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1. Annular substructures in the transition disks around LkCa 15 and J1610

   https://doi.org/10.1051/0004-6361/202038027  

   Facchini, S.; Benisty, M.; Bae, J.; Loomis, R.; Perez, L.; Ansdell, M.; Mayama, S.; Pinilla, P.; Teague, R.; Isella, A.; et al (July 2020, Astronomy & Astrophysics)

   We present high-resolution millimeter continuum ALMA observations of the disks around the T Tauri stars LkCa 15 and 2MASS J16100501-2132318 (hereafter, J1610). These transition disks host dust-depleted inner regions, which have possibly been carved by massive planets, and they are of prime interest to the study of the imprints of planet-disk interactions. While at moderate angular resolution, they appear as a broad ring surrounding a cavity, the continuum emission resolves into multiple rings at a resolution of ~60 × 40 mas (~7.5 au for LkCa 15, ~6 au for J1610) and ~7 μ Jy beam −1 rms at 1.3 mm. In addition to a broad extended component, LkCa 15 and J1610 host three and two narrow rings, respectively, with two bright rings in LkCa 15 being radially resolved. LkCa 15 possibly hosts another faint ring close to the outer edge of the mm emission. The rings look marginally optically thick, with peak optical depths of ~0.5 (neglecting scattering), in agreement with high angular resolution observations of full disks. We performed hydrodynamical simulations with an embedded, sub-Jovian-mass planet and show that the observed multi-ringed substructure can be qualitatively explained as the outcome of the planet-disk interaction. We note, however, that the choice of the disk cooling timescale alone can significantly impact the resulting gas and dust distributions around the planet, leading to different numbers of rings and gaps and different spacings between them. We propose that the massive outer disk regions of transition disks are favorable places for planetesimals, and possibly second-generation planet formation of objects with a lower mass than the planets carving the inner cavity (typically few M Jup ), and that the annular substructures observed in LkCa 15 and J1610 may be indicative of planetary core formation within dust-rich pressure traps. Current observations are compatible with other mechanisms contributing to the origin of the observed substructures, in particular with regard to narrow rings generated (or facilitated) at the edge of the CO and N 2 snowlines. 

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2. Molecules with ALMA at Planet-forming Scales (MAPS): A Circumplanetary Disk Candidate in Molecular-line Emission in the AS 209 Disk

   https://doi.org/10.3847/2041-8213/ac7fa3  

   Bae, Jaehan; Teague, Richard; Andrews, Sean M.; Benisty, Myriam; Facchini, Stefano; Galloway-Sprietsma, Maria; Loomis, Ryan A.; Aikawa, Yuri; Alarcón, Felipe; Bergin, Edwin; et al (July 2022, The Astrophysical Journal Letters)

   Abstract We report the discovery of a circumplanetary disk (CPD) candidate embedded in the circumstellar disk of the T Tauri star AS 209 at a radial distance of about 200 au (on-sky separation of 1.″4 from the star at a position angle of 161°), isolated via 13 CO J = 2−1 emission. This is the first instance of CPD detection via gaseous emission capable of tracing the overall CPD mass. The CPD is spatially unresolved with a 117 × 82 mas beam and manifests as a point source in 13 CO, indicating that its diameter is ≲14 au. The CPD is embedded within an annular gap in the circumstellar disk previously identified using 12 CO and near-infrared scattered-light observations and is associated with localized velocity perturbations in 12 CO. The coincidence of these features suggests that they have a common origin: an embedded giant planet. We use the 13 CO intensity to constrain the CPD gas temperature and mass. We find that the CPD temperature is ≳35 K, higher than the circumstellar disk temperature at the radial location of the CPD, 22 K, suggesting that heating sources localized to the CPD must be present. The CPD gas mass is ≳0.095 M Jup ≃ 30 M ⊕ adopting a standard 13 CO abundance. From the nondetection of millimeter continuum emission at the location of the CPD (3 σ flux density ≲26.4 μ Jy), we infer that the CPD dust mass is ≲0.027 M ⊕ ≃ 2.2 lunar masses, indicating a low dust-to-gas mass ratio of ≲9 × 10 −4 . We discuss the formation mechanism of the CPD-hosting giant planet on a wide orbit in the framework of gravitational instability and pebble accretion. 

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3. Large Binocular Telescope Search for Companions and Substructures in the (Pre)transitional Disk of AB Aurigae

   https://doi.org/10.3847/1538-4357/ac4be4  

   Jorquera, Sebastián; Bonnefoy, Mickaël; Betti, Sarah; Chauvin, Gaël; Buenzli, Esther; Pérez, Laura M.; Follette, Katherine B.; Hinz, Philip M.; Boccaletti, Anthony; Bailey, Vanessa; et al (February 2022, The Astrophysical Journal)

   Abstract Multiwavelength high-resolution imaging of protoplanetary disks has revealed the presence of multiple, varied substructures in their dust and gas components, which might be signposts of young, forming planetary systems. AB Aurigae bears an emblematic (pre)transitional disk showing spiral structures observed in the inner cavity of the disk in both the submillimeter (Atacama Large Millimeter/submillimeter Array (ALMA); 1.3 mm, 12 CO) and near-infrared (Spectro-polarimetric High-contrast Exoplanet Research; 1.5–2.5 μ m) wavelengths, which have been claimed to arise from dynamical interactions with a massive companion. In this work, we present new deep K s (2.16 μ m) and L ′ (3.7 μ m) band images of AB Aurigae obtained with the L/M-band Infrared Camera on the Large Binocular Telescope, aimed for the detection of both planetary companions and extended disk structures. No point source is recovered, in particular at the outer regions of the disk, where a putative candidate ( ρ = 0.″681, PA = 7.°6) had been previously claimed. The nature of a second innermost planet candidate ( ρ = 0.″16, PA = 203.°9) cannot be investigated by the new data. We are able to derive 5 σ detection limits in both magnitude and mass for the system, going from 14 M Jup at 0.″3 (49 au) down to 3–4 M Jup at 0.″6 (98 au) and beyond, based on the ATMO 2020 evolutionary models. We detect the inner spiral structures (<0.″5) resolved in both CO and polarimetric H -band observations. We also recover the ring structure of the system at larger separation (0.″5–0.″7) showing a clear southeast/northwest asymmetry. This structure, observed for the first time at L ′ band, remains interior to the dust cavity seen at ALMA, suggesting an efficient dust trapping mechanism at play in the disk. 

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4. The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO). I. Program Overview and Summary of First Results

   https://doi.org/10.3847/1538-4357/addebe  

   Zhang, Ke; Pérez, Laura M; Pascucci, Ilaria; Pinilla, Paola; Cieza, Lucas A; Carpenter, John; Trapman, Leon; Deng, Dingshan; Agurto-Gangas, Carolina; Sierra, Anibal; et al (July 2025, The Astrophysical Journal)

   We present the Atacama Large Millimeter/submillimeter Array Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO), a large program of the ALMA. AGE-PRO aims to systematically trace the evolution of gas disk mass and size throughout the lifetime of protoplanetary disks. It uses a carefully selected sample of 30 disks around M3-K6 stars in three nearby star-forming regions: Ophiuchus (0.5–1 Myr), Lupus (1–3 Myr), and Upper Sco (2–6 Myr). Assuming the three regions had similar initial conditions and evolutionary paths, we find the median gas disk mass appears to decrease with age. Ophiuchus disks have the highest median gas mass (6M_Jup), while the Lupus and Upper Sco disks have significantly lower median masses (0.68 and 0.44M_Jup, respectively). Notably, the gas and dust disk masses appear to evolve on different timescales. This is evidenced by the median gas-to-dust mass ratio, which decreases from 122 in the youngest disks (<1 Myr) to 46 in Lupus disks, and then increases to 120 in the Upper Sco disks. The median gas disk sizes range between 74 and 110 au, suggesting that typical gas disks are much smaller than those of well-studied, massive disks. Population synthesis models suggest that magnetohydrodynamic wind-driven accretion can reproduce median disk properties across all three regions, when assuming compact disks with a declining magnetic field over time. In contrast, turbulent-driven models overestimate gas masses of >1 Myr disks by an order of magnitude. Here, we discuss the program’s motivation, survey design, sample selection, observation and data calibration processes, and highlight the initial results. 

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5. The MIRI Excesses Around Degenerates (MEAD) Survey. II. A Probable Planet Detected via IR Excess around WD 0644+025

   https://doi.org/10.3847/1538-3881/ae3c0e  

   Poulsen, Sabrina; Debes, John; Messier, Ashley; Le_Bourdais, Érika; Melis, Carl; Cracraft, Misty; Boucher, Samuel; Kilic, Mukremin; Kenyon, Scott; Wyatt, Mark C; et al (February 2026, The Astronomical Journal)

   Abstract The MIRI Excesses Around Degenerates (MEAD) Survey is a Cycle 2 JWST program designed to image nearby white dwarfs with MIRI at 10 and 15μm. This survey targeted 56 white dwarfs within 25 pc to search for mid-infrared excesses, flux deficits from collision-induced absorption, and resolved substellar companions. In this paper we present our analysis of WD 0644+025, an unusually massive white dwarf (0.95M_⊙) and the MEAD target exhibiting the most significant mid-infrared excess. The observed JWST MIRI photometry shows a 7.3σexcess at 15μm and a 3.6σexcess at 10μm, which may be associated with either a planetary companion or a circumstellar dust disk. This excess corresponds to a companion mass of 6.8M_Jup(T_eff= 261 ±9 K) with orbital distance <11.8 au, although substantially lower masses are possible if we consider a closely orbiting isolated companion. No spatially resolved sources are detected within 200 au, with contrast curve analysis excluding planets more massive than 2M_Jupbeyond ∼12 au. Metal pollution is confirmed in both archival Keck HIRES spectra from 1999 and new observations from 2025, with no evidence suggesting that the accretion rate has substantially changed over the decades. We explore possible dust disk morphologies to describe the observed IR excess and find that traditional debris disks struggle to fit our data. WD 0644+025 thus represents a compelling case study in the growing population of white dwarfs with cold infrared excesses and highlights JWST’s ability to probe planetary system remnants inaccessible to prior infrared observatories. 

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