bluuebunny/crossref_metadata_2025 huggingface dataset:
The Sulphur Abundance in Planetary Nebulae
Authors: Ratag Mezak A.
Published: July 2016

Ratag et al (1997) determined the chemical abundances of He, O, N, Ne, S, Ar, and Cl in ~110 planetary nebulae which are likely to be in the Galactic Bulge. The abundances are derived by employing theoretical nebular models as interpolation devices in establishing the ICFs. The overall agreement between the abundances obtained by employing the model-ICFs and those derived from the theoretical models is reasonably good. Based on this, it is of interest to study the reliability of various ICFs as well as to derive some alternative ICFs. The focus of the present study is sulphur.
Structure and Evolution of Planetary Nebula Haloes
Authors: Steffen Matthias , Schönberner Detlef
Published: July 2016

The density structure of the extended haloes of Planetary Nebulae (PN) is generally believed to reflect the previous history of heavy mass loss during the final stages of stellar evolution on the asymptotic giant-branch (AGB). In this review, we discuss different interpretations of the observed PN halo structures in the light of recent numerical simulations combining detailed AGB and post-AGB stellar evolution calculations with time-dependent hydrodynamical wind models.
The Multiple Shell PN NGC 2438: Shell Modeling and the Influence of Different Central Star Models
Authors: Armsdorfer Birgit , Kimeswenger Stefan , Rauch Thomas
Published: July 2016

Modeling the shells of multiple shell planetary nebulae using different model spectra for hot central stars, we found that a blackbody model leads to wrong nebular parameters. We model the density profile of the outer shells, varying the results of hydrodynamical simulations. This leads to a spatial excitation profile which reproduces well the observations.
Ubiquitous High Speed Ejecta in Pne - MyCn 18
Authors: Meaburn J. , Bryce M. , Harman D. J. , López J. A.
Published: July 2016

Supersonic and even hypersonic outflows have been found in a wide variety of PNe using the Manchester Echelle spectrometer (MES; Meaburn et al. 1984). Dramatic examples of these extreme motions found over many years are highlighted here for comparison with their most recent discovery in the bipolar PN, MyCn 18.
Velocity Fields in 9 Southern Planetary Nebulae
Authors: Gesicki Krzysztof , Acker Agnes
Published: July 2016

In 1997 and 1998 we observed 16 PN with the ESO 1.4 m CAT telescope, in the Hα and [NII] lines. We selected 9 PN with fairly symmetric line profiles, these PN we analyzed with the “Torun codes”.
Radio Recombination Lines as a Tool for Study Dynamics of Planetary Nebulae
Authors: Gulyaev Sergei
Published: July 2016

An observational program for study dynamics of planetary nebulae with the help of RRL is discussed. The expansion velocities may be found from observations of radio recombination lines in different wavelength. The method is free of the microturbulence problem inherent in standard spectroscopic methods. Set of theoretical models was computed for NGC 7027. Observations of RRL with n > 150 may allow making choice between models with high and low microturbulence.
Imaging and Spectroscopy of Type I Planetary Nebulae
Authors: Bohigas Joaquín
Published: July 2016

Optical spectra and images in the main optical emission lines were obtained for 21 type I planetary nebulae (PNe). IR images directed towards the detection of shocked molecular hydrogen were secured in 17 of these objects. No evidence of shocked H2 could be found in A 14 and Sh 2-71, and its existence needs to be confirmed in JnEr 1 and M 1-57. Bipolarity is obvious in most of these sources. A 24, JnEr 1 and M 3-5 may be bipolars seen nearly pole-on. The chemical composition of nearly half of these objects indicates that third dredge-up episodes may have occured in their progenitor star. The presence of shock waves in the ionized component is inferred in 9 PNe, where the temperature ratio T(O+2)/T(N+) is large and the Hα/[S II]6724 line ratio small, a typical combination in shock excited plasmas. A larger sample of type I PNe shows that small Hα/[S II]6724 line ratios are usually associated with large temperature ratios.
The Structure of NGC 6309: BRET or Bipolar Outflow?
Authors: Vázquez R. , Miranda L. F. , Olguín L. , Torrelles J. M. , López J. A.
Published: July 2016

Multiwavelength and multitechnique observations towards NGC 6309 are presented. The data consist of λ3.6-cm continuum, ground- and space-based imaging, and high and low-dispersion longslit spectra. The structure of the central region seems to be a distorted, ring of 20″ in diameter. The lack of [N II] emission is conspicuous, as revealed by imaging and low dispersion spectra. Notably, the kinematics of the point-symmetric (PS) structures of NGC 6309 indicates the presence of lobes or cavities as those generally found in bipolar nebulae. The results lead to conclude that the origin of this peculiar morphology is not related to BRETs, but rather to that of a bipolar PN with PS structures in its lobes.
PN and Galactic Chemical Evolution
Authors: Maciel Walter J. , Costa Roberto D. D.
Published: July 2016

Recent applications of PN to the study of galactic chemical evolution are reviewed, such as PN and stellar populations, abundance gradients, including their space and time variations, determination of the He/H radial gradient and of the helium-to-metals enrichment ratio, and the [O/Fe] x [Fe/H] relation in the solar neighbourhood and in the galactic bulge.
Recent HST Surveys of Planetary Nebulae in the Magellanic Clouds
Authors: Shaw Richard A. , Stanghellini Letizia , Mutchler Max , Balick Bruce , Palen Stacy , Villaver Eva , Blades J. Chris , Jacoby George , De Marco Orsola
Published: July 2016

The study of the formation and evolution of planetary nebulae (PNs) has been a subject of active investigation for several decades. In the past 15 years the relationship between nebular morphology and nebular/stellar evolution has been investigated in some detail. Although important insights have been gained, the connection between PN formation and even basic morphological features of the evolving nebula is far from clear. One of the most vexing problems to overcome is the difficulty of obtaining, at least for Galactic PNs where statistical distances must be adopted, reliable dimensions, ages, luminosities, and other physical quantities that are essential for understanding the evolutionary state of individual nebulae. Our emphasis of late has been to obtain high-resolution images of a large sample of PNs in the Magellanic Clouds, where uncertainties in the distances are minimal and selection effects due to, e. g., dust absorption in the Galactic plane do not apply.
Dynamics of the Halo of the Andromeda Galaxy M31
Authors: Halliday C. , Carter D. , Jackson Z. C. , Bridges T. J. , Evans N. W. , Wilkinson M. I.
Published: July 2016

We present an investigation of the halo dynamics of M31 using planetary nebulae velocities. We have performed on-band [OIII] and off-band continuum imaging for a 3.6 square degree area centred on M31 and follow-up spectroscopy for over 600 planetary nebulae candidates. In the future the halo mass will be measured and the mass distribution and velocity anisotropy will be constrained as a function of radius.
Modern Techniques in Galaxy Kinematics: CDI and the Planetary Nebula Spectrograph
Authors: Douglas N. G. , Kuijken K. , Romanowsky A. J. , Merrifield M. R. , Arnaboldi M. , Freeman K. , Taylor K.
Published: July 2016

We report here the successful commissioning of the PN.Spectrograph, the first special-purpose instrument for the measurement of galaxy kinematics through the PN population.
Brown Dwarfs as Ejected Stellar Embryos: Observational Perspectives
Authors: Reipurth Bo , Clarke Cathie
Published: July 2016

We discuss a scenario in which brown dwarfs are formed like stars, except that their full collapse phases are interrupted through dynamical interactions in small multiple systems, leading to the ejection of the lightest member. This disintegration is a stochastic process, often resulting in the expulsion of newborn low mass stars, but when it occurs early enough the ejected stellar embryo will be a substellar object. This process may be so common at early ages that a large fraction of the ubiquitous brown dwarfs could have formed in this manner. Detailed gas dynamical simulations are required in order to better understand the details of the decay of small newborn multiple systems. We discuss the observational consequences of the ejection hypothesis, noting especially the importance of binaries with brown dwarf components as an observational test. Finally, we note that brown dwarfs that have recently been ejected may be so disturbed, by infall from the collapsing core and also by heavy accretion from perturbed circumstellar disks, that traditional spectral and luminosity criteria may fail to identify their substellar nature.
Orbital Migration and the Brown Dwarf Desert
Authors: J. Armitage Philip , A. Bonnell Ian
Published: July 2016

The orbital elements of extreme mass ratio binaries will be modified by interactions with surrounding circumstellar disks. For brown dwarf companions to Solar-type stars the resulting orbital migration is sufficient to drive short period systems to merger, creating a brown dwarf desert at small separations. We highlight the similarities and the differences between the migration of brown dwarfs and massive extrasolar planets, and discuss how observations can test a migration model for the brown dwarf desert.
Probing the Bottom End of the IMF in Orion with Gemini
Authors: W. Lucas Phil , F. Roche Patrick , C. Riddick Fiona
Published: July 2016

We present very deep JHK imaging of the Trapezium Cluster obtained with Gemini South/Flamingos and Gemini North/Hōkūpa'a. These images probe the IMF down to ˜ 2 MJup in a total area of ˜ 8 arcmin2. Several very faint new planetary mass candidates are detected and sources previously detected with UKIRT are verified. Photometry of 124 point sources in this field produces a Luminosity Function which drops to zero at K=18.75. Allowing for modest extinction this corresponds to a possible turn-down in the IMF near 5 Mjup. A minority of PMOs exhibit large K band excesses attributed to hot dust, confirming their extreme youth. Some of the faintest sources are associated with short trails of light of uncertain nature. These may provide a clue to the origin of PMOs, perhaps marking evacuated paths cleared by rapidly moving objects.
A Deep Photometric Search for Substellar Mass Objects in Taurus
Authors: Magnier E. A. , Dougados C. , Ménard F. , L. Martín E. , Magazzù A.
Published: July 2016

We have performed a photometric search for brown dwarf candidates in Taurus using the CFH12K wide-field mosaic camera. We are in the process of obtaining follow-up spectroscopy of likely brown dwarf candidates. We summarize the current state of the photometric analysis and the optical spectroscopy obtained to date. We also discuss the evidence for accretion in these systems.
The Brown Dwarf Deficit in Taurus: Evidence for a Non-Universal IMF
Authors: Briceño César , L. Luhman Kevin , Hartmann Lee , R. Stauffer John , Davy Kirkpatrick J.
Published: July 2016

We present the results of a deep, optical/IR wide field imaging survey of selected fields in the nearby (d~ 140 pc) Taurus star-forming region. We report the discovery of 9 new members with spectral types M5.75–M9.5. We derive an Initial Mass Function encompassing 54% of the known members in Taurus. Comparison with dense regions like the Trapezium Cluster in Orion shows that Taurus has produced x2 less brown dwarfs. We suggest that the lower frequency of brown dwarfs in Taurus may result from the low-density star-forming environment, leading to larger minimum Jeans masses.
Very Low Mass Stellar Populations in Star-Forming Regions: Near-Infrared Luminosity Functions and Mass Functions
Authors: Oasa Yumiko
Published: July 2016

We briefly describe recent studies of the low-mass young stellar populations including substellar objects and of their luminosity functions and mass functions, especially at lower-ends, in different star-forming regions. The mass function is determined by the technique based on the near-infrared photometry for estimating stellar luminosities and then translating them into stellar masses. We compare the local environmental characteristics of regions in which high-mass stars form with those of regions producing only low-mass stars and intermediate stars. We find that there exist numerous very low-mass YSO candidates including young brown dwarfs and young isolated objects with planetary masses in common. Further, the luminosity functions and mass functions in the star-forming regions might not have a uniform shape below the hydrogen-burning limit.
Spectroscopy of Brown Dwarf Candidates in the NGC 1333 Molecular Cloud
Authors: Wilking Bruce , Mikhail Ayman , Carlson Glenn , R. Meyer Michael , Greene Thomas
Published: July 2016

We present an analysis of low-resolution infrared spectra for 25 brown dwarf candidates in the NGC 1333 molecular cloud. Candidates were chosen on the basis of their association with the high column density cloud core, and near-infrared fluxes and colors. We compare the depths of water vapor absorption bands in our candidate objects with a grid of dwarf, subgiant, and giant standards to determine spectral types which are independent of reddening. These data are used to derive effective temperatures and bolometric luminosities which, when combined with theoretical tracks and isochrones for pre-main sequence objects, enable us to estimate masses and ages. Depending on the models considered, a total of 9 to 20 brown dwarfs are identified with a median of age of <1 Myr.
Disks in Brown Dwarf Systems
Authors: Testi Leonardo , Natta Antonella , Comerón Fernando , Oliva Ernesto , D'Antona Francesca
Published: July 2016

We discuss evidence for and properties of disks associated with brown dwarfs in the star-forming region ρ Oph. We derived photospheric parameters from low resolution near infrared spectroscopy and modeled the mid-infrared excess of nine substellar object candidates in the ρ OphISOCAM survey of Bontemps et al. (2001). In all cases, the mid-infrared excess is consistent with the SED expected from irradiated disks. These results suggest that circumstellar disks are commonly associated to young brown dwarfs and planetary-mass objects. Finally, we discuss the possibility of using these data to discriminate between various formation scenarios for substellar objects.
Probing Dust around Brown Dwarfs: The Naked LP 944–20 and the Disk of Cha Hα2
Authors: Apai Dániel , Pascucci Ilaria , Henning Thomas , F. Sterzik Michael , Klein Randolf , Semenov Dimitri , Guenther Eike , Stecklum Bringfried
Published: July 2016

We present the first mid-infrared (MIR) detection of a field brown dwarf (BD) and the first ground-based MIR measurements of a disk around a young BD candidate. We prove the absence of warm dust surrounding the field BD LP 944–20. In the case of the young BD candidate Cha Hα2, we find clear evidence for thermal dust emission from a disk. Surprisingly, the object does not exhibit any silicate feature as previously predicted. We show that the flat spectrum can be explained by an optically thick flat dust disk but not by a flared one.
New M and L Dwarfs Confirmed with CorMASS
Authors: Wilson J. C. , A. Miller Neal , Gizis J. E. , Skrutskie M. F. , Houck J. R. , Davy Kirkpatrick J. , Burgasser A. J. , Monet D. G.
Published: July 2016

We present new M and L-dwarfs confirmed through follow-up of 2MASS color-selected objects with the CorMASS near-infrared spectrograph (R ˜ 300) on the Palomar 60-inch telescope as part of a continuing follow-up survey. Most of the objects are bright (Ks < 13).
Ultracool Neighbors from 2MASS
Authors: L. Cruz Kelle , Neill Reid I. , Lowrance P. J. , Davy Kirkpatrick J. , Liebert J. , Gorlova N. , Cooper C.
Published: July 2016

We present initial results of an all-sky search for cool, low-mass stars and brown dwarfs within 20 pc. We have used the near-infrared photometry provided by the 2-Micron All Sky Survey (2MASS) Second Incremental Data Release to create a target list of 1793 candidates with 6 < J < 17 and J – K > 1. Follow-up observations and existing data have enabled over 85% of the sample to be classified. Spectral types and distances have been derived for over 250 nearby dwarfs, including 39 newly discovered L dwarfs. In this poster, we discuss our selection methods and present preliminary results.
Searching for Wide Binary Brown Dwarfs around Nearby Stars
Authors: Albert Loïc , Doyon René , Nadeau Daniel
Published: July 2016

We have started a program to search for Brown Dwarf (BD) companions to nearby stars (5 ≤ d ≤ 10 pc) on long period orbits (up to 2000 AU) using wide field optical/infrared imaging. Our goals in surveying a volume-limited sample of stars are: 1) to determine the binary fraction of widely separated BDs and help constrain the BD formation processes, 2) to search for very cold BDs, 3) to provide a better determination of the age and luminosity of a BD sample. Observations are currently conducted at three observatories, CFHT (3.6m), CTIO (4m) and Observatoire du mont Mégantic (1.6m) and should yield a sample of ~100 star systems to a detection limit of J ≈ 20.
Faint Companion Detection Using Noise Removal with Speckle Interferometry
Authors: Tyler David W.
Published: July 2016

I use simulated adaptive optics data to demonstrate a noise removal technique exploiting prior knowledge of the angular support of the object. Using both detector-noise limited and speckle-noise limited data, I show that this method can result in significant increases in the sensitivity of speckle interferometry to faint companions under demanding observing conditions.
Light Time Effects in Pulsating Variables and Brown Dwarfs
Authors: Yang Jiang Shi
Published: July 2016

Dwarf cepheids DY Her, AD CMi, and BE Lyn show light time effects, which may be caused by orbital motion due to a low mass unseen companion. Their mass is probably between 0.015 to 0.07 M⊙, so they may be brown dwarfs.
Modeling Brown Dwarfs, L Dwarfs, and T Dwarfs
Authors: Burrows Adam
Published: July 2016

In this contribution, I review a subset of our recent efforts in spectral and opacity modeling aimed at guiding the study of brown dwarfs, L dwarfs, and T dwarfs. I discuss theoretical calculations of the alkali line profiles, newly generated CrH opacities, new evidence for refractory rainout in T dwarfs from optical spectral measurements, and the controversy concerning the distinction between brown dwarfs and planets.
T Dwarf Photometric Variability
Authors: Artigau Etienne , Nadeau Daniel , Doyon René
Published: July 2016

We report on a J and H photometric variability survey of 10 T dwarfs. Four brown dwarfs in the sample show significant J band variability at the 99% confidence level or higher. The amplitude of variation ranges from 2 to 17%. Our data show evidence of variability for late as well as early T dwarfs.
Status of IR Array Technology for Wide-Field NIR Survey Cameras
Authors: Hodapp Klaus W. , Hall Donald N. B.
Published: July 2016

Over the past two decades, infrared detector arrays have evolved from small, highly experimental devices to large format arrays being used in numerous facility class instruments. The next generation of infrared arrays will allow the design of mosaic instruments with very large fields of view that offer exciting new opportunities for large scale surveys in the infrared.
Brown Dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS)
Authors: Hambly Nigel
Published: July 2016

During the final quarter of 2003, UKIRT will take delivery of WFCAM. This new wide–field camera will have a FOV of 0.2 square degrees, and is therefore well suited to large–scale survey work. A consortium of more than 60 astronomers has successfully bid for a large fraction of all UKIRT time over the next 5 years to undertake several public surveys using this new facility. These surveys are collectively known as the UKIRT Infrared Deep Sky Survey (UKIDSS). In this short paper I will describe the project and review the prospects for BD research using UKIDSS data, highlighting some of the major science goals related to BDs that we hope will be achieved.
Microlensing by Free-Floating Brown Dwarfs
Authors: Zinnecker Hans
Published: July 2016

We propose a near-infrared microlensing survey of the central 2 degree field of the Galactic Center, in an attempt to estimate the surface density and mass distribution of distant free-floating brown dwarfs in the bulge and in the disk, acting as lenses of bright stars towards the Galactic Center. We estimate the probability (optical depth) of microlensing events to be 10-7 and the typical timescale (full-width) of the amplification lightcurve to be about 1 week. The necessary wide-field NIR survey technology should soon be available on UKIRT, CFHT, and with VISTA at ESO/Paranal.
Gamma-ray bursts: the most powerful cosmic explosions
Authors: Kaper Lex
Published: July 2016

With the detection of gamma-ray burst (GRB) afterglows, the cosmological origin of GRBs has been firmly established. Recent observations suggest that (long-duration) GRBs are due to the collapse of a massive star forming a black hole. Besides theoretical arguments, observational evidence supporting this hypothesis comes from the coincidence of several GRBs with a supernova. Also, all accurately located GRBs are contained in the optical (restframe UV) extent of distant, blue galaxies. Some of these host galaxies show relatively high star-formation rates, which is expected when massive stars and GRBs are physically linked. Alternatively, GRBs can be produced by the merging of a binary neutron star system, such as the Hulse-Taylor binary pulsar. Very likely GRBs trace the massive-star populations in distant galaxies. With their enormous brightness, GRBs are powerful probes of the early universe, providing information on the properties of their host galaxies, the cosmic star-formation history, and potentially the first generations of massive stars.
Instabilities in the winds of hot stars
Authors: Gomez Edward L. , Williams Robin J.R.
Published: July 2016

We present work investigating the stability of line-driven winds using a non-Sobolev approach. We find that the dense shell structures which characterise the growth of radiation-driven instabilities in one dimensional simulations break up into numerous bow-shaped clumps in two-dimensions.
Wind models and synthetic UV spectra for O-type stars
Authors: Hoffmann Tadziu L. , Pauldrach Adalbert W.A. , Puls Joachim
Published: July 2016

Spectral analysis of hot stars requires adequate model atmospheres, which take into account the effects of non-LTE and radiation-driven winds properly. Here we present significant improvements of our approach in constructing detailed atmospheric models and synthetic spectra for O-type stars (model code wm-basic; see Pauldrach, Hoffmann & Lennon 2001). The most important ingredients of these models with regard to a realistic description of stationary winds are: (i) a rigorous treatment of line blocking and blanketing; (ii) a consistent determination of the radiative line acceleration; (iii) a considerably improved and enhanced atomic data archive providing the basis for a detailed multilevel non-LTE treatment and an adequate representation of the radiative line driving; and (iv) the inclusion of EUV and X-ray radiation produced by cooling zones originating from shock-heated matter. This new tool not only allows to constrain the properties of stellar winds, the stellar parameters, and the abundances via a comparison of observed and synthetic spectra, but also provides the astrophysically important information about the ionizing fluxes of these stars. We use this new method to compute selfconsistent wind parameters for a series of Galactic stars analyzed in the optical and verify the theoretically predicted dependence of the wind momentum on metallicity.
Long-term spectral variability of the O4If+ star HD 15570 in the open cluster IC 1805
Authors: Polcaro V. Francesco , Viotti Roberto F. , Norci Laura , Rossi Corinne , Eenens Philippe R.J. , Corral Luis J.
Published: July 2016

We present preliminary results concerning the O4If+ star HD 15570. Of-type supergiants are believed to represent an evolved evolutionary stage of very high mass stars (Minit > 40 M⊙). Their low numbers and extreme peculiarity make each of these objects worth of continuous monitoring. HD 15570 dominates the very young open cluster IC 1805 and is thought to have had an initial mass ≥ 100 M⊙. Low-, intermediate- and high-resolution spectra were collected at the Loiano and San Pedro Mártir telescopes since 1992. The comparison of our high- and low-resolution spectra shows clear variability of a number of spectral features. It is worth noticing, that the variation of Hα seems to follow a repeated secular trend, increasing its equivalent width from ~ 3Å to more than 8 Å in a few years. At the same time, its profile is varying, from a shape quite similar to the theoretical one corresponding to the Klein & Castor (1978) model C, to a much more developed P-Cygni profile, with a deep blue absorption wing. The possibility of instrumental effects is ruled out by the remarkable constancy of the nearby diffuse interstellar band at 6613 Å and of the He ii 6683 Å absorption. The Hβ profile variability is evident from the comparison of the 1996 and 1998 high-resolution spectra. The emission component, which is clearly visible at all epochs, is absent in the 1996 spectrum when the line appears in pure absorption. No relevant line-profile variation seems to be present in the He ii and N iii lines contributing to the ‘feature f’, that looks remarkably constant, as well as Hγ, while their equivalent widths seem to show a modest amount of random variability.
New neon-abundance results in Galactic WN and WC stars
Authors: Smith John-David T.
Published: July 2016

The fast, dense winds which characterize Wolf-Rayet stars obscure their underlying cores, and complicate the verification of evolving core and nucleosynthesis models. A powerful technique for probing WR core evolution involves measuring abundances of wind-borne nuclear processed elements. Neon, in particular, undergoes a remarkable change in abundance during the later stages of a WR star's lifetime. By the end of the WC phase, it becomes the fourth most abundant element, after He, C and O (Maeder 1983).
The stellar wind geometry of η Carinae
Authors: Smith Nathan , Davidson Kris , Gull Theodore R. , Ishibashi Kazunori
Published: July 2016

HST-stis spectroscopy of the Homunculus reflection nebula around η Carinae provides a rare opportunity to observe a star from more than one direction, and reveals that η Car has an aspherical stellar wind. Relatively high velocities and strong absorption are seen near the polar axis, suggesting higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. The bipolar wind geometry may imply that intrinsically asymmetric ejection helped form the Homunculus. It is also critical for understanding this star's variability and evolution.
FUSE observations of the SMC Wolf-Rayet binary Sand 1 (WO4+O4V): atmospheric eclipses and colliding winds
Authors: St-Louis Nicole , Moffat Anthony F.J. , Marchenko Sergey V.
Published: July 2016

We present FUSE observations of the SMC WO4+O4V binary Sand 1. Our spectra show variations in S iv, C iii, C iv and O vi lines, which we attribute mainly to emission from the shock cone, resulting from the collision between the two winds, and to atmospheric eclipses of the O-star continuum light by the WR wind. From this variability, we deduce a cone opening angle of 120°.
UV and optical quantitative spectroscopy of early B-type supergiants in M 33
Authors: Urbaneja Miguel A. , Herrero Artemio , Lennon Daniel J. , Najarro F. , Puls Joachim , Smartt Stephen J. , Kudritzki Rolf-Peter
Published: July 2016

We present the analysis of UV and optical spectra of M 33 early B-type supergiants. Stellar parameters, metal abundances (Si, Mg, O and N) and mass loss rates are derived from anlyses of optical spectra by means of non-LTE unblanketed unified model atmospheres (fastwind code, Santolaya-Rey, Puls & Herrero 1997). These analyses use wind terminal velocities previously derived from the analysis of UV P-Cygni profiles. Stellar radial gradients of Si, O and Mg are derived for the M 33 disk. Differential abundances of those elements with respect to Galactic counterparts are also presented, along with nitrogen. Finally, the wind momenta of M 33 stars is derived and compared with the one found for Galactic B-type supergiants.
Near-IR spectroscopic search for binary companions to dusty WC stars
Authors: Varricatt Watson P.
Published: July 2016

Many late WC type Wolf-Rayet (WR) stars are known to form dust in their winds. While, in the case of episodic dust makers, it is now clear that dust formation takes place due to a colliding wind phenomenon, we still do not know for sure if binarity is the main reason for dust formation in persistent dust makers. This work is to understand, if persistent dust formation is also due to colliding winds in close binary systems. A systematic search for colliding winds is taken up via high resolution spectroscopy of the He i λ1.083μm emission line. Preliminary indications of binarity in many persistent dust makers are seen.
The winds of Luminous Blue Variables and the mass of AG Carinae
Authors: Vink Jorick S. , de Koter Alex
Published: July 2016

We present radiation-driven wind models for Luminous Blue Variables and predictions of their mass-loss rates. A comparison between our theoretical results and observations of AG Car shows that the variable mass loss behaviour of LBVs is due the recombination/ionisation of Fe iv/iii and Fe iii/ii. A present-day mass of 35 M⊙ for AG Car is derived.
Rotating stellar interior models at Z=10−5 and CNO yields for early galactic evolution
Authors: Meynet Georges , Maeder André
Published: July 2016

We calculate a grid of star models with and without the effects of axial rotation for stars in the mass range between 2 and 60 M⊙ for the metallicity Z = 10–5. We find that in these models primary nitrogen is produced during the He-burning phase by rotational diffusion of 12C into the H-buraing shell. The intermediate mass stars of very low Z are the main producers of primary 14N, but massive stars also contribute to this production; no significant primary nitrogen is made in models at metallicity Z = 0.004 or above. We calculate the chemical yields in He, C, N, O and heavy elements and discuss the chemical evolution of the CNO elements at very low Z. Remarkably, the C/O vs. O/H diagram is mainly sensitive to the interval of stellar masses, while the N/O vs. O/H diagram is mainly sensitive to the average rotation of the stars contributing to the element synthesis.
The evolution of close helium star to neutron star binaries
Authors: Dewi Jasinta D.M. , Pols Onno R.
Published: July 2016

We present the evolution of helium stars in binary systems with a 1.4 M⊙ neutron-star companion which will produce double neutron-star binaries, i.e., systems with helium stars more massive than 2.5 M⊙. We found that mass transfer from helium star less massive than ~ 3.3 M⊙ will end up in a common-envelope phase. If the neutron star has enough time to complete the spiral-in before the core of the helium star collapses, the system will become a very tight double neutron-star binary (P ≈ 0d.01). More massive helium stars do not go through a dynamically-unstable mass transfer. The outcome of binaries with helium star in this range of mass is double-neutron star systems with period of 0d.1-1d, suggesting them to be the progenitor of the observed Galactic double neutron-star pulsars B 1913+16 and B 15344+12. Wide DNS pulsars like J 1518+4904 are produced from helium star-neutron star binaries which avoid Roche-lobe overflow. We are also able to distinguish the progenitors of Type Ib supernovae (as the high-mass helium stars or systems in wide orbits) from those of Type Ic supernovae (as the lower-mass helium stars or systems in close orbits).
On the possibility of partial matter mixing in rotating massive stars
Authors: Staritsin Eugenij I.
Published: July 2016

The principal role of strong horizontal diffusion in overcoming the inhibiting effect of mean molecular weight gradient and in producing partial matter mixing between convective core and radiative envelope of a rotating star, is shown.
Distribution of star-forming complexes and the structure of our Galaxy
Authors: Russeil Delphine
Published: July 2016

The determination of the external galaxies morphology is generally based on their appearance on optical images. At these wavelengths young stellar population and their associated H ii regions, which can be grouped into star-forming complexes, appear preferentially located along spiral arms. Hence, it is naturally to use the same tracers to delineate the arms of our own Galaxy. But, where for external galaxies the distribution of star-forming complexes along the spiral arms is generally evident from direct imaging, for our Galaxy the spiral arms are strung out along the line of sight, leading to the superposition and mixing of information from the different complexes in the spiral arms making it difficult to distinguish them. Thus to access to the spatial distribution of young objects, hence to the large scale structure of our Galaxy, it is required first to identify and collect star-forming complexes (molecular clouds – H ii regions – OB stars) and then to determine their distance. In this framework I review the observational results and difficulties concerning the distribution of star-forming complexes and the determination of the structure of our Galaxy.
Massive star population in circumnuclear star-forming regions
Authors: Álvarez-Álvarez Mar , Díaz Ángeles I. , Castellanos Marcelo
Published: July 2016

Due to their high luminosity, the importance of understanding the massive star formation and evolution of giant Hii regions has become more and more evident in the last few years. A mayor scenario where giant H ii regions form and develop are the very inner parts of some galaxies. These bursts frequently are arranged in a ring-like pattern. We present a study of the stellar populations and gas physical conditions in circumnuclear star-forming regions (CNSFR) based on broad- and narrow-band photometry and spectrophotometric data, which have been analyzed with the use of evolutionary population synthesis and photo-ionization models. It is found that most CNSFRs show composite stellar populations of slightly different ages. They seem to have the highest abundances found in H ii region-like objects, showing also N/O overabundances and S/O underabundaces by a factor of about three. Also, CNSFRs as a class segregate from the disk H ii region family, clustering around higher ionizing temperatures.
Metallicity and Binarity in WC and WO Stars
Authors: Norci Laura , Polcaro V. Francesco , Viotti Roberto F.
Published: July 2016

Median values of the fwhm and equivalent width Wλ of the C iv 581 nm, O v 559 nm and 465 nm emission lines were derived from an extended statistical analysis of WC and WO stars (Norci et al. 2002; see Table 1). We find that the C iv equivalent width shows an increasing trend towards earlier WC subtypes, reaching a maximum value of 95 nm (± 32 %) for the Galactic WC4-6 stars, and decreases by about a factor of three in the hotter WO stars (Figure 1, left). The line appears about twice as strong in the LMC than in the Galactic WC4 stars, and the difference is particularly evident in the non-Galactic WO stars. Such an effect is absent in the O v 559 nm line, which smoothly increases towards WCE and WO stars, with no significant difference between Galactic and non-Galactic WC4 and WO stars. Thus this C anomaly is not an ionization effect; it is, therefore, probably due to a cause that selectively operates on C rather than on O. Different physical conditions in the winds of Galactic and non-Galactic stars, possibly related to the different initial metallicity Z, could be responsible for the anomaly.
Feedback of massive stars on the ISM: a XMM-Newton view of the LMC superbubble N 51D
Authors: Bomans Dominik J. , Rossa Jörn , Weis Kerstin , Dennerl Konrad
Published: July 2016

N 51D (= DEM L 192) appears at first glance as a nearly circular, 120 pc diameter bubble of ionized gas around the LMC OB association LH 54. A deeper look reveals a complex web of filaments and deviations from radial expansion. Using a deep XMM-Newton pointing centered on N 51D we find that diffuse soft X-ray emitting gas fills the whole superbubble as delineated by the Hα filaments. Contrary to recent findings for galactic winds, the correlation between Hα and X-ray surface brightness is not good. The X-ray spectrum of this diffuse gas cannot be fitted with the LMC abundance pattern, but implies an overabundance of at least oxygen and neon, consistent with recent enrichment from supernovae Type II. Some indications for enhanced mixing at the brightest region of the Hα shell and for a beginning outflow of the hot gas were also detected.
QSO absorption lines, winds, and the high-redshift intergalactic medium
Authors: Carswell Robert F.
Published: July 2016

The close similarities in the spectra of the Lyα absorption forests in separate images of gravitationally lensed QSOs at high redshifts provide upper limits for the filling factor of the universe for gas that has undergone recent hydrodynamic disturbances. Strong winds blowing for a substantial fraction of the local Hubble time do not significantly affect the low density regions which fill a large fraction of the volume of the universe. Many of the higher density absorbers appear to be photo-ionized and show some heavy element enrichment. They also contain a cosmologically significant fraction of the baryons and the heavy elements in the universe at that stage of its evolution.
Massive stars in galaxies at high redshift: SMM J 14011+0252
Authors: de Mello Duilia F. , Wiklind Tommy , Leitherer Claus
Published: July 2016

We present high resolution VLT spectra of the optical identification of the high-redshift galaxy SMM J 14011+0252. We concentrate on the C iv 1550Å region of the spectra and compared the data with a spectral synthesis model generated with starburst99.
The ionized gas in and around the Wolf-Rayet galaxy NGC 1741
Authors: López-Sánchez Ángel R. , Esteban César , Rodríguez Mónica
Published: July 2016

Interaction can be the main mechanism that triggers star formation in Wolf-Rayet galaxies. The compact group HCG 31 has one of this objects, NGC 1741. We present new observations of this compact interacting group, in order to analyse the physical conditions and chemical composition of the ionized gas, as well as to estimate the ages of the starbursts.
Complex molecules in Wolf-Rayet ring nebula NGC 2359
Authors: Rizzo J. Ricardo , Martín-Pintado Jesús , Desmurs Jean-François
Published: July 2016

We report the detection and analysis of several molecules arising from the WR nebula NGC 2359 around the WN4 star WR 7 (HD 56925). We have detected 3mm and 1mm rotational lines from 13CO, C18O, HCO+, CS, CN and HCN, and determined lower limits for the SiO. The survey was performed in the southeastern part of the optical nebula, where we previously inferred the presence of dense (104 cm–3) material.
LBV (candidate) nebulae: bipolarity and outflows
Authors: Weis Kerstin
Published: July 2016

The most massive evolved stars (above 50 M⊙) undergo a phase of extreme mass loss, in which their evolution is reversed from a redward to a blueward motion in the H-R diagram. In this phase, the stars are known as Luminous Blue Variables and they are located in the H-R diagram close to the Humphreys-Davidson limit. It is far from understood what causes the strong mass loss or what triggers the so-called giant eruptions, active events in which in a short time a large amount of mass is ejected. Here I present results from a larger project, devoted to better understand LBVs through studying the LBV nebulae. These nebulae are formed as a consequence of the strong mass loss. The analysis concentrates on the morphology and kinematics of these nebulae. Of special concern is the frequently observed bipolar nature of the LBV nebulae. Bipolarity seems to be a general feature and strongly constrains models of the LBV phase, especially of the formation of the nebulae. In addition, we find outflows from LBV nebulae, the first evidence for ongoing instabilities in the nebulae.
Special session on the masses of the most massive stars and the Ω-limit
Authors: Moffat Anthony F.J. , Puls Joachim
Published: July 2016

This is a brief report on the highlights of this informal session attended by over 50 symposium participants for three hours on the day preceeding the symposium.
Photometric and spectroscopic observations of the 53 Per star: ζ Cas
Authors: Sadsaoud H. , Le Contel D. , Chapellier E. , González-Bedolla S. , Le Contel J.M.
Published: July 2016

ζ Cas (HR 153, mv=3.66, vsini=18 kms-1) was classified as a 53 Per variable by Smith (1980). He detected variations in the profile of the 4552 Å Si III line with a period of 0.9 day. The radial velocity and the luminosity were observed to be constant by Abt & Levy (1978) and by Jerzykiewicz (1993) respectively.
Spectroscopical analysis of δ Scuti stars
Authors: Solano E. , Fernley J.
Published: July 2016

δ Scuti are pulsating stars with a characteristic period of several hours, lying in the A2-F5 spectral range and placed on or a little above the main sequence. Unlike the well-known “classical” RR Lyrae or Cepheids, which show a homogeneous pulsational behaviour (i.e. radial modes with large amplitudes), δ Scuti stars have peculiarities: their amplitudes vary from millimagnitudes to tenths of magnitude and their pulsation modes can be both radial and non-radial.
g-Mode instability in the main sequence B-type stars
Authors: Dziembowski W.A. , Moskalik P. , Pamyatnykh A.A.
Published: July 2016

We show that the OPAL opacities, in addition to explaining the origin of β Cep stars pulsations, also predict existence of a large region in the Main Sequence band at lower luminosities, where high-order g-modes of low harmonic degrees, l, are unstable. The excitation mechanism remains the same and is due to the usual κ-effect acting in the metal opacity bump (T ≈ 2 × 105K). The new instability domain nearly bridges the gap in spectral types between δ Set and β Cep stars. Periods of unstable modes are in the range 0.4–3.5 days for l = 1 and l = 2. We propose that this excitation mechanism causes photometric variability in the Slowly Pulsating B-type stars (SPB stars, Waelkens 1991) and perhaps in other B stars whose variability in the same period range has been reported.
The stability of massive stars
Authors: Glatzel W. , Kiriakidis M. , Fricke K.J.
Published: July 2016

An investigation of the stability properties of stellar models describing massive stars is motivated observationally by the necessity to explain the observed Humphreys - Davidson (HD) limit and the variability of the most massive stars known, i.e. the existence of luminous blue variables (LBVs). Theoretically, a determination of the upper mass limit for stable stellar objects together with its physical explanation and interpretation is of fundamental interest.
Photospheric and circumstellar variability of the rapidly rotating O star HD 93521
Authors: Fullerton A. W. , Gies D. R. , Bolton C. T.
Published: July 2016

HD 93521 is an O9.5 V star with several well-documented peculiarities, including: an extremely large projected rotational velocity (400 km/s according to Conti & Ebbets 1977); absorption line profile variations (Fullerton 1990); weak emission at Hα (Irvine 1989); evidence for a rotationally-modified stellar wind in its UV resonance lines (Massa 1992; Howarth & Reid 1993); and stellar wind variability in the form of discrete absorption components (Prinja & Howarth 1986). Thus, HD 93521 provides an ideal laboratory for studying the interaction between rapid rotation and variability in both photospheric layers and the circumstellar environment.
Pulsation in Rapidly Rotating Stars
Authors: Clement Maurice J.
Published: July 2016

The line-profile variables observed on the upper main sequence have been interpreted by some astronomers to be the manifestation of nonaxisymmetric oscillations. More specifically, most of these variables can be modelled by prograde or corotating equatorial waves. In the absence of rotation, these waves have surface velocity distributions which are given simply by spherical harmonics. Unfortunately, the corresponding velocity fields in the presence of rotation are much more difficult to calculate. In this paper, I will summarize what is known about the effect of rapid rotation on the normal mode eigenfunctions of main sequence stars. The principal conclusions are as follows: Low-order, axisymmetric modes couple very strongly to rotation and their velocity distributions are very much different from those of their zero-rotation counterparts. On the other hand, higher-order (shorter wavelength), nonaxisymmetric modes couple only weakly to rotation and, therefore, retain many of the spherical harmonic properties that they possess in the absence of rotation.
Fossil magnetic fields and rotation of early-type stars
Authors: Dudorov A.E.
Published: July 2016

Observational data of the last 10 years allow two main conclusions:

a) Main sequence stars can be separated in two classes: - magnetic (Bp) stars with surface strengths of a dipole or quadrupole magnetic field of Bs ≈ n · (102 − 103) G, n = 2,3,4…7, and - normal main sequence stars (F-O) with magnetic fields Bs ≈ 1 − 100 G (< 300 G);

b) Typical star formation takes place in interstellar molecular clouds with magnetic field strengths B ≈ 10-5 G (See Dudorov 1990).
Multiwavelength observations of the Be-star/X-ray binary EXO2030+375 during outburst
Authors: Norton A.J. , Coe M.J. , Everall C. , Roche P. , Bildsten L. , Chakrabarty D. , Prince T.A. , Stollberg M.T. , Wilson R.B.
Published: July 2016

EXO2030+375 consists of a neutron star in an eccentric 46 day orbit around a 20th magnitude Be-star companion (Coe et al., 1988; Parmar et al., 1989; Stollberg et al., 1993). The Be-star is thought to be surrounded by a shell/disc of material which is responsible for the infrared excess and Balmer emission lines which are characteristic of Be-stars in general. At periastron, the neutron star passes through this circumstellar material, giving rise to enhanced accretion onto the neutron star surface. As a result of this, the X-ray emission (pulsed at the neutron star spin period of 41.8s) increases dramatically, so producing the transient, outburst behaviour which is commonly seen in Be-star / X-ray binaries.
EXOSAT observations of the Be/X-ray binaries 2S0114+65 and 4U2206+54
Authors: Saraswat Priyamvada , Apparao Krishna M.V.
Published: July 2016

The X-ray source 2S0114+65 was identified as a Be star from its optical spectrum. The X-ray spectrum is hard and spectral fits indicate the presence of a large amount of circumstellar matter around the X-ray source. The source also undergoes transient X-ray outbursts as well as flaring activity is present. 2S0114+65 was observed with the EXOSAT satellite on four occasions: on 1983 July 28, 1985 December 29, 1986 January 1 and 2. We have carried out an analysis of the X-ray data on this star.
Photometric and Hα observations of LSI+61°303
Authors: Paredes J. M. , Martí J. , Figueras F. , Jordi C. , Rosselló G. , Torra J. , Marziani P. , Fabregat J. , Reglero V. , Coe M. J. , Everall C. , Roche P. , Unger S. J. , Grunsfeld J. M. , Norton A. J. , Zamanov R.
Published: July 2016

The Be massive X-ray binary LSI+61°303 is a 26.5 days periodic radiosource (Taylor & Gregory, 1984), exhibiting radio outbursts maxima between phases 0.6–0.8. Evidence of a photometric period of similar value has also been reported (Paredes & Figueras, 1986; Mendelson & Mazeh, 1989). The previous spectroscopic radial velocity observations of Hutchings & Crampton (1981) are in agreement with the radio period, and give support to the presence of a companion. We present new optical and infrared photometric observations and high resolution Hα spectra of LSI+61°303.