About Me
Bio: I'm Daniele Fasano and I'm a postdoc at the Osservatorio Astronomico di Roma at Monte Porzio, Rome. I'm part of the LBT/SHARK-VIS instrument team, where I perform both remote and in situ observations with the instrument, while also analysing the data using High Contrast Imaging techniques.
Research Interests: My research focuses on the interactions between newly formed planets and the environment surrounding them. I combine theoretical models, both numerical and and analytical, of planet disc interactions with interferometric observations at sub-millimiter wavelengths using the Atacama Large Millimiter/sub-millimiter Array of continuum dust emission and gas line kinematics. Recently, I started exploring the visible range of the spectra, observing and studying the Halpha emission of accreting planets and the light scattered by the dust grains present in the disc.
Publications: My ADS page
Research
Intro As a PhD student in the PROTOPLANETS group, I started my research projects within the exoALMA collaboration, an ALMA large program performing a planet hunting campaign in the sub-mm regime. I then moved towards my own personal projects studying the dust emission of PDS 70 and HD 34700. I'm now working in the LBT/SHARK-VIS instrument team, currently analysing both old and new data we acquired with this instrument.
I. Planet-driven spirals in protoplanetary discs: Limitations of the semi-analytical theory for observations
Detecting protoplanets during their formation stage is an important but elusive goal of modern astronomy. Kinematic detections via the spiral wakes in the gaseous disc are a promising avenue to achieve this goal. We aim to test the applicability of a commonly used semi-analytical model for planet-induced spiral waves to observations in the low and intermediate planet mass regimes. In contrast to previous works that proposed using the semi-analytical model to interpret observations, in this study we analyse for the first time both the structure of the velocity and density perturbations. We ran a set of FARGO3D hydrodynamic simulations and compared them with the output of the semi-analytic model in the code WAKEFLOW. We divided the disc into two regions. We used the density and velocity fields from the simulation in the linear region, where density waves are excited. In the non-linear region, where density waves propagate through the disc, we then solved Burgers' equation to obtain the density field, from which we computed the velocity field. We find that the velocity field derived from the analytic theory is discontinuous at the interface between the linear and nonlinear regions. After ~0.2 rp from the planet, the behaviour of the velocity field closely follows that of the density perturbations. In the low mass limit, the analytical model is in qualitative agreement with the simulations, although it underestimates the azimuthal width and the amplitude of the perturbations, predicting a stronger decay but a slower azimuthal advance of the shock fronts. In the intermediate regime, the discrepancy increases, resulting in a different pitch angle between the spirals of the simulations and the analytic model. The implementation of a fitting procedure based on the minimisation of intensity residuals is bound to fail due to the deviation in pitch angle between the analytic model and the simulations. In order to apply this model to observations, it needs to be revisited so that it can also account for higher planet masses. ADS link.
II. Inner disc and circumplanetary material in the PDS 70 system
The two giant protoplanets directly imaged in the dust-depleted cavity of PDS 70 offer a unique opportunity to study ongoing planet formation. Both planets have been detected in infrared thermal emission and in Hα, indicating active accretion. We calibrate and analyse archival ALMA Band 6 and 7 observations of PDS 70 from 2019, 2021, and 2023 to search for circumplanetary material and assess its motion. Using 2D visibility modelling of the high-resolution (~0.11"x0.08" in Band 6; ~0.05"x0.05" in Band 7) dust continuum from the outer disc, we subtract the model and image the cavity at multiple epochs. We re-detect compact dust emission around PDS 70 c in all datasets with >3.8σ significance, and tentatively detect emission near PDS 70 b at ~3σ in Band 6, with peak fluxes of 59±17μJy/beam and 46±14μJy/beam. The relative astrometry of the compact emission around PDS 70 c is consistent with the expected position of the planet between 2019-2023. We find a peak flux difference up to 64±34μJy/beam at 1σ, but Bayesian analysis indicates no significant variability. We detect no flux variability in the inner disc. The inferred dust mass near PDS 70 c and in the inner disc ranges from 0.008-0.063M⊕ and 0.04-0.31M⊕, respectively, consistent with prior estimates. Finally, we measure Band 6-7 spectral indices of 2.5±1.2 (PDS 70 c) and 3.2±0.5 (inner disc), suggesting that the inner disc emission is dominated by optically thin dust. ADS link.
II.The circumbinary disc of HD 34700A: II. Analysis of a strong dust asymmetry
ALMA observations have shown that substructures are ubiquitous in protoplanetary discs. A sub-group, the transition discs, shows large cavities and rings in the dust continuum. Among these, some present very high contrast asymmetries possibly due to the presence of vortices. HD 34700A is a binary system featuring a cavity, a ring, and multiple spiral arms detected in scattered light, a prominent crescent in the ALMA continuum, and a complex gas morphology possibly connected with ongoing infall. We present new ALMA band 6 (1.3 mm) continuum images of the circumbinary disc around HD 34700A and compare them with two other systems showcasing high (≳30, measured as the peak-to-azimuthal-average ratio) contrast continuum asymmetries, IRS 48 and HD 142527. We aim to characterise the crescent morphology, discuss their possible origin, and, in the case of the vortex scenario, assess the efficiency of dust trapping in these systems. Methods. We performed visibility modelling of the new high-resolution (0⋅''11 × 0⋅''09) ALMA band 6 continuum data of HD 34700A, together with improved visibility modelling of the other two targets. We detected a 0⋅''46 (161 au) large cavity and resolved a ring with an asymmetric crescent and an extended tail at 0⋅''53 (186 au) with a peak intensity of 1.9 mJybeam−1, corresponding to the second highest contrast (~62) ever detected with ALMA in a protoplanetary disc. We also detected unresolved emission inside the cavity, which we attribute to an inner disc. Our visibility model is in remarkable agreement with the HD 34700A data, featuring only localised residuals in the region of the disc corresponding to the tail of the asymmetry. For HD 142527, we obtained very good overall agreement with the data, recovering both the double peaked asymmetric ring and the inner disc emission. In the case of IRS 48, we recovered the general morphology of the asymmetry, but we could not reproduce the fainter ring. We then ran a hydrodynamic model of a vortex with different dust fluids, reproducing the general morphology observed in the HD 34700A and IRS 48 systems, with the emission around the vortex showing a mild asymmetry between the leading and trailing sides. With a combination of visibility, dust evolution, and hydrodynamical models, we have constrained the morphology of the dust continuum emission of HD 34700A for the first time, and improved existing models for IRS 48 and HD 142527. The high azimuthal contrast of the asymmetries rules out the orbit clustering of eccentric cavities scenario, while the dust evolution models we consider suggest that the vortex scenario is a plausible option. ADS link.
