arXiv subjects

S. Facchini

Publications and source records attributed to S. Facchini.

At least 19 recordsLinked to original sources

arXiv2026

A Quiet Host in an Active Planet-Forming Disk: Optical Spectroscopy of WISPIT 2

WISPIT 2 is a young pre-main-sequence star hosting a multi-ringed transition disk and two directly imaged protoplanets, including the accreting WISPIT 2b, making it the closest known analogue to PDS 70. We present the first optical spectrum of its central star, obtained with HFOSC on the 2-m Himalayan Chandra Telescope, and derive its atmospheric parameters, test its youth, and constrain its accretion state. We analyse low-resolution spectra with iSpec and validate the pipeline at HFOSC resolution against Gaia FGK Benchmark Stars and K-type pre-main-sequence templates. We measure T_eff = 4551 +/- 150 K, log g = 4.32 +/- 0.18, and a low-resolution, model-dependent global metallicity [M/H] = -0.17 +/- 0.16. The surface gravity and Li I equivalent width support the pre-main-sequence nature of the host. H-alpha remains in net absorption but is partially filled by weak emission at only 1.5-2.0 sigma, approximately 1.1 dex below the expected chromospheric-noise level and therefore consistent with chromospheric activity rather than detectable accretion. We place a 95% upper limit on the stellar accretion rate of 3.6 x 10^-11 solar masses per year, below even the lowest monitored value for PDS 70 and implying a host-to-planet accretion-rate ratio below approximately 18. Both known double-protoplanet hosts therefore show strongly suppressed or undetectable stellar accretion. Larger spectroscopic samples are needed to determine whether this is common in multi-protoplanet transition disks.

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arXiv2026

Extending dynamical mass measurements: probing GI as a possible origin of mm-dust spirals

Constraining the total mass of protoplanetary disks is crucial to determine the availability of material for planet formation. Yet, providing accurate and precise measurements of the disk mass is challenging. Investigating the gas dynamics is a powerful, tracer-independent method to precisely characterize disk masses. By fitting the velocity rotation curves of different molecular tracers with an accurate model including the disk thermal stratification and self-gravity, we constrain the stellar masses, disk masses, and scale radii for the disks around HD 97048 and WaOph 6. We obtain $M_\star=2.226 ^{+0.054}_{-0.049}\ M_\odot$, $M_\mathrm{d}=0.3 ^{+0.055}_{-0.061}\ M_\odot$ and $R_\mathrm{c}=172 ^{+24}_{-14}$ au for HD 97048, and $M_\star=0.956\ ^{+0.006}_{-0.006}\ M_\odot$, $M_\mathrm{d}=0.21 ^{+0.045}_{-0.038}\ M_\odot$ and $R_\mathrm{c}=647 ^{+193}_{-155}$ au for WaOph 6. We also measure the corresponding gas-to-dust and disk-to-star mass ratios. We efficiently extend the dynamical method to characterize embedded sources exhibiting features of absorption, for which a careful analysis is required to avoid biases in the retrieved velocity profiles. We prove the importance of including a beam smearing correction to the curves: if not, this observational effect can systematically bias the velocity profiles, altering the disk mass estimates up to $\sim45\%$. We provide comprehensive estimates of the systematic uncertainties on the best-fit parameters by bootstrapping over both the retrieved geometry and 2D thermal structure of the two disks: the overall uncertainty on the disk masses is $\sim20\%$. Finally, we investigate the connection between disk stability and the appearance of spiral morphologies in the mm continuum emission, by comparing the Toomre parameter of all dynamically weighed disks to date, showing that disks with mm-dust spirals have systematically lower values of Q.

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arXiv2026

X-Shooter survey of disk accretion in Upper Scorpius II. A lack of correlation between accretion rates and disk properties

The evolution of protoplanetary discs is intertwined with the process of planet formation, growth and migration. Studies of nearby star forming regions of different ages and properties provide the necessary information needed to understand the processes dictating their evolution. This paper presents the results of a spectroscopic study of the stellar and accretion properties of a large sample of 127 stars with protoplanetary discs in the Upper Scorpius region with disc dust masses inferred from ALMA continuum measurements. The accretion luminosity is derived from the excess UV continuum emission with respect to the photospheric and chromospheric one self-consistently with the stellar spectral types, extinction and luminosity, using FRAPPE. We apply a new method to evaluate upper limits to the accretion luminosity. In ~50% of cases we evaluate upper limits on the accretion luminosity, either because the S/N of the data is insufficient or because the measured value of the accretion luminosity is below the estimate of the emission due to chromospheric activity. The results show that the mass accretion rate has a weak correlation with the stellar mass, while no correlation is observed with disc properties such as dust mass or gas disc radius. The dispersion is larger than what is found in younger star forming regions such as Lupus and Cham. I, and suggests a fading of the correlations with age. We find no evidence that membership to Upper Scorpius sub-groups, nor the properties of known binary or transition discs can explain the origin of this dispersion. The lack of correlation and large dispersion of accretion rates challenge the current expectations of evolutionary models. The observed properties point to a decoupling of the inner and outer disc by the age of Upper Scorpius and a fading of the relations observed in younger star forming regions.

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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{\deg} 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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arXiv2026

The Circumbinary Disk of HD 34700A: I. CO gas kinematics indicate spirals, infall, and vortex motions

We present the first high-resolution ($\sim$ 0.14") Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 dust continuum and CO molecular line emission observations of the quadruple system HD 34700. In particular, HD 34700AaAb is a spectroscopic binary ($M_{\rm{bin}}=4\,M_\odot$) surrounded by two low-mass companions at large separations. Its circumbinary disk is highly substructured, featuring numerous spiral arms and a large cavity observed in infrared (IR) scattered light. We analyzed the CO line channel and intensity moment maps. By fitting a Keplerian model to the line channel emission, we identified the residual motions and conducted a line spectra analysis. We resolved an asymmetric continuum crescent on top of a dust ring at 0.39" (138 au), colocated with the IR ring. The CO molecule line emissions trace a smaller cavity in gas, whose edge aligns with the inner rim of the ring detected in H$\alpha$ emission at 0.20" (65 au). The $^{12}$CO line emission and kinematics trace highly non-Keplerian motions ($\sim0.1\Delta\upsilon_{\rm kep}$), and these CO spiral features align well with the spiral structures in scattered light. The $^{12}$CO line spectra analysis reveals a streamer above the southeastern disk plane, likely falling onto the disk. The $^{13}$CO and C$^{18}$O kinematics largely follow the disk's underlying Keplerian rotation, while $^{13}$CO exhibits tentative signs of anticyclonic vortex flows at the continuum crescent location. Our multimolecular line study suggests that the circumbinary disk of HD 34700A is highly perturbed in its upper layers, possibly warped and influenced by infalling material. While late-stage infall may account for the IR spirals and the formation of the vortex through Rossby wave instability, an embedded massive companion within the cavity may also contribute to these features.

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arXiv2025

Observations of sulfuretted species in HL Tau

Protoplanetary disks inherit their chemical composition from their natal molecular cloud, but the extent to which this material is preserved versus reset through chemical reprocessing remains an open question. Understanding this balance is a major topic in astrochemistry. Comparing the chemical composition of the envelope and the protoplanetary disk is key to solving the topic. The goal of this paper is to investigate the chemical differences between the disk and the surrounding envelope by comparing the column density ratios of a few selected species in each region. The source we focus on is HL Tau. We present new NOEMA observations of HL Tau targeting the following species: CS, H2CO, H2S, and SO2. We produced zeroth-, first-, and second-moment maps for the species where emission was detected and used them to analyze the spatial distribution and kinematic properties of the different molecules in the disk and the envelope. We derived the column densities and compared the values derived for the envelope and disk. We also computed the rotational diagram for the SO2 detected transitions. Assuming two different temperature regimes, 17 and 58 K, we derived column densities for the species surveyed in the disk and compared them with values derived for the envelope. We find large differences in the derived column density ratios of the surveyed molecules, especially for N(CS)/N(H2S), which is 40 to 50 times larger in the envelope. We attribute these variations to the different excitation and UV-irradiation regimes in the disk and envelope. We also note strong gradients in the ratios between different positions of the disk and tentatively attribute them to different levels of turbulence at different azimuths. The observed differences in molecular ratios in the envelope and the disk are suggestive of chemical reprocessing of the gas during the formation and evolution of the protoplanetary disk.

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arXiv2025

Zooming into the water snowline: high resolution water observations of the HL Tau disk

Water is one of the central molecules for the formation and habitability of planets. In particular, the region where water freezes-out, the water snowline, could be a favorable location to form planets in protoplanetary disks. We use high resolution ALMA observations to spatially resolve H$_2$O, H$^{13}$CO$^+$ and SO emission in the HL Tau disk. A rotational diagram analysis is used to characterize the water reservoir seen with ALMA and compare this to the reservoir visible at mid- and far-IR wavelengths. We find that the H$_2$O 183 GHz line has a compact central component and a diffuse component that is seen out to ~75 au. A radially resolved rotational diagram shows that the excitation temperature of the water is ~350 K independent of radius. The steep drop in the water brightness temperature outside the central beam of the observations where the emission is optically thick is consistent with the water snowline being located inside the central beam ($\lesssim 6$ au) at the height probed by the observations. Comparing the ALMA lines to those seen at shorter wavelengths shows that only 0.02%-2% of the water reservoir is visible at mid- and far-IR wavelengths, respectively, due to optically thick dust hiding the emission whereas 35-70% is visible with ALMA. An anti-correlation between the H$_2$O and H$^{13}$CO$^+$ emission is found but this is likely caused by optically thick dust hiding the H$^{13}$CO$^+$ emission in the disk center. Finally, we see SO emission tracing the disk and for the first time in SO a molecular outflow and the infalling streamer out to ~2". The velocity structure hints at a possible connection between the SO and the H$_2$O emission. Spatially resolved observations of H$_2$O lines at (sub-)mm wavelengths provide valuable constraints on the location of the water snowline, while probing the bulk of the gas-phase reservoirs.

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arXiv2025

Direct Measurement of Extinction in a Planet-Hosting Gap

Recent disk observations have revealed multiple indirect signatures of forming gas giant planets, but high-contrast imaging has rarely confirmed the presence of the suspected perturbers. Here, we exploit a unique opportunity provided by the background star AS209bkg, which shines through a wide annular gap in the AS209 disk, to perform transmission spectrophotometry and directly measure the extinction from gap material for the first time. By combining new VLT/SPHERE and JWST/NIRCam observations with archival HST data from 2005, we model the spectral energy distribution (SED) of AS209bkg over a 19-year baseline. We find that the SED and its variability are best explained by increasing extinction along the line of sight as AS209bkg approaches the gap edge in projection. The extinction is best described by a combination of ISM-like extinction component and a grey extinction component. This points to the presence of grains in the disk outer gap that are larger than in the ISM. We find that the extinction in the gap at $\lambda\sim4.0~\mu$m is $A_{4\,\mu\mathrm{m}} = 2.7^{+0.7}_{-0.7}$ mag, while at H$\alpha$ ($\lambda=0.656~\mu$m), where most searches for accretion signatures take place, the extinction could be as high as $A_\mathrm{H\alpha} = 4.2^{+0.9}_{-1.2}$ mag ($A_V=4.6^{+1.0}_{-1.3}$ mag). This suggests that even wide, deep gaps can significantly obscure emission from protoplanets, even those following a hot-start evolutionary model. Our extinction measurements help reconcile the discrepancy between ALMA-based predictions of planet-disk interactions and the non-detections from sensitive optical and near-infrared imaging campaigns.

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arXiv2025

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): Evidence of planet-disk interaction in the 2MASSJ16120668-3010270 system

The architectures of exoplanet systems are likely set during the initial planet-formation phase in the circumstellar disk. To understand this process, we have to study the earliest phases of planet formation. Complex sub-structures, believed to be driven by embedded planets, have been detected in a significant portion of disks observed at high angular resolution. We aim to extend the sample of such disks to low stellar masses and to connect the disk morphology to the expected proto-planet properties. We resolve the disk in the 2MASSJ16120668-3010270 system for the first time in scattered near-infrared light on scales of 10 au using VLT/SPHERE and reveal an exceptionally structured disk. We find an inner disk (inside 40 au) with two spiral arms, separated by a gap from an outer ring. By comparison with hydrodynamic models, we find that these structures are consistent with the presence of an embedded gas giant with a mass range between 0.1 and 5 MJup depending on the employed model. Our SPHERE observations find a tentative candidate point source within the disk gap, which may be consistent with this mass range if it indeed traces thermal emission by an embedded planet. This interpretation is somewhat strengthened by the proximity of this signal to compact mm continuum emission in the disk gap, which may trace circumplanetary material. It is, however, unclear if this tentative companion candidate could be responsible for the observed disk gap size, given its close proximity to the inner disk. The 2MASSJ16120668-3010270 system is one of only a few systems that shows this exceptional morphology of spiral arms located inside a scattered light gap and ring. We speculate that this may have to do with a higher disk viscosity compared with other systems such as PDS 70.

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arXiv2025

A correlation between accretion and outflow rates for Class II Young Stellar Objects with full and transition disks

Magnetothermal (MHD) winds and jets originate in a wide range of regions of protoplanetary disks (1-30 au) and are thought to be the primary mechanisms driving accretion onto the central star. One indirect signature of these processes is the free-free emission from ionized gas close to the star. We analyze a sample of 31 Class II disks: 18 full disks (FD) and 13 transition disks (TD). All sources show evidence of excess free-free emission over the contribution of the thermal dust. We investigate the origin of this emission and whether it is associated with other observables. We first analyzed a sample of objects in Taurus, exploring correlations with the properties of the central star, the disk, and other disk-wind tracers. We compared our findings with a sample of TD for which free-free emission was shown to be likely associated with an MHD-wind/jet. We found no correlation between the detected free-free emission and either the X-ray or the [OI]6300A line properties. We found a strong correlation between the ionized mass loss rate, as inferred from the free-free emission, and the accretion rate, suggesting that free-free emission in FD is associated with an MHD-wind/jet. The detected free-free emission in both TD and FD is likely similarly associated with an ionized gas close to the star from an MHD-wind/jet. The free-free emission detected in TD shows hints of shallower correlations with accretion properties than in FD. Whereas the efficiency in transforming accretion into outflow might differ in TD and FD, considering the correlations between free-free emission and accretion properties, this difference could simply result from a bias toward strong accretors in the TD sample. Therefore, observations of a more complete and uniform sample are necessary to determine whether this change in correlations holds only for strong accretors or for TD in general.

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arXiv2025

Protoplanetary disk insights from the first ERIS/APP survey at 4 {\mu}m

We present high-contrast imaging observations of seven protoplanetary disks at 4um using the ERIS on the VLT. This study focuses on detecting scattered light from micron-sized dust particles and assessing the potential of the vAPP coronagraph for disk and planet characterization. Observations were performed in pupil-stabilized mode with the vAPP coronagraph. Data were reduced using reference differential imaging and angular differential imaging techniques, incorporating principal component analysis for point-source detection. Contrast curves and detection limits were computed for planetary companions and disk features. The infrared disk signal was resolved in all systems, with first-time 4um detections around AS 209 and Elias 2-24, revealing mostly axisymmetric structures extending up to 60au. Two gaps were detected in the radial profiles of TW Hya (22au, 35au) and AS 209 (50au, 100au). For Elias 2-24, scattered light emission matched ALMA observations of inner disk structures, marking their first mid-infrared detection. In the case of HD 100546, the vAPP uncovered flared disk structures and faint spiral arms consistent with previous observations. HD 163296 shows a bright inner dust ring, confirming disk asymmetries and features, but we did not detect any planet candidate within the achieved contrast limits. The disk around PDS 70 exhibits clear features, with faint structures detected within the cavity. The observations achieved contrasts enabling the detection of planets down to 800 K, but no companions were detected, implying either low-mass planets, cooler formation scenarios, or a large dust extinction of Av>20 mag. The vAPP performed robustly for imaging structures in protoplanetary disks at 4um, providing critical insights into disk morphology and constraints on planet formation processes. No planetary-mass companions with temperatures >1000K are present in our sample.

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arXiv2025

Radial variations in nitrogen, carbon, and hydrogen fractionation in the PDS 70 planet-hosting disk

Element isotopic ratios are powerful tools to reconstruct the journey of planetary material, from the parental molecular cloud to protoplanetary disks, where planets form and accrete their atmosphere. Radial variations in isotopic ratios in protoplanetary disks reveal local pathways which can critically affect the degree of isotope fractionation of planetary material. In this work we present spatially-resolved profiles of the 14N/15N, 12C/13C, and D/H isotopic ratios of the HCN molecule in the PDS 70 disk, which hosts two actively-accreting giant planets. ALMA high spatial resolution observations of HCN, H13CN, HC15N, and DCN reveal radial variations of fractionation profiles. We extract the HCN/HC15N ratio out to ~120 au, which shows a decreasing trend outside the inner cavity wall of the PDS 70 disk located at ~50 au. We suggest that the radial variations observed in the HCN/HC15N ratio are linked to isotope selective photodissociation of N2. We leverage the spectrally resolved hyperfine component of the HCN line to extract the radial profile of the HCN/H13CN ratio between ~40 and 90 au, obtaining a value consistent with the ISM 12C/13C ratio. The deuteration profile is also mostly constant throughout the disk extent, with a DCN/HCN ratio ~0.02, in line with other disk-averaged values and radial profiles in disks around T Tauri stars. The extracted radial profiles of isotopologue ratios show how different fractionation processes dominate at different spatial scales in the planet-hosting disk of PDS 70.

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arXiv2025

The two-dimensional pressure structure of the HD 163296 protoplanetary disk as probed by multi-molecule kinematics

[Abridged] Gas kinematics is a new and unique way to study planet-forming environments by an accurate characterization of disk velocity fields. High angular resolution ALMA observations allow deep kinematical analysis of disks, by observing molecular line emission at high spectral resolution. In particular, rotation curves are key tools for studying the disk pressure structure and estimating fundamental disk parameters, such as mass and radius. In this work, we explore the potential of a multi-molecule approach to gas kinematics to provide a 2D characterization of the HD 163296 disk. From the high quality data of the MAPS Large Program we extracted the rotation curves of rotational lines from seven distinct molecular species, spanning a wide radial and vertical range. To obtain reliable rotation curves for hyperfine lines, we extended standard methodologies to fit multi-component line profiles. We then sampled the likelihood of a thermally stratified model that reproduces all the rotation curves simultaneously, taking into account the molecular emitting layers and disk thermal structure. We obtained dynamical estimates of the stellar mass $M_\star=1.89$ M$_\odot$, the disk mass $M_\text{d}=0.12$ M$_\odot$, and scale radius $R_\text{c}=143$ au. We also explore how rotation curves and the parameter estimates depend on the adopted emitting layers: the disk mass proves to be the most affected by these systematics, yet the main trends we find do not depend on the adopted parameterization. Finally, we investigated the impact of thermal structure on gas kinematics, showing that the thermal stratification can efficiently explain the measured rotation velocity discrepancies between tracers at different heights. Our results show that such a multi-molecule approach, tracing a large range of emission layers, can provide unique constraints on the ($R,z$) pressure structure of protoplanetary disks.

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arXiv2024

A New Look at Disk Winds and External Photoevaporation in the $\sigma$-Orionis Cluster

Disk winds play a crucial role in the evolution of protoplanetary disks. Typical conditions for star and planet formation are in regions with intermediate or strong UV radiation fields produced by massive stars. The $\sigma$-Orionis cluster is the ideal site to study disk winds under these conditions; its outer parts can be used to study disk evolution, while its innermost regions to study the effect of external irradiation. For this, we analyze the $\rm [OI]\,\lambda$6300, $\rm [NII]\,\lambda$6583, and $\rm [SII]\,\lambda$6731,$\lambda$6716 lines using high-resolution MIKE spectra of 27 classical T Tauri stars and complemented by intermediate-resolution X-shooter data. We decompose the line profiles into multiple Gaussian components. We calculated luminosities, line ratios, and kinematic properties of these components. We found that the $\rm [OI]\,\lambda$6300 line luminosity and kinematic properties are similar to those found in low-mass star-forming regions (SFRs). The frequency of single-component $\rm [OI]\,\lambda$6300 line profiles reflects the expected evolutionary stage given the intermediate age of $\sigma$-Orionis. This points to internal processes contributing to the line emission. However, the highly irradiated disks do not follow the accretion - [OI] luminosity relation found in low-mass SFRs, and all exhibit single-component line profiles. Line ratios of highly ionized species of [NII] and [SII] show higher ratios than typical values found in low-mass SFRs. The innermost regions of $\sigma$-Orionis are clearly affected by external irradiation, evidenced by the lack of correlation in the accretion - [OI] luminosity relation. The broad line widths of close-in sources, however, indicate a contribution from internal processes, such as magnetohydrodynamical winds and/or internal photoevaporation. This suggests a coevolution of internal and external winds in $\sigma$-Orionis.

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arXiv2024

Binary orbit and disks properties of the RW Aur system using ALMA observations

The dynamical interactions between young binaries can perturb the material distribution of their circumstellar disks, and modify the planet formation process. In order to constrain the impact and nature of the binary interaction in the RW Aur system (bound or unbound), we analyzed the circumstellar material at 1.3 mm wavelengths, as observed at multiple epochs by ALMA. We analyzed the disk properties through parametric visibility modeling, and we used this information to constrain the dust morphology and the binary orbital period. We imaged the dust continuum emission of RW Aur with a resolution of 3 au, and we find that the radius enclosing 90% of the flux (R90%) is 19 au and 14 au for RW Aur A and B, respectively. By modeling the relative distance of the disks at each epoch, we find a consistent trend of movement for the disk of RW Aur B moving away from the disk of RW Aur A at an approximate rate of 3 mas/yr (about 0.5 au/yr in sky-projected distance). By combining ALMA astrometry, historical astrometry, and the dynamical masses of each star, we constrain the RW Aur binary stars to be most likely in a high-eccentricity elliptical orbit with a clockwise prograde orientation relative to RW Aur A, although low-eccentricity hyperbolic orbits are not ruled out by the astrometry. Our analysis does not exclude the possibility of a disk collision during the last interaction, which occurred $295_{-74}^{+21}$ yr ago relative to beginning of 2024. Evidence for the close interaction is found in a tentative warp of 6 deg in the inner 3 au of the disk of RW Aur A, in the brightness temperature of both disks, and in the morphology of the gas emission. A narrow ring that peaks at 6 au around RW Aur B is suggestive of captured material from the disk around RW Aur A.

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arXiv2024

ALMA high-resolution observations unveil planet formation shaping molecular emission in the PDS 70 disk

With two directly detected protoplanets, the PDS 70 system is a unique source in which to study the complex interplay between forming planets and their natal environment. The large dust cavity carved by the two giant planets can affect the disk chemistry, and therefore the molecular emission morphology. On the other hand, chemical properties of the gas component of the disk are expected to leave an imprint on the planetary atmospheres. In this work, we reconstruct the emission morphology of a rich inventory of molecular tracers in the PDS 70 disk, and we look for possible chemical signatures of the two actively accreting protoplanets, PDS b and c. We leverage Atacama Large Millimeter/submillimeter Array (ALMA) band 6 high-angular-resolution and deep-sensitivity line emission observations, together with image and $uv$-plane techniques, to boost the detection of faint lines. We robustly detect ring-shaped emission from $^{12}$CO, $^{13}$CO, C$^{18}$O, H$^{13}$CN, HC$^{15}$N, DCN, H$_2$CO, CS, C$_2$H, and H$^{13}$CO$^{+}$ lines in unprecedented detail. Most of the molecular tracers show a peak of the emission inside the millimeter dust peak. We interpret this as the direct impact of the effective irradiation of the cavity wall, as a result of the planet formation process. Moreover, we have found evidence of an O-poor gas reservoir in the outer disk, which is supported by the observations of bright C-rich molecules, the non-detection of SO, and a lower limit on the $\mathrm{CS/SO}$ ratio of $\sim1$. Eventually, we provide the first detection of the c-C$_3$H$_2$ transitions at 218.73 GHz, and the marginal detection of an azimuthal asymmetry in the higher-energy H$_2$CO (3$_{2,1}$-2$_{2,0}$) line, which could be due to accretion heating near PDS 70b.

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arXiv2024

The SPHERE view of the Chamaeleon I star-forming region

We used VLT/SPHERE to observe 20 systems in the Cha I cloud in polarized scattered light in the near-infrared. We combined the scattered light observations with existing literature data on stellar properties and with archival ALMA continuum data to study trends with system age and dust mass. We also connected resolved near-infrared observations with the spectral energy distributions of the systems. In 13 of the 20 systems included in this study we detected resolved scattered light signals from circumstellar dust. For the CR Cha, CT Cha, CV Cha, SY Cha, SZ Cha, and VZ Cha systems we present the first detailed descriptions of the disks in scattered light. The observations found typically smooth or faint disks, often with little substructure, with the notable exceptions of SZ Cha, which shows an extended multiple-ringed disk, and WW Cha, which shows interaction with the cloud environment. New high S/N K- band observations of the HD 97048 system in our survey reveal a significant brightness asymmetry that may point to disk misalignment and subsequent shadowing of outer disk regions, possibly related to the suggested planet candidate in the disk. We resolve for the first time the stellar binary in the CS Cha system. Multiple wavelength observations of the disk around CS Cha have revealed that the system contains small, compact dust grains that may be strongly settled, consistent with numerical studies of circumbinary disks. We find in our sample that there is a strong anti-correlation between the presence of a (close) stellar companion and the detection of circumstellar material with five of our seven nondetections located in binary systems.

astro-ph.GA↗

arXiv2024

The SPHERE view of the Orion star-forming region

We present SPHERE/IRDIS H-band data for a sample of 23 stars in the Orion Star forming region observed within the DESTINYS (Disk Evolution Study Through Imaging of Nearby Young Stars) program. We use polarization differential imaging in order to detect scattered light from circumstellar dust. From the scattered light observations we characterize the disk orientation, radius and contrast. We analyse the disks in context of the stellar parameters and the environment of the Orion star-forming region. We use ancillary X-shooter spectroscopic observations to characterize the central stars in the systems. We furthermore use a combination of new and archival ALMA mm-continuum observations to characterize the dust masses present in the circumstellar disks. Within our sample we detect extended circumstellar disks in 10 of 23 systems. Of these, three are exceptionally extended (V351 Ori, V599 Ori and V1012 Ori) and show scattered light asymmetries which may indicate perturbations by embedded planets or (in the case of V599 Ori) by an outer stellar companion. Our high resolution imaging observations are also sensitive to close (sub)stellar companions and we detect 9 such objects in our sample of which 5 were previously unknown. We find in particular a possible sub-stellar companion (either a very low mass star or a high mass brown dwarf) 137 au from the star RY Ori. We find a strong anti-correlation between disk detection and multiplicity, with only 2 of our 10 disk detections located in stellar multiple systems. We also find a correlation between scattered light contrast and the millimetre flux suggesting that disks that have a high dust content are typically bright in near-infrared scattered light. Conversely we do not find significant correlations between scattered light contrast of the disks and the stellar mass or age.

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