bluuebunny/crossref_metadata_2025 huggingface dataset:
Subaru Coronagraphic Search for Companion Brown Dwarfs
Authors: Itoh Yoichi , Tamura Motohide , Hayashi Saeko S. , Oasa Yumiko , Fukagawa Misato , Suto Hiroshi , Murakawa Koji , Naoi Takahiro
Published: July 2016

Near-infrared coronagraphic images of GG Tau and GK Tau are presented as preliminary results of the search for young brown dwarfs around T Tauri stars.
Microlensing Constraints on Low-Mass Companions
Authors: Scott Gaudi B.
Published: July 2016

Microlensing is sensitive to binary, brown dwarf (BD), and planetary companions to normal stars in the Galactic bulge with separations between about 1–10 AU. The accurate, densely-sampled photometry of microlensing events needed to detect planetary companions has been achieved by several follow-up collaborations. Detailed analysis of microlensing events toward the bulge demonstrates that less than 45% of M-dwarfs in the bulge have MJup companions between 1 and 5 AU. Detection of binary and BD companions using microlensing is considerably easier; however, the interpretation is hampered by their non-perturbative influence on the parent lightcurve. I demonstrate that ~ 25% of BD companions with separations 1 – 10AU should be detectable with survey-quality data (~ 1 day sampling and ~ 5% photometry). Survey data is more amenable to generic, brute-force analysis methods and less prone to selection biases. An analysis of the ~ 1500 microlensing events detected by OGLE-III in the next three years should test whether the BD desert exists at separations 1 – 10AU from M-dwarfs in the Galactic bulge.
M-Dwarf Multiplicity Rate in the Solar Vicinity
Authors: Marchal L. , Delfosse X. , Forveille T. , Ségransan D. , Beuzit J. L. , Udry S. , Perrier C. , Mayor M. , Halbwachs J.-L.
Published: July 2016

We present results based on a 6 year survey of a solar vicinity M-dwarf sample. We have obtained their multiplicity rate and orbital elements for the binaries. Such results could give us keys for a better understanding of stellar formation.
Model Atmospheres and Spectra: The Role of Dust
Authors: Allard France , Guillot Tristan , Ludwig Hans-Günter , Hauschildt Peter H , Schweitzer Andreas , Alexander David R. , Ferguson Jason W.
Published: July 2016

Brown dwarf atmospheres form molecules, then high temperature condensates (corundum, titanates, silicates, and iron compounds), and then low temperature condensates (ices) as they cool down over time. These produce large opacities which govern entirely their spectral energy distribution. Just as it is important to know molecular opacities (TiO, H2O, CH4, etc.) with accuracy, it is imperative to understand the interplay of processes (e.g. condensation, sedimentation, coagulation, convection) that determines the radial and size distribution of grains. Limiting case models have shown that young, hot brown (L) dwarfs form dust mostly in equilibrium, while at much cooler stages (late T dwarfs) all high temperature condensates have sedimented out of their photospheres. But this process is gradual and all intermediate classes of brown dwarfs can partly be understood in terms of partial sedimentation of dust. With new models accounting for these processes, we describe the effects they may have upon brown dwarf spectral properties.
Clouds and Clearings in the Atmospheres of the L and T Dwarfs
Authors: Marley M. S. , Ackerman A. S. , Burgasser A. J. , Saumon D. , Lodders K. , Freedman R.
Published: July 2016

A sophisticated approach to condensate opacity is required to properly model the atmospheres of L and T dwarfs. Here we review different models for the treatment of condensates in brown dwarf atmospheres. We conclude that models which include both particle sedimentation and upwards transport of condensate (both gas and particles) provide the best fit for the L dwarf colors. While a globally uniform cloud model fits the L dwarf data, it turns to the blue inJ-Ktoo slowly to fit the T dwarfs. Models which include local clearings in the global cloud deck, similar to Jupiter's prominent five-micron hot spots, better reproduce the available photometric data and also account for the observed resurgence of FeH absorption in early type T dwarfs.
The Classification of L Dwarfs: Is It Based on Clouds or Temperature?
Authors: Stephens Denise C.
Published: July 2016

A continuous L dwarf classification sequence requires the combined use of far optical (visible) and near infrared spectral indices. However, the visible and near infrared indices currently in use assign subtypes that differ by up to three subclasses due to differences in cloud opacity for objects with the same effective temperature. Therefore, it may be impossible to combine visible and near infrared spectral indices to create one L dwarf classification system, and two classification variables may be necessary.
An Efficient Low-Resolution NIR Classification Scheme for M, L, and T dwarfs and Its Application to Young BDs
Authors: Testi L. , Natta A. , Baffa C. , Comoretto G. , Gennari S. , Ghinassi F. , Licandro J. , Magazzù A. , Oliva E. , D'Antona F.
Published: July 2016

We present the preliminary results of a programme aimed at defining a low-resolution near-infrared spectral classification scheme for faint M, L, and T-dwarfs. The method is based on the global shape of R˜100 complete near-infrared spectra from 0.8 to 2.4μm as obtained through a high-throughput prism-based optical element, the Amici device, mounted inside the NICS instrument at the TNG 3.5m telescope (Baffa et al. 2001; Oliva 2000). The aim of our project is to provide an efficient classification scheme based on very low-resolution near infrared spectroscopy, which can be carried on at a 4m-class telescope. The results for the L-type dwarfs have already been presented in Testi et al. (2001), sample spectra for the M and T-dwarfs range are shown in Figure 1. A preliminary application of the method to the classification of young embedded brown-dwarf candidates has been successfully attempted by Testi et al. (2002) and Natta et al. (2002). The method is shown to be accurate and competitive: the high system throughput coupled with the possibility of obtaining in a “single shot” the complete spectrum of the objects make the NICS/TNG system more efficient than existing large telescopes.
Modeling of Optical and IR Spectra of M and Brown Dwarfs
Authors: Pavlenko Yakiv V.
Published: July 2016

Procedure and results of computation of optical and infrared spectra of ultracool (1000 < Teff < 3000 K) objects are discussed. LTE synthetic spectra and spectral energy distributions in wide spectral region λλ 0.6–10 microns) are computed for model atmospheres from grids of different authors taking into account opacities provided by water and other molecules.

Essential interest will be paid for problems of realization of lithium and deuterium tests which can be used for assessment of objects of sub-stellar masses and big planets and refining of scenarios of evolution of young stars and substellar objects.
News of Effective Temperatures of L Dwarfs
Authors: Schweitzer Andreas , Gizis John E. , Allard France , Hauschildt Peter H.
Published: July 2016

In this work we report recent spectral analyses of L dwarfs and our success in measuring Teff and log(g). Using dust filled atmospheres for early L dwarfs and rained out atmospheres for late L dwarfs we could derive Teff of 1400 to 2000 K for L8 to M9.5 dwarfs respectively. We also give an outlook what we can achieve with future models that are improving the fits to intermediate L dwarfs and IR spectra.
Parallaxes of Brown Dwarfs at USNO
Authors: Harris Hugh C. , Dahn Conard C. , Vrba Frederick J. , Guetter Harry H. , Canzian Blaise , Henden Arne A. , Levine Stephen E. , Luginbuhl Christian B. , Monet Alice K. B. , Monet David G. , Pier Jeffery R. , Stone Ronald C. , Walker Richard L.
Published: July 2016

Trigonometric parallaxes have been measured by Dahn et al. (2002) for 28 cool dwarfs and brown dwarfs, including 17 L dwarfs and three T dwarfs. Broadband CCD and near-IR photometry (VRIz*JHK) have been obtained for these objects and for 24 additional late-type dwarfs. These data have been supplemented with astrometry and photometry from the literature, including parallaxes for the brighter companions of ten L and two T dwarfs. The absolute magnitudes and colors are reviewed here. The I - J color and the spectral type are both good predictors of absolute magnitude for late-M and L dwarfs. MJ becomes monotonically fainter with I - J color and with spectral type through late-L dwarfs, then brightens for early-T dwarfs. In contrast, the J - K color correlates poorly with absolute magnitude for L dwarfs. Using several other parameters from the literature (Li detection, Hα emission strength, projected rotation velocity, and tangential velocity), we fail to uncover any measurable parameter that correlates with the anomalous J - K color.
Mass-Luminosity Relations of Very Low Mass Stars
Authors: Ségransan D. , Delfosse X. , Forveille T. , Beuzit J.L. , Perrier C. , Udry S. , Mayor M.
Published: July 2016

We present new accurate masses at the bottom of the main sequence as well as an improved empirical mass-luminosity relation for very low mass stars in the visible and near infrared. Masses were obtained by combining very accurate radial velocities and adaptive optics images of multiple stars obtained at different orbital phases.
Variability of L Dwarfs in the Near Infrared
Authors: Caballero José A. , Béjar Víctor J. S. , Rebolo Rafael
Published: July 2016

We have obtained series of images in the near infrared J and Ks bands for seven L-type dwarfs with a duration of 3 to 6 hours. We present results on: 1) the amplitude of variability associated with atmospheric changes over time scales from minutes to several hours; 2) the search for cool companions in wide orbits; 3) the search for transits of brown dwarfs and planetary companions in very close orbits.
Conference Summary
Authors: Jameson R. F.
Published: July 2016

The subject of brown dwarfs has grown enormously since the announcement of the first brown dwarfs in 1995. Thus this conference is the largest conference ever devoted solely to brown dwarfs, with 150 delegates, 82 talks and 52 posters. This summary will struggle, therefore, to give a complete picture and, of course, it is only the impression of one individual.
The earliest O-type stars
Authors: Walborn Nolan R.
Published: July 2016

High-quality, blue-violet digital spectroscopy has been assembled of most previously known (and one new) members of the O3 class that exhibit N iv emission and N v absorption lines, with the collaboration of most specialists in the field. A detailed comparative study has led to the introduction of new spectral types O2 and O3.5 to describe the range of classification criteria present. Primary reliance has been placed on the N iv/N iii selective emission-line ratio, because of various difficulties affecting the interpretation of weak He i absorption lines in some of these spectra, which are discussed. Some representative spectra defining the new types are shown. The majority of the O2 - O3 class members reside in the LMC. Their large ranges of luminosities and masses suggest a close evolutionary connection to the WN class, as do several spectroscopic and spatial relationships. The salient characteristics of O2-O3 spectra in the ultraviolet longward of 1200 Å have been established for some time by IUE and HST data. Recently, the rich 900-1200 Å range has been well covered for the first time by FUSE; in a collaboration with its hot-star team, a comprehensive atlas of OB spectra in the Magellanic Clouds has been prepared. Several O2 stars are included, one of which is newly discovered, and some examples of these data are also shown.
Formation of massive binaries
Authors: Zinnecker Hans
Published: July 2016

The formation of massive stars is one of the major unsolved problems in stellar astrophysics. However, only few if any of these are found as single stars, on average massive stars have more than one companion. Many of them are born in dense stellar clusters and several clusters have an excess of massive short-period spectroscopic binaries, with severe implication for binary-related stellar evolution including mergers, and also for the origin of massive runaway stars. The multiplicity of massive stars seems to increase with increasing primary mass and with increasing density of young star clusters. These observations suggest that massive binary and multiple systems originate mainly from dynamical gravitational interactions and accretion-induced protostellar collisions in dense clusters. If true, the binary properties of massive stars in less dense OB associations should be less extreme. This prediction should be tested by future observations. The paper reviews both the latest observations and theoretical ideas related to the origin of massive binaries. It concludes with a speculation on how the binary properties might change with metallicity (e.g., LMC/SMC).
Self-consistent coupling of radiative transfer and dynamics in dust driven winds
Authors: Berruyer Nicole , Lafon Jean-Pierre J. , Liberatore Stéphane
Published: July 2016

The aim is to determine the role and influence of the hypothesis concerning both dynamics and radiative transfer in models of winds and mass loss of evolved stars, when the radiative force on dust grains plays a major role in the structuration of the circumstellar envelope of the star. The flow is described successively using two models coupling the grains-gas dynamics in a self-consistent way with radiative transfer for two different approaches of the dynamics: the Momentum Coupling Hypothesis and the Full Problem. Complete radiative transfer including multiple scattering, absorption and thermal emission is taken into account. The medium is not necessarily optically thin. In all cases, numerical iterations couple dynamics with transfer. This study emphasizes the importance of the drift velocity between the grains and the gas and the inertia of dust together with hydrodynamics and transfer coupling.
Quantitative Analysis of O-Type Stars Properties, at Low Metallicity
Authors: Bouret Jean-Claude , Lanz Thierry M. , Heap Sara R. , Hubeny Ivan , Hillier D. John , Lennon Daniel J. , Evans Christopher J. , Smith Linda J.
Published: July 2016

We have investigated the properties of main-sequence O-type stars in the SMC. Mass-loss rates, luminosities and Teff are much smaller for these stars than for Galactic ones, resulting in a steeper wind-momentum relation.
The massive Wolf-Rayet binary WR 98 (WN7/WC+08-9)
Authors: Gamen Roberto C. , Niemela Virpi S.
Published: July 2016

We present the discovery of OB type absorption lines superimposed to the emission line spectrum, and the first double-lined orbital elements, for the massive Wolf-Rayet binary WR 98 (HDE 318016, WN7/C+08-9), a spectroscopic binary in a circular orbit with a period of 47.825 d. The semi-amplitudes of the orbital motion of the emission lines differ from line to line, indicating a mass ratio in the range q ≡ MWR/MOB = 1–1.8.
Near-UV nebular absorption lines of η Carinae
Authors: Gull Theodore R. , Vieira Gladys L. , Danks Anthony C.
Published: July 2016

The notorious η Carinae was observed with the stis from 2380 Å to 3160 Å with a resolving power of ~ 130000. Over 500 absorption lines have been identified as originating from Fe i, Fe ii, Ti ii, V ii, Cr ii, Ni ii, Co ii, Mn ii, Mg i and Mg ii. Most of the lines have multiple components ranging from −145kms–1, –385kms–1 to –587kms–1. Many interstellar absorption velocity systems, also found in the spectra of other Carina stars, are seen in the spectrum of η Car. While ISM absorption lines originate from the ground energy level, the nebular lines originate from energy levels well above the ground state. We are still evaluating the origin and location of these velocity systems in line of sight.
Theoretical X-ray line profiles from colliding wind binaries
Authors: Henley David B. , Stevens Ian R. , Pittard Julian M.
Published: July 2016

We present theoretical X-ray line profiles calculated for a range of model colliding wind systems. In particular we have investigated how the line profiles vary with wind parameters. These profiles will be compared with high-resolution grating spectra of colliding wind binaries and will provide new insights into the structure of the X-ray emitting regions in such systems.
FUSE observations of Luminous Blue Variables
Authors: Iping Rosina C. , Sonneborn George , Massa Derck L.
Published: July 2016

P Cyg, AG Car, HD 5980 and η Car were observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. FUSE covers the spectral range from 980 Å to 1187 Å at a resolution of 0.05 Å. In this paper we discuss the far-UV properties of these LBVs and explore their similarities and differences. The FUSE observations of P Cyg and AG Car, both spectral type B2pe, are very similar. The atmospheres of both η Car and HD 5980 appear to be somewhat hotter and have much higher ionization stages (Si iv, S iv, and P v) in the FUSE spectrum than P Cyg and AG Car. There is a very good agreement between the FUSE spectrum of P Cygni and the model atmosphere computed by John Hillier with his code cmfgen. The FUSE spectrum of η Car, however, does not agree very well with existing model spectra.
The dominant X-ray wind in massive star binaries
Authors: Pittard Julian M. , Stevens Ian R.
Published: July 2016

We investigate which shocked wind is responsible for the majority of the X-ray emission in colliding wind binaries, an issue where there is some confusion in the literature, and which we show is more complicated than has been assumed. We find that where both winds rapidly cool (typically close binaries), the ratio of the wind speeds is often more important than the momentum ratio, because it controls the energy flux ratio, and the faster wind is generally the dominant emitter. When both winds are largely adiabatic (typically long-period binaries), the slower and denser wind will cool faster and the stronger wind generally dominates the X-ray luminosity.
Clumps and shocks in the outer winds of hot stars
Authors: Runacres Mark C. , Owocki Stanley P.
Published: July 2016

We present a moving periodic box technique to study the outer-wind evolution of instability-generated structure in hot-star winds. This has considerable computational and conceptual advantages
A gallery of cool hypergiants — imaging their circumstellar environments
Authors: Schuster Michael T. , Humphreys Roberta M. , Smith Nathan , Davidson Kris , Gehrz Robert D.
Published: July 2016

High resolution imaging with HST-wfpc2 of seven of the most luminous evolved cool stars shows that the three OH/IR stars NML Cyg, VX Sgr and S Per have circumstellar nebulae while no ejecta was detected for the M-type supergiant μ Cep and the yellow hypergiants ρ Cas, HR 8752 and HR 5171a.
The role of rotation and mass loss in the evolution of massive stars
Authors: Maeder André , Meynet Georges
Published: July 2016

Rotation affects all the outputs of the evolution and nucleosynthesis of massive stars. We discuss the evolution of the rotational velocities, the internal ω-gradients, the tracks in the H-R diagram, the age determinations, the evolution of the surface N/C abundance ratios, the B/R number ratios of blue to red supergiants and the lifetimes in the WR stages.
Testing convective mixing in massive stars
Authors: Eid Mounib F. El , Flower Philip J.
Published: July 2016

Stellar evolution sequences are presented for stars in the mass range 5-21 M⊙ with initial metallicity Z = 0.002 and initial helium abundance Y = 0.25 resembling average composition of the Small Magellanic Cloud. The stellar models are calculated with different treatment of convective mixing in regions of varying molecular weight gradient. The stellar sequences are used to study the morphology of the well-observed star cluster NGC 330 in the SMC. We argue that convective mixing should be inhibited in inhomogeneous stellar regions in order to understand the morphology of NGC 330. In other words, our contribution emphasizes the important role of semi-convection in the evolution of massive stars.
Searching for hydrogen in Type Ib supernovae, and for helium and hydrogen in Type Ic supernovae
Authors: Branch David
Published: July 2016

Identifying the progenitors of Type Ib and Type Ic supernovae requires knowing, among other things, whether SNe Ib eject hydrogen, and whether SNe Ic eject helium, and perhaps even hydrogen. Recently it has become clear that some SNe Ib do eject hydrogen, and it may be that all SNe Ib do. Two arguments that have been made in the past that SNe Ic eject helium are difficult to confirm, but I discuss other possible evidence that SNe Ic eject helium, as well as hydrogen. If so, these elements extend to lower ejection velocities than in SNe Ib. The spectroscopic differences between SNe Ib and SNe Ic may depend on the radial distributions of the helium and hydrogen as well as on the ejected masses of helium and hydrogen. We should consider the possibility that SNe Ic are more mixed up.
Inventory of black hole binaries
Authors: Orosz Jerome A.
Published: July 2016

A small group of X-ray binaries currently provides the best evidence for the existence of stellar-mass black holes. These objects are interacting binary systems where the X-rays arise from accretion of material onto a compact object (i.e., an object with a radius of less than a few hundred km). In some favourable cases, optical studies of the companion star lead to dynamical mass estimates for both components. In 17 cases, the mass of the compact object in an X-ray binary has been shown to exceed the maximum mass of a stable neutron star (about 3 M⊙), which leads to the conclusion that these objects are black holes. In this contribution I will review the basic properties of these black hole binaries.
Hypernovae and their nucleosynthesis
Authors: Nomoto Ken'ichi , Maeda Keiichi , Umeda Hideyuki , Ohkubo Takuya , Deng Jingsong , Mazzali Paolo
Published: July 2016

We review the characteristics of nucleosynthesis in ‘hypernovae’, i.e., core-collapse supernovae with very large explosion energies (≳ 1052 ergs). The hypernova yields show the following characteristics: (i) the mass ratio between the complete and incomplete Si burning regions is larger in hypernovae than normal supernovae. As a result, higher energy explosions tend to produce larger [(Zn, Co, V)/Fe] and smaller [(Mn, Cr)/Fe], which could explain the trend observed in very metal-poor stars; (ii) because of enhanced α-rich freeze-out, 44Ca, 48Ti, and 64Zn are produced more abundantly than in normal supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars strongly suggest a significant contribution of hypernovae; and (iii) oxygen burning takes place in more extended regions in hypernovae to synthesize a larger amount of Si, S, Ar, and Ca (‘Si’), which makes the ‘Si’/O ratio larger. The abundance pattern of the starburst galaxy M 82 may be attributed to hypernova explosions. We thus suggest that hypernovae make important contribution to the early Galactic (and cosmic) chemical evolution.
Progenitor models of Wolf-Rayet binaries: short-period WNE+O binaries with mass ratios q ≃ 0.5
Authors: Petrovic Jelena , Langer Norbert
Published: July 2016

We identify two possible paths for the progenitor evolution of observed WNE+O binaries with WNE/O mass ratios close to 0.5 and periods between 7 and 10 d. We show, through detailed binary evolution models, that with the assumption that the O-type star expels most of the matter flowing at it during mass transfer, one possibility to obtain the observed systems is through Case A mass transfer. We find a second solution using standard common envelope evolution. We conclude that in either case the O-type star in the three investigated systems did not accrete significant amounts of mass. We discuss the intricate situation that in other cases massive close binaries may evolve conservatively.
A spectroscopic survey of the WNL population in the LMC: very preliminary results
Authors: Schnurr Olivier , Moffat Anthony F.J. , St-Louis Nicole , Foellmi Cedric , Skalkowski Gwen , Shara Michael M. , Niemela Virpi S. , Vennes Stéphane
Published: July 2016

We present very preliminary results of a spectroscopic survey of all known 47 WNL stars in the LMC.
Detecting the progenitors of core-collapse supernovae
Authors: Smartt Stephen J.
Published: July 2016

A novel project to directly detect the progenitor stars of nearby core-collapse supernovae in pre-discovery archive images is briefly described.
UCH II regions in extragalactic clusters and associations
Authors: Johnson Kelsey E.
Published: July 2016

In recent years, a number of extragalactic massive stars clusters have been detected which are still deeply embedded in their birth material In many cases, these clusters are only visible in the mid-IR to radio regimes, and have typically been detected as ‘inverted’ spectrum radio sources. These clusters appear to have properties which are analogous to those of ultracompact H ii (UCH ii) regions in the Galaxy, albeit vastly scaled up in total mass and luminosity. The ultra-young clusters appear to form with a continuum of masses, and the most massive are consistent with being the progenitors of globular clusters. Here I will overview the properties of the currently known sample of ultradense H ii (UDH ii) regions and examine their relation to Galactic UCH ii regions.
Young open clusters in the Carina region
Authors: Carraro Giovanni , Marigo Paola , Ventura Paolo , Romaniello Martino , Patat Ferdinando
Published: July 2016

We present results of a new investigation (Carraro et al. 2002) aimed at clarifying the mutual relationship between the three most prominent young open clusters close to η Carinæ, namely Trumpler 16, Trumpler 14 and Collinder 232.
The chaotic ISM of the post(?)-starburst galaxy NGC 1569
Authors: Dufour Reginald J. , Buckalew Brent A. , Shopbell Patrick L. , Walter Donald K.
Published: July 2016

We present the results and analysis of HST-wfpc2 imagery of the starburst galaxy NGC 1569 (d = 2.2 Mpc), which permit unprecedented resolution (~ 1pc) of the ionized gas and stellar population. The primary data in our analysis consists of images taken through narrow-band filters isolating Hβ, Hα, [O iii]λ5007, and [S ii]λλ6717+30, as part of go Program 8133. A variety of color-coded and grey-scaled maps of the morphology, ionization structure, and dust distribution are presented. Unsharp masks of the Hα images show a very chaotic structure for the ionized gas, with numerous filaments and arc-like bright rim features across the entire galaxy, but without significant large-scale ionization variations. Variations in the ionization and line-of-sight reddening occur on smaller scales (~ 10 – 50 pc), with numerous low-ionization semi-stellar knots seen throughout the main body of the galaxy, even within the ‘hole’ in the ionized gas distribution around the central super star clusters previously noted from H i maps. Several of these features have strong [S ii] emission indicative of being supernova remnants. We combine these data with archival wide-band HST-wfpc2 imagery to quantitatively evaluate the source(s) of the (largely photo-) ionized gas.
A HST imaging survey of a sample of 61 Galactic Wolf-Rayet stars — the WC8-9 subsample
Authors: Wallace Debra J. , Moffat Anthony F.J. , Shara Michael M. , Gies Douglas R. , Niemela Virpi S. , Nelan Edmund
Published: July 2016

A HST-wfpc2 survey of Galactic Wolf-Rayet stars was undertaken over a five year period, in an effort to discover new close visual companions, tight clusters, and/or association memberships. In total, 61 Galactic WR stars were observed, with nine objects being members of the subclasses WC8 and WC9, which are associated with dust production. For these nine, we present images of WR 11, WR 48a, WR 69, WR 70, WR 81, and WR 92. We refer to Wallace et al. (2002) for discussion of WR 98a, WR 104, and WR 112. Overall, we find for separations of approximately ≥ 150 mas, that the binary/association properties of the WC8/WC9 sample are statistically indistinguishable from the overall WR population. These statistics are limited, however, by the small numbers of each WR subclass observed.
The Local Group census: IC-10
Authors: Wright Shelley A. , Greimel Robert , Lennon Daniel J. , Corradi Romano L.M. , Walton Nicholas A.
Published: July 2016

We have begun a census of various stellar groups in Local Group Galaxies, using the wide field camera on the Isaac Newton Telescope on La Palma. Here we present a preliminary color-magnitude diagram for the dwarf irregular galaxy IC-10. At present time, metallicity of IC-10 is measured to be Z = 0.005 (Garnett 1990). Comparison with recent literature values of reddening and distance suggest that IC-10's distance is ~ 1 Mpc. Our comprehensive wide-field survey encompasses both broad (g′, r′, i′) and narrow-band (O iii, He ii, Hα, S ii, Strömgren y) observations to look for emission-line objects, including Wolf-Rayet stars and Luminous Blue Variables. The analysis also yields the coordinates of massive stars to an accuracy sufficient for follow-up multi-object spectroscopic observations.
Ring nebulae around massive stars throughout the Hertzsprung-Russell diagram
Authors: Chu You-Hua
Published: July 2016

Massive stars evolve across the H-R diagram, losing mass along the way and forming a variety of ring nebulae. During the main sequence stage, the fast stellar wind sweeps up the ambient interstellar medium to form an interstellar bubble. After a massive star evolves into a red giant or a luminous blue variable, it loses mass copiously to form a circumstellar nebula. As it evolves further into a WR star, the fast WR wind sweeps up the previous mass loss and forms a circumstellar bubble. Observations of ring nebulae around massive stars not only are fascinating, but also are useful in providing templates to diagnose the progenitors of supernovae from their circumstellar nebulae. In this review, I will summarize the characteristics of ring nebulae around massive stars throughout the H-R diagram, show recent advances in X-ray observations of bubble interiors, and compare supernovae's circumstellar nebulae with known types of ring nebulae around massive stars.
Integrated photometric and spectroscopic properties of massive stellar clusters in Wolf-Rayet galaxies
Authors: Buckalew Brent A. , Dufour Reginald J. , Castañeda Héctor O.
Published: July 2016

We report here the first results of an extensive optical/near-infrared imaging and spectroscopic study of massive stellar clusters in Wolf-Rayet (WR) galaxies using observations obtained from KPNO (USA), OAN (Mexico), the HST and the 2MASS data archive. We have collected spectra, B-imagery and 2MASS JHK imagery of approximately 60 prominent stellar clusters in 23 WR galaxies. One-third of the clusters have a WR stellar signature at He ii λ4686. In this poster, we present the comparison of the derived ages and masses of clusters with WR stars (WRCs) against clusters not containing WR stars (nWRCs). The results show that the mean age of the WRCs distribution is 5.2 ± 1.8 Myr and 6.4 ± 2 Myr for the nWRCs. The mean ages of the two cluster groups are not statistically different. The WRCs masses appear to be more evenly distributed than the nWRC masses and one typically finds that the WRC mass in a particular galaxy is larger than the nWRC mass.
Physical conditions in H II galaxies
Authors: Kehrig Carolina , Telles Eduardo , Cuisinier François
Published: July 2016

We present a spectrophotometric survey of 111 H ii galaxies. Observations were made at the ESO 1.52m telescope, with the b&c spectrograph. Our sample presents a great overlap with Terlevich et al. 1991. Additional targets come from the Calan-Tololo an Marseille catalogues. All objects have been observed and analysed homogeneously. We analyse their statistical properties and derive physical conditions (reddening, electron temperature, electron density), as well as chemical abundances.
Measuring the evolution of H II and starburst galaxies
Authors: Leão João R.S. , Lacerda Reiner R. , Fernandes Roberto Cid
Published: July 2016

The evolution of starbursts and their young stellar populations is usually studied using evolutionary population synthesis and photo-ionization calculations. We give a more empirical approach to this issue by appling empirical population synthesis techniques to samples of starburst and H ii galaxies, to measure their evolutionary state and correlate the results with their emission line properties. The results are presented using an evolutionary diagram whose axis are the strengths of the young, intermediate and old age components of the population mix. We also recover the long known prediction that the WHβ and the gas extinction decrease as the starburst ages.
Physical properties of low-luminosity galaxies at z ≈ 2
Authors: Lemoine-Busserolle Marie , Contini Thierry , Pelló Roser , Le Borgne Jean-Francois , Kneib Jean-Paul , Lidman Chris
Published: July 2016

We report the results obtained from VLT-isaac near-IR spectroscopy of two low-luminosity z ≃ 1.9 galaxies located in the core of the lensing cluster AC 114. The amplification factor allowed to obtain, for the first time, physical properties (SFR, abundance ratios, mass, etc.) of star-forming galaxies, 1 - 2 mag fainter than in previous studies of LBGs at z ≈ 3.
Synthetic high-resolution line spectra of star-forming galaxies below 1200 Å, based on FUSE spectral libraries of hot stars
Authors: Robert Carmelle , Pellerin Anne , Aloisi Alessandra , Leitherer Claus , Hoopes Charles G. , Heckman Timothy M.
Published: July 2016

We have generated far-UV stellar libraries using spectra of hot stars in the Galaxy and the Large and Small Magellanic Clouds. These libraries were implemented into the stellar population synthesis codes starburst99 and lavalsb and used to compute synthetic spectra of star-forming galaxies. Model spectra for galaxies are presented and variations of the hot star photospheric and wind profiles are discussed. This poster summarizes the work of Robert et al. (2002).
Multiwavelength studies of β Cephei stars
Authors: Cugier H. , Pigulski A. , Polubek G. , Monier R.
Published: July 2016

As first pointed out by Moskalik and Dziembowski (1992) all β Cephei stars lie within the domain of H–R diagram where κ-mechanism effectively drives pulsations in the stellar layers with T ≈ 2×105 K. For most of these objects a chemical composition described by X = 0.70 and Z = 0.02 is sufficient to account for the pulsations, cf. Dziembowski and Pamyatnykh (1993). Recently, Cugier, Dziembowski and Pamyatnykh (1993) have investigated how the present knowledge about nonadiabatic observables of β Cephei stars affects methods of identification of the spherical harmonic degree, l. They found that good photometric and radial velocity data should result in unambiguous identification of l. Cugier, Dziembowski and Pamyatnykh also concluded that nonadiabatic observables can be used to obtain mean stellar parameters of pulsating stars.
Stability of the pulsation of 12 (DD) Lacertae
Authors: Pigulski A.
Published: July 2016

The results of the study of period changes of all pulsational components in the multiperiodic β Cephei-type star, 12 Lac, are summarized.
Period variations in the Beta Cep star α Lup
Authors: Chapellier E. , Valtier J.C.
Published: July 2016

α Lup (HR 5469) is a multiperiodic beta Cep star. According to Shobbrook (1979) and Lampers & Goossens (1982) the main period (P=0.25985 day) corresponding to the radial mode is constant. The amplitude of the secondary period, attributed to a non radial mode, is so small that it does not affect the determination of maximum dates.
Period variations in the Beta Cep star β Cru
Authors: Valtier J.C. , Chapellier E. , Le Contel J.M.
Published: July 2016

β Cru (HR 4853) is a multiperiodic β Cep star. The main period has been found constant between 1958 and 1973 by Cuypers (1982). In order to extend the basis of the ephemeris, we computed two values of radial velocity maxima from individual measurements published by Campbell & Moore (1928) and Sahade & Albarracin (1952). In lack of simultaneous spectroscopic and photometric observations, we used an arbitrary value equal to 0.25 period for the phase lag.
Multiperiodicity in light variations of 53 Persei: results from optical photometry in 1990 October–1991 January
Authors: Huang L. , Guo Z. , Hao J. , Percy J.R. , Fieldus M.S. , Fried R. , Palovski R. K. , Božić H. , Ružić Ž. , Paparó M. , Vetö B. , Dukes R.
Published: July 2016

The B type star 53 Persei was discovered in 1977 by Smith (1977) as the prototype of a separate group of B-type variables showing light and line profile variability. The physical cause of the variability was thought to be nonradial pulsation (NRP) (see, e.g. Smith et al. 1984). However, the NRP model for this star has been questioned by Balona (1986) who suggested the rotational modulation (RM) model to explain the variability. In order to resolve the long lasting debate about 53 Persei, a campaign was initiated to organize coordinated optical photometry and spectroscopy from the ground, and Far-UV photometry from Voyager in 1991 January. This paper presents the results of period analysis on the groundbased UBV data. In another paper, Smith & Huang (1994) report the new identification of pulsation modes using Voyager Far-UV photometry combined with the results from optical observations. Some preliminary results from APT uvby observations taken at a single site are also cited for comparison.
Convective zones in the envelope of massive stars
Authors: Alberts Frank M.
Published: July 2016

In the calculation of stellar models with the Cox–Stewart opacities no convective zones in the outer layers of massive stars appear. The new OPAL opacities (Rogers & Iglesias, 1992) show a significant bump in the opacity near temperatures of log T = 5.2. This opacity effect results in a small convective zone in the envelope of stars with mass ranging from 15 M⊙ to 150 M⊙, apart from possible convective zones caused by ionization. This was also briefly mentioned by Glatzel & Kiriakidis (1993). For stars on the main sequence this zone is small, about 1% of its radius on the zero age main sequence up to 7% at the onset of the core helium burning and contains a negligible amount of mass. For helium burning stars, however, this convective zone moves inward, keeping the same size but containing more and more mass.
Pulsations of Be stars: time series analysis of He I λ4921
Authors: Hahula M. E. , Gies D. R.
Published: July 2016

We present the results of time series observations of He I λ4921 in the spectra of 10 Be stars. The spectra were obtained during multi-wavelength campaigns of IUE spectroscopy, optical photometry and polarimetry, and spectroscopy undertaken to study the connection (if any) between nonradial pulsation (NRP) and mass loss in Be stars. Power spectra have been calculated for the time series of intensity variations within the profiles. These were used to determine periodic variability and phase content to analyze the variations in the context of the NRP model. The observations were made at three observatories (Table 1). All the spectra record at least Hβ and He I λ4921 with a S/N > 200 per pixel and a resolution of ≈ 0.2 Å. We have concentrated the analysis on He I λ4921 as a probe of photospheric variability. This line is generally free of emission (unlike He I λ6678), but in some cases an Fe II λ4924 shell component appears in the red wing.
Overstability of nonradial pulsations in rotating early type stars
Authors: Saio Hideyuki , Lee Umin
Published: July 2016

We present the result of nonadiabatic analysis for nonradial pulsations in uniformly rotating main sequence models.

The angular dependence of the amplitude of a nonradial pulsation mode with an azimuthal order m in a rotating star is represented by a sum of terms proportional to spherical harmonics Ylm(θ, ø) with l = |m|, |m| + 2,… (even mode) or l = |m| + 1, |m| + 3,… (odd mode; see e.g. Saio and Lee 1991 for detail). (In this paper we consider only even modes.) This property makes the analysis complex compared with the case without rotation, in which a single Ylm expresses the angular dependence of a given mode. In our numerical analysis the summation is truncated, in which only first two terms are taken into account. Lee and Saio (1987) give the differential equations for nonadiabatic nonradial pulsations in a uniformly rotating star. Treating the angular frequency of rotation as a free parameter, we applied the nonadiabatic analysis to a main-sequence evolutionary model, for which the effect of rotation is neglected.
Effects of rotation on the main sequence evolution of a 5M⊙ star
Authors: Fliegner J. , Langer N.
Published: July 2016

The way rotation influences the main sequence evolution of early type stars depends strongly on their internal angular momentum distribution. Their convective core mass is not always decreased as a consequence of a reduced “effective mass” due to rotation, since rotation laws close to uniform specific angular momentum may increase Δrad and thereby the convective core mass (Clement). In addition, rotationally induced mixing processes may redistribute angular momentum and chemical elements inside the stars (e.g. Endal & Sofia 1978).
The abundance anomalies in a rotationally evolved 20 M⊙ OBN star model
Authors: Eryurt D. , Kirbiyik H. , Kizilouǧlu N. , Cİvėlek R. , Weiss A.
Published: July 2016

Walborn (1970, 1971) observationally found that OB stars showed nitrogen and carbon abundance anomalies in their atmospheres. Schönberner et al. (1988) found that OBN stars had helium enriched atmospheres. Several different suggestions have been made so far to explain the abundance anomalies in these stars (Paczynski 1973; Walborn 1976; Bolton and Rogers 1978). Maeder (1987) and Weiss et al. (1988) call attention to some possible effects of rotation in mixing chemical elements in Wolf-Rayet stars and B-supergiant stars respectively. They suggested that rotational mixing could explain the high He/H ratios and the high N/C and N/O ratios in the progenitor of 1987A Supernova. Saio et al. (1988) in an attempt to explain the nitrogen and helium enhancement in the progenitor of SN 1987A invoked extensive mixing in their models. They pointed out that such an effective mixing may be produced by rapid rotation. Such observations and ideas were the motivation for the present study.
The circumstellar environment of σ Orionis E
Authors: Short C. Ian , Bolton C. T.
Published: July 2016

The light and spectrum of the magnetic, chemically peculiar Be star σ Orionis E (=HD 37479) vary with the rotational period of 1.19081 d because of the effects of inhomogeneities in the photosphere and circumstellar matter (Walborn and Hesser 1976, Landstreet and Borra 1978, Hunger 1974). In this paper, we describe a model for the distribution of the Hα emitting material in the magnetosphere based on analysis of 24 high quality spectra covering the entire rotation period and published data from other sources.
ROSAT Observations of B and Be Stars
Authors: Cassinelli Joseph P. , Cohen David H.
Published: July 2016

We present results from a survey of X-ray emission properties of near main-sequence B stars, including several Be and β Cephei stars. The main conclusions of our survey are: 1) The X-rays are soft, probably because the shock velocity jumps are small since the terminal wind speeds are small. 2) A major fraction of the wind emission measure is hot, assuming wind theory estimates for the density distribution. A large fraction of the wind is not expected to be hot in current wind shock models. 3) A hard component is found to be present in τ Sco; possible causes are discussed. 4) For the Be stars, the X-rays emission is from a normal B-star wind that is coming from the poles as in the WCD model of Be stars. 5) None of the stars, including the β Cep stars, show noticeable variability in their X-rays. For the normal B stars we conclude from the lack of variability that the shocks are in the form of fragments in the wind instead of spherical shells. 6) Our observations suggest that all B stars are X-ray sources and that there is a basal amount of X-ray luminosity of about 10-8.5Lboi. The hot component in τ Sco and the high X-ray luminosity of B stars detected in the all-sky survey suggests that there is a source of X-ray emission in addition to wind shocks in some B stars.
Infrared spectroscopy of Be/X-ray binaries
Authors: Everall C. , Coe M.J. , Roche P. , Norton A. J. , Unger S. J.
Published: July 2016

We present infrared spectra of 4 Be/X-ray binaries in the K band, and 4 spectra in the J, H and K bands of 2 more sources. The HI IR emission lines are useful determinators of the conditions in the inner regions of the circumstellar disk about the Be star, due to optical depth effects. These are preliminary results, and hope to be followed up by high resolution echelle spectra, where we wish to estimate the velocity field, temperature and density structure of the circumstellar material.
Be star disk structure as implied by X-ray observations
Authors: Saraswat Priyamvada , Apparao Krishna M.V.
Published: July 2016

Compared to several other Be/X-ray binaries, 4U1907+09 has been observed more frequently due to the fact that it is found in an ‘on’ state more often. It also has a short orbital period of ~ 8 days as compared to the long orbital periods commonly found in these binaries. But despite the attention it has received, the exact nature of the primary remains elusive. While some observers maintain it to be a Be/X-ray binary, others prefer to put it into the class of OB supergiants.
FeII line widths as tracers for the geometry of Be star envelopes
Authors: Hanuschik R. W.
Published: July 2016

The geometry of Be star envelopes is not directly observable, apart from those very few cases where interferometry has been successful. This is even more true for the kinematical conditions in these envelopes. An indirect measure of kinematics, density law and geometry can be achieved by comparing line widths of photospheric absorption lines (⇔ v* sin i) and circumstellar emission lines (⇔ v(r) sin i). Hitherto existing determinations of line widths have been, however, quite unsatisfactory. The reason is that in these studies Balmer line parameters were used [see Hanuschik (1989) and references therein] which are strongly broadened by radiative transfer and Thomson scattering in addition to kinematic broadening. Because the question of geometry and kinematics is of crucial importance for understanding the Be phenomenon, I have started a new study, using measurements of the Fe ii λ5317 line. This line shows almost optically thin emission and is broadened primarily by kinematics.
FeII, FeIII and MgII spectra of Be stars
Authors: Barrera L. H. , Dachs J. , Berghöfer T. W.
Published: July 2016

For a total of 33 bright Be stars, archival high-dispersion spectrograms obtained by the International Ultraviolet Explorer (IUE) satellite were analyzed together with optical spectrograms in order to study the FeII, FeIII and MgII spectra in the entire 1600 Å to 6500 Å wavelength range. Ultraviolet FeII resonance lines are always found to be in absorption which usually is of interstellar origin. By applying curve-of-growth methods to equivalent widths measured for FeII multiplets UV-1 through UV-8, column densities of interstellar FeII are derived ranging typically between about 1014 and 1015 cm-2. For a few program stars showing shell-type spectra in the optical region, additional FeII resonance absorption lines are detected starting from excited fine-structure levels above the ground state, pointing to FeII absorption occurring in the dense circumstellar envelope in front of these star. Analysis of their equivalent widths is used to infer typical column densities of circumstellar ground state FeII ions of order 1015 cm-2.