bluuebunny/crossref_metadata_2025 huggingface dataset:
Dust in the Intergalactic Medium of Galaxy Clusters
Authors: Stickel M.
Published: July 2016

Far-infrared (FIR) observations with ISOPHOT aboard the Infrared Space Observatory were carried out to observe the thermal FIR emission from diffuse intracluster dust (ICD) in galaxy clusters and outlying dust structures in the elliptical galaxies M86 and NGC 5128 (Centaurus A). Extended FIR emission from ICD has only been detected in the Coma cluster. It is likely caused by tidal interactions, since Coma is a dynamically young cluster with on-going gravitational interactions in the centre and infalling galaxy groups. M86 has a complex FIR morphology with a compact double source near its centre and several off-centre sources. The brightest FIR source lies between M86 and the nearby spiral NGC 4402 and represents the first direct detection of a localized intracluster dust cloud not associated with optical or neutral hydrogen emission. Overall, the FIR data do not support the ram pressure dust stripping scenario suggested on the basis of IRAS data, but indicate a significant influence of tidal interactions. NGC 5128 shows obvious optical signs of interaction, most notably a central dust lane and stellar shells. The FIR emission of outlying dust 15 kpc from the centre has been discovered where previously HI and molecular gas closely associated with the shells had been found. NGC 5128 is the first case of a shell galaxy where all components of the interstellar medium (ISM) are detected far off the nucleus, indicating an inner disk origin of the outlying material.
Evidence for Gas Accretion in Galactic Disks
Authors: van der Hulst Thijs , Sancisi Renzo
Published: July 2016

Studies of the HI in galaxies have clearly shown that subtle details of the HI distribution and kinematics often harbour key information for understanding the structure and evolution of galaxies. Evidence for the accretion of material has grown over the past many years and clear signatures can be found in HI observations of galaxies. We have obtained new detailed and sensitive HI synthesis observations of three nearby galaxies which are suspected of capturing small amounts of HI and show that indeed accretion of small amounts of gas is taking place in these galaxies. This could be the same kind of phenomenon of material infall as observed in the stellar streams in the halo and outer parts of our galaxy and M 31.
The Hydrogen Clouds in the Galactic Halo
Authors: Lockman Felix J.
Published: July 2016

New 21cm observations with the Green Bank Telescope show that a significant fraction of the HI in the inner Galaxy's halo ~ 1 kpc from the midplane exists in the form of discrete clouds. Some look very much like a Spitzer (1968) “standard” diffuse cloud but with their HI in two phases. They mark the transition between the neutral disk and the highly ionized halo. The dominant motion of the clouds is Galactic rotation, but some have random velocities of as much as 50 km s−1. They are part of the Galaxy and are not related to high-velocity clouds, yet their origin is obscure.
The Ionization Equilibrium of Iron in H II Regions
Authors: Rodríguez M. , Rubin R.H.
Published: July 2016

We study the ionization equilibrium of Fe using photoionization models that incorporate improved values for the relevant atomic data. The previously available photoionization models predict concentrations of Fe3+ which are a factor of 3-8 higher than the values inferred from emission lines of [Fe III] and [Fe IV]. Our new models reduce these discrepancies to factors of 2-5. We comment on the possible reasons behind the remaining discrepancies, and present an updated ionization correction factor for obtaining the Fe abundance from the Fe++ abundance.
The Near-IR Luminosity-Metallicity Relationship for Dwarf Irregular Galaxies
Authors: Saviane Ivo , Riegerbauer R. , Held E. V. , Ivanov V. , Alloin D. , Bresolin F. , Momany Y. , Rich R. M. , Rizzi L.
Published: July 2016

We briefly describe our on-going investigation of the near-IR luminosity-metallicity relationship for dwarf irregular galaxies in nearby groups of galaxies. The motivations of the project and the observational databases are introduced, and a preliminary result is presented. The 12 + log(O/H) vs. H plane must be populated with more low-luminosity galaxies before a definite conclusion can be drawn.
Fe II Emission as a Probe of Iron Abundance at Low-z Quasars
Authors: Verner Ekaterina
Published: July 2016

Whether the Fe/α enrichment is due to SN Ia explosions or massive objects is a key problem to be addressed in constructing our picture of galactic evolution in the Early Universe. Observations in the rest-frame of Mg II emission at 2800 Å and the broad emission complex of Fe II spanning 2000-3000 Å in high-z quasars should allow to determine the time in the Universe when increases in Fe abundance occur. This in turn provides us constraints on the stellar initial mass function and QSO formation and even the cosmological parameters. However a problem remains in developing a reliable model for this complex ion that accurately predicts the emission line spectra seen in luminous AGN at high redshift. The Fe II/Mg II emission ratios using new 830-level Fe II model are investigated with the intent to explain the observed Fe II/Mg II emission scatter.
Chemical Evolution in Hierarchical Clustering Scenarios
Authors: Tissera Patricia B. , Scannapieco Cecilia
Published: July 2016

We present first results of an implementation of chemical evolution in a cosmological hydrodynamical code, focusing the analysis on the effects of cooling baryons according to their metallicity. We found that simulations with primordial cooling can underestimate the star formation rate from z < 3 and by up to ≈ 20%. We constructed simulated spectra by combining the star formation and chemical history of galactic systems with spectral synthesis models and assess the impact of chemical evolution on the energy distribution.
Chemical Abundances and Hierarchical Clustering
Authors: Tissera P. B. , Lambas D.G.
Published: July 2016

In this contribution we study the chemical enrichment of the interstellar medium and stellar population of the building blocks of current typical galaxies in the field, in cosmological hydrodynamics simulations. The simulations include detailed modeling of chemical enrichment by SNIa and SNII In our simulations the missing metal problem is caused by chemical elements being locked up in stars, in the central regions (or bulges) mainly. Supernova energy feedback could help to reduce this concentration by expelling metals to the intergalactic medium.
Sizes of Intervening C IV Absorbers from High Resolution Spectroscopy of APM 0827+5255
Authors: Tzanavaris Panayiotis , Carswell Robert F.
Published: July 2016

Some intervening C IV absorbers in the Keck/HIRES spectrum of APM 0827+5255 give rise to absorption lines for which the observed optical depths for the doublet components are not in the expected 2 : 1 ratio. We model this effect as coverage of one line of sight to this gravitationally lensed quasar and perform a set of simulations to select a sample of lines for which our model provides an explanation for the effect. We use lines in this sample to obtain estimates for minimum absorber sizes from total coverage and the separations of the lines of sight for a range of lens redshifts, z1, and two cosmologies. We also obtain best estimates for overall sizes from a statistical “hit and miss” approach. For z1 = 0.7 our results set a lower limit to sizes of C IV absorbers of ~ 0.3 h−172 kpc (~ 0.5 h−172 kpc) for ΩM = 1, ΩA = 0 (ΩM = 0.3, ΩA = 0.7).
Chandra X-ray Observations of Dwarf Starburst Galaxies
Authors: Ott Jürgen , Walter Fabian , Brinks Elias , Klein Ulrich
Published: July 2016

We obtained X-ray observations for a sample of eight nearby dwarf starburst galaxies from the Chandra X-ray Observatory. Five galaxies of our sample show extended (size: 1-10 kpc), diffuse X-ray emission which can be attributed to a hot thermal plasma. This phase of the interstellar medium purportedly drives the expansion of supergiant shells. A comparison of the derived gas parameters with theoretical models reveals that the hot gas in principle is capable to escape from the gravitational potential of the host galaxy. However, the outflows appear to be contained in those cases where an extended envelope or massive tidal features of neutral gas exist.
X-Ray Emission from Expanding Shells in NGC 3077
Authors: Ott Jürgen , Martin Crystal L. , Walter Fabian
Published: July 2016

Deep Chandra observations of NGC 3077, a starburst dwarf galaxy in the M81 triplet, resolve the X-ray emission from several supershells. The emission is brightest in the cavities defined by expanding shells detected previously in Hα emission. Thermal emission models fitted to the data imply temperatures ranging from 1.3 to 4.9 × 106 K. The total 0.3–6.0 keV X-ray luminosity is 2 − 5 × 1039ergs−1 (depending on the selected thermal plasma model). Most (85%) of the X-ray luminosity in NGC 3077 comes from the hot interstellar gas; the remainder comes from six X-ray point sources. The radial density profile of the hot gas is not as steep as that expected in a freely expanding wind (e.g., as seen in the neighboring starburst galaxy M 82) implying that the hot gas is still confined by the Hα shells.
SN Heating Efficiency of the ISM of Starburst Galaxies
Authors: Melioli C. , de Gouveia Dal Pino E. M. , D'Ercole A. , Raga A.
Published: July 2016

The interstellar medium heated by supernova explosions (SN) may acquire an expansion velocity larger than the escape velocity and leave the galaxy through a supersonic wind. Galactic winds are effectively observed in many local starburst galaxies (Lehnert & Heckman 1996). The SN ejecta are transported out of the galaxies by such winds which must affect the chemical evolution of the galaxies. The effectiveness of the processes mentioned above depends on the heating efficiency (HE) of the SNs, i.e., the ratio between the kinetic plus internal energy density of the ambient gas and the SN energy density. In a starburst region, several SN explosions occur at a large rate inside a relatively small volume. If the successive generations of SN remnants (SNRs) interact with each other very fast, then a superbubble of high temperature and low density will rapidly develop, before a significant increase of the ambient gas density that could lead to substantial losses of energy by radiation. In this case, it is common to assume a value for HE of the order of unity, since most of the available energy of the SNs will be transferred to the ambient gas in the form of kinetic and internal energy, instead of being radiated away. However this assumption fails to reproduce both the chemical and dynamical characteristics of most starburst (SB) galaxies. In order to solve this paradigm, we have constructed a simple semi-analytical model, considering the essential ingredients of a SB environment, i.e., a three-phase medium composed by hot diffuse gas, SNRs and clouds, which is able to qualitatively trace the thermalisation history of the ISM in a SB region and determine the HE evolution (Melioli, de Gouveia Dal Pino, & D'Ercole, A&A, 2003, submitted). Our study has also been accompanied by fully 3-D radiative cooling, hydrodynamical simulations of SNR-SNR and SNR-clouds interactions (see Melioli, de Gouveia Dal Pino, & Raga 2003, in preparation).
The Enrichment of Galaxies by Quasar Outflows
Authors: Chartas G. , Brandt W. N. , Gallagher S. C. , Garmire G. P.
Published: July 2016

Our recent Chandra and XMM-Newton observations of the gravitationally lensed broad absorption line quasars (BALQSOs) APM 08279+5255 and PG 1115+080 have provided new insights into the structure of quasar outflows and the enrichment of their host galaxies by quasar winds (Chartas et al. 2002, 2003). Our spectral analysis of these observations suggests the presence of X-ray BAL material accelerated to relativistic velocities of up to ~ 0.4c, considerably larger than the observed velocities of the UV BAL absorbers in these objects. We present constraints on the quasar mass-outflow rates based on the observed relativistic outflow velocities and locations of the X-ray BAL material.
Case Studies of Mass Transfer and Star Formation in Galaxy Collisions
Authors: Struck Curtis
Published: July 2016

The amount, timing and ultimate location of mass transfer and induced star formation in galaxy collisions are sensitive functions of orbital and galaxy structural parameters. I discuss the role of detailed case studies and describe the results for two systems, Arp 284 and NGC 2207/IC 2163, that have been studied with both multiwaveband observations, and detailed dynamical models. The models yield the mass transfer and compressional histories of the encounters and the “probable causes” or triggers of individual star-forming regions.
Tidal Remnants and Intergalactic H II Regions
Authors: Oosterloo Tom , Morganti Raffaella , Sadler Elaine M. , Ferguson Annette , van der Hulst Thijs , Jerjen Helmut
Published: July 2016

We report the discovery of two small intergalactic H II regions in the loose group of galaxies around the field elliptical NGC 1490. The H II regions are located at least 100 kpc from any optical galaxy but are associated with a number of large H I clouds that are lying along an arc 500 kpc in length and that have no optical counterpart on the Digital Sky Survey. The sum of the H I masses of the clouds is almost 1010M⊙ and the largest H I cloud is about 100 kpc in size. Deep optical imaging reveals a very low surface brightness counterpart to this largest H I cloud, making this one of the H I richest optical galaxies known (MHI/LV ~ 200). Spectroscopy of the H II regions indicates that the abundance in these H II regions is only slightly sub-solar, excluding a primordial origin of the H I clouds. The H I clouds are perhaps remnants resulting from the tidal disruption of a reasonably sized galaxy, probably quite some time ago, by the loose group to which NGC 1490 belongs. Alternatively, they are remnants of the merger that created the field elliptical NGC 1490. The isolated H II regions show that star formation on a very small scale can occur in intergalactic space in gas drawn from galaxies by tidal interactions. Many such intergalactic small star formation regions may exist near tidally interacting galaxies.
Kinematic Properties of the TDG Candidates of CG J1720-67.8
Authors: Temporin Sonia
Published: July 2016

I use integral field and long-slit spectra from the AAT and the Magellan telescope to investigate the kinematics of several clumps, recently identified along the prominent tidal tail of CG J1720-67.8 and suggested as possible tidal dwarf galaxy (TDG) candidates. A comparison of photometric and spectroscopic data with evolutionary synthesis models suggests burst ages of ~ 6 Myr for these clumps/TDG candidates.
Stellar Associations in the Tail of NGC 4038
Authors: Saviane I. , Hibbard J. E. , Rich R. M.
Published: July 2016

We have used the Hubble Space Telescope and Wide Field Planetary Camera 2 to image the putative tidal dwarf galaxy located at the tip of the Southern tidal tail of NGC 4038/9, the Antennae. We resolve individual stars, and identify two stellar populations. Hundreds of massive stars are present, concentrated into tight OB associations on scales of 200 pc, with ages ranging from 2-100 Myr. An older stellar population is distributed roughly following the outer contours of the neutral hydrogen in the tidal tail; we associate these stars with material ejected from the outer disks of the two spirals. The older stellar population has a red giant branch tip at I = 26.5 ± 0.2 from which we derive a distance modulus (m - M)0 = 30.7 ± 0.25. The implied distance of 13.8 ± 1.7 Mpc is nearly a factor of two closer than commonly quoted distances for NGC 4038/9. In contrast to the previously studied core of the merger, we find no super star clusters. One might conclude that SSCs require the higher pressures found in the central regions in order to form, while spontaneous star formation in the tail produces the kind of O-B star associations seen in dwarf irregular galaxies.
Tidal Dwarf Galaxy Candidates in Hickson Compact Groups of Galaxies
Authors: Amram Philippe , de Oliveira Claudia Mendes , Plana Henri , Balkowski Chantal
Published: July 2016

The detailed study of the internal kinematics of tidal dwarf galaxy (TDG) candidates detected in optical and/or HI observations is most important to address the question about their origins. We are conducting a program to measure the kinematics of TDG candidates in compact groups using a Fabry-Perot instrument which allows us to study the 2-D velocity maps of the objects with high spatial and spectral resolutions. Our main goal is to select TDG candidates which have kinematics independent of the possible parent galaxies. In this paper, we describe our results for Stephan's quintet (SQ) and HCG 31. We find that the dynamical masses of the TDG candidates in SQ range from 108 up to 1010M⊙. Two objects to the E and S of HCG 31 A+C present counterrotating patterns with amplitudes of 30 and 40 km s−1. Region F, which was previously thought to be the best example of TDG presents no rotation.
On the Nature of Dwarf Galaxies in the Interacting Group HCG 31
Authors: López-Sánchez Ángel R. , Esteban César , Rodríguez Mónica
Published: July 2016

We have analysed the morphology, kinematics, colors and chemical composition of the ionized gas of the different objects belonging to the interacting compact group HCG 31 in order to get a global view of the origin and evolution of the dwarf galaxies present in it.
Large scale distribution of gas, dust and stars deduced from observations from the UV to the IR
Authors: Koornneef J.
Published: July 2016

We introduce an as yet unpublished set of OAO-II observations of stellar associations in the Large Magellanic Cloud (LMC). Cross-correlation of the photometric characteristics of these fields with the infrared fluxes at these same positions obtained by the IRAS satellite provides information on the local stellar population, the amounts of interstellar extinction and thermal dust emission.
Structure and kinematics in the northeastern outer parts of the SMC
Authors: Hatzidimitriou D. , Cannon R. D. , Hawkins M.R.S.
Published: July 2016

We present preliminary results from a study of the radial velocities of red horizontal branch stars in the north-eastern outer parts of the Small Magellanic Cloud (SMC). The sample is located in an area with a large line-of-sight depth of 15 kpc. It is suggested that there is a correlation between line-of-sight distance and radial velocity for these stars, with the more distant ones showing significantly higher velocities.
Young star clusters in the LMC
Authors: Freeman K. C. , Elson R.A.W.
Published: July 2016

We discuss the integrated colours, kinematics, formation, dynamical evolution and initial mass functions of the young globular star clusters in the Large Magellanic Cloud (LMC). Because these clusters are so young, they offer us insights, unobtainable from the old globular clusters in our Galaxy, into the formation and early dynamical evolution of globular clusters.
The age-abundance relations and age distributions for the star clusters of the Magellanic Clouds
Authors: Da Costa G. S.
Published: July 2016

A sample of Large Magellanic Clouds (LMC) and Small Magellanic Clouds (SMC) clusters for which ages have been directly determined from main sequence turnoff photometry has been compiled. According to this sample, the LMC and SMC cluster age distributions are very different. The LMC contains a large population of 1 to 3 Gyr old clusters as well as a small number of clusters that appear to be as old as the Galactic halo globular clusters. Surprisingly however, only a single cluster is known with an age in the interval between 3 Gyr and the age, taken as 15 Gyr, of the oldest clusters. The SMC age distribution, on the other hand, is much broader. It extends back to approximately 12 Gyr but there appear to be no SMC clusters as old as the oldest in the LMC. The sample of clusters is also used to discuss the age-abundance relations for both galaxies. Little can be learned for the LMC but it appears that the chemical evolution of the SMC differed in form from that experienced in the solar neighbourhood. The first results of an imaging survey designed to find LMC clusters with ages exceeding 3 Gyr are also described.
Candidate protostars in the vicinity of 30 Doradus
Authors: Hyland A. R. , Jones T. J.
Published: July 2016

Four candidate protostars have been identified, with luminosities of 1-5×'l04L⊙ and masses of 10-20M⊙, in a magnitude-limited near-infrared survey of the 30-Dor complex. Each is associated with a dense knot in the nebular arcs. We suggest that both the knots and the associated star formation result from the compression of interacting arcs of mass-loss winds from hot massive stars in the central cluster and other nearby clusters. This mode of star formation appears to be highly efficient. In the 30-Dor region there is a clear spatial separation of the young blue stars and older red stars, strengthening the evidence for a multiple starburst in the region.
Dynamical evolution of binary clusters and colliding galaxies
Authors: Sugimoto D. , Ebisuzaki T. , Makino J.
Published: July 2016

Merging of stellar systems is investigated by means of N-body simulations. We discuss the synchronization instability to trigger sudden merging, the origin of the ellipticity in the merger remnants, the distribution of stars in the halo, and the survival of the colour gradient of stars against the violent relaxation of the merging process.
Infrared imaging of intermediate age LMC/SMC clusters
Authors: Zinnecker H. , Ferraro F. , Fusi Pecci F. , Renzini Alvio , Buonanno R. , Corsi C.E. , Terndrup D.M.
Published: July 2016

Infrared colour-magnitude diagrams (K vs. J-K) have been obtained for eight intermediate age (˜0.1-1 Gyr) Large Magellanic Cloud (LMC) clusters and one Small Magellanic Cloud (SMC) cluster (NGC 419). The data have been obtained from infrared array camera images taken at the CTIO 1.5m telescope and reduced using the software package ROMAFOT. We believe that we have observed the onset of the extended red giant branch, i.e. the discontinuous change in the infrared colour and in the number of infrared bright stars per unit optical cluster luminosity. The most luminous stars (K = 10-12.5) must be on the asymptotic giant branch; some of them are very red (J - K > 1.5) and must be carbon stars.
Luminous blue variable stars in the Magellanic Clouds
Authors: Wolf Bernhard
Published: July 2016

The main characteristics of the luminous blue variables (LBVs) in the MCs with S Dor-type outbursts are reviewed. At quiescence they are luminous OB supergiants occupying an inclined instability strip in the HRD. The most luminous LBVs are the hottest ones. During outburst, dense envelopes are expelled of equivalent spectral-type middle A to early F. LBVs occupy at maximum a vertical strip in the HRD at a temperature of about 8000K. The observed amplitudes in the visual range increase from 1 mag (e.g. R71; T=14500K at quiescence) to 2.5 mag (e.g. R127; T=33000K at quiescence). The existence of an amplitude-luminosity relation is suggested which can be used to derive extragalactic distances, if calibrated with the LBVs of the LMC. Whereas four LBVs are known to be members of the LMC, none is known in the SMC. This could be a consequence of the lower metal abundance in this galaxy.
Wolf-Rayet stars in the Magellanic Clouds
Authors: Smith Lindsey F.
Published: July 2016

The most striking feature of the Wolf-Rayet stars in the Magellanic Clouds is their subtype distribution. The range of WC subtypes found in the Large and Small Cloud agrees with evolutionary model predictions at the corresponding metallicities. It follows that the WR subtype distribution in any external galaxy is a clear indicator of the metallicity in that galaxy.

The fluxes in the emission lines of WC stars appear to be consistent within the LMC. This can be used (with some precautions) in the Milky Way and other galaxies to determine reddening, distance and the numbers of WR stars in compact regions.
Winds of hot stars in the Magellanic Clouds
Authors: Kudritzki R. P. , Pauldrach A.W.A. , Puls J. , Voels S. R.
Published: July 2016

The Magellanic Clouds provide a unique laboratory in which to study the metallicity dependence of stellar winds. If proved by observations, such a dependence would have important consequences for stellar evolution, nucleosynthesis, energy balance of the ISM, star formation and so on. In addition, the diagnostics of emitting gaseous nebulae in metal-poor galaxies would be affected, since the photospheric ionizing radiation of massive hot stars is modified by metal absorption in the surrounding stellar winds (see recent review by Kudritzki et al. 1990). Moreover, the method of using mass-loss rates M and terminal velocities vi, to determine stellar distances, radii and masses (Kudritzki & Hummer 1990) would need further modification.
SN 1987A and its role in the LMC
Authors: Danziger I. J. , Bouchet P. , Gouiffes C. , Lucy L. B.
Published: July 2016

A brief review is presented of results obtained at ESO on dust formation, evolution of line profiles and luminosities, and chemical abundances including the radioactive species. The most recent evolution of the bolometric light curve is discussed.
First Australia Telescope observations of SNR 0540-693
Authors: Kesteven M. J. , Manchester R. N. , Staveley-Smith L.
Published: July 2016

Observations of the LMC SNR 0540-693 using the Australia Telescope Compact Array at a wavelength of 6cm show that the remnant consists of a central core coincident with the associated pulsar and a partial ring of about 65 arcsec diameter.
Effects of envelope overshoot on intermediate mass stars
Authors: Alongi M. , Bertelli G. , Bressan A. , Chiosi C.
Published: July 2016

We find that a certain amount of non-local overshoot at the base of the outer convective envelope affects the evolution of intermediate mass stars in the H-R diagram, producing extended loops even for models computed with significant overshoot from the central convective core, improving in this way upon a weak point of models with core overshoot.
New element abundances in NGC 330
Authors: Richtler T. , Spite M. , Spite F.
Published: July 2016

We present element abundances based on high dispersion spectra of four stars in the SMC cluster NGC 330. The metallicities range from −0.8 to −1.1 dex, depending on the reddening.
Michigan 160: a precursor to the LMC?
Authors: Staveley-Smith L.
Published: July 2016

The tidal interaction between the Magellanic Clouds and the Galaxy is an important factor in influencing the physical and dynamical evolution of the Clouds (e.g. the Magellanic Stream) as well as the genesis and evolution of their respective stellar populations. However, how important is the influence of the Galaxy? This is a key question since we know that relatively isolated, magellanic-type galaxies do exist (e.g. NGC 3109 and NGC 4449) and have been just as efficient at star-formation as the LMC. It is possible in fact that the star formation in the clouds is primarily stochastic in nature and is relatively insensitive to the global forces which seem to have shaped stellar formation processes in massive spiral and elliptical galaxies. Unsupported by a massive bulge or halo component, cold gas disks are inherently susceptible to radial and bar-like instabilities (Efstathiou et al. 1982) which are very efficient at creating the dynamical pressures required for rapid star-formation. With this in mind, a detailed comparison of 'field' magellanic-type galaxies with the LMC and SMC is of some importance.
Chemical abundances and chemical evolution of the Magellanic Clouds: Prospects for the future
Authors: Dopita M. A.
Published: July 2016

The prospects for future advances in understanding the chemical evolution of the Magellanic Clouds is reviewed on the basis of results presented at IAU Symposium #148. These are divided into three areas, the metallicity - age relationships, the current abundance set, and the theory of the chemical evolution of the Clouds.
Molecules in the Magellanic Clouds
Authors: Booth R. S. , De Graauw Th.
Published: July 2016

In this short review we describe recent new observations of millimetre transitions of molecules in selected regions of the Magellanic Clouds. The observations were made using the Swedish-ESO Submillimetre Telescope, SEST, (Booth et al. 1989), the relatively high resolution of which facilitates, for the first time, observations of individual giant molecular clouds in the Magellanic Clouds. We have mapped the distribution of the emission from the two lowest rotational transitions of 12CO and 13CO and hence have derived excitation conditions for the molecule. In addition, we have observed several well-known interstellar molecules in the same regions, thus doubling the number of known molecules in the Large Magellanic Cloud (LMC). The fact that all the observations have been made under controlled conditions with the same telescope enables a reasonable intercomparison of the molecular column densities. In particular, we are able to observe the relative abundances among the different isotopically substituted species of CO.
Ultra-high-energy cosmic rays in the Magellanic Clouds
Authors: Protheroe R. J.
Published: July 2016

Ultra-high-energy (UHE) γ-rays have been detected from several X-ray binaries. UHE γ-rays from sources in the LMC will interact in the microwave background producing electrons which emit synchrotron radiation in the X-ray and γ-ray bands. This radiation might be observable.
Metallicity effects on the Cepheid distance scale
Authors: Freedman Wendy L. , Madore Barry F.
Published: July 2016

We are undertaking empirical tests for the effects of metallicity on the zero-point of the Period-Luminosity relations for Cepheids in M31 and in the Small Magellanic Cloud (SMC), as compared to the Large Magellanic Cloud (LMC). For M31 we have used BVRI data on comparable sets of Cepheids in three radially separated, and chemically different, fields in order to solve simultaneously for the reddenings and the true distance moduli to each of these fields. Recent theory predicts that the reddening-corrected moduli should differ by 0.8 mag given the observed metallicity range in our M31 Cepheid sample; we observe a maximum range of only 0.17 mag. For the SMC BVRIJHK data, treated in a similar fashion, the predicted theoretical effects on the short wavelength (B and V) data may be visible, but with low statistical certainty and at a reduced amplitude with respect to the predictions.
Orbits of the Magellanic Clouds
Authors: Ninkovic Slobodan , Filipovic Miroslav
Published: July 2016

We use a simple, spherically symmetric model for the Galaxy based on the rotation curve for the inner parts. We extrapolate beyond the rotation curve boundary, assuming a dark corona whose total mass is a model parameter. For each mass value assume we calculate the allowed angular-momentum interval for which a cloud is neither tidally disrupted, nor escapes. On the basis of this investigation we reach a conclusion about the expected mass of the Galaxy.
String of young clusters linking the Magellanic Clouds
Authors: Grondin L. , Demers S. , Kunkel W. E. , Irwin M. J.
Published: July 2016

We present deep CCD photometry of three associations lying between the Magellanic Clouds and sitting on the HI ridge. ZAMS fittings show that these clusters are located at the distance of the Clouds. Furthermore, a slight distance gradient is observed. Main sequences matched to isochrones reveal that these aggregates are very young, no more than 108 years old. An age difference from east to west is also suggested.
The Magellanic Stream
Authors: Shuter W. L. H.
Published: July 2016

This model was devised in an attempt to resolve the discrepancy between the values derived for the mass of the Galaxy from distant satellites and from the Magellanic Stream. In contrast to most previous models, the orbit of the Magellanic Cloud system is not bound to the Galaxy, and the Stream was developed as the result of a tidal encounter between M31 and the Magellanic Cloud system about 6 Byr ago.
The effect of the Magellanic Clouds on the mass distribution in the galaxy
Authors: Song G. X.
Published: July 2016

The disk of the Milky Way suffered from the tidal effect as the Magellanic Clouds were passing by. Numerical stimulations were performed to study the evolution of the mass distribution in this disk. These simulations were run with the galactic disk initially flat, and different sets of the initial position and velocity of the Magellanic Clouds were considered. One of the most conspicuous observational facts is the warp of the disk of the Milky Way. Results show that the characteristics of this warp are related to the orbit of the Magellanic Clouds.
Structure and Evolution of AGB Stars
Authors: Blöcker Thomas
Published: July 2016

An overview of the structure and evolution of Asymptotic Giant Branch stars is presented. We focus upon the occurrence of thermal pulses, hot bottom burning and mass loss and summarize briefly the corresponding nucleosynthesis and mixing events. The interplay between these important evolutionary features is discussed.
Improved synthetic TP-AGB models
Authors: Marigo P.
Published: July 2016

We present recent improvements and results of an extensive analysis of the TP-AGB phase performed by means of a synthetic model (Marigo 1998a, b; Marigo et al. 1998a, b). The improvements concern: i) the use of a homogeneous and accurate set of analytical relations (Wagenhuber & Groenewegen 1998); ii) a new treatment of envelope burning in the most massive TP-AGB stars (M > 3.5M⊙) to account for the possible break-down of the core mass-luminosity relation; iii) a better treatment of the third dredge-up to infer if and when the process takes place.

Extensive calculations of synthetic TP-AGB models have been carried out over the mass range (0.8M⊙ ÷ 5M⊙) and for three sets of initial metallicity (Z = 0.019, Z = 0.008, Z = 0.004). The formation of carbon stars is investigated addressing the following issues: a) the reproduction of the observed luminosity functions of carbons stars in both Magellanic Clouds, and b) the formation of very bright and optically obscured carbon stars.
Effective Temperature Scales of Red Giant Stars
Authors: Alexander David R. , Ferguson Jason W. , Wing Robert F. , Johnson Hollis R. , Hauschildt Peter H. , Allard France
Published: July 2016

We have completed a grid of spherically symmetric AGB star atmospheres using the state of the art spectral synthesis code PHOENIX. Models are constructed for stars with masses of 1 M⊙and 1.5 M⊙, spanning the range 10 to 3300 L⊙in luminosity and 2500 to 5200 K in effective temperature. We find that grains of Al2O3and CaTiO3among other species form in atmospheres cooler than Teff= 3000 K. In the coolest models the grains cause a weakening of the TiO absorption features in the red and near infrared of up to 30% through both a depression of the continuum and a depletion of the TiO number abundance. We use spectrophotometric observations from a number of catalogs to determine effective temperature – spectral class and effective temperature – color relationships. We also compare synthetic colors calculated from our models with observations of M giants on Wing's 8-color narrow-band system of classification photometry.
Pulsation Modes in Mira and Semiregular Variables
Authors: Feast Michael
Published: July 2016

The most direct evidence for the pulsation mode of Mira and SR variables comes from the linear diameters derived from individual parallaxes and angular diameters, together with the observed periods. The data now available strongly suggest that most, if not all, Miras and SRs pulsate in the same mode. If comparison is made with conventional models, this mode is the first overtone. Uncertainties in deriving the pulsational radius of a Mira from the observations do not appear significant enough to affect this conclusion. Evidence from SRs and Miras in globular clusters supports this conclusion and shows that the pulsation mode does not depend on metallicity. Analysis of light curves leads to broadly the same conclusions, if less directly. The light curves indicate that periodicities other than the main one may also be present and that mode switching may occur in some stars.
Measurements of the changes in angular diameter of Mira variables with pulsation phase
Authors: Young J. S. , Baldwin J. E. , Boysen R. C. , Haniff C. A. , Pearson D. , Rogers J. , St-Jacques D. , Warner P. J. , Wilson D. M. A.
Published: July 2016

We report the direct detection of cyclic diameter variations in the Mira variable χ Cygni. Interferometric observations made between 1997 July and 1998 September, using the Cambridge Optical Aperture Synthesis Telescope (COAST) indicate periodic changes in the apparent angular diameter with amplitude 45 per-cent of the smallest value.

The measurements were made in a 50 nm bandpass centred on 905 nm, which is only moderately contaminated by molecular absorption features. To assess the effects of atmospheric stratification on the apparent diameter measured in this band, we have also measured near-infrared diameters for a sample of five Miras, in both the J-band (1.3 μm) and Wing's (1971) 1.04 μm band, which is expected to isolate essentially pure continuum emission. We present J-band visibility curves which indicate that the intensity profiles of the stars in the sample differ greatly from each other.
MACHO observations of LMC red giants: Mira and semi-regular pulsators, and contact and semi-detached binaries
Authors: Wood P.R. , Alcock C. , Allsman R.A. , Alves D. , Axelrod T.S. , Becker A.C. , Bennett D.P. , Cook K.H. , Drake A.J. , Freeman K.C. , Griest K. , King L.J. , Lehner M.J. , Marshall S.L. , Minniti D. , Peterson B.A. , Pratt M.R. , Quinn P.J. , Stubbs C.W. , Sutherland W. , Tomaney A. , Vandehei T. , Welch D.L.
Published: July 2016

The MACHO data base has been used to examine light curves of all red giant stars brighter than Mbol ∼ −2 in a 0.5° × 0.5° area of the LMC bar. Periods, often multiple, have been searched for in all stars found to be variable. Five distinct period-luminosity sequences have been found on the low mass (M ≲ 2.25M⊙) giant branch. Comparison of observed periods, luminosities and period ratios with theoretical models identifies Miras unambiguously as radial fundamental mode pulsators, while semi-regular variables can be pulsating in the 1st, 2nd or 3rd overtone, or even the fundamental. All these variables lie on just 3 of the 5 distinct sequences, and they all appear to be on the AGB.

The fourth sequence contains red giants on the first giant branch (FGB) or at the red end of the core-helium burning loops of intermediate mass stars (M ≳ 2.25M⊙). The light curves of these stars strongly suggest that they are contact binaries, and they make up ∼0.5% of stars within 1 mag. of the FGB tip. Stars on the fifth sequence show semi-regular, eclipse-like light curves. The light curves and periods of these stars suggest that they are in semi-detached binaries, transfering mass to an invisible companion via a stellar wind or Roche lobe overflow. They make up ∼25% of AGB stars. If the existence of these red giant contact and semi-detached binaries is confirmed, then extant theories of binary star evolution will require substantial modification.
Crystalline silicates in AGB and post-AGB stars
Authors: Waters L.B.F.M. , Molster F.J.
Published: July 2016

We discuss ISO spectroscopy of oxygen-rich dust shells surrounding evolved stars. The dust that condenses in the outflows of stars on the Asymptotic Giant Branch consists mainly of amorphous silicates and simple oxides. For high mass loss rates, crystalline silicates begin to appear at modest abundance. These crystalline silicates are cold and Fe-poor. ISO spectroscopy for the first time allows quantitative mineralogy of oxygen-rich circumstellar dust. Crystalline silicates are found at high abundance in sources with peculiar (disk) geometry, such as long-lived circum-binary disks. Some C-rich post-AGB stars, notably the Red Rectangle and several nebulae surrounding [WC] central stars of Planetary Nebulae, also show crystalline silicates. We speculate on the origin and evolution of the crystalline dust component in evolved stars.
Silicate and ice emission bands in the ISO spectrum of the PAH-emitting carbon-rich planetary nebula CPD-56°8032
Authors: Cohen Martin , Barlow M. J. , Sylvester R. J. , Liu X.-W. , Cox P. , Lim T. , Schmitt B. , Speck A. K.
Published: July 2016

Combined ISO SWS and LWS spectroscopy is presented of the late WC-type planetary nebula nucleus CPD-56†8032 and its carbon-rich nebula. The extremely broad coverage (2.4–197 μm) enables us to recognize the clear and simultaneous presence of emission features from both oxygen- and carbon-rich circumstellar materials. Removing a smooth continuum highlights bright emission bands characteristic of polycyclic aromatic hydrocarbons (hereafter PAHs) in the 3–15 μm region, bands from crystalline silicates longwards of 18 μm, and the 43- and 62-μm bands of crystalline water ice. We discuss the probable evolutionary state and history of this unusual object in terms of (a) a recent transition from an O-rich to a C-rich outflow following a helium shell flash; or (b) a carbon-rich nebular outflow encountering an O-rich comet cloud orbiting in a Kuiper-belt-like distribution.
On the Origin of the 21 Micron Feature in Post-AGB Stars
Authors: Kwok Sun , Volk Kevin , Hrivnak Bruce J.
Published: July 2016

The unidentified emission feature at 21 μm is now observed in 12 sources, all being objects in transition between the asymptotic giant branch and planetary nebulae phases. The relations between the 21 μm and other emission features, such as the PAH features and the broad 30 μm feature, and the possible origins of the 21 μm feature are discussed.
Millimeter-wave Interferometry of Circumstellar Envelopes
Authors: Lucas Robert , Guélin Michel
Published: July 2016

We present some of the most significant results obtained in the last few years with the IRAM Plateau de Bure interferometer and with other instruments on the detailed mapping of circumstellar envelopes.
Long-term evolution of AGB wind envelopes: Insights from hydrodynamical models
Authors: Steffen M. , Schönberner D. , Szczerba R.
Published: July 2016

Up to now, hydrodynamical models of dust-driven AGB winds do not generally take into account the ‘long-term’ changes of the stellar parameters (on stellar evolution time scales of 103 to 105 yrs), although it is well known that the luminosity and (very likely) the mass loss rate undergo significant variations when so called ‘thermal pulses’ occur on the upper AGB. In this review we demonstrate that time-dependent radiation hydrodynamics calculations are needed to understand the formation, structure, and spectral energy distribution of detached dust shells detected by IRAS and ISO. Combined with appropriate models, these observations can reveal part of the previous mass loss history on the AGB and allow an empirical check of presently adopted mass loss laws.

Based on insights from hydrodynamical simulations, we discuss the two competing scenarios that have been put forward to explain the origin of the very thin molecular shells recently discovered around some carbon stars. We find that the signature of a short mass loss ‘eruption’ broadens quickly with time due to the related velocity gradient across the shell. Hence, this scenario is not considered a likely explanation of detached CO shells. On the other hand, the alternative mechanism, interaction of winds, is shown to be capable of producing very thin shells of greatly enhanced gas density in the dusty outflows from AGB stars by sweeping up matter at the interface between both type of winds.
Infrared and Millimeter Views of the Helix: the Nearest, Massive, Neutral Remnant of a Circumstellar Envelope
Authors: Huggins P.J. , Cox P. , Forveille T. , Bachiller R. , Young K.
Published: July 2016

We present new, infrared and millimeter views of the Helix nebula which illustrate the critical role of remnant, neutral AGB envelopes in the formation and evolution of planetary nebulae. Large scale ∼ 1 000″ mapping of the entire nebula in the CO (J = 2 − 1) line with the CSO reveals the global structure of the envelope. The CO emission forms the familiar ring structure seen in optical images of the Helix, and indicates a massive remnant with ≳ 50% the mass of the ionized nebula. High resolution CO mapping with the IRAM 30 m telescope shows that the whole envelope is fragmented into an intricate array of small clumps, closely related to the cometary globules seen in the central, ionized cavity. 5–17 μm spectroscopy of the Helix with ISOCAM reveals a remarkable near infrared spectrum, dominated by the pure (v = 0 − 0) rotational lines of H2. The H2 lines are excited to a temperature of ∼ 900 K, and likely arise in warm, outer layers of the small clumps seen in CO. Imaging of the H2 emission with ISOCAM over the whole nebula provides a striking portrait of the fragmented neutral envelope. 3-dimensional views of the envelope are also presented, based on CO mapping and using 3-dimensional visualization techniques. Point symmetries dominate the toroidal structure, and suggest an origin for the Helix in equatorial mass-loss on the AGB, shaped by the action of bipolar outflows or jets.
Sakurai's object – stellar evolution in real time
Authors: Asplund Martin
Published: July 2016

The born-again giant Sakurai's object is currently experiencing its second stage as an AGB-star. Furthermore, Sakurai's object has shown an unprecedented rapid stellar evolution since discovery in 1996, both in terms of a continued cooling of the photosphere and spectacular changes in chemical composition on a time-scale of a mere few months. The surface cooling and abundance alterations of H, Li and the s-elements are the direct consequences of the expansion, mixing and nucleosynthesis which has ensued as a result of a final He-shell flash occurring while the star was descending the white dwarf cooling track. Sakurai's object shows striking similarities with the R CrB stars in both chemical composition and visual variability.
Dust formation events in the envelopes of the peculiar post-AGB stars FG Sge and V4334 Sgr (Sakurai's object)
Authors: Yudin B. F. , Tatarnikov A. M.
Published: July 2016

Distinctive features of dust condensation events in the circumstellar shells of the born-again AGB stars FG Sge and V4334 Sgr are described together with updated optical, IR and bolometric light curves.
The Galactic Disk Distribution of Dust Emission Features in Planetary Nebulae
Authors: Casassus S. , Roche P.F.
Published: July 2016

The properties of the carbon and oxygen chemical balance in planetary nebulae (PNe) are analysed through mid infrared spectroscopy of warm dust emission features in a sample of 72 objects. The adoption of a statistical distance scale shows that the galactic disk distribution of warm dust types in PNe is rather homogeneous with height over the galactic plane, and that there is a trend for the proportion of PNe with O rich dust signatures to decrease with galactocentric radius. Models of the galactic distribution of PNe compositions require a minimum progenitor mass of 1.2M⊙, although the observational constraints suffer from the smallness of the sample. This initial investigation is however an incentive to pursue the use of warm dust emission in PNe to study their progenitor population in various galactic environments.
Obscured Asymptotic Giant Branch stars in the Magellanic Clouds
Authors: van Loon Jacco Th.
Published: July 2016

We report on some recent advances in the study and understanding of heavily obscured AGB stars in the Magellanic Clouds.
Distance Scales and the Local Group
Authors: Feast Michael
Published: July 2016

A review is given of a number of basic distance indicators as applied to some members of the local group. Particular attention is given to galaxies whose distances have been determined by more than one method. This allows one to test the internal consistency of the indicators.