The masses of open star clusters and their tidal tails and the stellar initial mass function

被引：0
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作者：
Wirth, Henriette [1 ]
Dinnbier, František [1 ]
Kroupa, Pavel [1 ,2 ]
Šubr, Ladislav [1 ]
机构：
[1] Charles University, Faculty of Mathematics and Physics, Astronomical Institute, V Holešovičkách 2, Praha,18000, Czech Republic
[2] Helmholtz Institut für Strahlen und Kernphysik, Universität Bonn, Nussallee 14-16, Bonn,53115, Germany
来源：
Astronomy and Astrophysics | 2024年 / 691卷
关键词：
Context. Unresolved binaries have a strong influence on the observed parameters of stellar clusters (SCs). Aims. We quantify this influence and compute the resulting mass underestimates and stellar mass function (MF). Methods. N-body simulations of realistic SCs were used to investigate the evolution of the binary population in a SC and its tidal tails. Together with an empirically gauged stellar mass-luminosity relation; the results were then used to determine how the presence of binaries changes the photometric mass and MF of the SC and its tails as deduced from observations. Results. Tail 1 (T1); which is the tidal tail caused by gas expulsion; contains a larger fraction of binaries than both the SC and Tail 2 (T2); which forms after gas expulsion. Additionally; T1 has a larger velocity dispersion. Using the luminosity of an unresolved binary; an observer would underestimate its mass. This bias sensitively depends on the companion masses due to the structure of the stellar mass-luminosity relation. Combining the effect of all binaries in the simulation; the total photometric mass of the SC is underestimated by 15%. Dark objects (black holes and neutron stars) increase the difference between the real and observed mass of the SC further. For both the SC and the tails; the observed power-law index of the MF between a stellar mass of 0.3 and 0.7 Mo is smaller by up to 0.2 than the real one; the real initial mass function (IMF) being steeper by this amount. This difference is larger for stars with a larger velocity dispersion or binary fraction. Conclusions. Since the stars formed in SCs are the progenitors of the Galactic field stars; this work suggests that the binary fractions of different populations of stars in the Galactic disc will differ as a function of the velocity dispersion. However; the direction of this correlation is currently unclear; and a complete population synthesis will be needed to investigate this effect. Variations in the binary fractions of different clusters can lead to perceived variations of the deduced stellar MFs. © The Authors 2024;
D O I：
10.1051/0004-6361/202347839
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