Simulations of the Hyades

¹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
e-mail: aernst@ari.uni-heidelberg.de
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ National Astronomical Observatories of China, Chinese Academy of Sciences, Datun Lu 20A, Chaoyang District, 100012 Beijing, PR China
⁴ The Kavli Institute for Astronomy and Astrophysics at Peking University, Yi He Yuan Lu 5, Hai Dian Qu, 100871 Beijing, PR China
⁵ Main Astronomical Observatory, National Academy of Sciences of Ukraine, Akademika Zabolotnoho 27, 03680 Kyiv, Ukraine

Received: 5 September 2011
Accepted: 4 October 2011

Abstract

Context. Using recent observational data we present N-body simulations of the Hyades open cluster.

Aims. We make an attempt to determine the initial conditions of the Hyades cluster at the time of its formation to reproduce the present-day cumulative mass profile, stellar mass and luminosity function (LF).

Methods. We performed direct N-body simulations of the Hyades in an analytic Milky Way potential. They account for stellar evolution and include primordial binaries in a few models. Furthermore, we applied a Kroupa initial mass function and used extensive ensemble-averaging.

Results. We find that evolved single-star King initial models with King parameters W₀ = 6−9 and initial particle numbers N₀ = 3000 provide good fits to the present-day observational cumulative mass profile within the Jacobi radius. The best-fit King model has an initial mass of 1721   M_⊙ and an average mass loss rate of  −2.2   M_⊙/Myr. The K-band LFs of models and observations show reasonable agreement. Mass segregation is detected in both observations and models. If 33% primordial binaries are included, the initial particle number is reduced by 5% as compared to the model without primordial binaries.

Conclusions. The present-day properties of the Hyades can be reproduced well by a standard King or Plummer initial model when choosing appropriate initial conditions. The degeneracy of good-fitting models can be quite high due to the large dimension of the parameter space. More simulations with different Roche-lobe filling factors and primordial binary fractions are required to explore this degeneracy in more detail.