Water delivery to the TRAPPIST-1 planets

Three of the seven rocky planets (e, f, and g) in TRAPPIST-1 system orbit in the habitable zone of the host star. Therefore, water can be in liquid state at their surface being essential for life. Recent studies suggest that these planets formed beyond the snow line in a water-rich region. The initial water reservoir can be lost during the planet formation due to the stellar activity of the infant low-mass star. However, a potential subsequent water delivery event, like the late heavy bombardment (LHB) in the Solar system, can replenish planetary water reservoirs. To study this water delivery process, we set up a simple model in which an additional 5 -50 M⊕ planet is embedded in a water-rich asteroid belt beyond the snow line of TRAPPIST-1. Asteroids perturbed out from the chaotic zone of the putative planet can enter into the inner system and accreted by the known planets. Our main finding is that the larger is the orbital distance of planet, the higher is the amount of water delivered to the planet by an LHB-like event

The Type II-P Supernova 2017eaw: From Explosion to the Nebular Phase

The nearby SN 2017eaw is a Type II-P ("plateau") supernova (SN) showing early-time, moderate CSM interaction. We present a comprehensive study of this SN, including the analysis of high-quality optical photometry and spectroscopy covering the very early epochs up to the nebular phase, as well as near-ultraviolet and near-infrared spectra and early-time X-ray and radio data. The combined data of SNe 2017eaw and 2004et allow us to get an improved distance to the host galaxy, NGC. 6946, of D similar to 6.85 +/- 0.63 Mpc; this fits into recent independent results on the distance of the host and disfavors the previously derived (30% shorter) distances based on SN 2004et. From modeling the nebular spectra and the quasi-bolometric light curve, we estimate the progenitor mass and some basic physical parameters for the explosion and ejecta. Our results agree well with previous reports on a red supergiant progenitor star with a mass of similar to 15-16 M-circle dot. Our estimation of the pre-explosion mass-loss rate ((M)over dot similar to 3 x 10(-7)-1 x 10(-6)M(circle dot) yr(-1)) agrees well with previous results based on the opacity of the dust shell enshrouding the progenitor, but it is orders of magnitude lower than previous estimates based on general light-curve modeling of Type II-P SNe. Combining late-time optical and mid-infrared data, a clear excess at 4.5 mu m can be seen, supporting the previous statements on the (moderate) dust formation in the vicinity of SN 2017eaw

Oligarchic growth in a fully interacting system

Context. In the oligarchic growth model, protoplanets develop in the final stage of planet formation via collisions between planetesimals and planetary embryos. The majority of planetesimals are accreted by the embryos, while the remnant planetesimals acquire dynamically excited orbits. The efficiency of planet formation can be defined by the mass ratio between formed protoplanets and the initial mass of the embryo-planetesimal belt. Aims. In numerical simulations of the oligarchic growth, the gravitational interactions between planetesimals are usually neglected due to computational difficulties. In this way, computations require fewer resources. We investigated the effect of this simplification by modeling the planet formation efficiency in a belt of embryos with self-interacting or non-self-interacting planetesimals. Methods. We used our own graphics processing unit-based direct N-body integrator for the simulations. We compared 2D models using different initial embryo numbers, different initial planetesimal numbers, and different total initial belt masses. For a limited number of cases, we compared the 2D and 3D simulations. Results. We found that planet formation efficiency is higher if the planetesimal self-interaction is taken into account in models that contain the commonly used 100 embryos. The observed effect can be explained by the damping of planetesimal eccentricities by their self-gravity. The final numbers of protoplanets are independent of planetesimal self-gravity, while the average mass of the formed protoplanets is larger in the self-interacting models. We also found that the non-self-interacting and self-interacting models qualitatively give the same results above 200 embryos. Our findings show that the higher the initial mass of the embryo-planetesimal belt, the higher the discrepancy between models that use self-interacting or non-self-interacting planetesimals is. The study of 3D models showed quantitatively the same results as the 2D models for low average inclination. We conclude that it is important to include planetesimal self-interaction in both 2D and 3D models in cases where the initial embryo number is less than 200