bluuebunny/crossref_metadata_2025_split huggingface dataset:
Getting a Kick out of the Stellar Disk(s) in the Galactic Center
Authors: Perets H. B. , Kupi G. , Alexander T. 
Published: May 2008

AbstractRecent 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

AbstractBy 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

AbstractCurrent 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

AbstractWe 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

AbstractThe 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

AbstractGlobular 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

AbstractWe 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

AbstractWe 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

AbstractWe 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

AbstractWe 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

AbstractEvidence 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

AbstractWe 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

AbstractRecent 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

AbstractWe 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

AbstractSince 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

AbstractWe 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

AbstractIn 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

AbstractWe 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

AbstractThe 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

AbstractShort 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

AbstractGiant 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

AbstractWe 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

AbstractHere 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

AbstractAs 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.