bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Counterparts to Be/X-ray Binaries in the Magellanic Clouds
Authors: Buckley David A. H. , Stevens James B. , Coe Malcolm J.
Published: July 2016

We discuss the optical identification of 9 Be/X-ray binary optical counterparts of X-ray sources in the Magellanic clouds, most of them discovered in ROSAT observations. Imaging CCD photometry (using BV RC and Hα filters) was employed to search the typically 20 arcsec radius error circles for early-type stars exhibiting Hα emission. Spectroscopy of 5 candidates confirmed the presence of Hα emission. Based on the positional coincidences, we propose Be star optical counterparts to all of 9 X-ray sources: 6 from ROSAT and one each from ASCA, EXOSAT and HEAO-1. All of the sources exhibit the typical X-ray characteristics of Be/neutron star X-ray binaries: transient nature or strong variability, relatively hard X-ray spectra and, in 5 cases, detections of probable neutron star spin periods in the range 8.9 to 91.1 seconds.
Ground-based & WFPC2 Imaging of Fornax: Spatial Variations in Star Formation History
Authors: Grebel Eva K. , Stetson Peter B.
Published: July 2016

Fornax shows a radial age gradient. The old population is the most extended one similar to what was found in other dwarf galaxies, while younger populations are more centrally concentrated. With ≈ −1.2 dex the dominant intermediate-age population is much more metal-rich than the oldest populations traced by Fornax's globular clusters (≈ −2 dex, 15–11 Gyr). Star formation appears to have proceeded continuously with decreasing rates rather than in distinct episodes. Fornax contains the youngest population ever found in a dwarf spheroidal galaxy, 100–200 Myr, which makes its apparent lack of gas even more puzzling.
Wide Field Observations of the Ursa Minor dSph Galaxy
Authors: Martínez-Delgado D. , Aparicio A.
Published: July 2016

In this paper we present preliminary results of a wide field photometry survey of Ursa Minor and discuss the presence of an intermediate-age population and tidal tails in it.
The Andromeda Dwarf Spheroidal Galaxies
Authors: Armandroff Taft E. , Da Costa Gary S.
Published: July 2016

Our current knowledge of M31's dwarf spheroidal companions is reviewed. Two topics of recent interest constitute the bulk of this review. First, color-magnitude diagrams reaching below the horizontal branch have been constructed for two M31 dwarf spheroidals, based on images from HST/WFPC2. The horizontal branches are predominantly red in both galaxies, redder than expected for their metallicity based on Galactic globular clusters. Thus, the second parameter effect is seen in the M31 halo. Second, recent surveys have revealed three new dwarf spheroidal companions to M31. Thus, dwarf spheroidal galaxies are not as rare around M31 as previously thought and as a result, some properties of the M31 companion system have changed.
Nearby Blue Compact Dwarf Galaxy NGC 6789
Authors: Drozdovsky I. , Tikhonov N.
Published: July 2016

We present the results of a detailed BVRI and Hα study of the isolated nearby blue compact dwarf (BCD) galaxy NGC 6789. Judging from the literature the observed galaxy has not yet been resolved into stars up to now. On CCD frames obtained with 6m BTA telescope and 2.5m Nordic telescope the galaxy is well resolved. Its colour-magnitude diagram confirms the two component (core-halo) galaxy morphology, which consists of two stellar populations distinct in structure and colour: an inner high surface-brightness young population within 150 pc from the center of the galaxy, and a relatively low surface-brightness intermediate-age population extending out to at least 600 pc. The distance to the galaxy, estimated from the tip of the red giant branch (TRGB) is 2.1 Mpc which places NGC 6789 close to the Local Group. From the mean colour of the RGB, the mean metal abundance of the halo population is estimated as [Fe/H] ≃ −1 dex.
ROSAT HRI and PSPC Observations of M32
Authors: Zang Z. , Meurs E.J.A.
Published: July 2016

The X-ray emission from M32 has been studied with ROSAT PSPC and HRI observations. A new analysis of the best available exposure with M32 in the central part of a PSPC frame improves on a previously published analysis and indicates only one source associated with M32. Our analysis of the dedicated HRI exposure of M32 also leads to different conclusions than published recently. At HRI resolution M32 appears as an extended source, probably a little offset from the optical nucleus. Possible interpretations are discussed, which are relevant to the question whether a low-level active nucleus may be present or not.
Structure and Evolution of Stellar Populations in Local Group Galaxies
Authors: Einasto J. , Tenjes P.
Published: July 2016

We use detailed modeling of stellar populations of nearby galaxies to calculate population parameters. Our sample of galaxies includes most galaxies of the Local Group and several more distant giant galaxies. Available data are sufficient to decompose galaxies into the nucleus, the metal rich core, the bulge, the halo, the young and old disks, and the dark halo. We compare mass-to-luminosity ratios and colors of bulges, disks and halos with results of models of galactic chemical evolution. The luminosity-weighted mean of the mass-to-luminosity ratio of visible stellar population is M/LB = 4 ± 1.4 in solar units. This ratio is surprisingly constant for galaxies of very different absolute magnitude.
The Stellar Content in the Central Region of M81
Authors: Joly Monique , Boisson Catherine , Pelat Didier
Published: July 2016

Using long slit spectroscopy, we investigate the stellar population and reddening gradients inside the central regions of the nearby spiral galaxy M81. Observational data are analyzed using a new mathematical method. The basic elements to construct the synthetic spectra are taken from a database of star spectra. We show the ability of this method to define detailed stellar populations and to differentiate between age and metallicity effects.
Internal Dynamics of Local Group Galaxies
Authors: Freeman K. C.
Published: July 2016

This talk reviews the internal dynamics of some of the different classes of Local Group galaxies. These include the dwarf spheroidal galaxies, the pure disk galaxy M33, the LMC and M31. The talk concludes with some general remarks about bulges and halos.
Orbits versus Star Formation Histories: A Progress Report
Authors: Grebel Eva K. , Kolatt Tsafrir , Brandner Wolfgang
Published: July 2016

Milky Way dwarf companions and satellites of distant spirals seem to show a preference for polar orbits. We suggest that five out of six M31 dwarf spheroidal companions as well as two dwarf irregulars may also be located near a polar plane.

We briefly discuss preliminary results from a statistical approach to study correlations between star formation histories and orbits of Local Group dwarf galaxies, such as a possible correlation between star formation episodes and galaxy separations.
Thermal Infrared Survey of LMC, SMC and Sagittarius Dwarf Galaxy
Authors: Käufl H.U. , Tolstoy E. , Wiedemann G. , Loup C. , Reimann H. G. , Waters L.B.F.M. , Zijlstra A.
Published: July 2016

The ESO VLT with its suite of infrared instruments (e.g. ISAAC, VISIR) allows for an area-limited deep survey for infrared-bright point sources in nearby local group galaxies. Data in four colours can be collected: 3, 5, 10, and 20μm; the 10/20μm data can be complemented with TIMMI2, a new instrument presently under construction for ESO's 3.6m telescope on La Silla. The scientific result will be a complete catalogue of obscured Asymptotic Giant Branch Stars in the LMC, the SMC and the Sagittarius Dwarf Galaxy (SDG). Using mostly twilight time, such a survey can be done for an area of ≈ 100 □arcmin per year per galaxy. At 10μm the limiting flux is expected to be 2–3 orders of magnitude fainter than the IRAS point source catalogue. This catalogue would give the first coherent sample of AGB stars with precise distances and consequently absolute bolometric luminosities. It may lead to a substantially better understanding of the mass loss of AGB stars, an important, but as of today largely enigmatic phase of stellar evolution. As a byproduct many more IR-bright objects in the Magellanic Clouds, e.g. dust envelopes around normal stars, luminous blue variable stars (LBV) or compact obscured HII-regions, will be discovered. For the SDG no LBVs or YSOs are expected as it had no star formation for the past 5 Gyr.
Wolf-Rayet binaries: old friends and new acquaintances
Authors: Niemela Virpi S. , Gamen Roberto , Morrell Nidia I. , Giménez Benítez Sixto
Published: July 2016

Observations of WR stars in binary systems are discussed, emphasizing constraints on our knowledge of the binary frequency of WR stars, and of WR stars as a distinctive class of objects. Radial velocity orbits of newly discovered binaries, e.g., WR 29, a short period WN7+OB binary in our Galaxy, and SMC/AB 7, a massive WN+O7 binary in the Small Magellanic Cloud, are presented. New spectroscopic observations of binary systems with previously known orbits are also reported, showing in the case of WR 21 evidence of change of the orbital elements as derived from different spectral lines. An elliptic orbit for CV Ser is also illustrated.
Probing Wolf-Rayet wind structures: helping hands from WR+O binaries
Authors: Marchenko Sergey V.
Published: July 2016

For binaries with well-known orbital parameters we describe methods to restrict some characteristics of the WR star in the binary, such as Te and RWR(τ ≃ 1). The presence of a hot, luminous companion helps to address the question of spherical symmetry of the WR wind and reveal the ionization stratification in the wind. Also, we discuss the restrictions which can be imposed on the wind velocity law(s).
Some aspects of the spectral variability of WR 141
Authors: Ivanov Millen M. , Georgiev Leonid N. , Valchev T. S. , Efremova B. V. , Zhekov Svetozar A.
Published: July 2016

An analysis of the behaviour of the He II 5411 line wings is presented. The spectral classification of the companion is discussed on the basis of a simple geometric model of the colliding stellar winds zone.
Searching for Luminous Blue Variables in nearby galaxies
Authors: King Nicole L. , Walterbos René A.M. , Gallagher Jay S.
Published: July 2016

We have identified five new candidate LBVs in the NE half of M 31 and provide age limits for these objects through the color-magnitude diagrams of their potential parent OB associations. We note that three of the five candidates are not in OB associations nor are they in prominent H II regions.
Dynamics and variability of winds in WR+O binaries
Authors: Gayley Kenneth G. , Owocki Stanley P.
Published: July 2016

The presence of a nearby O star offers the potential for studying the response of a Wolf-Rayet wind to external irradiation from a well-understood UV source. The O starlight offers not only a passive diagnostic probe, but also the potential for a dynamical interaction whose nature relates directly to fundamental issues of how WR winds are driven. It may even decelerate the WR wind prior to the wind/wind interaction, an effect we term radiative braking. We report on recent progress in WR+O wind-wind interaction models that incorporate the influence of the O starlight on the incident WR wind, and also the effect of the WR starlight on the acceleration of the O-star wind. A recurrent theme is the importance of feedback between the line force and the gas dynamics, and the leveraging that results.
Thermal instability in the wind of Wolf-Rayet stars
Authors: Gonçalves Denise R. , Jatenco-Pereira Vera , Opher Reuven
Published: July 2016

In this study, we investigate the formation of clumps at the base of the wind of early-type stars via thermal instability in the presence of Alfvén wave heating. As a result we show the existence of two stable equilibrium regions, one at high temperature, the diffuse medium, and another at low temperature, the clumps. We show that the two stable equilibrium regions can coexist over a narrow range of pressures describing the diffuse medium and the clumps.
Evolution and nucleosynthesis of Wolf-Rayet stars
Authors: Ødegaard Knut Jørgen Røed
Published: July 2016

Using a dynamical stellar code, detailed evolutionary models have been computed that follow the evolution and nucleosynthesis of massive stars from the pre-MS up through their most advanced stages.
HST-STIS spectroscopy of the Bubble Nebula, NGC 7635
Authors: Buckalew Brent , Dufour Reginald J. , Ghavamian Parviz , Hartigan Patrick , Walter Don K. , Hester Jeff J. , Scowen Paul A.
Published: July 2016

We report the results of long-slit spectroscopy of the wind-blown bubble and photo-evaporating knots around the O6.5IIIf star BD+60°2522 made with the HST-Space Telescope Imaging Spectrograph. The Of star is the primary ionizing source for the H II region NGC 7635, located in the Perseus Arm. The spectra were taken through a 0″.2 x 52″ slit with low and medium resolution gratings covering the wavelength range 2900-6870 Å. Observations with two slit orientations were made; one across the line of embedded knots to the west of the Of star and the second running from the Of star across the bubble to the NE.

The 2D-STIS spectra permit us to subtract the surrounding H II region's diffuse emission from that of the knots and the bubble, and to study the spatial variations in various emission lines in these features to a resolution of ∼ 0″.2, an order of magnitude improvement over the best ground-based spectra of this object in the literature. We present high spatial-resolution emission-line and line-ratio profiles across the bubble and knots, and compare them with the predicted variations from photo-ionization, photo-evaporation, and wind-shock models. We also present an analysis of temperatures, densities, and abundances in the features from higher S/N spectra extracted over selected lengths of the slit.
New observational results on the colliding wind WR+O binary WR 30a
Authors: Gosset Eric , Royer Pierre , Rauw Gregor , Manfroid Jean , Vreux Jean-Marie
Published: July 2016

WR30a (MS 4) was first suspected as a possible Wolf-Rayet star by McConnell & Sanduleak (1970) during a deep objective-prism survey performed around the Carina Nebula region. From subsequent studies, the spectrum turned out to be composite, with a WR component classified W04 (or alternatively WC4, W05 and WC3) and an 0 component classified 04. Niemela (1995) reported the first, and up-to-now unique, radial velocity study for that star. She noticed large variations of CIV λ4658 from night to night, suggesting that WR30a might be a short period binary. A plot of the C IV emission-line velocities versus the He II absorption ones clearly indicates that they are exhibiting opposite binary motions. The apparent velocity amplitudes imply a rather low mass ratio Mwo4/Mo4 = 0.15, although the radial velocities of the C IV line could be distorted due to line-profile variations.
Molecular gas associated with Wolf-Rayet ring nebulae
Authors: Marston Anthony P. , Welzmiller Jaydene T. , Bransford Mark A. , Black John H. , Bergman P.
Published: July 2016

We present the first 12CO 1→0 emission-line maps of the vicinities of two Wolf-Rayet stars (WR 16 and WR 75) and their associated ring nebulae. We illustrate that sizeable amounts of molecular gas appear associated with these ring nebulae and therefore that the mass of gas in ring nebulae is significantly higher than inferred from observations of the ionized gas component alone. We discuss the possible stellar and interstellar origins of these molecular materials and the implications for the evolution of massive stars up to the WR phase.
Radio light-curve for WR 146 (HM19-3, WC6+O8.5), a colliding wind binary
Authors: Setia Gunawan Diah Y.A. , de Bruyn A. Ger , van der Hucht Karel A. , Williams Peredur M.
Published: July 2016

We report preliminary results of monitoring the flux from the Wolf-Rayet object WR 146 with the Westerbork Synthesis Radio Telescope at 21 cm since 1989. We find the average flux density slowly rising in the period 1989–1997, with evidence of shorter time-scale variability.
Imaging and spectroscopy of the LMC He II nebula N 44C and its ionizing star
Authors: Galarza Vanessa C. , Garnett Donald R. , Chu You-Hua
Published: July 2016

We present results from new HST imaging and spectroscopy of the peculiar Large Magellanic Cloud H II region N 44C and its ionizing star. While this nebula exhibits strong He II recombination emission, the source of the He+ ionizing photons has not been found. The UV spectrum of the ionizing star suggests an approximate spectral class of 07–08; the UV Si IV, He II, and N IV features do not show P-Cygni profiles, indicating that the ionizing star is not a supergiant. No companion star has yet been detected. Ground-based and HST optical spectroscopy of the ionized gas shows that the nebular abundances of C, N, O and He are not anomalous relative to other LMC H II regions, suggesting that no previous WR/SN companion has disappeared. Echelle spectroscopy has also ruled out the presence of high velocity shocked gas. Deep ROSAT imaging shows no X-ray point source in this location. The “fossil X-ray binary” hypothesis of Pakull & Motch (1989) remains the best explanation for the ionization of this nebula; however, convincing evidence for this hypothesis remains elusive.
Metal abundances in the Galactic Center
Authors: Najarro De La Parra Francisco , Hillier D. John , Figer Donald F.
Published: July 2016

Recent progress in model atmospheres for hot stars is presented. The impact of nlte wind-blanketed models is shown by comparison with the ‘old’ standard model. In order to confindently use the IR-spectra of objects at the Galactic Center (with high extinction) to derive their physical properties and trace the metal content, the consistency between results from optical and IR analysis is checked in a calibration study using the B1.5Ia+ star HDE 316285. With the above consistency proved, we started a detail investigation of the Pistol Star. Preliminary results are presented.
Infrared observations of young massive stars
Authors: Stecklum Bringfried , Feldt Markus , Henning Thomas , Pfau Werner
Published: July 2016

Infrared observations of young massive stars yield crucial insights on the birth of high-mass stars and their interaction with the parent molecular cloud. Results for IRAS23140+6121, G254.681+0.219, and NGC6334F obtained by near- and mid-infrared imaging are presented for a brief illustration.
Models for Wolf-Rayet and O star populations in starbursts: new developments and applications to large samples of Wolf-Rayet galaxies
Authors: Schaerer Daniel
Published: July 2016

We summarise recent developments on synthesis models for massive star populations with a particular emphasis on Wolf-Rayet stars. Quantitative analyses of the stellar content of WR galaxies are reviewed. Comparing observations of WR galaxies from various samples with synthesis models we derive constraints on their burst properties. The observations indicate very short burst periods and are generally compatible with a Salpeter IMF and a large upper mass cut-off. The use of the Hβ equivalent width as an age indicator works well for WR galaxies. We briefly summarise comparisons of stellar populations in super star clusters which also provide useful contraints on evolutionary models for massive stars e.g., at very low metallicities inaccessible in the Local Group. In particular the observed WN and WC populations favour the high mass loss models of Meynet et al. (1994). Finally we review recent work on the origin of nebular He II emission. From the new catalogue of WR galaxies and high excitation HII regions of Schaerer et al. (1999) we find a close relation between the presence of nebular He II and WR stars. The analysis of individual WR galaxies including IZw 18 supports the suggestion of Schaerer (1996) that hot WR stars are responsible for the hard ionizing flux.
Wolf-Rayet galaxies at many radio wavelengths and Hα: radio super-star-clusters
Authors: Beck Sara C. , Kovo Orly , Turner Jean L.
Published: July 2016

We have observed nine Wolf-Rayet galaxies at 20,6, 3.6 and 2 cm from the VLA and at Hα from the Wise Observatory, and have mapped the radio spectral index in each galaxy on sub-arcsec scales. We find that more than half the WR sample has distinct regions where the radio spectrum rises between 6 and 2 cm. We believe that this is the radio signature of the youngest super-star-clusters which are otherwise invisible, and which require NLyc ≳ 1052, or equivalent to 750 stars of the 07 subtype. We call these sources radio super-star-clusters.
Massive close binaries and evolutionary synthesis of young starbursts
Authors: Dionne Dany
Published: July 2016

With an evolutionary synthesis code, I follow the evolution of a starburst composed of massive close binaries (MCBs) and of single stars at various metallicities. Evolutionary tracks for MCBs have been developed in collaboration with D. Vanbeveren and C. de Loore. The models reproduce the observed WR/O ratio in the Magellanic Clouds.
Role of starbursts in LINERs
Authors: Huang JieHao , Chen Y. , Ji L. , Gu Q. S.
Published: July 2016

We report our preliminary results on the role of starbursts in LINERS by use of Wolf-Rayet galaxies as a tool. The essence of this approach lies in the different FIR-radio relation of WR galaxies from the pure AGN's.
The kinematics of the Wolf-Rayet galaxy pairs NGC 1741 and NGC 7714/7715
Authors: Rosado Margarita , Georgiev Leonid , Dultzin-Hacyan Deborah , Cruz-González Irene
Published: July 2016

We present preliminary results of the kinematics of the Wolf-Rayet galaxy pairs: NGC 1741 and NGC 7714/7715.
H II galaxies as distance estimators at high redshift
Authors: Melnick Jorge , Terlevich Roberto J. , Terlevich Elena , Joguet Benoit
Published: July 2016

Owing to their large luminosities per unit mass H II galaxies allow us to investigate in considerable detail the process of high mass star formation out to redshifts of cosmological importance. In this contribution we discuss the calibration of the correlation between the Hβ luminosity and the emission line width of H II galaxies as a distance indicator. We show that H II galaxies can be reliably used as distance indicators out to redshifts z > 3 provided that their line widths and fluxes can be determined with accuracies better than 10%.
The earliest phases of galaxy evolution: massive stars
Authors: Chiappini Cristina , Matteucci Francesca , Beers Timothy C. , Nomoto Ken'Ichi
Published: July 2016

In this work we study the very early phases of the evolution of our Galaxy by means of a chemical evolution model which reproduces most of the observational constraints in the solar vicinity and in the disk. We have restricted our analysis to the solar neighborhood and present the predicted abundances of several elements (C, N, 0, Mg, Si, S, Ca, Fe) over an extended range of metallicities [Fe/H] = −4.0 to 0.0 compared to previous models. We adopted the most recent yield calculations for massive stars taken from different authors (Woosley & Weaver 1995; Thielemann et al. 1996) and compared the results with a very large sample of data, one of the largest ever used to this purpose. We have obtained this by selecting the most rec.ent and higher quality abundance data from a number of sources and renormalizing them to the same solar abundances. These data have been analysed with a new and powerful statistical method which allows us to quantify the observational spread in measured elemental abundances and obtain a more meaningful comparison with the predictions from our chemical evolution model.
The effect of close binary evolution on the chemical enrichment of galaxies
Authors: De Donder Erwin , Vanbeveren Dany
Published: July 2016

During their various evolutionary phases, stars enrich the interstellar gas (ISG) with chemical elements. In our study we investigate the effect of binaries on the chemical enrichment of the ISG. To derive the true yields for a population of single and binary stars we use a Population Number Synthesis code which is described in detail in Vanbeveren et al. (1998). We account for the enrichment through stellar wind (SW), supernova explosion (SN) of single and binary stars including type Ia, planetary nebula (PN), and through binary interaction (BI). When black hole (BH) formation occurs, it is assumed that all matter is swallowed by the hole. This happens for single stars with a mass larger than 25 M⊙ and for interacting binary components heavier than 40 M⊙. Type Ia SNe are treated according to the scenario of Li & van den Heuvel (1997). We conclude that including binaries: (a) increases the production of helium, up to a factor ∼ 1.8 for 100% binaries (note that the helium yield increases linearly with binary frequency); and (b) drastically changes the ratio of the relative helium to metallicity enrichment dY/dZ (even for Z = 0.02) resulting in values higher than 3.5 for binary frequencies ≥ 40%, which is in good agreement with the observations.
The GRAPE project: Current Status and Future Outlook
Authors: Makino Junichiro
Published: July 2016

I'll briefly overview the present status and the future of the GRAPE project. GRAPE (GRAvity PiPE) project is a project to design, develop and use special-purpose computers for astrophysical N-body simulations to do large-scale N-body simulations. Our first machine, GRAPE-1 was completed in 1989 and offered the speed of 240 Mflops. Since then, we have continued to develop newer and faster machines, and the newest machine, the GRAPE-6, has achieved the peak speed of 32 Tflops. I'll briefly discuss GRAPE-6 and its parallel architecture, and then discuss the possible form of GRAPE-7, the next generation machines.
Cluster CMDs from N-body Simulations: Stellar and Binary Evolution on GRAPE
Authors: Hurley Jarrod R.
Published: July 2016

The Colour-Magnitude diagram (CMD) is an important observational tool for use in the study of star clusters. Thus it is important to include a consistent treatment of stellar and binary evolution in N-body codes to allow the generation and interaction of the full range of stellar populations. In this way realistic cluster models can be compared with observed cluster populations via the respective CMDs. Preliminary results of such an approach using the Aarseth NBODY4 code on the GRAPE-6 are presented here. In particular, by using a stellar evolution algorithm that includes metallicity as a free parameter, the stellar populations of clusters at various stages of evolution can be studied. Interesting formation cases directly influenced by the cluster environment are highlighted for various stellar sub-populations.
Missing Link Found? — The “runaway” path to supermassive black holes
Authors: Ebisuzaki Toshikazu
Published: July 2016

Observations of stellar kinematics, gas dynamics and masers around galactic nuclei have now firmly established that many galaxies host central supermassive black holes (SMBHs) with masses in the range 106 ∼ 109M⊙. However, how these SMBHs formed is not well understood. One reason for this situation is the lack of observations of intermediate-mass BHs (IMBHs), which could bridge the gap between stellar-mass BHs and SMBHs. Recently, this missing link (i.e., an IMBH) has been found in observations made by ASCA and Chandra of the central region of the starburst galaxy M82 (Matsumoto and Tsuru 1999, Ptak and Griffith 1999, Matsumoto et al. 2001, Kaaret et al. 2001). Subsequent observations by SUBARU have revealed that this IMBH apparently coincides with a young compact star cluster. Based on these findings, we propose a new formation scenario for SMBHs. In this scenario, IMBHs first form in young compact star clusters through runaway merging of massive stars. While these IMBHs are forming, the host star clusters sink toward the galactic nucleus through dynamical friction, and upon evaporation deposit their IMBHs near the galactic center. The IMBHs then form binaries and eventually merge via gravitational radiation, forming an SMBH.
Evolution of Galaxies in Clusters
Authors: Funato Yoko
Published: July 2016

In this paper I show recent results of our studies on the evolution of an isolated cluster of galaxies using N-body simulations. In Sensui, Funato & Makino (1999) only one initial cluster model are investigated. In the present study, we varied the initial model of galaxies and clusters, and studied the dependence of evolution on initial conditions. We found that the mass of galactic halos are stripped and a common halo develops for any cluster models. Using result of scattering experiments of two halo-halo encounters, we show that the growth rate of the common halo (and complimentarily decrease rate of average mass of galactic halos) can be explained as a result of stripping due to cumulative encounters between two galactic halos.

We also found that the galaxies evolved so as to satisfy the relation between the masses of galaxies mgx and their velocity dispersion σgx expressed as mgx ∝ σ3∼4gx for all galaxy models as a consequence of their dynamical evolution through galaxy-galaxy interactions. We discuss the relation between our result and the observed Faber-Jackson relation.
Connecting cosmological simulations to the real world
Authors: Frenk C.S.
Published: July 2016

A timely combination of new theoretical ideas and observational discoveries has brought about significant advances in our understanding of cosmic evolution. Computer simulations have played a key role in these developments by providing the means to interpret astronomical data in the context of physical and cosmological theory. In the current paradigm, our Universe has a flat geometry, is undergoing accelerated expansion and is gravitationaly dominated by elementary particles that make up cold dark matter. Within this framework, it is possible to simulate in a computer the emergence of galaxies and other structures from small quantum fluctuations imprinted during an epoch of inflationary expansion shortly after the Big Bang. The simulations must take into account the evolution of the dark matter as well as the gaseous processes involved in the formation of stars and other visible components. Although many unresolved questions remain, a coherent picture for the formation of cosmic structure in now beginning to emerge.
Cosmological Simulations with Adaptive Smoothed Particle Hydrodynamics
Authors: Martel Hugo , Shapiro Paul R.
Published: July 2016

We summarize the ideas that led to the Adaptive Smoothed Particle Hydrodynamics (ASPH) algorithm, with anisotropic smoothing and shock-tracking. We then identify a serious new problem for SPH simulations with shocks and radiative cooling — false cooling — and discuss a possible solution based on the shock-tracking ability of ASPH.
The orbital evolution of satellite galaxies
Authors: Hashimoto Yoshikazu , Makino Junichiro
Published: July 2016

In most of previous theoretical and numerical works on the orbital evolution of satellite galaxies, the classical Chandrasekhar's formula has been adopted. However, a recent direct N-body result “(van den Bosh et al. 1999)” demonstrated that the orbital evolution is rather different from what is predicted from the Chandrasekhar's formula. The reason for this discrepancy, however, was not clear.
Dynamical Friction between Lopsided Disks and Spherical Halos
Authors: Ideta Makoto
Published: July 2016

It has long been known that some spiral galaxies have a large-scale lopsided structure (e.g., Baldwin, Lynden-Bell, & Sancisi 1980). The frequency of the lopsidedness in disk galaxies reaches to half of H i disks (e.g., Richter & Sancisi 1994) and one third of stellar disks (e.g., Zaritsky & Rix 1997). The fraction of lopsided disks is large, nevertheless their origin is not understood well. Although some theoretical models are proposed to explain the lopsidedness, dynamical friction between lopsided disks and spherical halos has not been taken into account. Then, in this contribution, we have examined the effect of dynamical friction on lopsided disks. To avoid discreteness noise due to small number of particles on the estimate of dynamical friction, we have used the matrix method.
On The Dynamics of Non-Stationary Stellar Cluster in Galaxy
Authors: Kozhanov T.S. , Omarkulov K.A.
Published: July 2016

We followed Wielen's (1974) and Osipkov's, Kozhanov's (1986) procedure to derive the equation of motion of a cluster in the solar neighborhood in taking into account of a galactic tidal field, which is assume to have axial symmetry, and gravitational influence of spherical stellar clouds.

On the basic of this equations and using the linear approximation for the galactic field (Wielen 1974) one can derive virial equation of Jacobi for variable masses of stellar clusters. The non-stability by Lagrange condition, describing behavior of this system is obtained.
Peanuts in barred analytic potentials
Authors: Patsis P. A. , Skokos Ch. , Athanassoula E.
Published: July 2016

We investigate the orbital behavior in a class of analytic potentials in order to isolate the families of orbits which lead to the appropriate appearance of boxy/peanut features. This is the first step towards understanding the orbits of particles in N-body simulations of barred galaxies. Our final goal is to find out which dynamical mechanisms determine the peanut or boxy shapes.
The Starburst-AGN Connection: 3-D Structure of the Massive Gas Disk around the Nucleus
Authors: Wada Keiichi , Norman Colin A.
Published: July 2016

The structure of obscuring matter in the environment of active galactic nuclei with associated nuclear starbursts is investigated using 3-D hydrodynamical simulations, in which the multi-phase inhomogeneous interstellar matter and its interaction with the supernovae are consistently followed. A globally stable, torus-like, but highly inhomogeneous and turbulent structure is found. To achieve the high column densities as suggested by observations of some Seyfert 2 galaxies with nuclear starbursts, the viewing angle should be larger than about 70° from the pole-on for a 108M⊙ massive black hole. We propose that nuclear starbursts and the mass of the black hole that determines the geometry of the obscuring torus.
Stochastic Biasing of Galaxies and Dark Halos in Cosmological Hydrodynamic Simulations
Authors: Yoshikawa Kohji
Published: July 2016

We perform an extensive analysis of nonlinear and stochastic biasing of galaxies and dark halos in spatially flat low-density CDM universe using cosmological hydrodynamic simulations. We identify galaxies by linking cold and dense gas particles which satisfy the Jeans criterion. We compare their biasing properties with the predictions of an analytic halo biasing model. Dark halos in our simulations exhibit reasonable agreement with the predictions only on scales larger than 10Mpc/h, and on smaller scales the volume exclusion effect of halos due to their finite size becomes substantial. Interestingly the biasing properties of galaxies are better described by extrapolating the halo biasing model predictions.
Current Models for the Evolution of AGB Stars
Authors: Herwig Falk
Published: July 2016

While the basic properties of AGB stellar evolution are well established, comprehensive observational studies of late phases of intermediate mass stars continue to generate puzzles for current stellar models. Here, I review current techniques to model AGB stars, and I discuss important aspects of current research of AGB (and post-AGB) stellar evolution with a particular focus on how these interrelate.
Nature of the H2 Emission Around Planetary Nebulae Precursors
Authors: García-Hernández D.A. , Manchado A. , García-Lario P. , Domínguez-Tagle C. , Conway G. M. , Prada F.
Published: July 2016

We present near-IR spectroscopy of a sample of 30 IRAS sources recently identified as late AGB stars, post-AGB stars or early PNe. The spectra obtained are centred at various wavelengths covering the molecular hydrogen v=1→0 S(1) 2.122 μm and v=2→1 S(1) 2.248 μm emission lines, the recombination lines of hydrogen Brγ 2.166 μm, Pfγ 3.741 μm and Brα 4.052 μm, and the CO[v=2→0] first overtone bandhead at 2.294 μm. As a result of these observations we have increased from 4 to 13 the total number of proto-PNe detected in H2 and we have confirmed that the onset of H2 emission takes place in the post-AGB phase. When the molecular hydrogen is fluorescence-excited the detection rate is found to be directly correlated with the evolutionary stage of the central star, rather than with the nebular morphology. In contrast, shocked-excited H2 is detected only in strongly bipolar proto-PNe, sometimes even at an early stage in the post-AGB phase. The strong correlation of shocked-excited H2 emission with bipolarity found confirms the result previously reported by Kastner et al. (1996) in evolved PNe. However, our results show that this correlation does not exist in the case of fluorescence-excited molecular hydrogen. (to be published in A&A).
IRAS 01005+7910, A High Galactic Latitude Post-AGB Star
Authors: Hu Jingyao
Published: July 2016

Hu et al (1993) have selected a sample of proto-planetary nebula candidates based on the IRAS color-color diagram. IRAS 01005+7910 is one object of this sample. We have observed this object photometrically (Table 1) and spectroscopically (Fig. 1). From its spectral type of B2I and optical color of B - V = 0.23, we can derive the reddening as E(B - V) = 0.39 and interstellar/circumstellar absorption Av = 1.20. If it is a normal B-type supergiant, the distance module will be m - M = 16.05 and distance d = 16.2 kpc. Due to the galactic latitude b = 16.6, it should be located at about 4.6 kpcabove the galactic plane. This does not fit with normal B-type supergiant and we considered that it is a post-AGB star located at high galactic latitude. Recently Hrivnak et al (2000) found that this object shows carbon-rich features in the infrared. A paper on observations, reduction and discussions of this object has been submitted to the Chinese Journal of Astronomy and Astrophysics.
Formation and Evolution of Planetary Nebulae: A Radiation Hydrodynamics Study
Authors: Perinotto M. , Calonaci C. , Schönberner D. , Steffen M. , Blöcker T.
Published: July 2016

The formation and evolution of a planetary nebula is based on the occurrence of a strong AGB wind and the rapid evolution of the central star with corresponding changes of its ionizing flux and wind power. We have studied the influence of different mass-loss histories in combination with various central-star properties.
Wind Models for O-type Stars
Authors: Hoffmann T. L. , Pauldrach A.W.A.
Published: July 2016

We present fully consistent models for O-type stars that reproduce the observed UV spectra simultaneously with the observed terminal velocities and mass loss rates. We demonstrate how, as a consequence, the models can be used to determine the stellar parameters from the observed UV spectra alone.
FUSE Observations of the Central Star of Abell 78
Authors: Werner Klaus , Dreizler Stefan , Koesterke Lars , Kruk Jeff W.
Published: July 2016

FUSE high resolution spectra of two PG1159 type central stars (K1-16 and NGC 7094) have revealed an unexpected iron deficiency of at least 1 or 2 dex (Miksa et al. 2002). Here we present early results of FUSE spectroscopy of the CSPN Abell 78. It is shown that iron is strongly deficient in this star, too.
Dust Features in the Infrared Spectra of Planetary Nebulae
Authors: Volk Kevin
Published: July 2016

I review some aspects of the infrared continuum emission of planetary nebulae, with particular emphasis on the various dust features. The original presentation with colour figures can be found at http://www.iras.ucalgary.ca/~volk/iau209.html.
Sub-arcsecond Mid-infrared Images of NGC 7027 and BD+30°3639
Authors: Volk Kevin , Kwok Sun
Published: July 2016

Many carbon-rich PNe show strong emission features due to various stretching and bending modes of aromatic hydrocarbon bonds (AHB). Comparisons between ISO spectra of evolved carbon stars, proto-planetary nebulae (PPNe), and PNe have shown that the AHB features develop late in the PPN phase (Kwok et al. 1999). In order to test the formation history of this carbonaceous component, it would be desirable to image the spatial distributions of the dust components. The Gemini Telescopes, optimized for infrared observations with adaptive optics capabilities, offer the unique opportunity for such observations. In this paper, we present the preliminary results of imaging of NGC 7027 and BD+30°3639 with the OSCIR mid-infrared camera at Gemini North.
Large-Scale Extended Emission Around the Helix Nebula
Authors: Speck A. K. , Meixner M. , Fong D. , McCullough P. R. , Moser D. E. , Ueta T.
Published: July 2016

We have presented new observations of the ionized gas, molecular gas and cool dust in the Helix nebula (NGC 7293). The ionized gas is observed in the form of a Hα image, which is constructed using images from the Southern H-Alpha Sky Survey Atlas (SHASSA). The molecular emission was mapped using the H2v = 1 → 0 s(1) line at 2.122μm. The far-infrared (FIR) observations were obtained using ISOPHOT on the Infrared Space Observatory (ISO).
Extinction Maps and Dust Distribution of Planetary Nebulae
Authors: Lee Ting-Hui , Kwok Sun , Lim Jeremy
Published: July 2016

We present an indirect method to probe the dust distribution in PNe. Using the free-free continuum flux density and Hβ recombination line flux relationship and the Case B Hα/Hβ line ratio, we determined the expected Hα flux from the radio continuum maps. The dust optical depth distribution of each planetary nebula was then derived from the expected to observed Hα flux ratio. With HST WFPC2 and VLA A-array observations, dust optical depth maps with resolution as high as ~ 0.1″ can be obtained.
Dust Extinction and Elemental Abundances of NGC 7027
Authors: Zhang Y. , Liu X.-W. , Luo S.-G.
Published: July 2016

Extinction toward NGC 7027 has been extensively studied. Seaton (1979) found the extinction across the nebula is variable and presented a two-component model to explain the radio and infrared observations. Middlemass (1990) presented a wedge-shaped extinction model, assuming the extinction increases linearly across the surface of the nebula. Walton et al. (1988) obtained an extinction map and found a mean extinction of EB-V = 1.02, and a lower extinction of EB-V = 0.8 towards the central star (CS). Based on high-resolution imaging, Robberto et al. (1993) and Wolff et al. (2000) obtained higher extinction of EB-V = 1.07 and 1.10 towards the CS, respectively.
Scattering by Dust in Planetary Nebulae: Polarization as a Diagnostic Tool
Authors: Walsh J. R. , Walsh L.
Published: July 2016

There is a wealth of evidence for the presence of dust in PN from continuum and line emission in the IR, spatially varying extinction and ERE emission in the optical and strength of resonance lines in the UV. The dust emits strongly in the IR but in the UV-optical absorbs and scatters the radiation from the central star and the gaseous emission envelope. Linear polarization of PN light is thus an expected consequence of the presence of dust both within and outside the ionized region. Intrinsic scattering haloes of PN can be confused with local (telescope + atmospheric) scattering; polarimetry however allows the morphology of a dusty halo to be studied. Spectropolarimetry of emission line profiles allows the kinematics of the dust relative to the gaseous emission to be uniquely studied. Polarization contributes to understanding the scattering properties of the grains in PN and how they relate to those of the general ISM to which they will subsequently contribute.
Temperature Variations and Abundance Determinations in Planetary Nebulae
Authors: Torres-Peimbert Silvia , Peimbert Manuel
Published: July 2016

It is argued that an important fraction of PNe present large temperature variations that are not due to observational errors nor to incomplete atomic physics. Seven possible causes for these variations are reviewed, one of them is presented for the first time.
Recombination-line Abundances for the Third-Row Element, Magnesium
Authors: Barlow M. J. , Liu X.-W. , Péquignot D. , Storey P. J. , Tsamis Y. G. , Morisset C.
Published: July 2016

We have obtained optical recombination-line abundances for the third-row element magnesium in ten planetary nebulae. The nebulae in our sample include four (NGC 7009, NGC 6153, M 2–36 and M 1–42) for which we have previously found very large enhancements, relative to solar, in the recombination line abundances of the second-row elements carbon, nitrogen, oxygen and neon (Liu et al. 1995, Liu et al. 2000, Liu et al. 2001). Nebular temperature fluctuations appear unable to account for these effects. However, models that invoke high-density clumps, particularly clumps which are hydrogen-deficient, appear more viable as an explanation for the high recombination line abundances that are observed (see Liu et al. 2000 for more details). While it may be possible to appeal to astrophysical nucleosynthetic processes to enhance the CNONe second-row elements in AGB stars, such effects are not expected to modify the abundances of third-row elements such as magnesium. We have therefore measured and dereddened the intensities of the 4481 Å 4f-3d line of Mg II, relative to Hβ, in order to investigate whether magnesium recombination line abundances are enhanced or not.
Sulfur, Chlorine & Argon Abundances in a Southern Sample of Planetary Nebulae
Authors: Milingo Jacquelynne B. , Henry Richard B.C. , Kwitter Karen B.
Published: July 2016

We present S/O, Cl/O, and Ar/O abundance ratios for 45 predominantly Type II southern PNe. These abundances are based upon line strengths from newly acquired spectrophotometry covering an extended optical range from 3600 - 9600 Å. The following average abundance ratios were obtained from this sample: S/O=0.011±0.0064, Cl/O=0.00031±0.00012, and Ar/O=0.0051±0.0020. This study, together with a sample of northern PNe, is aimed at producing a large homogeneous set of observations and abundances. Specifically, we are addressing the lack of homogeneously observed, reduced, and analyzed data sets that include the NIR [S III] lines at 9069 and 9532 Å. The data provided by these PNe samples enables us to look for consistency between S+2 abundances inferred from these lines and from the more accessible, albeit weaker, [S III] line at 6312 Å. We find reasonable agreement between S+2 determined from the NIR lines and the λ6312 line. This speaks positively for the use and reliability of the NIR lines, despite clearly recognized telluric effects in that portion of the spectrum. The consistent ionic abundance results breathe new life into our treatment of the telluric problem and the use of these strong lines for extrapolating total sulfur abundance. Type II PNe reside close to the Galactic disk and provide S, Cl, Ar, and O abundances free from nucleosynthetic self-contamination. These two qualities allow us to study massive star yields and map the distribution of these elements in radial abundance gradients. Finally, we compare our observed abundance trends with model predictions that are based on several sets of published stellar yields. (A companion paper in this volume by Kwitter & Henry discusses the northern subset observed at KPNO; see also Milingo et al. IIA, 2002, ApJS, 138, 279 and Milingo et al. IIB, 2002, ApJS, 138, 285)
Physical Conditions and Abundances in NGC 6543
Authors: Wesson R. , Liu X.-W.
Published: July 2016

We present analysis of the physical conditions and chemical abundances in NGC 6453, the Cat's Eye Nebula. Using archival HST images in conjunction with ground-based long-slit scanning spectra, we have produced an [O III] forbidden line temperature map of the nebula, which shows that the temperature remains constant at around 8000 K across the nebula. From the long-slit spectra, we have determined abundances both from collisionally excited lines (CELs) and optical recombination lines (ORLs). The ORL abundances are higher than the CEL abundances by a factor of approximately two.