Exploring the dynamical evolution of Cepheid multiplicity in star clusters and its implications for B-star multiplicity at birth

被引：0

作者：

Dinnbier, František ^{[1
]}

Anderson, Richard I. ^{[2
]}

Kroupa, Pavel ^{[1
,3
]}

机构：

[1] Astronomical Institute, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, Praha 8,180 00, Czech Republic

[2] Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, Versoix,1290, Switzerland

[3] Helmholtz-Institut für Strahlen-und Kernphysik, University of Bonn, Nussallee 14-16, Bonn,53115, Germany

来源：

Astronomy and Astrophysics | 1600年 / 690卷

关键词：

Context. Classical Cepheid variable stars provide a unique probe of binary evolution in intermediate-mass stars over the course of several tens to hundreds of Myr. In addition; understanding binary evolution with the inclusion of cluster dynamics is desirable for obtaining a more complete picture of these stars; especially as they play a vital role in distance determinations. Aims. We studied the binary and multiple properties of Cepheids; assuming that all mid-B stars form in binaries inside star clusters. We also estimated the birth multiplicity of mid-B stars by comparing the observed multiplicity statistics of Cepheids with models based on particular assumptions. Methods. The clusters were modelled with the NBODY6 code; including synthetic stellar and binary evolutionary tracks. The Cepheids were identified from their position on the Hertzsprung-Russell diagram. Results. The dynamical cluster environment results in a higher binary fraction among the Cepheids that remain in star clusters (≈60%) than among the Cepheids which have escaped to the field (≈35%). The fraction of Cepheids in triples (≈30% and ≈10% in clusters and field; respectively) follows the same trend. In clusters; the binary; triple; and multiple fraction decreases with increasing cluster mass. More massive clusters have binaries of shorter orbital periods than lower mass clusters and field Cepheids. Mergers are very common with ≈30% of mid-B stars not evolving to Cepheids because of the interaction with their companion. Approximately 40% of Cepheids have merged with their companion; and the merger event impacts stellar evolution; so that ≈25% of all Cepheids occur at an age by more than 40% different than what would be expected from their mass and the current cluster age; the expected age of Cepheids can differ from the age of their host cluster. Our models predict that one in five Cepheids is the result of a merger between stars with mass below the lower mass limit for Cepheids; in clusters; these objects occur substantially later than expected from their mass. Approximately 10% of binary Cepheids have a different companion from the zero-Age main sequence (ZAMS) one; and ≈3 to 5% of all Cepheids have a compact companion (≈0.15% of all Cepheids are accompanied by a black hole). Conclusions. The binary fraction derived from our simulations (42%) underestimates the observed binary Cepheid fraction by approximately a factor of 2. This suggests that the true multiplicity fraction of B-stars at birth could be substantially larger than unity and; thus; that mid-B stars may typically form in triple and higher order systems. © The Authors 2024;

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