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2 Acta Astronomica

2 2025

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Strong Candidates for Visual Components in Hierarchical Systems with Light-Time Effect

Tokarek J. J., Dimitrov W.

Acta Astronomica

2025

Vol. 75, No. 2

97--126

We present a search for visual companions of multiple systems with the LITE effect using DR3 data from the Gaia mission. Then, we verified if we can determine the relative positions and velocities of the two components in three-dimensional space with sufficient accuracy. Finally, we checked if closed orbits are possible for such values. We used fits of clone orbits with a scatter consistent with the errors of the parameters determined. We used covariance matrices provided by Gaia to create the normal distribution of the astrometric parameters. Most of the visual companions found are already listed in publications and catalogs. In some cases the positions in the three-dimensional space of the two components of the visual pair were unambiguous, i.e., the uncertainty ranges did not overlap. We selected a group of eight objects from among those in Zakirov's catalog, for which the positions and velocities of the main system and the visual companion are very similar. In most cases, we were able to find closed orbits by calculating the orbits of clones. In addition, we selected a wider group of 40 candidates with slightly worse parameters determined. Three of them were also studied in detail.

Evolution of Intermediate Mass Stellar Clusters

Kowalski B., Wiśniowski T., Rickman H., Wajer P.

Acta Astronomica

2025

Vol. 75, No. 2

127--158

We present N-body simulations of open clusters covering a time span starting from birth and ending after 200 Myr. These clusters initially contain 5000 stars and are set up with both 3D and fractal geometries. The structural parameters are intentionally chosen so as to allow lifetimes exceeding 100 Myr. The results are analyzed with regard to bulk properties such as mass, size, number of stars, virial ratio and binary fraction, and the internal structure as evidenced by the radial profiles of mass density and stellar number density. Thus, we are able to characterize the progress of evolutionary features like mass segregation, virialization and two-body relaxation. We find that mass segregation proceeds more quickly in clusters without primordial mass segregation, likely because these allow for closer contact between low and high mass stars as two-body relaxation sets in. By studying the long-term evolution of the virial ratio, we have found that this is on average larger than the equilibrium value and shows an oscillating behavior with a characteristic frequency, possibly caused by periodic trapping of high-velocity stars in the high density region close to the center. Using simulated surface brightness profiles, we show that our cluster models are consistent with observed core radii in young clusters. We find indications that the binary fraction decreases with time in clusters without primordial mass segregation and increases in primordially mass segregated clusters. We find evidence that binary destruction and formation are continually ongoing phenomena. Primordial binaries tend to either be destroyed within 40 Myr or to exist until 200 Myr. In fractal clusters we observe both an increased binary destruction rate and an increased binary formation rate during the early times as compared to 3D clusters. This is likely due to the stars being concentrated to filaments with super-high densities.