Quantifying the Universality of the Stellar Initial Mass Function in Old Star Clusters

We present a new technique to quantify cluster-to-cluster variations in the observed present-day stellar mass functions of a large sample of star clusters. Our method quantifies these differences as a function of both the stellar mass and the total cluster mass, and offers the advantage that it is insensitive to the precise functional form of the mass function. We applied our technique to data taken from the ACS Survey for Globular Clusters, from which we obtained completeness-corrected stellar mass functions in the mass range 0.25-0.75 M$_{\odot}$ for a sample of 27 clusters. The results of our observational analysis were then compared to Monte Carlo simulations for globular cluster evolution spanning a range of initial mass functions, total numbers of stars, concentrations, and virial radii. We show that the present-day mass functions of the clusters in our sample can be reproduced by assuming an universal initial mass function for all clusters, and that the cluster-to-cluster differences are consistent with what is expected from two-body relaxation. A more complete exploration of the initial cluster conditions will be needed in future studies to better constrain the precise functional form of the initial mass function. This study is a first step toward using our technique to constrain the dynamical histories of a large sample of old Galactic star clusters and, by extension, star formation in the early Universe.Comment: 11 pages, 4 figures, 4 tables, accepted for publication in MNRAS, proof corrections made in updated versio

Changes in epigeic spider community in primary succession on a brown-coal dump

A descriptive model of primary succession of spiders on a brown-coal dump is presented. Multivariate methods (cluster analysis and detrended correspondence analysis), and community indexes were applied to evaluate changes in community composition of epigeic spiders. Two different rehabilitation age stages were investigated. The cluster analysis helped to determine a case of horizontal asynchronous succession. The DCA was able to distinguish divergent trends of succession from the initial stage. Successional trends in species replacements were observed. In all aspects of succession there was found to be directional towards a "ruderal steppe" subclimax

Metallicity in the Galactic Center: The Arches cluster

We present a quantitative spectral analysis of five very massive stars in the Arches cluster, located near the Galactic center, to determine stellar parameters, stellar wind properties and, most importantly, metallicity content. The analysis uses a new technique, presented here for the first time, and uses line-blanketed NLTE wind/atmosphere models fit to high-resolution near-infrared spectra of late-type nitrogen-rich Wolf-Rayet stars and OfI+ stars in the cluster. It relies on the fact that massive stars reach a maximum nitrogen abundance that is related to initial metallicity when they are in the WNL phase. We determine the present-day nitrogen abundance of the WNL stars in the Arches cluster to be 1.6% (mass fraction) and constrain the stellar metallicity in the cluster to be solar. This result is invariant to assumptions about the mass-luminosity relationship, the mass-loss rates, and rotation speeds. In addition, from this analysis, we find the age of the Arches cluster to be 2-2.5Myr, assuming coeval formation

How well do we know the age and mass distributions of the star cluster system in the Large Magellanic Cloud?

[ABRIDGED] The LMC star cluster system offers the unique opportunity to independently check the accuracy of age and mass determinations based on a number of complementary techniques, including isochrone analysis. Using our sophisticated tool for star cluster analysis based on broad-band spectral energy distributions (SEDs), we reanalyse the Hunter et al. (2003) LMC cluster photometry. Our main aim is to set the tightest limits yet on the accuracy of ABSOLUTE age determinations based on broad-band SEDs, and therefore on the usefulness of such an approach. Our broad-band SED fits yield reliable ages, with statistical absolute uncertainties within Delta[log(Age/yr)] = 0.4 overall. The systematic differences we find with respect to previous age determinations are caused by conversions of the observational photometry to a different filter system. The LMC's cluster formation rate (CFR) has been roughly constant outside of the well-known age gap between ~3 and 13 Gyr, when the CFR was a factor of ~5 lower. We derive the characteristic cluster disruption time-scale, log(t_4^dis/yr) = 9.9 +- 0.1, where t_dis = t_4^dis (M_cl/10^4 Msun)^0.62. This long characteristic disruption time-scale implies that we are observing the INITIAL cluster mass function (CMF). We conclude that the youngest mass and luminosity-limited LMC cluster subsets show shallower slopes than the slope of alpha = -2 expected (at least below masses of a few x 10^3 Msun), which is contrary to dynamical expectations. This may imply that the initial CMF slope of the LMC cluster system as a whole is NOT well represented by a power-law, although we cannot disentangle the unbound from the bound clusters at the youngest ages.Comment: 14 pages, 8 figures, resubmitted to MNRAS after responding to referee repor

An empirical initial-final mass relation from hot, massive white dwarfs in NGC 2168 (M35)

The relation between the zero-age main sequence mass of a star and its white-dwarf remnant (the initial-final mass relation) is a powerful tool for exploration of mass loss processes during stellar evolution. We present an empirical derivation of the initial-final mass relation based on spectroscopic analysis of seven massive white dwarfs in NGC 2168 (M35). Using an internally consistent data set, we show that the resultant white dwarf mass increases monotonically with progenitor mass for masses greater than 4 solar masses, one of the first open clusters to show this trend. We also find two massive white dwarfs foreground to the cluster that are otherwise consistent with cluster membership. These white dwarfs can be explained as former cluster members moving steadily away from the cluster at speeds of <~0.5 km/s since their formation and may provide the first direct evidence of the loss of white dwarfs from open clusters. Based on these data alone, we constrain the upper mass limit of WD progenitors to be >=5.8 solar masses at the 90% confidence level for a cluster age of 150 Myr.Comment: 14 pages, 3 figures. Accepted for publication in the Astrophysical Journal Letters. Contains some acknowledgements not in accepted version (for space reasons), otherwise identical to accepted versio

On the Effects of Subvirial Initial Conditions and the Birth Temperature of R136

We investigate the effect of different initial virial temperatures, Q, on the dynamics of star clusters. We find that the virial temperature has a strong effect on many aspects of the resulting system, including among others: the fraction of bodies escaping from the system, the depth of the collapse of the system, and the strength of the mass segregation. These differences deem the practice of using "cold" initial conditions no longer a simple choice of convenience. The choice of initial virial temperature must be carefully considered as its impact on the remainder of the simulation can be profound. We discuss the pitfalls and aim to describe the general behavior of the collapse and the resultant system as a function of the virial temperature so that a well reasoned choice of initial virial temperature can be made. We make a correction to the previous theoretical estimate for the minimum radius, $R_{min}$, of the cluster at the deepest moment of collapse to include a Q dependency, $R_{min}\approx Q + N^{(-1/3)}$, where $N$ is the number of particles. We use our numerical results to infer more about the initial conditions of the young cluster R136. Based on our analysis, we find that R136 was likely formed with a rather cool, but not cold, initial virial temperature ($Q\approx 0.13$). Using the same analysis method, we examined 15 other young clusters and found the most common initial virial temperature to be between 0.18 and 0.25.Comment: Accepted for publication in MNRA

Spanish Tourist Behaviour: A Specific Objective-base Segmantation

This work uses data from the Spanish Tourism Demand Segments Survey (N=6900) conducted by the IESA-CSIC for Turismo Andaluz, SA. The objective of the paper is to develop a statistical segmentation or typology of Spanish tourists based on objective aspects of tourist behaviour measured in the survey including destinations visited, theme of the trip, lodging, transportation and travel group. Initial categorical data are reduced using multiple correspondence analysis and grouped through cluster analysis. Afterwards, identified segments are evaluated to analyse their tourist profiles with a view to examining sociological perspectives of tourist behaviour.Tourist Demand, Segmentation, Spain, Domestic Tourism, Multiple Correspondence Analysis, Cluster Analysis

Cluster growing process and a sequence of magic numbers

We present a new theoretical framework for modelling the cluster growing process. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster sizes of more than 100 atoms. We demonstrate that in this way all known global minimum structures of the Lennard-Jonnes (LJ) clusters can be found. Our method provides an efficient tool for the calculation and analysis of atomic cluster structure. With its use we justify the magic numbers sequence for the clusters of noble gases atoms and compare it with experimental observations. We report the striking correspondence of the peaks in the dependence on cluster size of the second derivative of the binding energy per atom calculated for the chain of LJ-clusters based on the icosahedral symmetry with the peaks in the abundance mass spectra experimentally measured for the clusters of noble gases atoms. Our method serves an efficient alternative to the global optimization techniques based on the Monte-Carlo simulations and it can be applied for the solution of a broad variety of problems in which atomic cluster structure is important.Comment: 10 pages, 3 figure