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1

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.

2

Multiple Stellar Encounters on Protoplanetary Disks in Birth Clusters of Stars

Jiménez-Torres J. J.

Acta Astronomica

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2020

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Vol. 70, No. 1

53--74

EN

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.

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The Optical Gravitational Lensing Experiment. The Catalog of Stellar Proper Motions toward the Magellanic Clouds

Poleski R., Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K.

Acta Astronomica

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2012

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Vol. 62, No. 1

1-22

EN

We present a catalog of over 6.2 million stars with measured proper motions. All these stars are observed in the direction of the Magellanic Clouds within the brightness range 12

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The Optical Gravitational Lensing Experiment. High Proper Motion Stars in the OGLE-III Data for Magellanic Clouds Fields

Poleski R., Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K.

Acta Astronomica

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2011

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Vol. 61, No. 3

199--216

EN

We present the results of a search for High Proper Motion (HPM) stars, i.e., the ones with μ>100 mas/yr, in the direction to the Magellanic Clouds. This sky area was not examined in detail as the high stellar density hampers efforts in performing high-quality astrometry. Altogether 549 HPM stars were found with median uncertainties of proper motions per coordinate equal to 0.5 mas/yr. The fastest HPM star has the proper motion of 722.19±0.74 mas/yr. For the majority of objects (70%) parallaxes were also measured. The highest value found is π=91.3±1.6 mas. The parallaxes were used to estimate absolute magnitudes which enriched with color information show that 21 of HPM stars are white dwarfs. Other 23 candidate white dwarfs were selected of HPM stars with no measurable parallaxes using color-magnitude diagram. The search for common proper motion binaries revealed 27 such pairs in the catalog. The completeness of the catalog is estimated to be >80% and it is slightly higher than for previous catalogs in the direction to the Magellanic Clouds.