arXiv subjects

Carlo F. Manara

Publications and source records attributed to Carlo F. Manara.

At least 19 recordsLinked to original sources

arXiv2026

The future of high-resolution UV spectroscopy: Science with a UV Échelle spectrograph on the Habitable Worlds Observatory, or a dedicated mission

High-resolution UV spectroscopy serves a diversity of science cases, from small bodies to planets, stars, and galaxies, but is currently limited to the Hubble Space Telescope and bright targets. Major advances require increasing sensitivity by at least one order of magnitude. Here we present the UV science cases for PEGASUS (Planets, Earths, Galaxies, And Stars UV Spectrograph), a UV Échelle high-resolution spectrograph concept, with $R = λ/δλ\sim 100\,000$ (full range 10 000-140 000) and covering 90--400 nm, with a foreseen extension to at least 800 nm. PEGASUS is ideally suited for the Habitable Worlds Observatory (HWO), enabling transformative science across the UV/optical wavelength ranges. PEGASUS will be unique in high sensitivity (effective area) and high spectral resolution -- an uncharted territory -- as well as robustness, thanks to the simplicity of its design. Its UV science cases include: I) Formation and evolution of planets and their habitability: properties of exoplanets and atmospheres, protoplanetary disks, Solar System bodies; II) Stellar lives and deaths at their extremes: the first stars and the origin of the elements, compact and massive stars, Supernovae; III) Gas and metals in the baryon cycle of galaxies: the interstellar, circumgalactic, and intergalactic medium and their roles in galaxy growth. These are essential for the Astro Decadal 2020 Survey, Voyage 2050, and HWO. While this paper focuses on high-impact science enabled by UV high-resolution spectroscopy, PEGASUS will extend into the optical regime and lower spectral resolution, making it a multi-purpose, widely used, workhorse spectrograph for HWO.

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arXiv2026

Dust Substructures and Line Perturbations driven by a Forming Planet in J16120

Hints of planet formation have been independently reported within the gap of the disc around 2MASS J16120668-301027 from millimetre continuum, infrared, and H-alpha observations. In this work, we present new evidence for ongoing planet formation based on Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations, detecting 0.87 mm dust continuum emission together with 12CO (J=3-2) and 13CO (J=3-2) line emission. Visibility modelling of the continuum data reveals an inner disc and two dust rings peaking at 23 and 75 au. The continuum morphology is better reproduced by an eccentric disc model (e approximately 0.1) than by an axisymmetric disc. We further investigate the gas kinematics through modelling of the 12CO channel maps. The residual line-width map shows a localised increase in velocity dispersion at the position of a previously reported circumplanetary disc candidate (deprojected radius approximately 32 au, position angle approximately 170 degrees) and along its orbit. This signal is spatially coincident with kink-like features and a transition from sub-Keplerian to super-Keplerian velocities. In addition, the velocity residual map exhibits an arc-like structure extending outward from the planet candidate, while the gas kinematics, despite substantial uncertainties, is consistent with inflow towards the candidate's orbital radius. The observed increase in velocity dispersion agrees with predictions from planet-disc interaction simulations, which produce enhanced turbulence both at the planet location and along its orbital path. Taken together, the continuum morphology and gas kinematic signatures provide compelling new evidence for ongoing planet formation within the disc gap.

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arXiv2026

A closer look at the WISPIT 2 host star. Evidence for a spectroscopic binary

While hundreds of protoplanetary discs have been studied in great detail, the detection of protoplanets still embedded in their native discs remains rare. WISPIT 2 is only the second laboratory allowing for direct study of planet formation while in progress. The recently discovered system hosts two giant protoplanets in a multi-ringed disc. Here, we aim at characterising the WISPIT 2 host star spectroscopically to determine its stellar properties, accretion rate, and inner disc diagnostics, providing a more complete picture of the system. We present optical and near-infrared spectroscopic observations obtained with the ESO VLT/X-Shooter and 2.2 m/FEROS instruments. We model the stellar spectrum to determine the spectral type and effective temperature, analyse the emission lines to estimate the accretion rate, and search for evidence of a close stellar companion using radial velocity measurements. Our observations reveal that WISPIT 2 is a spectroscopic binary. The binary has a period of $4.8\pm 0.1$ days, which corresponds to a semi-major axis of $0.072$ au or $15.54 R_\odot$, assuming co-planarity with the disc and a circular orbit. The binary system consists of a $\sim 0.97 M_{\odot}$ primary of spectral type K3 ($T_{\rm eff} \sim 4700K$), and a $\sim 0.33M_\odot$ secondary (mass ratio $\sim$0.34). We detect weak H$α$ emission, implying an accretion rate of $\sim 2 \times 10^{-11}\,M_{\odot}\,\mathrm{yr}^{-1}$. However, this value is below the chromospheric level, suggesting little to no ongoing accretion onto the young stars. This discovery makes the WISPIT 2 disc the first circumbinary system with directly imaged protoplanets, establishing this system as a unique benchmark for studying planet formation and disc evolution around binary stars.

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arXiv2026

Characterization of the MUSE NFM PSF as a function of atmospheric conditions: TipTop calibration

The Multi Unit Spectroscopic Explorer (MUSE) achieves exceptional spatial resolution in narrow-field mode (NFM) thanks to the GALACSI adaptive optics (AO) system. However, limitations in point spread function (PSF) characterization still hinder the full exploitation of its capabilities. In particular, the current exposure time calculator (ETC) lacks an accurate PSF model, preventing users from reliably predicting the signal-to-noise ratio of NFM observations during proposal preparation. To address this limitation, we analyzed a large set of archival standard-star observations to quantify how NFM PSF properties vary with observing conditions, including airmass, seeing, coherence time, wind speed, and wavelength. We then used this reference dataset to calibrate TipTop, a fast AO PSF simulation tool that will be integrated into the next release of the MUSE NFM ETC. Our results demonstrate that calibration against real on-sky data is essential for accurate PSF modeling. In particular, we find that reproducing realistic PSFs requires both an additional static aberration term and an airmass-dependent tip-tilt jitter component. The calibration performs well at wavelengths longer than 7000 A, while additional corrections are still required at shorter wavelengths, likely due to unmodeled chromatic aberrations. Once implemented in the ETC, this tool will provide condition-dependent NFM PSF predictions and more reliable signal-to-noise estimates.

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arXiv2026

Exploring the radial velocity variations of RY Lup with VLT/ESPRESSO: Binary versus spot hypotheses

Stellar multiplicity is a possible cause for creating protoplanetary disc substructures, as tidal forces from a close-in spectroscopic companion can carve out gaps and shape disc architecture. However, in young, active systems, the radial velocity (RV) signatures are often complicated by stellar activity. We investigate RY Lup, a classical T Tauri star hosting a disc with a ~60 au cavity, where studies with Gaia astrometry and VLT/SPHERE imaging hinted at an unseen companion. Using high-resolution VLT/ESPRESSO spectra and the least-squares deconvolution (LSD) technique, we analyse RV variations over 327 days. We detect significant line profile variations with a periodic signal of ~3.75 days, aligning with prior photometric estimates. The variations are compatible with a close-in binary system at ~0.04 au and a mass ratio of q ~ 0.6. Combined analysis of RV data and ALMA dynamical mass estimates, using 13CO and 18CO, reveals a highly misaligned system. The nearly face-on binary i ~ 13 deg is misaligned to both the inner and outer discs i ~ 50 deg and ~70 deg, respectively. The derived orbital separation is compatible with the inner disc size, with the inner rim at a = 0.12 au, measured from VLTI/GRAVITY, which suggests a highly warped disc structure. Nonetheless, the short orbital period conflicts with the derived eccentricity (e ~ 0.23). To explore alternative explanations, we assess the impact of stellar spots on RV signals. While the LSD deformations can be modelled by different cool spot configurations, a 15% dispersion in retrieved v sin i values -- coupled with the lack of a significant periodic signal -- suggests that spots alone cannot explain the observed variability. As neither hypothesis is ruled out, we recommend future combined RV and interferometric monitoring to clarify the nature of the spectroscopic variability.

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arXiv2026

From Young to Older Disks: JWST/MIRI Evidence for Fading Molecular Emission and Hints for Elevated C/O in Upper Scorpius

We present JWST/MIRI spectroscopy of 14 disks in the older (~5-10 Myr) Upper Scorpius (USco) association and use slab of gas in local thermal equilibrium to infer basic gas properties. We find that half of these disks are molecular rich, with detections of H$_2$O, CO$_2$, HCN, C$_2$H$_2$, and H$_2$, while the other half are molecular poor, showing no molecular emission other than H$_2$. We further combine this sample with 10 other USco disks from the AGE-PRO program and compare the combined older sample to young (~1-3 Myr) JDISCS Cycle~1 systems, which are analyzed in a similar manner. We find that USco disks have lower detection rates of major molecular species but a significantly higher detection rate of rarer C-bearing molecules such as C$_4$H$_2$. At a given accretion luminosity, molecular line luminosities are systematically lower in USco than in young disks, and the scaling relations with accretion luminosity differ between the two populations. Moreover, we find that about half of the older disks, preferentially the millimeter faint, and likely more compact disks, have observable mass ratios of C- to O-bearing molecules that are higher than the maximum values in the young sample. These results point to reduced inner-disk molecular gas masses, cooler emitting layers, and higher inner gas C/O ratios in older disks, the latter being consistent with pebble drift. Taken together, our findings provide evidence for chemical evolution of inner disk gas from young to older systems, with important implications for the accretion of primordial planetary atmospheres.

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arXiv2026

The Ultraviolet View of Star and Planet Formation: Disks, Accretion, and Outflows with the Hubble Space Telescope into the 2030s

The spatial distribution and lifetime of molecular gas in the inner regions of young circumstellar disks are key to understanding the formation of planetary systems. Gas-rich disks are observed to disperse in the first ~10 Myr, and recent observational and theoretical evidence suggests that circumstellar disks winds may dominate the removal of angular momentum from the disk, allowing it to dissipate through accretion onto the central star and through low-velocity (<~30 km/s) outflows. The Hubble Space Telescope has revolutionized our understanding of the disks, accretion, and outflow processes that drive the evolution of planet-forming disks and is poised to answer the key questions in the field in the coming decade. We describe how HST's ultraviolet capabilities can address these questions and identify key goals and high-priority observations for HST into the 2030s.

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arXiv2026

The 12CO Gas Structures of Protoplanetary Disks in the Upper Scorpius Region

We present measurements of key protoplanetary disk properties inferred from parametric models of ALMA 12CO spectral line visibilities. We derive gas-disk radii, integrated fluxes, optically thick emission layers, and brightness temperature profiles for the disk population of the old (4 - 14 Myr) Upper Scorpius star-forming region. We measure CO emission sizes for 37 disks with bright CO J=3-2 emission (S/N > 10 on the integrated flux; out of the 83 disks with CO detections), finding that the median radius containing 90% of the flux is ~84 au, with radii spanning from 23 up to 243 au. We report a correlation between the 12CO brightness temperatures and stellar luminosities, with a Pearson coefficient of 0.6, and we use it to prove that the 12CO optically thick emission layer primarily emanates from a region below the super-heated dust, which is optically thin to the stellar irradiation. Moreover, we derive 33 CO emission surface height profiles, finding a median aspect ratio ~ 0.16 in a range from ~0.01 up to ~0.45 over the sample. Finally, we comment on the multiple systems in our sample, of which only some were already known. These results re-affirm how it is possible to derive bulk disk properties by modeling moderate angular resolution ALMA visibilities.

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arXiv2026

Compact CO emission and no evidence of radial drift. ALMA observations of the faintest planet-forming disks in Lupus

A large fraction of planet-forming disks observed with ALMA show faint CO emission, often interpreted as strong CO depletion. However, faint emission may also arise from spatially unresolved disks, whose sizes are overestimated, making them appear intrinsically faint. The limited sensitivity of previous observations has prevented testing this scenario, hindering our understanding of disk evolution and planet formation. We present new ALMA Band 7 observations of 12CO (J=3-2) and 13CO (J=3-2) in 17 of the faintest disks in Lupus, aiming to assess whether compact disk structure can explain their weak CO emission. The data reach an angular resolution of 0.25arcsec (about 20 au at 160 pc) and are an order of magnitude deeper than archival observations. We apply line stacking to enhance sensitivity and compare the derived CO luminosities with physical-chemical models of compact and extended disks, also estimating gas and dust sizes. We detect both isotopologues in 10 disks, only 12CO in 4, and neither in 3. Several disks are consistent with being intrinsically compact and optically thick in both lines, providing an alternative to the CO depletion scenario. The inferred gas radii (Rco less than 40 au) support this interpretation and suggest that a significant fraction of disks may be born compact, in line with recent Class 0/I results. Gas-to-dust size ratios show no clear evidence for dust evolution, indicating these disks are not drift-dominated.

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arXiv2026

Astrometric view of companions in the inner dust cavities of protoplanetary disks

Protoplanetary disks with inner dust cavities (often referred to as "transition disks") are potential signposts of planet formation. We use Gaia astrometry to search for planetary and stellar companions in a sample of 98 transition disks, assessing the occurrence rate of such companions and their potential influence on cavity formation. For the 98 Young Stellar Objects (YSOs), we compute Gaia proper motion anomalies which, together with the RUWE, identify companions with mass ratios $q \gtrsim 0.01$ at $\sim$0.1-30 au. We assess the impact of disk gravity, accretion, disk-scattered light, dippers, starspots, jets, and outflows on the measured proper motion anomalies, concluding that astrometric techniques such as the one of this work can be robustly applied to YSOs. Significant proper motion anomalies are found in 31 transition disks (32% of the sample), indicative of companions. We recover 85% of known companions within our sensitivity range. We model the semi-major axis and mass required for a companion to reproduce the observed astrometric signals. Most inferred companions have $M > 30$ M$\rm{_{J}}$, placing many within or near the stellar mass regime. Seven sources host companions compatible with a planetary mass ($M < 13$ M$\rm{_{J}}$, HD 100453, J04343128+1722201, J16102955-3922144, MHO6, MP Mus, PDS 70, and Sz 76). For the non-detections, we provide the companion masses and semi-major axes that can be excluded in future searches. About half (53%) of detected companions cannot be reconciled with having carved the observed dust cavities. We find that transition disks host as many companions within our sensitivity range as do randomly sampled groups of YSOs and main-sequence stars. If dust cavities are shaped by companions, such companions must reside at larger orbital separations than those of the companions detected here, and we predict them to be of planetary mass. [abridged]

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arXiv2026

Benchmarking pre-main sequence stellar evolutionary tracks using disk-based dynamical stellar masses

Stellar masses are a fundamental property to understand models of pre-main sequence evolution, but their values derived from Hertzsprung-Russell (HR) diagrams are strongly model dependent. We benchmark pre-main sequence stellar evolutionary tracks using stellar masses dynamically estimated by fitting a parametric model to ALMA observations of the $^{12}$CO $(J=3-2)$ line transition emitted by the disks orbiting 20 sources in the old ($4-14$ Myr) Upper Scorpius star forming region. We derive stellar masses from HR diagram fitting for ten different stellar evolutionary models, which we then compare with their stellar dynamical masses for comparison in the stellar mass range $0.1-1.3 \> M_\odot$. Models with a moderate-to-low fraction of cold stellar spots ($f=17\%$) most accurately reproduce the dynamical stellar masses ($100\%$ of the targets agree within $\pm1σ$). While a higher spot coverage ($f=34\%$) provides similar stellar mass predictions similar to magnetic equipartition models, larger fractions ($f\geq51\%$) significantly disagree with dynamical masses. Magnetic equipartition models overestimate stellar masses up to a factor $\sim20\%$, whereas non-magnetic models underestimate them up to $\sim12\%$. For some models, there is evidence that the stellar mass discrepancies are anticorrelated with dynamical stellar masses. When stellar dynamical mass priors are considered in HR diagram fitting, the median age of a single source can change up to $\sim25\%$, while the median ages inferred across different tracks become consistent, with the age scatter decreasing by $\gtrsim77\%$. These results provide strong empirical constraints for testing and developing evolutionary models of pre-main sequence stars.

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arXiv2025

Characterizing the Low-Mass Pre-Main-Sequence Population in the Low-Metallicity Star-Forming Region Dolidze 25 Using VLT-MUSE

The metallicity of the star-forming environment is a fundamental parameter shaping the evolution of protoplanetary disks and the formation of planetary systems, yet its influence remains poorly constrained. We present a spectroscopic study of low-mass pre-main sequence (PMS) stars ($M < 1 \, M_\odot$) in the exceptionally metal-poor cluster Dolidze~25 ($Z \approx 0.2 \, Z_\odot$), using VLT/MUSE observations to probe accretion processes and disk evolution in a subsolar environment. We identify 132 cluster members using a combination of \textit{Gaia} astrometry and spectroscopic youth indicators, including lithium absorption and Balmer emission. The stellar parameters are derived using low-metallicity BT-Settl models yielding effective temperatures, extinctions, luminosities enabling robust estimates of stellar masses and ages. Mass accretion rates ($\dot{M}_\mathrm{acc}$) derived from H$α$ emission span $10^{-10}$--$10^{-8} \, M_\odot\,\mathrm{yr}^{-1}$ with a median value of $8 \times 10^{-10}\,M_\odot\,\mathrm{yr}^{-1}$. These rates are comparable to those in solar-metallicity regions of similar age, such as Lupus and Orion, indicating minimal metallicity dependence in accretion processes. Our analysis shows that using solar-metallicity templates to fit low-metallicity stars leads to systematic overestimations of $T_\mathrm{eff}$ (by approximately $300\,\mathrm{K}$) and $A_V$ (by around $0.5\,\mathrm{mag}$), underscoring the importance of employing metallicity-matched models for reliable characterization in low-$Z$ environments. We present flux-calibrated, extinction-corrected spectra of these metal-poor PMS stars as a valuable resource for future investigations of disk evolution in subsolar regimes.

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arXiv2025

Coordinated Space- and Ground-based Monitoring of Accretion Bursts in a Protoplanetary Disk: The Orbital and Accretion Properties of DQ Tau

Multiplicity in pre-main-sequence (PMS) systems shapes circumstellar and circumbinary disks, often producing features such as inner cavities, spiral arms, and gas streamers that facilitate mass transfer between the disk and stars. Consequently, accretion in eccentric close binaries is highly variable and synchronized with their orbits, producing bursts near periastron passages. In this study, we examine the orbital and accretion properties of the eccentric Classical T-Tauri binary DQ Tau using medium- to high-resolution spectroscopy from the Very Large Telescope (VLT) X-Shooter and UVES instruments. The data were taken during a monitoring of inner disk chemistry with JWST, and our analysis is needed for correct interpretation of JWST data. We refine the orbital parameters and report an increment in the argument of periastron of 30 degrees. This apsidal motion may be caused by the massive disk acting as a third body. We also explore the possibility that it is due to a still undetected additional (sub-)stellar companion, estimating a lower limit of 15 MJ for its mass at the cavity edge (a=3 abin). We investigate accretion of the primary and secondary using the Ca II 849.8 nm emission line. The primary accretes more at periastron than in previous quiescent phases, while the secondary dominates post-periastron. Additionally, we report elevated Lacc at apastron, possibly due to interaction with irregularly shaped structures near the closest approach to the circumbinary disk. Finally, we derive each star's accretion luminosity across disentangled epochs and compare it to UV-excess-based results, finding good agreement. The individual Lacc values can be used as input for chemical models.

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arXiv2025

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY) - II. Time series of Balmer line profiles of Delorme 1(AB)b

Accretion processes in the planetary-mass regime remain poorly constrained, yet they strongly influence planet formation, evolution, and the composition of circumplanetary disks (CPDs). We investigate the resolved Balmer hydrogen emission-line profiles and their variability in the ~13Mjup, 30-45 Myr-old companion Delorme to constrain the underlying accretion mechanisms. Using VLT/UVES, we obtained 31 new epochs of high-resolution optical spectra (330-680 nm, R = 50,000), probing variability from hours to years. We analyze the shape and flux variability of hydrogen emission lines and compare them to two proposed origins: magnetospheric accretion funnels and localized accretion shocks. We detect Balmer lines from Halpha to H10 (6564-3799 AA) and a UV continuum excess, both indicative of ongoing accretion. All features are variable. The hydrogen lines decompose into two static components that vary only in flux. The broader velocity component correlates strongly with the UV excess and is qualitatively consistent with magnetospheric funnel models, but not with shock models. This component dominates the shape variability. The narrower component, which correlates less with the UV excess, is better matched by shock-emission models and drives most of the flux variability. Line fluxes show low variability on hour timescales but up to ~100% over weeks, similar to T Tauri stars. Our findings support magnetospheric accretion as the origin of the broad component. The narrow component may arise from accretion shocks or chromospheric activity. Higher-cadence observations could reveal rotational modulations and help constrain the object's rotation period and accretion geometry.

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arXiv2025

The likelihood of not detecting cavity-carving companions in transition discs -- A statistical approach

Protoplanetary discs with cavities, also known as ``transition discs'', constitute ~10% of protoplanetary discs at sub-mm wavelengths. Among several explanations, one hypothesis suggests these cavities are carved by undetected stellar or planetary companions. We present a novel approach to quantify the likelihood that a cavity-carving companion goes undetected because it is either too close to the star (i.e., has a small projected separation) or too faint to be resolved. We generate two independent samples of stellar and planetary companions with random sky orientations, assuming distributions in eccentricity, mass ratio, and time-weighted orbital phases, to study the statistical properties of the cavities they produce. We calculate the likelihood that a companion appears with a projected separation $d$ relative to its semi-major axis $a_{bin}$ ($d/a_{bin}$). Then, using a disc truncation model, we calculate the likelihood that companions carve a cavity with size $a_{cav}$ relative to its semi-major axis $a_{bin}$ and projected separation $d$, deriving distributions of $a_{bin}/a_{cav}$ and $d/a_{cav}$. We find that stellar companions carve cavities with median sizes ~3 times larger than their projected separation $d$ ($a_{cav}\sim3d$, $a_{cav}\sim1.7 d$ for planets), but with a statistically significant tail towards larger values ($a_{cav}\gg 3d$). We estimate the likelihood that cavity-carving companions go undetected due to projection effects when the system is observed with spatial resolution $R$, $P(d< R)$. Considering observational constraints on companion masses, we apply this framework to 13 well-known transition discs. We find that undetected stellar companions are unlikely in 8 out of 13 systems we considered, with 5 notable exceptions: ABAur, MWC758, HD135344B, CQTau and HD169142. The presence of undetected planets cannot be excluded in any of the transition discs considered.

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arXiv2025

Short- and long-term variations of the high mass accretion rate classical T Tauri star DR Tau

Classical T Tauri stars are newly formed, low mass stars which may display both periodic and random variations in their brightness. The interaction between the star and its circumstellar disk is time-dependent, leading to short or long-term changes in the environment, and hence variability of the system. By compiling a large dataset with high-cadence photometric (Kepler, TESS), and high-resolution spectroscopic observations (CFHT/ESPaDOnS) of the highly variable T Tauri star DR Tau, we aim to examine the short- and long-term variability of the system, and identify the underlying physical mechanisms. Our results reveal that DR Tau exhibits stochastic photometric variability not only on daily, but also on hourly timescale with peak-to-peak amplitude of 1.4 mag probably originating from accretion related variations. Our ground-based multifilter photometry shows that the amplitude of the variability decreases with increasing wavelength. This trend towards the infrared wavelengths suggests that part of the disk may be optically thick and invariable. The spectroscopic analysis showed that the H$α$ line presents the most complex line profile with several components but the significance of the components changes over time. This suggests the presence and variation of both accretion flow and wind. Broad and narrow components can be clearly distinguished in the He I and the Ca II lines, suggesting contribution from both the accretion flow and the post-shock region. DR Tau exhibits high level of photometric and spectroscopic variability on both short- and long-timescales, which is caused by the combination of accretion, wind, stellar activity, and obscuration by circumstellar matter; and the significance of the physical mechanisms causing the observed variability changes over time.

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arXiv2025

JWST's sharper view of EX Lup: cold water from ice sublimation during accretion outbursts

The unstable accretion phases during pre-main-sequence evolution of T Tauri stars produce variable irradiation and heating of planet-forming regions. A strong accretion outburst was observed with Spitzer-IRS in 2008 in EX Lup, the prototype of EXor variables, and found to increase the mid-infrared water and OH emission and decrease organic emission, suggesting large chemical changes. We present here two JWST-MIRI epochs of quiescent EX Lup in 2022 and 2023 obtained over a decade after the 2008 outburst and several months after a moderate burst in 2022. With JWST's sharper spectral view, we can now analyze water emission as a function of temperature in the two MIRI epochs and, approximately, also in the previous Spitzer epochs. This new analysis shows a strong cold water vapor ``burst" in low-energy lines during the 2008 outburst, which we consider clear evidence for enhanced ice sublimation due to a recession of the snowline, as found in protostellar envelopes. JWST shows that EX Lup still has an unusually strong emission from cold water in comparison to other T Tauri disks, suggesting > 10-yr-long freeze-out timescales in the inner disk surface. EX Lup demonstrates that outbursts can significantly change the observed organic-to-water ratios and increase the cold water reservoir, providing chemical signatures to study the recent accretion history of disks. This study provides an unprecedented demonstration of the chemical evolution triggered by accretion outbursts in the Class II phase and of the high potential of time-domain experiments to reveal processes that may have fundamental implications on planet-forming bodies near the snowline.

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arXiv2025

Coordinated Space and Ground-Based Monitoring of Accretion Bursts in a Protoplanetary Disk: Establishing Mid-Infrared Hydrogen Lines as Accretion Diagnostics for JWST-MIRI

In this paper, we establish and calibrate mid-infrared hydrogen recombination lines observed with JWST as accretion tracers for pre-main-sequence stars that accrete from circumstellar disks. This work is part of a coordinated, multi-observatory effort that monitored the well-known binary system DQ Tau over three orbital periods, capturing its periodic accretion bursts. In this first paper, we present 9 epochs of MIRI-MRS spectra with near-simultaneous LCO photometry and VLT X-Shooter spectroscopy. This program caught exceptional accretion variability, spanning almost two orders of magnitude between the peak of the first periastron accretion burst and the following quiescent phases. The MIRI spectra show H I line luminosities that vary in step with the accretion-luminosity time series measured with LCO and X-Shooter. The tight correlation with accretion and the large line widths, which MIRI resolves for the first time, support an accretion-flow origin for mid-infrared H I transitions. Combining these three exceptional datasets, we derive accurate relations between mid-infrared line and accretion luminosities for three H I transitions (10-7, 7-6, 8-7), and improve upon a previous relation based on Spitzer spectra. These new relations equip the community with a direct measurement of the accretion luminosity from MIRI-MRS spectra. A MIRI-derived accretion luminosity is fundamental for time-domain chemistry studies, as well as for studies of accretion in embedded/distant sources that are currently inaccessible in the optical. With these new relations, we provide accretion luminosities for an archival sample of 38 MRS spectra of protoplanetary disks published to date.

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