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Multiple Stellar Encounters on Protoplanetary Disks in Birth Clusters of Stars

Jiménez-Torres J. J.

Acta Astronomica

2020

Vol. 70, No. 1

53--74

We investigate the orbital modification of planetesimals in protoplanetary disks due to multiple stellar encounters in star formation clusters. We modeled multiple encounters with different flyby masses ranging from 0.02 M⊙ up to 0.5 M⊙, approach distances within 400 a.u. and virial velocities to simulate conditions of encounters in star formation regions. We propose an analysis of mass densities as a function of time and found that densities from 3×103 M⊙/pc3 to 1.4×104 M⊙/pc3 can produce from one up to three stellar encounters on a cross sectional area with a radius of 400 a.u. containing a 100 a.u. planetary disk in a period of time of 1×106 yr. We found that the orbital structure of observed transneptunian objects such as 2005 QU182 and the sednoid 2012 VP113 can simultaneously be produced with multiple encounters. We also found that the effect of multiple encounters with low mass stars (<0.5 M⊙) can reproduce similar orbital eccentricities and inclinations as produced by a single stellar encounter with a mass in the order of 1 M⊙. This corresponds to a realistic scenario considering that low mass stars represent the majority of the new born stars in a birth cluster of stars. We provide a relation between the number of stellar encounters on a cross sectional area and the stellar mass density. With interferometers such as ALMA, the influence of stellar encounters in star formation regions may become testable, which suggests the incorporation of different planetary disk conditions in future studies.

System of Long-Period Comets as Indicator of the Large Planetary Body on the Periphery of the Solar System

Guliyev A. S., Guliyev R. A.

Acta Astronomica

2019

Vol. 69, No. 2

177--203

We study some particular aspects of the hypothesis about the existence of a highly inclined massive celestial body at a distance of 250-400 au. The analysis covers 1249 long-period comets (LPCs) observed up to 2017, having q and Q greater than 0.1 au and 30 au respectively. A plane or planes around which the concentration of perihelia occurs have been searched. The search for such planes has been carried out for groups of LPCs, separated by clusters in T (discovery date), e, q, H (absolute magnitude), Q, 1/aori ("original" a), etc. In almost all cases two types of planes or zones have been detected: the first one is very close to the ecliptic, the other one has the parameters: ip=86°, Ωp=271°. According to the tested hypothesis there is a massive perturber at a distance of 250-400 au from the Sun. We show that the number of aphelia and distant nodes of long-period comet orbits within this interval (250-400 au) significantly exceeds the expected value. The distributions of Q and distant comet nodes may signal the presence of a massive perturber near 300 au. We have estimated that the most probable orbital elements of the hypothetical planet are a=339±34 au, e=0.16±0.02, ω=57°±15°, Ω=272.°7±3°, i=86°±2°. To test the stability of such an orbit as well as its influence on other planets, a model of solar system that includes only the Jovian planets and the putative perturber was integrated for 1 billion years, assuming that the mass of the highly inclined perturber is about 10 Earth masses.