bluuebunny/crossref_metadata_2025 huggingface dataset:
Substructure of Galaxy Clusters and Cosmological Constant
Authors: Suwa Tamon , Habe Asao , Yoshikawa Kohji , Okamoto Takashi
Published: July 2016

We calculate some indicators, which are closely related with galaxy clusters' substructure, for each cluster obtained in numerical simulations in OCDM and ΓCDM, and make a statistical comparison between two models. In ΓCDM the indicators, multipole moment power ratios and center shifts, are larger than those in OCDM. This result is consistent with the analytical prediction; galaxy clusters' formation epoch in ΓCDM is later than in OCDM and then clusters in OCDM are more relaxed than those in ΓCDM. We show that these indicators for X-ray surface brightness are useful tools to distinguish between OCDM and ΓCDM.
Effect of LMC on the Galactic Warp
Authors: Tsuchiya Toshio
Published: July 2016

Multi-scale interaction between LMC, the Galactic halo, and the disk is examined by N-body simulations. The Galactic models are constructed most realistically to satisfy available observational constraints. LMC is orbiting in a ellipse with pericentric radius of 50kpc, and the Galactic halo is assumed to be well beyond the orbit. By using hybrid algorithm I have succeeded to follow the evolution with million particles. The orbiting satellite excites density enhancement as a wake, and the wake exerts a tidal force on the disk. Through this multi-scale interaction, an integral warp is excited. Its amplitude is, however, a few 100pc, and impossible to explain the observed Galactic warp.
Abundance Ratios of M82 and Nucleosynthesis of Hypernovae
Authors: Umeda Hideyuki , Nomoto Ken'ichi , Tsuru Takeshi Go , Nakamura Takayoshi
Published: July 2016

The abundance in M82 is Si and S rich, and can not be explained by the combination of conventional Type I and II supernova yields. We show that these abundance patterns, as well as the observed hot plasma energy to metal mass ratios can be explained by the hypernova nucleosynthesis. This hypothesis is consistent with the expected age after the star-burst of M82.
Introductory Review
Authors: Kwok Sun
Published: July 2016

Our current state of understanding of the planetary nebulae (PNe) phenomenon is reviewed in the context of modern stellar evolution and dynamical models. Also discussed are a number of new problems that have emerged as the result of recent space (x-ray, UV, optical, and infrared) observations. The roles of PNe in the chemical (atomic, molecular, and solid-state) enrichment of the galaxy and as tracers of the large scale structure of the Universe are also discussed.
New M-Type Variables in Galactic Dark Clouds
Authors: Melikian N. D. , Magnan C. , Karapetian A. A. , Sarkissian J. M.
Published: July 2016

We present the results of the classification of newly discovered M-type variables obtained as part of an H-alpha survey of Galactic dark cloud regions.
Parameterizing the Third Dredge up in AGB Stars
Authors: Karakas A. I. , Lattanzio J. C. , Pols O. R.
Published: July 2016

We present new evolutionary sequences for low and intermediate mass stars (1M⊙ to 6M⊙) for three different metallicities, z = 0.02, 0.008 and 0.004. We evolve the models from the pre-main sequence to the thermally-pulsing asymptotic giant branch (AGB) phase. We have two sequences of models for each mass, one which includes mass-loss and one without mass-loss. For an overview of AGB evolution and nucleosynthesis, see Herwig (2002) and Lattanzio (2002).
The Extended Atmosphere and Evolution of the RV Tau Star R Scuti
Authors: Matsuura M. , Zijlstra A. A. , Yamamura I. , Bedding T. R.
Published: July 2016

We identify H2O, CO, SiO and CO2 bands in near-infrared ISO/SWS spectra of the RV Tau star R Sct. These molecules originate from an atmosphere around the photosphere. RV Tau stars are commonly considered as post-AGB stars. We argue that R Sct may be a thermal-pulsing AGB star, observed in a helium-burning phase.
The s-process in Post-AGB Stars
Authors: Van Winckel Hans
Published: July 2016

In this contribution an overview is given of recent accurate chemical abundance studies in post-AGB stars. The intrinsic nature of the enrichement and the spread in metallicity together with the absence of strong molecular veiling make post-AGB stars very useful to constrain AGB (chemical) evolutionary models. S-process enrichment is, however, not a general characteristic of post-AGB stars and a photospheric chemical study is not always a good tracer for the evolved status of an object.
Synthetic Post-AGB Evolution
Authors: Frankowski Adam
Published: July 2016

A synthetic method for tracing the evolution of the post-AGB stars is presented. The main advantage of this procedure, based on the published numerical evolutionary sequences, is that it is simple, fast, and allows to treat post-AGB objects of arbitrary mass.
Proto-Planetary Nebulae
Authors: Hrivnak Bruce J.
Published: July 2016

The study of proto-planetary nebulae (PPNs) leads to a better understanding of both the preceding asymptotic giant branch and the succeeding planetary nebula phases of stellar evolution. Recent results are reviewed, emphasizing the properties of the central stars and the shape and chemistry of the nebulae. The study of PPNs is seen to be important in its own right.
Photometric and Polarimetric Observations of AGB and Post AGB Stars
Authors: Melikian N. D. , Magnan C. , Karapetian A. A. , Sarkissian J. M.
Published: July 2016

Photometric and polarimetric observations of Long-Period Variables (LPVs), carried out at Byurakan Observatory over the last few years, have yielded some interesting results. In particular, one of the important results obtained for Mira type variables is that there is a certain correlation between brightness and polarization: the maximum degree of polarization is midway on the increasing branch of the light curve and in all probability its change has a periodic character. More recently an important result has been obtained for a post AGB star SAO 124414. The polarimetric and photometric observations of this star were carried out over a period of 3 years. At an almost constant brightness, strong, irregular changes of light polarization were observed in three bands (BVR) of the spectrum. The analysis of the observations does not show periodicity in changes of polarization. In this report the observational results for SAO 124414 are presented. In the study of the evolution of red giants and supergiants, future observations of this star taken simultaneously in optical and radio wavelengths, could be very significant.
Hydrodynamics of Clumpy Flows: Application to the PNe
Authors: Poludnenko A. Y. , Prank A. , Blackman E. G.
Published: July 2016

Many astrophysical flows occur in inhomogeneous media. We present results of a hydrodynamic numerical study of the interaction of a steady, planar shock/supersonic postshock flow with a system of embedded cylindrical clouds in a two-dimensional geometry and describe an analytical model of the evolution of such systems. Finally we discuss mass-loading in such systems and the applicability of the results to the planetary nebulae (PNe).

The most recent results and animations of the numerical experiments described in this paper can be found at www.pas.rochester.edu/~wma.
Planetary Systems Around Red Giants and Formation of Planetary Nebulae
Authors: Rudnitskij G. M.
Published: July 2016

The effects of planetary systems around pre-AGB and AGB stars on their pulsations, optical spectra and on the shape of future planetary nebulae are discussed. The physical phenomena considered include include gas drag on the planet embedded in the ever denser circumstellar gas of a red giant and shock waves arising. intensity of the H2O The lack of variability in many red giants may be due to their low metallicity and absence of planetary systems around them.
The Bizarre Central Star of SuWt2
Authors: Exter Katrina , Bond Howard , Pollacco Don , Dufton Philip
Published: July 2016

SuWt2 has been found to contain a double lined and eclipsing binary system. Surprisingly, both components appear to be A-type stars with masses of about 3 M⊙ moving in essentially circular orbits with a period of 4.9 days. We see no indications of a hotter component in the optical or IUE spectra. We discuss the possibility that this is a triple system.

Deep Hα + [N II] images show the nebula to be an inclined ring (≃600 to the line of sight) while spectra show anomalous line ratios (eg I([N II] 6584) ≥≥ I(Hα)) which maybe indicative of recombination in a changing radiation field. Further modeling is ongoing.
Spectroscopic Masses for post-AGB Stars and Planetary Nebula Nuclei
Authors: Schmidt Mirosław , Tylenda Romuald
Published: July 2016

We compare the observed positions of post-AGB stars and planetary nebula nuclei in the log g and Teff diagram. We show that these positions and the resulting stellar masses are not fully consistent with theoretical expectations.
Water and OH Maser Emission from the Planetary Nebula K3-35
Authors: Gómez Yolanda , Miranda Luis F. , Anglada Guillem , Torrelles JosÉ M.
Published: July 2016

Water-vapour masers, typical of the envelopes in giant stars, are not expected to persist in planetary nebulae due to the ultraviolet radiation of the remnant star that progressively destroys the molecules. Recently, we have reported the first unambiguous detection of water maser emission in a planetary nebula, K 3–35 (Miranda et al. 2001). The water masers in K3–35 were detected at the center of the nebula, along the minor axis, at a radius of ~85 AU and also at the surprisingly large distance of 5000 AU from the star, at the tips of the bipolar lobes. The existence of these water molecules is puzzling, and probably we are observing the very moment of transformation of a giant star into a planetary nebula. Miranda et al. (2001) also report the presence of polarization in the OH 1665 MHz masers, which are distributed towards the central star in a torus-like structure. Here we review the main results on this source.
A Collimated Molecular Jet in W 43A Traced by Water Maser Emission
Authors: Imai Hiroshi , Sasao Tetsuo , Obara Kumiko , Omodaka Toshihiro , Diamond Philip J.
Published: July 2016

We present VLBA observations of the spatial and velocity distributions of 22 GHz H2O and 1612 MHz OH masers in the OH/IR star W 43A. These masers have the same systemic velocity and are, therefore, likely to be associated with the common stellar object. However, the kinematical structures of them are quite different and independent. Most of the H2O masers are extremely collimated spatially and kinematically. The H2O maser jet also seems to be precessing. On the other hand, the OH masers exhibit clear arc-shaped structures indicating a spherically-expanding shell with weak collimation. The W 43A jet is very likely to be predominantly composed of hot molecules traced by H2O maser emission and formed in the immediate vicinity of an unknown star next to another OH/IR star. Such a “molecular jet” is likely to appear only during the short period before a star forms an elongated planetary nebula.
The Iron Project and TIPTOPbase: Atomic Data and Opacities for Astrophysics
Authors: Nahar Sultana N.
Published: July 2016

The Iron Project (IP) is an extension of the Opacity Project, an international collaboration of atomic physicists and astrophysicists. The aim of the IP is the development and application of new methods in theoretical atomic physics to the calculation of large-scale atomic data of high accuracy for radiative and collisional processes for astrophysically important elements.
Thermal and Density Structures and Elemental Abundances in the Bipolar PN Mz 3
Authors: Zhang Y. , Liu X.-W.
Published: July 2016

Mz 3 is a young bipolar planetary nebula (PN) with lobes extending over ~ 50 arcsec on the sky. It consists of a bright core, two approximately spherical bipolar lobes and two outer large filamentary bipolar nebulae. The salient features of Mz 3 are more easily studied than other bipolar nebula because of its large angular extent. It is very bright in the far-infrared. There is an extended shell of warm dust surrounding the central star. And the bipolar lobes are filled with hot ionized gas. Cohen et al. (1978) found that Mz 3 is He-rich. Based on the LWS observations of the far-IR fine-structure lines, Liu et al. (2001) derived a high N/O ratio in Mz 3 and identified the bipolar nebula as a Type-I PN.
Physical Conditions and Abundances in Abell 30
Authors: Wesson R. , Liu X-W. , Barlow M. J.
Published: July 2016

Abell 30 is one of a small number of PN known as born-again PN, which appear to be old nebulae whose central star has undergone a further ejection of highly processed material. It consists of a large, faint, spherical shell, in which several bright knots are embedded. The knots were first noted by Jacoby (1979), and analysis of their abundances by Hazard et al (1980) and Jacoby & Ford (1983) showed that they are extremely hydrogen-deficient.
Dynamics of [WR] Planetary Nebulae
Authors: Mellema Garrelt
Published: July 2016

The formation of PNe around [WC] stars is modelled with a numerical hydrodynamics code. It is found that the PN around [WC] are expected to expand faster, and be more turbulent. It is shown that the observed lack of differences with ‘normal’ PNe, can have implications for models of the origin of asphericity in PNe.
Evidence of Jets in the Bipolar Planetary Nebulae M 1-91 and M 1-92
Authors: Arrieta A. , Torres-Peimbert S. , Olguín L. , Georgiev L.
Published: July 2016

For M1-91 we find that the ratio of the 6717/6731 [S II] narrow band images shows two symmetrical very collimated high density regions, or jets, along the major axis.

We infer many properties of M 1-92 from the similarity of the spectral features with the symbiotic star MWC 560. We show that M 1-92 could also have a jet along the major axis and that from the NW knot we receive scattered light from the central region that has traveled along the line of symmetry.
Spectroscopy of the Three Planetary Nebulae in the Sagittarius Dwarf Galaxy
Authors: Walsh J. R. , Zijlstra A. A. , Péquignot D.
Published: July 2016

Two planetary nebulae previously classified as Galactic were discovered, on the basis of their radial velocities, to be located in the Sagittarius Dwarf galaxy (Zijlstra & Walsh, 1996, A&A, 312, L21). At the distance of Sagittarius of ~25kpc, they are the closest extra-galactic PN. A detailed analysis based on ground-based spectra and radio continuum data was published (Dudziak et al. 2000, A&A, 363, 717); it was shown that the two nebulae are on the same evolutionary track with initial mass of 1.2M⊙and almost identical light element abundances. One of the nebulae, Wray 16–423, underwent PN ejection about 1500yr before its twin He 2-436. On the basis of their similarity, a differential abundance analysis could be conducted. Third dredge-up carbon was found to be more abundant in He 2-436 and the first conclusive evidence for third-dredge-up oxygen enrichment was revealed (Péquignot et al. 2000, A&A, 361, L1).
New Ionization-Correction Factors for the Chemical Composition Determination of Galactic Planetary Nebulae and HII Regions in Blue Compact Dwarf Galaxies
Authors: Holovatyy V.V. , Havrylova N.V. , Melekh B.Ya.
Published: July 2016

The photoionization models (PhM) grid of the planetary nebulae (PN) and the HII regions in the blue compact dwarf galaxies (BCDG) was calculated. For grids modeling we used the CLOUDY94 code (Ferland G.J. 1999). Free parameters for PN grid were: (1) energy distribution, that corresponds to temperature of each of 15 chosen models (Clegg & Middlemass 1987); (2) chemical composition of nebular gas in models; (3) filling factor with its values, for every model, being equal to 0.1, 0.5 and 1. For HII regions the free parameters were: (1) energy distribution in the spectra of nuclei emission obtained for HII regions in BCDG by our method (Golovaty 1987, Melekh 2000) from high-quality observations (Izotov, Thuan, & Lipovetsky 1994, Izotov, Thuan, & Lipovetsky 1997, Thuan, Izotov, & Lipovetsky hys. J. 1995) of these objects (the method uses stellar atmosphere models of O-B stars (Schaerer et al. 1996, Schaerer & de Koter 1997)); (2) nebular gas filling factor with the values ranging from 0.0001 to 1; (3) the relative abundance of heavy elements; (4) the concentration of hydrogen atomsnH. All PhM were assumed to be spherically-symmetrical. As a result, 135 PN PhM and 270 HII regions PhM were calculated.
The LMC Planetary Nebula N66 Revisited: Nebular Kinematics and Stellar Models
Authors: Peña M. , Hamann W.-R. , Ruiz M. T.
Published: July 2016

LMC-N66 is an extraordinary planetary nebula whose central star underwent a violent mass loss event which has lasted for 10 years. The outburst reached its maximum in 1994. Since then the star has been slowly fading. During the stellar outburst, the nebular lines have shown no changes.

The nebula shows a complex morphology. Two very bright lobes at both sides of the central star, almost aligned in the E-W direction, constitute the main body of the nebula. Several knots and filaments are conspicuous over the surface lying preferentially on the S-E and N-W directions. A couple of faint, extended loops are also detected in the S-E and N-W directions at both sides of the star. The extension of these loops are larger than 0.5 pc at the LMC distance. A no emitting-zone in the S-W quadrant, seems to be part of a dusty toroid around the central star, although the central star is not obscured by such a dark material (see Blades et ale 1992 for a description of N66 morphology).
Planetary Nebulae in the SMC
Authors: Jacoby George H. , De Marco Orsola , Ciardullo Robin
Published: July 2016

Using the ESO 2.2m telescope with the 8K x 8K mosaic CCD, we surveyed 2.8 square degrees (~1.6° x 1.7°) of the SMC to search for faint planetary nebulae (PN). In this region, 34 PN were previously known; we identified 25 new objects. All of these are faint and have been spectroscopically confirmed. We estimate that there should be ~140 PN in the entire SMC to the limits of a survey like this one, which is complete to 6 mag down the planetary nebula luminosity function (PNLF). For a complete survey (8 mag down the PNLF), there should be ~220 PN. A strong new feature is evident in the PNLF as a deficiency at 4 mags below the brightest PN.

The survey spectra that were used to confirm the candidates as PN show that the fainter PN exhibit a higher incidence (~28%) of strong [N II] emission (where I([N II]/I(Hα) > 1) relative to the bright Sanduleak et al. (1978) sample (~6%). We propose that the very faint SMC PN are selectively biased toward the chemically enriched Type I objects derived from younger, more massive progenitors.
Studies of Extragalactic Planetary Nebulae with VLT+FORS: Detection, Photometry and Slitless Radial Velocities of 535 PNs in the Flattened Elliptical Galaxy NGC 4697
Authors: Méndez R. H. , Riffeser A. , Kudritzki R. P. , Matthias M. , Freeman K. C. , Arnaboldi M. , Capaccioli M. , Gerhard O.
Published: July 2016

We describe a procedure for the efficient measurement of large quantities of PN radial velocities (RVs) in early-type galaxies, using the Focal Reducer and Spectrograph (FORS) at the Cassegrain foci of the ESO Very Large Telescope. The PNs are detected using the classic on-band/off-band filter technique. The radial velocity is obtained by measuring and calibrating the displacement of a PN image on the CCD produced by the insertion of a grism in the light path. Since no slits are used, it is possible to measure RVs for all the detected PNs, irrespective of their number and distribution in the field. All the images needed to find the PNs and measure their brightness and RVs can be collected in just one observing run, without the complicated preparation procedures typical of multi-object slit spectroscopy. The RVs have errors of about 40 km/s.
The Low Mass End of the Young Cluster IC2391
Authors: y Navascués David Barrado , R. Stauffer John
Published: July 2016

By collecting optical and infrared photometry, as well as medium resolution spectroscopy, we have discovered a sample of low mass stars and brown dwarfs in the young cluster IC2391. Using the lithium depletion boundary near the substellar limit, we have estimated the age of the cluster as ~50 Myr. We have also studied the Hα emission in this sample.
The Missing M Dwarfs
Authors: F. Jameson Richard , D. Dobbie Paul , J. Pinfield David , T. Hodgkin Simon
Published: July 2016

We present evidence for a drop in the luminosity function around spectral type M7–M8. This shows in both field stars and the clusters σ–Orionis, the Trapezium, IC 348, IC 2391, α–Perseii, the Pleiades and, possibly, the globular cluster M4. This can be explained by a sudden drop in the luminosity-mass relation. Theoretical models, which include dust, do not show this effect, although they predict dust forming at about spectral type M7. We suggest that this drop in the luminosity-mass relation could be modelled by considering larger size dust grains. The drop in the luminosity-mass relation suggests that star/brown dwarf masses below M7–M8 will be larger than predicted by current models.
Ground-Based Optical Deep Pencil Beam Surveys
Authors: Boeshaar P. C. , Margoniner V.
Published: July 2016

The initial results of the Deep Lens Survey (http://dls.bell-labs.com) to identify possible brown dwarfs and extremely metal poor red halo subdwarfs near the hydrogen burning limit are presented. Individual deep CCD high galactic latitude survey fields appear to offer a low probability of discovering field BD's, but taken collectively offer an opportunity to begin addressing questions regarding the scale height and distribution of these objects. In all likelihood, the very depth of such surveys will greatly increase our knowledge of the coolest extreme halo objects, which currently are known in far fewer numbers than T dwarfs. Ultimately, the large volume surveyed by the Large Synoptic Survey Telescope will identify vast numbers of such objects, providing a more complete picture of their spatial distribution.
Multiplicity of Nearby Free-floating Late M and L Dwarfs: HST-WFPC2 Observations of Candidates and Bona Fide Binary Brown Dwarfs
Authors: Bouy Hervé , Brandner Wolfgang , L. Martín Eduardo , Delfosse Xavier , Allard France , Basri Gibor
Published: July 2016

We review the results of HST/WFPC2 observations of a sample of 50 very-low-mass objects in the solar neighborhood (30 from our own program and 20 from the archive). Using high spatial resolution HST/WFPC2 images, we observed these objects in two filters (F814W and F675W) in order to identify close companions, measure their colours, and obtain first epoch data of the newly discovered binaries. In addition to 3 previously known binaries we discovered 3 new multiple systems. Second epoch data are required to confirm that they are real common proper motion pairs. Binary properties like multiplicity, distribution of binary separations and brightness ratios hold clues on the origin and evolution of free-floating brown dwarf binaries.
The Search for Brown Dwarfs around White Dwarfs
Authors: Farihi J. , Becklin E. E. , Zuckerman B.
Published: July 2016

The infrared search for substellar companions to nearby white dwarfs has been going on for a little more than a decade. The most recent phase has been a wide field proper motion search carried out primarily at Steward Observatory, where we are complete down to J = 18. Earlier phases included near field searches at the IRTF and Keck Observatory. In the last year we have discovered ten previously unrecognized faint proper motion companions. Of the recent discoveries, most are white dwarfs and a few M dwarfs. GD165B, discovered in 1988 as part of our program, is still the only known companion to a white dwarf with spectral type later than M.
A Near-Infrared Spectral Sequence of Late M, L, and T Dwarfs
Authors: Cushing Michael C. , Rayner John T. , Vacca William D.
Published: July 2016

We present the initial results of a medium resolution, 0.8 to 4.2 μm spectroscopic survey of M, L, and T dwarfs. We have identified the most prominent molecular and atomic absorption features found in the spectra of these late-type dwarfs. We have also compared the spectra to a laboratory FeH emission spectrum and identified nearly 100 features common to the FeH spectrum and the dwarf spectra from 0.99 to 1.8 μm.
X-Ray Detection of Brown Dwarfs with Chandra
Authors: Wolk Scott J.
Published: July 2016

I review recent observations of brown dwarfs by theChandraX-ray Observatory. These observations fall in 2 categories, young stellar clusters which contain brown dwarfs and brown dwarf candidates and directed pointings at brown dwarfs and very low mass stars. Surprisingly, there are already over 60 published detections of brown dwarfs byChandra.A review of the X–ray characteristics shows these objects are subject to flaring and their temperatures and luminosities have a vast range which is related to age.
Periodic Variability of the Brown Dwarf Kelu-1
Authors: Clarke F. J. , Tinney C. G. , Hodgkin S. T.
Published: July 2016

We present results of two observing campaigns aimed at characterising variability of the L2 brown dwarf Kelu-1. The first campaign in March 2000 detected photometric variability at the 1.2% level, with a strong period of 1.8 hours. Followup spectroscopic observations with the VLT in February 2002 show no evidence of significant variability in the dust sensitive molecular lines, but do show evidence for variability in the EW(Hα) with a period of 1.8 hours. Radial velocity measurements rule out a close substellar companion. Kelu-1 appears to be a single brown dwarf with a rotation period of 1.8 hours.
The Next Generation Sky Survey and the Quest for Cooler Brown Dwarfs
Authors: Davy Kirkpatrick J.
Published: July 2016

The Next Generation Sky Survey (NGSS) is a proposed NASA MIDEX mission to map the entire sky in four infrared bandpasses – 3.5, 4.7, 12, and 23 μm. The seven-month mission will use a 50-cm telescope and four-channel imager to survey the sky from a circular orbit above the Earth. Expected sensitivities will be half a million times that of COBE/DIRBE at 3.5 and 4.7 μm and a thousand times that of IRAS at 12 and 23 μm. NGSS will be particularly sensitive to brown dwarfs cooler than those presently known. Deep absorption in the methane fundamental band at 3.3 μm and a predicted 5-μm overluminosity will produce uniquely red 3.5-to-4.7 μm colors for such objects. For a limiting volume of 25 pc, NGSS will completely inventory the Solar Neighborhood for brown dwarfs as cool as Gl 229B. At 10 pc, the census will be complete to 500 K. Assuming a field mass function with α = 1, there could be one or more brown dwarfs warmer than 150 K lying closer to the Sun than Proxima Centauri and detectable primarily at NGSS wavelengths. NGSS will enable estimates of the brown dwarf mass and luminosity functions to very cool temperatures and will provide both astrometric references and science targets for NGST.
Chemical abundances of massive stars in Local Group galaxies
Authors: Venn Kim A. , Kaufer Andreas , Tolstoy Eline , Kudritzki Rolf-Peter , Przybilla Norbert , Smartt Stephen J. , Lennon Daniel J.
Published: July 2016

The relative abundances of elements in galaxies can provide valuable information on the stellar and chemical evolution of a galaxy. While nebulae can provide abundances for a variety of light elements, stars are the only way to directly determine the abundances of iron-group and s-process and r-process elements in a galaxy. The new 8m and 10m class telescopes and high-efficiency spectrographs now make high-quality spectral observations of bright supergiants possible in dwarf galaxies in the Local Group. We have been concentrating on elemental abundances in the metal-poor dwarf irregular galaxies, NGC 6822, WLM, Sextants A, and GR 8. Comparing abundance ratios to those predicted from their star formation histories, determined from color-magnitude diagrams, and comparing those ratios between these galaxies can give us new insights into the evolution of these dwarf irregular galaxies. Iron-group abundances also allow us to examine the metallicities of the stars in these galaxies directly, which affects their inferred mass loss rates and predicted stellar evolution properties.
Stellar parameters of Wolf-Rayet stars from far-UV to mid-IR observations
Authors: Crowther Paul A.
Published: July 2016

Recent results for Galactic and Magellanic Cloud Wolf-Rayet stars are summarised based on line-blanketed, clumped model atmospheres together with UV, optical and IR spectroscopy. The trend towards earlier WN and WC spectral types with decreasing metallicity is explained via the sensitivity of classification diagnostics to abundance/wind density, such that WR mass-loss rates are metallicity dependent. Pre-supernovae masses for WC stars are determined, in reasonable agreement with CO-cores of recent Type Ic SN.
The Wind Momentum-Luminosity relationship: blue supergiants in the spiral galaxy NGC 300
Authors: Bresolin Fabio , Kudritzki Rolf-Peter , Gieren Wolfgang
Published: July 2016

We have carried out the wind analysis of six A-type supergiants in NGC 300. The derived Wind Momentum-Luminosity Relationship is compared with that of Galactic and M 31 blue supergiants and with theoretical models.
Candidate LBVs in Local Group galaxies
Authors: Corral Luis J. , Herrero Artemio
Published: July 2016

We present the results of photometric searches for LBV candidates (LBVc) made in some Local Group galaxies. We found eight candidates in a southern region of M 33 with characteristics similar to Var B and Var C. In IC 10, a galaxy without any LBV or LBVc reported before, we found one candidate.
Radiatively driven winds: shaping bipolar LBV nebulae
Authors: Dwarkadas Vikram V. , Owocki Stanley P.
Published: July 2016

Massive stars which are fast rotators can give rise to asymmetric winds. These winds may result in the formation of aspherical wind-blown nebulae. In this work the theory of radiatively-driven winds from massive stars is used to model the formation of bipolar nebulae around LBV stars.
Spectroscopic studies of OB stars in the Magellanic Clouds with VLT-UVES
Authors: Evans Christopher J. , Crowther Paul A. , Fullerton Alexander W. , Hillier D. John
Published: July 2016

We present results from optical and ultraviolet analysis of nine LMC/SMC supergiants. Temperatures, mass-loss rates and CNO abundances are obtained using the non-LTE, line-blanketed model atmosphere code of Hillier & Miller (1998). In general, the derived temperatures are significantly lower than those determined from unblanketed, plane-parallel models.
Discovery of weak magnetic fields in early B-type stars
Authors: Henrichs Huib F. , Neiner Coralie , Geers Vincent C.
Published: July 2016

We summarize recent results of magnetic measurements of three bright early B-type stars, β Cep, ζ Cas, and V2052 Oph, which were found to be oblique rotators with a weak magnetic dipole field with typical strength of a few hundred Gauss. From stellar wind studies we could derive their rotational periods very accurately, and match the stellar wind with the magnetic phase. From model atmosphere fits we derive the angles of rotational and magnetic axis. All three stars show some chemical abundance anomaly, presumably associated with the magnetic properties. The stars are also pulsating variables. This is of high asteroseismological interest, since these are the only early-type stars known with observationally determined rotation, pulsation and magnetic properties.
Colliding winds in the WR+OB binary θ Muscae (WR 48, WC5+O6-7V)
Authors: Hill Grant M. , Moffat Anthony F.J. , St-Louis Nicole
Published: July 2016

Spectra, providing full phase coverage, of the 19 d WC6+OB binary θ Mus (WR 48, HD 113904), have been obtained and show dramatic variations of the C iii λ5696 emission line profile. We have modeled these line profile variations assuming the winds from the WR star and its close OB companion are colliding and forming a shock region from which extra emission originates.
Radio continuum observations of massive stars in open cluster NGC 6231 and the Sco OB1 association
Authors: Gunawan Diah Y.A. Setia , Chapman Jessica M. , Stevens Ian R. , Rauw Gregor , Leitherer Claus
Published: July 2016

We present results of the Australia Telescope Compact Array (ATCA) radio continuum observations of massive stars in the Sco OB1 association. Most stars detected in the program show spectral indices lower than value expected from thermal free-free emission.
B-type supergiants in M 31
Authors: Trundle Carrie , Dufton Philip L. , Lennon Daniel J. , Smartt Stephen J. , Urbaneja Miguel A.
Published: July 2016

We present the spatial distribution of chemical species in M 31, as derived from intermediate resolution spectra of seven B-type supergiants, lying within four OB associations, covering a galactocentric distance of 5 – 12 kpc. We do not detect any systematic oxygen gradient across this galactocentric range. We find that the inner regions of M 31 are not, as previously thought, very ‘metal-rich’. Our abundances of C, N, O, Mg, Si, Al, S and Fe in the M 31 supergiants are very similar to those of massive stars in the solar neighbourhood.
FUSE far-ultraviolet spectroscopy of Wolf-Rayet stars
Authors: Willis Allan J. , Crowther Paul A. , Hutchings John B. , Fullerton Alexander W. , Brownsberger Kenneth R. , Massa Derck L. , Walborn Nolan R.
Published: July 2016

An overview of a new far-ultraviolet spectral atlas of Wolf-Rayet stars in the Galaxy and the Large and Small Magellanic Clouds is presented.
Discovery of narrow O VI emission from SN 1987A
Authors: Sonneborn George , Lundqvist Peter , Iping Rosina C. , Massa Derek L.
Published: July 2016

The 1032, 1038 Å emission lines of O vi were detected from SN 1987A by the FUSE satellite observations in 2000 and 2001. The lines are extremely narrow (fwhm < 35kms–1), indicating that the emission is not a by-product of the various circums tellar shock phenomena. The most likely origin of the O vi emission lines is recombination of the SN progenitor's red giant wind that was photoionized by the SN shock breakout on 1987 Feb 23.
Spectroscopic analysis of new-born massive stars in SMC N 81
Authors: Martins Fabrice , Schaerer Daniel , Heydari-Malayeri Mohammad
Published: July 2016

We present the first results of a spectroscopic study of young massive stars in the SMC high excitation blob N 81. These stars have Mv values which are ~ 2 mag smaller than those of normal dwarf stars. Their UV HST-stis spectra reveal features typical of O-type stars, but surprisingly weak wind components. The preliminary modeling of these spectra with the code cmfgen (Hillier & Miller 1998) indicates mass loss rates of the order of 10–9 M⊙ yr–1. If confirmed, such a weak wind may indicate either a breakdown of the wind-momentum luminosity relation at low luminosity, or a steeper slope of this relation at low metallicity.
Outflows from ellipticals: the role of supernovae
Authors: Matteucci Francesca , Pipino Antonio
Published: July 2016

Models of supernova (SN) driven galactic winds for ellipticals are presented. We assume that ellipticals formed at high redshift and suffered an intense burst of star formation. The role of supernovae of Type II and Type Ia in the chemical enrichment and in triggering galactic winds is studied. In particular, several recipes for SN feed-back together with detailed nucleosynthesis prescriptions are considered. It is shown that SNe of Type II have a dominant role in enriching the interstellar medium of elliptical galaxies whereas Type Ia SNe dominate the enrichment and the energetics of the intracluster medium.
The massive star Initial Mass function
Authors: Schaerer Daniel
Published: July 2016

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a ‘universal’ Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lowerMupand/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally, we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich H ii regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit ofMup≳ 60 – 90 M⊙.
On the ionizing populations in GEHRs: unveiling integrated properties from the analysis of the Wolf-Rayet population
Authors: Castellanos Marcelo , Díaz Ángeles I. , Terlevich Elena
Published: July 2016

In recent years, the detection of Wolf-Rayet stars in Giant Extragalactic H ii Regions (GEHRs) has yielded several questions about our current understanding of massive stars evolution and hot expanding atmospheres, the age of the ionizing populations and their impact onto the physical properties of GEHRs. Here, we present spectrophotometric observations of four extragalactic GEHRs which show WR features in their spectra. Our goal is to reproduce simultaneously the observed WR properties and the emission-line spectra with the help of current evolutionary synthesis models.
Evolution of supernovae in the winds of massive stars
Authors: Dwarkadas Vikram V.
Published: July 2016

Core-collapse supernovae (SNe) arise from massive stars, which lose mass in the form of stellar winds throughout their lifetimes. We study herein the evolution of the SNe as they grow in the circumstellar medium formed by mass loss from the progenitor star.
Mrk 1087: a puzzling suspected Wolf-Rayet galaxy
Authors: Esteban César , López-Sánchez Ángel R. , Rodríguez Mónica
Published: July 2016

We present new observations of Mrk 1087 that indicate this galaxy is experiencing a strong star formation event due to the interaction with -at least- two nearby galaxies, one of them is a star-forming dwarf. We also discover that some of the surrounding non-stellar objects are tidal dwarfs hosting weak starbursts.
CFHT Fabry-Perot 2D spectroscopy in Hα of the ejected Wolf-Rayet ring nebula M1-67: universal multifractal analysis and turbulent status
Authors: Grosdidier Yves , Moffat Anthony F.J. , Blais-Ouellette Sébastien , Joncas Gilles , Acker Agnès
Published: July 2016

Using CFHT-sis Fabry-Perot interferograms of the Wolf-Rayet ring nebula M1-67, we present an investigation of the statistical properties of fluctuating gas motions using structure functions (SFs) traced by Hα emission-line centroid velocities. We consider the SFs 〈|Δv(r)|p〉 of order p, i.e., the spatially averaged moments of order p of the spatial velocity increments at projected spatial scale r of M1-67's velocity field: we test for (i) SF scaling, 〈|Δv(r)|p〉 ∝ rζ(p), and (ii) nonlinearity of the observed scaling exponents ζ(p)s, as expected for intermittent flows. We find that there is a clear correlation at scales 0.02-0.22 pc between the mean quadratic differences of radial velocities and distance over the surface of M1-67. The first and second order SFs are found to scale as 〈|Δv(r)|〉 ∝ r0.5 and 〈|Δv(r)|2〉 ∝ r0.9 (Grosdidier et al. 2001). The former scaling law strongly suggests that supersonic turbulence is at play in M1-67, on the other hand, the latter scaling law agrees very well with Larson-type laws for velocity turbulence. Additionally, we can discuss the nature of the turbulence in terms of Universal Multifractals (UM), a continuous-scale limit of multiplicative cascades (Schertzer & Lovejoy 1987) and derive the level of intermittency in the nebula.
A Chandra study of the morphological structure of the Wolf-Rayet dwarf starburst galaxy NGC 4214
Authors: Hartwell Joanna M. , Stevens Ian R. , Strickland David K. , Heckman Timothy M.
Published: July 2016

We present results from a Chandra X-ray observation of the dwarf starburst galaxy NGC 4214, a galaxy containing several young star forming regions. Starburst regions are known to be associated with diffuse X-ray emission, and in this case X-ray emission from the galaxy shows an interesting morphological structure with a bright X-ray ring of emission within the galaxy.
Molecular gas around the Wolf-Rayet star WR 18 (WN4)
Authors: Marston Anthony P.
Published: July 2016

Optically observed ring nebulae and H i cavities around Wolf-Rayet stars have enabled us to obtain information on the history of mass-loss associated with these massive evolved stars. However, such studies have left a number of unanswered questions regarding the amount of mass-loss and the conditions of the stars during a sequence of mass-loss phases. Here we discuss the molecular gas environments of the WR star WR 18, which has an associated optical ring nebula NGC 3199. Our observations show that significant amounts of molecular gas appear close to and associated with the star. Mapping of molecular CO near the star shows that molecular materials appear to substantially avoid areas of optical emission and, instead, form a distorted clumpy shell interior to NGC 3199. Molecular emission lines are broader than lines seen in the interstellar medium and suggest the shell is composed of ejecta. This is further corroborated by the enhanced abundances of molecules containing C, N and O. Implications of the observations for the evolution of WR 18 are discussed.
Ultraviolet spectra of star-forming galaxies with time-dependent dust obscuration
Authors: Martins Lucimara P. , Leitherer Claus , Calzetti Daniela
Published: July 2016

We present a new approach to probe the properties of the most massive, ionizing stars with respect to the less massive, non-ionizing stars. The new technique utilizes stellar-wind lines, instead of the previously employed nebular lines. This allows us to probe the timescale of the dust dispersal in a very young obscured starburst from purely stellar diagnostics.
Towards observations of Population III galaxies
Authors: Schaerer Daniel , Pelló Roser
Published: July 2016

We are undertaking various studies of primordial galaxies with the following main aims:

(i)

synthesize the properties of rest-frame UV-optical spectra of Population III galaxies and ‘transition objects’ between Pop III and normal starbursts;

(ii)

devise optimal search strategies for the detection of Pop III and related objects with ground-based and space observations;

(iii)

simulate photometric and spectroscopic observations of Pop III galaxies to quantify the feasibility of such studies especially for future ground-based instruments; and

(iv)

study the physics of Pop III and ‘transition’ galaxies and their implications on cosmology and the physics of galaxies
Rapid spectroscopic and photometric variability in the Be star Alpha Eridani
Authors: Leister N.V. , Janot-Pacheco E. , Buck M.T.C. , Dias M.P. , Hubert A.M. , Hubert H. , Floquet M. , Briot D.
Published: July 2016

We present here a preliminary report on the analysis of simultaneous photometric and spectroscopic observations of the Be star α Eri, taken during 1992 at the Laboratório Nacional de Astrofísica. α Eri (Archenar, HR472, HD10144, B3–4 III-IV) is the brightest Be star in the sky. It shows activity cycles in a time scale of a few years. Balona et al. (1987) presented a comprehensive study of the star based on photometric and spectroscopic observations. They found a periodicity of 1.26 days in both radial velocity and light variations and argued that a spotted star rotating at this period is the simplest working model that explains the observations.
The Magnetic Fields of the A and B Stars
Authors: Moss D.
Published: July 2016

The strong magnetic fields found in the Ap and Bp stars are reviewed, with critical attention to the competing dynamo and fossil theories for their origin. A number of difficulties for the dynamo theory are identified. Whilst the fossil theory is not free of problems, they appear less severe. From the modulation of certain spectral lines, rather weaker fields are deduced to be present above the surface of Be stars. The question of whether observed spectral transients might arise from magnetic fluctuations is discussed.
Analysis of IUE spectrograms for Be stars
Authors: Eversberg T. , Dachs J. , Berghöfer T. W. , Huilai C. , Lemmer U.
Published: July 2016

Archival high-dispersion spectrograms obtained by the International Ultraviolet Explorer satellite in the short-wavelength (λλ1150–2000Å) region were inspected and analyzed for a total of 33 Be stars, including one Oe star (HR 6397) and three stars showing shell-type spectra in the optical region (48 Lib, ɛ Cap, o Aqr). The following atomic and ionic transitions were investigated: Hi-Lyα, Cii-UV1, Ciii-UV4, Civ-UV1, Nv-UV1, Siii-UV1…-UV4, Siiii-UV2, Siiv-UV1.
Photometry of early type stars in open clusters (NGC 1444, NGC 1662, NGC 2129, NGC 2169 and NGC 7209)
Authors: Peña J. H. , Peniche R.
Published: July 2016

This is part of a series which has the purpose of examining the nature of the stars belonging to open clusters. The aim of this series is, among others things, to study short period pulsating stars, mainly of the Delta Scuti type, by first establishing the membership of each star to the cluster, to determine the abundance of the Be and Ap phenomena and blue stragglers in open clusters for clusters of different ages and metalicities and, eventually, to study the chemical enrichment of the galaxy when age, dynamics and metalicity are known for a fair number of clusters.
Line-profile variable ɛ Per: spectroscopic binary and (?) mild Be star
Authors: Tarasov A.E. , Kostunin V.V. , Harmanec P. , Horn J. , Koubský P. , Blake C. , Walker G.A.H. , Yang S.
Published: July 2016

ɛ Per (45 Per, HR 1220, HD 24760, ADS 2888A) is a star which was used for years as a spectrophotometric and MKK classification standard. Nowadays it is known as an archetype of early-type line-profile variables (LPV). The variations are so pronounced that they were misinterpreted for a composite spectrum (B0.5+A2) and the star was even reported to be a double-lined spectroscopic binary (Petrie 1958). Since 1983, the characteristics of line-profile variability in the spectrum of ɛ Per have been intensively studied (Bolton 1983, Smith 1985, Gies & Kullavanijaya 1988). The recent investigations of RV variations of ɛ Per led to the conclusion that ɛ Per is a spectroscopic binary with a period of about 14.05 days and a rather eccentric orbit (Harmanec & Tarasov 1990). The issue of the binary nature (with a very eccentric orbit) is of utmost importance since it could be causally related to the extremely large observed line-profile variations (e.g., Polfliet & Smeyers 1990, Tassoul & Tassoul 1992).
Difference between Be stars and shell stars from Hα emission
Authors: Chen H. , Taylor A. R.
Published: July 2016

We examine Hα equivalent widths versus spectral-types for 41 Be stars. Although the Wα value is scattered for a given spectral-type, a well-defined upper limit exists. Most shell stars are located in the upper limit region. The shell stars all have v sin i/vcri larger than the normal Be stars in the upper limit region. This strongly suggests that the distinction between shell stars and normal Be stars of high equivalent width is a result of variation in inclination angle i. Polarization data also support this hypothesis.