Program

Of the 6000 detected exoplanets, only a small fraction have been found orbiting stars younger than 100 Myrs old. However, such planetary systems offer invaluable insight into planet formation and early evolution processes. In this talk, I will discuss some of the leading theories of planet formation and how one can leverage populations of young transiting exoplanets to probe planet composition, internal structure, and system dynamics. Finally, I will highlight future missions aimed at detecting young exoplanets, and the scientific possibilities that open up as a result.

Atmospheric escape, often driven largely by stellar irradiation, plays a major role in the development of young exoplanets. Stars tend to be quite active in their early life, so understanding how stellar variability influences the mass-loss rate is an important aspect of modelling young systems. The helium metastable triplet at 1083.3nm is an excellent line to study escape observationally. However, this line has been shown to be sensitive to features of the host star like elemental abundances and temperature distribution in the corona, and we explore this further here. Simulations with atmospheric escape models like ATES and sunbather reveal that the spectral lines originating from coronal plasma at different temperatures contribute to the partial or complete ionization of a substantial fraction of helium in hot Jupiter atmospheres, but the exact nature of this temperature-ionization relationship is not straightforward. This is relevant as it is the balance between the recombination of singly ionized helium and the ionization of metastable helium that ultimately affects the metastable helium population and hence the line strength. Therefore, modelling the coronal temperature structure in different activity states of a young star is important for fitting observations of escaping helium and building a more accurate picture of photoevaporation from young planets.

The majority of directly imaged exoplanets are young giant planets, with ages from 5 to 100 Myr, overlapping brown dwarf companions at similar separations. Characterization of these imaged giant planets and substellar companions allows us to examine multiple formation channels and refine our theoretical understanding of planet formation. One of the long-sought observational efforts is to identify observables, such as orbital dynamics, spins, and chemical abundances, that separate these populations, which shed light on their formation pathways. In this talk, I present the largest high-resolution (R~35,000) spectroscopic survey to date of 32 directly imaged planets and brown dwarf companions using Keck/KPIC K-band high-resolution spectroscopy. Adding companions with spin measurements from the literature, we construct a curated spin sample of 43 benchmark companions and giant planets and 54 free-floating brown dwarfs and planetary-mass objects. We find the first clear evidence of distinct rotation speeds between imaged giant planets and brown dwarf companions at 4-4.5 σ assuming inclinations aligned with their orbits, while under randomly oriented inclinations the significance is at 1.6-2.1 σ. The higher fractional breakup velocities of planets can be interpreted as less angular momentum loss through circumplanetary disk braking during the planet formation phase. Our findings hold when considering various assumptions about planets. Notably, the mass ratio below 0.8% provides a clean distinction for rotation between giant planets and brown dwarf companions, indicating that both mass and mass ratios, which connect to the disk properties, are important to determine the terminal rotation of planets. Thus, we show that rotation is the most clear observable to disentangle the populations of imaged giant planets and brown dwarf companions, along with the well-known orbital eccentricities. Our novel analysis of specific angular momentum for 200+ isolated brown dwarfs and free-floating planetary objects with spin measurements indicates that their spins are also dependent on the disk environment. For atmospheric characterizations, I highlight our recent K-band abundance results on imaged planets and companions, including the first clear molecular detection of CO and H2O in the protoplanet PDS 70 b, which shows a C/O ratio similar to its host star and much lower than the high gas disk C/O ratio measured by ALMA. We also find a surprising non-detection of molecules on the protoplanet candidate AB Aur b under excellent observing conditions. This talk is concluded by highlighting our new H-band capability and the first KPIC H-band detection of a late-M companion, and connecting it to the new science enabled by the upcoming Keck/HISPEC, which will probe refractory species such as FeH in J and H bands for imaged giant planets at close separations, complementary to VLT/HiRISE and VLT/CRIRES+, and to what JWST/NIRSpec has offered to probe the refractory species such as H2S in longer wavelengths.

We present the discovery of the exoplanet HD 143811 AB b in the Sco-Cen star-forming region, which is a rare example of a directly imaged exoplanet orbiting a short-period stellar binary. To characterize the host binary, we utilize archival high-resolution spectroscopy from FEROS on the MPG/ESO 2.2-meter telescope to measure radial velocities of both components of the binary and fit the orbit. From the orbit fit, we measure a precise orbital period of 18.59098 ± 0.00007 days. When we combine the orbit fit with unresolved photometry and evolutionary models, we derive masses of ~1.3 MSun and ~1.15 MSun for each star. To characterize the companion, we use two GPI epochs and one Keck/NIRC2 epoch to measure the planet’s SED, which we combine with the system age to calculate a model-dependent mass of ~5.6 MJup, well within the planetary regime. We discuss the implications of this discovery for planet formation around binary stars by comparing HD 143811 AB b to other directly imaged planets in Sco-Cen around both single stars and binaries. With future observations, we will constrain the 3D orientations of both orbits,  test for coplanarity, and determine the stability of this young planetary system. 

Circumplanetary disks play a critical role in the formation of giant planets; however, their physical properties remain poorly constrained observationally. SR 12 c is a 13 Mjup directly-imaged gas giant orbiting its host binary at a separation of 1200 AU. As a young and actively accreting planet, it provides a rare opportunity to probe both the planet formation process and the surrounding environment. Following our previous ALMA detection of its circumplanetary disk, we present new JWST/MIRI imaging observations and constrain the disk's temperature structure and geometry through analytic modeling. Phenomenologically, the emission is well described by a two-component blackbody with a significant temperature contrast. Using more physically motivated models, we find that the disk is likely geometrically flat, and viscous heating does not appear to dominate its temperature profile. Additionally, the absence of a strong silicate feature suggests grain growth and vertical settling within the disk. Together with our complementary HST UV/optical observations, our programs provide the broadest wavelength coverage to date for a young, accreting giant planet.

Young planets (<50 Myr) provide strong tests of planet formation and evolution theories by allowing us to observe sculpting processes in situ. However, differentiating between models has been limited by the small population of known young transiting planets. To address this, the TESS Investigation - Demographics of Young Exoplanets (TI-DYE) survey utilizes advancements in TESS light-curve reduction and updated young stellar cluster lists to significantly expand the census of planets in this critical age range. Our discoveries include additional planets in previously known systems (e.g., HIP 67522 c; 17 Myr) and an expansion of the lower age limit for transit detection (IRAS 04125+2902 b; 3 Myr). Many more discoveries are expected as we search for planets in the Orion, Vela, Sco-Cen, and Taurus-Auriga regions. With this expanded sample, we can compare the occurrence rates of young versus mature planets to determine which mechanisms dominate the formation of close-orbiting sub-Neptunes.

In this talk, I will discuss our team's efforts to detect and characterize young transiting planet candidates previously identified in surveys of young star clusters using data from NASA's TESS and ESA's Gaia missions. We refine the systems' properties using follow-up observations, including ground-based photometry, high-resolution spectroscopy, and adaptive optics/speckle imaging. We confirm the youth of the host stars based on their rapid rotations, strong lithium absorptions, and kinematic memberships in nearby young open clusters. Radial velocity monitoring reveals variability consistent with stellar activity, but constrains the companion mass to substellar regimes. Multi-band photometry, high-resolution imaging, and RV analysis collectively rule out false-positive scenarios, validating the candidates as bona fide planets. Given their periods and radii, we find these planets reside within the Neptunian desert, near the so-called Neptunian ridge. I will also share our future plans for further characterization these young systems including their orbits and atmospheres.

Understanding the early evolution of planetary systems, within their first 100 Myr, is critical to explaining the incredible diversity of exoplanets observed today. During this dynamic phase, processes like orbital migration due to gravitational or tidal interactions and atmospheric escape driven primarily by stellar radiation profoundly sculpt planetary system architectures. These mechanisms are thought to create the so-called Neptunian Desert, a region largely devoid of Neptune-sized planets on short-period orbits. Planets found residing at the edge of this desert are not expected to have formed in-situ and are likely experiencing intense atmospheric escape. However, our understanding of these processes remains largely theoretical due to a scarcity of known planetary systems with robustly determined young ages.
To help fill this gap, we have validated TOI-5973b as an ideal and unique sub-Saturn planet. First, its host star is unambiguously young. Its membership in the ∼40 Myr open cluster UBC165/UPK168 provides the most reliable age estimate, derived from PARSEC2 isochrone fitting. This young age is strongly corroborated by three independent youth indicators: strong Li I 670.8 nm absorption, a rapid ∼0.7-day rotation period, and excess Gaia photometric variability associated with rotation.
Second, we have exhaustively vetted this candidate. While statistical validation with triceratops yields a low False Positive (FP) probability of ∼0.8%, the primary remaining FP scenario involves an unresolved stellar companion. We confidently rule out this specific scenario with two key pieces of evidence: achromatic transit depths seen in LCO/MuSCAT3 data, and a single-lined spectroscopic profile from Subaru/HDS, both of which are inconsistent with stellar imposters. Furthermore, using Gemini/MAROON-X RV data, we confirmed that the object is significantly less massive than a brown dwarf, even under conservative assumptions regarding stellar jitter due to rapid rotation. This firmly establishes its planetary nature.
A very young planet found in this region offers a precious snapshot of transient evolutionary processes in action. The validation of TOI-5973b will unlock the next phase of our research, where we will directly probe the physical mechanisms that dictate a planet’s ultimate fate. Our follow-up plan consists of three key investigations: First, we will measure the Rossiter-McLaughlin effect to determine the stellar obliquity. This provides a fossil record of its dynamical history, allowing us to distinguish between different orbital migration scenarios. Second, we will perform transmission spectroscopy targeting the He triplet at 1083 nm to directly detect and characterize its potential atmospheric escape. Third, with a bright Kmag = 11.5 host star, this young planet is an exceptional target for detailed atmospheric characterization with JWST. By measuring atmospheric properties such as the C/O ratio and metallicity, we can directly trace the chemical record of its formation location.

Thousands of exoplanet discoveries have transformed our understanding of planetary systems, yet the earliest stages of planetary evolution remain poorly constrained. Young exoplanets, those within the first few hundred million years after formation, provide critical snapshots of the processes shaping planetary evolution. However, their density characterisation is hindered by strong, time-variable stellar activity that dominates radial velocity (RV) measurements. Complicating their mass, hence density, measurements. We present a framework for mitigating stellar variability, showing that contemporaneous high-cadence photometry can outperform traditional spectroscopic diagnostics in modelling high-precision RVs. This enables the detection of planetary signals significantly smaller than the stellar activity amplitude and allows robust mass measurements for young transiting planets. This approach is being applied within an ongoing ESO Large Programme (>250 hours) targeting 13 transiting planets in 7 young stellar systems, effectively doubling the current sample of well-characterised young transiting planets. By expanding this sample, the program will map the mass-radius-age parameter space at early times and provide key empirical constraints on atmospheric evolution processes, including photoevaporation and core-powered mass loss. In particular, it will enable direct tests of the origin and early evolution of population-level features such as the Neptunian desert. These results highlight the critical synergy between photometric surveys (e.g. NGTS, PLATO) and state-of-the-art RV instruments, and provide a scalable pathway to overcoming stellar activity in the study of young planetary systems.

The intrinsic variability resulting from the magnetic activity of young, active stars represents one of the most significant hurdles in the detection and characterization of exoplanets. Studying these young systems is essential for understanding critical evolutionary processes, such as atmospheric mass-loss, orbital migration, and the structural contraction of nascent "inflated" planets. However, the high levels of stellar activity typical of these targets produce "jitter" in both photometric and spectroscopic observations, often masking planetary signals or generating spurious ones that mimic planet signatures. In fast-rotating stars, this challenge is compounded by the fact that spectral lines are significantly enlarged due to rotational broadening, which dominates over other broadening effects. Consequently, the cross-correlation function (CCF) profile is not accurately described by the standard Gaussian fit used in traditional radial velocity (RV) pipelines, necessitating the development of more sophisticated modeling techniques.
To address these issues, we present SpotCCF, a new tool designed to model the stellar photosphere and its surface inhomogeneities by analyzing deformations of the CCF profile. Unlike conventional methods, SpotCCF models the CCF through a rotational profile convolved with a Lorentzian function, while accounting for the specific distortions induced by the presence of multiple starspots.
We applied this tool to more than 300 high-resolution HARPS-N spectra of the young (~23 Myr) solar-mass star V1298 Tau, a landmark multi-planet system used to study the initial conditions of close-in architectures. By fitting the CCFs with a multi-spot model, we successfully extracted the spot configurations, identifying two primary distributions: larger spots preferentially located at high latitudes (45–90°) and smaller spots at lower latitudes (0–10°). Furthermore, our analysis of these spot movements suggests a solar-like differential rotation for V1298 Tau, characterized by a lower rotation velocity at higher latitudes.
The application of SpotCCF to V1298 Tau provided a significant improvement in RV extraction, yielding an optimized time series with a dispersion 40% to 60% lower than standard pipelines like TERRA. This substantial reduction in noise is achieved by partially mitigating the contribution of stellar activity modulated by the star’s rotation. To further validate our method, we performed detection sensitivity tests by injecting synthetic planetary signals into the data. The results demonstrate that SpotCCF can reliably recover a lower-amplitude signal (K ~ 37 m/s, corresponding to ~ 0.35 Mjupiter compared to the K >= 75 m/s required for identification in the TERRA dataset. Ultimately, our method enhances the ability to disentangle stellar and planetary signals, providing a robust framework for advancing our understanding of both stellar activity and the early evolution of planetary systems.

Mapping young exoplanet demographics is crucial for explaining the diversity seen in mature planetary systems. However, high levels of stellar magnetic activity in youth can severely impede characterizing young exoplanets, particularly when using radial velocities to measure planet masses. I will present an intensive observing campaign to measure the mass of the Jupiter-sized IRAS 04125+2902 b, which is the youngest known transiting planet (3 Myr). Observations include high cadence photometry and NIR spectroscopy (Habitable-zone Planet Finder) which can be combined to separate the stellar activity signal from the planet’s Doppler signal in radial velocities. I will showcase the long-term stability of the stellar activity signal, indicating long-lived surface active regions that are easy to model using Gaussian processes to capture the temporally coherent noise. The 90% mass limit is 35 Earth masses (0.11 Jupiter masses), a ~30% reduction from the current literature estimate. While IRAS 04125+2902 b is Jupiter-sized, it is very low density and likely a progenitor of a sub-Saturn or even a sub-Neptune.

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 rotation 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 (RM) measurements for both AU Mic b and c, which happened to transit back-to-back on August 24 and 25, 2024, using the Magellan Planet Finder Spectrograph (PFS), accompanied by contemporaneous photometry from LCOGT and CHEOPS. We confirm the aligned orbit of AU Mic b (lambda_b = 1° ± 12°) and find two possible solutions for AU Mic c: we slightly favor an aligned solution (lambda_c = −10° ± 16°) but cannot rule out a polar solution (lambda_c = 87° +36°/−29°). Broader considerations, including dynamical stability and transit probability, also support the mutually aligned scenario. An unexpected stellar signal during ingress and poor TTV predictions for 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 observations highlight 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 that are fortuitously free from strong stellar contamination.

The engulfment of planet and brown dwarf companions by their host stars is expected to occur primarily within the first 100 million years of stellar system formation, while the star is still in its pre-main sequence phase. These engulfment events are expected to alter the host star’s photospheric composition in a manner that reflects the composition of the accreted material. However, the extent and duration of this enrichment depends on several factors, including timing and depth of companion engulfment, as well as internal stellar mixing processes such as convective, diffusion and thermohaline mixing. For the first time, we model the accretion of substellar companions onto pre-main sequence low mass stars and examine the evolution of the resulting engulfment signatures through to the main sequence. Our results provide a theoretical framework for interpreting observed stellar abundance anomalies which will assist in constraining the formation and early dynamical evolution of stars and their companions.

Young low-mass stars exhibit enhanced magnetic activity and frequent flaring during their early evolution, producing intense X-ray and ultraviolet (XUV) radiation that can strongly influence the survival of planetary atmospheres. Close-in planets are particularly susceptible to atmospheric erosion, while those at larger orbital separations may retain substantial envelopes, potentially leading to divergent evolutionary pathways within planetary systems. This mechanism is widely invoked to explain the observed bimodal distribution in exoplanet radii via photoevaporation during the early stages of star–planet evolution.Constraining this process requires a detailed characterization of stellar activity during the pre-main-sequence phase, even in systems without currently known planets. We present early results from SAYS — the Stellar Activity in Young Stars survey — an ongoing observational program designed to quantify the temporal variability of chromospheric emission in very young M dwarfs. SAYS utilizes time-resolved, low-resolution optical spectroscopy from Indian ground-based facilities, complemented where available by photometric data from space- and ground-based surveys.
Rather than restricting the sample to known planet-hosting stars, which remain observationally limited, SAYS targets a broader population of young M dwarfs to statistically constrain the range of activity levels and variability timescales relevant for planetary atmosphere evolution. We detect significant intra-night variability in Balmer emission diagnostics on timescales of tens of minutes in several targets, including one of the youngest known M dwarfs, indicating rapidly evolving chromospheric conditions and changes in optical depth. In contrast, other targets exhibit comparatively stable emission over similar timescales, underscoring the diversity of activity states in young stellar populations.
These observations provide empirical constraints on the variability and intensity of stellar radiation fields that drive atmospheric escape, and serve as inputs for photoionization and radiative transfer modeling (e.g., with CLOUDY), bridging observations and theory in the study of star–planet interactions.

Planetary-mass objects near the L/T transition ( Teff ~ 1300 K) exhibit enhanced spectroscopic variability compared to field brown dwarfs. We present a comprehensive analysis of SIMP J013656.5+093347, a nearby, young, and highly variable planetary-mass object, using two decades of near-infrared (J- and K-band) observations from ground- and space-based facilities, including CFHT, OMM, Perkins Observatory, JWST, Spitzer, and Hubble. Analysis of the light-curve morphology over this baseline reveals recurring features consistent with complex beating patterns. We further perform a harmonic decomposition of each epoch, characterizing the number of detected harmonics—interpreted as signatures of planetary-scale waves—as well as their associated periods and amplitudes. Our results show that higher-order harmonics evolve on timescales of days while the overall spectrophotometric variability amplitude declines over decades, indicating an atmosphere whose structure evolves across multiple temporal scales.

I will present the results of a comprehensive study of the heavily-evaporating exoplanet WASP-12b (Shu-lin,L. 2010, Nature 463, 1054–1056), addressing whether its escaping planetary atmospheric material is sufficient to form an observable circumstellar disk as predicted by Fossati et al. ( 2013, ApJ,766L,20F). The idea is that the circumstellar material lost by the planet blocks the stellar emission at the position of lines probing stellar activity at both near-ultraviolet and optical wavelengths; affecting dramatically the estimation of stellar activity, e.g. HIRES archival spectra of the Ca II H and K lines of WASP-12 show broad depressions in the line cores, deeper than those of other inactive and similarly distant stars and similar to WASP-12's Mg II h and k line profiles. Our approach combines theoretical magnetohydrodynamic (MHD) modeling and an observational campaign. The MHD model, which incorporates radiative losses from optically thin plasma, successfully predicts the existence and stability of such a disk around the host star, revealing its key characteristics and dynamic evolution. Our complete theoretical models confirm the presence of this disk.
We, also, estimated whether the effect of the circumstellar disk on obscuring the stellar radiation is observable in the Ariel waveband.Complementing this, we have initiated an observational campaign using the TNG telescope to search for compatible observable features.

Detecting planets in open clusters offers a unique opportunity to test planet formation theories in clustered environments. The precisely determined ages of young open clusters make their planets particularly valuable for tracing the early evolution of planetary systems. As the second paper of the UPiC project, this study focuses on stars in stellar groups that host transiting planets or planetary candidates. We categorize these stellar groups into Open Clusters (OCs) and Moving Groups (MGs) based on the Jacobi radius to investigate potential differences in their planetary systems. By cross-matching the latest star cluster catalogs with catalogs of transiting planets and candidates, we have compiled the most extensive catalog to date, containing 106 confirmed planets and 168 candidates within OCs and MGs. We refitted the structural parameters of these stellar groups and identified substructures using the HDBSCAN and Gaussian Mixture Model (GMM) algorithms. Our analysis reveals the density evolution of both MGs and OCs during their first Gyr. We find that MGs consistently exhibit a significantly higher planet fraction than OCs, regardless of sample selection, particularly for Hot Jupiters. Furthermore, exoplanet radii show a clear dichotomy at early stages: most sub-Jupiters evolve into Neptune-sized planets within 100 Myr, while super-Jupiters undergo only minimal contraction. These results suggest that young sub-Jupiters (< 100 Myr) represent puffy, Neptune-mass planets undergoing vigorous photoevaporation, whereas Jupiter-mass planets can maintain their atmospheres. We also report evidence for the early emergence of the hot-Neptune desert at 100 Myr in both OCs and MGs.

Cool stars are intrinsically active and heterogeneous, and their surface inhomogeneities can imprint signals on transit spectra that mimic or obscure planetary atmospheric features. This contamination, known as the Transit Light Source Effect (TLSE), poses a major challenge for atmospheric characterization, particularly in systems observed with the precision of JWST. Robust interpretation of exoplanet spectra therefore requires a detailed understanding of the host star. Here, we present JWST observations of multiple near-sequential transits of a late K-type star hosting five transiting planets. Several of these planets share similar transit chords across the stellar disk, enabling a direct probe of stellar surface heterogeneity through comparative transit analysis. The availability of both small, likely rocky planets and a larger sub-Neptune in the same system offers a unique opportunity: transits of the rocky planets can be used to constrain TLSE and stellar contamination, which can then be applied to isolate the atmospheric signal of the sub-Neptune. This approach provides a powerful framework for disentangling stellar and planetary signals in active multi-planet systems and demonstrates how stellar heterogeneity can be leveraged, rather than avoided, to improve atmospheric characterization. The method is broadly applicable to the growing population of compact multi-planet systems orbiting cool stars.

M dwarfs host the known majority of potentially habitable exoplanets, yet their intense early flaring activity represents one of the dominant mechanisms driving photochemistry in planetary atmospheres. We present a self-consistent framework for characterising and modelling such stellar activity, combining the temporal and spectral energy distributions, with application to atmospheric chemical evolution studies.
We characterised the flaring behaviour of M-K dwarfs in young moving groups from photometry and far-ultraviolet observations, demonstrating that rotation period, rather than age, serves as the most reliable proxy for flare activity. We show that mid-size and large flares in young M dwarfs are better described by a piecewise power law, with significant differences between optical and FUV flare behaviour.
We present the Young M Dwarf Flare (YMDF) model, developed from the ground up using radiative-hydrodynamic simulations of stellar atmospheres incorporating high- and low-energy electron beams. By comparing synthetic and observed flare spectra, we identify the modelling frameworks best suited for representing flare activity, and validate the resulting synthetic spectra and light curves against HST-COS FUV spectroscopy and light curves, and TESS photometry.
Finally, coupling YMDF with the VULCAN photochemical kinetics code, we simulate one year of atmospheric chemical evolution for young primordial exo-Earth, super-Earth and mini-Neptune atmospheres spanning low water vapour to extreme steam compositions at a range of equilibrium temperatures. YMDF produces substantially greater chemical stress than older M dwarf flare activity models, with cumulative activity potentially capable of permanently altering atmospheric mixing ratios, particularly in trace species.  In water-dominated atmospheres, we further find that photochemical processes yield an abiotic oxygen production regardless of planet size, with implications for the long-term volatile retention and observational characterisation.

Transmission spectroscopy has reported sub-solar C/O ratios (<0.55) for atmospheres of some transiting gas giants/dwarfs (e.g., Sing et al. 2024; Welbanks et al. 2024). However, static disk chemistry models (e.g., Öberg et al. 2011) predict super-solar C/O ratios for protoplanetary disk gas and, consequently, for planetary envelopes. In this study, we consider two possible origins of such low atmospheric C/O ratios–formation and internal evolutionary origins–and propose how to distinguish them with young exoplanetary systems.
Possible mechanisms for the formation origin include evaporation of radially-drifting pebbles in the protoplanetary disk and of accreting pebbles in the envelope during planet formation to supply heavy elements (e.g., Brouwers et al. 2018). In contrast, a possible mechanism for the internal evolutionary origin is the transport of heavy elements with sub-solar C/O from the planetary interior. Recent studies of Jupiter and Saturn have suggested the presence of diluted cores, in which the heavy-element abundance decreases continuously with radius (e.g., Wahl et al. 2017; Mankovich & Fuller 2021). In gas giants with such internal structures, heavy elements may be transported into the atmosphere through internal mixing with time (Knierim & Helled, 2025), providing another possible origin of low C/O ratios.
Thus, both formation and internal evolution may produce low C/O ratios. Distinguishing between them is important for understanding the diversity of planet formation and evolution; however, this may be challenging because most currently observed planets are older than 1 Gyr when internal mixing might have already been completed. The C/O ratios of young planets may provide an important clue to the origin of low atmospheric C/O.
In this study, we investigate the atmospheric C/O evolution of gas giants with diluted cores as a candidate internal evolutionary origin, focusing on when low C/O can be realized. We use MESA (Paxton et al. 2011–2019; Jermyn et al. 2023) together with the planetary module MESPA (Helled, Müller, & Knierim 2025). The initial entropy and diluted-core profiles are taken from Knierim & Helled (2025), and the initial atmospheric C/O is given from gas-phase values in the model of Öberg et al. (2011). We also include internal heating, in which a fraction of the incident stellar irradiation is transported into the deep envelope (Komacek & Youdin 2017). This is motivated by the fact that some planets appear to show low C/O together with hotter interior states than predicted by standard gas-giant evolution models (Fortney et al. 2020).
As a result, in some of our model setups, sub-solar C/O can be realized by ~10 Myr. This suggests that low C/O inferred for young planets may not uniquely determine its origin. On the other hand, in strongly heated environments, characterized by high equilibrium temperatures and high energy transport efficiencies, the post-formation reduction of atmospheric C/O tends to become less effective. This suggests that strongly irradiated young planets, particularly hot to ultra-hot Jupiters, may be promising observational targets for distinguishing the origin of low atmospheric C/O. In this presentation, we discuss the implications of these results for observations of young planets.

Estimating how close-in planetary systems evolve requires occurrence-rate measurements that account for both selection effects and uncertainties in host-star properties. I present a hierarchical Bayesian framework that jointly models the stellar population and planet occurrence as functions of stellar and planetary parameters. Instead of adopting point estimates for individual stars, the model propagates the full posterior uncertainties and correlations in stellar age, mass, and metallicity into the population-level inference. This makes it possible to distinguish intrinsic trends in planet occurrence from trends that arise from the host-star sample itself.
I first applied this framework to giant planets around Sun-like stars in the California Legacy Survey. The results suggest that hot-Jupiter occurrence declines with stellar age on Gyr timescales, indicating that close-in giant planets may continue to evolve after formation, possibly through tidal or dynamical processes. I then extend the same framework to short-period planets in the Kepler sample.
The broader goal is to place the occurrence of close-in planets on a common statistical footing across stellar populations, and to clarify how age, mass, and metallicity shape planetary-system architectures.

Understanding the early evolution of planetary systems requires a robust characterization of the environments in which stars and protoplanetary disks form. In young star-forming regions, the properties of interstellar dust regulate key physical processes, including gas cooling, disk evolution, and mass accretion onto Young Stellar Objects (YSOs). In particular, the extinction law provides a powerful diagnostic of the dust grain size distribution, the chemical processing history of the interstellar medium (ISM), and the impact of stellar feedback in dense star-forming environments.
We present a comprehensive spectroscopic analysis of the extinction properties in NGC 346, a massive star-forming region in the Small Magellanic Cloud, based on JWST/NIRSpec multi-object spectroscopy. Using hydrogen recombination lines from the Brackett and Pfund series together with molecular hydrogen transitions, we derive the extinction law by comparing the observed line ratios with their theoretical intrinsic values. This approach allows us to constrain the total-to-selective extinction parameter, R_lambda, over a statistically significant sample of lines of sight toward the immediate surroundings of YSOs.
Applying this analysis to the full NIRSpec dataset, we map spatial variations of the extinction law across the region and assess how dust properties differ from those observed in nearby solar-metallicity star-forming regions. In particular, we test for the presence of a “greyer” near-infrared extinction component indicative of an enhanced population of large dust grains, potentially produced by dust processing in dense, feedback-dominated environments.
With a metallicity of about 1/8Zsun, NGC 346 provides a unique laboratory for studying star and planet formation under conditions that more closely resemble those prevailing during Cosmic Noon, the epoch at redshift z~2 of peak star formation in the Universe. Constraining the extinction law in these environments is essential for accurately deriving accretion diagnostics and fundamental stellar parameters of YSOs in extreme SFRs. More broadly, our results provide critical constraints on the environmental conditions that regulate protoplanetary disk evolution and shape the earliest stages of planet formation in low-metallicity systems.

We present a new demographics analysis of the full Gemini Planet Imager Exoplanet Survey (GPIES), which was conducted from 2014 to 2019 at Gemini South. With over 500 stars imaged at high contrast and 7 detected planets, GPIES places powerful constraints on the population of giant planets between 10-100 AU from their host star. We discuss updates since our original analysis of demographics from the first 300 GPIES stars, and compare our results to other demographics analyses. We also extend our demographics framework for giant planets to include RV data from the California Legacy Survey (Rosenthal et al. 2021, Fulton et al. 2021) to better constrain the turnover in planet occurrence rate near the snow line. This combined approach has started to map out a more complete demographics picture of giant planets from the edge of the host star out to 100 AU. Looking ahead, we discuss implications for future demographics surveys of giant planets, from Gaia DR4 to GPI2.

Survival of planetary atmospheres governs the habitability of terrestrial exoplanets. Over the last three decades, multiple Earth-sized planets have been confirmed within the habitable zones (HZs) of nearby stars, and exoplanet science is shifting from detection to characterization. Planets in the HZs of M dwarfs are prime targets because of frequent transits and relatively large planet-to-star cross-sectional area ratios. However, close-in exoplanets around M dwarfs are exposed to intense X-ray and extreme ultraviolet (XUV) radiation and frequent stellar flares, strongly enhancing atmospheric escape. Water vapor in the upper atmosphere is photodissociated, and the resulting hydrogen escapes readily. On planets with relatively strong gravity such as Venus, heavier oxygen atoms require non-thermal escape mechanisms. Ion escape driven by the interaction between the upper atmosphere and the stellar wind is expected to be the dominant non-thermal loss pathway from unmagnetized planets, and its rate governs the pace of planetary dehydration. The hot oxygen corona, composed of non-thermal oxygen atoms produced via dissociative recombination in the ionosphere, plays a crucial role in ion escape. On Venus-like planets, hot oxygen atoms remain gravitationally bound but populate high altitudes where they can be ionized and picked up by the stellar wind. However, its contribution under diverse stellar environments has remained poorly understood, as previous work has been constrained to solar system conditions and many models have neglected the corona or assumed static profiles.
This study investigates the effect of the hot oxygen corona on ion escape from Venus-like exoplanets under diverse stellar environments. A one-dimensional ionosphere–thermosphere model and a Monte Carlo hot oxygen corona model are developed and coupled with global magnetohydrodynamic simulations, enabling systematic exploration over a broad parameter space of stellar XUV fluxes and wind conditions.
Steady-state simulations demonstrate that the hot oxygen corona becomes a critical contributor to ion escape under overpressure conditions, where stellar wind dynamic pressure exceeds ionospheric thermal pressure. In this regime, O⁺ escape rates are significantly enhanced due to deep stellar wind penetration, efficient ionization of hot oxygen, and tailward acceleration. The distinct pressure-dependent responses observed at Venus and Mars are explained by differences in their pressure states. Transient flare simulations show that the hot oxygen corona enables stellar flares to enhance ion escape beyond steady-state levels, even for identical time-integrated XUV energy. This arises from a timescale gap between rapid ionospheric density increase via photoionization and slower thermospheric expansion. During this transient window, dissociative recombination efficiently produces hot oxygen transported to high altitudes before collisional thermalization suppresses the enhancement.
These results demonstrate that the hot oxygen corona plays a crucial role in controlling ion escape from Venus-like planets under the overpressure conditions, and that frequent stellar flares drive more efficient, corona-originated ion outflow than steady-state irradiation. For unmagnetized Venus-like exoplanets in the HZs of M dwarfs, the combined effects can significantly reduce atmospheric lifetime. The numerical framework developed here provides a predictive tool for assessing ion escape across diverse stellar environments.

The evolution of protoplanetary disks is key to understanding how planets form. On the other hand, the formation of planets is crucial to understanding how protoplanetary disks evolve. The two phenomena are interconnected, and observing the formation of planets in their evolving disks is essential for further developing our understanding of both processes.
Another ingredient that must be taken into account is the evolutionary pathways of the region where planets form.
In this contribution, I aim to present some interesting findings on the protoplanetary disk population around cool stars and solar-type stars within the Corona Australis (CrA) star-forming complex, one of the closest and most isolated molecular clouds. CrA belongs to a chain of clusters that show age gradients with distance from the galactic plane. I will provide suggestions regarding its formation history by examining the stellar and disk populations, the stellar multiplicity, and the interstellar absorption in the complex.  

Measuring the stellar obliquity of mutli-transiting planetary systems helps to distinguish whether whether a single planet's orbit was tilted or if the entire protoplanetary disk was misaligned. Here we present the stellar obliquity measurements of three multi-transiting systems at different ages (young, adolescent, mature). Combining our observations and dynamical analysis, we find the transiting planets in these three systems are aligned and coplanar. In conjunction with past observations, it is suggested that multi-transiting systems tend to be aligned and coplanar.

We study the accretion-related activity in Young Stellar Objects (YSOs) thanks to the release of the deepest stellar catalog of the Carina Nebula star-forming region (Tramuto et al., in subm. to ApJ), from a dedicated Dark Energy Camera (DECam) z-band campaign (PI: P. Hartigan; Hartigan et al., in subm. To ApJ).
We retrieved dense time-domain data of variable sources including YSOs in this rich stellar nursery, with unprecedented details and depth.
As a useful output for the scientific community that focuses on the early stage of stellar evolution, we will provide (Tramuto et al.) a catalog of ~1200 YSOs candidates with their associated period that we derived from the DECam Light Curves (LCs), using an algorithm we created adding a multi-metric ranking to the Lomb-Scargle Periodogram, to perform better against aliases.
Given this significant sample of YSOs LCs in Carina, we decided to statistically analyse their morphological behaviour adopting a ‘Symmetry vs Periodicity’ classification (Q vs M; Cody et al. 2014). This enabled us to provide information on whether each YSO appears to be bursting, dipping, or symmetric, as well as its periodicity features.
One main goal regards the physics behind these different types of time variability, and its relationship with the peculiar environment given by this active stellar nursery, with different surrounding conditions depending on the sub-cluster considered.
We therefore combined the optical LCs morphological analysis provided by this unprecedented DECam survey, with independent Near and Mid-IR data, given by J, H, K magnitudes from MYStIX (Feigelson et al. 2013), 3.6-8.0 $\mu m$ fluxes from Spitzer/IRAC (Teixeira et al. 2012), as well as the Chandra X-Ray Luminosities.
We thus analyse the correlation between LC morphology, IR markers of circumstellar disks, and X-Ray indications of ongoing accretion.

The characterization of young exoplanetary atmospheres represents one of the most exciting frontiers in modern astronomy, offering a unique window into the early stages of planetary evolution. As these planets are still in their formative years, their atmospheric composition, thermal profiles, and dynamical structures encapsulate the critical fingerprints of their birth and subsequent migration history. In this study, we present a high-resolution transmission spectroscopy of AU Mic b, a young(~22Myr) Neptune-sized planet orbiting a M dwarf, obtained using the InfraRed Doppler (IRD) spectrograph (0.97 – 1.73 μm) on the Subaru Telescope.
Our analysis focuses on searching for H2O and CH4, which are expected to exhibit strong absorption features given AU Mic b’s equilibrium temperature and the observed wavelengths. Recent JWST studies of young planets have reported approximately solar metallicity and relatively cloud/haze-free atmospheres (Thao et al. 2024 & Barat et al. 2025). Based on these results, we employed cross-correlation techniques, assuming a cloud/haze-free, H/He-dominated atmosphere in chemical equilibrium. While our injection-recovery tests confirmed that such signals could be successfully recovered, analysis of the actual data yielded no robust detection. This lack of a definitive signal allows us to place meaningful constraints on the atmospheric properties of AU Mic b. We interpret this non detection as a potential indication of a gray opacity source, such as high-altitude clouds or photochemical hazes, which effectively mask the underlying spectral lines.
Furthermore, we discuss these findings in the broader context of young planetary systems. By comparing AU Mic b with other young exoplanets of similar ages such as HIP 67522b or V 1298 Tau b, our results highlight a significant atmospheric diversity and suggest that even planets formed in similar environments may undergo divergent evolutionary paths depending on their host star.

We present near- to mid-infrared spectroscopy of the young (2 Myr), wide-orbit planetary mass companion SR 12 c, recently observed with JWST at unprecedented spectral resolution and sensitivity. With a mass of only ~11-15 Jupiter masses, and a projected separation of nearly 1000 au from its cool (K+M type) binary host, SR 12 c represents an important and uniquely accessible case study of a circumplanetary disk. It is one of only three such objects detected to date in ALMA continuum observations, alongside the PDS 70 system and the free-floating planet OTS 44.
Using JWST/MRS spectra at R~3000, we characterize the circumplanetary disk dust temperature and composition of SR 12 c, and discover the presence of multiple complex gas-phase hydrocarbon species, allowing us to trace their temperature, density, and distribution in the circumplanetary disk. SR 12 c is the planetary-mass object with the broadest observed wavelength coverage to date, spanning the ultraviolet through the submillimeter. We place its NIR-MIR spectra and derived atmospheric and disk properties in context with previous accretion studies, and provide a direct comparison of its disk gas and dust properties with the nature of disks surrounding more massive stars.
The combination of high spectral resolution and broad wavelength coverage also makes SR 12 c an excellent test case for detailed thermochemical modeling of its disk, an approach until now only applied to stellar systems. This young circumplanetary disk represents a critical addition to the small but growing population of disks identified around the coolest substellar objects, and holds important ramifications for our understanding of planetary atmosphere evolution as well as the formation of potential satellites. Our results indicate that the complex, carbon-rich chemistry observed around the lowest-mass stars and brown dwarfs can extend in a self-similar manner to even the smallest disks surrounding young giant planets.

Many fundamental questions of brown dwarf formation remain unanswered. For example, how did they form? What are their predominant formation channels? What proportion of them form like stars and what proportion form like planets? To inform this question we examine accretion rates of stellar and substellar objects, as their accretion rates are a useful probe into formation pathways and disk evolution. Stellar accretion rates tend to scale linearly with the mass of the star, albeit with large variance. This trend becomes less robust at substellar masses.  We present the Simulation Tool for Accretion Rates and (Sub)stellar POpulation Properties (STARSPOP); a Monte Carlo simulation tool that models possible sources of observational uncertainty and physical effects (e.g. age, variability) that cause accretion rate variance. We present our efforts to compare simulation results to  the Comprehensive Archive of Substellar and Planetary Accretion Rates catalog (CASPAR, Betti et. al 2023), a uniformly re-derived catalog of all observed accreting substellar objects. STARSPOP successfully replicates the properties of the observed stellar distribution, but cannot fully reproduce observations of substellar objects. We investigate possible reasons for the increased residual spread in the substellar regime, such as modeling a separate population of objects that formed via disk fragmentation. Modeling accretion rate variance can grant us a thorough understanding of substellar accretion rates and can give us insight into their formation and accretion physics. 

M dwarfs dominate the stellar population of the Galaxy and are prime targets for exoplanet research programmes. They are also key laboratories to study dynamo-generated magnetic fields and the subsequent phenomena — starspots, flares, high-energy radiation, and stellar winds — which influence the evolution of stellar angular momentum and planetary environments.
Despite their importance, the long-term evolution of M dwarf surface magnetic fields, as well as the possible existence of magnetic cycles, remain poorly constrained. The ESA PLATO mission will provide long-duration, high-precision photometry, offering an unparalleled opportunity to study stellar variability over several years. To fully exploit this potential, it is essential to combine PLATO measurements with spectropolarimetric monitoring, which enables direct measurements of surface magnetic fields (field modulus, large-scale topology) and chromospheric activity.
We have therefore initiated a long-term spectropolarimetric campaign using the SPIRou near-infrared instrument at CFHT, targeting early M dwarfs in the PLATO South Field. The sample was selected based on activity and rotation, and includes young fast rotators as well as young intermediate rotators (≈1 to 17-day periods), including several members of young associations such as AB Doradus. These targets are particularly relevant for studying planetary systems, their youth and magnetic activity make them ideal for planet environmental characterization, and even in the absence of detected planets, they remain representative of the typical magnetic environments experienced by planets orbiting young M dwarfs.
In this contribution, we present the target selection strategy and first results, including Zeeman-Doppler Imaging (ZDI) maps. Our findings provide new constraints on the diversity and evolution of large-scale magnetic fields in low-mass stars, establishing a physically grounded framework to interpret PLATO photometric variability in terms of underlying magnetic activity. Finally, these magnetic maps will serve as essential inputs for stellar wind models, enabling estimates of atmospheric loss for planets orbiting young M dwarfs.

The characterization of the magnetospheres of pre-main sequence stars with exoplanets and low-mass companions is crucial for understanding how they interact with their natal environments, including their impact on the evolution of companions and protoplanetary disks. We used spectropolarimetric observations obtained with ESO HARPSpol to study magnetic fields and magnetospheres of nearly face-on PMS stars, some of them known to host planets and low-mass companions. With these observations, we were able for the first time to create snapshots of the magnetospheres of four PMS stars using dynamical spectra of their emission hydrogen lines. For one of these PMS stars, we carried out the first 2D magnetohydrodynamical simulations of a magnetosphere, using the NIRVANA MHD code.