bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Hardness of Primordial Binaries on Evolution of Star Clusters
Authors: Tanikawa A. , Fukushige T. 
Published: May 2008

AbstractWe performed N-body simulations of star clusters with primordial binaries using a new code, GORILLA. It is based on Makino and Aarseth (1992)'s integration scheme on GRAPE, and includes a special treatment for relatively isolated binaries. Using the new code, we investigated effects of hardness of primordial binaries on whole evolution of the clusters. We simulated seven N=16384 equal-mass clusters containing 10% (in mass) primordial binaries whose binding energies are 1, 3, 10, 30, 100, 300, and 1000kT, respectively. Additionally, we also simulated a cluster without primordial binaries and that in which all binaries are replaced by stars with double mass, as references of soft and hard limits, respectively. We found that, in both soft (≤ 3kT) and hard (≥ 1000kT) limits, clusters experiences deep core collapse and shows gravothermal oscillations. On the other hands, in the intermediate hardness (10-300kT), the core collapses halt halfway due an energy releases of the primordial binaries.
Dynamical Evolution of Star Clusters with Intermediate Mass Black Holes and Primordial Binaries
Authors: Trenti Michele 
Published: May 2008

AbstractThe evolution of a star cluster is strongly influenced by the presence of primordial binaries and of a central black hole, as dynamical interactions within the core prevents a deep core collapse under these conditions. We present the results from a large set of direct N-body simulations of star clusters that include an intermediate mass black hole, single and binary stars. We highlight the structural and dynamical differences for the various cases showing in particular that on a timescale of a few relaxation times the density profile of the star cluster does no longer depend on the details of the initial conditions but only on the efficiency of the energy generation due to gravitational encounters at the center of the system.
The Binary Fraction of NGC 6397
Authors: Davis D. Saul , Richer Harvey B. , Anderson Jay , Brewer James 
Published: May 2008

AbstractThe binary fraction, η, of a globular cluster (GC) is a key parameter in determining its dynamical evolution, as well as its content of rare stars, such as cataclysmic variables and blue stragglers. The precise value of η for a GC was historically difficult to constrain due to an inability to obtain reliable photometry for faint objects in dense stellar fields. However, today, the HST allows us to image the main sequence of the nearest GCs to their terminations. Using HST observations we constrain η for NGC 6397. While the necessary computing power is now available to realistically simulate entire GCs, large discrepancies in the assumed primordial binary fraction, ηp, of GCs still exist. Estimates range from 5% (Hurley et al. 2007) to 100% (Ivanova et al. 2005). The N-body models of Hurley et al. (2007) suggest that η beyond the half-mass radius remains close to ηp, while cluster evolution can increase the value in the core. We find η for NGC 6397 is 15.2±0.8% in a field centered on the core, and 1.1±0.3% in a field beyond the half mass radius. These findings suggests ηp ~ 1%.
Binaries and the Dynamical Mass of Star Clusters
Authors: Kouwenhoven M. B. N. , de Grijs R. 
Published: May 2008

AbstractThe total mass of a distant star cluster is often derived from the virial theorem, using line-of-sight velocity dispersion measurements and half-light radii, under the implicit assumption that all stars are single (although it is known that most stars form part of binary systems). The components of binary stars exhibit orbital motion, which increases the measured velocity dispersion, resulting in a dynamical mass overestimation. In these proceedings we quantify the effect of neglecting the binary population on the derivation of the dynamical mass of a star cluster. We find that the presence of binaries plays an important role for clusters with total mass Mcl ≤ 105 M⊙; the dynamical mass can be significantly overestimated (by a factor of two or more). For the more massive clusters, with Mcl ≥ 105 M⊙, binaries do not affect the dynamical mass estimation significantly, provided that the cluster is significantly compact (half-mass radius ≤qslant 5 pc).
Mass Transfer in Binary Systems: A Numerical Approach
Authors: Lajoie C.-P. , Sills A. 
Published: May 2008

AbstractWe present preliminary work on the formation scenario of blue straggler stars by mass transfer in binary systems. More precisely, using Smoothed Particle Hydrodynamics (SPH), we want to model only the outer parts of the stars in order to get a much greater spatial resolution of the mass transfer flow itself. The inner boundary conditions are achieved using the so-called ghost particles and by replacing the inner mass by a central point mass. Stability of this central point mass is crucial, and it is shown that we get reasonable results. These simulations should give us indications on which layers of the donor star are actually transferred to the other star as well as how mass is transferred and how it settles on the accretor. This work is aimed at getting distinct observational signatures which would help identifying the dominant formation mechanism of blue straggler stars.
Is our Sun a Singleton?
Authors: Malmberg D. , Davies M. B. , Chambers J. E. , De Angeli F. , Church R. P. , Mackey D. , Wilkinson M. I. 
Published: May 2008

AbstractMost stars are formed in a cluster or association, where the number density of stars can be high. This means that a large fraction of initially-single stars will undergo close encounters with other stars and/or exchange into binaries. We describe how such close encounters and exchange encounters can affect the properties of a planetary system around a single star. We define a singleton as a single star which has never suffered close encounters with other stars or spent time within a binary system. It may be that planetary systems similar to our own solar system can only survive around singletons. Close encounters or the presence of a stellar companion will perturb the planetary system, often leaving planets on tighter and more eccentric orbits. Thus planetary systems which initially resembled our own solar system may later more closely resemble some of the observed exoplanet systems.
A Search for Spectroscopic Binaries in the Globular Cluster M4
Authors: Sommariva V. , Piotto G. , Rejkuba M. , Bedin L. R. , Heggie D. C. , Milone A. , Mathieu R. D. , Moretti A. 
Published: May 2008

AbstractWe present preliminary results from an observational campaign aimed at the study of the binary fraction and binary radial distribution in Galactic globular clusters. In particular, we concentrate on the ongoing observational campaign for the search of spectroscopic binaries.
Blue Straggler Stars in Galactic Globular Clusters: Tracing the Effect of Dynamics on Stellar Evolution
Authors: Ferraro Francesco R. , Lanzoni Barbara 
Published: May 2008

AbstractIn this contribution we review the main observational properties of Blue Stragglers Stars (BSS) in galactic GCs. A flower of results on the BSS frequency, radial distribution, and chemical composition are presented and discussed.
Pulsars in Globular Clusters
Authors: Ransom Scott M. 
Published: May 2008

AbstractGlobular clusters produce orders of magnitude more millisecond pulsars per unit mass than the Galactic disk. Since the first cluster pulsar was uncovered 20 years ago, at least 138 have been identified – most of which are binary millisecond pulsars. Because their origins involve stellar encounters, many of the systems are exotic objects that would never be observed in the Galactic disk. Examples include pulsar-main sequence binaries, extremely rapid rotators (including the current record holder), and millisecond pulsars in highly eccentric orbits. These systems are allowing new probes of the interstellar medium, the equation of state of material at supra-nuclear density, the masses of neutron stars, and globular cluster dynamics.
Observational Evidence for the Origin of X-ray Sources in Globular Clusters
Authors: Verbunt Frank , Pooley Dave , Bassa Cees 
Published: May 2008

AbstractLow-mass X-ray binaries, recycled pulsars, cataclysmic variables and magnetically active binaries are observed as X-ray sources in globular clusters. We discuss the classification of these systems, and find that some presumed active binaries are brighter than expected. We discuss a new statistical method to determine from observations how the formation of X-ray sources depends on the number of stellar encounters and/or on the cluster mass. We show that cluster mass is not a proxy for the encounter number, and that optical identifications are essential in proving the presence of primordial binaries among the low-luminosity X-ray sources.
Black Hole Motion as Catalyst of Orbital Resonances
Authors: Boily C. M. , Padmanabhan T. , Paiement A. 
Published: May 2008

AbstractThe motion of a black hole about the centre of gravity of its host galaxy induces a strong response from the surrounding stellar population. We consider the case of a harmonic potential and show that half of the stars on circular orbits in that potential shift to an orbit of lower energy, while the other half receive a positive boost. The black hole itself remains on an orbit of fixed amplitude and merely acts as a catalyst for the evolution of the stellar energy distribution function f(E). We then consider orbits in the logarithmic potential and identify the response of stars near resonant energies. The kinematic signature of black hole motion imprints the stellar line-of-sight mean velocity to a magnitude ≃ 13% the local root mean-square velocity dispersion σ. The high velocity dispersion at the 5:2 resonance hints to an observable effect at a distance ≃ 3 times the hole's influence radius.
Stellar Exotica in 47 Tucanae
Authors: Knigge C. , Dieball A. , Maíz-Apellániz J. , Long K. S. , Zurek D. R. , Shara Mike M. 
Published: May 2008

AbstractWe have used far-ultraviolet spectroscopy and broad-band photometry to identify and study dynamically-formed stellar exotica in the core of 47 Tucanane. Here, we present a subset of our main results, including: (i) the spectroscopic confirmation of three cataclysmic variables; (ii) the discovery of stripped sub-giant core in a binary system with a dark primary; (iii) the discovery of a Helium white dwarf; (iv) the discovery of a blue straggler with a white dwarf companion.
The Imprints of IMBHs on the Structure of Globular Clusters: Monte-Carlo Simulations
Authors: Umbreit Stefan , Fregeau John M. , Rasio Frederic A. 
Published: May 2008

AbstractWe present the first results of a series of Monte-Carlo simulations investigating the imprints of a central black hole on the core structure of globular clusters. We investigate the three-dimensional and the projected density profile of the inner regions of idealized as well as more realistic globular cluster models, taking into account a stellar mass spectrum, stellar evolution and allowing for a larger, more realistic, number of stars than was previously possible with direct N-body methods. We compare our results to other N-body simulations published previously in the literature.
The Formation and Evolution of Very Massive Stars in Dense Stellar Systems
Authors: Belkus Houria , Van Bever Joris , Vanbeveren Dany 
Published: May 2008

AbstractThe early evolution of dense stellar systems is governed by massive single star and binary evolution. Core collapse of dense massive star clusters can lead to the formation of very massive objects through stellar collisions (M≥ 1000M⊙). Stellar wind mass loss determines the evolution and final fate of these objects, and determines whether they form black holes (with stellar or intermediate mass) or explode as pair instability supernovae, leaving no remnant. We present a computationally inexpensive evolutionary scheme for very massive stars that can readily be implemented in an N-body code. Using our new N-body code ‘Youngbody’ which includes a detailed treatment of massive stars as well as this new scheme for very massive stars, we discuss the formation of intermediate mass and stellar mass black holes in young starburst regions. A more detailed account of these results can be found in Belkus, Van Bever & Vanbeveren (2007).
Tracing Intermediate-Mass Black Holes in the Galactic Centre
Authors: Löckmann Ulf , Baumgardt Holger 
Published: May 2008

AbstractWe have developed a new method for post-Newtonian, high-precision integration of stellar systems containing a super-massive black hole (SMBH), splitting the forces on a particle between a dominant central force and perturbations. We used this method to perform fully collisional N-body simulations of inspiralling intermediate-mass black holes (IMBHs) in the centre of the Milky Way.
Environmental Effects on the Globular Cluster Blue Straggler Population: a Statistical Approach
Authors: Moretti Alessia , De Angeli Francesca , Piotto Giampaolo 
Published: May 2008

AbstractBlue stragglers stars (BSS) constitute an ubiquitous population of objects whose origin involves both dynamical and stellar evolution. We took advantage of the homogeneous sample of 56 Galactic globular clusters observed with WFPC2/HST by Piotto et al. (2002) to investigate the environmental dependence of the BSS formation mechanisms. We explore possible monovariate relations between the frequency of BSS (divided in different subsamples according to their location with respect to the parent cluster core radius and half mass radius) and the main parameters of their host GC. We also performed a Principal Component Analysis to extract the main parent cluster parameters which characterise the BSS family.
XMM-Newton and Chandra Observations of Neutron Stars and Cataclysmic Variables in the Globular Cluster NGC 2808
Authors: Servillat M. , Webb N. A. , Barret D. , Cornelisse R. , Dieball A. , Knigge C. , Long K. S. , Shara M. M. , Zurek D. R. 
Published: May 2008

AbstractWe report on XMM-Newton and Chandra observations of the globular cluster NGC 2808. We detect one quiescent low mass X-ray binary of the 3±1 expected, if these systems are formed through encounters, and we show evidence for the presence of 20±10 bright cataclysmic variables in the core with a luminosity above 4×1031 erg s−1. We also review the specific nature of cataclysmic variables in globular clusters with reference to recent VLT/FORS1 observations of a cataclysmic variable in M 22.
Giant Elliptical Galaxies: Globular Clusters and UCDs
Authors: Harris William E. 
Published: May 2008

AbstractExplorations of the globular cluster populations in many nearby galaxies are revealing increasing connections to other dense stellar systems such as UCDs, DGTOs, and nuclear star clusters in dwarf galaxies. The nearest giant elliptical, NGC 5128, is now giving us a much-improved delineation of the GC Fundamental Plane of structural parameters, and indicates as well that the known correlation between GC scale size and metallicity is likely to be at least partly a projection effect coupled with the different spatial distributions of the metal-poor and metal-rich clusters. New photometry of the huge cluster populations around the giant Brightest Cluster Ellipticals, which allows us to study samples of many thousands of GCs at once, are now beginning to turn up surprising examples of “sequences” of high-mass GCs leading up to the UCD regime. Lastly, new modelling of cluster formation through a specially tuned semi-analytic galaxy formation code strongly suggests that the mass-metallicity relation now known to affect the blue GC sequence can arise fairly naturally out of such models, if significant numbers of the massive GCs actually represent the remnant nuclei of stripped dwarf satellites.
Observational Constraints on the Formation and Evolution of Globular Cluster Systems
Authors: Zepf Stephen E. 
Published: May 2008

AbstractThis paper reviews some of the observational properties of globular cluster systems, with a particular focus on those that constrain and inform models of the formation and dynamical evolution of globular cluster systems. I first discuss the observational determination of the globular cluster luminosity and mass function. I show results from new very deep HST data on the M87 globular cluster system, and discuss how these constrain models of evaporation and the dynamical evolution of globular clusters. The second subject of this review is the question of how to account for the observed constancy of the globular cluster mass function with distance from the center of the host galaxy. The problem is that a radial trend is expected for isotropic cluster orbits, and while the orbits are observed to be roughly isotropic, no radial trend in the globular cluster system is observed. I review three extant proposals to account for this, and discuss observations and calculations that might determine which of these is most correct. The final subject is the origin of the very weak mass-radius relation observed for globular clusters. I discuss how this strongly constrains how globular clusters form and evolve. I also note that the only viable current proposal to account for the observed weak mass-radius relation naturally effects the globular cluster mass function, and that these two problems may be closely related.
Clues to Globular Cluster Evolution from Multiwavelength Observations of Extragalactic Systems
Authors: Kundu Arunav , Maccarone Thomas J. , Zepf Stephen E. 
Published: May 2008

AbstractWe present a study of the globular cluster (GC) systems of nearby elliptical and S0 galaxies at a variety of wavelengths from the X-ray to the infrared. Our analysis shows that roughly half of the low mass X-ray binaries (LMXBs), that are the luminous tracers of accreting neutron star or black hole systems, are in clusters. There is a surprisingly strong correlation between the LMXB frequency and the metallicity of the GCs, with metal-rich GCs hosting three times as many LMXBs as metal-poor ones, and no convincing evidence of a correlation with GC age so far. In some of the galaxies the LMXB formation rate varies with GC color even within the red peak of the typical bimodal cluster color distribution, providing some of the strongest evidence to date that there are metallicity variations within the metal-rich GC peak as is expected in a hierarchical galaxy formation scenario. We also note that any analysis of subtler variations in GC color distributions must carefully account for both statistical and systematic errors. We caution that some published GC correlations, such as the apparent ‘blue-tilt’ or mass-metallicity effect might not have a physical origin and may be caused by systematic observational biases.
Dynamical Evolution of the Mass Function of the Galactic Globular Cluster System
Authors: Shin Jihye , Kim Sungsoo S. , Takahashi Koji 
Published: May 2008

AbstractUsing the most advanced anisotropic (2D) Fokker-Planck (FP) models, we calculate the evolution of the mass functions of the Galactic globular cluster system (GCMF). Our models include two-body relaxation, binary heating, tidal shocks, dynamical friction, stellar evolution, and realistic cluster orbits. We perform 2D-FP simulations for a large number of virtual globular clusters and synthesize these results to study the relation between the initial and present GCMFs. We found two probable IGCMFs that eventually evolve into the Milky Way GCMF : truncated power-law, and log-normal model with higher initial low mass limit and peak mass than the earlier studies.
TKira—A Hybrid N-Body Code
Authors: Mamikonyan Ernest N. , McMillan Stephen L. W. , Portegies Zwart Simon F. , Vesperini Enrico 
Published: May 2008

AbstractAccurately modeling the evolution of a star cluster in a strong tidal field poses unique computational challenges. We present a hybrid code that combines the strengths of two different approaches to computing gravitational forces. The internal, collisional, dynamics of the cluster is followed with a direct N-body integrator, Kira, while the galactic tidal field is modeled with a cosmological code, GADGET, that uses a Barnes-Hut tree to evaluate gravitational forces in O(N log N) time. The quadrupole moment at the center of mass of the cluster is used to compute the external potential and provides a mechanism for mass loss. This forms a robust, bidirectional interaction. The advantages of combining two highly-developed and well-established software packages at such high level are obvious and many; not the least of the these is the ability to include other physical processes, e.g., stellar evolution. One problem to which we applied this technique is the evolution of a dense star cluster near the Galactic Center. We are also using this code to explore the effects of the strong time variation in the tidal field of merging galaxies on the evolution of young star clusters forming during the merger.
6th and 8th Order Hermite Integrator Using Snap and Crackle
Authors: Nitadori Keigo , Iwasawa Masaki , Makino Junichiro 
Published: May 2008

AbstractWe present sixth- and eighth-order Hermite integrators for astrophysical N-body simulations, which use the derivatives of accelerations up to second order (snap) and third order (crackle). These schemes do not require previous values for the corrector, and require only one previous value to construct the predictor. Thus, they are fairly easy to be implemented. The additional cost of the calculation of the higher order derivatives is not very high. Even for the eighth-order scheme, the number of floating-point operations for force calculation is only about two times larger than that for traditional fourth-order Hermite scheme. The sixth order scheme is better than the traditional fourth order scheme for most cases. When the required accuracy is very high, the eighth-order one is the best.
Climate Change Assessment for the Baltic Sea Basin
Authors: Reckermann Marcus , Von Storch Hans , Isemer Hans‐Jörg 
Published: May 2008

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change [IPCC, 2007] has had a big impact on the public perception and acknowledgment of global climate change. However, regional climate change assessments are urgently needed to complement the big picture with regional results and scenarios of higher resolution, which local decision makers and stakeholders can use [Visbeck, 2008; von Storch and Meinke, 2008].An outstanding example of a regional assessment is the BALTEX (Baltic Sea Experiment) Assessment of Climate Change for the Baltic Sea Basin (BACC; http://www.baltex‐research.eu/BACC/), which was compiled by a consortium of 84 scientists from 13 countries around the Baltic Sea [BACC Author Team, 2008]. The assessment covers various disciplines related to climate research and related impacts.
Ocean Color Reveals Increased Blooms in Various Parts of the World
Authors: Kahru Mati , Mitchell B. Greg 
Published: May 2008

The magnitude of phytoplankton blooms has increased significantly in many areas of the world during the past 11 years, as shown in data from ocean color sensors on board satellites. These areas with increased blooms are likely to be environmentally stressed and undergoing undesirable environmental changes such as a higher frequency of harmful algal blooms and oxygen depletion in bottom layers of oceans, estuaries, and lakes. These changes can disrupt traditional fisheries and recreational use in many coastal areas.An algal bloom is a rapid increase in the concentration of phytoplankton algae that occurs when conditions turn favorable for algal growth. A typical example of a bloom is the phytoplankton spring bloom. Algal blooms are natural phenomena that remove dissolved carbon and nutrients. In addition, they produce new biomass that supports higher trophic levels including fish and fisheries. However, the blooms also lead to excessive turbidity, oxygen depletion in the bottom layers, and the possible death of fish, benthic animals, and bottom vegetation.