bluuebunny/crossref_metadata_2025 huggingface dataset:
Flows and Shocks in Variable Fluxes of Seyfert galaxies
Authors: Pronik I. I.
Published: July 2016

Data collected from the optical through infrared to the radio show that the Seyfert galaxies NGC 1275, NGC 3227, NGC 4151, NGC 5548 and NGC 7469 exhibit signs of flows or jets. The characteristics of night-to-night variations of Balmer line profiles and/or intranight continuum variations were obtained and investigated at the Crimean Astrophysical Observatory. They permit to suppose, that short term variability of the Balmer lines and intranight continuum variations can be produced in short lived shocks as a result of strong energy output in the form of gas flows or jets.
Outflowing Components in the Prototype Narrow-Line Seyfert 1 Galaxy Markarian 478
Authors: Yuan Qirong , Brotherton Micheal , Green Richard F. , Kriss Gerard A.
Published: July 2016

Markarian 478 is the prototype narrow-line Seyfert 1 galaxy. Based on its spectra taken by the FUSE, HST/FOS, and Kitt Peak Observatory 2m Telescope, we find a tendency that the emission lines of increasing ionization level show increasing excess flux at their blue wings and an increasing line peak velocity shift. This may indicate an outflowing component in the Broad-Line Region (BLR) where the ionization level increases with ejection velocity. In the mean time, the associated absorption lines are present on the blue wings of the high-ionization emission doublet O VI λλ1032, 1038 and Lyman β line. The physical condition of some absorbing components can be well constrained with the assistance of photoionization models. The flux ratios at the blue wings of emission lines of various ionization levels, as a function of outflow velocity, could also put important constraints on the physical condition of the outflowing components.
The Evolution of Tidal Debris
Authors: Mihos J. Christopher
Published: July 2016

Galaxy interactions expel a significant amount of stars and gas into the surrounding environment. I review the formation and evolution of the tidal debris spawned during these collisions, and describe how this evolution depends on the large scale environment in which the galaxies live. In addition to acting as a long-lived tracer of the interaction history of galaxies, the evolution of this material - on both large scales and small - has important ramifications for galactic recycling processes, the feeding of the intracluster light and intracluster medium within galaxy clusters, and the delayed formation of galactic disks and dwarf galaxies.
Recycling of Ghost Galaxies: the Origin of giant HI Ring around NGC 1533
Authors: Bekki Kenji , Couch Warrick J. , Ryan-Weber Emma , Webster Rachel
Published: July 2016

We propose that the giant HI ring recently discovered by HIPASS for S0 galaxy NGC 1533 is formed by unequal-mass merging between gas-rich LSB (low surface brightness: “ghost”) galaxies and HSB disks. The NGC 1533 progenitor HSB spiral is transformed into a barred S0 during merging and the outer HI gas disk of the LSB is transformed into the giant HI ring. We also discuss two different possibilities for the origin of isolated star-forming regions (“ELdot” objects) in the giant gas ring.
Triggering Star Formation by Galaxy-Galaxy Interactions
Authors: Tissera P.B. , Alonso M.S. , Lambas D.G. , Coldwell G.
Published: July 2016

We analyzed the effects of having a close companion on the star formation activity of galaxies in the 8K galaxy pair catalog selected from the 2dFGRS. We found that, statistically, galaxies with rp < 25h−1 kpc and ΔV < 100km s−1 have enhanced star formation with respect to isolated galaxies with the same luminosity and redshift distribution. Our results suggest that the physical processes at work during tidal interactions can overcome the effects of environment, except in dense regions.
The Chemical Evolution of the Intra-Cluster Medium
Authors: Domainko Wilfried , Kapferer Wolfgang , Schindler Sabine , van Kampen Eelco , Kimeswenger Stefan , Ruffert Maximilian
Published: July 2016

We present numerical simulations of the dynamical and chemical evolution of galaxy clusters. from X-ray spectra it is evident that the Intra-Cluster Medium (ICM) is abundant in metals. As heavy elements are only produced in stars the processed material must have been ejected by cluster galaxies into the ICM. Several different mechanisms for interaction between the cluster galaxies and the ICM are possible but their efficiency of metal enrichment of the cluster and their time evolution are still not known. Suggested processes which remove enriched material from the galaxies are ram-pressure stripping, galactic winds, superwinds driven by starburst activity and jets from active galaxies. First results of high resolution hydrodynamic simulations on cluster scales are presented to investigate the effect of these different pollution mechanisms.
Molecular Gas in Tidal Dwarf Galaxies: On-going Galaxy Formation
Authors: Braine J. , Duc P.-A. , Lisenfeld U. , Brinks E. , Charmandaris V. , Leon S.
Published: July 2016

We investigate the process of galaxy formation as can be observed in the only currently forming galaxies - the so-called Tidal Dwarf Galaxies, hereafter TDGs - through observations of the molecular gas detected via its CO (Carbon Monoxide) emission. Molecular gas is a key element in the galaxy formation process, providing the link between a cloud of gas and a bona fide galaxy. We have now detected CO in 9 TDGs with an overall detection rate of 80%, showing that molecular gas is abundant in TDGs, up to a few 108M⊙. The CO emission coincides both spatially and kinematically with the HI emission, indicating that the molecular gas forms from the atomic hydrogen where the HI column density is high. A possible trend of more evolved TDGs having greater molecular gas masses is observed, in accord with the transformation of HI into H2. Although uncertainties are still large for individual objects as the geometry is unknown, we find that the “dynamical” masses of TDGs, estimated from the CO line widths, do not seem to be greater than the “visible” masses (HI + H2 + a stellar component), i.e., TDGs require no dark matter. We provide evidence that TDGs are self-gravitating entities, implying that we are witnessing the ensemble of processes in galaxy formation: concentration of large amounts of gas in a bound object, condensation of the gas, which is atomic at this point, to form molecular gas and the subsequent star formation from the dense molecular component.
VLA HI and OVRO CO Interferometry of a Tidal Dwarf Galaxy
Authors: Brinks Elias , Duc Pierre-Alain , Walter Fabian
Published: July 2016

We present high resolution interferometric observations of the cool atomic and cold molecular ISM of the TDG candidate Arp 245N, an object resembling a dwarf galaxy in the northern tidal tail of the interacting system NGC 2992/3. We observed the HI line with the NRAO VLA and the CO(1→0) transition with the OVRO millimeter interferometer at 5“ – 6” angular resolution (750 pc linear resolution). These datacubes offer the required spatial and velocity resolution to determine whether the mass concentration near the tip of the tail is a genuine feature, and hence a good TDG candidate, or an artefact caused by a fortuitous alignment of our line of sight with the direction of the tail. A preliminary analysis seems to confirm that Arp 245N is a self-gravitating entity.
Are Cluster Dwarfs Recycled Galaxies?
Authors: Conselice Christopher J.
Published: July 2016

Although cluster dwarf galaxies are often neglected due to their faintness, recent observations demonstrate they may be critical for understanding the physical processes behind galaxy formation. Dwarfs are the most common galaxy type and are particularly abundant in clusters. Recent observational results suggest that dwarfs in dense environments do not all form early in the universe, as expected in hierarchical structure formation models. Many of these systems appear to be younger and more metal rich than dwarfs in lower density areas, suggesting they are possibly created by a tidal process. Several general galaxy cluster observations, including steep luminosity functions and the origin of intracluster light, are natural outcomes of these processes.
Two Formation Paths for Cluster Dwarf Galaxies?
Authors: Poggianti Bianca M. , Kashikawa Nobunari , Bridges Terry , Mobasher Bahram , Komiyama Yutaka , Carter Dave , Okamura Sadanori , Yagi Masafumi
Published: July 2016

A surprising result of our recent spectroscopic survey of galaxies in the Coma cluster has been the discovery of a possible bimodal distribution in the metallicities of faint galaxies at MB > −17. We identified a group of dwarfs with luminosity-weighted metallicities around solar and a group with [M/H] around −1.5. A metallicity bimodality among galaxies of similar luminosities is unexpected and suggests that faint cluster galaxies could be an heterogeneous population that formed through more than one evolutionary path, possibly as a consequence of the cluster environment.
An overview of the structure and kinematics of the Magellanic Clouds
Authors: Westerlund B. E.
Published: July 2016

A vast amount of observational data concerning the structure and kinematics of the Magellanic Clouds is now available. Many basic quantities (e.g. distances and geometry) are, however, not yet sufficiently well determined. Interactions between the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC) and our Galaxy have dominated the evolution of the Clouds, causing bursts of star formation which, together with stochastic self-propagating star formation, produced the observed structures. In the youngest generation in the LMC it is seen as an intricate pattern imitating a fragmented spiral structure. In the SMC much of the fragmentation is along the line of sight complicating the reconstruction of its history. The violent events in the past are also recognizable in complex velocity patterns which make the analysis of the kinematics of the Clouds difficult.
Distribution of young stars and gas in the Small Magellanic Cloud
Authors: Lequeux J.
Published: July 2016

The relations between the distributions of interstellar gas and young stars in the central parts of the SMC are discussed, based on their distributions over the sky, radial velocities and distances. There are large differences between stars and gas. The existence of two main complexes is confirmed. There is no strong evidence for a distance in depth between these complexes larger than about 10 kpc, although Cepheid observations suggest a large total depth in some regions. Further, more accurate observations of Cepheids, especially of their mean radial velocities, are required for a better understanding of the structure of the SMC.
Radio continuum emission from the Magellanic Clouds
Authors: Klein U. , Haynes R.F. , Wielebinski R. , Wayte S.R. , Harnett J.I. , Bajaja E. , Murray J.D. , Hunt A.J. , Wark R. , Sciacca L. , Buczilowski U. R.
Published: July 2016

New radio continuum surveys of the Large and the Small Magellanic Cloud have been completed recently at four frequencies, using the Parkes 64-m telescope. Here we shall discuss briefly the overall radio morphology of the Clouds at different frequencies and discuss the detected linear polarization. A preliminary integrated radio continuum spectrum of the Large Magellanic Cloud is also presented. Various aspects of future studies will be outlined.
New results on the structure and stellar content of the outer regions of the SMC
Authors: Gardiner L. T. , Hawkins M.R.S.
Published: July 2016

Surface distribution contour maps of the HB/clump population and the < 1 Gyr main sequence population for the outer regions of the Small Magellanic Cloud (SMC) are presented. Aspects of the stellar population synthesis, large-scale structure and evolutionary history of the SMC halo are discussed.
Dust in the Magellanic Clouds
Authors: Hodge Paul
Published: July 2016

The dust content of the Magellanic Clouds can be studied using optical, ultraviolet, infrared and, indirectly, radio wavelength data. All recent studies show that the dust content is lower than that of the Milky Way Galaxy for both Clouds and that the optical properties of the dust are different. At ultraviolet wavelengths, the 2165 Å “bump” in the extinction curve is significantly smaller than in the Galaxy (this now appears NOT to be a consequence of the lower heavy element abundances) and the far ultraviolet (shortward of ˜2000 Å) extinction is greater than in the Galaxy (this IS likely to be a consequence of the lower heavy element abundances). New optical data on background galaxies suggest that the total extinction in the central parts of both the LMC and the SMC is approximately 1.5 magnitudes. High local extinction values are derived from uv and optical observations of star-forming regions, where a spatial correlation with CO detections is sometimes, but not always, found.
Large-scale structure and kinematics of the Magellanic Clouds from carbon star studies
Authors: Azzopardi M. , Rebeirot E.
Published: July 2016

Initially, carbon stars have been searched for through their CN bands in the near infrared. However, C stars can also be identified efficiently by the C2 Swan bands in the blue-green spectral region. Schmidt telescopes with objective-prisms have been used intensively for the detection of C stars. More recently, transmission gratings at the prime foci of large telescopes have made possible deeper surveys at limiting magnitudes that insure carbon star detection in the Magellanic Clouds (MCs) with a reasonable degree of completeness; completeness is even better in the regions where both observational techniques have been used. Statistical studies are now possible. The C star surface distribution and global kinematics derived from radial velocity measurements of selected C stars, when compared to those of other objects, show that the field Small Magellanic Cloud (SMC) C stars are not a young population, in agreement with studies of C stars in SMC clusters.
The star formation histories of the Magellanic Clouds
Authors: Butcher H. R.
Published: July 2016

Existing observations of the Magellanic Clouds suggest substantially different star-forming histories for the two systems. The reliability of this conclusion is discussed in the context of the uncertainties and age resolutions of various empirical methods of studying galaxy evolution. An attempt is also made to relate likely evolutionary scenarios for the Clouds to the histories of other Local Group systems, to the evolution seen in galaxies at high redshift, and to possible histories determined by interaction with the Galaxy.
Star clusters in the Magellanic Clouds
Authors: van den Bergh S.
Published: July 2016

Star clusters in the Magellanic Clouds (MCs) differ from those in the Galaxy in a number of respects: (1) the Clouds contain a class of populous open clusters that has no Galactic counterpart; (2) Cloud clusters have systematically larger radii rh than those in the Galaxy; (3) clusters of all ages in the Clouds are, on average, more flattened than those in the Galaxy. In the Large Magellanic Cloud (LMC) there appear to have been two distinct epochs of cluster formation. LMC globulars have ages of 12-15 Gyr, whereas most populous open clusters have ages <5 Gyr. No such dichotomy is observed for clusters in the Small Magellanic Cloud (SMC) The fact that the SMC exhibits no enhanced cluster formation at times of bursts of cluster formation in the LMC, militates against encounters between the Clouds as a cause for enhanced rates of star and cluster formation.
The kinematics and abundances of star clusters in the Large Magellanic Cloud
Authors: Schommer R. A.
Published: July 2016

We present velocities for 75 star clusters in the Large Magellanic Cloud (LMC), based on individual star measures at the Calcium triplet The spectra are also used to derive abundances for most of the clusters, and an age-metallicity relation is presented for the inner and outer regions. One half of the clusters are objects in the outer parts of the LMC (radius ≥5°), which had no previous velocity determinations. Published velocities for intermediate and old clusters are shown to have had systematic errors. We compare these velocities with various rotation curve analyses of the LMC, and test aspects of the twisted disk model of Freeman et al. (1983, hereafter FIO). Our outer cluster sample and the intermediate age inner clusters form a disk which agrees with the parameters of the optical isophotes and inner HI rotation curve. The oldest clusters are still enigmatic; they appear to be flattened and rotate much as FIO have described, although the parameters are poorly determined in this small sample.
A new survey for Hα-emission-line stars and related objects in the SMC
Authors: Meyssonnier M. , Azzopardi M.
Published: July 2016

New identifications of the Hα-emission-line objects in the Small Magellanic Cloud (SMC) have been made with the Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory (CTIO).
Radial velocities for three distant LMC globular clusters
Authors: Storm Jesper , Carney Bruce W.
Published: July 2016

In an attempt to investigate the large scale structure and dynamics of the old population of the LMC, we have obtained high precision radial velocities for three extremely outlying (10°-15° from the LMC center) globular clusters. Our results agree well with the results from Freeman et al. (1983) that the clusters move in a disk like system. Depending on the assumptions used we can put a lower limit to the LMC mass of about 0.5-2.5×1010M⊙
Properties of two star clusters of the LMC: NGC 2164, NGC 1850
Authors: Vallenari A. , Chiosi C. , Bertelli G. , Meylan G. , Ortolani S.
Published: July 2016

We present the photometry of two clusters NGC 2164 and NGC 1850 located in the Large Magellanic Cloud (LMC). The ages are determined taking into account the presence either of convective overshoot or of semiconvection in the stellar models. The experimental luminosity functions are compared with the theoretical models.
Effects of data incompleteness and metallicity on the mass functions of young LMC star clusters
Authors: Richtler T. , Sagar R. , Vallenari A. , De Boer Klaas S.
Published: July 2016

The young globular clusters in the Magellanic Clouds offer a good number statistic and a reasonably wide mass interval which are required for the derivation of any statistically reliable slope of the Initial Mass Function (IMF). Elson et al. (1989) and Mateo (1988) are amongst those few who utilized this potential first. These authors, however, arrive at different conclusions. Elson et al. find quite flat mass function slopes in comparison with the values given by Mateo. Here we present IMF slopes based on B, V CCD photometry for four young LMC clusters, NGC 1711, 2004, 2164 and 2214 and discuss the effects on them of cluster metallicity and of uncertainties in the incompleteness of the data.
The chemical evolution of the Magellanic Clouds
Authors: Spite F. , Spite M.
Published: July 2016

New observations give more details and some confirmation about the chemical evolution of the Clouds. From more numerous data, information is beginning to emerge about the importance of mixing in the Clouds.
Abundances in Magellanic Cloud planetary nebulae
Authors: Barlow M. J.
Published: July 2016

The enhanced nitrogen abundances in planetary nebulae (PN) show the effects of CN-cycle processing at the time of the first dredge-up, while their very enhanced carbon abundances show the effects of the third dredge-up. The efficiency of both the first and third dredge-ups increases with decreasing initial metallicity. ON-cycle depletion of oxygen via the second dredge-up does not appear to have been significant in LMC Type I planetary nebulae (those with N/O > 0.5) – these nebulae have experienced the third dredge-up and envelope-burning, giving enhanced C+N abundances. The LMC Type I PN show enhanced Ne/O ratios. Enrichment rates in nitrogen and carbon by PN are estimated for the ISM s of the Magellanic Clouds.
RR Lyrae stars in the Magellanic Clouds
Authors: Walker Alistair R.
Published: July 2016

RR Lyrae variables are a component of the oldest stellar populations. In the Magellanic Clouds they occur in a few clusters and in the general field. Recent observations have concentrated on obtaining accurate photometry for the cluster variables and the evolved stars of their parent clusters; these data have been used to determine abundances, distances and ages. Results from this work are reviewed.
Radio pulsars in the Magellanic Clouds
Authors: Mcconnell D. , Mcculloch P.M. , Hamilton P.A. , Ables J.G. , Hall P.J. , Jacka C.E. , Hunt A.J.
Published: July 2016

The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) have been searched for radio pulsars using the 64-m Parkes radiotelescope. The search has resulted in the discovery of four pulsars. Observed dispersion measures to each suggest that three lie in the Clouds (two in the LMC, one in the SMC) and that the fourth, which was found in the direction of the LMC, is a foreground object belonging to the galactic pulsar population.
Star formation histories in dwarf irregular galaxies in the Local Group
Authors: Greggio L. , Marconi G. , Focardi P. , Tosi M.
Published: July 2016

The process of star formation (SF) and the modalities with which it occurs in galaxies of different sizes are still poorly understood. On the other hand, interpretation of the chemical and photometric properties of galaxies requires the adoption of adequate laws for the SF rate and Initial Mass Function (IMF) in model computations. Dwarf irregular galaxies in the Local Group offer the chance to study their SF history through analysis of their HR diagrams, which can be derived down to V 25, corresponding to MV0, i.e. to main sequence stars of 2 M⊙. Therefore, for these galaxies, we can derive information on the star formation activity which has occurred over the last 1 Gyr approximately. In this framework, we have undertaken CCD observations of Dwarf irregular galaxies in the Local Group with ESO telescopes and briefly present here the results obtained for DDO 210, Sextans B and NGC 3109.
The spectrum of SN 1987A in the LMC in July 1987
Authors: Huang C. C.
Published: July 2016

Spectroscopic observations of SN 1987A in the LMC in July 1987 are presented. The appearance of SN 1987A's optical spectrum was dominated by strong H I and Na I lines showing broad P-Cygni profiles. The nebular emission lines of [O I] 6300, 64 appeared in mid-July. The enhancement of s-processed elements of Ba II and Sr II in SN 1987A is briefly discussed.
Radio imaging of the supernova remnant N132D in the Large Magellanic Cloud
Authors: Dickel John R. , Milne D. K.
Published: July 2016

The first high resolution radio image of the supernova remnant N132D shows a complex shell structure.
A photometric and spectroscopic study of R Coronae Borealis stars in the LMC
Authors: Lawson W. A. , Cottrell P. L. , Pollard K. R.
Published: July 2016

Over the last several years we have obtained photometric observations of the four suspected (W Men, HV 5637, HV 12671, HV 12842) R Coronae Borealis (RCB) stars in the Large Magellanic Cloud (LMC). Fourier analyses of the light curves has revealed some periodicity in HV 12842, where there appear to be at least two closely spaced periods of 55 and 60 d. High resolution spectra of HV 12842, obtained with the Ango-Australian Telescope (AAT), indicate that it has similar atmospheric properties to a number of warmer galactic RCB and hydrogen-deficient Carbon (HdC) stars, e.g. R CrB, RY Sgr and XX Cam.
The anomalous A-type supergiants in the Magellanic clouds - evidence for post-red supergiant evolution
Authors: Humphreys R. M. , Kudritzki R. P. , Groth H.
Published: July 2016

A group of A-type stars in the field of the Small Magellanic Cloud (SMC) were noticed by Humphreys (1983) to have anomalously strong hydrogen (H) lines and a Balmer jump that are too strong for their luminosities. Their visual luminosities, based on membership in the SMC, are about two magnitudes brighter than one would expect from the appearance of the Balmer series. Humphreys also found that their colours are too red in U-B by 0.2 to 0.3 mag, but show little or no change in B-V relative to normal A-type supergiants; this is consistent with the strong Balmer jump in these stars' spectra. She also concluded that the objects do belong to the SMC.

Earlier, Sanduleak (1972) had identified a group of stars with similar properties in the LMC, but, because of their strong hydrogen lines, rejected them as members. However, Fehrenbach and Duflot (1972) recognized about 30 stars with A and F type spectra with unusually strong H lines. They concluded that they were members of the Large Magellanic Cloud (LMC) because of their large negative radial velocities.
The variable star population of NGC 1866
Authors: Welch Douglas L. , Côté Patrick , Mateo Mario , Madore Barry F.
Published: July 2016

We report the results of an extensive photometric and radial velocity study of the variable stars in the Large Magellanic Cloud (LMC) cluster NGC 1866. We find:
Molecular gas in the Small Magellanic Cloud
Authors: Rubio Monica
Published: July 2016

We summarize the results of observations of molecular gas from the Small Magellanic Cloud (SMC) made with low angular resolution (8'.8). These observations show that the CO emission is weak (TA˜ 0.04K) and that the CO luminosities of the Clouds are low compared to those of Galactic molecular clouds. The factor to convert the CO luminosity to molecular hydrogen column density for the SMC is ˜20 and three times larger than those derived for clouds in our Galaxy and in the Large Magellanic Cloud (LMC) respectively. In addition, we present preliminary results of high resolution (40″) observations of SMC molecular clouds made with the SEST telescope.
NaI and CaII interstellar absorption in the field of SN 1987A
Authors: Molaro P. , Vladilo G. , D'Odorico S. , Dennefeld M. , Ferlet R. , Vidal-Madjar A.
Published: July 2016

We present CaII and NaI spectra for a sample of stars in a 30'×30' field connecting 30 Dor with SN 1987A. Observations were taken with the CES spectrograph linked via fibres with the 3.6m ESO telescope at a resolution of ˜ 6 km s−1. The LMC gas shows a complex structure with both single and multiple components spanning 250 to 300 km s−1. Results can be interpreted using the multi-layer structure suggested by 21 cm observations. Comparing our optical absorptions with 21 cm emissions yields evidence that layers with increasing radial velocity are located one behind the other. The intermediate velocity components are numerous in CaII, but rare in NaI. Towards Sk-69 211, for which we have the highest S/N CaII spectrum, we have detected a number of components comparable to that found in SN 1987A. The 64 km s−1 cloud is detected in a well-confined region of the field, showing remarkable constancy in the radial velocity, which we interpret as evidence that this cloud is located close to the Galaxy.
Depth structure in the gas in Shapley III along three lines of sight
Authors: Bomans Dominik J. , De Boer Klaas S. , Koornneef Jan
Published: July 2016

Shapley Constellation III in the Large Magellanic Cloud (LMC) is surrounded by a ring of HII regions, called Supershell LMC 4 (Meaburn 1980). In the direction of the centre of this spatial strucutre very little neutral interstellar gas is found (McGee & Milton 1964). The spatial arrangement suggests that a hole exists in the gas layer of the LMC, one which may be blown out by the effect of the winds of the stars of Constellation III or by supernova blasts from the same area. Shock waves moving into surrounding neutral gas triggered star formation in the outer shell. Left inside would be a volume of diluted, and probably hot, ionized gas.

To probe the spatial structure of the gas we have collected high dispersion IUE spectra of some stars inside LMC 4. We have analysed the interstellar lines from the various elements and ions available and are able to derive the velocity structure of the lines of sight observed (Bomans & de Boer 1989). We see a well-defined absorption component near 230 km s−1 and a broader structure around 280 km s−1. The column density of neutral gas is small, as confirmed from the HI 21-cm profiles of Rohlfs et al. (1984). We have redetermined the spectral type of the stars from the IUE spectra in order to estimate the strength of the stellar Lyman-Alpha (Lα) line. Two stars are of early enough type to allow the determination of N(H) from Lα.
Dynamical Modelling of AGB Star Atmospheres
Authors: Höfner Susanne
Published: July 2016

Time-dependent dynamics is an important ingredient for understanding the atmospheres of pulsating AGB stars. The shock waves created by stellar pulsation modify the atmospheric structure and, consequently, influence the mass loss and the observable properties. So far, hydrostatic model atmospheres have been used in most cases to analyse photospheric spectra, neglecting the effects of dynamics. The recent progress in observational techniques, however, has demonstrated the importance of consistent time-dependent models. The main topics of this contribution are to discuss fundamental physical processes and technical problems in constructing dynamical model atmospheres, to review the present status of modelling and to indicate possible future developments.
Dust formation in oxygen-rich circumstellar shells around long–period variables
Authors: Sook Jeong Kyung , Martin Winters Jan , Sedlmayr Erwin
Published: July 2016

We present the first steps of our work aimed at a consistent time-dependent modeling of oxygen–rich circumstellar dust shells (CDS) around pulsating AGB stars. The nature of the most likely nucleation seeds is investigated for this situation and we find that TiO2 is a most promising candidate to serve as the primary condensate, forming already at temperatures well above 1 000 K. These nuclei evolve to macroscopic dust grains by heterogeneous growth processes involving several chemical species. We investigate the varying chemical composition of the resulting dust grains as they evolve as a function of time in a fluid element moving through the CDS of an oxygen–rich long-period variable star (LPV).
The chemistry of carbon dust formation
Authors: Cherchneff Isabelle , Cau Piero
Published: July 2016

We shall review the various types of chemistry involved in the formation of carbonaceous material present in carbon-rich AGB stars, mainly amorphous carbon, silicon carbide and other metal carbides discovered in pre-solar Stardust extracted from meteorites. The chemistry is discussed in the context of laboratory experiments and their application to circumstellar AGB winds. Emphasis is put on polycyclic aromatic hydrocarbons (PAHs), titanium carbide clusters and silicon carbide grains. Attempt to explain the condensation sequences derived from the study of pre-solar grains of meteoretical origin is made on the basis of physio-chemical models which describe the periodically shocked gas close to the photosphere of AGB stars.
Infrared appearance of dust forming LPVs
Authors: Winters Jan Martin , Le Bertre Thibaut , Keady John J.
Published: July 2016

The consistent treatment of the physical problem describing a dust forming circumstellar shell yields, besides the time variation of the hydrodynamic and thermodynamic shell structure, also the temporal evolution of the grain–size distribution function. We discuss the influence of the dynamical behavior of corresponding dust shell models on the resulting infrared light curves, brightness distributions, and CO infrared line profiles. Some remarks on the grain–size distribution are also given.
A MERLIN movie of mass-loss from RT Vir
Authors: Richards A. M. S. , Cohen R. J. , Bains I. , Yates J. A.
Published: July 2016

We used MERLIN to observe RT Vir at 22 GHz at six epochs during 10 weeks. The water maser emission comes from a thick expanding shell with an elliptical velocity field. MERLIN has a velocity resolution of 0.1 km s−1 and milli-arcsecond angular resolution, revealing details within the individual maser clouds, typically 12 mas in diameter spanning 15 velocity channels. The brightest peak doubles in intensity to 800 Jy/beam. Features at velocities close to the stellar velocity show the largest proper motions of ∼ 3 mas away from the centre of emission. Some features are seen near the outer limits to the maser shell at early epochs only, but new masers appear close to the inner rim. The variability of individual maser features is not a simple function of the stellar luminosity.
Circumstellar Chemistry of AGB Winds
Authors: Glassgold A. E.
Published: July 2016

Carbon-rich AGB stars are an excellent place to study circumstellar chemistry. The best case is IRC +10216, where observations at optical, infrared, and radio wavelengths have led to the discovery of more than 50 molecules. When the detected species are grouped in chemically related families, the observed spatial distributions and abundances can be understood with a photochemical model. Most of the species are either progenitors that arise in the photosphere or inner envelope, or are unsaturated radicals and hydrocarbon chains photochemically produced in the outer envelope. The few saturated molecules with a single heavy atom are probably produced on grain surfaces. Inside the ionization radius of atomic carbon, the circumstellar envelope of IRC +10216 is weakly ionized by suprathermal particles. The HCO+ detected and mapped in the J = 1 − 0 line by the IRAM telescopes can be interpreted as arising from either partially-excluded galactic cosmic rays or β-particles emitted by radioactive nuclei dredged up from the H-burning zone into the wind. An estimate of the ionization rate due to 26Al based on the 26Al/27Al ratio of “mainstream” pre-solar grains is the same order of magnitude as determined from the measured abundance of HCO+ in IRC +10216.
ISO results on circumstellar envelopes
Authors: Barlow M. J.
Published: July 2016

This review covers spectroscopic results obtained with ISO on molecular and atomic line emission from the circumstellar envelopes of oxygen-rich AGB stars and post-AGB objects and from cool supergiant stars. As well as the SWS detection of the 4.27-μm CO2 band in absorption and emission from cool star envelopes, several new emission bands which have been detected in SWS spectra between 13.9 and 16.2 μm have been identified with CO2 bands. Strong H2O line emission has been observed in the LWS and SWS spectra of high mass loss rate O-rich AGB and M supergiant stars, confirming the predicted importance of this molecule as a coolant in their outflows. The proposed infrared radiative pump mechanism for circumstellar OH masers has been directly confirmed for the first time via measurements for several stars of the OH infrared pumping lines between 34.6 μm and 163 μm. Water vapour emission lines are not present in the spectra of O-rich post-AGB objects, having been replaced by broad emission features at 43 and 62 μm due to crystalline water ice that has condensed in the very cool outflows.
Variability of 22 GHz H2O masers in circumstellar shells
Authors: Engels D. , Winnberg A. , Brand J. , Walmsley C.M.
Published: July 2016

We have monitored different types of late-type stars in the 22 GHz maser line of water vapor with single-dish telescopes and the Very Large Array over several years. We find that the emission pattern in the circumstellar shells of Semi-Regular (SR) and Mira variables mapped by the VLA remain stable on the scale of several years while the maser profiles from the single-dish telescopes vary strongly. Thus the strong variability is mainly due to incoherent intensity fluctuations of the individual maser lines, which have lifetimes less than a year.

In contrast to this, the variability in OH/IR stars and M-Supergiants is more regular and is mainly a response to the long-period variations of the central star. H2O maser in many OH/IR stars are “extinguished” most of the time, as the excitation temperature is only high enough during the phases close to the maximum of the variability.

The strength of the profile variability is decreasing as a function of the radial distance of the maser shell from the star. This gives a natural explanation for the increasing regularity of the maser variations along the sequence SR-, Mira variables, OH/IR stars, M-Supergiants.
The final 105 years of stellar AGB evolution in the presence of a pulsating, dust-induced “superwind”
Authors: Schröder K.-P. , Winters J.M. , Sedlmayr E.
Published: July 2016

We have computed mass-loss histories and tip-AGB stellar evolution models in the presence of a dust-induced, carbon-rich “superwind”, in the initial mass-range of 1.1 to about 2.5 solar masses and for nearly solar composition (X=0.28, Y=0.70, Z=0.02). Consistent, actual mass-loss rates are used in each time-step, based on pulsating and “dust-driven” stellar wind models for carbon-rich stars (Fleischer et al. 1992) which include a detailed treatment of dust-formation, radiative transfer and wind acceleration. Our tip-AGB mass-loss rates reach about 4 · 10−5M⊙yr−1 and become an influencial factor of stellar evolution.

Heavy outflows of 0.3 to 0.6 M⊙ within only 2 to 3·104 yrs, exactly as required for PN-formation, occur with tip-AGB models of an initial stellar mass Mi ≳ 1.3M⊙. The mass-loss of our “superwind” varies strongly with effective temperature (Ṁ ∝ T−8eff, see Arndt et al. 1997), reflecting the temperature-sensitive micro-physics and chemistry of dust-formation and radiative transfer on a macroscopic scale. Furthermore, a thermal pulse leads to a very short (100 to 200 yrs) interruption of the “superwind” of these models.

For Mi ≲ 1.1M⊙, our evolution models fail to reach the (Eddington-like) critical luminosity Lc required by the radiatively driven wind models, while for the (initial) mass-range in-between, with the tip-AGB luminosity LtAGB near Lc, thermal pulses drive bursts of “superwind”, which could explain the outer shells found with some PN's. In particular, a burst with a duration of only 800 yrs and a mass-loss of about 0.03 M⊙, occurs right after the last AGB thermal pulse of a model with Mi ≈ 1.1M⊙. There is excellent agreement with the thin CO shells found by Olofsson et al. (e.g., 1990, 1998) around some Mira stars.
How Binary Stars affect Galactic Chemical Evolution
Authors: Tout Christopher A. , Karakas Amanda I. , Lattanzio John C. , Hurley Jarrod R. , Pols Onno R.
Published: July 2016

At least 60% of stars appear to be binary and about half of these are close enough to interact. Because of the enormous expansion on the AGB, many of these interactions will involve an AGB star and a relatively compact companion, anything from a low-mass main-sequence star to a degenerate remnant. Mass loss plays the dominant role in determining the lifetime and the extent of nuclear processing of the AGB phase. Binary interaction will increase the mass loss from the AGB star and curtail its evolution, either through Roche-lobe overflow, common-envelope evolution or the driving of an enhanced stellar wind. These processes will tend to reduce the metals, particularly carbon, returned to the inter-stellar medium. On the other hand merged systems or companions that accrete a substantial amount of mass themselves evolve into AGB stars that can synthesize and return more carbon than the two individuals would have alone. By synthesizing large populations of stars, with nucleosynthesis and binary interaction, we estimate a reduction in carbon yield owing to binary star evolution of as much as 15%.
AGB stars and galactic dynamics
Authors: Dejonghe H. , Van Caelenberg K.
Published: July 2016

AGB stars, seen as a stellar population, can be used to probe the dynamical state of galaxies. The relevant data are mostly positions and line-of-sight velocities, sometimes together with information on chemical composition and/or age. As of now, dynamical models have been made for OH/IR stars and Planetary Nebulae. Other candidates are C stars, S stars, and Miras. We review the methods used and the results obtained so far, for the Milky Way and for (relatively nearby) extragalactic stellar systems.
Evolutionary Histories of Dwarf Galaxies in the Local Group
Authors: Grebel Eva K.
Published: July 2016

The star formation histories of Local Group (LG) dwarf galaxies and more distant potential LG members are reviewed. Problems in defining the spatial extent of the LG and membership are briefly discussed. The morphological types found in the LG are presented, and it is suggested that we see continuous evolution from low-mass dwarf irregulars (dIrrs) to dwarf spheroidal galaxies (dSphs) in the LG.

Star formation histories for LG dwarfs and nearby LG candidates are compiled using population boxes. No two dwarfs, irrespective of morphological type, show the same evolutionary history, and all vary widely in ages of their subpopulations and in their enrichment history. The lack of gas in dSphs and certain dwarf ellipticals (dEs) is puzzling, both with respect to their star formation histories and the expected mass loss from red giants, but a new photoionization scenario may reconcile these contradictions. Old populations, often spatially very extended, may be a common property of dwarf galaxies, though their fractions can be very small. Almost all types of dwarf galaxies studied in detail so far show spatial variations in ages and abundances such as radial age/metallicity gradients. The observed star formation histories impose constraints on merger and accretion scenarios.

Properties of the Milky Way dwarf spheroidals are compared to the M31 dSphs and discussed in the framework of the ram pressure/tidal stripping scenario. It is demonstrated that the newly discovered LG dwarfs follow the same relationship for central surface brightness, mean metallicity, and absolute magnitude as the other LG dwarfs.
Radio and X-ray Study of SNRs in the Magellanic Clouds
Authors: Filipović M.D. , Pietsch W. , White G. L. , Haberl F. , Staveley-Smith L. , Jones P. A. , Haynes R. F. , Sasaki M.
Published: July 2016

We present our high-resolution radio-continuum and X-ray study of supernova remnants (SNRs) in the Magellanic Clouds (MCs). These investigations are based on Australia Telescope Compact Array (ATCA) radio-continuum and ROSAT X-ray observations. Our main aim is to study a complete sample of the MC SNRs and H II regions.
The Star Formation History of Leo I
Authors: Gallart C. , Freedman W. L.
Published: July 2016

We advance some results of our study of the star formation history of the Local Group dSph galaxy Leo I, obtained through the analysis of its deep HST color-magnitude diagram (CMD) using model CMDs computed from stellar evolutionary models. We conclude that most star formation (≃ 90%) took place in Leo I between 7 and 1 Gyr ago. It seems to have started at a very low rate ≃ 15 Gyr ago and continued, also at a very low rate, from 1 Gyr ago until the present time. A constant Z=0.0004 and a large fraction of binary stars are required to obtain the best agreement with both the distribution of stars across the CMD and with its morphology. An IMF like the one obtained by Kroupa et al. (1993) for the solar neighborhood, or steeper, is compatible with the data.
CFHT Wide-Field Deep Imaging of M33
Authors: Cuillandre J.-C. , Lequeux J. , Loinard L.
Published: July 2016

28′ x 28′ deep V- and I-band images of the center and of the SE field of M33 have been obtained at the prime focus of the Canada-France-Hawaii 3.6m telescope. They allowed to map separately the young blue stars, the red supergiants, the red giants and the extreme AGB stars. The disk as traced by red giants has a surprisingly sharp edge. The young blue stars trace the spiral structure very well, but the detailed comparison with H I and CO maps does not show a very good correspondence. The simple spiral-shock model of star formation proposed for the South arm of M33 is not confirmed. On the edge of the galaxy, star formation starts at a column density of H I of about 3 x 1020 atom cm−2. The colour-magnitude diagram for the halo stars shows a broadened red giant branch with a mean metallicity [Fe/H] ≃ −1.0. The shape of the red giant branch confirms the distance modulus of 24.82±0.20 for M33.
Color-Luminosity Relations for the Resolved Hot Stellar Populations in the Centers of M31 and M32
Authors: Brown Thomas M. , Ferguson Henry C. , Stanford S. A. , Deharveng Jean-Michel
Published: July 2016

We present Faint Object Camera (FOC) ultraviolet images of the central 14 x 14″ of Messier 31 and Messier 32. The hot stellar population detected in the composite UV spectra of these galaxies is partially resolved into stars, and we measure their colors and apparent magnitudes. We detect 433 stars in M31 and 138 stars in M32, down to limits of mF275W = 25.5 mag and mF175W = 24.5 mag. We investigate the luminosity functions of the sources, their spatial distribution, their color-magnitude diagrams, and their total integrated far-UV flux. Although M32 has a weaker UV upturn than M31, the luminosity functions and color-magnitude diagrams of M31 and M32 are surprisingly similar, and are inconsistent with a majority contribution from any of the following: post-AGB stars more massive than 0.56 M⊙, main sequence stars, or blue stragglers. The luminosity functions and color-magnitude diagrams are consistent with a dominant population of stars evolving from the extreme horizontal branch (EHB) along tracks of mass 0.47–0.53 M⊙. These stars are well below the detection limits of our images while on the zero-age EHB, but become detectable while in the more luminous (but shorter) post-HB phases. Our observations require that only a very small fraction of the main sequence population (2% in M31 and 0.5% in M32) in these two galaxies evolve though the EHB and post-EHB phases, with the remainder rapidly evolving through bright post-AGB evolution with few resolved stars expected in the small field of view covered by the FOC.
Differential Abundances of B-type Supergiants in M33
Authors: Monteverde M. I. , Herrero A.
Published: July 2016

In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants. In the following study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. Determination of atmospheric parameters is based on analyses of silicon ionisation balance.

Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral standards in our Galaxy.

We compare our results with the abundances expected from studies of H II regions.
Analyses of Wolf-Rayet Stars in Local Group Galaxies
Authors: Schmutz Werner , De Marco Orsola , Schild Hans , Crowther Paul , Howarth Ian
Published: July 2016

We have started a project to observe and analyze Wolf-Rayet stars in the galaxies of the Local Group. The first observing run was marred with disastrous weather and therefore, we do not yet have any results to report. Instead, we briefly summarize the motivation of our project.
The New Local Group Galaxy Candidates Cas dSph, Peg dSph = And VI, and Cam A
Authors: Gallart C. , Martínez-Delgado D. , Aparicio A. , Freedman W. L.
Published: July 2016

We present observations of the new Local Group galaxy candidates Cassiopeia dSph, Pegasus dSph = And VI and Camelopadalis A. Our deep color-magnitude diagrams show that the first two galaxies are certainly Local Group members, and likely dSph galaxies at a distance similar to that of the Andromeda galaxy. Cam A seems to be a star-forming galaxy situated considerably further away.