arXiv subjects

G. P. Rosotti

Publications and source records attributed to G. P. Rosotti.

15 recordsLinked to original sources

arXiv2026

Azimuthal brightness modulation reveals hidden rings in CI Tau

Protoplanetary disks often host substructures such as rings and gaps, which trace key processes in planet formation and dust evolution. However, narrow rings may remain unresolved due to limited observational resolution, hiding critical information about early planetesimal formation and the amount of dust present. We apply the azimuthal brightness modulation method, based on the modulation produced by multiple unresolved optically thick rings embedded in an optically thin background Scardoni+2024, to multi-wavelength ALMA observations of CI Tau to identify unresolved rings and constrain their geometry and optical depth. We analysed CI Tau archival ALMA continuum observations in bands 3, 6, and 7, extracting azimuthal brightness profiles along narrow annuli and comparing them with forward modeled synthetic observations of inclined disks containing unresolved rings. We detect the azimuthal signature at $\sim22$ au in all three bands, consistent with unresolved, optically thick rings embedded in a lower optical depth background. Multi wavelength modelling constrains the rings' geometry and optical depth, consistent with conditions expected for streaming instability and early planetesimal formation. Our results demonstrate the applicability of this azimuthal signature technique to real disks, reveal fine scale dust substructures in CI Tau, and illustrate a new method to study the early stages of planet formation below the nominal resolution limit.

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arXiv2026

Warps survive beyond fly-by encounters in protoplanetary disks. RW Aur A as a case study

Stellar fly-bys can have multiple dynamical effects on protoplanetary disks, including warping and the excitation of spiral arms. Since observations indicate that warps are common, we aim to investigate these effects for different fly-by trajectories. We further link our models to observations by applying them to the RW Aur system, which is a fly-by candidate with a relatively well constrained trajectory. We investigate the disk dynamics in grid-based hydrodynamical simulations, which allow for a lower disk viscosity than commonly used SPH models. We post-process our simulations of the RW Aur system with radiative transfer models to create synthetic images of the dust continuum and gas kinematics. Fly-bys inclined with respect to the original disk plane can excite warps of a few degrees: the exact outcome depends on the specific geometry of the encounter. Specifically, we find that the position of the periastron with respect to the initial disk plane plays a role for the resulting warp strength. Within our parameter set, the strongest warp is excited for a retrograde fly-by with a periastron that is not in the same plane as the disk. Our models show that the warp can persist even after the perturber can no longer be clearly linked to the system, implying that past fly-bys are a possible origin of observed warps. Excited spirals arms, on the other hand, are much more short-lived than the warp. The RW Aur system presents a perfect opportunity to apply these results: we find that a warp of about 5° can be excited, and that the strong spiral arms have already disappeared at the current time of observation 300 years after periastron). This compares well with existing continuum observations, and our synthetic kinematic evaluations hint at remnant structures in the gas density that may be detectable.

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arXiv2025

DBNets2.0: simulation-based inference for planet-induced dust substructures in protoplanetary discs

Dust substructures in protoplanetary discs can be signatures of embedded young planets whose detection and characterisation would provide a better understanding of planet formation. Traditional techniques used to link substructures' morphology to the properties of putative embedded planets present several limitations that the use of deep learning methods has partly overcome. In our previous work, we developed DBNets, a tool exploiting an ensemble of Convolutional Neural Networks (CNNs) to estimate the mass of putative planets in disc dust substructures. This inference problem, however, is degenerate as planets of different masses could produce the same rings and gaps if other physical disc properties were different. In this paper, we address this issue improving our simulation-based inference pipeline to estimate the full posterior distribution for the planet mass and three additional disc properties: the disc $α$-viscosity, the scale height and the dust Stokes number. We also address some minor issues of our previous tool. The new pipeline involves a CNN that summarises the input images in a set of summary statistics, followed by an ensemble of normalising flows that model the inferred posterior for the target properties. We tested our pipeline on a dedicated set of synthetic observations using the TARP test and standard metrics, demonstrating its accuracy and precision. Additionally, we use the results obtained on the test set to study the degeneracies between pairs of parameters. Finally, we apply the developed pipeline to a set of 49 gaps in 34 protoplanetary discs' continuum observations. The results show typically low values of $α$-viscosity, disc scale heights, and planet masses, with 83% of them being lower than 1M$_J$. These low masses are consistent with the non-detections of these putative planets in direct imaging surveys. Our tool is publicly available.

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arXiv2025

Planetesimal formation via the streaming instability in simulations of infall dominated young disks

Protoplanetary disks naturally emerge during protostellar core-collapse. In their early evolutionary stages, infalling material dominates their dynamical evolution. In the context of planet formation, this means that the conditions in young disks are different from the typically considered disks where infall has subsided. High inward velocities are caused by the advection of accreted material which is deficient in angular momentum, rather than being set by viscous spreading, and accretion gives rise to strong velocity fluctuations. Therefore, we aim to investigate when it is possible for the first planetesimals to form and subsequent planet formation to commence. We analyze the disks obtained in numerical 3D nonideal magnetohydrodynamical simulations, which serve as a basis for 1D models representing the conditions during the Class 0/I evolutionary stages. We integrate the 1D models with an adapted version of the TwoPopPy code to investigate the formation of the first planetesimals via the streaming instability. In disks with temperatures such that the snow line is located at ~10 AU and where it is assumed that velocity fluctuations felt by the dust are reduced by a factor of 10 compared to the gas, ${\sim}10^{-3}M_\odot$ of planetesimals may be formed already during the first 100 kyr after disk formation, implying the possible early formation of giant planet cores. The cold-finger effect at the snow line is the dominant driver of planetesimal formation, which occurs in episodes and utilizes solids supplied directly from the envelope, leaving the disk solid reservoir intact. However, if the cold-finger effect is suppressed, early planetesimal formation is limited to cold disks with efficient dust settling whose dust-to-gas ratio is initially enriched to $ε_0\geq 0.03$.

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arXiv2025

Hidden under a warm blanket: If planets existed in protostellar disks, they would hardly produce observable substructures

The onset of planet formation is actively under debate. Recent mass measurements of disks around protostars suggest an early start of planet formation in the Class 0/I disks. However, dust substructures, one possible signature of forming planets, are rarely observed in the young Class 0/I disks, while they are ubiquitous in the mature Class II disks. It is not clear whether the lack of dust substructures in the Class 0/I disks indicates absence of planets or whether it is due to other physical effects such as temperature and dust opacity. Here we consider the effect of temperature on the ability of planets to produce dust substructures. We prescribe the evolution of the disk and the protostar from Class 0 to Class II phase and calculate the disk temperature using radiative transfer models at various stages of the evolution. We use the mid-plane temperature to calculate the disk scale height and the minimum planet mass needed to open observable dust gaps using the thermal criterion. We find that this minimum planet mass decreases as a function of time. Particularly, we find that if a planet up to ${\sim}5$ M$_{\oplus}$ in the inner ${\sim}5$ au or up to ${\sim}10-50$ M$_{\oplus}$ at radii ${\gtrsim}5$ au was already formed in the early protostellar phase ($t< 2\times 10^5$ yr) it would barely produce any dust substructures. We conclude that a major contribution to the observed lack of substructures (if produced by planets) in the early protostellar phase - lowering their frequency by ${\sim}50\%$ - could be elevated temperatures rather than the absence of planets.

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arXiv2024

Correlations among complex organic molecules around protostars: Effects of physical structure

Column density ratios of complex organic molecules are generally constant across protostellar systems with some low-level scatter. However, the scatter in formamide (NH$_2$CHO) to methanol (CH$_3$OH) column density ratio is one of the highest. This larger scatter is sometimes interpreted as evidence of gas-phase formation of NH$_2$CHO. In this work we propose an alternative interpretation in which this scatter is produced by differences in the snowline locations related to differences in binding energies of these species and the small-scale structure of the envelope and the disk system. We also include CH$_3$CN in our work as a control molecule which has a similar binding energy to CH$_3$OH. We use radiative transfer models to calculate the emission from these species in protostellar systems with and without disks. The abundances of these species are parameterized in our models. Then we fit the calculated emission lines to find the column densities as done in real observations. We find a correction factor of ~10 to be multiplied by gas-phase $N_{NH_2CHO}/N_{CH_3OH}$ to give the true abundance ratio of these two species in the ices. We find that models with different physical parameters produce a scatter in $N_{NH_2CHO}/N_{CH_3OH}$, comparable with that of observations. The scatter in $N_{NH_2CHO}/N_{CH_3OH}$ is larger than that of $N_{CH_3CN}/N_{CH_3OH}$ in models consistent with the observations. We show that the scatter in $N_{NH_2CHO}/N_{CH_3OH}$ will be lower if we correct for the difference in sublimation temperatures of these two species in observations of ~40 protostellar systems with ALMA. The scatter in $N_{NH_2CHO}/N_{CH_3OH}$ can be partially explained by the difference in their binding energies. We conclude that gas-phase chemistry routes for NH$_2$CHO are not necessary to explain the larger scatter of $N_{NH_2CHO}/N_{CH_3OH}$ compared with other ratios.

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arXiv2023

Constraining turbulence in protoplanetary discs using the gap contrast: an application to the DSHARP sample

Constraining the strength of gas turbulence in protoplanetary discs is an open problem that has relevant implications for the physics of gas accretion and planet formation. In this work, we gauge the amount of turbulence in 6 of the discs observed in the DSHARP programme by indirectly measuring the vertical distribution of their dust component. We employ the differences in the gap contrasts observed along the major and the minor axes due to projection effects, and build a radiative transfer model to reproduce these features for different values of the dust scale heights. We find that (a) the scale heights that yield a better agreement with data are generally low ($\lesssim 4$ AU at a radial distance of $100$ AU), and in almost all cases we are only able to place upper limits on their exact values; these conclusions imply (assuming an average Stokes number of $\approx10^{-2}$) low turbulence levels of $α_{\rm SS}\lesssim10^{-3}-10^{-4}$; (b) for the 9 other systems we considered out of the DSHARP sample, our method yields no significant constraints on the disc vertical structure; we conclude that this is because these discs have either a low inclination or gaps that are not deep enough. Based on our analysis we provide an empirical criterion to assess whether a given disc is suitable to measure the vertical scale height.

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arXiv2023

Demographics of young stars and their protoplanetary disks: lessons learned on disk evolution and its connection to planet formation

Since Protostars and Planets VI (PPVI), our knowledge of the global properties of protoplanetary and debris disks, as well as of young stars, has dramatically improved. At the time of PPVI, mm-observations and optical to near-infrared spectroscopic surveys were largely limited to the Taurus star-forming region, especially of its most massive disk and stellar population. Now, near-complete surveys of multiple star-forming regions cover both spectroscopy of young stars and mm interferometry of their protoplanetary disks. This provides an unprecedented statistical sample of stellar masses and mass accretion rates, as well as disk masses and radii, for almost 1000 young stellar objects within 300 pc from us, while also sampling different evolutionary stages, ages, and environments. At the same time, surveys of debris disks are revealing the bulk properties of this class of more evolved objects. This chapter reviews the statistics of these measured global star and disk properties and discusses their constraints on theoretical models describing global disk evolution. Our comparisons of observations to theoretical model predictions extends beyond the traditional viscous evolution framework to include analytical descriptions of magnetic wind effects. Finally, we discuss how recent observational results can provide a framework for models of planet population synthesis and planet formation.

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arXiv2022

Importance of source structure on complex organics emission III. Effect of disks around massive protostars

Complex organic molecules are only detected toward a fraction of high-mass protostars. The goal of this work is to investigate whether high-mass disks can explain the lack of methanol emission from some massive protostellar systems. We consider an envelope-only and an envelope-plus-disk model and use RADMC-3D to calculate the methanol emission. High and low millimeter (mm) opacity dust are considered for both models separately and the methanol abundance is parameterized. Viscous heating is included due to the high accretion rates of these objects in the disk. In contrast with low-mass protostars, the presence of a disk does not significantly affect the temperature structure and methanol emission. The shadowing effect of the disk is not as important for high-mass objects and the disk mid-plane is hot because of viscous heating, which is effective due to the high accretion rates. Consistent with observations of infrared absorption lines toward high-mass protostars, we find a vertical temperature inversion, i.e. higher temperatures in the disk mid-plane than the disk surface, at radii < 50au for the models with $L=10^4$ L$_{\odot}$ and large mm opacity dust as long as the envelope mass is >550 M$_{\odot}$. The large observed scatter in methanol emission from massive protostars can be mostly explained toward lower luminosity objects with the envelope-plus-disk models including low and high mm opacity dust. The methanol emission variation toward sources with high luminosities cannot be explained by models with or without a disk. However, the $L/M$ of these objects suggest that they could be associated with hypercompact/ultracompact HII regions. Therefore, the low methanol emission toward the high-luminosity sources can be explained by them hosting an HII region where methanol is absent.

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arXiv2022

Inward and outward migration of massive planets: moving towards a stalling radius

Recent studies on the planet-dominated regime of Type II migration showed that, contrary to the conventional wisdom, massive planets can migrate outwards. Using `fixed-planet' simulations these studies found a correlation between the sign of the torques acting on the planet and the parameter $K'$ (which describes the depth of the gap carved by the planet in the disc). We perform `live-planet' simulations exploring a range of $K'$ and disc mass values to test and extend these results. The excitation of planet eccentricity in live-planet simulations breaks the direct dependence of migration rate (rate of change of semi-major axis) on the torques imposed, an effect that `fixed-planet' simulations cannot treat. By disentangling the contribution to the torque due to the semi-major axis evolution from that due to the eccentricity evolution, we recover the relation between the magnitude and sign of migration and $K'$ and argue that this relation may be better expressed in terms of the related gap depth parameter $K$. We present a toy model in which the sign of planetary migration changes at a limiting value of $K$, through which we explore planets' migration in viscously evolving discs. The existence of the torque reversal shapes the planetary system's architecture by accumulating planets either at the stalling radius or in a band around it (defined by the interplay between the planet migration and the disc evolution). In either case, planets pile up in the area $1-10$ au, disfavouring hot Jupiter formation through Type II migration in the planet-dominated regime.

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arXiv2022

Importance of source structure on complex organics emission II. Can disks explain lack of methanol emission from some low-mass protostars?

Some protostellar systems show little or no millimetre line emission of complex organics. This can be interpreted as a low abundance of these molecules, alternatively they could be present in the system but are not seen in the gas. The goal is to investigate the latter hypothesis for methanol. We will attempt to answer the question: Does the presence of a disk and optically thick dust reduce methanol emission even if methanol is abundant in the ices and gas? Using the radiative transfer code RADMC-3D, methanol emission lines from an envelope-only model and an envelope-plus-disk model are calculated and compared with each other and the observations. Methanol emission from the envelope-only model is always stronger than from the envelope-plus-disk model by at least a factor 2 as long as the disk radius is larger than 30 au (for L=8 L$_{\odot}$). In most cases, this is due to lower temperatures and, hence, the smaller amount of warm methanol inside the snow surface of the envelope-plus-disk model. The intensities drop by more than an order of magnitude for models including high mm opacity dust grains and disk radii of at least 50 au (for L=8 L$_{\odot}$) due to continuum over-subtraction. The line intensities from the envelope-only models overproduce the observations of protostars with lower methanol emission even with large dust optical depth effects. The envelope-plus-disk models can explain the bulk of the observations. However, they can only reproduce the observations of sources with high luminosities and low methanol emission when dust optical depth effects especially continuum over-subtraction in the disk becomes effective. Therefore, both the effects of disk and dust optical depth should be considered to explain the observations. In conclusion: Absence of methanol emission does not imply absence of methanol molecules in either gas or ice.

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arXiv2021

Early planet formation in embedded protostellar disks: Setting the stage for the first generation of planetesimals

(Abridged) Recent surveys of young star formation regions have shown that the average Class II object does not have enough dust mass to make the cores of giant planets. Younger Class 0/I objects have enough dust in their embedded disk, which begs the questions: can the first steps of planet formation occur in these younger systems? The first step is building the first planetesimals, generally believed to be the product of the streaming instability. Hence the question can be restated: are the physical conditions of embedded disks conducive to the growth of the streaming instability? Here we model the collapse of a `dusty' proto-stellar cloud to show that if there is sufficient drift between the falling gas and dust, regions of the embedded disk can become sufficiently enhanced in dust to drive the streaming instability. We include four models, three with different dust grain sizes and one with a different initial cloud angular momentum to test a variety of collapse trajectories. We find a `sweet spot' for planetesimal formation for grain sizes of a few 10s of micron since they fall sufficiently fast relative to the gas to build a high dust-to-gas ratio along the disk midplane, but have slow enough radial drift speeds in the embedded disk to maintain the high dust-to-gas ratio. Unlike the gas, which is held in hydrostatic equilibrium for a time due to gas pressure, the dust can begin collapsing from all radii at a much earlier time. The streaming instability can produce at least between 7-35 M$_\oplus$ of planetesimals in the Class 0/I phase of our smooth embedded disks, depending on the size of the falling dust grains. This first generation of planetesimals could represent the first step in planet formation, and occurs earlier in the lifetime of the young star than is traditionally thought.

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arXiv2021

PENELLOPE: the ESO data legacy program to complement the Hubble UV Legacy Library of Young Stars (ULLYSES) I. Survey presentation and accretion properties of Orion OB1 and $σ$-Orionis

The evolution of young stars and disks is driven by the interplay of several processes, notably accretion and ejection of material. Critical to correctly describe the conditions of planet formation, these processes are best probed spectroscopically. About five-hundred orbits of the Hubble Space Telescope (HST) are being devoted in 2020-2022 to the ULLYSES public survey of about 70 low-mass (M<2Msun) young (age<10 Myr) stars at UV wavelengths. Here we present the PENELLOPE Large Program that is being carried out at the ESO Very Large Telescope (VLT) to acquire, contemporaneous to HST, optical ESPRESSO/UVES high-resolution spectra to investigate the kinematics of the emitting gas, and UV-to-NIR X-Shooter medium-resolution flux-calibrated spectra to provide the fundamental parameters that HST data alone cannot provide, such as extinction and stellar properties. The data obtained by PENELLOPE have no proprietary time, and the fully reduced spectra are made available to the whole community. Here, we describe the data and the first scientific analysis of the accretion properties for the sample of thirteen targets located in the Orion OB1 association and in the sigma-Orionis cluster, observed in Nov-Dec 2020. We find that the accretion rates are in line with those observed previously in similarly young star-forming regions, with a variability on a timescale of days of <3. The comparison of the fits to the continuum excess emission obtained with a slab model on the X-Shooter spectra and the HST/STIS spectra shows a shortcoming in the X-Shooter estimates of <10%, well within the assumed uncertainty. Its origin can be either a wrong UV extinction curve or due to the simplicity of this modelling, and will be investigated in the course of the PENELLOPE program. The combined ULLYSES and PENELLOPE data will be key for a better understanding of the accretion/ejection mechanisms in young stars.

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arXiv2020

X-Shooter survey of disk accretion in Upper Scorpius I. Very high accretion rates at age>5 Myr

Determining the mechanisms that drive the evolution of protoplanetary disks is a necessary step to understand how planets form. Here we measured the mass accretion rate for young stellar objects at age >5 Myr, a critical test for the current models of disk evolution. We present the analysis of the spectra of 36 targets in the ~5-10 Myr old Upper Scorpius region for which disk masses were measured with ALMA. We find that the mass accretion rates in this sample of old but still survived disks are similarly high as those of the younger (<3 Myr old) star-forming regions of Lupus and Cha I, when considering the dependence on stellar and disk mass. In particular, several disks show high mass accretion rates >10^-9 Msun/yr while having low disk masses. Furthermore, the median values of the measured mass accretion rates in the disk mass ranges where our sample is complete at a level ~60-80% are compatible in these three regions. At the same time, the spread of mass accretion rates at any given disk mass is still >0.9 dex even at age>5 Myr. These results are in contrast with simple models of viscous evolution, which would predict that the values of the mass accretion rate diminish with time, and a tighter correlation with disk mass at age>5 Myr. Similarly, simple models of internal photoevaporation cannot reproduce the observed mass accretion rates, while external photoevaporation might explain the low disk masses and high accretion rates. A partial possible solution to the discrepancy with the viscous models is that the gas-to-dust ratio of the disks at >5 Myr is significantly different and higher than the canonical 100, as suggested by some dust and gas disk evolution models. The results shown here require the presence of several inter-playing processes, such as detailed dust evolution, external photoevaporation and possibly MHD winds, to explain the secular evolution of protoplanetary disks.

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arXiv2019

Spiral arms in the proto-planetary disc HD100453 detected with ALMA: evidence for binary-disc interaction and a vertical temperature gradient

Scattered light high-resolution imaging of the proto-planetary disc orbiting HD100453 shows two symmetric spiral arms, possibly launched by an external stellar companion. In this paper we present new, sensitive high-resolution ($\sim$30 mas) Band 7 ALMA observations of this source. This is the first source where we find counterparts in the sub-mm continuum to both scattered light spirals. The CO J=3-2 emission line also shows two spiral arms; in this case they can be traced over a more extended radial range, indicating that the southern spiral arm connects to the companion position. This is clear evidence that the companion is responsible for launching the spirals. The pitch angle of the sub-millimeter continuum spirals ($\sim 6 ^{\circ}$) is lower than the one in scattered light ($\sim 16 ^{\circ}$). We show that hydrodynamical simulations of binary-disc interaction can account for the difference in pitch angle only if one takes into account that the midplane is colder than the upper layers of the disc, as expected for the case of externally irradiated discs.

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