SCYON Abstract

Received on January 10 2013

Gravitational conundrum? Dynamical mass segregation versus disruption of binary stars in dense stellar systems

AuthorsRichard de Grijs (1,2), Chengyuan Li (1,3), Yong Zheng (1,3), Licai Deng (4,5), Yi Hu (4), M. B. N. Kouwenhoven (1), and James E. Wicker (4)
Affiliation(1) Kavli Institute for Astronomy and Astrophysics, Peking University, China
(2) Department of Astronomy and Space Science, Kyung Hee University, Republic of Korea
(3) Department of Astronomy, Peking University, China
(4) National Astronomical Observatories, Chinese Academy of Sciences, China
(5) Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, China
Accepted byAstrophysical Journal


Upon their formation, dynamically cool (collapsing) star clusters will, within only a few million years, achieve stellar mass segregation for stars down to a few solar masses, simply because of gravitational two-body encounters. Since binary systems are, on average, more massive than single stars, one would expect them to also rapidly mass segregate dynamically. Contrary to these expectations and based on high-resolution Hubble Space Telescope observations, we show that the compact, 15--30 Myr-old Large Magellanic Cloud cluster NGC 1818 exhibits tantalizing hints at the >~ 2σ level of significance (> 3σ if we assume a power-law secondary-to-primary mass-ratio distribution) of an increasing fraction of F-star binary systems (with combined masses of 1.3 - 1.6 M(sun)) with increasing distance from the cluster center, specifically between the inner 10 to 20'' (approximately equivalent to the cluster's core and half-mass radii) and the outer 60 to 80''. If confirmed, this will offer support of the theoretically predicted but thus far unobserved dynamical disruption processes of the significant population of ''soft'' binary systems---with relatively low binding energies compared to the kinetic energy of their stellar members---in star clusters, which we have access to here by virtue of the cluster's unique combination of youth and high stellar density.