Leonardo Testi

Water and methanol are the fundamental constituents of interstellar and cometary ices; understanding their abundances in disks is therefore of high importance to reveal how this ice reservoir evolves across the timeline of star and planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 5 line emission observations of water and methanol in the warm Herbig disks of HD 100546 and IRS 48. While the IRS 48 disk is methanol-rich, water vapor is not detected, implying a high methanol-to-water column density ratio of >0.2, possibly reflecting a distinct ice composition. Methanol and water are both detected in the HD 100546 disk, leading to a CH ₃ OH/H ₂ O ratio of ∼0.02, consistent with the median of the cometary distribution and with the lower edge of the distribution of young stellar objects (YSOs). We suggest that the gas-phase methanol-to-water ratio in the HD 100546 disk directly reveals the ice reservoir subsequently sublimated in the warm disk stage. Moreover, we report a methyl formate-to-methanol ratio in the IRS 48 disk of ∼0.2, consistent with the upper edge of the distribution of YSOs. The methyl formate-to-methanol ratio in the HD 100546 disk is ∼2, much higher than in younger and older sources, possibly reflecting a chemical enhancement of gas-phase methyl formate. We additionally constrain non-LTE conditions, optical depths, and emitting regions of the methanol lines in both disks. These results offer a new opportunity to probe the chemical trail of molecular complexity in the intermediate-disk stage, bridging early and late phases of the star and planet formation history.

Context . Observing the earliest stages of high-mass star formation in the mid-infrared (mid-IR) is challenging because the extinction is high and the resolution limited. Millimeter vibrationally and torsionally excited transitions of several molecules have been proposed as indirect probes of local mid-IR radiation fields around young stellar objects (YSOs). Aims . We investigate the excitation and spatial distribution of torsionally excited methanol (CH ₃ OH) in 12 high-mass star-forming clumps in different evolutionary stages, assessing their potential as tracers of the mid-IR luminosity of embedded protostars. Methods . We analyzed rotational transitions of methanol within the same torsionally excited states v _t ≥1 in the Atacama Large Millimeter/submillimeter Array (ALMA) 890 µm observations and compared them with Spitzer 24 µm data by plotting line luminosities normalized by methanol abundance against mid-IR luminosities. Results . The torsionally excited methanol emission is generally compact and systematically coincident with ALMA dust continuum peaks and 24 µm emission, even in faint sources. The only clump without an IR counterpart also shows no v _t ≥1 emission, supporting radiative pumping as the dominant excitation mechanism. We found a promising power-law trend between v _t ≥1 methanol lines and 24 µm luminosities, largely independent of the methanol abundance. Conclusions . CH ₃ OH v _t ≥1 transitions appear to be promising tracers of local mid-IR radiation fields of embedded protostars, providing core-scale information even in highly extincted regions. As a pilot study, our results suggest that extending our study to a larger statistical sample is crucial for testing and improving this method.

Context. Most stars form in massive stellar clusters, where intense far-ultraviolet (FUV) radiation from OB stars can accelerate the dispersal of protoplanetary disks through external photoevaporation. Quantifying the impact of this process on disk evolution remains challenging, particularly in distant and crowded star-forming regions. Aims. We investigate the low-mass stellar population in the highly irradiated center of Trumpler 14 and examine how the local FUV radiation field influences circumstellar disk evolution. Methods. We extracted stellar spectra from VLT/MUSE observations using an enhanced background-optimized extraction method, carefully corrected for instrumental response as a function of wavelength and finally derived the stellar parameters with the SAPSAL deep-learning framework. We combined these results with a probabilistic estimate of the local FUV field and near-infrared photometry to identify disk-bearing stars. Results. We identify 310 bona fide cluster members with an age of 0.66 ^+0.73 _−0.35 Myr and local radiation fields spanning log(FUV)≃4.2 − 6.0 G ₀ . Conclusions. The fraction of stars exhibiting near-infrared excess decreases from 30% at the lowest FUV fluxes to under 5% at log(FUV)≳5.6 G ₀ , while no significant correlation is found between our simplified estimate of the optical veiling and the local FUV field. The pronounced decline in the disk fraction with ambient FUV flux provides strong evidence for external photoevaporation rapidly dispersing circumstellar disks in the core of Trumpler 14. Our results confirm previous disk dispersal estimates and extend to higher values of the FUV field strength.

The mechanism driving the evolution and dispersal of protoplanetary discs has a substantial impact on the theories of planet formation. To date, neither the viscous paradigm nor the Magneto-Hydrodynamic (MHD) wind-driven framework have been ruled out by the observations. The statistical richness of the observed samples provides a unique opportunity to test evolutionary models through population synthesis. However, comparisons between models and observations are normally carried out by eye, and a more statistically rigorous approach has not yet been implemented. We present DEMOS , a Bayesian inference tool that aims to infer the model parameters and initial conditions that best reproduce the full distribution of global properties of disc populations. This framework relies on a comparison between observations and synthetic populations generated with the 1D disc population-synthesis code Diskpop . We tested the tool with both the MHD wind model and the viscous framework with internal photoevaporation. Applying DEMOS to synthetic populations, we find that, for both models, it accurately recovers the model parameters of disc populations and their associated uncertainties, including cases in which initial conditions are correlated with the stellar mass. In the optimal scenario in which disc masses, accretion rates and disc sizes are available, the tool can also constrain the angular-momentum transport parameter. We show that, although parameter estimates are the most precise with samples of ∼100 discs, the tool also yields meaningful constraints for smaller populations of 10–30 discs. We further find that the predictions obtained with DEMOS closely align with those found by previous works when applied to the same datasets. We anticipate that DEMOS will be a valuable tool to infer the initial conditions of observed disc populations, to design observational programmes, and to assess which evolutionary model best reproduces the data. This statistical framework can be easily extended to test more evolutionary models, such as late-infall or external photoevaporation models.

Context . The distribution of bio-essential elements is key to assessing the chemical ‘fertility’ for life in a galactic context. Among these, phosphorus plays a central role in biomolecules, but it is relatively scarce and difficult to measure in stellar spectra. Aims . We aim to characterise phosphorus abundances in nearby FGK stars and quantify how P co-varies with other bio-related elements in different Galactic disk populations. Methods . We analysed phosphorus abundances for 233 FGK stars in the solar neighbourhood from the Hypatia Catalog. We studied [P/Fe] as a function of [Fe/H] and other elemental abundances, separating thin- and thick-disk stars. We used non-parametric tests and bootstrap resampling to derive median trends, confidence intervals, correlation coefficients, and residual correlations at fixed [Fe/H]. We also investigated molar ratios involving P relevant to planetary mineralogy. Results . We find a [P/Fe]–[Fe/H] trend broadly similar to that of α elements, supporting a dominant origin in core-collapse supernovae, with some deviations that suggest additional nucleosynthetic channels. Phosphorus shows strong positive correlations with several CHNOPS, α , and Fe-peak elements, especially in the thin disk, where stars with higher phosphorus abundances are enriched in multiple bio-essential and rock-forming species. These co-enrichment patterns remain significant in residual analyses at fixed [Fe/H], indicating that they are not a trivial by-product of global metallicity. Thin-disk stars also exhibit higher abundances than thick-disk stars for many elements. The molar P/Mg and P/Si ratios of the Sun are representative of the local stellar population, whereas the relatively elevated solar P/O may have favoured phosphorus bioavailability on Earth. Conclusions . Our study provides a systematic and statistically robust view of how P co-varies with other CHNOPS and α elements in the solar neighbourhood. The results reveal a genuine multi-element co-enrichment pattern beyond metallicity effects and support the use of phosphorus as a tracer of the chemical fertility of galactic environments.

Context . Orion is the closest region hosting active star formation and young OBA stars. Accurately determining the far-ultraviolet (FUV) flux at its stellar population is essential to connect stellar and protoplanetary disc properties to the environment. Aims . We (1) accurately estimated the FUV flux and its distribution at a numerous stellar population of Orion by statistically accounting for the uncertainty in parallax measurements, and (2) investigated the relation between stellar accretion and external FUV radiation field by comparing observations and disc evolution models. Methods . We selected a large stellar population in Orion (within a 6° radius of the Orion Nebula Cluster core), assigned sub-cluster memberships, and used the two-dimensional sub-cluster geometry to infer three-dimensional separations from OBA stars and compute the FUV flux (and its uncertainty) at each stellar position. We studied the accretion luminosities ( L _acc ) inferred from H _α emission in Gaia XP spectra of Orion sources and determined their detection fraction as a function of age and FUV flux. We compared the results with population synthesis models of viscous discs experiencing external photoevaporation. Results . We provided a publicly available table of FUV fluxes at ~8600 stars in Orion. Most of this stellar population is weakly FUV irradiated, 10 ⁴ G ₀ . Gaia -based L _acc decreases with age, and H _α detection fraction declines more rapidly in regions with strong FUV fluxes (≳10 ² G ₀ ) than in regions exposed to weaker FUV fluxes (≲10 ² G ₀ ), broadly consistent with the model. This result may suggest that external photoevaporation efficiently depletes strongly FUV irradiated accretion discs, but it is not sufficient to reliably confirm this conclusion. Conclusions . The tools we provided for accurately computing FUV fluxes at the Orion stellar population will be essential for targeting sources in future observations aimed at assessing the role of external photoevaporation on protoplanetary disc. Our study highlights the need for additional measurements of stellar and disc properties across the Orion population, covering the FUV flux range 1–10 ⁵ G ₀ .

Giant planets form in protoplanetary discs, where the coupled dynamical and chemical evolution of gas and solids determines the composition of the material they accrete. We investigate how planet formation and migration in evolving discs shape the primordial elemental makeup of giant planet atmospheres. Our aim is to establish a multi-element framework linking atmospheric compositions to the formation pathways of planets and the time-dependent chemical properties of their natal discs. We coupled one-dimensional models of viscously evolving discs – incorporating radial dust drift and a comprehensive treatment of volatile chemistry – with N -body simulations of planetesimals interacting with a growing and migrating giant planet. Four chemical scenarios (inheritance and reset under low and high ionisation) and three representative grain sizes (0.1, 20, and 100 μm) were explored. The coupled outputs were post-processed to track the accretion of carbon, oxygen, nitrogen, and sulphur, and to derive atmospheric elemental ratios normalised to stellar values (* denotes stellar normalisation). We identified three atmospheric classes corresponding to distinct accretion regimes: gas-dominated (GD), characterised by N/O* > C/O* > C/N* and unconstrained or substellar S/N* (near-stellar C/S*); planetesimal-dominated (PD), showing N/O* < C/O* < C/N*, S/N* ≥ C/N*, and C/S* ≤ C/O*; and drift-enhanced (DE), exhibiting N/O* < C/O* < C/N* and markedly super-stellar volatile-to-refractory ratios. We see that N/O*, C/N*, and S/N* vary systematically with migration extent, although degeneracies arise for planets forming beyond the CO and N ₂ snow lines; in addition, C/O* remains largely insensitive. Metallicity alone does not uniquely trace the balance between solid and gas accretion in drift-dominated regimes. Variations in the disc’s chemical state and dust size imprint distinctive volatile-ratio patterns across the atmospheric classes, providing complementary constraints on disc properties. This multi-element framework establishes predictive trends to guide the interpretation of atmospheric spectra from current and forthcoming facilities, such as JWST and Ariel, in the context of giant planet formation.

Context. The evolution of protoplanetary discs is intertwined with the process of planet formation, growth and migration. Studies of nearby star-forming regions of different ages and properties provide the information needed to understand the processes governing their evolution. Aims. This paper presents the results of a spectroscopic study of the stellar and accretion properties of a large sample of 127 stars with protoplanetary discs in the Upper Scorpius region, a relatively old (5–10 Myr), nearby (∼145 pc) star-forming region, with disc dust masses inferred from ALMA continuum measurements. Methods. We derived the accretion luminosity from the excess UV continuum emission with respect to the photospheric and chromospheric emission self-consistently with the stellar spectral types, extinction, and luminosity, using the FitteR for Accretion ProPErties of T Tauri stars (FRAPPE) code. We applied a new method to evaluate upper limits on the accretion luminosity. In ∼50% of cases, we could only evaluate upper limits on the accretion luminosity, either because the signal-to-noise ratio of the data was insufficient or because the measured value of the accretion luminosity was below the statistical estimate of the emission due to chromospheric activity. Results. The mass accretion rate shows a weak correlation with stellar mass, while we find no correlation with disc properties such as dust mass or gaseous disc radius. The dispersion is larger than that found in younger star-forming regions such as Lupus and Chamaeleon I, and suggests fading of the correlations with age. We find no evidence that the observed dispersion can be explained by membership in Upper Scorpius sub-groups, or by the properties of known binary systems or transition discs. Conclusions. The lack of correlation and the large dispersion of accretion rates challenge the current expectations of evolutionary models. The observed properties point to a decoupling of the inner and outer discs by the age of Upper Scorpius and a fading of the relations observed in younger star-forming regions, which calls for further development of current theoretical frameworks to be explained.

Aims . To advance our understanding of dust properties in class 0/I young stellar objects, it is essential to resolve and characterize their structures at multiple wavelengths and investigate how both grain growth and environmental factors shape their spectral properties. Methods . We present 0.″5 angular resolution ALMA observations of the GSS 30 complex at 1.2–3.0 mm, collected as part of the FAUST large programme, with a linear resolution of 69 au. We analysed the dust continuum emission and performed model fitting to constrain the dust mass and the disk structure. Results . For IRS3, the spectral index increases radially from 2.0 at the centre to 2.5 at the disk edge. In contrast, it decreases from 2.0 to as low as 1.6–1.8 along the outflow direction. An asymmetric distribution shows α as low as 1.6 to the northeastern blueshifted lobe, possibly due to cold outer envelope dust obscuring warmer inner regions. Spectral energy distribution fitting indicates maximum dust grain sizes of tens of microns and a dust mass of 650–1510 M _⊕ . IRS1 is connected with an extended structure to the north-east. It may be an outflow–disk complex or a trailing structure associated with a circumbinary disk, although we cannot rule out the possibility that it could also be a gas streamer accreting onto IRS1. At the centre of IRS1, the spectral index is < 0.8, which is consistent with marginally optically thick free-free emission. IRS2 exhibits brightness variations over 420 seconds of observation, with a multi-epoch comparison suggesting a flare lasting tens of minutes, indicating magnetic activity in the central star. Conclusions . This study presents a detailed millimetre multi-wavelength analysis of the GSS 30 IRS3 and IRS1 systems, highlighting the crucial role of environmental factors – specifically dust obscuration and the connecting streamer structures – in shaping the observed morphology of these early-stage disks. We also find that the IRS2 exhibits millimetre variability, which may originate from magnetic flares at the surface of the protostar.

In recent years, extreme adaptive optics have enabled high-resolution, high-contrast scattered-light observations of protoplanetary disks. Interpreting these observations requires an understanding of the scattering surface, which is shaped by the distribution of small dust grains and determines how the disks appear in scattered light. We aim to exploit measurements of the scattering surface height to directly constrain the masses of small dust grains in disks. Starting from radiative transfer principles, we developed a semi-analytical model of the stellar radiation path and its interaction with the disk, deriving the height of the scattering surface as a function of disk parameters, such as the mass, temperature, and opacity. We validated our predictions against the radiative transfer code . Using measured scattering heights, we inferred the mass of the dust in small grains and the particle size distribution for a sample of ten disks. MCFOST We confirmed prior results indicating that the scattering surface coincides with the surface where the integrated optical depth along the stellar path is on the order of unity. The thermal structure of the disk significantly affects the surface height, while dust settling and anisotropic scattering have minor effects. Applying our model to observations, we measured small dust mass fractions on the order of 10^-3 globally. Using models of the dust opacity, we show this is typical for modest amounts of grain growth (a_ max ≳ 0.1mm) and power-law indices of the grain size distribution ∼ 3-3.5, as commonly found in grain growth models. Scattering height measurements, together with the disk’s thermal structure, help set constraints on the small dust content of protoplanetary disks.