arXiv subjects

Antonio Garufi

Publications and source records attributed to Antonio Garufi.

At least 37 records · Page 2Linked to original sources

arXiv2023

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): Diverse outcomes of binary-disk interactions

Circumstellar disks do not evolve in isolation, as about half of solar-type stars were born in binary or multiple systems. Resolving disks in binary systems provides the opportunity to examine the influence of stellar companions on the outcomes of planet formation. We aim to investigate and compare disks in stellar multiple systems with near-infrared scattered-light imaging as part of the Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS) program. We used polarimetric differential imaging with SPHERE/IRDIS at the VLT to search for scattered light from the circumstellar disks in three multiple systems, CHX 22, S CrA, and HP Cha. We performed astrometric and orbit analyses for the stellar companions using archival HST, VLT/NACO, and SPHERE data. Combined with the age and orbital constraints, the observed disk structures provide insights into the evolutionary history and the impact of the stellar companions. The small grains in CHX 22 form a tail-like structure surrounding the close binary, which likely results from a close encounter and capture of a cloudlet. S CrA shows intricate structures (tentative ringed and spiral features) in the circumprimary disk as a possible consequence of perturbations by companions. The circumsecondary disk is truncated and connected to the primary disk via a streamer, suggesting tidal interactions. In HP Cha, the primary disk is less disturbed and features a tenuous streamer, through which the material flows towards the companions. The comparison of the three systems spans a wide range of binary separation (50 - 500 au) and illustrates the decreasing influence on disk structures with the distance of companions. This agrees with the statistical analysis of exoplanet population in binaries, that planet formation is likely obstructed around close binary systems, while it is not suppressed in wide binaries.

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arXiv2022

The SPHERE view of three interacting twin disc systems in polarised light

Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages (a so-called 'fly-by'), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems: AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the individuals' contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205. We discuss the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution, namely with ALMA continuum and gas emission. Collective observational data can constrain the systems' geometry and stellar trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.

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arXiv2022

Reference-star differential imaging on SPHERE/IRDIS

Reference-star differential imaging (RDI) is a promising technique in high-contrast imaging that is thought to be more sensitive to exoplanets and disks than angular differential imaging (ADI) at short angular separations (i.e., <0.3"). However, it is unknown whether the performance of RDI on ground-based instruments can be improved by using all the archival data to optimize the subtraction of stellar contributions. We characterize the performance of RDI on SPHERE/IRDIS data in direct imaging of exoplanets and disks. We made use of all the archival data in H23 obtained by SPHERE/IRDIS in the past five years to build a master reference library and perform RDI. In the point-source detection, RDI can outperform ADI at small angular separations (<0.4") if the observing conditions are around the median conditions of our master reference library. On average, RDI has a gain of ~0.8 mag over ADI at 0.15" separation for observations under median conditions. We demonstrate that including more reference targets in the master reference library can indeed help to improve the performance of RDI. In disk imaging, RDI can reveal more disk features and provide a more robust recovery of the disk morphology. We resolve 33 disks in total intensity (19 planet-forming disks and 14 debris disks), and 4 of them can only be detected with RDI. Two disks are resolved in scattered light for the first time. Three disks are detected in total intensity for the first time. The master reference library we built in this work can be easily implemented into legacy or future SPHERE surveys to perform RDI, achieving better performance than that of ADI. To obtain optimal RDI gains over ADI, we recommend future observations be carried out under seeing conditions of 0.6"-0.8".

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arXiv2022

Efficient Dust Radial Drift Around Young Intermediate-mass Stars

The radial velocities and direct imaging observations of exoplanets have suggested that the frequency of giant planets may decrease for intermediate-mass stars ($2.5-8\,M_\odot$). The key mechanism that could hinder their formation remains unclear. From a theoretical point of view, planet formation around intermediate-mass stars may take place on longer timescales, which -- coupled with fast migration and efficient photoevaporation -- may prevent planetary formation in these environments. In this letter, we investigate the temporal evolution of the radial drift for dust particles in disks when stellar evolution is taken into account. We demonstrate that the particle drift velocity around intermediate-mass stars sharply increases after 1$-$2 Myr, potentially forming a difficult barrier to overcome in the first steps of planet formation. This high radial drift could explain the lack of disk detections around intermediate-mass stars older than 3$-$4 Myr, as opposed to low-mass stars ($<2.5\,M_\odot$), where the drift may not be the most impactful factor for the disk evolution. Future high-resolution images of these disks can help us to explain why planets around intermediate-mass stars may be rare. In addition, we can explore whether the role of efficient dust radial drift does in fact hinder planet formation around intermediate-mass stars -- or otherwise.

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arXiv2021

High-resolution ALMA observations of V4046Sgr: a circumbinary disc with a thin ring

The nearby V4046 Sgr spectroscopic binary hosts a gas-rich disc known for its wide cavity and dusty ring. We present high resolution ($\sim$20 mas or 1.4 au) ALMA observations of the 1.3mm continuum of V4046 Sgr which, combined with SPHERE--IRDIS polarised images and a well-sampled spectral energy distribution (SED), allow us to propose a physical model using radiative transfer (RT) predictions. The ALMA data reveal a thin ring at a radius of 13.15$\pm$0.42 au (Ring13), with a radial width of 2.46$\pm$0.56 au. Ring13 is surrounded by a $\sim$10 au-wide gap, and it is flanked by a mm-bright outer ring (Ring24) with a sharp inner edge at 24 au. Between 25 and $\sim$35 au the brightness of Ring24 is relatively flat and then breaks into a steep tail that reaches out to $\sim$60 au. In addition, central emission is detected close to the star which we interpret as a tight circumbinary ring made of dust grains with a lower size limit of 0.8 mm at 1.1 au. In order to reproduce the SED, the model also requires an inner ring at $\sim$5 au (Ring5) composed mainly of small dust grains, hiding under the IRDIS coronagraph, and surrounding the inner circumbinary disc. The surprisingly thin Ring13 is nonetheless roughly 10 times wider than its expected vertical extent. The strong near-far disc asymmetry at 1.65 $μ$m points at a very forward-scattering phase function and requires grain radii of no less than 0.4 $μ$m.

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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

Near-IR observations of the young star [BHB2007]-1: A sub-stellar companion opening the gap in the disk

The presence of planets or sub-stellar objects still embedded in their native protoplanetary disks is indirectly suggested by disk sub-structures like gaps, cavities, and spirals. However, these companions are rarely detected. We present VLT/NACO high-contrast images in $J$, $H$, $K_S$, and $L^{\prime}$ band of the young star [BHB2007]-1 probing the inclined disk in scattered light and revealing the probable presence of a companion. The point source is detected in the $L^{\prime}$ band in spatial correspondence with complementary VLA observations. This object is constrained to have a mass in the range of 37-47 M$_{Jup}$ and is located at 50 au from the central star, inside the 70 au-large disk cavity recently imaged by ALMA, that is absent from our NACO data (down to 20 au). This mass range is compatible with the upper end derived from the size of the ALMA cavity. The NIR disk brightness is highly asymmetric around the minor axis, with the southern side 5.5 times brighter than the northern side. The constant amount of asymmetry across all wavelengths suggests that it is due to a shadow cast by a misaligned inner disk. The massive companion that we detect could, in principle, explain the possible disk misalignment, as well as the different cavity sizes inferred by the NACO and ALMA observations. The confirmation and characterization of the companion is entrusted to future observations.

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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

On the diversity of asymmetries in gapped protoplanetary disks

Protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. These disks show asymmetries and rings in the millimeter continuum, caused by dust trapping in pressure bumps, and potentially vortices or horseshoes. The origin of the asymmetries and their diversity remains unclear. We present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by CO isotopologue data. We compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk, and find that the asymmetries correspond to higher Stokes numbers or low gas surface density. We discuss which asymmetric structures can be explained by a horseshoe, a vortex or spiral density waves. Second, we reassess the gas gap radii from the $^{13}$CO maps, which are about a factor 2 smaller than the dust ring radii, suggesting that companions in these disks are in the brown dwarf mass regime ($\sim 15-50 M_{\rm Jup}$) or in the Super-Jovian mass regime ($\sim 3-15 M_{\rm Jup}$) on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions ($q>$0.05) for the majority of the sample at the gap location, but it remains possible at even smaller radii. Third, we find that spiral arms in scattered light images are primarily detected around high luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass.

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arXiv2020

Dynamical Evidence of a Spiral Arm--Driving Planet in the MWC 758 Protoplanetary Disk

More than a dozen young stars host spiral arms in their surrounding protoplanetary disks. The excitation mechanisms of such arms are under debate. The two leading hypotheses -- companion-disk interaction and gravitational instability (GI) -- predict distinct motion for spirals. By imaging the MWC 758 spiral arm system at two epochs spanning ${\sim}5$ yr using the SPHERE instrument on the Very Large Telescope (VLT), we test the two hypotheses for the first time. We find that the pattern speeds of the spirals are not consistent with the GI origin. Our measurements further evince the existence of a faint "missing planet" driving the disk arms. The average spiral pattern speed is $0.\!^\circ22\pm0.\!^\circ03$ yr$^{-1}$, pointing to a driver at $172_{-14}^{+18}$ au around a $1.9$ $M_\odot$ central star if it is on a circular orbit. In addition, we witness time varying shadowing effects on a global scale that are likely originated from an inner disk.

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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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arXiv2019

Disks Around T Tauri Stars with SPHERE (DARTTS-S) II: Twenty-one new polarimetric images of young stellar disks

Near-IR polarimetric images of protoplanetary disks enable us to characterize substructures that might be due to the interaction with (forming) planets. The available census is strongly biased toward massive disks around old stars, however. The DARTTS program aims at alleviating this bias by imaging a large number of T Tauri stars with diverse properties. In this work, we present new SPHERE images of 21 circumstellar disks, which is the largest sample released to date. The targets of this work are significantly younger than those published thus far with polarimetric near-IR (NIR) imaging. Scattered light is unambiguously resolved in 11 targets, and some polarized unresolved signal is detected in 3 additional sources. Some disk substructures are detected. However, the paucity of spirals and shadows from this sample reinforces the trend according to which these NIR features are associated with Herbig stars, either because they are older or more massive. Furthermore, disk rings that are apparent in ALMA observations of some targets do not appear to have corresponding detections with SPHERE. Inner cavities larger than 15 au are also absent from our images, even though they are expected from the spectral energy distribution. On the other hand, 3 objects show extended filaments at larger scale that are indicative of strong interaction with the surrounding medium. All but one of the undetected disks are best explained by their limited size (less than 20 au), and the high occurrence of stellar companions in these sources suggests an important role in limiting the disk size. One undetected disk is massive and very large at millimeter wavelengths, implying that it is self-shadowed in the NIR. This work paves the way toward a more complete and less biased sample of scattered-light observations, which is required to interpret how disk features evolve throughout the disk lifetime.

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arXiv2018

Disks ARound TTauri Stars with Sphere (DARTTS-S) I: Sphere / IRDIS Polarimetric Imaging of 8 prominent TTauri Disks

We present the first part of our DARTTS-S (Disks ARound TTauri Stars with SPHERE) survey: Observations of 8 TTauri stars which were selected based on their strong (sub-)mm excesses using SPHERE / IRDIS polarimetric differential imaging (PDI) in the J and H bands. All observations successfully detect the disks, which appear vastly different in size, from $\approx$80 au in scattered light to $>$400 au, and display total polarized disk fluxes between 0.06% and 0.89% of the stellar flux. For five of these disks, we are able to determine the three-dimensional structure and the flaring of the disk surface, which appears to be relatively consistent across the different disks, with flaring exponents $α$ between $\approx$1.1 and $\approx$1.6. We also confirm literature results w.r.t. the inclination and position angle of several of our disk, and are able to determine which side is the near side of the disk in most cases. While there is a clear trend of disk mass with stellar ages ($\approx$1 Myr to $>$10 Myr), no correlations of disk structures with age were found. There are also no correlations with either stellar mass or sub-mm flux. We do not detect significant differences between the J and H bands. However, we note that while a high fraction (7/8) of the disks in our sample show ring-shaped sub-structures, none of them display spirals, in contrast to the disks around more massive Herbig Ae/Be stars, where spiral features are common.

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arXiv2018

Evolution of protoplanetary disks from their taxonomy in scattered light: spirals, rings, cavities, and shadows

The variety of observed protoplanetary disks in polarimetric light motivates a taxonomical study to constrain their evolution and establish the current framework of this type of observations. We classified 58 disks with available polarimetric observations into six major categories (Ring, Spiral, Giant, Rim, Faint, and Small disks) based on their appearance in scattered light. We re-calculated the stellar and disk properties from the newly available GAIA DR2 and related these properties with the disk categories. More than a half of our sample shows disk sub-structures. For the remaining sources, the absence of detected features is due to their faintness, to their small size, or to the disk geometry. Faint disks are typically found around young stars and typically host no cavity. There is a possible dichotomy in the near-IR excess of sources with spiral-disks (high) and ring-disks (low). Like spirals, shadows are associated with a high near-IR excess. If we account for the pre-main sequence evolutionary timescale of stars with different mass, spiral arms are likely associated to old disks. We also found a loose, shallow declining trend for the disk dust mass with time. Protoplanetary disks may form sub-structures like rings very early in their evolution but their detectability in scattered light is limited to relatively old sources (more than 5 Myr) where the recurrently detected disk cavities allow to illuminate the outer disk. The shallow decrease of disk mass with time might be due to a selection effect, where disks observed thus far in scattered light are typically massive, bright transition disks with longer lifetime than most disks. Our study points toward spirals and shadows being generated by planets of fraction-to-few Jupiter masses that leave their (observed) imprint on both the inner disk near the star and the outer disk cavity.

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arXiv2017

Three years of SPHERE: the latest view of the morphology and evolution of protoplanetary discs

Spatially resolving the immediate surroundings of young stars is a key challenge for the planet formation community. SPHERE on the VLT represents an important step forward by increasing the opportunities offered by optical or near-infrared imaging instruments to image protoplanetary discs. The Guaranteed Time Observation Disc team has concentrated much of its efforts on polarimetric differential imaging, a technique that enables the efficient removal of stellar light and thus facilitates the detection of light scattered by the disc within a few au from the central star. These images reveal intriguing complex disc structures and diverse morphological features that are possibly caused by ongoing planet formation in the disc. An overview of the recent advances enabled by SPHERE is presented.

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arXiv2017

Variable dynamics in the inner disk of HD 135344B revealed with multi-epoch scattered light imaging

We present multi-epoch VLT/SPHERE observations of the protoplanetary disk around HD 135344B (SAO 206462). The $J$-band scattered light imagery reveal, with high spatial resolution ($\sim$41 mas, 6.4 au), the disk surface beyond $\sim$20 au. Temporal variations are identified in the azimuthal brightness distributions of all epochs, presumably related to the asymmetrically shading dust distribution in the inner disk. These shadows manifest themselves as narrow lanes, cast by localized density enhancements, and broader features which possibly trace the larger scale dynamics of the inner disk. We acquired visible and near-infrared photometry which shows variations up to 10% in the $JHK$ bands, possibly correlated with the presence of the shadows. Analysis of archival VLTI/PIONIER $H$-band visibilities constrain the orientation of the inner disk to $i = 18.2°^{+3.4}_{-4.1}$ and ${\rm PA} = 57.3°\pm 5.7°$, consistent with an alignment with the outer disk or a minor disk warp of several degrees. The latter scenario could explain the broad, quasi-stationary shadowing in N-NW direction in case the inclination of the outer disk is slightly larger. The correlation between the shadowing and the near-infrared excess is quantified with a grid of radiative transfer models. The variability of the scattered light contrast requires extended variations in the inner disk atmosphere ($H/r \lesssim 0.2$). Possible mechanisms that may cause asymmetric variations in the optical depth ($Δτ\lesssim1$) through the atmosphere of the inner disk include turbulent fluctuations, planetesimal collisions, or a dusty disk wind, possibly enhanced by a minor disk warp. A fine temporal sampling is required to follow day-to-day changes of the shadow patterns which may be a face-on variant of the UX Orionis phenomenon.

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arXiv2017

Evolution of protoplanetary disks from their taxonomy in scattered light: Group I vs. Group II

High-resolution imaging reveals a large morphological variety of protoplanetary disks. To date, no constraints on their global evolution have been found from this census. An evolutionary classification of disks was proposed based on their IR spectral energy distribution, with the Group I sources showing a prominent cold component ascribed to an earlier stage of evolution than Group II. Disk evolution can be constrained from the comparison of disks with different properties. A first attempt of disk taxonomy is now possible thanks to the increasing number of high-resolution images of Herbig Ae/Be stars becoming available. Near-IR images of six Group II disks in scattered light were obtained with VLT/NACO in Polarimetric Differential Imaging, which is the most efficient technique to image the light scattered by the disk material close to the stars. We compare the stellar/disk properties of this sample with those of well-studied Group I sources available from the literature. Three Group II disks are detected. The brightness distribution in the disk of HD163296 indicates the presence of a persistent ring-like structure with a possible connection with the CO snowline. A rather compact (less than 100 AU) disk is detected around HD142666 and AK Sco. A taxonomic analysis of 17 Herbig Ae/Be sources reveals that the difference between Group I and Group II is due to the presence or absence of a large disk cavity (larger than 5 AU). There is no evidence supporting the evolution from Group I to Group II. Group II are not evolved version of the Group I. Within the Group II disks, very different geometries (both self-shadowed and compact) exist. HD163296 could be the primordial version of a typical Group I. Other Group II, like AK Sco and HD142666, could be smaller counterpart of Group I unable to open cavities as large as those of Group I.

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arXiv2016

Vortices and spirals in the HD135344B transition disk

In recent years spiral structures have been seen in scattered light observations and signs of vortices in millimeter images of protoplanetary disks, both probably linked with the presence of planets. We present ALMA Band 7 (335 GHz or 0.89 mm) continuum observations of the transition disk HD135344B at unprecedented spatial resolution of 0.16", using superuniform weighting. The data show that the asymmetric millimeter dust ring seen in previous work actually consists of an inner ring and an outer asymmetric structure. The outer feature is cospatial with the end of one of the spiral arms seen in scattered light, but the feature itself is not consistent with a spiral arm due to its coradiance. We propose a new possible scenario to explain the observed structures at both wavelengths. Hydrodynamical simulations show that a massive planet can generate a primary vortex (which dissipates at longer timescales, becoming an axisymmetric ring) and trigger the formation of a second generation vortex further out. Within this scenario the two spiral arms observed at scattered light originate from a planet at ~30 AU and from the secondary vortex at ~75 AU rather than a planet further out as previously reported.

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