bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Group Dynamics
Authors: Lynden-Bell D.
Published: July 2016

The distance from the Local Group to the ‘sphere’ of small galaxies that no longer expand with the Universe determines the time since the Big Bang, t x M1/2, where M is the mass of the Local Group. Adopting Feast's new distance scale, this distance is found to be 1.35 ± 0.1 Mpc. The velocity of approach and the distance to M31 give a different combination of t and M, thus both can be deduced. We find the time since the Big Bang
and
The importance of accurate distances for such results is stressed. If all distances are revised by a factor λ then both t and M change by that factor.
Near-Infrared Catalogue of the Magellanic Clouds: DENIS (Deep Near-IR Southern Sky Survey)
Authors: Cioni M. R. , Habing H. J. , Loup C. , Groenewegen M.A.T. , Epchtein N. ,   the DENIS Consortium
Published: July 2016

We report here on a preliminary analysis of the DENIS new IR point source catalogue of the Magellanic Clouds. After subtracting the contribution of foreground stars we interpret the colour-colour diagrams and colour-magnitude diagrams that characterize the Asymptotic Giant Branch (AGB). The AGB stars cause a clear bump in the luminosity function and they are distributed in two distinct regions, according to the spectral type (C-rich and O-rich), in the colour-luminosity diagram.
Reconstructing the Star Formation History of the Magellanic Clouds
Authors: Harris Jason , Zaritsky Dennis , Grebel Eva K. , Thompson Ian
Published: July 2016

We are developing an algorithm to determine the star formation history (SFH) of a mixed stellar population. We will apply the algorithm to hundreds of regions in our Magellanic Clouds Photometric Survey data and reconstruct the spatially resolved star formation history of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). In this paper, we demonstrate the algorithm on a typical region in the LMC, focussing on the obstacles and challenges facing us in attempting to reliably extract the SFH from photometric data.
The Carbon Star Population in the Fornax Dwarf Spheroidal Galaxy Revisited
Authors: Azzopardi M. , Muratorio G. , Breysacher J. , Westerlund B. E.
Published: July 2016

Our systematic searches for carbon stars in the Fornax dwarf spheroidal galaxy at the Canada-France-Hawaii Telescope have led to more than a doubling of the number of carbon stars known in this system, to 104. Furthermore, low-luminosity carbon stars resembling those we had previously found in the Small Magellanic Cloud have been identified in this system. We review the carbon star surveys carried out in the Fornax dwarf and present our main results. The Fornax carbon star population is compared to those of other Galactic halo dwarf systems.
Young Stellar Populations in M31, M33, and NGC 6822
Authors: Hutchings J. B. , Cavanagh B. , Bianchi L. , Chandar R. , Scuderi S.
Published: July 2016

We have been pursuing a program of hot star UV spectroscopy in local group galaxies over several years with HST. We have also obtained WFPC2 images in parallel and pointed exposures with several broad band filters.

• The imaging data have been used to generate colour-magnitude plots of central fields, clusters and halo fields in M31, M33 and NGC 6822. We have compared these with high-mass model isochrones from recent models, to examine the stellar populations that are indicated. M33 contains a substantial young cluster population whose mass and age appear to be related. The western outer wisps of NGC 6822 contain a relatively young population of stars.

• Most of the spectra have been reported and modelled in published papers: we note here the first comparison of stars in NGC 6822 with others from local group galaxies.

• We have also discussed the interstellar extinction in M31 and find it is similar to the Galaxy after allowance for comparable amounts of halo extinction that resembles that of the Magellanic Clouds.
Spectroscopy of Blue Stars with Hα Emission in M33
Authors: Sholukhova O.
Published: July 2016

Results of follow-up multi-object spectroscopy of 173 blue stars with Hα emission in the galaxy M33, carried out on the 6-m telescope, are presented. The stars have been originally selected as candidates for LBV and SS 433-type stars. The spectra have been obtained in the region of Hα. All the objects have fallen into two groups – stars with probable intrinsic Hα emission and stars where this emission may belong to H II regions. A number of criteria have been used at the selection, the principal one being the width of Hα emission. 57 stars in whose spectra the Hα line was broad have been selected. Spectra of the most interesting stars are presented. On the basis of luminosity and spectral type, stars were selected which may be considered as hypergiants or LBV candidates (3 of them – N41, N512, N517 are the most reliable). Two stars (v532, N35) have spectra similar to MCA1-B (Ofpe/WN9). The object I 322 is discussed as a candidate for an SS 433-type star.
Massive Star Formation and Evolution in Local Group Galaxies: Successes and Difficulties
Authors: Maeder André
Published: July 2016

Local Group galaxies allow us to test some properties of massive star evolution which are inaccessible in our Galaxy, in particular the effects of different metallicities. Thus, after showing that we still do not know the exact process by which massive stars are formed, we examine the differences in the distributions of O-stars, blue and red supergiants and WR stars in the Local Group. The number ratios WR/O and WN/WC are well accounted for by stellar models in which the mass-loss rates depend on the metallicity, Z, as predicted by stellar wind theories. The number ratio of red supergiants to WR stars is growing for decreasing Z. Although this behaviour is qualitatively well explained, the models need some extra mixing to fit the observational data. The same is true for the explanation of the He- and N-excesses in O, B and A supergiants. Rotation and related mixing processes certainly play a major role in massive star evolution. The relative number of Be-stars is higher at lower Z, which suggests that rotation is faster, also with more mixing, in small, irregular low-metallicity galaxies.
Investigation of Dust Extinction in Sb Galaxies using Scale Length Ratios
Authors: Cunow Barbara
Published: July 2016

For a sample of 16 Sb galaxies, disc scale lengths rD in B and I are investigated in order to study the dust content. The ratios rD(B)/rD(I) increase from 1.0 for face-on galaxies to 1.5 for edge-on galaxies. Scale length ratios derived from model images increase from face-on to edge-on view by ≤ 10% only, regardless of whether the model galaxies are optically thin or optically thick.
Implication of Dark Matter Content in Dwarf Spheroidal Galaxies
Authors: Hirashita H. , Takeuchi T. T. , Kamaya H.
Published: July 2016

We investigate the dark matter (DM) content in the Local Group dwarf spheroidal galaxies (dSphs) by examining the correlations among their physical quantities. Two origins of the large velocity dispersions of the dSphs are possible: [1] the existence of DM and [2] tidal heating by the Galaxy. The correlation tests support both [1] and [2]. We finally mention circumstantial evidence for the existence of DM in the dSphs.
Proper Motions of Local Group Satellites
Authors: Irwin Mike
Published: July 2016

Many direct attempts to measure the proper motions of Galactic satellite galaxies are either in progress or have recently been completed. In this review I will summarise and examine the current state of knowledge in this field and will also highlight several indirect methods that can be used as alternative estimators or constraints on the proper motions of satellite galaxies throughout the Local Group. A good example of this latter approach is provided by the Sagittarius dwarf galaxy, where ongoing tidal disruption of the system has left a giant arc of debris tracing out its orbital path.
Visual and Near-Infrared Photometry of Nearby Dwarf Spheroidals
Authors: Kerschbaum F. , Nowotny W. , Hron J. , Schultheis M.
Published: July 2016

This paper is based on photometry from two different observational approaches. Both are of an explorative character and act as feasibility studies. For the future we plan to use these methods to study Asymptotic Giant Branch (AGB) stars in nearby galaxies.

First, we present results on broad-band photometry in BessellVandI, as well as narrow-band measurements in the Wing 778 nm and 812 nm filters of a galactic globular cluster using the new Austrian Oe-FOSC (Oesterreich Faint Object Spectrograph and Camera), a copy of the ESO Instrument EFOSC mounted on our 1.5 m-telescope.

The second part of the contribution deals with the possibilities of using GunnI, JandKSmeasurements originating from the DENIS (DEep Near Infrared Survey of the Southern Sky) project on similar objects. A few southern dwarf spheroidals already observed within DENIS (covering now some 40% of the southern hemisphere) are selected.
Non-thermal radio emission from Wolf-Rayet stars
Authors: Chapman Jessica M. , Leitherer Claus , Koribalski Bärbel
Published: July 2016

We have used the Australia Telescope Compact Array to search for radio continuum emission at λ 3, 6, 13 and 20 cm from a distance-limited sample of 36 southern Wolf-Rayet stars within 3 kpc of the Sun. The observations were taken between 1994 and 1997. Radio continuum emission has been detected from 16 sources at 3 cm. Of these 11 sources were detected at 6 cm, seven sources were detected at 13 cm and 2 sources were detected at 20 cm (Chapman et al. 1999).
Narrow-band photometry of the eclipsing WN7+O binary WR 22
Authors: Royer Pierre , Rauw Gregor , Manfroid Jean , Gosset Eric , Vreux Jean-Marie
Published: July 2016

In the present paper, we discuss photometric observations of the February 1996 eclipse of the very massive WR+O binary WR 22. Our data were obtained with a set of narrow-band filters, specially designed for the study of WR stars.
Progress in model atmosphere studies of Wolf-Rayet stars
Authors: Crowther Paul A.
Published: July 2016

Recent progress in the quantitative analysis of Wolf-Rayet stars is reviewed, emphasising the role played by choice of spectral diagnostics, clumping and line-blanketing on derived stellar properties. The ionizing properties of WR stars are discussed, based on clumped, line-blanketed models for WN and WC stars. The role of metallicity and mass-loss is assessed, and the role of H II regions as probes of predicted Lyman continuum distributions. Suggestions are made for differences in observed properties of WCE and WO subtypes.
Dynamics and variability of winds from single Wolf-Rayet stars
Authors: Owocki Stanley P. , Gayley Kenneth G.
Published: July 2016

We review the dynamics of winds from single Wolf-Rayet stars, with emphasis on the following specific points:

(a)

The classical “momentum problem” (to explain the large inferred ratio of wind to radiative momentum, η Mv∞/(L/c) ≫ 1) is in principle readily solved through multiple scattering of radiation by an opacity that is sufficiently “gray” in its spectral distribution. In this case, one simply obtains η ≃ τ, where τ is the wind optical depth;

(b)

Lines with a Poisson spectral distribution yield an “effectively gray” cumulative opacity, with multi-line scattering occuring when the velocity separation between thick lines Δv is less than the wind terminal speed v∞. In this case, one obtains η ≃ v∞/Δv;

(c)

However, realistic line lists are not gray, and leakage through gaps in the line spectral distribution tends to limit the effective scattering to η ≲ 1;

(d)

In WR winds, ionization stratification helps spread line-bunches and so fill in gaps, allowing for more effective global trapping of radiation, and thus η > 1;

(e)

However, photon thermalization can reduce the local effectiveness of line-driving near the stellar core, making it difficult for radiation alone to initiate the wind;

(f)

The relative complexity of WR wind initiation may be associated with the extensive turbulent structure inferred from observed variabililty in WR wind emission lines;

(g)

Overall, the understanding of WR winds is perhaps best viewed as an “opacity problem”, i.e., identifying the enhanced opacity that can adequately block the radiation flux throughout the wind, and thus drive a WR mass loss that is much greater than from OB stars of comparable luminosity.
New models of massive and Wolf-Rayet stars with mass loss and rotation
Authors: Maeder André
Published: July 2016

We give results of models of massive stars which have a detailed physical treatment of rotation, including structural equations for shellular rotation, new treatments of shears in differentially rotating stars and of meridional circulation, together with mass loss rates depending on rotation. For a 20 M⊙ star, He- and N-enrichments at the stellar surface already occur during the MS phase for moderately low rotational velocities, thus most supergiants are enriched in helium and nitrogen. A long B- and A-supergiant phase results from rotational mixing, with some primary nitrogen formed at this stage. For the most massive stars, rotation makes the star to enter the WR stage during the MS phase thus avoiding the LBV and red supergiant stage.

The WR life-times are considerably increased by rotation and the minimum mass for forming WR stars is lowered. Interestingly enough, the increase of the WN life-time is larger than for WC stars, so that rotation leads to a decrease of the WC/WN number ratio. Also, the fraction of transition WN/WC stars is much larger at higher rotation.

Finally, on the basis of clusters in the SMC, in the LMC and towards the galactic interior and exterior, we show that for clusters with ages between about 1 and 3 x 107 yr the fraction of Be stars with respect to normal B stars is larger at lower metallicities. This may suggest a higher rotation at lower metallicities for massive stars, due to a different history of star formation.
Gamma-ray observations and massive stars
Authors: Diehl Roland
Published: July 2016

Gamma-rays from astrophysical sources testify energetic processes such as nucleosynthesis and cosmic ray collisions. Gamma-rays are observable from throughout the Galaxy, unattenuated by interstellar matter, provided their intensity exceeds the current instrumental sensitivity level (∼ 10−5ph cm−2s−1 at 1 MeV). Massive stars are at the origin of relevant sources: The all-sky image in the 1.809 MeV γ-ray line from radioactive 26Al traces nucleosynthesis throughout the Galaxy. The structure of this emission along the plane of the Galaxy suggests massive stars as dominating sources of this radioactivity. Discrimination of the contribution from core collapse supernova against that from WR-wind ejected hydrostatic nucleosynthesis products may be obtained from 60Fe γ-ray line observations, or from spatial-profile consequences of the metallicity dependence of 26Al production in theories for both source sites. As a single source, the nearest WR star in the γ2 Vel system is found to eject less 26Al into interstellar space than current theories predict. However, a more adequate comparison must be based on a time-dependent 26Al light-curve of the system. Furthermore, continuum γ-ray production in WR binaries through wind-wind interaction, and constraints on the low-energy cosmic ray origin in WR winds through characteristic nuclear deexcitation line studies are targets of research. Studies stimulated by COMPTEL'S 3–7 MeV excess report from the Orion region indicate that the γ-ray line measurements could separate the origins from supernova ejecta and wind material. The COMPTEL Orion result is now attributed chiefly to an instrumental artifact, and has been withdrawn. Nevertheless, the search for MeV emission from massive star clusters, as well as from interacting binaries such as WR 140, promises a unique test of particle acceleration scenarios related to the source mechanism for cosmic ray production.
Why should we compare Wolf-Rayet codes?
Authors: De Marco Orsola , Schmutz Werner , Koesterke Lars , Hamann Wolf-Rainer , de Koter Alex
Published: July 2016

We have modeled the spectrum of WR135 with a co-moving frame code and then used identical input parameters with a Sobolev-approximation code. Helium lines compare well in strength and shape, while carbon lines are found to be much stronger in the co-moving frame code. The reason for this discrepancy is being investigated. The present comparison shows that tests have to be extended to more complex atomic models and compatibility between different codes should not be taken yet for granted.
A tailored analysis of the WN8 star WR 40
Authors: Herald Jim E. , Schulte-Ladbeck Regina E. , Hillier D. John
Published: July 2016

We present the results of a tailored analysis of the spectra of WR40 (HD 96548, WN8) utilizing new line blanketed non-LTE model atmospheres. Synthetic spectra are compared with observation from 900 to 10,000 Å, with emphasis on far-UV HUT observations and the IUE regime. We identify the important line complexes in this region and deduce the Fe abundance. Improved stellar parameters and abundances of other metals are determined. A comparison of our new model results with non-line blanketed results is made.
Shear-turbulence in rotating massive stars
Authors: Staritsin Eugene
Published: July 2016

Shear-turbulence in a radiative envelopes of rotating main sequence massive stars transports angular momentum from the deeper layers to the stellar surface. This process enlarges the influence of rotation on the stellar radius. As a result, the width of the main sequence increases.
Dust-formation episode of the long-period WC+O binary WR 137: direct imaging with HST-NICMOS2
Authors: Marchenko Sergey V. , Moffat Anthony F.J. , Grosdidier Yves
Published: July 2016

We have resolved, for the first time in any WR+OB system, IR-emitting dust in the close environment of the long-period binary WR 137. The dust emission occurs in a few clumps within about 0″.5 of the star, as well as in a jet-like structure with total extension of about 0″.25.
ISO-SWS spectra of Planetary Nebulae with low-mass [WC] central stars: a mixed C- and O-rich dust chemistry
Authors: Morris Patrick W. , Waters L.B.F.M. , Beintema Douwe A.
Published: July 2016

The timing of PNe formation around low-mass WC stars is unsettled with respect to pulsations early in the post-AGB phase, or later thermal pulses (e.g., Tylenda & Gorny 1997). The chemistry of the dust in the nebulae can be used to trace the mass-loss history. Using ISO-SWS spectroscopy, the PNe BD+30°3639 [WC9] and He2–113 [WC11] have been identified by Waters et al. (1998) to exhibit emission from C-rich dust (PAHs) in the surrounding envelopes at λ 15 μm, while O-abundant silicate features are present at longer wavelengths. Figure 1 shows the PAH features, which include additional WCPNe observations to extend the range of stellar spectral subtypes.
A search for new stellar wind sources using the Canadian Galactic Plane Survey (CGPS)
Authors: Pineault Serge
Published: July 2016

The CGPS is a project undertaken at the Dominion Radio Astrophysical Observatory (DRAO), in collaboration with a consortium of university astronomers, to image the atomic hydrogen and the radio continuum emission from the interstellar medium of the Galaxy. We describe the contributions this project can make to WR star research, in particular, and to the study of stellar wind sources, in general. Specific examples are presented.
The X-ray history of WR 140 in modest comparison with the radio
Authors: Pollock Andy M.T. , Corcoran Mike F. , Stevens Ian R. ,   the XMEGA group
Published: July 2016

We present the X-ray lightcurve of the canonical colliding-wind binary WR 140 from the time of the last periastron through late 1997. Variations in column density, and intrinsic and absorbed X-ray flux agree well with the expectations of colliding wind theory in which the winds from the stars are spherically symmetric.
Colliding stellar winds: magnetic field structure in the interaction region
Authors: Zhekov Svetozar A. , Myasnikov A.V. , Barsky E.V.
Published: July 2016

The geometry structure of the magnetic field in colliding stellar winds is studied. It is shown that the magnetic field influence in the interaction region depends mainly on the ratio of the wind ram pressures of the components, the ratio of the stellar linear rotational velocity to the wind velocity of the magnetized star, and the stellar separation. For the radiative colliding winds the magnetic field influence increases with the importance of the radiative losses. An asymmetric magnetic field structure appears for a given set of binary parameters and the interaction region might be an asymmetric source of non-thermal radio emission.
Massive stars and their interstellar environment in the Magellanic Clouds
Authors: Dopita Michael A. , Kim Sungeun , Sally Oey M. , Lozinskaya Tatyana M.
Published: July 2016

The winds of massive stars play a major role in setting up and controlling both the phase structure of the interstellar medium in galaxies and the vertical distribution of gas in galactic disks. In turn, these processes provide feedback into control of the star formation rate. Thanks to their proximity, these processes can be studied in detail in the Magellanic Clouds. Here we describe the results of a deep emission-line image survey of the ring nebula population, and a global high-resolution H I and H II survey of the Large Magellanic Cloud. These data provide a new insight into the process of feedback between the disk and the halo gas in disk galaxies in general, and the LMC in particular.
The starburst galaxy IC 10
Authors: Hodge Paul W. , Zucker Daniel B.
Published: July 2016

The heavily-reddened Local Group galaxy IC 10 has been studied at narrow-band emission-line wavelengths and in U, B, V, and I with the APO 3.5m telescope. The four-color data are being used to measure and map the foreground and internal reddening. The color-magnitude diagram clearly isolates the main sequence from the red supergiants and from the abundant foreground stars. The absolute magnitudes of the main sequence stars, together with the anomalously-abundant WR stars reported by Massey & Armandroff, indicate that the galaxy is currently undergoing a fairly extensive burst of star-formation.
Synthetic spectra of young starbursts: exploring the metallicity dependence
Authors: de Koter A. , Heap S.R. , Hillier D.J. , Hubeny D. I.
Published: July 2016

We present first results of fully synthetic UV spectra of young starbursts. With this we mean that the spectra used to model the OB and WN stars result from unified non-LTE model atmospheres, in which stellar winds are accounted for. An important aim of this project is to construct meaningful models for young starbursts at low metallicities. We discuss the presence of He II emission as a function of maximum initial mass and age of the burst.
HST-NICMOS observations of extensive triggered star formation within the 30 Doradus Nebula
Authors: Walborn Nolan R. , Barbá Rodolfo H.
Published: July 2016

The extensive ‘second generation’ of star formation within the 30 Doradus Nebula, evidently triggered by the R136 central cluster around its periphery, has been imaged with HST-NICMOS. Many new infrared sources and structures are found in these images.
Wolf-Rayet galaxies: the past is prologue
Authors: Conti Peter S.
Published: July 2016

Wolf-Rayet galaxies are those starburst systems in which the presence of Wolf-Rayet stars is inferred from the appearance of broad emission lines, notably λ4686 HeII. The ages of the bursts are only a few Myr when WR stars are present. Many (all?) of these starburst galaxies are interacting or merging systems. This talk will review the methods used to estimate the hot star populations in these galaxies, with emphasis on optical spectrophotometry. It will be important to keep in mind that the discovery of WR stars in starburst galaxies is highly dependent on spectral resolution, signal to noise, and the local properties of the object since one is searching for broad but weak emission lines superimposed upon a galaxy continuum. A brief comparison of the inferred numbers of O-type and WR stars in a galaxy, compared to the predictions of the most recent burst models, reveals good agreement in most cases. The exceptions might be understood in terms of geometric dilution (i.e., the stars and the ionized nebular gas are not co-spatial).
New Wolf-Rayet galaxies – IMF in starbursts
Authors: Huang JieHao , Gu Q. S. , Ji L. , Zheng W.
Published: July 2016

We report the discovery of two new Wolf-Rayet galaxies: Mrk 1039, and F8208+2816. Two broad WR bumps at 5808Å and 4650Å indicate the presence of WCE and WNL star populations in these two sources. Comparison of the observed EW(HeII λ4686) and EW(CIV λ5808) with recent models of WR populations in young starbursts provide an indication that the stellar initial mass function in some WR galaxies might not be Salpeter-like.
The near-infrared colours of H II galaxies
Authors: Telles Eduardo , Sampson Leda , Tapia Mauricio , Terlevich Roberto , Kunth Daniel
Published: July 2016

We present preliminary results of our near-infrared JHK images of a sample of H II galaxies observed at UKIRT. The presence of knots of enhanced emission in the near-IR may indicate the existence of luminous super star clusters which will serve to unveil the basic units which constitute the starburst phenomenon in galaxies. Based on near-IR colours we will further discuss the history of star formation in these bursting dwarf galaxies.
Environmental effects in galaxies – searching for massive stars
Authors: de Mello Duíla F. , Maia Marcio A.G. , Schaerer Daniel , Leitherer Claus
Published: July 2016

In order to study the influence of the environment in galaxies we have selected a sample from the catalog by Maia et al. (1994) which contains objects in low and high density areas of the Southern sky. These samples have been observed with the Brazilian-ESO 1.52m telescope and long-slit spectra are being analyzed. With our database we will be able to investigate the role of the environment in the galaxy population. We will be able to search for WR features and massive stars. It is our goal to compare the general properties of these galaxies with typical starburst galaxies which are dominated by episodes of massive star formation.
High-resolution radio data of molecular gas in dwarf starburst galaxies
Authors: Meier David S. , Turner Jean L. , Beck Sara C.
Published: July 2016

Star-formation in dwarf starburst galaxies can be quite intense for their sizes, especially in the very young ones characterized by Wolf-Rayet emission features. Since stars form out of molecular gas (H2), it is important to investigate in detail, where the molecular gas is relative to the star formation in such young starbursts. The molecular gas may also indicate what might have triggered the starburst. The ISM in dwarfs can be quite warm, is the molecular gas also warm? In an attempt to investigate the properties of molecular gas in WR galaxies we have obtained high resolution images of the J = 2–1 transitions of CO for two dwarf starbursts, NGC5253 and He2–10. Both galaxies are nearby dwarf starbursts with WR emission features (e.g., Conti 1991). NGC 5253 may be one of the youngest starbursts known (e.g., Rieke, Lebofsky & Walker 1988).
Seyfert galaxies: a perspective with ISO-PHOT
Authors: Pérez García Ana M. , Rodríguez Espinosa J.M.
Published: July 2016

We present mid and far-infrared energy distributions of the CfA Seyfert sample, obtained with the Infrared Space Observatory photometer (ISO-PHOT). To analyse the CfA Seyfert SEDS, we apply an inversion method: the Inverse Planckian Transform, assuming that the mid- and far-IR emission is thermal. We obtain the spectral temperature distribution of sources that reproduces the observed SEDS. We compare the parameters of the spectral components found showing that there are not differences between Seyfert 1 and Seyfert 2 as for their temperatures while the emission between 12 and 25 μm is anisotropic.
The fate of superbubbles in dwarf starburst galaxies
Authors: Silich Sergey A. , Tenorio-Tagle Guillermo
Published: July 2016

2D calculations of the evolution of the remnants generated by the strong mechanical energy produced by a central starburst in dwarf galaxies are presented. We show how the extended H I halos inhibit a galactic wind and thus the exit of metals from these galaxies.
Special session of the XMEGA group
Authors: Corcoran Michael F. , Pittard Julian M. , Marchenko Sergey V. ,   the XMEGA group
Published: July 2016

On the day prior to the Symposium, we held a special session to review the current status of the XMEGA observations, to discuss upcoming observations, and to plan for future observing programs
Type Ia Supernovae and Planets in Star Clusters
Authors: Shara Michael M. , Hurley Jarrod R.
Published: July 2016

Star clusters are remarkably efficient (relative to the field) at making type Ia supernovae candidates: very short period, massive double-white-dwarf stars and giant-white dwarf binaries. The high frequency of these systems is the result of dynamical encounters between (mostly) primordial binaries and other cluster stars. Orbital hardening rapidly drives the degenerate binaries to periods under ∼ 10 hours. Gravitational radiation emission and mergers then produce supra-Chandrasekhar objects in less than a Hubble time.

We also find that free-floating planets can remain bound to a star cluster for much longer than was previously assumed: of the order of the cluster half-mass relaxation timescale as opposed to the crossing-time. The planets in our N-body study are of Jupiter mass and are initially placed in circular orbits of between 0.05 and 50 AU about a parent star whose mass is chosen from a realistic initial mass function. This result is important in the context of the preliminary detection of a population of free-floating sub-stellar objects in the globular cluster M22.
Star Cluster Simulations Including Stellar Evolution
Authors: McMillan Stephen L. W.
Published: July 2016

The past few years have seen dramatic improvements in the scope and realism of star cluster simulations. Accurate treatments of stellar evolution, coupled with robust descriptions of all phases of binary evolution, have been incorporated self-consistently into several dynamical codes, allowing for the first time detailed study of the interplay between stellar dynamics and stellar physics. The coupling between evolution, dynamics, and the observational appearance of the cluster is particularly strong in young systems and those containing large numbers of primordial binary systems, and important inroads have been made in these areas, particularly in N-body simulations. I discuss some technical aspects of the current generation of N-body integrators, and describe some recent results obtained using these codes.
The Evolution of Magnetic Fields in Galaxy Clusters
Authors: Bartelmann Matthias , Dolag Klaus , Lesch Harald
Published: July 2016

Cosmological simulations of magnetic fields in galaxy clusters show that remarkable agreement between simulations and observations of Faraday rotation and radio haloes can be achieved assuming that seed fields of ∼ 10−9 G were present at redshifts ∼ 15−20. The structure of the seed field is irrelevant for the final intracluster field. On average, the field grows exponentially with decreasing cluster redshift, but merger events cause steep transient increases in the field strength. Typical field-reversal scales are of order 50h−1kpc. In most cases, the intracluster fields are dynamically unimportant. Assuming secondary electron models, the average structure of cluster radio haloes can naturally be reproduced.
The Evolution of Galaxies in Clusters
Authors: Dubinski John , Koranyi Dan , Geller Margaret
Published: July 2016

We report on recent numerical investigations of the dynamical evolution of galaxies in clusters. Simulations of spiral galaxies falling into forming clusters show the development of the morphology-density relationship and the formation of regular and giant elliptical galaxies. The regular elliptical merger remnants end up in a fundamental plane very similar to the observed relation. The giant ellipticals have much in common with their real counterparts but their central velocity dispersions are too high. We also quantify the amount and distribution of diffuse light in clusters.
A Simulation of Galaxy Formation by Radiation-SPH
Authors: Susa Hajime , Umemura Masayuki
Published: July 2016

We investigate galaxy formation with Radiation-SPH simulations in order to find the effects of ultraviolet background radiation field on the star formation in the forming galaxies. We find the ultraviolet background radiation field can delay the star formation in protogalactic clouds, especially at low redshift (z < 2). This result suggests that galaxies formed at lower redshift tend to be late type galaxies, and early type galaxies tend to be formed at higher redshift.
Application of DSMC method to astrophysical flows
Authors: Matsuda Takuya , Mizutani Hiromi , Boffin Henri. M. J.
Published: July 2016

The Direct Simulation Monte Carlo (DSMC) method, developed originally to calculate rarefied gas dynamical problems, is applied to continuous flow including shocks assuming that the Knudsen number is sufficiently small. In particular, we study the formation of spiral shocks in the accretion disc of a close binary system. The method involves viscosity and thermal conduction automatically, and can thus simulate turbulent viscosity.
Environmental Effects on Evolution of Cluster Galaxies
Authors: Okamoto Takashi , Nagashima Masahiro
Published: July 2016

Using a combination of a cosmological N-body simulation and a semi-analytic galaxy formation model, we investigate environmental effects on cluster galaxies with the ACDM cosmology. We find that stripping of hot gas from galacitc halos as they infall into larger objects sufficiently suppresses star formation in the cluster and successfully reproduces the observed gradients of SFR when we normalize our model to reproduce the observed properties of local galaxies. Consequently, the effect of ram-pressure stripping of cold gas from galactic disks becomes quite small and it is observationally negligible. Therefore, the deficiency of galaxies with intermediate bulge-to-disk luminosity ratios under the hierarchical structure formation cannot be resolved even if we include the ram-pressure stripping in our modeling.
Galactic disc formation from cold fractal gas
Authors: Semelin B. , Combes F.
Published: July 2016

It is likely that cold molecular clouds formed early, even before galaxies. In this work, we try to assess the consequences of using cold fractal gas for disc formation instead of hot gas, with a focus on angular momentum loss through dynamical friction. Using numerical simulations, we show that the dynamical friction from the dark matter halo on the cold gas fractal structures is not affected by the morphology of the structures, but is affected by their dynamical nature: their deformations and fluctuations. We argue that for typical values of the physical parameters during disc formation, the friction at small scale is reduced.
Surface Abundance Anomalies of Main Sequence Stars in Globular Clusters — A Probe into Interactions between Stars
Authors: Shimada Masaaki , Fujimoto Masayuki Y. , Yamada Shimako , Sugimoto Daiichiro
Published: July 2016

In most of globular clusters, surface abundance anomalies are observed not only from red giant stars but also from main sequence stars. We discuss the possibility that the latter anomalies can be explained in terms the pollution due to mass transfer during close encounters with red giants, the latter of which have already developed the anomalies through their internal processes. If this is the case, the main sequence stars with the abundance anomalies may serve as a probe into the star-star interactions in dense cores of globular clusters.
Clustering of dark halos on the lightcone
Authors: Yoshida Naoki , Hamana Takashi , Suto Yasushi , Evrard August
Published: July 2016

We present a phenomenological model to predict the clustering of dark matter halos on the light-cone. The model is constructed by combining several existing theoretical models. We test our model against the Hubble Volume N-body simulation and examine its validity. A good agreement is found in two-point correlation functions of dark matter halos between our model predictions and measurements from the simulation. The model is quite general and thus can be applied to a wider range of astrophysical objects, such as galaxies and quasars.
Chemical Composition of New Galactic Bulge Planetary Nebulae
Authors: Van De Steene Griet C. , Jacoby George H.
Published: July 2016

We did photo-ionization modelling of 10 new Planetary Nebulae within 2° of the Galactic Center. We found that these PNe would originate mainly from low mass, old, metal poor stars.
Nucleosynthesis in AGB Stars: the Role of Dredge-Up and Hot Bottom Burning
Authors: Lattanzio John
Published: July 2016

We review the basics of AGB nucleosynthesis in thermal pulses, in the hydrogen burning shell, and by Hot Bottom Burning.
The Changing Period of R Hya
Authors: Zijlstra Albert A. , Bedding Timothy R.
Published: July 2016

We discuss the period evolution of the Mira variable R Hya. We show, using observations dating back to 1662, that it has evolved from a stable 500-day period to a stable 380-day period. The onset of the period evolution coincided with a sharp decline in mass-loss rate. We suggest that mass-loss fluctuations over a period of a few hundred years may be common in Miras, and relate to a non-linear pulsation instability.
A Multi-Wavelength Study of the Oxygen-Rich AGB Star CIT 3: Bispectrum speckle interferometry and dust-shell modelling
Authors: Hofmann K.-H. , Blöcker T. , Weigelt G. , Balega Y.
Published: July 2016

CIT 3 is an oxygen-rich long-period variable evolving along the Asymptotic Giant Branch and is one of the most extreme infrared AGB objects. Due to substantial mass loss it is surrounded by an optically thick dust shell which absorbs almost all visible light radiated by the star and finally re-emits it in the infrared regime. We present the first near infrared bispectrum speckle-interferometry observations of CIT 3 in the J-, H-, and K′-band (resolution: 48 mas, 56 mas, and 73 mas). The interferograms were obtained with the Russian SAO 6 m telescope. While CIT 3 appears almost spherically symmetric in the H- and K′-band it is clearly elongated in the J-band along a symmetry axis of position angle −28°. Two structures can be identified: a compact elliptical core (eccentricity ~0.8) and a fainter north-western fan-like structure (full opening angle ~ 40°). The development of such asphericities close to the central star suggests that CIT 3 is in the very end of its AGB evolution or even in transition to the proto-planetary nebula phase where most objects are observed in axisymmetric geometry.
Imaging and Polarimetry of the Dust Shells Around Post-AGB Stars
Authors: Gledhill Tim , Bains Indra , Yates Jeremy
Published: July 2016

We have completed a polarimetric survey of 46 post-AGB stars which indicates that where an extended circumstellar envelope is seen then it is axisymmetric to some degree. This suggests that all post-AGB envelopes are axisymmetric and that the responsible mechanism must be ubiquitous.
Planetary Nebulae in the Scheme of Binary Evolution
Authors: Soker Noam
Published: July 2016

In this review I present the binary model for the shaping of planetary nebulae (PNe) as I view it, in the context of historical evolution of other models for the shaping of PNe over more than 30 years. In describing the binary model, I concentrate on works published since the last IAU meeting on PNe. I think stellar companions are behind the shaping of bipolar PNe, i.e., having two lobes with an equatorial waist between them, and extreme elliptical PNe, e.g., having a dense equatorial ring, but no lobes. The question of whether a planet is required to spin the progenitor in order to form a moderate elliptical PN, or whether single stars can form moderate elliptical PNe, I consider to be an open question.
Revised Abundances & Ionizing Fluxes for [WC]-Type PN Central Stars Using Line Blanketed Models
Authors: Crowther Paul A. , Abbott Jay B. , Hillier D. John , De Marco Orsola
Published: July 2016

UV (IUE), far-UV (FUSE) and optical (INT) spectroscopy of four Galactic [WC]-type PN central stars are analysed by means of sophisticated model atmosphere codes which allow for detailed line blanketing and clumping, and make comparisons with earlier non-LTE models. Crucially, we find no systematic difference between carbon abundances amongst late and early-type [WC] stars, removing the main obstacle against evolution from [WCL] to [WCE] subtypes.
Photochemistry and Molecular Formation in Planetary Nebulae
Authors: Hasegawa Tatsuhiko I.
Published: July 2016

Photo-chemical processes in hot neutral gas are summarized that are likely responsible for the destruction and formation of observed molecules in planetary nebulae. According to the hot gas scenario, detected simple molecules such as CN, HCN, C2H, and HCO+are destroyed in a matter of a week, but are constantly and quickly re-formed.
Molecular Line Observations of the Protoplanetary Nebula, IRAS 19312+1950
Authors: Deguchi Shuji , Nakashima Jun-ichi
Published: July 2016

We give a summary of radio molecular-line and infrared imaging observations of the newly found O-rich protoplanetary nebula, IRAS 19312+1950. This object exhibits a bipolar nebulosity of size ~ 30″ on the near-IR (JHK) images. A ring-like structure with a diameter of about 10″ is seen surrounding the central star. Toward this object, we detected thermal lines of CO, HCO+, SO, and SiO (O-bearing) molecules and CN, CS, HNC, NH3, N2H+, and HC3N (C- and N-bearing) molecules, as well as H2O and SiO masers lines. The line profiles of 12CO, HCN, SO, and HCO+ are composed of broad (Δv ~ 30–40 km s-1) and narrow (Δv < 5 km s-1) components. The SiO profile (J = 2—1 v = 0 thermal line) has only broad component, and the line profiles of non-O-bearing molecules (except HCN) have only a narrow component. Both components are spatially strongly peaked in intensity at the center of this object within a ~ 15″ telescope beam. We infer that both components originate from cool material surrounding the central star. This object is most likely an O-rich protoplanetary nebula with high mass loss rate and envelope chemistry similar to that of OH 231.8+0.4.
Dust Properties of Planetary Nebulae
Authors: Kimeswenger Stefan
Published: July 2016

Shells of planetary nebulae (PNe) are usually modeled applying photoionization only although there is a significant fraction of dust embedded in the nebular shells. The calculated temperature and dust-to-gas ratio from IRAS colors is “faked” by the IR flux continuum contribution from the gas and by transiently heated dust grains. Also the effects of grain growth time and thus maximum grain size lead to strong deviations from the model input values, adopting the IRAS data fits.
ISO Spectra of Planetary Nebulae
Authors: Volk Kevin , Kwok Sun
Published: July 2016

It has been well known since the IRAS mission that dust emission represents a significant fraction of the energy output from PNe (Zhang & Kwok 1991). Although the dust component in PNe was long thought to be due to the remnants of the envelopes of AGB stars (Kwok 1982), we now know that dust in PNe has a much richer chemical composition. In addition to amorphous silicates and SiC features commonly seen in AGB stars, PNe have been found to have strong aromatic infrared features (Russell et al. 1977), crystalline silicate features (Waters et al. 1997), and an unidentified emission feature at 30 μm (Forrest et al. 1981). In this paper, we show the ISO spectra of a number of PNe illustrating the diverse dust chemistry in PNe.
Upper Limit to the Deuterium Abundance in Planetary Nebulae
Authors: Hébrard G. , Péquignot D. , Walsh J. R. , Morisset C. , Vidal-Madjar A. , Ferlet R.
Published: July 2016

We recently reported the first detection of the deuterium Balmer series in emission in H II regions, performed at the CFHT (Hébrard et al. 2000a) and at the VLT (Hébrard et al. 2000b). These narrow lines are excited by UV continuum fuorescence and arise at the atomic interface between H II regions and molecular clouds.

Following this discovery, we used the CFHT with the Gecko spectrograph to observe Balmer lines in planetary nebulae. The non-detection of the deuterium Balmer lines in planetary nebulae represents the first observational evidence that this isotope was, as expected, destroyed in the parent stars.
A Survey of Recombination-line Abundances in Planetary Nebulae and H II Regions
Authors: Tsamis Y. G. , Barlow M. J. , Liu X.-W. , Danziger I. J.
Published: July 2016

We have derived C, N and O abundances, relative to H, using optical recombination lines (ORLs), for a number of galactic planetary nebulae and for three Magellanic Cloud PNe (LMC N66, N141, SMC N87) and compared them with the corresponding abundances derived from collisionally-excited lines (CELs). Our goal was to investigate the fact that PNe ORL abundances are in most cases larger than those obtained from CELs. Our scanning, long-slit observations were combined with large-aperture IUE, IRAS and ISO data to yield integrated abundances for more than half of our target objects.
Photoionization Models of Chemically Inhomogeneous Planetary Nebulae
Authors: Tylenda Romuald
Published: July 2016

We have constructed photoionization models of NGC 6153, M 2–36, and M1–42. These planetary nebulae show large differences, both, in the CNO and Ne abundances as derived from recombination lines and collisionally excited lines, as well as, in the electron temperature determined from Balmer jump and [OIII] lines. The model nebulae have low mass (about 1% of the total nebular mass) inclusions where the CNO and Ne abundances are enhanced by a factor of 200 or so.
Extracting Point Source Spectra / Recovering Extended Object Spectra Using Richardson-Lucy Restoration
Authors: Walsh J. R. , Lucy L. B.
Published: July 2016

Long slit spectra of astronomical objects either contain point sources, characterized by a known Point Spread Function (PSF), which is often wavelength dependent, and extended sources, such as nebulae, whose spatial extent is not a priori known. The analysis of long slit spectra consists in separating the spectrum into either: the point source(s), free of the background (“extraction”); or the extended source(s), free of contaminating point source spectra. Depending on the scientific aim, one or both of these data are of interest, such as the spectrum of the central star of a planetary nebula AND the line and continuum spectrum of the nebula with the star removed. In the simple case of a point source with a background gradient, the spectrum of the point source can be simply extracted by subtracting a background fit by a low order function and summing (perhaps with weights, as in optimal extraction) the point source signal at each spectral element in the cross-dispersion direction. When the background is complex or there are many point sources, there is no guide as to how to fit the extended source spectrum beneath the point sources. Simple methods can give a poor estimate of the spectra of point sources and the spectrum of the background in the vicinity of the stars. The application of image restoration algorithms to the spatial component of long slit spectra offers a potential solution.
Giant Emission Structures and Dust-poor Holes around Planetary Nebulae on IRAS SkyView Images?
Authors: Weinberger Ronald
Published: July 2016

A systematic search of the wider neighborhood of Planetary Nebulae (PNe) on IRAS SkyView images revealed structures like bipolar dust blobs, curved filaments and dust-poor cavities which in several cases suggest that they are genuine and not just due to projection effects.