bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-IR spectroscopic monitoring of WR 140 (WC7pd+O4-5) during the 2001 periastron passage
Authors: Varricatt Watson P. , Williams Peredur M. , Ashok Nagarhalli M.
Published: July 2016

The near-IR spectrum of the periodic dust making WCpd+O4-5 binary WR 140 was monitored to cover the 2001 periastron passage and maximum colliding-wind activity. The He i λ1.083μm emission-line profile showed the appearence of a subpeak on epochs close to periastron passage. The evolution of the subpeak was consistent with the motion of the stars and the colliding wind region. The appearance and evolution of the emission subpeak suggests that the theoretical 1/r dependence of X-ray flux does not hold, so that there is no need to change the values of eccentricity and epoch of periastron passage derived from the RV orbit. JHK spectra show variations of the continuum and and dilution of the emission lines, in agreement with the production and cooling of dust.
Search for magnetic fields in A-type supergiants
Authors: Verdugo Eva , Talavera Antonio , de Castro Ana I. Gómez , Henrichs Huib F.
Published: July 2016

We have searched for magnetic signatures in A-type supergiants. The obtained magnetic values for seven of these stars are presented here.
Observed instabilities in OB and Wolf-Rayet stars
Authors: Marchenko Sergey V.
Published: July 2016

A wealth of recent observations confirms that the fast, dense winds of OB and Wolf-Rayet (WR) stars are highly structured, with the structures resulting from the inherently unstable nature of a radiatively-driven wind, as well as being triggered from the underlying photosphere. This review mainly addresses variability patterns observed in the winds and photospheric regions of presumably single stars. Schematically we divide the detectable structures into two broad categories: small-scale and large-scale inhomogeneities, with the former mainly of a stochastic behavior/origin, and the latter frequently demonstrating a recurrent, even periodic, behavior. We then discuss the nature and nurture of instabilities, highlighting phenomenological similarities and differences in the variability of OB and WR stars.
The pre-supernova evolution of rotating massive stars
Authors: Heger Alexander , Woosley Stan E. , Langer Norbert
Published: July 2016

Massive stars are born rotating rigidly with a significant fraction of critical rotation at the surface. Consequently, rotationally-induced circulation and instabilities lead to chemical mixing in regions that would otherwise be stable, as well as a redistribution of angular momentum. Differential rotation also winds up magnetic fields, causing instabilities that can power a dynamo and magnetic stresses that lead to additional angular momentum transport. We follow the evolution of typical massive stars, their structure and angular momentum distribution, from the zero-age main sequence until iron core collapse. Without the action of magnetic fields, the resulting angular momentum is sufficiently large to significantly affect the explosion mechanism and neutron star formation. Sub-millisecond pulsars result that could encounter the r-mode instability. In helium cores massive enough, at least at low metalicity, the angular momentum is also sufficiently great to form a centrifugally supported accretion disk around a central black hole, powering the engine of the ‘collapsar’ model for GRBs. Including current estimates of the effect of magnetic fields still allows the formation of rapidly rotating (~ 5-10 ms) pulsars, but might leave too little angular momentum for collapsars.
Explosions from stellar collapse
Authors: Fryer Chris L.
Published: July 2016

The collapse of a massive star releases a considerable amount of gravitational potential energy. This energy is believed to be the power source of some of the largest explosions in the universe: supernovae, hypernovae, gamma-ray bursts. In this proceedings, we review the mechanisms by which the potential energy from stellar collapse can be tapped to produce these strong explosions, emphasizing how our understanding of massive stars can help constrain these mechanisms.
Aspherical supernova explosions
Authors: Höflich Peter A. , Baade Dietrich , Khokhlov Alexei M. , Wang Lifan , Wheeler J. Craig
Published: July 2016

Core collapse supernovae (SN) are the final stages of stellar evolution in massive stars during which the central region collapses, forms a neutron star (NS), and the outer layers are ejected. Recent explosion scenarios assumed that the ejection is due to energy deposition by neutrinos into the envelope, but detailed models do not produce powerful explosions. There is new and mounting evidence for an asphericity and, in particular, for axial symmetry in several supernovae which may be hard to reconcile within the spherical picture. This evidence includes the observed high polarization and its variation with time, pulsar kicks, high velocity iron-group and intermediate-mass elements material observed in remnants, direct observations of the debris of SN 1987A, etc. Some of the new evidence is discussed in more detail. To be in agreement with the observations, any successful mechanism must invoke some sort of axial symmetry for the explosion. We consider jet-induced/dominated explosions of core collapse supernovae. Our study is based on detailed 3-d hydrodynamical and radiation transport models. We find that the observations can be explained by low velocity, massive jets which stall well within the SN envelope. Such outflows may be produced by MHD-mechanisms, convective dominated accretion disks on the central object or asymmetric neutrino emissions. Asymmetric density/chemical distributions and, for SN 2002ap, off-center energy depositions have been identified as crucial for the interpretation of the polarization.
Evolution of Wolf-Rayet stars in binary systems: analysis of distributions of masses and orbital eccentricities
Authors: Cherepashchuk Anatol M. , Karetnikov Valentin G.
Published: July 2016

It is shown that up to 90% of the known WR+O binaries have been formed as a result of the mass transfer in O+O binary systems.
Model atmospheres of massive zero-metallicity stars
Authors: Lentz Eric J. , Hauschildt Peter H. , Aufdenberg Jason P. , Baron Ed
Published: July 2016

We have calculated detailed, fully non-LTE, model atomospheres for massive zero-metal stars. We find the atmospheres of massive primordial stars become unbound due to radiation pressure on lines and continua over a much larger fraction of their evolution than previously expected.
The Galactic distribution of Wolf-Rayet stars: an optical and infrared approach
Authors: van der Hucht Karel A.
Published: July 2016

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars (van der Hucht 2001), lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries since then bring the census to ≳ 253 WR stars, including ≳ 27 WNL and 13 WCL stars within 50 pc of the Galactic Center. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood (d < 3 kpc) a projected surface density of 2.7 WR stars per kpc2, a NWC/NWN number ratio of 1.3, and a WR binary frequency of 40%. Compared with other Local Group galaxies, the NWC/NWN number ratio in the solar neighborhood is a factor ~2 above the observed metallicity-dependent trend. This could imply that some 30 galactic WN stars in the d < 3 kpc volume are still hiding. Preliminary results of infrared photometric distance determinations are shown. The galactocentric distance (RWR) distribution per subtype shows RWN and RWC decreasing with later WN and WC subtypes. The observed trend is more indicative of WNE → WCE and WNL → WCL subtype evolution than of WNL → WNE and WCL → WCE subtype evolution.
Wolf-Rayet stars in Local Group starbursts
Authors: Drissen Laurent
Published: July 2016

I describe recent spectroscopic observations of Wolf-Rayet stars in three giant H ii regions of M 33 and in the Local Group starburst galaxy IC 10.
Stellar content of obscured compact H II regions
Authors: Hanson Margaret M. , Kaper Lex , Bik Arjan , Comerón Fernando , Puls Joachim , Jokuthy Alexander , Kudritzki Rolf-Peter
Published: July 2016

Near-infrared, spectroscopic studies of central ionizing sources of very young H ii regions is presented in conjunction with a recently available, sophisticated atmospheric code to constrain the physical conditions and environment of very massive stars at very early stages of evolution. Combining high quality near-infrared spectroscopy of very young massive stars with model atmosphere calculations should allow for the most accurate quantitative determination of Teff, rotation, L, and log g, and to search for binaries and possible disk or in-fall signatures in forming or recently formed massive stars. These characteristics make up a vital boundary condition constraining theories on massive star formation.
Cygnus OB2 at all wavelengths
Authors: Knödlseder Jürgen
Published: July 2016

The Cygnus X region is one of the most nearby star formation regions within our Galaxy, that is recognised by prominent emission throughout the entire electromagnetic spectrum, from radio to gamma-ray waves. The centre is populated by the peculiar stellar cluster Cyg OB2, traditionally classified as OB association, but in the light of modern data more likely the prototype of a young globular cluster within our own Galaxy. Heavily shredded by dense molecular clouds this object has been less thoroughly studied than other, more distant star formation complexes in the Milky Way. I will review our current knowledge about this object, by exposing its properties and that of its environment throughout the entire electromagnetic spectrum. Particular emphasis will be given to infrared, radio-continuum, X-ray, and gamma-ray line observations that find in Cyg OB2 a text-book case for multiwavelength studies.
Galactic starburst NGC 3603 from X-rays to radio
Authors: Moffat Anthony F.J. ,   the XMEGA consortium
Published: July 2016

While NGC 3603 is often quoted as the most massive visible Giant H ii Region in the Galaxy, there are other similar and even more massive regions now being found towards the inner Galaxy in the near-IR. Nevertheless, NGC 3603 still retains the status of clone to the dense core-object in 30 Dor, R 136 — but 7x closer and 49x less crowded! This paper summarizes the most recent findings concerning NGC 3603's color-magnitude diagram (CMD), initial mass function (IMF), mass segregation and stellar content — including its unusually luminous H-rich WNL members — down to its pre-main-sequence stars near the H-burning limit. Of special relevance are new high-resolution X-ray and radio images as related to merging/colliding winds and three massive proplyd-like objects. NGC 3603 is a somewhat younger, hotter, scaled-down version of typical starbursts found in other galaxies.
Wolf-Rayet stars at 1 - 2 Mpc
Authors: Crowther Paul A. , Abbott Jay B. , Drissen Laurent , Schild Hansrüdi , Schmutz Werner , Royer Pierre , Smartt Stephen J.
Published: July 2016

We present new narrow-band imaging and optical spectroscopy of Wolf-Rayet stars in the Local Group dwarf galaxy IC 10 (Gemini-N- gmos) and Sculptor group spiral galaxy NGC 300 (VLT fors2).
Young stellar populations in several photometric systems
Authors: Girardi Léo , Bertelli Gianpaolo , Chiosi Cesare , Marigo Paola
Published: July 2016

We report on two recent improvements to the library of stellar models from Padova. (i) A new set of massive stellar models has been computed for the metallicity Z = 0.001, thus filling an important gap in the previously existing library. (ii) We started a project aiming to convert the complete set of isochrones into a wide variety of photometric systems.
A HST study of young massive star clusters in compact H II regions of the Magellanic Clouds
Authors: Heydari-Malayeri Mohammad , Charmandaris Vassili , Deharveng Lise , Meynadier Frédéric , Rosa Michael R. , Schaerer Daniel , Zinnecker Hans
Published: July 2016

We present our results on high resolution imaging and spectroscopy using the HST of six high-excitation ‘blobs’ (HEB). HEBs constitute a rare class of compact H ii regions in the Magellanic Clouds. Contrary to the typical H ii regions of these galaxies, which are extended structures with sizes greater than 50 pc, the compact H ii regions are an order of magnitude smaller having diameters of less than about 3 pc. HEBs are believed to be the final stages in the evolution of the ultra-compact H ii regions, whose Galactic counterparts are detected only at infrared and radio wavelengths. We find that despite their small size, HEBs are in general excited by more than one newborn massive star. Color-magnitude diagrams of the exciting stellar population indicate that it is consistent with an O6-O8 type, and far-UV spectroscopy with HST-stis of several of these stars further confirms their youth. Surprisingly though, it also shows an astonishing weakness of their wind profiles and their sub-luminosity, up to ~ 2 mag fainter in MV than the corresponding dwarfs. Our analysis suggests that these stars are probably in the Hertzsprung-Russell diagram locus of a particularly young class of massive stars, the so-called Vz luminosity class, as they are arriving on the zero age main sequence.
A near-infrared survey for galactic Wolf-Rayet stars
Authors: Homeier Nicole L. , Blum Robert D. , Conti Peter S. , Pasquali Anna , Damineli Augusto
Published: July 2016

Most of the Milky Way's evolved massive stellar population is hidden from view. We can attempt to remedy this situation with near-infrared observations, and in this paper we present our method for detecting Wolf-Rayet stars in highly extincted regions and apply it to the inner Galaxy. Using narrow-band filters at K-band wavelengths, we demonstrate how WR stars can be detected in regions where they are optically obscured. Candidates are selected for spectroscopic follow-up from our relative line and continuum photometry. The final results of applying this method with a near-IR survey in the Galactic plane will provide a more complete knowledge of the structure of the galactic disk, the role of metallicity in massive stellar evolution, and environments of massive star formation. In this paper we briefly describe the survey set-up and report on recent progress. We have discovered four emission-line objects in the inner Galaxy: two with nebular emission lines, and two new WR stars, both of late WC subtype.
Synthetic X-ray emission from starburst regions
Authors: Norci Laura , Meurs Evert J.A.
Published: July 2016

We have used a population synthesis programme to calculate the soft X-ray emission from the 30 Dor cluster. Contributions from the single and binary stellar population are included. The intended future use of the programme is the simulation of extra-galactic starbursts. Nearby clusters with violent star-formation activity provide suitable training grounds. Using our programme, we confirm that the stellar population of 30 Dor cannot by itself produce the totality of the observed soft X-ray emission.
Wolf-Rayet populations in starburst galaxies
Authors: Norris Richard P.F. , Smith Linda J. , Crowther Paul A.
Published: July 2016

Recent advances in atmosphere codes now permit the calculation of realistic grids of hot star atmospheres. Here we use the new O and WR star atmosphere of Smith, Norris & Crowther (2002) with an updated version of the evolutionary synthesis code starburst99 to predict the population of WR stars in a variety in astrophysical conditions. We present a series of synthetic starburst spectra in the optical region which shows the time evolution of the WR-bumps at ~ 4650 Å and ~ 5800 Å.
Classification of Wolf-Rayet stars in NGC 595 in M 33 through high-spatial resolution observations
Authors: Royer Pierre , Lundström Ingemar , Vreux Jean-Marie
Published: July 2016

NGC 595 is, after NGC 604, the second most luminous H ii region in the Milky Way's neighbouring spiral galaxy M 33. Its Wolf-Rayet star content has mainly been unveiled by two different channels. On the one hand, the stellar population of NGC 595 has been resolved and its WR stars identified through online/off-line H ii λ4686 observations realised with the HST. Nevertheless, due to the limited number of filters used, this did not give any information on the WR spectral subtypes. On the other hand, spectroscopic observations of NGC 595, realised at optical and ultraviolet wavelengths, have enabled the determination of some spectral subtypes, but this time, the lack of angular resolution did not allow to resolve the whole population. Thanks to our photometric technique, based on five dedicated narrow-band filters, we present here a determination of the spectral subtypes of NGC 595 WR stars which for the first time combines high-angular resolution and high-‘spectroscopic’ discrimination capabilities.
Hidden star clusters in the starburst galaxy He 2-10
Authors: Vacca William D. , Johnson Kelsey E. , Conti Peter S.
Published: July 2016

N-band (10.8 μm) imaging of the blue compact starburst galaxy He 2-10 reveals the presence of four emission regions, which have no optical or near-IR counterparts. These sources correspond to the ‘ultradense H ii’ regions recently identified in 2cm and 6cm radio maps of this galaxy. We have used the N-band data to place constraints on the properties of the stellar clusters, that are deeply embedded within these dust-emitting regions.
Massive stars in low-redshift galaxies
Authors: Treyer Marie-A.
Published: July 2016

I summarize the method commonly used to estimate the current star formation rate per unit volume as a function of redshift from various star formation diagnostics, as well as the often conflicting results from the various multi-wavelength datasets collected in recent years. Combined together, and with the help of theoretical and empirical models, these results allow us to address the issues of excitation, reddening, metallicity, and star formation history in individual galaxies at low redshift. They seem to point to the fact, that a lot of the star formation in the local universe, and potentially at all redshift, occurs in burst mode rather than continuously.
Massive star populations in Lyman break galaxies
Authors: Pettini Max , Rix Samantha A. , Steidel Charles C. , Shapley Alice E. , Adelberger Kurt L.
Published: July 2016

Massive stars provide most of our current knowledge of the first star forming galaxies in the universe via their ultraviolet and optical spectra redshifted into the visible and near-infrared bands. Here I briefly review the growing body of data on these early stellar populations from which star formation rates, the initial mass function, chemical abundances, ages, and dust reddenings are being deduced. New evidence also shows the dramatic impact which massive stars have on their galactic and intergalactic environments.
Abundances ratios in star-forming galaxies: clues to galaxy evolution
Authors: Contini Thierry , Treyer Marie-A. , Mouhcine Mustapha
Published: July 2016

We show in this contribution that detailed studies of chemical abundances in UV-selected, H ii and starburst nucleus galaxies, together with the development of new chemical evolution models, put strong constraints on the evolutionary stage of starburst galaxies in terms of star formation history. Although the samples of high-redshift galaxies are still too small for statistical studies, the preliminary results give insight into the nature and evolution of distant star-forming objects and their link with present-day galaxies.
Gamma-rays from massive stars in Cygnus and Orion
Authors: Diehl Roland , Kretschmer Karsten , Plüschke Stefan , Cerviño Miguel , Hartmann Dieter H.
Published: July 2016

Radioactive 26Al, ejected by massive stars through winds and supernova explosions, leads to γ-ray line emission that can serve as a probe of the interstellar environment in and near young star clusters. The ~ 1 Myr decay time of 26Al is long enough to allow transport over significant distances, which can cause substantial angular offsets between γ-ray emission and cluster stars. Details of such offsets are determined by the morphology of the ISM. We discuss observations in Cygnus and Orion, and models based on population synthesis methods.
The Wolf-Rayet population in the galaxy CTS 1026
Authors: Gräfener Götz , Koesterke Lars , Hamann Wolf-Rainer
Published: July 2016

The blue compact H ii galaxy CTS 1026 shows very strong WR emission features (Wλ(4680) = 17 Å and Wλ(5800) = 10 Å). We present high s/n optical spectra of the nucleus of this object, augmented by IUE UV spectra. By analysis of the WR profile shapes, we determine the dominant spectral types and the number of WN and WC stars in the star forming region. The number of O-type stars is determined by comparing the observed UV to optical flux distribution to population synthesis models.
Chemical abundances of the H II regions NGC 5461 and NGC 5471 in M 101, Derived from echelle spectrophotometry
Authors: Luridiana Valentina , Esteban César , Peimbert Manuel , Peimbert Antonio
Published: July 2016

We present high resolution spectroscopic data of the two giant extragalactic H ii regions NGC 5461 and NGC 5471 in M 101. We calculate the physical conditions in the two nebulae with a large number of diagnostics, and determine their chemical abundances by applying ionization correction factors (icfs) to the observed ionic abundances. The comparison of the icfs based on photo-ionization models (Luridiana & Peimbert 2001; Luridiana et al. 1999) to those computed following the prescriptions by Mathis & Rosa (1991) shows large discrepancies for several elements, including nitrogen, neon and chlorine.
Shocked CO and 13CO around Wolf-Rayet ring nebulae
Authors: Rizzo J. Ricardo , Martín-Pintado Jesús , Desmurs Jean-François
Published: July 2016

We show CO and 13CO maps toward the WR nebulae NGC 2359, NGC 6888 and Anon (WR 134). We determine global parameters and discuss the probable origin of this gas. Nowadays it is becoming clear that molecule formation and survival is be possible around massive evolved stars.
Spectrophotometry of six high-excitation compact H II regions in the Magellanic Clouds
Authors: Testor Gérard
Published: July 2016

Series of CCD long-slit spectra have been obtained in the 3600-10000 Å range, with the ESO 1.5m telescope, for the six brightest compact H ii regions in the LMC and SMC: N 11A, N 160 A1-A2 and N 88A, N 81 and N 26A-B, respectively. For each region the spectral type of its complex exciting source is given. From the emission-line intensities we have derived the gas electron density and temperature, and computed the chemical abundances of He, O, N, Ne, S, and Ar, which we compare with the ones found for other H ii regions in the Magellanic Clouds.
The stellar population in the dwarf starburst galaxy NGC 1705
Authors: Vázquez Gerardo A. , Leitherer Claus , de Mello Duilia , Heckman Timothy M. , Meurer Gerhardt R. , Martin Crystal L. , Sembach Kenneth R.
Published: July 2016

We report preliminary results from high-resolution UV spectroscopy of the super star cluster 1 in the nearby dwarf starburst galaxy NGC 1705, using HST-stis. These new observations can help us to quantify accurately the stellar content in this super cluster. Together with high quality spectra from SMC stars and the evolutionary synthesis code starburst99, we estimate an age for this cluster of 12±3 Myr, in agreement with previous studies. The measured dynamical mass and the theoretical L/M ratio suggest a normal IMF down to the hydrogen-burning limit.
A high-resolution study of η Carinae's outer ejecta
Authors: Weis Kerstin , Corcoran Michael F. , Davidson Kris , Humphreys Roberta M.
Published: July 2016

η Car is a very luminous and unstable evolved star. Outflowing material ejected during the star's giant eruption in 1843 surrounds it as a nebula, which consists of an inner bipolar region, coined the Homunculus, and the Outer Ejecta. The outer ejecta is very filamentary and shaped irregularly. Kinematic analysis, however, shows a regular bi-directional expansion, despite of the complex morphology. Radial velocities in the outer ejecta reach 2000 km s–1 and give rise to X-ray emission, as first detected by ROSAT. We will present a detailed study of the outer ejecta based on HST images, high-resolution echelle spectra for kinematic studies, images from Chandra-acis and HST-stis spectra.
Summary of the Symposium
Authors: Conti Peter S.
Published: July 2016

I have put together a necessarily limited summary of the main threads of this Symposium.
Special session on recent advances in nebular diagnostics
Authors: Schaerer Daniel , Crowther Paul A. , Oey M. S.
Published: July 2016

Nebular emission-line spectra offer fundamental tests for models of stellar atmospheres, and ultimately, they offer important probes of massive star properties in situations where the stars themselves are unresolved or obscured. Presentations in the first half of this special session focused on the impact of revised stellar properties for O-type and Wolf-Rayet stars on the effective temperature scale and on their Lyman continuum fluxes, whilst the second half emphasized the relationship of nebular diagnostics with stellar atmospheres.
High-resolution spectroscopy of Beta Cephei stars
Authors: Waelkens C. , Van Winckel H. , de Mey K.
Published: July 2016

We give a progress report on an observational program intended to determine detailed chemical abundances of β Cephei stars and constant stars with similar temperature and gravity. There is some evidence that non-variable stars have a lower metal content than variables, as the recently found pulsation mechanism would suggest.
Photometric variability in early B stars I. 53 Arietis
Authors: Bedolla Salvador González
Published: July 2016

Known as well as β CMa stars, the classical β Cep stars are a group of variables of spectral type between BO to B2 and luminosity classes II to IV with light and radial velocity periods between 3 and 7 hours and radial velocity ranges usually < 50 km/sec. Their photometric amplitudes are usually < 0.1 mag in the visible. The light curves are approximately sinusoidal (however, multiple modes are frequently detected with low amplitudes), which lag about 90° behind the radial velocity curve and the color changes in the blue and visual spectral regions are small. Color and luminosity show that maximum temperature coincides with minimum radius. Probably not all the stars in this spectral range are variables; most investigators searching in this region for β Cep variables have observed that a large number of stars in this zone are constant in light. Also, the β Cep stars are not different spectroscopically from nonvariable stars of the same MK type.
NRP mode typing for 53 Persei: results from Voyager photometry
Authors: Smith Myron A. , Huang Lin
Published: July 2016

Huang et al. (1994) have conducted an extensive photometric campaign on the prototypical nonradially pulsating (NRP) star 53 Per and confirmed the pair of frequencies at 0.46 cy d-1 (dominant) and 0.60 cy d-1 originally reported by BS79. In an analysis of these two modes, SP79 underestimated the effects of the Balmer jump on this star's color variation, leading them to an erroneous conclusion that geometric effects dominate the color variations and also that the modes are described by indices l=3, -m = 3 and 2. Herein we describe results from Voyager 2 observations obtained during Lin's optical campaign. The amplitudes derived for these Far-UV data using the optical ephemeris provide for the first time a large enough wavelength baseline to discriminate in favor of thermal effects over geometrical ones in producing NRP light variations. In addition, they allow the dominant mode to be constrained to l = 2 (or 1).
The peculiar binary system HR 8891 (ET And)
Authors: Kuschnig R. , Weiss W. W. , Piskounov N. , Ryabchikova T. , Kreidl T.J. , Alvarez M. , Bedolla S.G. , Bus S.J. , Guo Z. , Hao J. , Huang L. , Kupka F. , Le Contel D. , Le Contel J.M. , Osip D.J. , Panov K. , Polosukchina N. , Sareyan J.P. , Schneider H. , Valtier J.C. , Zboril M. , Žižňovský J. , Zverko J.
Published: July 2016

ET And is a binary system with a B9 Si star as the main component (Porb = 48.308d, e=0.46). Controversial claims in the literature concerning pulsation with periods ranging from few minutes to few hours and with variable amplitudes indicated a challenging target and motivated us to organize several photometric and spectroscopic observing campaigns. The problem with pulsation of ET And is that Teff and log g put this star in the cool domain of Slowly Pulsating B-type (SPB) stars, but the pulsation periods would be too short by a factor of about four, relatively to the shortest hitherto known periods for SPB stars.
TAMS companions of classical cepheids
Authors: Evans Nancy Remage
Published: July 2016

IUE low resolution spectra are an excellent way to determine the temperatures of the hot companions of binary Cepheids. The spectral types of the companions are derived by comparing the spectra with the spectra of standard stars. Absolute magnitudes are calculated from the magnitude difference between the two stars and the absolute magnitude of the Cepheid. In this study, eight binaries containing a Cepheid and a hot companion evolved beyond the ZAMS are discussed.
Pulsation of Wolf–Rayet stars: WR40
Authors: Schneider H. , Kiriakidis M. , Weiss W.W. , Glatzel W. , Fricke K.J.
Published: July 2016

In the past several Wolf–Rayet stars have been investigated photometrically by different authors to search for fast pulsations. So far all results were negative. However, in 1992 Blecha, Schaller & Maeder published a 627sec period with a semi–amplitude of about 2.5mmag for the Southern Wolf–Rayet star WR40 (HD96548).
Activity of the Be star 28 Cygni: 1985–1991
Authors: Ružić Ž. , Vujnović V. , Pavlovski K. , Božić H. , Percy J. R. , Attard A. , Harmanec P. , Horn J. , Koubský P. , Juza K.
Published: July 2016

28 Cyg (V1624 Cyg, HD 191610, HR 7708; B2e, v sin i = 310 km s-1) has been the target of several observational projects, and in 1988 of a large international campaign. This attention was inspired by several photometric studies and especially by the 1985 nearly simultaneous optical and UV spectroscopic monitoring by Peters & Penrod (1988). They found that the line-profile variations were controlled by two frequencies, 1.45 c/d, and 7.43 c/d, which they identified with sectorial pulsations of modes l = 2, m = +2 and l = 10, m = +10. Rapid changes (0.5 to 1 hr) of the CIV wind profile were found; its equivalent width appeared to correlate with the phase of the l = 2 mode. Pavlovski & Ružić (1990) - who independently analysed Hvar 1985 UBV photometry of 28 Cyg - found periodic light variations with a double-wave light curve and a frequency of 1.54 c/d. However – because of the residual scatter around the mean light–curve – the authors tentatively suggested possible multiperiodicity (1.54, 1.33, and 0.95 c/d).
Time-series analysis of the O4 supergiant ζ Puppis
Authors: Reid Andy
Published: July 2016

Preliminary results of a time-series analysis on a sequence of high dispersion, high-signal-to-noise, optical echelle spectra of the O4 supergiant, ζ Puppis (HD 66811), are presented. Lines of Hei λ5876Å, Heii λ5411Å, Niv λ6381Å and Civ λλ5801, 5812Å are analysed; they show variations in line shape and equivalent width, with ‘bumps’ and ‘dips’ seen moving from blue to red within the line profile. The qualitative pattern of variability seen in all these lines is similar.

A Fourier technique, incorporating the iterative clean algorithm, was used on the individual wavelength samples. A periodicity of 8.5-hrs was detected in Heii, and strongly suspected in the remaining absorption lines. This periodicity seems to rule out wind variability as the principal origin for the optical line profile variations seen in ζ Puppis.
Observations of Magnetic Fields in B Stars
Authors: Bohlender David A.
Published: July 2016

Globally ordered magnetic fields are known to exist in non-degenerate stars with spectral types between approximately F0 and B2. Among the B stars, and in order of increasing effective temperature, these include the Bp Si stars, helium-weak stars, and the helium-strong stars. These rather remarkable objects present us with an excellent opportunity to quantitatively examine the possible effects of magnetic fields on the photospheres, winds, and circumstellar environments of hot stars. In this paper we review some of the observations of the magnetic fields and field geometries of magnetic B stars, and also briefly discuss the success of attempts to measure magnetic fields in hotter OB and Be stars. We point out some of the interesting observational similarities of the helium-weak and helium-strong stars to Be and other hot stars, including their spectroscopic and photometric variability, variable winds as demonstrated by the UV resonance lines of C IV and Si IV, and their non-thermal radio emission. Continuing work also suggests that a considerable fraction of the rapidly rotating magnetic helium-peculiar stars are in fact variable Be and Be shell stars.
Effects of X-rays on the ionization state of Be star winds
Authors: MacFarlane J. J.
Published: July 2016

It is important to understand the ionization state of Be star winds for several reasons, including: (1) if known, mass loss rates can be determined from UV P Cygni profiles; (2) the radiation line driving force which accelerates the winds depends on the ionization distribution; and (3) analysis of line profiles, in conjunction with polarization data, can help assess the credibility of various hypotheses for the assymetric nature of Be star winds.
The polarization of Hβ in γ Cas
Authors: Jiang Y.M. , Walker G.A.H. , Dinshaw N. , Matthews J.M.
Published: July 2016

High resolution (0.15 Å/pixel) spectropolarimetry across the Hβ emission line of the Be star γ Cas is presented (solid line in Figure B), as well as the intensity profile (Figure A). Earlier observations of the linear polarization across the emission lines (PL) in Be stars (Coyne 1975, Poeckert 1975) found that PL is inversely proportional to the total intensity of the emission line. However, our data clearly show that the width of the polarization profile is much wider than that of the emission line. The dotted line in Figure B gives PL, based on the relationship of:
which follows directly from Coyne (1975), where IA is the intensity of the underlying Hβ absorption feature, Itotal the observed intensity profile, and PC the polarization in the adjacent continuum. The underlying stellar profile of Hβ (dotted line in Figure C), adopted from models by Hubeny (1988), gives a good match to the wings of the depolarization profile.
Long-term spectroscopic and polarimetric variations of the Be star κ Dra
Authors: Arsenijevic J. , Jankov S. , Krsljanin S. , Hubert A.M. , Hubert H. , Chambon M.T. , Chauville J. , Floquet M. , Mekkas A.
Published: July 2016

The bright Be star κ Dra (HD 109387, B5 III, v.sini=249 km/s) is one of the rare mid B type stars which have presented FeII emission lines during strong emission phases. Spectroscopic variations were previously reported by many authors over different time scales: years, days and hours. Juza et al. (1991) proposed that κ Dra was the primary component of a binary system with Porb. = 61.55 days. Short-term and long-term variations in the linear optical polarization were also reported by Arsenijevic et al. (1986). We have tried, with our extensive joint material, to search for correlation between long-term spectroscopic and polarimetric variations with the aim of obtaining information on the behaviour of the circumstellar envelope.
Rapid variability of Hα emission line in Be stars
Authors: Anandarao B. G. , Chakraborty A. , Swaminathan R. , Lokanadham B.
Published: July 2016

We have initiated an observational campaign on some bright Be stars in order to investigate the rapid variability in emission lines using a Fabry-Perot spectrometer(λ/δλ = 104; FSR = 21.3Å) at the Nasmyth focus of the 1.22 m JRO telescope at Hyderabad, India. The PMT dark counts were 1 – 2sec-1. Here we report our first observations on four stars.
Stark broadening of stellar Pt II lines
Authors: Dimitrijević Milan S.
Published: July 2016

Lines of Pt II have been discovered in Hg Mn stars by Dworetsky (1969). The analysis of a few strong Pt II transitions, which are also observed in IUE spectra of stars, has shown (Dworetsky et al., 1984) “that Pt is, like Hg, among the most overabundant elements in the atmospheres of Hg Mn stars, with enhancements of the order of 104 to 105 over the solar system abundances”. Dworetsky et al. (1984) selected also the four Pt II lines which might be used for astrophysical applications. Moreover, they determined the corresponding theoretical gf values. The aim of this contribution is to investigate the Stark broadening of these Pt II lines and to provide the corresponding Stark widths.
Variability in the Circumstellar Envelope of Be Stars
Authors: Hubert A.M.
Published: July 2016

A progress report will be given on recent studies of circumstellar variability of Be stars, their implications on the formation process, the dynamics, the structure and the morphology of the envelope. The following points are discussed: recurrence of outbursts, simultaneous infall and outflow events, variability in hot regions versus variability in the cool envelope, the establishment and vanishing of Be and Be-shell phases, periodic medium-term and quasi-periodic long-term phenomena, and constraints on models.
Short-term spectroscopic variations of the southern Be star 48 Lib
Authors: Floquet M. , Hubert A.M. , Hubert H. , Janot-Pacheco E. , Leister N.V.
Published: July 2016

48 Lib (B3IV, vsin i=395 km/s) is a well known Be shell star. Cuypers et al. (1989) found a period of 0.4017 d, the single wave light curve being asymmetric. Rapid variations in the radial velocity of metallic shell lines have been found by Ringuelet-Kaswalder (1963) with a period of 0.115 d.
Growth of the line-profile variation region during Be episodes
Authors: Kambe E.
Published: July 2016

We have found that the range in wavelength of the line-profile variations (lpv) in the Be star λ Eridani increases by some 20% during its emission phases. This growth is associated with a possible increase in the equatorial velocity of the star during emission. We discuss the significance of this in connection with other features of the lpv and our earlier discovery of a weak correlation between the amplitude of the lpv and Be outbursts in ζ Ophiuchi.
Long-term periodic variability in UV absorption lines of the Be star γ Cas: on the relation with V/R variations in the Hβ line
Authors: Telting John H. , Kaper Lex
Published: July 2016

We present a quantitative study of the variability in ultraviolet resonance lines of Nv, Siiv and Civ of the Be star γ Cas, following up on the work of Henrichs et al. (1983). For this purpose we used 133 IUE spectra obtained over a period of eleven years. Variability occurs in the form of discrete absorption components (DACs), which are formed in the fast-outflowing radiatively driven part of the stellar wind. We constructed a template spectrum from spectra containing no or minor extra absorption due to DACs and modelled the isolated DACs in the obtained quotient spectra. Besides the frequently observed narrow components (vt typically ≤ 250 km/s) at high velocity, we found several broad components occurring at low and intermediate wind velocities.

We confirm the finding of Doazan et al. (1987) who reported that the number of observed DACs is associated with the cyclic V/R variability of the Balmer-emission lines. This V/R variability most probably originates in the slowly outflowing high-density equatorial disc-like wind of the star (see e.g. Telting et al. 1993 for the case of γ Cas). We show that when V/R≪1 the central optical depth of DACs is significantly lower than when V/R≪1. In our interpretation this is due to a correlation between the column density associated with the DACs and the phase of the V/R cycle.

We find that the Hβ observations of Doazan et al. are consistent with a model in which the cyclic V/R variability is due to a global, one-armed oscillation moving through an equatorial disc (Okazaki 1991, Papaloizou et al. 1992, Savonije and Heemskerk 1993). We suggest that the higher column density of DACs in phases of V/R≪1 is the result of the higher density in the region of their origin, namely close to or in the part of the equatorial disc which is rotating towards the observer.
On the formation of Balmer emission lines in the model envelopes of Be stars
Authors: Kogure T. , Suzuki S. , Mon M.
Published: July 2016

We consider the formation of the Balmer emission lines and the decrement Hα/Hβ/Hγ, by solving the non-LTE problems in elementary regions of the envelope divided by equal line-of-sight velocities. These envelope-elements are characterized by different optical depths in the Balmer lines and by different dilution factors for the incident stellar radiation. It is shown that the decrements sensitively depend on these parameters of the envelope-elements. We show that the observed spectral-type dependence and large scatter of the decrements among Be stars can be explained in terms of the variation of these physical parameters.
Some observational appearances of m=1 density waves in Be star disks
Authors: Okazaki Atsuo T.
Published: July 2016

One-armed (i.e., m = 1) density waves are the only global waves in nearly Keplerian disks (Kato 1983). Their frequencies are much smaller than the angular frequency of disk rotation. Based on this theory, Okazaki (1991) proposed that the long-term V/R variations of Be stars are phenomena caused by the global m = 1 oscillations in the equatorial disks. Hummel and Hanuschik (1993) showed that line profiles of disks with m = 1 perturbation patterns are in agreement with the observed V/R variability.
Infrared emission lines of Mg II in B stars
Authors: Aaron Sigut T. A. , Lester J. B.
Published: July 2016

Recently, Chang et. al. (1992) and Carlsson, Rutten and Shchukina (1992) (CRS) demonstrated the non-LTE formation mechanism behind the 12 μm Mg I emission lines (6g–7h, 6h–7i) observed in the solar spectrum (Murcray et. al., 1981). CRS stress the generality of this mechanism showing that it is a natural consequence of the recombination flow from the large Mg II reservoir through the Rydberg levels of Mg I. We have noted the close parallel between Mg I in the solar atmosphere and Mg II in the atmospheres of B stars (where Mg III plays the role of the reservoir) and investigated the operation of this mechanism in high-ℓ infrared transitions of Mg II. We have employed a 58 level Mg II atom including all energy levels through n = 25 and a total of 491 linearized radiative transitions. The coupled equations of radiative transfer and statistical equilibrium were solved with the MULTI code in its local operator form (Carlsson, 1992).
Identifying near-IR variable Be stars
Authors: Dougherty S.M. , Taylor A.R.
Published: July 2016

Near-IR variable Be stars are identified from multi-epoch observations spanning 20 years using a statistical technique. In this manner, observations from different observing sites can be meaningfully combined and compared. A more thorough investigation of the incidence and properties of IR variability in Be stars as a class of stars is then possible.
High-precision continuum rectification: Towards an Abundance Analysis of Be and Bn Stars
Authors: Kolb M. , Baade D.
Published: July 2016

We sketch a new method for the accurate flux calibration and normalization of stellar spectra. This is of particular importance for the analysis of rapidly rotating early–type stars. Some preliminary log g determinations by profile fitting of H γ are presented.
A simple model for a radiatively driven metallic wind in A0 stars
Authors: Babel J.
Published: July 2016

Litle is known about the wind of main sequence A7 to B4 stars. We here investigate the case of a radiatively driven wind for an A0 star and obtain stringent limits on the mass loss rate. We also show that frictional heating lead to the presence of a chromospheric region very near the photosphere.
Non-thermal velocities in the stellar wind of early-type stars
Authors: de Vos R. , Blomme R.
Published: July 2016

Turbulence is known to be important in the stellar wind of early-type stars. We explore the influence of turbulence that depends on the distance to the star.
Improved modelling for spatially resolved spectroscopy of a P Cyg envelope
Authors: Bourguine M. , Chalabaev A.
Published: July 2016

Our study, of which we give here a progress report, addresses two problems. The first is to develop methods and software permitting to compare a wide range of theoretical models of stars with envelopes with observational data produced or expected to be produced by high angular resolution optical interferometry combined with spectroscopy. The second problem is to find out the modes of interferometric observations (base length, spectral resolution etc) that are most informative for determining the physical parameters of stellar envelopes.
Stellar winds in A-type supergiants
Authors: Verdugo E. , Talavera A.
Published: July 2016

A-type supergiants are just at the boundary between the early type supergiants, with strong stellar winds driven by radiation pressure and the cool supergiants in which the origin of mass loss is the dissipation of mechanical energy. The mechanisms involved in the mass loss processes in A supergiants as a whole, are still uncertain.
The ESO radial velocity program. Status and results
Authors: Kürster Martin , Endl Michael , Els Sebastian , Hatzes Artie P. , Cochran Willam D. , Rouesnel Frédéric , Dennerl Konrad , Döbereiner Stefan
Published: July 2016

We present results from our precision radial velocity (RV) program at ESO La Silla. The achievable RV precision after the upgrade of the CES spectrograph is demonstrated. We apply the method of pooled variance diagrams to compare our short-term with our long-term precision. For the active planet-hosting star ι Hor we determine the influence of stellar activity and the rotation period, and address the question of a second long-period planet. For the RV signal in ∊ Eri we demonstrate the distinctness of the time scales present in the RV and Call data, providing further support for the planetary interpretation in this active star.
Planetary mass limits using Hipparcos astrometry
Authors: Arenou Frédéric , Palasi Julienne
Published: July 2016

Using Hipparcos and Tycho-2 data, together with the radial velocity information, a statistical analysis is applied to all the orbital solutions of planetary candidates, in order to avoid a bias towards small inclinations. There are hints of additional, longer period companions.
HD 83443: a system with two Saturns
Authors: Mayor M. , Naef D. , Pepe F. , Queloz D. , Santos N. C. , Udry S. , Burnet M.
Published: July 2016

We report the discovery of an extrasolar planetary system with two Saturnian planets around the star HD 83443. The new planetary system is unusual by more than one aspect, as it contains two very low–mass gaseous giant planets, both on very tight orbits. Among the planets detected so far, the inner planet has the smallest semi–major axis (0.038 AU) and period (2.985 days) whereas the outer planet is the lightest one with m2 sin i = 0.53 MSat. A preliminary dynamical study confirms the stability of the system.
Companion Detection Limits with Adaptive Optics Coronagraphy
Authors: Oppenheimer B. R. , Dekany R. G. , Troy M. , Hayward T. , Brandl B.
Published: July 2016

We present a study of the Palomar Adaptive Optics System and the PHARO near infrared camera in coronagraphic mode. The camera provides two different focal plane occulting masks–opaque circular disks 0.43 and 0.97″ across. Three different pupil plane apodizing masks (Lyot masks) are also provided. The six different combinations of Lyot mask and focal plane mask suppress differently the point spread function of a bright star centered on the focal plane mask. We obtained images of the bright nearby star Gliese 614 with all six different configurations in the K filter. We measured the dynamic range achievable with these configurations. Within 2.5″, the dynamic range is at least 8 magnitudes at the 5σ level and as high as 12 in a 1 s exposure. This represents a substantial gain over similar techniques without adaptive optics.