bluuebunny/crossref_metadata_2025 huggingface dataset:
The Star Formation History in Nearby Dwarf Galaxies: the Fossil Record in the Color-Magnitude Diagram
Authors: Aparicio A.
Published: July 2016

Dwarf galaxies may play a key role in the formation and evolution of bigger systems. This makes knowing how they form and evolve and, in particular, how their star formation histories (SFHs) have proceeded since their birth, a topic of major interest. For nearby galaxies, the color-magnitude diagram (CMD) contains stars formed over all their lifetime. It is hence a fossil record of their SFHs. The analysis with synthetic CMDs provides a powerful tool to retrieve them.

In this paper, I discuss the critical issues related to the computation of synthetic CMDs, present a short summary of the currently available results for the SFH extending the full life of galaxies and make a few critical considerations about the powerfulness and draw-backs of the method.
Stellar Population Gradients in Phoenix and Leo I
Authors: Martínez-Delgado D. , Gallart Carme , Aparicio A. , Freedman W.
Published: July 2016

The study of gradients in the stellar populations of dwarf galaxies will give us necessary information to construct detailed models of their formation and evolution. We find clear traces of these gradients, in the sense of stars being older for larger galactocentric distances, in two interesting nearby dwarfs: Phoenix and Leo I.
Submillimetre Continuum Imaging of Large-scale Outflows in Nearby Starburst Galaxies
Authors: Leeuw L. L. , Robson E. I. , Hughes D. H.
Published: July 2016

We present SCUBA imaging observations of the nearby prototype starburst galaxy M82, in order to study large-scale outflows observed in such galaxies and associated with starburst phenomena. We use (1) deep 450 μm continuum maps to investigate the structure and details of the large-scale outflows and (2) 850 μm linear-polarization maps to investigate the relation between nuclei and halo magnetic fields.
Miras and Mass Loss in the Local Group
Authors: Zijlstra Albert A. , Bedding Timothy R.
Published: July 2016

Evolved AGB stars pass through a phase of heavy mass loss during which they become optically obscured. We describe an observational program to find and study such stars in the Magellanic Clouds. Many of the obscured stars are found to be luminous carbon stars, a population previously missing. We discuss the Mira PL relation, valid before the onset of the heaviest mass loss. We find that a number of semi-regulars fit this relation, based on Hipparcos parallaxes. No evidence is seen for a Z-dependence, giving a powerful potential distance indicator. We derive a distance modulus to the LMC of m − M = 18.63 ± 0.09 as well as a bright calibration for the Horizontal Branch in globular clusters.
Age and Mass of the Local Group from Satellite Galaxy Dynamics
Authors: Whiting Alan B.
Published: July 2016

The present kinematics of an unrelaxed system such as the Local Group can be used to investigate its dynamics on a cosmological time scale. In particular, the classical timing argument of Kahn & Woltjer may be extended to distant satellite galaxies of the Local Group whose distances and velocities are known with some accuracy. Including a correction for the fact that the Local Group was not always dynamically isolated, I derive a mass for the Group of about 1.6 x 1012M⊙ and an age of 1.0 to 1.2 x 1010 years.
The Search for Galaxy Orientation in the Local Group
Authors: Flin P.
Published: July 2016

The analysis of 34 galaxies being members of the Local Group shows that their planes are distributed randomly.
Correcting the PL Relation?
Authors: Laney C. D.
Published: July 2016

Metal-poor Cepheids do not appear to have smaller radii or cooler temperatures than more metal-rich Cepheids. A correction to the LMC modulus of 0.4 mag, due to metal-poor Cepheids being fainter for their periods, is inconsistent with the data at the 6σ level or greater.
The continuum energy distribution of single galactic Wolf-Rayet stars
Authors: den Hond Bas A. , Conti Peter S. , Lamers H.
Published: July 2016

For eleven single galactic WR stars, the continuum energy distribution from the UV to the radio was obtained from literature data. Although a power law with α = 2.79 could describe all the distributions, there appear to be deviations that depend on stellar type.
ISO-PHOT observations of Wolf-Rayet winds
Authors: Runacres Mark C. , Blomme Ronny , Vyverman Koen , Cohen Martin , Leitherer Claus , Owocki Stanley P. , Haas Martin
Published: July 2016

We use ISO-PHOT maps around five WN stars to derive their far-infrared fluxes. In some cases we also detect a nebula around the star.
Line-blanketing in massive stars: new results
Authors: Hillier D. John
Published: July 2016

Until recently, a major deficiency of most spectroscopic modeling of hot stars was the neglect of line-blanketing. With the availability of new atomic data, faster computers, suitable approximations, and improved numerical techniques it is now feasible to include non-LTE line-blanketing due to CNO and iron group elements in atmospheric calculations. We highlight the capabilities of the present generation of models. New blanketing results are presented for WN and WC Wolf-Rayet stars, and for LBVs. Line-blanketing alters individual line strengths in unpredictable ways, and can significantly influence the determination of stellar parameters. We specifically highlight the UV spectral region in which the effects of Fe blanketing are directly manifested. The importance of the charge exchange reaction Fe2+ + H ⇌ Fe+ + H+ for modeling of the Fe emission lines in the extreme P-Cygni star HDE 316285 is illustrated.
Colliding stellar winds: recent advances in modelling
Authors: Stevens Ian R. , Pittard Julian M.
Published: July 2016

We report on recent advances in the modelling of colliding stellar winds in WR binaries. Here, we concentrate on the modelling of X-ray observations using numerical gas-dynamics, in some cases including radiation hydrodynamics, and look in detail at a few systems, such as γ2 Velorum, η Carinae and HD 193793. We also report briefly on the modelling of infrared line-profile variability in a number of close WR+O-star systems, which can reveal further information on the dynamics of the interaction region. We discuss recent 3D-simulations and describe the exciting prospects that AXAF and XMM open up.
Ring nebulae: what they tell us about Wolf-Rayet stars
Authors: Marston Anthony P.
Published: July 2016

The environments of evolved massive stars provide an opportunity of obtaining information on the past, as well as current, condition of the stars themselves. In this review we will look at the incidence of ring nebulae around Wolf-Rayet stars, their differing morphologies at various wavelengths and the existence of multiple, concentric shells. We use this information to show that WRs are indeed evolved stars and that the various phases of evolution for a WR star are evidenced in their environments. Abundance measurements and kinematics show that complex forms of mass ejection are likely to have occurred in the evolution of WR stars providing clumpy structures of dust, and both ionized and neutral gas. Gas kinematics also provide estimates to the time-scales of each of the evolutionary phases of WR stars, which can be combined with estimates of nebular masses to provide the approximate values for such crucial parameters as total mass-loss and historical mass-loss rates. Overall, it is illustrated that studies of the environments of WR stars have the potential to provide important information about the mass-loss history of very massive stars, including estimates of the time period of each mass-loss phase, typical mass loss rates, total mass lost and likely evolutionary path. Some of the remaining problems relating to the use of ring nebulae as probes to the evolutionary history of WR stars are also discussed.
On the formation of wind bow-shocks around OB runaway stars
Authors: Kaper Lex , Comerón Fernando , Barziv Orly
Published: July 2016

The interaction of the stellar wind of a supersonically moving massive star with its surrounding interstellar medium can result in the formation of an observable bow-shock. Recent studies at optical and infrared wavelengths indicate the presence of wind bow-shocks around several OB runaways, including the high-mass X-ray binary system Vela X-1. A large fraction of runaway stars do not seem to form wind bow-shocks. Obviously, when the local sound speed is high (∼ 100 km s−1), as is the case e.g., inside a hot superbubble, the (subsonic) space velocity would not be sufficient to form a bow-shock. Two-dimensional time-dependent hydrodynamical simulations indicate that the bow-shock is generally unstable; for certain combinations of ISM and wind parameters a bow-shock is not formed at all. The runaway nature of Wolf-Rayet stars in relation to the formation of wind bow-shocks is also discussed.
Shock structures in stellar winds resulting from orbital motions of the star
Authors: Cantó Jorge , Raga Alejandro , Koenigsberger Gloria , Moreno Edmundo
Published: July 2016

We study the problem of a wind ejected from a star which orbits around a (wind-less) companion star. The orbital motion induces the formation of a spiral shock structure in the wind. An analytic formulation of the problem allows us to obtain the distance from the star at which the shock waves appear, and also the locus of the spiral, two-shock structure (i.e., the working surface). The full, three-dimensional structure of the working surface is found to have a spiral intersection with the orbital plane, and a cylindrical “hole” around the polar axis.
NGC 2359: VLA H I and radio continuum observations
Authors: Cappa Cristina , Miller Goss W. , Niemela Virpi S. , Ostrov Pablo G.
Published: July 2016

NGC 2359, a H II region located at a distance of 5 kpc from the Sun (e.g., Goudis et al. 1994), appears as a ring like nebula surrounding HD 56925, a Wolf-Rayet star of type WN4. The nebula consists of a filamentary shell, a southern bar and streamers of diffuse gas (cf. Schneps et al. 1981, SHWB). Here we report the results of H I 21-cm line and radio continuum observations in the direction of NGC 2359.
VLA observations of the interacting-wind binary system WR 147
Authors: Contreras M. Eugenia , Rodríguez Luis F.
Published: July 2016

Wolf-Rayet stars are losing mass via their strong winds. Some of them show thermal and non-thermal radio emission and from this group some have companions forming binary systems. It has been suggested that the synchrotron emission arises from the interaction region where the winds of the two stars collide. WR 147 seems to be one of these systems, having a companion and emitting thermal as well as non-thermal radiation. Besides, it has been suggested that it has an anisotropic wind. In the present work we continue studying the WR 147 system by observing it at a radio wavelength of 3.6 cm in two different epochs. We have looked for evidence to support the idea that WR 147 is a colliding-wind binary system. We have also looked for time variations in the source during the time interval of ∼ 1.4 years separating our observations.
WR146 — observing the OB-type companion
Authors: Dougherty Sean M. , Williams Peredur M.
Published: July 2016

Using both MERLIN and the VLA, we have succeeded in detecting the radio emission from three components in WR 146: the WR star, the wind-wind collision region, and for the first time, the stellar companion to the WR star. This allows the unique possibility of determining the mass loss rate ratio of the two winds, an important observable that is independent of distance.
M1-67, nebula ejected from the 200 km s−1 runaway WN8 star WR 124: constraints from HST imagery and complementary CFHT Fabry-Pérot interferometry
Authors: Grosdidier Yves , Moffat Anthony F.J. , Blais-Ouellette Sébastien , Joncas Gilles , Acker Agnès
Published: July 2016

First results concerning the HST-Hα imaging of M1-67 are found in Grosdidier et al. (1998). With the étalon of the Université Laval (Québec), we have obtained complementary Fabry-Pérot Hα data using CFHT-OSIS (August 1996, seeing ≃ 0′′.6, FSR ≃ 392 km s−1, 5.9 kms−1 velocity sampling, see Figure 1). From these data, M1-67 appears more-or-less as a spherical shell seen almost exactly along its direction of rapid spatial motion in the ISM (Moffat et al. 1982). The radial velocity of the center of expansion is rv 137kms−1 (Sirianni et al. 1998). Instead of appearing as a nice hollow-type shell projected on the sky, we probably see the cap of the bow-shock nearly straight on from behind. The far side is greatly intensity-enhanced compared to the near side, probably as a result of raming with the ISM. This was already claimed by Solf & Carsenty (1982). The bright bullets (see Grosdidier et al. 1998) are possibly, after all, Rayleigh-Taylor instabilities seen along the line of sight at or near the bow-shock head, as they slightly ‘fall’ back towards the star. More details will be found in Grosdidier et al. (1999 in preparation).
Spectroscopy of planetary nebulae with [WR] nuclei
Authors: Peña Miriam , Stasińska Grazyna , Esteban César , Koesterke Lars , Medina Selene , Kingsburgh Robin
Published: July 2016

We have started an extensive program of systematic observations of planetary nebulae excited by [WR] nuclei with the aim of understanding the evolutionary status of the central stars. Detailed analysis of the nebular and stellar properties might reveal the presence of abundance variations across the nebulae, and allows to detect possible interactions between the massive stellar wind and the nebula. Such an analysis requires spatially resolved spectra, together with a reliable procedure to derive chemical abundances. This is best achieved by constructing individual photo-ionization models that reproduce the main observed properties. Here we present the spectroscopic analysis made for different knots of PB6, NGC2452, NGC2867, NGC6905 and He2–55. All these nebulae are ionized by [WC 2–3] stars and present very high ionization degrees.
Molecular and atomic hydrogen in the environment of hot, massive stars
Authors: St-Louis Nicole , Gervais S. , Morel Thierry , Doyon Rene
Published: July 2016

Studies of the atomic and molecular components of the interstellar medium in the vicinity of hot, massive stars have the potential of revealing a wealth of information on the way the star affects the distribution and physical state of the surrounding ISM during its various evolutionary phases, as well as potentially providing some information on the star itself and its past evolution.
MERLIN observations of WR 147 (WN8(h)+B0.5V)
Authors: Watson Sarah K. , Davis Richard J. , Williams Peredur M.
Published: July 2016

WR147 was first discovered to be a strong radio, X-ray and infra-red emission source by Caillault et al. (1985). It was classified as a WN8 type star with a very large mass loss rate and unusual radio emission (α < 0) for a thermal source. This unusual behaviour was explained by MERLIN (Moran et al. 1989) and VLA (Churchwell et al. 1992) observations in which it was resolved into two components: a ‘thermal’ source associated with the Wolf-Rayet star and a non-thermal component ∼ 600 mas to the north. Churchwell et al. showed that the southern component had the expected spectral index of α ≃ 0.6 for free-free emission from a stellar wind. They also showed that the northern component had a spectral index of α ≃ −0.5 and was therefore a non-thermal source, now thought to be due to a colliding wind region.
X-ray evidence for wind-wind collision in the Wolf-Rayet binary V444 Cygni
Authors: Yokogawa Jun , Koyama Katsuji , Maeda Yoshitomo , Skinner Steve L.
Published: July 2016

We present results on the eclipsing binary V444 Cyg (WN5+O6) with the X-ray satellite ASCA. The observations were performed at orbital phases 0.0, 0.25 and 0.5 (the 06 star is in front at phase 0.5 and vice versa at phase 0.0). Two-temperature plasma model could reproduce X-ray spectra in each phase. The temperature of the soft component is lower (kT ≃ 0.6 keV), which is attributed to the individual O6/WN5 stars. The temperature of the hard component is higher (kT ≃ 2 keV), which exhibited phase-related time-variabilities in absorption column NH and luminosity LX; NH was maximal at phase 0.0 while LX was minimal at phase 0.5. These variabilities are consistent with the scenario that X-rays are emitted from plasma heated-up by wind-wind collision near the surface of the O6 star.
Properties of nearby giant star-forming regions
Authors: Hunter Deidre A.
Published: July 2016

I review the properties of two nearby giant H II regions — 30 Doradus and NGC 604, and of two nearby young star complexes now past the H II region phase — Constellation III and NGC 206. I discuss the stellar populations, mode of star formation, gas content, and kinematics as clues to what conditions may be like in more distant starburst environments.
Stellar properties of Galactic Centre He I sources
Authors: Dessart Luc , Crowther Paul A. , Smith Linda J. , Bohannan Bruce
Published: July 2016

The Galactic Centre (GC) region has in recent years attracted a lot of attention from the hot star community following the discovery of numerous He I emission line sources (Krabbe et al. 1991). Recent studies (e.g., Najarro et al. 1994) revealed stellar properties reminiscent of cool Wolf-Rayet stars, providing clues to the origin of the Lyman and He+ ionizing fluxes, and the luminosity in the central parsec of our galaxy. They allow the recent star formation history to be unveiled, and assess the effect of high metallicity on massive star evolution.
IC 10: a starburst galaxy resolved into individual stars
Authors: Hunter Deidre A.
Published: July 2016

We present a preliminary analysis of HST images of the Local Group galaxy IC 10. IC 10 has an unusual Wolf-Rayet star population and is believed to be undergoing a starburst. Nevertheless, stars to at least 6.5 M⊙ are seen and the young star clusters are comparable in richness and spatial concentration to LMC populous clusters.
ASCA observation of Henize 2-10
Authors: Ohyama Youichi , Taniguchi Yoshiaki
Published: July 2016

We present results of X-ray spectroscopy of the prototypical Wolf-Rayet galaxy Henize 2–10 with ASCA. We find that the X-ray spectrum is best described by a model with soft (kT ≃ 0.7 keV) and hard (kT ≃ 3.9 keV) components. The soft component is attributed to the hot gas associated with the superwind, and the hard component with a collection of the young sources (young SNRs and HMXBs) associated with the starburst.
Evolutionary population synthesis: the effect of binary systems
Authors: Mas-Hesse J. Miguel , Cerviño Miguel
Published: July 2016

We present in this contribution our set of multi-wavelength synthesis models including the evolution of single and binary stars. The main results we have obtained can be summarized as follows: (a) massive close-binary systems will start to experience mass transfer episodes after the first 4Myr of the starburst evolution; (b) as a result of these mass transfer processes, stars of relatively low initial mass can lose completely their envelope and become a Wolf-Rayet star. In this way, the formation of WR stars is extended over longer than 15 Myr, and does not stop at 6Myr as predicted by models including only single stars; (c) WR stars can thus be coeval with red supergiants, which peak at around 10 Myr for solar metallicities; (d) the accretion of mass will originate relatively massive stars at ages for which they should have already disappeared; these stars, together with the WR stars formed in rather evolved clusters, increase the production of ionizing photons, so that the Hβ equivalent width will not drop as rapidly as predicted by models considering only individual stars; and (e) the mass transfer to compact companions will produce an additional source of high-energy radiation in the form of high-mass X-ray binaries, not predicted either by standard synthesis models.
Hot molecular cores, sites of high mass star formation
Authors: Lizano Susana , Osorio Mayra
Published: July 2016

We model the flux-density distribution of hot molecular cores as in-falling envelopes of gas and dust onto a central massive star. The envelopes are heated by both the stellar luminosity and the accretion luminosity. We find that, in order to reproduce the observed fluxes, these objects require high mass accretion rates Ṁ ≃ 10−4−3 M⊙yr−1 infalling onto central late B-type stars. We discuss the implications of this intense accretion phase on the formation of massive stars.
Stellar populations in starburst galaxies
Authors: Joseph Robert D.
Published: July 2016

Many galaxies emit a dominant fraction of their bolometric luminosity in the infrared. The small mass-luminosity ratios suggest that these infrared luminosities cannot be sustained by a normal stellar population over a Hubble time. The commonly held explanation is that there has been a burst of star formation sufficiently recently that the full spectrum of the initial mass function up to the highest mass stars is contributing to the luminosity. Starburst galaxies therefore provide laboratories for studying the upper end of the initial mass function.

After a briefly summarizing studies of the IMF in the solar neighborhood and in nearby ‘normal’ galaxies, I will turn to studies of environments in which there appears to be evidence for a somewhat different IMF,viz., in starburst galaxies. I will discuss infrared spectroscopic diagnostics of a sample of the most luminous starburst galaxies and what this implies for the IMFs in these ‘violent’ star formation events.
Populations of WC and WN stars in Wolf-Rayet galaxies: new constraints on starburst parameters
Authors: Contini Thierry , Schaerer Daniel , Kunth Daniel
Published: July 2016

Detection and analysis of Wolf-Rayet star populations in young starbursts is a powerful tool to reveal the properties of the star-forming events. We present new high S/N optical spectra of a sample of well-known WR galaxies, in which we detected for the first time the spectral signature of WC stars. The detailed comparison of WN and WC star populations derived in these galaxies, with the most recent model predictions, allows us to put tight constraints on starburst parameters, such as the age and duration of the burts, and the IMF.
A prominent Wolf-Rayet feature in a high-excitation H II region of NGC 4258
Authors: Castellanos Marcelo , Díaz Angeles I. , Terlevich Elena , Luisa García-Vargas María
Published: July 2016

We report the observation of a prominent Wolf-Rayet feature in the high excitation H II region 74C (Courtés et al. 1993) of the spiral galaxy NGC4258. In order to reproduce the observed HeII λ4686 Å line luminosity, around 38 Wolf-Rayet stars in this region are needed.
Age indicators in starbursts before the Wolf-Rayet phase
Authors: Mayya Y. Divakara
Published: July 2016

Most of the commonly used tracers of age of starburst regions are based on the presence of massive O-type and Wolf Rayet stars, and hence are applicable only during the nebular and WR phases of starburst. The beginning of the WR phase coincides with the end of the RSG phase. The presence of RSGs in starburst regions can be directly inferred by the Calcium Triplet (CaT) and other characteristic absorption features. These features, accompanied by evolutionary population synthesis modeling, can be used for accurate age determinations of starburst regions. Spatially resolved CaT spectra of a sample of nearby starburst galaxies are being analyzed to determine the age of starbursts in them. Results for the starburst knots of M 82 are presented here.
A multi-frequency study of the Wolf-Rayet blue compact dwarf galaxy He2-10
Authors: Méndez David I. , Esteban César , Filipović Miroslav D. , Ehle Matthias , Haberl Prank , Haynes Raymond F.
Published: July 2016

We present preliminary results on multi-wavelength observations of the Wolf-Rayet Blue Compact Dwarf Galaxy He2–10. These observations include Hα and continuum imaging, high-resolution Hα spectroscopy, high-resolution radio-continuum mapping at 6.3 and 3.5 cm and X-ray mapping. The deep Hα image reveals that the galaxy consists of a complex system of different star-forming knots surrounded by kpc-scale bubble-like and filamentary structures. The most interesting structure is a bipolar superbubble centered on the most intense star-formation knot. High-resolution spectroscopy of this structure indicates that it is expanding with a velocity in the range 75–250 km s−1. This kind of outflows is likely to be produced by the mechanical action of stellar winds and supernovae explosions in the intense starbursts that the galaxy hosts. This scenario is consistent with the finding of a very steep radio spectral index in the extended radio continuum emission (α = −0.59) that confirms the presence of a large number of supernova remnants in the galaxy.
The influence of massive stars on the interstellar medium
Authors: Oey M. Sally
Published: July 2016

On scales ranging from pcs to kpcs, the relationship between stellar and gaseous galactic components forms the basis for interpreting observations of galaxies and understanding galaxy formation and evolution. Feedback effects from massive stars dominate the structure, ionization, kinematics, and enrichment of the gaseous ISM in star-forming galaxies. On galactic scales, the ionizing radiation from these stars creates populations of H II regions and the diffuse, warm ionized medium. Likewise, superbubbles created by stellar winds and supernovae strongly influence the structure, kinematics, and balance of the multiphase ISM. This contribution reviews these feedback effects of massive stars on the global ISM.
Massive stars shaping the ISM: H I holes and shells in nearby galaxies
Authors: Brinks Elias , Walter Fabian
Published: July 2016

Neutral hydrogen (H I) is a magnificent tool when studying the structure of the interstellar medium (ISM) as it is relatively easily observable and can be mapped at good spatial and velocity resolution with modern instruments. Moreover, it traces the cool (∼ 100 K) and warm (∼ 5000 K) neutral gas which together make up about 60%, or the bulk, of the ISM. The currently accepted picture is that stellar winds and subsequent supernovae are the origin for the clearly defined holes or bubbles within the more or less smooth neutral medium. The H I can therefore serve indirectly as a tracer of the hot interstellar medium (HIM) left behind after the most massive stars within an OB association have gone off as supernovae. A splendid example is the dwarf galaxy IC 2574 for which we discuss H I, optical and X-ray observations.
Dwarf-dwarf interactions: a common origin for dwarf Wolf-Rayet galaxies
Authors: Esteban César , Méndez David I.
Published: July 2016

We present some results of an observational programme devoted to obtain deep imagery and high-resolution spectroscopy for a sample of dwarf Wolf-Rayet galaxies. Our main result is that interaction with fainter optical companions could be the origin of the strong star formation episodes observed in, at least, an important fraction of the objects. In all the cases presented, the companions and the signatures of interaction or merging can only be detected when deep and detailed observations are taken. We predict that the fraction of dwarf WR galaxies (or even H II galaxies in general) with interacting signatures will increase when detailed observations for more objects are available.
When supernovae explode in a starburst: transitions among AGN types
Authors: Aretxaga Itziar
Published: July 2016

Among the Active Galactic Nuclei that have suffered type mutations, the classically classified Seyfert 2 NGC 7582 recently found at a Seyfert 1 stage, is perhaps one of the most puzzling cases, since it defies a well supported case for unification. We investigate the possibility that this type transition, common to another twelve AGN, is driven by supernovae exploding in a nuclear/circumnuclear starburst.
Morphology and structure of nearby starburst galaxies in the UV and optical
Authors: Conselice Christopher J. , Gallagher John S. , Homeier Nicole L. , Calzetti Daniela , Kinney Anne L.
Published: July 2016

We present results of a panchromatic morphological study to determine how UV and Hα morphology relates to the underlying stellar populations, the ISM, and structure of nearby starbursts.
ISO spectroscopy of nearby starburst galaxies
Authors: Kunze Dietmar , Lutz Dieter , Rigopoulou Dimitra , Thornley Michelle D. , Genzel Reinhard
Published: July 2016

We present spectroscopic mid-IR observations of prominent starburst galaxies obtained with the Short Wavelength Spectrometer onboard the Infrared Space Observatory. The wavelength range accessible by ISO-SWS (2.5–45 μm) contains a large number of emission lines of atomic and molecular hydrogen and several other atomic species. In this paper we discuss the interpretation of the [Ne III] 15.5 μm/[Ne II] 12.8 μm line-ratio, the faint [OIV]25.9 μm line and the pure rotational lines of molecular hydrogen observed in our target galaxies.
The First Ten Years of GRAPE
Authors: Sugimoto Daiichiro
Published: July 2016

GRAPE is a project for a special-purpose computer dedicated to classical many-body problems. Its primary use is for gravitational many-body problem of stellar systems. It was initiated in 1989, and now its performance is in the range of 100 Tera-flops equivalent. As an introduction to this symposium, development of the GRAPE project is reviewed, where motivation to it is the main concern of this paper rather than the computer itself.
The Gravitational Million-Body Problem
Authors: Heggie Douglas C.
Published: July 2016

We review what has been learned recently using N-body simulations about the evolution of globular clusters. While simulations of star clusters have become more realistic, and now include the evolution of single and binary stars, the prospect of reaching large enough N is still a distant one. Nevertheless more restricted kinds of simulations have recently brought valuable progress for certain problems of current observational interest, including the origin and structure of tidal tails of globular clusters. In addition, such simulations have forced us to rethink some basic aspects of stellar dynamics, including, in particular, the process of escape. Finally we turn to faster, approximate methods for studying star cluster dynamics, where the role of N-body simulations is one of calibration.
The interplay of rotation and relaxation in star clusters and galactic nuclei
Authors: Spurzem R. , Kim E. , Lee H.M.
Published: July 2016

The impact of rotation on the relaxational dynamics of dense stellar systems is reviewed; while in the past linear stability analysis and a few N-body models existed only, we report recent advances in the technique of 2D Fokker-Planck models for axisymmetric rotating star cluster, now extending into the post-core collapse phase. It is confirmed that rotating clusters, whether they are in a tidal field or not, evolve significantly faster in pre-collapse than non-rotating ones, while in post-collapse only those in a tidal field keep their larger speed of evolution. Consequences for observed shapes, density distribution, and kinematic properties of young and old star clusters are discussed.
Black Holes for Computational Astrophysicists
Authors: Richstone Douglas
Published: July 2016

Supermassive black holes are a ubiquitous feature of galaxy centers. Understanding the problems posed by their formation and co-evolution with their host galaxies is fertile ground for an astrophysicist with a computer.
Investigating the long-term evolution of galaxies: Noise, cuspy halos and bars
Authors: Weinberg Martin D.
Published: July 2016

I review the arguments for the importance of halo structure in driving galaxy evolution and coupling a galaxy to its environment. We begin with a general discussion of the key dynamics and examples of structure dominated by modes. We find that simulations with large numbers of particles (N ≳ 106) are required to resolve the dynamics. Finally, I will describe some new results which demonstrates that a disk bar can produce cores in a cuspy CDM dark-matter profile within a gigayear. An inner Lindblad-like resonance couples the rotating bar to halo orbits at all radii through the cusp, rapidly flattening it. This resonance disappears for profiles with cores and is responsible for a qualitative difference in bar-driven halo evolution with and without a cusp. Although the bar gives up the angular momentum in its pattern to make the core, the formation epoch is rich in accretion events to recreate or trigger a classic stellar bar. The evolution of the cuspy inner halo by the first-generation bar paves the way for a long-lived subsequent bar with low torque and a stable pattern speed.
The Angular Momentum Problem in CDM Cosmolgies: The End of the Beginning?
Authors: Couchman H.M.P. , Thacker R.J.
Published: July 2016

We show, by adopting a plausible model for star formation and energetic feedback in cosmological simulations of galaxy formation, that we are able to alleviate the angular momentum problem which has bedeviled many previous attempts to generate realistic disc galaxies in Cold Dark Matter cosmogonies. This paper highlights the “cooling catastrophe” as manifest in numerical cosmology and describes a simple prescription for modelling the sub-resolution physics of star formation and feedback in Smoothed Particle Hydrodynamic simulations. We show results for angular momentum and disc scale length for simulations with and without feedback.
High-Accuracy Treecode Based on Pseudoparticle Multipole Method
Authors: Kawai Atsushi , Makino Junichiro
Published: July 2016

We invented the pseudoparticle multipole method (P2M2), a method to express multipole expansion by a distribution of pseudoparticles. We can use this distribution of particles to calculate high order terms in both the Barnes-Hut treecode and FMM. The primary advantage of P2M2 is that it works on GRAPE. Although the treecode has been implemented on GRAPE, we could handle terms only up to dipole, since GRAPE can calculate forces from point-mass particles only. Thus the calculation cost grows quickly when high accuracy is required. With P2M2, the multipole expansion is expressed by particles, and thus GRAPE can calculate high order terms. Using P2M2, we realized arbitrary-order treecode on MDGRAPE-2. Timing result shows MDGRAPE-2 accelerates the calculation by a factor between 20 (for low accuracy) to 150 (for high accuracy). We parallelized the code so that it runs on MDGRAPE-2 cluster. The calculation speed of the code shows close-to-linear scaling up to 16 processors for N ≳ 106.
Interactive 3-D visualization of particle systems with Partiview
Authors: Levy Stuart
Published: July 2016

This paper describes partiview, a free software tool for interactive graphical display of collections of particles in 3-space, and its application in studying the results of N-body collisional stellar dynamics calculations from Starlab.
Heap-based algorithm and one-dimensional expanding Universe
Authors: Fanelli Duccio , Aurell Erik , Noullez Alain
Published: July 2016

A fast algorithm for studying one-dimensional systems that are Lagrangian integrable between collisions is presented. The algorithm is based on an event-driven scheme, and uses a heap ordered set of predicted future events. As an application, we discuss the case of an expanding one-dimensional Universe.
Dynamics of supermassive black holes
Authors: Hemsendorf Marc , Dorband Nils , Merritt David
Published: July 2016

We are showing first results from simulations studying the effect of Brownian motion of the central mass on a cusp. N-body simulations of cuspy stellar systems around supermassive black holes represent a very challenging computational task. The wide range of dynamical timescales combined with large particle numbers required here leads us to the implementation of a systolic force calculation into a Hermite direct force block time-step scheme. With this new algorithm, we are able to handle particle numbers as large as 900000 on the parallel computers accessible to us. Due to their extraordinary parallelism (up to 98% and more) we suggest to use the described schemes on a computer cluster where each computing node is connected to a GRAPE board.
A Numerical Study of the Chemo-Dynamical Evolution of Elliptical Galaxies
Authors: Kawata Daisuke , Gibson Brad K.
Published: July 2016

We investigate the chemo-dynamical evolution of elliptical galaxies, to understand the origin of the mass-dependence of photometric properties such as the colour-magnitude relation (CMR). Our three-dimensional TREE N-body/SPH numerical simulation takes into account both Type II and Type Ia supernovae and follows the evolution of the abundances of several chemical elements. We derive the photometric properties of the simulation end-products and compare them with the observed CMR.
Chemodynamical Evolution of the Milky Way
Authors: Kobayashi Chiaki , Nakasato Naohito , Nomoto Ken'ichi
Published: July 2016

We simulate the chemodynamical evolution of the Milky Way using our GRAPE-SPH code, and reproduce the age-metallicity relation, the [O/Fe]-[Fe/H] relation, and the metallicity distribution.
Core Evolution of Rich Stellar Clusters in the LMC
Authors: Mackey A.D. , Wilkinson M.I. , Gilmore G.F. , Hurley J.R.
Published: July 2016

Observations of rich LMC clusters reveal an increasing spread in core radius with increasing age. We use N-body simulations of clusters on elliptical orbits about the LMC to show that a time-varying tidal field can result in significant core expansion. The observed spread in core radii may therefore reflect a spread in orbital parameters between clusters.
Collisional Evolution of Galaxy Clusters: Fokker–Planck and N-body models
Authors: Takahashi Koji , Sensui Tomohiro , Funato Yoko , Makino Junichiro
Published: July 2016

We investigate the dynamical evolution of clusters of galaxies in virial equilibrium by using Fokker–Planck models and self-consistent N-body models. In particular we focus on the growth of the common halos and the development of the central density cusps in the clusters. We find good agreement between the Fokker–Planck and N-body models. At the cluster center the cusp approximated by a power law, ρ(r) ∝ r-α (α ∼ 1), develops. We conclude that this shallow cusp results from the combined effects of two-body relaxation and tidal stripping. The cusp steepness α weakly depends on the relative importance of tidal stripping.
N-body Simulation of the Evolution of a Protolunar Disk
Authors: Takeda Takaaki , Ida Shigeru
Published: July 2016

We performed N-body simulations of dense particulate disks and quantitatively analyzed angular momentum transfer processes therein. Angular momentum transfer is dominated by both gravitational torque and particles' collective motion associated with the structure. These processes depend on surface density, and do not depend on particle size or number if the structure is resolved enough.
Evolution of Merger Remnants with Supermassive Black Holes
Authors: Tinker Jeremy , Ryden Barbara
Published: July 2016

We present results of numerical simulations of mergers of spiral galaxies using GADGET (Springel, Yoshida, & White 2001). In three of these simulations one of the progenitor galaxies contained a central supermassive black hole (BH), as well as one simulation which did not contain a BH. The merger remnants were evolved to an age of ∼ 13 Gyr to examine the evolution of the shape of each merger remnant. The results of these simulations were compared to observations of elliptical galaxies, which show that older galaxies appear rounder than younger ones (Ryden, Forbes, & Terlevich 2001).

We found that the simulations in which the BH mass was fixed throughout the evolution influence the shape of their host galaxies on timescales less than 3 Gyr. These simulations show little trend of shape with age beyond this time. In the simulations in which the BH mass increased linearly over the duration of the simulation, there is a significant evolution of the shape of the remnant throughout its lifetime, comparable to the observational trend.
Evolution of Rotating White Dwarfs in Close Binaries and Diversity of Type Ia Supernovae
Authors: Uenishi Tatsuhiro , Nomoto Ken'ichi , Hachisu Izumi
Published: July 2016

Type Ia supernovae are very good, but not perfect, standard candles, because their observed brightness shows a little diversity. The origin of this dibersity needs to be understood for the application to cosmology.

In close binary systems, a white dwarf must be rotating faster and faster as it gains angular momentum from the accretion disk. Its rapid rotation affects its final mass and strucure just before a supernova expolosion. Brightness of supernovae can be changed if mass of their progenitors have some diversity.
A Rich New Vein of Planetary Nebulae From the AAO/UKST Hα Survey
Authors: Parker Q. A. , Hartley M. , Russeil D. , Acker A. , Morgan D. H. , Beaulieu S. , Morris R. , Phillipps S. , Cohen M.
Published: July 2016

We report on an unprecedented source of Planetary Nebulae (PN) discovered from AAO/UKST Hα survey images of the Southern Galactic Plane. A pristine region of PN discovery space is being sampled due to the excellent depth, coverage, resolution and uniformity of the Hα survey. Large numbers of new PN are being found (~1000 so far). They are typically more evolved, obscurred and of lower surface brightness than in most other surveys. The doubling of known PN should have a significant impact on many aspects of PN research.
Mass Loss from Carbon Stars: Circumstellar C2 Swan Band
Authors: Kimata Rie , Izumiura Hideyuki
Published: July 2016

We have searched 44 optical carbon stars for circumstellar C2 Swan (0,0) band absorption lines using the high dispersion echelle spectrograph for the 188 cm reflector at Okayama Astrophysical Observatory. We have detected the circumsteller C2 lines definitely in 18 stars, possibly in 6 stars, and not detected in 20 stars. We discuss the observed properties of the circumstellar C2 lines. We infer the C2 line-forming region is located at the innermost part of the circumstellar envelope.
Near-Infrared Monitoring of the Carbon Star IRC +10 216: A High Spatial-Resolution Time Sequence of Dust-Shell Evolution
Authors: Weigelt G. , Blöcker T. , Hofmann K.-H. , Men'shchikov A. , Winters J. M. , Balega Y.
Published: July 2016

The carbon star IRC +10 216 is a long-period Asymptotic Giant Branch (AGB) star suffering from strong stellar winds (several 10-5 M⊙/yr; Loup et al. 1993) which have led to an almost complete obscuration of the star by dust. Due to the high mass-loss rate, long period of P = 649 d (Le Bertre 1992), and carbon-rich chemistry of the dust-shell, IRC +10 216 is obviously in a very advanced stage of its AGB evolution. High-resolution near-infrared imaging of IRC +10 216 has revealed that on sub-arcsecond scales (100 mas) its dust shell is clumpy, bipolar, and changing on a time scale of only ~1 yr (Weigelt et al. 1997, 1998, Haniff & Buscher 1998, Osterbart et al. 2000, Tuthill et al. 2000). Since most dust shells around AGB stars are known to be spherically symmetric, whereas most proto-planetary nebulae (PPN) show an axisymmetric geometry (Olofsson 1996), it appears likely that IRC +10 216 has already entered the transition phase to the PPN stage. This suggests that the break of the dust-shell symmetry between the AGB and post-AGB phase already takes place at the end of the AGB evolution.
Past and Future Evolution of Sakurai's Object
Authors: Herwig Falk
Published: July 2016

We present a stellar evolution model sequence of the past and future evolution of the post-AGB born again star Sakurai's object (V 4334 Sgr). In order to match the short evolutionary time scale we have to assume that the convective ingestion of hydrogen-rich envelope material into the He-flash convection zone proceeds slower than predicted by the mixing length theory. For the future we predict a swift second evolution through the central star region before a second born-again evolution occurs.
NIR Spectroscopy of IRAS 16115-5044
Authors: Weldrake David T.F. , Wood Peter R. , Van de Steene Griet C.
Published: July 2016

IRAS 16115-5044 has been identified as a possible post-AGB star on the basis of its position in the IRAS 2-colour diagram (van der Veen et al. 1989). A study by Van de Steene and Pottasch (1993) failed to detect any radio-continuum flux from the object, suggesting it is still in the pre-planetary nebula phase, that is, the central star is not yet hot enough to ionize the circumstellar shell.

The central star is bright in the infrared (K=4.9) but faint in the visible which we attribute to an optically thick circumstellar shell (J-K=2.61, van der Veen et al. 1989). Oudmaijer et al. (1995) obtained a K-band spectrum of lRAS 16115-5044 longward of 2.2 microns, and did not detect any discernable features.
The Formation and Evolution of Planetary Nebulae
Authors: Schönberner Detlef , Steffen Matthias
Published: July 2016

We review our present knowledge about the formation and evolution of planetary nebulae and discuss the relevant processes responsible in creating and shaping planetary nebulae out of a cool AGB wind envelope. Based on 1D simulations we show that a hydrodynamical treatment along the upper AGB leads quite naturally to more realistic starting configurations for planetaries with density slopes steeper than r−2. Taking into account photoionization and wind interaction in a realistic manner, the hydrodynamics of post-AGB wind envelopes leads to density structures and velocity fields in close resemblance to observations of spherical or elliptical planetary nebulae.
Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae
Authors: Werner Klaus , Deetjen Jochen L. , Dreizler Stefan , Rauch Thomas , Kruk Jeff W.
Published: July 2016

The determination of effective temperatures of very hot central stars (Teff > 70 000 K) by model atmosphere analyses of optical H and He line profiles is afflicted with considerable uncertainty, primarily due to the lack of neutral helium lines. Ionization balances of metals, accessible only with UV lines, allow more precise temperature estimates. The potential of iron lines is pointed out. At the same time iron and other metal abundances, hardly investigated until today, may be derived from UV spectra. We describe recent HST spectroscopy performed for this purpose.

A search for iron lines in FUV spectra of the hottest H-deficient central stars (PG1159-type, Teff >100000 K) taken with FUSE was unsuccessful. The derived deficiency is interpreted in terms of iron depletion due to n-capture nucleosynthesis in intershell matter, which is now exposed at the stellar surface as a consequence of a late He shell flash.
FUSE Observations of Mass Loss in Planetary Nebulae
Authors: Iping Rosina , Sonneborn George
Published: July 2016

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite observed several high and low excitation planetary nebulae in the wavelength range 905–1187 Å at a spectral resolution of λ/Δλ ~ 15,000.
Planetary Nebulae and Wolf-Rayet Nebulae
Authors: Grosdidier Y.
Published: July 2016

In the present paper I review some important facts regarding the similarities and differences between Galactic planetary nebulae and Galactic Wolf-Rayet (WR) nebulae within the scope of stellar mass-loss history and its subsequent impact on the nebular dynamics and morphology. The case of planetary nebulae with [WR] nuclei, which allows one to perform a more direct comparison with WR nebulae, is emphasized. In particular, I describe the apparently ubiquitous turbulent-like phenomena originating in [WR] stellar atmospheres and the surrounding nebulae, and discuss the possible impact of turbulence on planetary nebula studies.
White Dwarf Central Stars of Planetary Nebulae
Authors: Napiwotzki Ralf
Published: July 2016

Results of a spectroscopic investigation of central stars of old planetary nebulae (PNe) are reported. The evolutionary status of the central stars is discussed and it is shown that most are in good agreement with standard post-AGB evolution, but some are best explained as descendents from the first RGB after binary interaction. The distance scale of PNe is discussed.