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Item The vertical structure of debris disks and the impact of gas.(2022-02-16) Olofsson, Johan; Thébault, Philippe; Kral, Quentin; Bayo, Amelia; Boccaletti, Anthony; Godoy, Nicolás; Henning, Thomas; van Holstein, Rob G.; Maucó, Karina; Milli, Julien; Montesinos, Matías; Rein, Hanno; Sefilian, Antranik A.The vertical structure of debris discs provides clues about their dynamical evolution and the collision rate of the unseen planetesimals. Thanks to the ever-increasing angular resolution of contemporary instruments and facilities, we are beginning to constrain the scale height of a handful of debris discs, either at near-infrared or millimeter wavelengths. None the less, this is often done for individual targets only. We present here the geometric modeling of eight discs close to edge-on, all observed with the same instrument (SPHERE) and using the same mode (dual-beam polarimetric imaging). Motivated by the presence of CO gas in two out of the eight discs, we then investigate the impact that gas can have on the scale height by performing N-body simulations including gas drag and collisions. We show that gas can quickly alter the dynamics of particles (both in the radial and vertical directions), otherwise governed by gravity and radiation pressure. We find that, in the presence of gas, particles smaller than a few tens of microns can efficiently settle toward the midplane at the same time as they migrate outward beyond the birth ring. For second generation gas (Mgas ≤ 0.1 M⊕), the vertical settling should be best observed in scattered light images compared to observations at millimeter wavelengths. But if the gas has a primordial origin (Mgas ≥ 1 M⊕), the disc will appear very flat both at near-infrared and sub-mm wavelengths. Finally, far beyond the birth ring, our results suggest that the surface brightness profile can be as shallow as ∼−2.25.Item The protoplanetary disc around HD 169142: circumstellar or circumbinary?(2021-12) Poblete, P. P.; Cuello, N.; Pérez, S.; Marino, S.; Calcino, J.; Macías, E.; Ribas, Á.; Zurlo, A.; Cuadra, J.; Montesinos, Matías; Zúñiga-Fernández, S.; Bayo, A.; Pinte, C.; Ménard, F.; Price, D. J.Stellar binaries represent a substantial fraction of stellar systems, especially among young stellar objects. Accordingly, binaries play an important role in setting the architecture of a large number of protoplanetary discs. Binaries in coplanar and polar orientations with respect to the circumbinary disc are stable configurations and could induce non-axisymmetric structures in the dust and gas distributions. In this work, we suggest that the structures shown in the central region of the protoplanetary disc HD 169142 are produced by the presence of an inner stellar binary and a circumbinary (P-type) planet. We find that a companion with a mass-ratio of 0:1, semi-major axis of 9:9 au, eccentricity of 0.2, and inclination of 90°, together with a 2 MJ coplanar planet on a circular orbit at 45 au reproduce the structures at the innermost ring observed at 1.3 mm and the shape of spiral features in scattered light observations. The model predicts changes in the disc’s dust structure, and star’s astrometric parameters, which would allow testing its veracity by monitoring this system over the next 20 years.Item Morphology of the gas-rich debris disk around HD 121617 with SPHERE observations in polarized light(2023-05) Perrot, Clément; Olofsson, Johan; Kral, Quentin; Thébault, Philippe; Montesinos, Matías; Kennedy, Grant; Bayo, Amelia; Iglesias, Daniela; van Holstein, Rob; Pinte, ChristopheContext. Debris disks are the signposts of collisionally eroding planetesimal circumstellar belts, whose study can put important constraints on the structure of extrasolar planetary systems. The best constraints on the morphology of such disks are often obtained from spatially resolved observations in scattered light. In this paper, we investigate the young (~16 Myr) bright gas-rich debris disk around HD 121617. Aims. We use new scattered light observations from VLT/SPHERE to characterize the morphology and the dust properties of the debris disk. From these properties, we can then derive constraints on the physical and dynamical environment of this system, for which significant amounts of gas have been detected. Methods. The disk morphology is constrained by linear polarimetric observations in the J band. Based on our modeling results and archival photometry, we also model the spectral energy distribution (SED) to put constraints on the total dust mass and dust size distribution. Finally, we explore different scenarios that could explain these new constraints. Results. We present the first resolved image in scattered light of the debris disk around HD 121617. We fit the morphology of the disk, finding a semi-major axis of 78.3 ± 0.2 au, an inclination of 43.1 ± 0.2°, and a position angle of the major axis with respect to north of 239.8 ± 0.3°, which is compatible with the previous continuum and CO detection with ALMA. Our analysis shows that the disk has a very sharp inner edge, possibly sculpted by a yet-undetected planet or gas drag. While less sharp, its outer edge is steeper than expected for an unperturbed disk, which could also be due to a planet or gas drag, but future observations probing the system farther from the main belt would help explore this possibility further. The SED analysis leads to a dust mass of 0.21 ± 0.02 M⊕ and a minimum grain size of 0.87 ± 0.12 μm, smaller than the blowout size by radiation pressure, which is not unexpected for very bright collisionally active disks.Item Cronomoons: origin, dynamics, and light-curve features of ringed exomoons(2021-12-14) Sucerquia, Mario; Alvarado-Montes, Jaime A.; Bayo, Amelia; Cuadra, Jorge; Cuello, Nicolás; Giuppone, Cristian A.; Montesinos, Matías; Olofsson, J.; Schwab, Christian; Spitler, Lee; Zuluaga, Jorge I.In recent years, technical and theoretical work to detect moons and rings around exoplanets has been attempted. The small mass/size ratios between moons and planets means this is very challenging, having only one exoplanetary system where spotting an exomoon might be feasible (i.e. Kepler-1625b i). In this work, we study the dynamical evolution of ringed exomoons, dubbed cronomoons after their similarity with Cronus (Greek for Saturn), and after Chronos (the epitome of time), following the Transit Timing Variations (TTV) and Transit Duration Variation (TDV) that they produce on their host planet. Cronomoons have extended systems of rings that make them appear bigger than they actually are when transiting in front of their host star. We explore different possible scenarios that could lead to the formation of such circumsatellital rings, and through the study of the dynamical/thermodynamic stability and lifespan of their dust and ice ring particles, we found that an isolated cronomoon can survive for time-scales long enough to be detected and followed up. If these objects exist, cronomoons’ rings will exhibit gaps similar to Saturn’s Cassini Division and analogous to the asteroid belt’s Kirkwood gaps, but instead raised due to resonances induced by the host planet. Finally, we analyse the case of Kepler-1625b i under the scope of this work, finding that the controversial giant moon could instead be an Earth-mass cronomoon. From a theoretical perspective, this scenario can contribute to a better interpretation of the underlying phenomenology in current and future observations.Item Characterizing the morphology of the debris disk around the low-mass star GSC 07396-00759(2021-07-15) Adam, C.; Olofsson, J.; van Holstein, R. G.; Bayo, A.; Milli, J.; Boccaletti, A.; Kral, Q.; Ginski, C.; Henning, Th.; Montesinos, Matías; Pawellek, N.; Zurlo, A.; Langlois, M.; Delboulbé, A.; Pavlov, A.; Ramos, J.; Weber, L.; Wildi, F.; Rigal, F.; Sauvage, J.-F.Context. Debris disks have commonly been studied around intermediate-mass stars. Their intense radiation fields are believed to e ciently remove the small dust grains that are constantly replenished by collisions. For lower-mass central objects, in particular M-stars, the dust removal mechanism needs to be further investigated given the much weaker radiation field produced by these objects. Aims. We present new observations of the nearly edge-on disk around the pre-main sequence M-type star GSC 07396-00759, taken with VLT/SPHERE IRDIS in Dual-beam Polarimetric Imaging (DPI) mode, with the aim to better understand the morphology of the disk, its dust properties, and the star-disk interaction via the stellar mass-loss rate. Methods. We model the polarimetric observations to characterize the location and properties of the dust grains using the Henyey-Greenstein approximation of the polarized phase function. We use the estimated phase function to evaluate the strength of the stellar winds. Results. We find that the polarized light observations are best described by an extended and highly inclined disk (i 84:3 0:3) with a dust distribution centered at a radius r0 107 2 au. Our modeling suggests an anisotropic scattering factor g 0:6 to best reproduce the polarized phase function S 12. We also find that the phase function is reasonably reproduced by small micron-sized dust grains with sizes s > 0:3 µm. We discuss some of the caveats of the approach, mainly that our model probably does not fully recover the semi-major axis of the disk and that we cannot readily determine all dust properties due to a degeneracy between the grain size and the porosity. Conclusions. Even though the radius of the disk may be over-estimated, our best fit model not only reproduces well the observations but is also consistent with previous published data obtained in total intensity. Similarly to previous studies of debris disks, we suggest that using a given scattering theory might not be su cient to fully explain key aspects such as the shape of the phase function, or the dust grain size. Taking into consideration the aforementioned caveats, we find that the average mass-loss rate of GSC 07396-00759 can be up to 500 times stronger than that of the Sun, supporting the idea that stellar winds from low-mass stars can evacuate small dust grains in an e cient way.Item The vertical structure of debris disks and the impact of gas.(2022-02-18) Olofsson, Johan; Thébault, Philippe; Kral, Quentin; Bayo, Amelia; Boccaletti, Anthony; Godoy, Nicolás; Henning, Thomas; van Holstein, Rob G.; Maucó, Karina; Milli, Julien; Montesinos, Matías; Rein, Hanno; Sefilian, Antranik A.The vertical structure of debris disks provides clues about their dynamical evolution and the collision rate of the unseen planetesimals. Thanks to the ever-increasing angular resolution of contemporary instruments and facilities, we are beginning to constrain the scale height of a handful of debris disks, either at near-infrared or millimeter wavelengths. Nonetheless, this is often done for individual targets only.We present here the geometric modeling of eight disks close to edge-on, all observed with the same instrument (SPHERE) and using the same mode (dual-beam polarimetric imaging). Motivated by the presence of CO gas in two out of the eight disks, we then investigate the impact that gas can have on the scale height by performing N-body simulations including gas drag and collisions. We show that gas can quickly alter the dynamics of particles (both in the radial and vertical directions), otherwise governed by gravity and radiation pressure. We find that, in the presence of gas, particles smaller than a few tens of microns can efficiently settle toward the midplane at the same time as they migrate outward beyond the birth ring. For second generation gas (𝑀gas ≤ 0.1 𝑀⊕), the vertical settling should be best observed in scattered light images compared to observations at millimeter wavelengths. But if the gas has a primordial origin (𝑀gas ≥ 1 𝑀⊕), the disk will appear very flat both at near-infrared and sub-mm wavelengths. Finally, far beyond the birth ring, our results suggest that the surface brightness profile can be as shallow as ∼ −2.25.