bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple staining method for observation of germinatedStrigaseeds
Authors: Long Shusheng , Lendzemo Venasius , Kuyper Thomas W. , Kang Zhengsheng , Vierheilig Horst , Steinkellner Siegrid
Published: May 2008

In vitrotechniques are essential forStrigaresearch and the development of appropriate control methods. In the laboratory, pre-screening of non-host or false-host plants ofStrigafor trap cropping or the screening of hosts for resistance involves visual evaluation ofStrigaseed germination that may be stimulated by plant parts or root exudates. This technique is presently laborious because the smallStrigaradicles are colourless. A number of solutions were evaluated to visualize the radicles ofStriga hermonthicato obtain a reliable, simple and fast staining method yielding good contrast for visual observation, with readily available, inexpensive and minimally toxic dyes and staining solutions. The inks Brilliant Blue (Pelikan), Blue (Geha) and Brilliant Green (Pelikan), in either vinegar or lactic acid, produced radicles with excellent contrast, whereas radicles stained with Brilliant Red (Pelikan), Black (Sheaffer), Brilliant Black (Pelikan) gave good contrast.Strigaradicles stained with Aniline Blue in vinegar or lactic acid, or Coomassie Brilliant Blue R250 in lactic acid, showed excellent contrast. Radicles stained with Ink Black (Sheaffer), Cotton Brown, or Rubin S in either vinegar or lactic acid also showed good contrast. With water as the diluent, only Lactophenol Blue showed excellent contrast. For health, safety and environmental concerns, availability and staining time, Blue ink in household vinegar (5% acetic acid) appears to be an excellent dye forStrigaradicles and could be used in routineStrigagermination assays.
Risk tolerance and retirement income composition
Authors: SCHWABISH JONATHAN A. , TOPOLESKI JULIE H.
Published: May 2008

Proposed changes to the Social Security system will affect the financial risk workers will face in their retirement differently across the income distribution. This study examines levels of financial risk workers face at different points in the lifetime earnings distribution. To do so, we use a microsimulation model that projects individual demographic and economic characteristics within the context of the Social Security system and the macroeconomy to assess the impact of two policy changes on the levels of lifetime benefits available to current and future retirees. Further, we incorporate data on pensions and savings to illustrate differences in the level and distribution of retirement funds across the earnings distribution. This exercise allows us to assess the financial risk workers face in their retirement, both within the Social Security system itself and within a broader view of the stream of total available retirement funds. We also use survey data to show that low earners are the least willing to tolerate such risk.
Saving incentives, old-age provision and displacement effects: evidence from the recent German pension reform
Authors: BÖRSCH-SUPAN AXEL , REIL-HELD ANETTE , SCHUNK DANIEL
Published: May 2008

In response to population aging, pay-as-you-go pensions are being reduced in almost all developed countries. In many countries, governments aim to fill the resulting gap with subsidized private pensions. This paper exploits the recent German pension reform to shed new light on the uptake of voluntary, but heavily subsidized private pension schemes. Specifically, we investigate how the uptake of the recently introduced ‘Riester pensions’ depends on state-provided saving incentives, and how well the targeting at families and low-income households works in practice.

We show that, after a slow start, private pension plans took off very quickly. While saving incentives were effective in reaching parents, they were less successful in attracting low-income earners, although Riester pensions exhibit a more equal pattern by income than occupational pensions and unsubsidized private pension plans.

We also provide circumstantial evidence on displacement effects between saving for old-age provision and other purposes. Households who plan to purchase housing are less likely to have a Riester pension. The same holds for households who attach high importance to a bequest motive. Occupational pensions and other forms of private pensions, however, act as complements rather than as substitutes.
The Influence of Gas Expulsion on the Evolution of Star Clusters
Authors: Baumgardt H. , Kroupa P.
Published: May 2008

We present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.
A Dynamical Origin for Early Mass Segregation in Young Star Clusters
Authors: McMillan Steve , Vesperini Enrico , Zwart Simon Portegies
Published: May 2008

Some young star clusters show a degree of mass segregation that is inconsistent with the effects of standard two-body relaxation from an initially unsegregated system without substructure, in virial equilibrium, and it is unclear whether current cluster formation models can account for this degree of initial segregation in clusters of significant mass. We show that mergers of small clumps that are either initially mass segregated, or in which mass segregation can be produced by two-body relaxation before they merge, generically lead to larger systems which inherit the progenitor clumps' segregation. We conclude that clusters formed in this way are naturally mass segregated, accounting for the anomalous observations and suggesting that this process of prompt mass segregation due to initial clumping should be taken into account in models of cluster formation and dynamics.
A Near-infrared Survey of the Rosette Complex: Clues of Early Cluster Evolution
Authors: Román-Zúñiga Carlos G. , Lada Elizabeth A. , Ferreira Bruno
Published: May 2008

The majority of stars in our galaxy are born in embedded clusters, which can be considered the fundamental units of star formation. We have recently surveyed the star forming content of the Rosette Complex using FLAMINGOS in order to investigate the properties of its embedded clusters. We discuss the results of our near-infrared imaging survey. In particular, we on the first evidence for the early evolution and expansion of the embedded clusters. In addition we present data suggesting a temporal sequence of cluster formation across the cloud and discuss the influence of the HII region on the star forming history of the Rosette.
The Formation and Dynamics of the SMC Cluster NGC 346
Authors: Smith Linda J.
Published: May 2008

The young resolved cluster NGC 346 in the SMC provides us with the opportunity to study the details of cluster formation and the efficiency of feedback mechanisms at low metallicity. I describe the latest results from a large-scale study of this cluster and its H II region N66. HST/ACS images reveal that NGC 346 is composed of a number of sub-clusters which appear to be coeval with ages of 3±1 Myr, strongly suggesting formation by the hierarchical fragmentation of a giant molecular cloud (Nota et al. 2006; Sabbi et al. 2007a). HST Hα images show that the central cluster and the sub-clusters still contain some of their residual gas. We present high resolution spectroscopy of the ionized gas, and find that it shows little evidence for gas motions. This suggests that, at the low SMC metallicity, the cluster O star winds are not powerful enough to sweep away the residual gas. Instead, we find that stellar radiation is the dominant process shaping the interstellar environment of NGC 346.
Monte Carlo Simulations of Star Clusters with Primordial Binaries. Comparison with N-body Simulations and Observations
Authors: Giersz Mirek , Heggie Douglas C.
Published: May 2008

We outline the steps needed in to calibrate the Monte Carlo code in order to perform large scale simulations of real globular clusters. We calibrate the results against N-body simulations for N = 2500, 10000 and for the old open cluster M67. The calibration is done by choosing appropriate free code parameters.
Tidal Tails of the Nearest Open Clusters
Authors: Chumak Yaroslav , Rastorguev Alexey
Published: May 2008

We show that an extended population of stars escaping an evolved cluster and moving along its galactic orbit forms at the final phases of its dynamical evolution. Here we present some results of the numerical simulations for nearest open clusters: Hyades, Pleiades, Praesepe, Alpha Persei, Coma, IC 2391, and IC 2602. We calculated the models of the stellar tails for nearest open clusters and estimated some parameters: sizes, densities, locations relative to the solar neighborhood. Stars of the nearest tails can be observed as moving clusters.
The Population of Open Clusters in the Nearest kpc from the Sun
Authors: Röser S. , Kharchenko N. V. , Piskunov A. E. , Schilbach E. , Scholz R.-D.
Published: May 2008

We present a volume-limited sample (d < 850 pc) of open clusters in the Galaxy identified from our studies on galactic open clusters based on data from the all-sky catalogue ASCC-2.5 with absolute proper motions and B, V magnitudes of 2.5 million stars. The astrophysical properties of this sample are discussed.
The Simple Underlying Dynamics of Globular Clusters
Authors: King Ivan R.
Published: May 2008

Although the overall dynamics of globular clusters involves many complexities, much of their dynamics can be understood on the basis of some simple and straightforward physical arguments. Those arguments are presented here, in an effort to lead the reader through the basic stages of cluster dynamics in a quick and easy way.
Effects of Stellar Collisions on Star Cluster Evolution and Core Collapse
Authors: Chatterjee Sourav , Fregeau John M. , Rasio Frederic A.
Published: May 2008

We systematically study the effects of collisions on the overall dynamical evolution of dense star clusters using Monte Carlo simulations over many relaxation times. We derive many observable properties of these clusters, including their core radii and the radial distribution of collision products. We also study different aspects of collisions in a cluster taking into account the shorter lifetimes of more massive stars, which has not been studied in detail before. Depending on the lifetimes of the significantly more massive collision products, observable properties of the cluster can be modified qualitatively; for example, even without binaries, core collapse can sometimes be avoided simply because of stellar collisions.
Star Cluster Life-times: Dependence on Mass, Radius and Environment
Authors: Gieles Mark , Lamers Henny J. G. L. M. , Baumgardt Holger
Published: May 2008

The dissolution time (tdis) of clusters in a tidal field does not scale with the “classical” expression for the relaxation time. First, the scaling with N, and hence cluster mass, is shallower due to the finite escape time of stars. Secondly, the cluster half-mass radius is of little importance. This is due to a balance between the relative tidal field strength and internal relaxation, which have an opposite effect on tdis, but of similar magnitude. When external perturbations, such as encounters with giant molecular clouds (GMC) are important, tdis for an individual cluster depends strongly on radius. The mean dissolution time for a population of clusters, however, scales in the same way with mass as for the tidal field, due to the weak dependence of radius on mass. The environmental parameters that determine tdis are the tidal field strength and the density of molecular gas. We compare the empirically derived tdis of clusters in six galaxies to theoretical predictions and argue that encounters with GMCs are the dominant destruction mechanism. Finally, we discuss a number of pitfalls in the derivations of tdis from observations, such as incompleteness, with the cluster system of the SMC as particular example.
N-body Simulations of Star Clusters
Authors: Anders Peter , Lamers Henny J. G. L. M. , Baumgardt Holger
Published: May 2008

Two aspects of our recent N-body studies of star clusters are presented:

1)

What impact does mass segregation and selective mass loss have on integrated photometry?

2)

How well do results compare from N-body simulations using NBODY4 and STARLAB/KIRA?
Binary Stars and Globular Cluster Dynamics
Authors: Fregeau John M.
Published: May 2008

In this brief proceedings article I summarize the review talk I gave at the IAU 246 meeting in Capri, Italy, glossing over the well-known results from the literature, but paying particular attention to new, previously unpublished material. This new material includes a careful comparison of the apparently contradictory results of two independent methods used to simulate the evolution of binary populations in dense stellar systems (the direct N-body method of Hurley, Aarseth, & Shara (2007) and the approximate Monte Carlo method of Ivanova et al. (2005)), that shows that the two methods may not actually yield contradictory results, and suggests future work to more directly compare the two methods.
Evolution of Compact Binary Populations in Globular Clusters: a Boltzmann Study
Authors: Banerjee Sambaran , Ghosh Pranab
Published: May 2008

We explore a Boltzmann scheme for studying the evolution of compact binary populations in globular clusters. We include processes of compact binary formation by tidal capture and exchange encounters, binary destruction by exchange and dissociation mechanisms and binary hardening by encounters, gravitational radiation and magnetic braking, as also the orbital evolution during mass transfer, following Roche lobe contact. From the evolution of compact-binary population, we investigate the dependence of the model number of X-ray binaries NXB on two essential cluster properties, namely, the star-star and star-binary encounter-rate parameters Γ and γ (Verbunt parameters). We find that the values of NXB and their expected scaling with the Verbunt parameters are in good agreement with results from recent X-ray observations of Galactic globular clusters.
A Post-Newtonian Treatment of Relativistic Compact Object Binaries in Star Clusters
Authors: Downing J. M. B. , Spurzem R.
Published: May 2008

Stellar mass compact object binaries are promising sources of gravitational radiation for the current generation of ground-based detectors, VIRGO and LIGO. Accurate templates for gravitational waveforms are needed in order to extract an event from the VIRGO/LIGO data stream. In the case of relativistic, compact object binaries accurate orbital parameters are necessary in order to produce such templates. Binary systems are affected by their stellar environment and thus the parameters of the binary population of a dense star cluster will be different from those of the field population. We propose to investigate the parameters of relativistic binary populations in dense star clusters using direct N-body simulations with a Post-Newtonian treatment of general relativity for the close binaries.
Getting a Kick out of the Stellar Disk(s) in the Galactic Center
Authors: Perets H. B. , Kupi G. , Alexander T.
Published: May 2008

Recent observations of the Galactic center revealed a nuclear disk of young OB stars, in addition to many similar outlying stars with higher eccentricities and/or high inclinations relative to the disk (some of them possibly belonging to a second disk). Binaries in such nuclear disks, if they exist in non-negligible fractions, could have a major role in the evolution of the disks through binary heating of this stellar system. We suggest that interactions with/in binaries may explain some (or all) of the observed outlying young stars in the Galactic center. Such stars could have been formed in a disk, and later on kicked out from it through binary related interactions, similar to ejection of high velocity runaway OB stars in young clusters throughout the galaxy.
Observations and Simulations of the Blue Straggler Star Radial Distribution: Clues on the Formation Mechanisms
Authors: Lanzoni Barbara
Published: May 2008

By means of high-resolution and wide-field observations in the UV and optical bands we have derived the radial distribution of the Blue Stragglers Star (BSS) population in a number of galactic globular clusters. Monte-Carlo dynamical simulations have then been used to interpret the observed radial distributions in terms of percentage of collisional and mass-transfer BSS populating each cluster. I will present the main results thus obtained and an overall cluster–to–cluster comparison for the whole sample collected so far, mainly focusing on the clues that such an approach provides about the BSS formation mechanisms.
Where the Blue Stragglers Roam: Searching for a Link Between Formation and Environment
Authors: Leigh Nathan , Sills Alison , Knigge Christian
Published: May 2008

Current observational evidence seems to indicate that blue stragglers are a dynamically created population, though exactly how the mechanism(s) of formation operates remains a mystery. We search for links between blue straggler formation and environment by considering only those stars found within one core radius of the cluster center. In so doing, we aim to isolate a sample that is representative of an approximately uniform cluster environment where, ideally, a single blue straggler formation mechanism is predominantly operating. Normalized blue straggler frequencies are found and apart from new anticorrelations with the central velocity dispersion and the half-mass relaxation time, we find no other statistically significant trends.

Concerns regarding the method of normalization used to calculate relative blue straggler frequencies are discussed, specifically whether the previously observed anticorrelation with total cluster mass (see Piotto et al. 2004) is a consequence of the normalization process. A new correlation between the observed number of blue stragglers in the core and the number predicted from single-single collisions alone is presented. This new link between formation and environment represents the first direct evidence that the blue straggler phenomenon has, at least in part, a collisional origin.
An X-ray Emitting Black Hole in a Globular Cluster
Authors: Maccarone T.J. , Bergond G. , Kundu A. , Rhode K.L. , Salzer J.J. , Shih I.C. , Zepf S.E.
Published: May 2008

We present optical and X-ray data for the first object showing strong evidence for being a black hole in a globular cluster. We show the initial X-ray light curve and X-ray spectrum which led to the discovery that this is an extremely bright, highly variable source, and thus must be a black hole. We present the optical spectrum which unambiguously identifies the optical counterpart as a globular cluster, and which shows a strong, broad [O III] emission line, most likely coming from an outflow driven by the accreting source.
Central Dynamics of Globular Clusters: the Case for a Black Hole in ω Centauri
Authors: Noyola Eva , Gebhardt Karl , Bergmann Marcel
Published: May 2008

The globular cluster ω Centauri is one of the largest and most massive members of the Galactic system. Its classification as a globular cluster has been challenged making it a candidate for being the stripped core of an accreted dwarf galaxy; this and the fact that it has one of the largest velocity dispersions for star clusters in our galaxy makes it an interesting candidate for harboring an intermediate mass black hole. We measure the surface brightness profile from integrated light on an HST/ACS image, and find a central power-law cusp of logarithmic slope -0.08. We also analyze Gemini GMOS-IFU kinematic data for a 5”x5” field centered on the nucleus of the cluster, as well as for a field 14″ away. We detect a clear rise in the velocity dispersion from 18.6 kms−1 at 14″ to 23 kms−1 in the center. Given the very large core in ω Cen (2.58'), an increase in the dispersion in the central 10″ is difficult to attribute to stellar remnants, since it requires too many dark remnants and the implied configuration would dissolve quickly given the relaxation time in the core. However, the increase could be consistent with the existence of a central black hole. Assuming a constant M/L for the stars within the core, the dispersion profile from these data and data at larger radii implies a black hole mass of 4.0+0.75−1.0×104M⊙. We have also run flattened, orbit-based models and find a similar mass. In addition, the no black hole case for the orbit model requires an extreme amount of radial anisotropy, which is difficult to preserve given the short relaxation time of the cluster.
On the Dynamical Capture of a MSP by an IMBH in a Globular Cluster
Authors: Devecchi B. , Colpi M. , Mapelli M. , Possenti A.
Published: May 2008

Globular clusters (GCs) are rich of millisecond pulsars (MSPs) and might also host single or binary intermediate–mass black holes (IMBHs). We simulate 3- and 4-body encounters in order to test the possibility that an IMBH captures a MSP. The newly formed system could be revealed from the timing signal of the MSP, providing an unambiguous measure of the BH mass. In current surveys, the number of expected [IMBH,MSP] binaries in the Milky Way is ~0.1. If next-generation radio telescopes (e.g. SKA) will detect ~10 times more MSPs in GCs, we expect to observe at least one [IMBH,MSP] binary.
Unveiling the Core of M 15 in the Far-Ultraviolet
Authors: Dieball A. , Knigge C. , Zurek D. R. , Shara M. M. , Long K. S. , Charles P. A. , Hannikainen D.
Published: May 2008

We present an analysis of our deep far- (FUV) and near-ultraviolet (NUV) photometry of the core region of the dense globular cluster M 15. Our FUV-NUV colour-magnitude diagram (CMD) is the deepest one presented for a globular cluster so far, and shows all hot stellar populations expected in a globular cluster, such as horizontal branch stars, blue stragglers, white dwarfs, cataclysmic variables and even main sequence stars. The main sequence turn-off is clearly visible and the main sequence stars form a prominent track that extends at least two magnitudes below the main sequence turn-off. We compare and discuss the radial distribution of the various stellar populations that show up in the FUV. We search for variability amongst our FUV sources and tentatively classify our variable candidates based on an analysis of the UV colours and variability properties. We find that RR Lyraes, Cepheids, and SX Phoenicis exhibit massive variability amplitudes in this waveband (several mags).
On the Origin of Hyperfast Neutron Stars
Authors: Gvaramadze V.V. , Gualandris A. , Zwart S. Portegies
Published: May 2008

We propose an explanation for the origin of hyperfast neutron stars (e.g. PSR B1508+55, PSR B2224+65, RX J0822–4300) based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star (or its helium core) which attained its peculiar velocity (similar to that of the neutron star) in the course of a strong three- or four-body dynamical encounter in the core of a young massive star cluster. This hypothesis implies that the dense cores of star clusters (located either in the Galactic disk or near the Galactic centre) could also produce the so-called hypervelocity stars – ordinary stars moving with a speed of ~ 1 000 km s−1.
Paucity of Dwarf Novae in Globular Clusters
Authors: Pietrukowicz P. , Kaluzny J.
Published: May 2008

We have conducted an extensive photometric search for dwarf nova (DN) outbursts in 16 Galactic globular clusters (GCs). The survey was based on the rich photometric data collected by the Cluster AgeS Experiment (CASE) team. We have identified two new DNe. Together with previously known systems this gives the total number of 12 known DNe in 7 Galactic GCs. Inserting artificial light curves of “DNe” into frames of investigated clusters allowed us to assess completeness of the search. Our results clearly show that outbursting cataclysmic variables (CVs) are very rare in GCs in comparison to field CVs where half of the systems belongs to DNe. Recent X-ray observations of GCs lead to identification of hundreds of compact binaries. Many of them are promising candidates for CVs. The theory also predicts that dozens of white/red dwarf binaries should form in the cores of GCs via dynamical processes or internal evolution of the binaries. Our results rises the question about possible causes of paucity of outbursts in GCs.
An Update on the ACS Virgo and Fornax Cluster Surveys
Authors: Côté Patrick , Ferrarese Laura , Jordán Andrés , Blakeslee John P. , Chen Chin-Wei , Infante Leopoldo , Mei Simona , Peng Eric W. , Tonry John L. , West Michael J.
Published: May 2008

We present a brief update on the ACS Virgo and Fornax Cluster Surveys —Hubble Space Telescopeprograms to obtainACSimaging for 143 early-type galaxies in the two galaxy clusters nearest to the Milky Way. We summarize a selection of science highlights from the surveys as including new results on the central structure of early-type galaxies, the apparent continuity of photometric and structural parameters between dwarf and giant galaxies, and the properties of globular clusters, diffuse star clusters and ultra-compact dwarf galaxies.
The Origin of the Universal Globular Cluster Mass Function
Authors: Parmentier G. , Gilmore G.
Published: May 2008

Evidence favouring a Gaussian initial mass function for systems of old globular clusters has accumulated over recent years. We show that a bell-shaped mass function may be the imprint of expulsion from protoclusters of the leftover star forming gas due to supernova activity. Owing to the corresponding weakening of its gravitational potential, a protocluster retains a fraction only of its newly formed stars. The mass fraction of bound stars extends from zero to unity depending on the star formation efficiency achieved by the protoglobular cloud. We investigate how such wide variations affect the mapping of the protoglobular cloud mass function to the initial globular cluster mass function. We conclusively demonstrate that the universality of the globular cluster mass function originates from a common protoglobular cloud mass-scale of about 106 M⊙ among galaxies. Moreover, gas removal during star formation in massive gas clouds is highlighted as the likely prime cause of the predominance of field stars in the Galactic Halo.
Masses and M/L Ratios of Bright Globular Clusters in NGC 5128
Authors: Rejkuba M. , Dubath P. , Minniti D. , Meylan G.
Published: May 2008

We present an analysis of the radial velocities and velocity dispersions for 27 bright globular clusters in the nearby elliptical galaxy NGC 5128 (Centaurus A). For 22 clusters we combine our new velocity dispersion measurements with the information on the structural parameters, either from the literature when available or from our own data, in order to derive the cluster masses and mass-to-light (M/L) ratios. The masses range from 1.2 × 105M⊙, typical of Galactic globular clusters, to 1.4 × 107M⊙, similar to more massive dwarf globular transition objects (DGTOs) or ultra compact dwarfs (UCDs) and to nuclei of nucleated dE galaxies. The average M/LV is 3±1, larger than the average M/LV of globular clusters in the Local Group galaxies. The correlations of structural parameters, velocity dispersion, masses and M/LV for the bright globular clusters extend the properties established for the most massive Local Group clusters towards those characteristic of dwarf elliptical galaxy nuclei and DGTOs/UCDs. The detection of the mass-radius and the mass-M/LV relations for the globular clusters with masses greater than ~ 2 × 106M⊙ provides the link between “normal” old globular clusters, young massive clusters, and evolved massive objects.
Formation of Galactic Nuclei by Globular Cluster Merging
Authors: Miocchi P. , Dolcetta R. Capuzzo
Published: May 2008

Recent HST observations have revealed that compact sources exist at the centers of many galaxies across the Hubble sequence. These sources are called “nuclear star clusters” (NCs), because their structural properties and scaling relationships are similar to those of globular clusters (GCs). It has been also found that the relationship between the masses of NCs and that of the host galaxies is similar to that obeyed by supermassive black holes (SBHs). In this observational frame, the hypothesis that galactic nuclei may be the remains of GCs driven inward to the galactic center by dynamical friction and there merged, finds an exciting possible confirm. In this short paper we report of our recent results on GC mergers obtained by mean of detailed N-body simulations.
Dancing with Black Holes
Authors: Aarseth S. J.
Published: May 2008

We describe efforts over the last six years to implement regularization methods suitable for studying one or more interacting black holes by direct N-body simulations. Three different methods have been adapted to large-N systems: (i) Time-Transformed Leapfrog, (ii) Wheel-Spoke, and (iii) Algorithmic Regularization. These methods have been tried out with some success on GRAPE-type computers. Special emphasis has also been devoted to including post-Newtonian terms, with application to moderately massive black holes in stellar clusters. Some examples of simulations leading to coalescence by gravitational radiation will be presented to illustrate the practical usefulness of such methods.
Virtual Laboratories and Virtual Worlds
Authors: Hut Piet
Published: May 2008

Since we cannot put stars in a laboratory, astrophysicists had to wait till the invention of computers before becoming laboratory scientists. For half a century now, we have been conducting experiments in our virtual laboratories. However, we ourselves have remained behind the keyboard, with the screen of the monitor separating us from the world we are simulating. Recently, 3D on-line technology, developed first for games but now deployed in virtual worlds like Second Life, is beginning to make it possible for astrophysicists to enter their virtual labs themselves, in virtual form as avatars. This has several advantages, from new possibilities to explore the results of the simulations to a shared presence in a virtual lab with remote collaborators on different continents. I will report my experiences with the use of Qwaq Forums, a virtual world developed by a new company (see http://www.qwaq.com).
Fully Self-Consistent N-body Simulation of Star Cluster in the Galactic Center
Authors: Fujii M. , Iwasawa M. , Funato Y. , Makino J.
Published: May 2008

We have developed a new tree-direct hybrid algorithm, “Bridge”. It can simulate small scale systems embedded within large-N systems fully self-consistently. Using this algorithm, we have performed full N-body simulations of star clusters near the Galactic center (GC) and compared the orbital evolutions of the star cluster with those obtained by “traditional” simulations, in which the orbital evolution of the star clusters is calculated from the dynamical friction formula. We found that the inspiral timescale of the star cluster is shorter than that obtained with traditional simulations. Moreover, we investigated the eccentricities of particles escaped from the star cluster. Eccentric orbit of the star cluster can naturally explain the high eccentricities of the observed stars.
Test of the Accuracy of Approximate Methods to Handle Distant Binary-Single Star Encounters
Authors: Funato Yoko , Heggie D.C. , Hut P. , Makino Jun
Published: May 2008

In the numerical simulations of evolution of star clusters, binary-single star interactions frequently take place. Since the direct integration of them is time consuming, distant interactions between binaries and field stars are often integrated by using some approximations. Traditionally the effect of the error caused by the approximated treatment is regarded as small enough to be ignored. However, if we have a binary-dominated core, the energy drift is large. In this study, we perform numerical experiments to evaluate the effect of neglecting the weak perturbation from distant single particles. We developed an N-body integrator which can manipulate multiple precision floating point numbers.
Embryo to Ashes Complete Evolutionary Tracks, Hands-off
Authors: Yaron O. , Kovetz A. , Prialnik D.
Published: May 2008

We present a new stellar evolution code and a set of results, showing its capability to calculate full evolutionary tracks for a wide range of masses and metalicities. The code is meant to be used also in the context of modeling the evolution of dense stellar systems, for performing live evolutionary calculations both for ‘normal’ ZAMS/PRE-MS models, but mainly for ‘non-canonical’ (i.e. merger-products) stellar configurations. For such tasks, it has to be robust and efficient, capable to run through all phases of stellar evolution without interruption or intervention. Here we show a few examples of evolutionary calculations for stellar populations I and II, and for masses in the range 0.25–64 M⊙.
The PSU/TCfA search for planets around evolved stars. Stellar parameters and activity indicators of targets.
Authors: Niedzielski Andrzej , Nowak Grzegorz , Zieliński Paweł
Published: May 2008

The main objective of the Penn State/Toruń Centre for Astronomy search for planets around evolved stars is the detection of planetary systems around massive, evolved stars. We are also interested in the evolution of these systems on stellar evolution timescales. In this paper we present our approach to determine the basic physical parameters of our targets GK-giants. We also discuss the stellar activity indicators used in our survey: line bisector and curvature, and Hα variability.
Diversity of close-in planets and the interactions with their host stars
Authors: Lin Douglas N.C. , Dobbs-Dixon Ian
Published: May 2008

Short period planets provide an exciting opportunity of constraining structural properties. Observations have revealed a diverse class of objects, including several at odds with aspects of conventional planet formation theories. Here we present several scenarios that may help in producing the observed diversity. For short period planets in particular, their proximity to their host stars suggests that star-planet interactions may play an important role in their orbital and structural evolution. We first show that the penetration of a non-synchronous stellar magnetic field into short period planets will provide a significant source of energy for planetary expansion and may help stall inward migration. In addition to magnetic dissipation, the intense irradiation from the host star will drive atmospheric flows, whose behaviour is strongly influenced by the opacity of the envelope. Finally, we explore the role of late stage planetesimal and embryo bombardment on the structure of gas-giant planets. Dynamical trapping during migration, followed by orbital destablization during the final stage of gas-giant growth, leads to a surge in the collision rate. Such collisions will lead to preferential core growth and inflated radii. All three of these processes, occurring late in the planetary formation process, will produce a large range in planetary properties and may account for the diversity we see today.
Silicate, ruby, opal – Why gas giants keep their jewels in the atmosphere
Authors: Helling Christiane
Published: May 2008

Giant gas-planets - and brown dwarfs - form dust clouds in their atmospheres which are made of a variety of gemstone-like and possible liquid materials. Our theoretical approach, where we calculate homogeneous nucleation, heterogeneous growth/evaporation, gravitational settling, and element consumption for composite dust grains, allows to access the evolution of the dust complex in the cloud, and hence also the elements remaining in the gas phase. The cloud formation process is imprinted into these remaining elements. Following a (T, p) trajectory into the atmosphere we observe that 1. metals disappear, 2. dust forms, 3. metals re-appear, 4. dust disappears. For the first time, our kinetic cloud formation approach is coupled with an 1D atmosphere simulation and, hence, synthetic spectra can be produced based on detailed cloud micro-physics. Results are demonstrated for metal-poor gas giants and the strong influence of the dust modelling on alkali-line profile is shown.
Astrobiological effects of F, G, K and M main-sequence stars
Authors: Cuntz M. , Gurdemir L. , Guinan E. F. , Kurucz R. L.
Published: May 2008

We focus on the astrobiological effects of photospheric radiation produced by main-sequence stars of spectral types F, G, K, and M. The photospheric radiation is represented by using realistic spectra, taking into account millions or hundred of millions of lines for atoms and molecules. DNA is taken as a proxy for carbon-based macromolecules, assumed to be the chemical centerpiece of extraterrestrial life forms. Emphasis is placed on the investigation of the radiative environment in conservative as well as generalized habitable zones.
Orbital migration and mass-semimajor axis distributions of extrasolar planets
Authors: Ida Shigeru , Lin D. N. C.
Published: May 2008

Here we discuss the effects of type-I migration of protoplanetary embryos on mass and semimajor axis distributions of extrasolar planets. We summarize the results of Ida & Lin (2008a, 2008b), in which Monte Carlo simulations with a deterministic planet-formation model were carried out. The strength of type-I migration regulates the distribution of extrasolar gas giant planets as well as terrestrial planets. To be consistent with the existing observational data of extrasolar gas giants, the type-I migration speed has to be an order of magnitude slower than that given by the linear theory. The introduction of type-I migration inhibits in situ formation of gas giants in habitable zones (HZs) and reduces the probability of passage of gas giants through HZs, both of which facilitate retention of terrestrial planets in HZs. We also point out that the effect of magneto-rotational instability (MRI) could lead to trapping of migrating protoplanetary embryos in the regions near an ice line in the disk and it significantly enhances formation/retention probability of gas giants against type-I migration.
Planet formation in binary stars
Authors: Kley Wilhelm
Published: May 2008

As of today more than 30 planetary systems have been discovered in binary stars. In all cases the configuration is circumstellar, where the planets orbit around one of the stars. The formation process of planets in binary stars is more difficult than around single stars due to the gravitational action of the companion. An overview of the research done in this field will be given. The dynamical influence that a secondary companion has on a circumstellar disk, and how this affects the planet formation process in this challenging environment will be summarized. Finally, new fully hydrodynamical simulations of protoplanets embedded in disks residing in a binary star will be presented. Applications with respect to the planet orbiting the primary in the system γ Cephei will be presented.
Giant impact, planetary merger, and diversity of planetary-core mass
Authors: Li S.-L. , Agnor C. , Lin D. N. C.
Published: May 2008

Transit observations indicate a large dispersion in the internal structure among the known gas giants. This is a big challenge to the conventional sequential planetary formation scenario because the diversity is inconsistent with the expectation of some well defined critical condition for the onset of gas accretion in this scenario. We suggest that giant impacts may lead to the merger of planets or the accretion of planetary embryos and cause the diversity of the core mass. By using an SPH scheme, we show that direct parabolic collisions generally lead to the total coalescence of impinging gas giants whereas, during glancing collisions, the efficiency of core retention is much larger than that of the envelope. We also examine the adjustment of the gaseous envelope with a 1D Lagrangian hydrodynamic scheme. In the proximity of their host stars, the expansion of the planets' envelopes, shortly after sufficiently catastrophic impacts, can lead to a substantial loss of gas through Roche-lobe overflow. We are going to examine the possibility that the accretion of several Earth-mass objects can significantly enlarge the planets' photosphere and elevate the tidal dissipation rate over the time scale of 100 Myr.
Baroclinic generation of potential vorticity in an embedded planet-disk system
Authors: JI Jianghui , OU Shangli , LIU Lin
Published: May 2008

We use a multi-dimensional hydrodynamics code to study the gravitational interaction between an embedded planet and a protoplanetary disk with emphasis on the generation of vortensity (Potential Vorticity or PV) through a Baroclinic Instability. We show that the generation of PV is very common and effective in non-barotropic disks through the Baroclinic Instability, especially within the coorbital region. Our results also complement previous work that non-axisymmetric Rossby-Wave Instabilities (RWIs) are likely to develop at local minima of PV distribution that are generated by the interaction between a planet and an inviscid barotropic disk. The development of RWIs results in non-axisymmetric density blobs, which exert stronger torques onto the planet when they move to the vicinity of the planet. Hence, large amplitude oscillations are introduced to the time behavior of the total torque acted on the planet by the disk. In current simulations, RWIs do not change the overall picture of inward orbital migration but cause a non-monotonic behavior to the migration speed. As a side effect, RWIs also introduce interesting structures into the disk. These structures may help the formation of Earth-like planets in the Habitable Zone or Hot Earths interior to a close-in giant planet.
Effects of dissipating gas drag on planetesimal accretion in binary systems
Authors: Xie Ji-Wei , Zhou Ji-Lin
Published: May 2008

We numerically investigate the conditions for planetesimal accretion in the circumprimary disk under the perturbing presence of a companion star, with focus on the γ Cephei system. Gas drag is included with a dissipating time scale of 105years. We show at the beginning(within 103∼ 104years), gas drag damps the ΔVbetween planetesimals of same sizes and increases ΔVbetween planetesimals of different sizes. However, after increasing to high values(300∼800m/s), we find the ΔVbetween bodies of different sizes decrease to very low values (below 10m/s) in a few 105yrs(depending on the gas-dissipating time scaleTdamp, radial sizeRpand semi-major axisapof planetesimals). Hence, the high ΔVis somewhat short-lived, and runaway accretion can be turned on later. We conclude that the conditions for planetary formation in binary systems (even close binary systems) are much better than what we expected before.
Psychische Gesundheit und Rückkehrvorstellungen am Beispiel von Flüchtlingen aus dem ehemaligen Jugoslawien
Authors: von Lersner Ulrike , Rieder Heide , Elbert Thomas
Published: May 2008

Zusammenfassung. Theoretischer Hintergrund: Viele Flüchtlinge aus dem ehemaligen Jugoslawien leben seit ca. 11 Jahren in Deutschland. Es fehlt bislang an Daten zu den Langzeitfolgen der traumatischen Kriegsereignisse und der Einflüsse von Exilfaktoren auf die psychische Gesundheit in dieser Population. Auch sind Zusammenhänge zwischen diesen Faktoren sowie die Einstellung zur Rückkehr nicht ausreichend untersucht. Fragestellung: Wie ist die psychische Gesundheit dieser Flüchtlinge nach durchschnittlich 11 Jahren im Exilland Deutschland einzuschätzen? Welche Motive sprechen aus Sicht der Betroffenen für und gegen eine freiwillige Rückkehr ins Herkunftsland? Methoden: n = 50 Flüchtlinge wurden zu ihrer aktuellen Lebenssituation, ihrer Einstellung zum Heimatland und zu freiwilliger Rückkehr befragt, sowie zu ihrer psychischen Gesundheit mit dem strukturierten Interview M.I.N.I. und den Fragebögen PDS und EUROHIS untersucht. Ergebnisse: Bei 78.0% liegt mindestens eine psychische Störung vor, es zeigen sich Zusammenhänge zwischen Lebenssituation in Deutschland, Rückkehrbereitschaft und psychischer Gesundheit. Schlussfolgerungen: Die psychische Belastung der Befragten ist sehr hoch, Ursachen hierfür sind sowohl die erhöhte Vulnerabilität auf Grund der Kriegsereignisse als auch die Belastung durch Postmigrationsfaktoren im Exil. Diese Faktoren sollten im Umgang mit Flüchtlingen in Deutschland berücksichtigt werden und haben auch Implikationen für die Planung von Rückkehrhilfeprogrammen.
Psychologische Prädiktoren für das Auftreten einer Major Depression nach schweren Unfällen
Authors: Kühn Manuela , Ehlert Ulrike , Rumpf Hans-Jürgen , Backhaus Jutta , Hohagen Fritz , Broocks Andreas
Published: May 2008

Zusammenfassung. Theoretischer Hintergrund/Fragestellung: Ziel unserer prospektiven Studie war die Identifikation von Prädiktoren für das Auftreten einer Depression im ersten halben Jahr nach einem Unfall. Methode: Es wurden 52 Unfallpatienten untersucht. Die Ersterhebung erfolgte innerhalb der ersten sechs Wochen nach dem Unfall. Ergebnisse: Depressive Patienten gaben kurz nach dem Unfall eine geringere Lebenszufriedenheit und soziale Unterstützung an und berichteten häufiger über psychische Störungen und traumatische Erlebnisse vor dem Unfall als Nicht-Depressive. Außerdem litten sie zum Zeitpunkt der Ersterhebung häufiger unter psychischen Störungen und fühlten sich durch die psychischen Symptome stärker beeinträchtigt. Schlussfolgerung: Die Ergebnisse legen nahe, dass Patienten mit einem Risiko für die Entwicklung einer Depression bereits kurz nach einem Unfall identifiziert werden können.
A method for estimating the ring current structure and the electric potential distribution using energetic neutral atom data assimilation
Authors: Nakano S. , Ueno G. , Ebihara Y. , Fok M.‐C. , Ohtani S. , Brandt P. C. , Mitchell D. G. , Keika K. , Higuchi T.
Published: May 2008

We present a technique for estimating ring current ion distributions and electric potential in the inner magnetosphere by incorporating data from the High‐Energy Neutral Atom (HENA) imager on the IMAGE satellite into a kinetic ring current model in the context of data assimilation. Data assimilation is an approach which adjusts a physics‐based model according to differences with observations. We perform the data assimilation using the particle filter (PF) which is applicable to high‐dimensional systems and observations with relatively low computational cost. In the present technique, the magnetospheric electric potential distribution is represented by the sum of a Volland‐Stern field and a deviation, and the deviation is improved in the assimilation process. The ring current ion distribution is then determined from the electric potential distribution. The method is tested by assimilating artificial data generated by another simulation. The results demonstrate that the ring current ion distribution is successfully reconstructed by the proposed algorithm and that the distorted structures of the electric potential distribution are also well reproduced. An example to illustrate how the present technique could be applied for assimilating a real IMAGE/HENA data set is also demonstrated. This technique provides a useful tool for investigating the global dynamic structure of ring current and electric potential.