Star Cluster Survival in Star Cluster Complexes under Extreme Residual Gas Expulsion

After the stars of a new, embedded star cluster have formed they blow the remaining gas out of the cluster. Especially winds of massive stars and definitely the on-set of the first supernovae can remove the residual gas from a cluster. This leads to a very violent mass-loss and leaves the cluster out of dynamical equilibrium. Standard models predict that within the cluster volume the star formation efficiency (SFE) has to be about 33 per cent for sudden (within one crossing-time of the cluster) gas expulsion to retain some of the stars in a bound cluster. If the efficiency is lower the stars of the cluster disperse mostly. Recent observations reveal that in strong star bursts star clusters do not form in isolation but in complexes containing dozens and up to several hundred star clusters, i.e. in super-clusters. By carrying out numerical experiments for such objects placed at distances >= 10 kpc from the centre of the galaxy we demonstrate that under these conditions (i.e. the deeper potential of the star cluster complex and the merging process of the star clusters within these super-clusters) the SFEs can be as low as 20 per cent and still leave a gravitationally bound stellar population. Such an object resembles the outer Milky Way globular clusters and the faint fuzzy star clusters recently discovered in NGC 1023.Comment: 21 pages, 8 figures, accepted by Ap

Formulation for the static permittivity of water and steam at temperatures from 238 K to 873 K at pressures up to 1200 MPa, including derivatives and Debye- Hückel coefficients

Journal ArticleA new formulation is presented of the static relative permittivity or dielectric constant of water and steam, including supercooled and supercritical states. The range is from 238 K to 873 K, at pressures up to 1200 MPa. The formulation is based on the ITS-90 temperature scale. It correlates a selected set of data from a recently published collection of all experimental data. The set includes new data in the liquid water and the steam regions that have not been part of earlier correlations. The physical basis for the formulation is the so-called #-factor in the form proposed by Harris and Alder. An empirical 12-parameter form for the g-factor as a function of the independent variables temperature and density is used. For the conversion of experimental pressures to densities, the newest formulation of the equation of state of water on the ITS-90, prepared by Wagner and Pruss, has been used. All experimental data are compared with the formulation. The reliability of the new formulation is assessed in all subregions. Comparisons with previous formulations are presented. Auxiliary dielectric-constant formulations as functions of temperature are included for the saturated vapor and liquid states. The pressure and temperature derivatives of the dielectric constant and the Debye-Hiickel limiting-law slopes are calculated, their reliability is estimated, and they are compared with experimentally derived values and with previous correlations. All equations are given in this paper, along with short tables. An implementation of this formulation for the dielectric constant is available on disk [A. H. Harvey, A. P. Peskin, and S. A. Klein, NIST/ASME Steam Properties, NIST Standard Reference Database 10, Version 2.1, Standard Reference Data Program, NIST, Gaithershurg, MD (1997)]

The effect of the dynamical state of clusters on gas expulsion and infant mortality

The star formation efficiency (SFE) of a star cluster is thought to be the critical factor in determining if the cluster can survive for a significant (>50 Myr) time. There is an often quoted critical SFE of ~30 per cent for a cluster to survive gas expulsion. I reiterate that the SFE is not the critical factor, rather it is the dynamical state of the stars (as measured by their virial ratio) immediately before gas expulsion that is the critical factor. If the stars in a star cluster are born in an even slightly cold dynamical state then the survivability of a cluster can be greatly increased.Comment: 6 pages, 2 figures. Review talk given at the meeting on "Young massive star clusters - Initial conditions and environments", E. Perez, R. de Grijs, R. M. Gonzalez Delgado, eds., Granada (Spain), September 2007, Springer: Dordrecht. Replacement to correct mistake in a referenc

The shape of the initial cluster mass function: what it tells us about the local star formation efficiency

We explore how the expulsion of gas from star-cluster forming cloud-cores due to supernova explosions affects the shape of the initial cluster mass function, that is, the mass function of star clusters when effects of gas expulsion are over. We demonstrate that if the radii of cluster-forming gas cores are roughly constant over the core mass range, as supported by observations, then more massive cores undergo slower gas expulsion. Therefore, for a given star formation efficiency, more massive cores retain a larger fraction of stars after gas expulsion. The initial cluster mass function may thus differ from the core mass function substantially, with the final shape depending on the star formation efficiency. A mass-independent star formation efficiency of about 20 per cent turns a power-law core mass function into a bell-shaped initial cluster mass function, while mass-independent efficiencies of order 40 per cent preserve the shape of the core mass function.Comment: accepted in Ap

The Disutility of Injustice

For more than half a century, the retributivists and the crime-control instrumentalists have seen themselves as being in an irresolvable conflict. Social science increasingly suggests, however, that this need not be so. Doing justice may be the most effective means of controlling crime. Perhaps partially in recognition of these developments, the American Law Institute\u27s recent amendment to the Model Penal Code\u27s purposes provision – the only amendment to the Model Code in the 47 years since its promulgation – adopts desert as the primary distributive principle for criminal liability and punishment. That shift to desert has prompted concerns by two groups – ironically, two groups traditionally opposed to one another. The first group – those concerned with what they see as the over-punitiveness of current criminal law – worries that setting desert as the dominant distributive principle means continuing the punitive doctrines they find so objectionable, and perhaps will make things worse. The second group – those concerned with ensuring effective crime control – worries that a shift to desert will create many missed crime-control opportunities; it will increase avoidable crime. The first group\u27s concern about over-punitiveness rests upon an assumption that the current punitive crime-control doctrines of which they disapprove are a reflection of the community\u27s naturally punitive intuitions of justice. However, as Study 1 makes clear, today\u27s popular crime-control doctrines in fact seriously conflict with people\u27s intuitions of justice by exaggerating the punishment deserved. The second group\u27s concern that a desert principle will increase avoidable crime exemplifies the common wisdom of the past half century that ignoring justice in pursuit of crime-control through deterrence, incapacitation of the dangerous, and other such coercive crime-control programs is cost free. However, Studies 2 and 3 suggest that doing injustice has real crime control costs. Deviating from the community\u27s shared principles of justice undermines the system\u27s moral credibility and thereby undermines its ability to gain cooperation and compliance and to harness the powerful forces of social influence and internalized norms. The studies reported here give assurance to both groups. A shift to desert is not likely to either undermine the criminal justice system\u27s crime-control effectiveness, and indeed it may enhance it, nor is it likely to increase the system\u27s punitiveness, and indeed it may reduce it

Planar laser-induced fluorescence imaging of Si and SiO during pulsed laser ablation of Si

Planar laser induced fluorescence has been used to acquire time sequence images of ground-state, neutral Si and SiO during laser ablation of an Si target in vacuum and in the presence of a background gas at a fluence of 3-4 J/cm^2. The SiO images, taken in air, strongly suggest that the observed SiO is created through reaction of silicon with oxygen at the contact front as the plume expands

The orbit structure of Dynkin curves

Let G be a simple algebraic group over an algebraically closed field k; assume that Char k is zero or good for G. Let \cB be the variety of Borel subgroups of G and let e in Lie G be nilpotent. There is a natural action of the centralizer C_G(e) of e in G on the Springer fibre \cB_e = {B' in \cB | e in Lie B'} associated to e. In this paper we consider the case, where e lies in the subregular nilpotent orbit; in this case \cB_e is a Dynkin curve. We give a complete description of the C_G(e)-orbits in \cB_e. In particular, we classify the irreducible components of \cB_e on which C_G(e) acts with finitely many orbits. In an application we obtain a classification of all subregular orbital varieties admitting a finite number of B-orbits for B a fixed Borel subgroup of G.Comment: 12 pages, to appear in Math