Resumen:

M dwarfs often exhibit magnetic activity that can affect radial velocity (RV) measurements inducing periodic signals that can be misinterpreted as planetary signals. GJ581, an M dwarf hosting a multiplanetary system, shows a reported stellar rotation period of 132 $\pm$ 6.3 days that closely matches the twice and four times the orbital periods of the d (66.6 days) and g (36.6 days) planets, respectively. This similarity raises questions about whether these signals are planets or artifacts of stellar rotation. In this study, we reanalyze the RV time series of GJ581 using publicly available data from HARPS, HIRES and CARMENES, as well as stellar activity indicators. Our aim is to confirm or dismiss the existence of these dubious planetary signatures in the GJ581 system. We computed a Generalized Lomb-Scargle periodogram analysis on the RVs to identify periodic signals. Moreover, we used a Keplerian fit to model the RV time series and Gaussian Process (GP) regression to model the stellar activity indicators. Our analysis shows a stellar rotation period of 132.24 $^{+1.82}_{-1.71}$ days, which aligns with previous studies. However, the RVs temporal stability analysis suggest that the signal d may not be attributed to a planet. Further statistical analysis, such as a simultaneous fit of the RVs with a Keplerian model and the activity indices with a GP, is required to determine the more favorable model for the data. Once our analysis is consistent with previous work, it will be applied to other M dwarfs.

Resumen:

Magnetically driven disk winds (MHD winds) are thought to be one of the main processes involved in the evolution and dispersal of protoplanetary disks, not only affecting the net accretion rate and gas mass loss but also introducing qualitative differences in the disk evolution in contrast with the classic alpha disk model, potentially impacting the formation and architecture of debris disks and planetary systems. We performed numerical simulations for the evolution of gas and dust protoplanetary disks, including viscous dissipation, X-ray photoevaporation and MHD winds, for different stellar masses and initial conditions of the disks. We studied the qualitative features observed in different disks and performed population synthesis in order to constrain the parameters that better reproduce the observables. Different disk wind regimes and viscous alpha parameters were implemented. Our presentation will focus on the obtained results and their correlation with key observables, such as gas accretion rates and lifetimes. The possible implications of these findings for planet and debris disk formation will also be discussed.

Resumen:

Planets form in discs of gas and dust around stars, and continue to grow by accretion of disc material while available. Massive planets clear a gap in their protoplanetary disc, but can still accrete gas through a circumplanetary disc. For high enough accretion rates, the planet should be detectable at infrared wavelengths. As the energy of the gas accreted on to the planet is released, the planet surroundings heat up in a feedback process. We aim to test how this planet feedback affects the gas in the coorbital region and the accretion rate itself. We modified the 2D code FARGO-AD to include a prescription for the accretion and feedback luminosity of the planet and use it to model giant planets on 10 au circular and eccentric orbits around a solar mass star. We find that this feedback reduces but does not halt the accretion on to the planet, although this result might depend on the near-coincident radial ranges where both recipes are implemented. Our simulations also show that the planet heating gives the accretion rate a stochastic variability with an amplitude $\sim10\%$. A planet on an eccentric orbit ($e = 0.1$) presents a similar variability amplitude, but concentrated on a well-defined periodicity of half the orbital period and weaker broad-band noise, potentially allowing observations to discriminate between both cases. Finally, we find that the heating of the co-orbital region by the planet feedback alters the gas dynamics, reducing the difference between its orbital velocity and the Keplerian motion at the edge of the gap, which can have important consequences for the formation of dust rings.

Resumen:

We examine the essential dynamics and thermodynamics underlying gas giant accretion processes. By using high-performance three-dimensional hydrodynamical simulations, we model a Jupiter-mass planet embedded within a viscous gaseous disk. Our methodology incorporates a non-isothermal energy equation, enabling accurate computation of gas and radiative energy diffusion. We further introduce a radiative feedback term, which encapsulates the intrinsic luminosity of the planet, in our computational framework. Our findings reveal the formation of an ionized envelope due to supersonic gas falling towards the planet, extending from 0.2 to 0.5 Hill radii near the planet. This envelope's radius, termed the 'ionization radius', demarcates a transition zone from pre-shock to shock regions, effectively establishing an accretion radius coinciding with the stopping radius. Notably, the stopping radius dictates the envelope's geometrical attributes. The study underscores a robust linear relationship between the planet's accretion rate and the shock luminosity emanating from this region, with conditions propitious for H alpha emission present within the envelope. H alpha emission is an important accretion tracer to detect forming planets; however, the physical conditions near the planet remain controversial. Importantly, our simulations show that the planet's radiative feedback reduces the velocity of the falling gas at higher altitudes ($\sim R_{\rm Hill}$), while simultaneously increasing the accretion rate within the ionization radius. This interaction promotes a 'fallback rate' towards the planet, culminating in enhanced shock luminosity. This research contributes to a better understanding of gas giant accretion's fundamental thermodynamic and dynamical properties, thereby carrying significant implications for detecting forming planets.

Resumen:

The Cassini-Huygens spacecraft took images of the last discovered Saturnian close-in small satellites. Having mean diameters d < 8 km and located in the regions of the ring system, they are Daphins (d=7.8 km), Pallene (d=4.4 km), Methone (d=3.2 km), Anthe (d=1.8 km), Aegaeon (d=0.7 km), S/2009 S 1 (d=0.3 km). The orbits of these small moons suffer complex gravitational perturbations of the non-central field of Saturn and the mid-sized satellites like Mimas. Some of these disturbances are resonant ones and contribute to their orbits' long-term stability. Additionally, all of them are involved gravitationally with the main rings, ring arcs, or diffuse rings. In this talk, we first review the last results in the literature on the orbital dynamics of these small bodies with emphasis on mean-motion resonances and secular perturbations. Next, we show how the resonances play a role in the satellites' survival in long-term time scales of million years. Finally, we apply all these results critically discussing the evolution of the satellites and their rings counterparts after their formation.

Resumen:

Protoplanetary disks are an essential component of the planet formation process. The number and size of planets in a system are directly constrained by the amount of dust and gas in the disk. We present disk dust masses measured using spectral energy distribution (SED) modeling of ~50 disks around T Tauri stars (TTS) in the Serpens star-forming region, including ALMA 1.33mm fluxes from the literature. The disk masses that we calculate are a factor of ~2 higher than those reported in the literature.  We find that this is because most works assume that the disk is optically thin at all mm wavelengths whereas our modeling finds that disks may be partially optically thick at mm wavelengths. Our results show that disks around TTS may have enough material to form planetary systems and could help alleviate the "missing" mass problem where there has been a reported discrepancy between the available mass in protoplanetary disks and the observable mass in observed exoplanet systems.