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On the Dynamical Evolution of Young Stellar Aggregates

Wiśniowski T., Rickman H., Wajer P.

Acta Astronomica

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2021

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Vol. 71, No. 3

243--260

EN

We report on N-body simulations of embedded stellar clusters over a time span of 10 Myr from inception until several crossing times after gas expulsion. We focus our attention on the survivability of bound stellar clusters following gas expulsion. The final values of the bound fraction are significantly larger in case the initial structure is relatively open with a Plummer radius of ≈1 pc than for a much stronger degree of concentration. However, only one of 12 simulated clusters shows any promise of leaving behind a long-lived, bound system. We tentatively conclude that the predictions of our model are in rough agreement with the observed "infant mortality" of newborn stellar aggregates. We also find that relaxation effects due to close encounters, while present, are significantly curtailed by the rapid expansion of the clusters.

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Fast Geometric Method for Calculating Accurate Minimum Orbit Intersection Distances

Wiśniowski T., Rickman H.

Acta Astronomica

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2013

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Vol. 63, No. 2

293--307

EN

We present a new method to compute Minimum Orbit Intersection Distances (MOIDs) for arbitrary pairs of heliocentric orbits and compare it with Giovanni Gronchi's algebraic method. Our procedure is numerical and iterative, and the MOID configuration is found by geometric scanning and tuning. A basic element is the meridional plane, used for initial scanning, which contains one of the objects and is perpendicular to the orbital plane of the other. Our method also relies on an efficient tuning technique in order to zoom in on the MOID configuration, starting from the first approximation found by scanning. We work with high accuracy and take special care to avoid the risk of missing the MOID, which is inherent to our type of approach. We demonstrate that our method is both fast, reliable and flexible. It is freely available and its source Fortran code downloadable via our web page.

3

On the Dynamical Evolution of Scattered Disk Objects Outside the Planetary System

Gabryszewski R., Rickman H.

Acta Astronomica

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2010

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Vol. 60, No. 4

373--385

EN

We report the results of dynamical simulations, covering Gyr timescales, of fictitious Scattered Disk Objects as a follow-up to an earlier study. Our dynamical model is similar in that it does not include external agents like passing stars or the Galactic tide. Only the four giant planets are explicitly treated as perturbers. We analyze the random-walk behavior of the inverse semi-major axis by means of a simplified circular restricted 3-body problem as an approximate analogue. Our results concerning the role of resonant effects and the transfer efficiency into the orbital energy domain of the inner Oort Cloud are in broad agreement with the earlier papers, and we confirm the important role of external objects (with perihelia beyond Neptune's orbit) in feeding the Oort Cloud. We estimate the efficiency of this transfer to be even somewhat higher than previously found.