Browsing by Author "Olofsson, J."

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    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.
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    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.