1,914 research outputs found

    The Impact of Rotation on Cluster Dynamics

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    The evolution of rotating, isolated clusters of stars up to core-collapse is investigated with n-body numerical codes. The simulations start off from axisymmetric generalisations of King profiles, with added global angular momentum. In this contribution I report on results obtained for two sets of single-mass cluster simulations. These confirm the more rapid evolution of even mildly-rotating clusters. A model is presented with rotational energy comparable to omega-Centauri's; it reaches core-collapse in less than half the time required for non-rotating model clusters.Comment: Talk given at the Strasbourg meeting Massive Star Clusters in November 1999; 7 pages, 3 figures xv-8bit giffed and tarred (= 100Kbytes); newpasp style file include

    The impact of mass loss on star cluster formation. I. Analytic results

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    We study analytically the disruptive effect of instantaneous gas removal from a cluster containing O stars. We setup an iterative calculation based on the stellar velocity distribution function to compute the fraction of stars that remain bound once the cluster has ejected the gas and is out of equilibrium. We show that the stellar bound fraction is a function of the initial cluster distribution function as well as the star formation efficiency, ϵ\epsilon, taken constant throughout the cluster. The case of the Plummer sphere is dealt with in greater details. We find for this case that up to ~ 50% of the stars may remain bound when ϵ\epsilon assumes values < 1/2, contrary to expectations derived from the virial theorem. The fraction of bound stars is expressed algebraically for polytropic distribution functions.Comment: to appear in M

    Evolution of star clusters in arbitrary tidal fields

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    We present a novel and flexible tensor approach to computing the effect of a time-dependent tidal field acting on a stellar system. The tidal forces are recovered from the tensor by polynomial interpolation in time. The method has been implemented in a direct-summation stellar dynamics integrator (NBODY6) and test-proved through a set of reference calculations: heating, dissolution time and structural evolution of model star clusters are all recovered accurately. The tensor method is applicable to arbitrary configurations, including the important situation where the background potential is a strong function of time. This opens up new perspectives in stellar population studies reaching to the formation epoch of the host galaxy or galaxy cluster, as well as for star-burst events taking place during the merger of large galaxies. A pilot application to a star cluster in the merging galaxies NGC 4038/39 (the Antennae) is presented.Comment: 12 pages, 8 figures. Accepted for publication in MNRA

    On the mass function of star clusters

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    Clusters that form in total 10^3 < N < 10^5 stars (type II clusters) lose their gas within a dynamical time as a result of the photo-ionising flux from O stars. Sparser (type I) clusters get rid of their residual gas on a timescale longer or comparable to the nominal crossing time and thus evolve approximately adiabatically. This is also true for massive embedded clusters (type III) for which the velocity dispersion is larger than the sound speed of the ionised gas. On expelling their residual gas, type I and III clusters are therefore expected to lose a smaller fraction of their stellar component than type II clusters. We outline the effect this has on the transformation of the mass function of embedded clusters (ECMF), which is directly related to the mass function of star-cluster-forming molecular cloud cores, to the ``initial'' MF of bound gas-free star clusters (ICMF). The resulting ICMF has, for a featureless power-law ECMF, a turnover near 10^{4.5} Msun and a peak near 10^3 Msun. The peak lies around the initial masses of the Hyades, Praesepe and Pleiades clusters. We also find that the entire Galactic population II stellar spheroid can be generated if star formation proceeded via embedded clusters distributed like a power-law MF with exponent 0.9 < beta < 2.6.Comment: 10 pages, 4 figures, accepted by MNRAS, small adjustments for consistency with published versio

    L’acteur et l’expérience de la conscience

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