputation concept with sequential non-negative matrix factorization (DI-sNMF). For well-recovered disks in both polarized and total intensity light, we parameterized the polarization fraction phase functions using a scaled beta distribution. We investigated the empirical DI-sNMF detectability of disks using logistic regression. For systems with SPHERE data in the Y, J, and H bands, we have summarized their polarized color at an approximately 90(degrees) scattering angle.Results. We obtained high-quality disk images in total intensity for 15 systems and in polarized light for 23 systems. The total intensity detectability of disks primarily depends on the host star brightness, which determines adaptive-optics control ring imagery and thus stellar signals capture using DI-sNMF. The peak of polarization fraction tentatively correlates with the peak scattering angle, which could be reproduced using certain composition for compact dust, yet more detailed modeling studies are needed. Most of the disks are blue in polarized J - K-s color and the fact that they are relatively redder as stellar luminosity increases indicates larger scatterers.Conclusions. High-quality disk imagery in both total intensity and polarized light allows for disk characterizations in the polarization fraction. Combining these techniques reduces the confusion between the disk and planetary signals.

Planets form in disks of gas and dust around young stars. The disk molecular reservoirs and their chemical evolution affect all aspects of planet formation, from the coagulation of dust grains into pebbles to the elemental and molecular compositions of the mature planet. Disk chemistry also enables unique probes of disk structures and dynamics, including those directly linked to ongoing planet formation. We review the protoplanetary disk chemistry of the volatile elements H, O, C, N, S, and P; the associated observational and theoretical methods; and the links between disk and planet chemical compositions. Three takeaways from this review are:

Molecular abundances in protoplanetary disks are highly sensitive to the local physical conditions, including gas temperature, gas density, radiation field, and dust properties. Often multiple factors are intertwined, impacting the abundances of both simple and complex species. We present a new approach to understanding these chemical and physical interdependencies using machine learning. Specifically, we explore the case of CO modeled under the conditions of a generic disk and build an explanatory regression model to study the dependence of CO spatial density on the gas density, gas temperature, cosmic-ray ionization rate, X-ray ionization rate, and UV flux. Our findings indicate that combinations of parameters play a surprisingly powerful role in regulating CO abundance compared to any singular physical parameter. Moreover, in general we find the conditions in the disk are destructive toward CO. CO depletion is further enhanced in an increased cosmic-ray environment and in disks with higher initial C/O ratios. These dependencies uncovered by our new approach are consistent with previous studies, which are more modeling intensive and computationally expensive. Our work thus shows that machine learning can be a powerful tool not only for creating efficient predictive models, but also for enabling a deeper understanding of complex chemical processes.

Complex mixtures of sulfates, silicates, and ice have been observed in a variety of planetary environments on Earth, Mars and the icy satellites of the solar system. Characterizing the properties of the corresponding compositional endmembers is important for understanding the interiors of a range of planetary bodies in which these phases are observed. To measure the electronic and vibrational properties of the pure ferrous iron endmember of the kieserite group, szomolnokite, (FeSO4.H2O), we have performed synchrotron 57Fe nuclear resonant inelastic and forward scattering experiments in the diamond-anvil cell up to 14.5 GPa. This pressure range covers depths within Earth's interior relevant to sulfur cycling in subduction zones and the range of pressures expected within icy satellite interiors. We find evidence of crystal lattice softening, changes in elastic properties, and changes in the electric field gradients of iron atoms associated with two structural transitions occurring within the experimental pressure range. We apply these findings to icy satellite interiors, including discussion of elastic properties, modeling of ice-sulfate aggregates, and implications for tidal observations.

The high-pressure melting curve of FeO controls key aspects of Earth's deep interior and the evolution of rocky planets more broadly. However, existing melting studies on wustite were conducted across a limited pressure range and exhibit substantial disagreement. Here we use an in-situ dual-technique approach that combines a suite of >1000 x-ray diffraction and synchrotron Mossbauer measurements to report the melting curve for Fe1-xO wustite to pressures of Earth's lowermost mantle. We further observe features in the data suggesting an order-disorder transition in the iron defect structure several hundred kelvin below melting. This solid-solid transition, suggested by decades of ambient pressure research, is detected across the full pressure range of the study (30 to 140 GPa). At 136 GPa, our results constrain a relatively high melting temperature of 4140 +/- 110 K, which falls above recent temperature estimates for Earth's present-day core-mantle boundary and supports the viability of solid FeO-rich structures at the roots of mantle plumes. The coincidence of the defect order-disorder transition with pressure-temperature conditions of Earth's mantle base raises broad questions about its possible influence on key physical properties of the region, including rheology and conductivity.

We report the discovery of TOI-4127 b, which is a transiting, Jupiter-sized exoplanet on a long-period (P 56.39879 0.00010 = + 0.00010 days) and a high-eccentricity orbit around a late F-type dwarf star. This warm Jupiter was first detected and identified as a promising candidate from a search for single-transit signals in TESS Sector 20 data, and was later characterized as a planet following two subsequent transits (TESS Sectors 26 and 53) and follow-up ground-based RV observations with the NEID and SOPHIE spectrographs. We jointly fit the transit and RV data to constrain the physical (Rp 1.096 0.032R = + 0.039 0.11 J, Mp 2.30 0.11M = +) and orbital parameters of the exoplanet. J Given its high orbital eccentricity (e 0.7471 0.0086 = +), TOI-4127 b is a compelling candidate for studies of warm 0.0078 Jupiter populations and of hot Jupiter formation pathways. We show that the present periastron separation of TOI4127 b is too large for high-eccentricity tidal migration to circularize its orbit, and that TOI-4127 b is unlikely to be a hot Jupiter progenitor unless it is undergoing angular momentum exchange with an undetected outer companion. Although we find no evidence for an external companion, the available observational data are insufficient to rule out the presence of a perturber that can excite eccentricity oscillations and facilitate tidal migration. Unified Astronomy Thesaurus concepts: Exoplanet astronomy (486); Exoplanet dynamics (490); Transit photometry (1709); Radial velocity (1332); Elliptical orbits (457)