arXiv subjects

Davide Fedele

Publications and source records attributed to Davide Fedele.

At least 19 recordsLinked to original sources

arXiv2025

FAUST XXX: Dust enhancement in the young binary L1551 IRS 5

Young binary stars with discs provide unique laboratories to study the earliest stages of planet formation in star-forming environments. The detection of substructure in discs around Class I protostars challenges current models of disc evolution, suggesting that planets may form earlier than previously expected ($<1$ Myr). In the context of the ALMA Large Program FAUST, we present observations of the circumbinary disc (CBD) around the young binary system L1551 IRS 5. The CBD exhibits two prominent over-densities in the continuum emission at the edge of the cavity, with the Northern over-density being about 20% brighter than the Southern one. By analysing the disc morphology and kinematics of L1551 IRS 5, we delineate dynamical constraints on the binary's orbital parameters. Additionally, we present 3D hydrodynamical models of the CBD to predict both the dust and the gas surface densities. Then, we compare the resulting synthetic observations with ALMA observations of the continuum emission at 1.3 mm and the C$^{18}$O line emission. Our analysis suggests that the density enhancements observed with ALMA in L1551 IRS 5 can be caused by interactions between the binary stars and the CBD, leading to dust concentration within the disc. We conclude that the observed over-density corresponds to a location where could potentially grow under favourable conditions.

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arXiv2025

VLT/ERIS observations of the V960 Mon system: a dust-embedded substellar object formed by gravitational instability?

V960~Mon is an FU Orionis object that shows strong evidence of a gravitationally unstable spiral arm that is fragmenting into several dust clumps. We report the discovery of a new substellar companion candidate around this young star, identified in high-contrast $L'$-band imaging with VLT/ERIS. The object is detected at a projected separation of $0.898 \pm 0.01$ arcseconds with a contrast of $(8.39 \pm 0.07) \times 10^{-3}$. The candidate lies close to the clumps previously detected in the sub-mm (at 1.3 mm) and is co-located with extended polarized IR signal from scattered stellar irradiation, suggesting it is deeply embedded. The object is undetected in the SPHERE $H$-band total intensity, placing an upper mass limit of $\sim38~M_\mathrm{Jup}$ from the contrast curve. Using evolutionary models at an assumed age of 1~Myr, we estimate a mass of $\sim660~M_\mathrm{Jup}$ from the L' brightness; however, this value likely includes a significant contribution from a disk around the companion. The discrepancy between near- and mid-infrared results again suggests the source is deeply embedded in dust. This candidate may represent an actively accreting, disk-bearing substellar object in a young, gravitationally unstable environment.

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arXiv2024

Multiple chemical tracers finally unveil the intricate NGC\,1333 IRAS\,4A outflow system. FAUST XVI

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

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arXiv2023

Full L- and M-band high resolution spectroscopy of the S CrA binary disks with VLT-CRIRES+

The Cryogenic IR echelle Spectrometer (CRIRES) instrument at the Very Large Telescope (VLT) was in operation from 2006 to 2014. Great strides in characterizing the inner regions of protoplanetary disks were made using CRIRES observations in the L- and M-band at this time. The upgraded instrument, CRIRES+, became available in 2021 and covers a larger wavelength range simultaneously. Here we present new CRIRES+ Science Verification data of the binary system S Coronae Australis (S CrA). We aim to characterize the upgraded CRIRES+ instrument for disk studies and provide new insight into the gas in the inner disk of the S CrA N and S systems. We analyze the CRIRES+ data taken in all available L- and M-band settings, providing spectral coverage from 2.9 to 5.5 $\mu$m. We detect emission from $^{12}$CO (v=1-0, v=2-1, and v=3-2), $^{13}$CO (v=1-0), hydrogen recombination lines, OH, and H$_2$O in the S CrA N disk. In the fainter S CrA S system, only the $^{12}$CO v=1-0 and the hydrogen recombination lines are detected. The $^{12}$CO v=1-0 emission in S CrA N and S shows two velocity components, a broad component coming from $\sim$0.1 au in S CrA N and $\sim$0.03 au in S CrA S and a narrow component coming from $\sim$3 au in S CrA N and $\sim$5 au in S CrA S. We fit local thermodynamic equilibrium slab models to the rotation diagrams of the two S CrA N velocity components and find that they have similar column densities ($\sim$1-7$\times$10$^{17}$ cm$^{-2}$), but that the broad component is coming from a hotter and narrower region. Two filter settings, M4211 and M4368, provide sufficient wavelength coverage for characterizing CO and H$_2$O at $\sim$5 $\mu$m, in particular covering low- and high-$J$ lines. CRIRES+ provides spectral coverage and resolution that are crucial complements to low-resolution observations, such as those with JWST, where multiple velocity components cannot be distinguished.

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arXiv2023

Empirical Determination of the Lithium 6707.856 {\AA} Wavelength in Young Stars

Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for kinematic analysis of further spectral lines. The Li feature at $\sim$ 6708 {\AA} is commonly used, especially in the case of young stellar objects for which it is one of the strongest absorption lines. However, this is a complex line comprising two isotope fine-structure doublets. We empirically measure the wavelength of this Li feature in a sample of young stars from the PENELLOPE/VLT programme (using X-Shooter, UVES and ESPRESSO data) as well as HARPS data. For 51 targets, we fit 314 individual spectra using the STAR-MELT package, resulting in 241 accurately fitted Li features, given the automated goodness-of-fit threshold. We find the mean air wavelength to be 6707.856 {\AA}, with a standard error of 0.002 {\AA} (0.09 km/s) and a weighted standard deviation of 0.026 {\AA} (1.16 km/s). The observed spread in measured positions spans 0.145 {\AA}, or 6.5 km/s, which is up to a factor of six higher than typically reported velocity errors for high-resolution studies. We also find a correlation between the effective temperature of the star and the wavelength of the central absorption. We discuss how exclusively using this Li feature as a reference for photocentric velocity in young stars could potentially be introducing a systematic positive offset in wavelength to measurements of further spectral lines. If outflow tracing forbidden lines, such as [O i] 6300 {\AA}, are actually more blueshifted than previously thought, this then favours a disk wind as the origin for such emission in young stars.

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arXiv2022

External or internal companion exciting the spiral arms in CQ Tau?

We present new high-contrast images in near-infrared wavelengths ($λ$ = 1.04, 1.24, 1.62, 2.18 and 3.78$μ$m) of the young variable star CQ Tau, aiming to constrain the presence of companions in the protoplanetary disc. We reached a Ks-band contrast of 14 magnitudes with SPHERE/IRDIS at separations greater than 0."4 from the star. Our mass sensitivity curve rules out giant planets above 4 M$_{\rm Jup}$ immediately outside the spiral arms at $\sim$60 au and above 2-3 M$_{\rm Jup}$ beyond 100 au to 5$σ$ confidence assuming hot-start models. We do, however, detect four spiral arms, a double-arc and evidence for shadows in scattered light cast by a misaligned inner disc. Our observations may be explained by an unseen close-in companion on an inclined and eccentric orbit. Such a hypothesis would also account for the disc CO cavity and disturbed kinematics.

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arXiv2022

FAUST III. Misaligned rotations of the envelope, outflow, and disks in the multiple protostellar system of VLA 1623$-$2417

We report a study of the low-mass Class-0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H$^{13}$CO$^+$ ($J=3-2$), CS ($J=5-4$), and CCH ($N=3-2$) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk as well as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12 degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circum-binary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be $5-16$ au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its opposite gradient is also discussed.

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arXiv2021

Tracing the formation history of giant planets in protoplanetary disks with Carbon, Oxygen, Nitrogen and Sulphur

The composition of giant planets is imprinted by their migration history and the compositional structure of their hosting disks. Studies in recent literature investigate how the abundances of C and O can constrain the formation pathways of giant planets forming within few tens of au from the star. New ALMA observations, however, suggest planet-forming regions possibly extending to hundreds of au. We explore the implications of these wider formation environments through n-body simulations of growing and migrating giant planets embedded in planetesimal disks, coupled with a compositional model of the protoplanetary disk where volatiles are inherited from the molecular cloud and refractories are calibrated against extrasolar and Solar System data. We find that the C/O ratio provides limited insight on the formation pathways of giant planets that undergo large-scale migration. This limitation can be overcome thanks to nitrogen and sulphur. Jointly using the C/N, N/O and C/O ratios breaks any degeneracy in the formation and migration tracks of giant planets. The use of elemental ratios normalized to the respective stellar ratios supplies additional information on the nature of giant planets, thanks to the relative volatility of O, C and N in disks. When the planetary metallicity is dominated by the accretion of solids C/N* $>$ C/O* $>$ N/O* (* denoting this normalized scale), otherwise N/O* $>$ C/O* $>$ C/N*. The S/N ratio provides an additional independent probe into the metallicity of giant planets and their accretion of solids.

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arXiv2021

Exploring the link between star and planet formation with Ariel

The goal of the Ariel space mission is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. The planetary bulk and atmospheric compositions bear the marks of the way the planets formed: Ariel's observations will therefore provide an unprecedented wealth of data to advance our understanding of planet formation in our Galaxy. A number of environmental and evolutionary factors, however, can affect the final atmospheric composition. Here we provide a concise overview of which factors and effects of the star and planet formation processes can shape the atmospheric compositions that will be observed by Ariel, and highlight how Ariel's characteristics make this mission optimally suited to address this very complex problem.

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arXiv2021

Thermal desorption of astrophysical relevant ice mixtures of acetaldehyde and acetonitrile from olivine dust

Millimeter and centimeter observations are discovering an increasing number of interstellar complex organic molecules (iCOMs) in a large variety of star forming sites, from the earliest stages of star formation to protoplanetary disks and in comets. In this context it is pivotal to understand how the solid phase interactions between iCOMs and grain surfaces influence the thermal desorption process and, therefore, the presence of molecular species in the gas phase. In laboratory, it is possible to simulate the thermal desorption process deriving important parameters such as the desorption temperatures and energies. We report new laboratory results on temperature-programmed desorption (TPD) from olivine dust of astrophysical relevant ice mixtures of water, acetonitrile, and acetaldehyde. We found that in the presence of grains, only a fraction of acetaldehyde and acetonitrile desorbs at about 100 K and 120 K respectively, while 40% of the molecules are retained by fluffy grains of the order of 100 μm up to temperatures of 190-210 K. In contrast with the typical assumption that all molecules are desorbed in regions with temperatures higher than 100 K, this result implies that about 40% of the molecules can survive on the grains enabling the delivery of volatiles towards regions with temperatures as high as 200 K and shifting inwards the position of the snowlines in protoplanetary disks. These studies offer a necessary support to interpret observational data and may help our understanding of iCOMs formation providing an estimate of the fraction of molecules released at various temperatures.

astro-ph.IM↗

arXiv2021

KMOS study of the mass accretion rate from Class I to Class II in NGC 1333

The mass accretion rate is the fundamental parameter to understand the process of mass assembly that results in the formation of a low-mass star. This parameter has been largely studied in Classical TTauri stars in star-forming regions with ages of 1-10Myr. However, little is known about the accretion properties of young stellar objects (YSOs) in younger regions and early stages of star formation, such as in the Class0/I phases. We present new NIR spectra of 17 ClassI/Flat and 35 ClassII sources located in the young (<1Myr) NGC1333 cluster, acquired with the KMOS instrument at the VLT. Our goal is to study whether the mass accretion rate evolves with age, as suggested by the widely adopted viscous evolution model, by comparing the properties of the NGC1333 members with samples of older regions. We measured the stellar parameters and accretion rates of our sample, finding a correlation between accretion and stellar luminosity, and between mass accretion rate and stellar mass. Both correlations are compatible within the errors with the older Lupus star-forming region, while only the latter is consistent with results from ChamaeleonI. The ClassI sample shows larger accretion luminosities with respect to the ClassII stars of the same cloud. However, the derived accretion rates are not sufficiently high to build up the inferred stellar masses, assuming steady accretion during the ClassI lifetime. This suggests that the sources are not in their main accretion phase and that most of their mass has already been accumulated during a previous stage and/or that the accretion is an episodic phenomenon. We show that some of the targets originally classified as Class I through Spitzer photometry are in fact evolved or low accreting objects. This evidence can have implications for the estimated protostellar phase lifetimes. Further observations are needed to determine if this is a general result.

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arXiv2021

FAUST II. Discovery of a Secondary Outflow in IRAS 15398-3359: Variability in Outflow Direction during the Earliest Stage of Star Formation?

We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 au to 1800 au, as part of the ALMA Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and C18O line emission, which extends from the source along a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blue-shifted with respect to the systemic velocity. A velocity gradient of 1.2 km/s over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution.

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arXiv2020

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) V: Sample, overview, and demography of disk molecular emission

We present an overview of the ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT), a campaign devoted to the characterization of the molecular emission from partly embedded, young stars. The project aims at better understanding the gaseous products that are delivered to planets by means of high-resolution maps of assorted lines probing disks at the time of the planet formation (less than 1 Myr). Nine different molecules are surveyed by our observations of six Class I/flat-spectrum sources. A series of accompanying articles analyze specific targets and molecules. Here we describe the sample and provide a general overview of the results, focusing on the spatial distribution, column densities, and abundance ratios of H$_2$CO, CS, and CN. The results of this work are a first step toward the characterization of the disk chemical evolution that need to be complemented by further observations of less exceptional disks and customized thermo-chemical modeling.

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arXiv2020

Planet migration, resonant locking and accretion streams in PDS70: Comparing models and data

The disc surrounding PDS 70, with two directly imaged embedded giant planets, is an ideal laboratory to study planet-disc interaction. We present three-dimensional smoothed particle hydrodynamics simulations of the system. In our simulations, planets, which are free to migrate and accrete mass, end up in a locked resonant configuration that is dynamically stable. We show that features observed at infrared (scattered light) and millimetre (thermal continuum) wavelengths are naturally explained by the accretion stream onto the outer planet, without requiring a circumplanetary disc around planet c. We post-processed our near-infrared synthetic images in order to account for observational biases known to affect high-contrast images. Our successful reproduction of the observations indicates that planet-disc dynamical interactions alone are sufficient to explain the observations of PDS 70.

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arXiv2020

Photoprocessing of formamide ice: route towards prebiotic chemistry in space

Aims. Formamide (HCONH2) is the simplest molecule containing the peptide bond first detected in the gas phase in Orion-KL and SgrB2. In recent years, it has been observed in high temperature regions such as hot corinos, where thermal desorption is responsible for the sublimation of frozen mantles into the gas phase. The interpretation of observations can benefit from information gathered in the laboratory, where it is possible to simulate the thermal desorption process and to study formamide under simulated space conditions such as UV irradiation. Methods. Here, two laboratory analyses are reported: we studied formamide photo-stability under UV irradiation when it is adsorbed by space relevant minerals at 63 K and in the vacuum regime. We also investigated temperature programmed desorption of pure formamide ice in the presence of TiO2 dust before and after UV irradiation. Results. Through these analyses, the effects of UV degradation and the interaction between formamide and different minerals are compared.We find that silicates, both hydrates and anhydrates, offer molecules a higher level of protection from UV degradation than mineral oxides. The desorption temperature found for pure formamide is 220 K. The desorption temperature increases to 250 K when the formamide desorbs from the surface of TiO2 grains. Conclusions. Through the experiments outlined here, it is possible to follow the desorption of formamide and its fragments, simulate the desorption process in star forming regions and hot corinos, and constrain parameters such as the thermal desorption temperature of formamide and its fragments and the binding energies involved. Our results offer support to observational data and improve our understanding of the role of the grain surface in enriching the chemistry in space.

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arXiv2020

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT): I. CO, CS, CN, and H2CO around DG Tau B

The chemical composition of planets is inherited by the distribution of the various molecular species in the protoplanetary disk at thetime of their formation. As of today, only a handful of disks has been imaged in multiple spectral lines with high spatial resolution. As part of a small campaign devoted to the chemical characterization of disk-outflow sources in Taurus, we report on new ALMA Band 6 observations with 20 au resolution toward the embedded young star DG Tau B. Images of the continuum emission reveals a dust disk with rings and, putatively, a leading spiral arm. The disk, as well as the prominent outflow cavities, are detected in CO, H2CO, CS, and CN while they remain undetected in SO2, HDO, and CH3OH. From the absorption of the back-side outflow, we inferred that the disk emission is optically thick in the inner 50 au. This morphology explains why no line emission is detected from this inner region and poses some limitations toward the calculation of the dust mass and the characterization of the inner gaseous disk. The H2CO and CS emission from the inner 200 au is mostly from the disk and their morphology is very similar. The CN emission significantly differs from the other two molecules as it is observed only beyond 150 au. This ring-like morphology is consistent with previous observations and the predictions of thermochemical disk models. Finally, we constrained the disk-integrated column density of all molecules. In particular, we found that the CH3OH/H2CO ratio must be smaller than 2, making the methanol non-detection still consistent with the only such a ratio available from the literature (1.27 in TW Hya).

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arXiv2020

Discovery of a low-mass companion embedded in the disk of the young massive star MWC 297 with VLT/SPHERE

We report the discovery of a low-mass stellar companion around the young Herbig Be star MWC 297. We performed multi-epoch high-contrast imaging in the near infrared (NIR) with the Very Large Telescope (VLT)/Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. The companion is found at projected separation of 244.7$\pm$13.2 au and a position angle of 176.4$\pm$0.1 deg. The large separation supports formation via gravitational instability. From the spectrum, we estimate a mass of 0.1-0.5 M$_{\odot}$, the range conveying uncertainties in the extinction of the companion and in evolutionary models at young ages. The orbit coincides with a gap in the dust disk inferred from the Spectral Energy Distribution (SED). The young age ($\lesssim$ 1 Myr) and mass ratio with the central star ($\sim 0.01$) makes the companion comparable to PDS 70~b, suggesting a relation between formation scenarios and disk dynamics.

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arXiv2019

Long lived dust rings around HD169142

Recent ALMA observations of the protoplanetary disc around HD~169142 reveal a peculiar structure made of concentric dusty rings: a main ring at $\sim$20 au, a triple system of rings at $\sim 55-75$ au in millimetric continuum emission and a perturbed gas surface density from the $^{12}$CO,$^{13}$CO and C$^{18}$O$(J=2-1)$ surface brightness profile. In this Letter, we perform three-dimensional numerical simulations and radiative transfer modeling exploring the possibility that two giant planets interacting with the disc and orbiting in resonant locking can be responsible for the origin of the observed dust inner rings structure. We find that in this configuration the dust structure is actually long lived while the gas mass of the disc is accreted onto the star and the giant planets, emptying the inner region. In addition, we also find that the innermost planet is located at the inner edge of the dust ring, and can accrete mass from the disc, generating a signature in the dust ring shape that can be observed in mm ALMA observations.

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