bluuebunny/crossref_metadata_2025 huggingface dataset:
AGB Mass-Loss History & Haloes Around Planetary Nebulae
Authors: Corradi Romano L.M. , Steffen Matthias , Schönberner Detlef , Perinotto Mario
Published: July 2016

Ionized haloes around planetary nebulae (PNe) are a quite common phenomenon, being found in about 70% of the elliptical PNe for which adequately deep images exist (cf. Corradi, these proceedings). Physically, one has to distinguish between two different kind of haloes. AGB haloes consist of photo-ionized matter still containing information about the mass loss history during the last thermal pulse cycle on the Asymptotic Giant Branch. A second kind of halo may develop when recombination sets in as a consequence of the fast luminosity drop during the advanced post-AGB evolution. These recombination haloes, which can be confused with real AGB haloes on a pure morphological basis, are not a signature of an AGB mass-loss episode (Corradi et al. 2000).
HST Measurements of the Angular Expansion, Kinematics and Distance of the Planetary Nebula Bd+30°3639
Authors: Harrington J. Patrick , Li Jianyang , Borkowski Kazimierz J.
Published: July 2016

The HST WFPC2 camera was used to obtain images of the planetary nebula BD+30°3639 at two epochs separated by 5.66 years. The expansion of the nebula in Hα and [N II] has been measured using several methods. Detailed expansion maps for both emission lines were constructed from nearly 200 almost independent features. There is good agreement between the (independent) Hα and [N II] proper motions. There are clear deviations from uniform radial expansion, with higher expansion rates in regions where the shell is faintest, such as the south-west quadrant.

HST STIS echelle spectra obtained in the C II] λ2326 multiplet provide well-resolved expansion velocities at two position angles. We find that the central velocity split is ±36.3 km s-1 at a position angle of 99°.

To determine the distance of BD+30°3639 by comparison of the angular expansion and the radial expansion, we must address the problem of the three dimensional shape of the nebula. We measured the angular expansion along the position of the 99° echelle slit, finding displacements of 4.25 mas yr-1 at the shell edge (2″.47 from the center). If the nebula were spherical, this would imply a distance of 1.80 kpc. But there is evidence that the nebula is elongated along the line of sight, which suggests that the actual distance is less. Radio continuum images from 5 and 15 GHz VLA observations provide information on the extent of the radial elongation. We fit the radio brightness variation and the echelle data by approximating the nebula as an ellipsoid. Our model has an axial ratio of 1.56, is inclined to the line of sight by 9°.7, and exhibits an expansion in the plane of the sky which is 2/3 that in the radial direction, leading to a distance of 1.2 kpc. Based on a recent model atmosphere (Crowther et al., these proceedings), this distance implies a stellar luminosity of 4250 L⊙.
Collimated Outflows in Planetary Nebulae
Authors: López José Alberto
Published: July 2016

The study of collimated outflows (COFs) in planetary nebulae (PNe) has experienced vigorous activity since the last IAU symposium on PNe, held in Groningen in 1996, for the understanding of the origin and evolution of these outflows is directly linked to the mechanisms of PN formation. Collimated outflows in planetary nebulae (PNe) have diverse characteristics and are observed as bipolar, multipolar, point-symmetric and jet-like outflows. The Hubble Space Telescope has been instrumental in revealing the complex structure and pervasive presence of COFs in a large number of PNe during the last lustrum. Significant advances have also been achieved in the study of the molecular component associated with these outflows. On the theoretical side, models that incorporate the influence of binary cores and magnetic fields have gained particular strength in explaining the origin of COFs. This review attempts to summarize some of the main progresses in the study of COFs during the last years.
Multiple Outflows in (Proto)-Planetary Nebulae
Authors: Cox
Published: July 2016

This paper describes the structural changes occuring in the circumstellar envelopes of stars evolving from the AGB to the planetary nebula phase, with an emphasis on the role of multiple outflows.
Interferometric Observations of OH and H2O Masers in Protoplanetary Nebulae Imaged with HST - A Unique Diagnostic of their Spatio-Kinematic Structure
Authors: Sahai Raghvendra , Claussen Mark J. , Morris Mark
Published: July 2016

Recently, high-resolution imaging surveys of young planetary nebulae (PNe) and protoplanetary nebulae (PPNe) have revealed that the majority of these objects are characterised by multipolar bubbles distributed roughly point-symmetrically around the central star (e.g. Sahai & Trauger 1998, Sahai 2000). Sahai & Trauger (1998) have proposed that episodic high-speed jet-like outflows, operating during the protoplanetary or very late-AGB phase, are the primary agent for shaping PNe. OH and H2O masers provide a unique and crucial probe of the kinematics of the circumstellar material in PPNe, because of the general lack of other emission-line diagnostics. Here we present new results from our ongoing study of PPNe usingHSTimages with interferometric OH & H2O maser-line data to unravel their detailed spatio-kinematic structure (e.g. Sahai et al. 1999a, Sahai, Claussen, & Morris 2002).
De-Centered Central Stars of Planetary Nebulae
Authors: McLean Aubrie , Guerrero Martín A. , Gruendl Robert A. , Chu You-Hua
Published: July 2016

The origin of the wide range of morphologies observed in planetary nebulae (PNe) is not well established. The influence of a binary companion of the central star can naturally explain this variety of morphologies, but very few PNe have known binary central stars. The evolution of the binary system with mass loss may result in the displacement of the central star from the nebular center. The large sample of PNe observed by HST is being used to search for de-centered central stars. Preliminary results indicate that the occurrence of de-centered central stars is widespread among all morphological types of PNe.
Chemical Evolution of the Small Magellanic Cloud: The Planetary Nebulae
Authors: Idiart Thais P. , Costa Roberto D.D.
Published: July 2016

In this work, the chemical history of the SMC is described through an observed sample of planetary nebulae (PNe). Age-abundance relations were derived through the [α-elements/H] (oxygen, argon, neon and sulphur) ratios estimated from PNe of different progenitor masses. In particular, oxygen abundances seem do not decrease due to O-N cycle operation. (This work was supported by FAPESP)
Intracluster Planetary Nebulae
Authors: Feldmeier John J.
Published: July 2016

We review the progress of research on intracluster planetary nebulae (IPN). In the past five years, hundreds of IPN candidates have been detected in the Virgo and Fornax galaxy clusters and searches are also underway in poorer galaxy groups. From the observations to date, and applying the known properties of extragalactic planetary nebulae, the intracluster light in Virgo and Fornax: 1) is significant, at least 20% of the total cluster stellar luminosity, 2) is elongated in Virgo along our line of sight, and 3) may derive from lower-luminosity galaxies, consistent with some models of intracluster star production. A fraction of IPN candidates are not true IPN, but emission-line sources of very large observed equivalent width (≥ 200 Å). The most likely source for these contaminating objects are Lyman-α galaxies at z ≈ 3.1. Follow-up spectroscopy of the IPN candidates will be crucial to discriminate against high red-shift galaxies and to derive the velocity field of the intracluster stellar population.
Modern Techniques in Galaxy Kinematics: Results from Planetary Nebula Spectroscopy
Authors: Romanowsky Aaron J. , Douglas Nigel G. , Kuijken Konrad , Arnaboldi Magda , Gerssen Joris , Merrifield Michael R.
Published: July 2016

We have observed planetary nebulae (PNe) in several early-type galaxies using new techniques on 4- to 8-meter-class telescopes. We obtain the first large data sets (≳ 100 velocities each) of PN kinematics in galaxies at ≳ 15 Mpc, and present some preliminary dynamical results.
The Ejection of Brown Dwarfs from Unstable Multiples
Authors: Delgado-Donate Eduardo , Clarke Cathie
Published: July 2016

We report on high-resolution hydrodynamic simulations of small stellar clusters that explore the effects of substructure in star-forming regions. These calculations, when applied to the substellar regime, provide clear evidence for dynamical interactions to play a key role as a formation mechanism for brown dwarfs. Several observational consequences of this process are discussed.
Brown Dwarfs in Southern Star Forming Regions
Authors: Comerón Fernando
Published: July 2016

Most of the star forming regions within 200 pc from the Sun are located South of the celestial equator. Brown dwarfs or strong candidates have been discovered in all of them, and have been often studied at multiple wavelengths. This paper summarizes some highlights of the research on young brown dwarfs in these regions.
The Substellar Luminosity and Mass Functions of the Trapezium Cluster Down to the Deuterium Burning Limit
Authors: A. Muench August , A. Lada Elizabeth , J. Lada Charles , F. Alves João
Published: July 2016

We have employed an advanced suite of Monte Carlo calculations to model the infrared luminosity function (KLF) of the Trapezium cluster and to derive its Sub-stellar Initial Mass Function down to the deuterium burning limit. Independent of the details, we find that sub-stellar objects can account for no more than ~ 22% of the total number of likely cluster members. This cluster's substellar IMF steadily declines in a power-law fashion over most of the brown dwarf regime, however the formation of a secondary peak in the cluster's substellar KLF suggests the existence of a corresponding secondary peak in the substellar IMF between 10 and 30 times the mass of Jupiter based upon the seemingly degenerate behavior of the theoretical substellar mass-luminosity relation.
Deep Near-Infrared Surveys and Young Brown Dwarf Populations in Star-Forming Regions
Authors: Tamura M. , Naoi T. , Oasa Y. , Nakajima Y. , Nagashima C. , Nagayama T. , Baba D. , Nagata T. , Sato S. , Kato D. , Kurita M. , Sugitani K. , Itoh Y. , Nakaya H. , Pickles A.
Published: July 2016

We are currently conducting three kinds of IR surveys of star forming regions (SFRs) in order to seek for very low-mass young stellar populations. First is a deep JHKs-bands (simultaneous) survey with the SIRIUS camera on the IRSF 1.4m or the UH 2.2m telescopes. Second is a very deep JHKs survey with the CISCO IR camera on the Subaru 8.2m telescope. Third is a high resolution companion search around nearby YSOs with the CIAO adaptive optics coronagraph IR camera on the Subaru. In this contribution, we describe our SIRIUS camera and present preliminary results of the ongoing surveys with this new instrument.
A Search for Disk Emission in Young Brown Dwarfs: L'-band Observations of σ Orionis and TW Hydrae
Authors: Jayawardhana Ray , R. Ardila David , Stelzer Beate
Published: July 2016

Studies of disks around young brown dwarfs are of paramount importance to our understanding of the origin, diversity and early evolution of sub-stellar objects. Here we present first results from a systematic search for disk emission in a spectroscopically confirmed sample of young objects near or below the sub-stellar boundary in a variety of star-forming regions. Our VLT and Keck L'-band observations of the σ Orionis and TW Hydrae associations suggest that if a majority of brown dwarfs are born with disks, at least the inner regions of those disks evolve rapidly, possibly clearing out within a few million years.
A Large Area Survey for Brown Dwarfs in the Pleiades
Authors: Hodgkin Simon
Published: July 2016

We present the preliminary findings of a deep imaging survey covering 17 square degrees in the Pleiades. We have identified in excess of 300 candidate cluster members in the i, i-z diagram. The survey is complete to ~ i=22, with candidates detected as faint as i=23.
2MASS Data Mining and the M, L, and T Dwarf Archives
Authors: Davy Kirkpatrick J.
Published: July 2016

Studies of brown dwarfs as a distinct galactic population have been largely pioneered by dedicated, vast-area surveys at deep optical and near-infrared wavebands. The Two Micron All Sky Survey has, because of its full-sky coverage and depth, been the most successful at providing new targets for further study. The author briefly reviews some of the ways in which 2MASS data have been used by brown dwarf researchers. One of the by-products – namely the 2MASS Team's follow-up spectroscopy of brown dwarf candidates – is potentially valuable as a scientific resource itself and is also being released to the public.
Globular Clusters: Low Mass Stars, Still No Brown Dwarfs!
Authors: Marchi Guido De
Published: July 2016

In spite of all the attempts to find them, no one has yet detected any brown dwarf in a globular cluster. Although powerful instruments such as the VLT and Advanced Camera could further push the frontiers of this search, globular clusters will probably hold tight to their secrets for a while longer. Nonetheless, the search for very low mass stars in globular clusters has taught us a lot about their original mass distribution (IMF) and its evolution in time. I shall review the results of an investigation carried out over what is presently the largest, most homogeneous sample, and discuss the reasons suggesting that: 1. dynamical evolution (internal and external) has reshaped the cluster mass function over time, but the imprint of the IMF is still visible; 2. the IMF appears to vary very little from cluster to cluster; 3. the most likely functional form of the IMF is that of a power law that rises to a peak at ˜ 0.3 M⊙ and tapers off at smaller masses.
Multiplicity, Kinematics, and Rotation Rates of Very Young Brown Dwarfs in Cha I
Authors: Joergens Viki , Neuhäuser Ralph , W. Guenther Eike , Fernández Matilde , Comerón Fernando
Published: July 2016

We have studied twelve very young (1–5 Myr) bona fide and candidate brown dwarfs in the Cha I star forming region in terms of their kinematic properties, the occurrence of multiple systems among them as well as their rotational characteristics. Based on high-resolution spectra taken with UVES at the VLT (8.2 m), radial and rotational velocities have been measured. A kinematic study of the sample showed that their radial velocity dispersion is relatively small suggesting that they are not ejected during their formation as proposed in recent formation scenarios. By means of time-resolved UVES spectra, a radial velocity survey for close companions to the targets was conducted. The radial velocities of the targets turned out to be rather constant setting upper limits for the mass M2 sin i of possible companions to 0.1 MJup – 2 MJup. These findings hint at a rather low (≤ 10%) multiplicity fraction of the studied brown dwarfs. Furthermore, a photometric monitoring campaign of the targets yielded the determination of rotational periods for three brown dwarf candidates in the range of 2.2 to 3.4 days. These are the first rotational periods for very young brown dwarfs and among the first for brown dwarfs at all.
Differential Simultaneous Imaging and Faint Companions: TRIDENT First Results from CFHT
Authors: Marois Christian , Nadeau Daniel , Doyon René , Racine René , A. H. Walker Gordon
Published: July 2016

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. Its main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6μm, that enables a precise subtraction of the primary star PSF while keeping the companion signal. Thirty-five stars have been observed in two observing missions, with no detection so far. It is shown that a faint companion with a ΔH of 10 magnitudes would be detected at 0.5″ from the primary.
A Search for Companions to L Dwarfs
Authors: Allen P. R. , Koerner D. W. , McElwain M. W. , Murphy G. R. , Reid I. Neill , Gizis J. E. , Davy Kirkpatrick J.
Published: July 2016

We present the results of two imaging surveys for companions to low-luminosity dwarfs, one with Keck to a limiting magnitude of K = 20, and the other with HST to a limiting magnitude of I = 23. No companions were found at separations of 0″.5 to 20″.0, but seven companions were found within 0″.5. Based on sub-stellar evolutionary models, we estimate the companion detection efficiency as a function of mass ratio. This modeling, coupled with the data, place strong upper limits on the mass ratios of unobserved companions. We conclude that no companions exist in the optimal sensitivity regions of both surveys for q > 0.85 (HST), and q > 0.4 (Keck).
VLT Spectra of the Companion Candidate Cha Hα 5/cc 1
Authors: Neuhäuser Ralph , Guenther Eike , Brandner Wolfgang
Published: July 2016

We obtained optical and infrared spectra of Cha Hα 5/cc 1, a faint possibly sub-stellar companion candidate next to the M6-type brown dwarf candidate Cha Hα 5 in Cha I, using FORS1 and ISAAC at the VLT. The VRIJHK colors of Cha Hα 5/cc 1 are consistent with either an L-type companion or a K-type background giant. Our spectra show that the companion candidate actually is a background star.
Photospheric Properties of L and T Dwarfs
Authors: Leggett S. K. , Fan X. , Geballe T. R. , Golimowski D. A. , Knapp G. R.
Published: July 2016

The photospheric spectra of all L and T dwarfs contain strong molecular bands and alkali absorption features, and those of L and early T dwarfs are also affected by dust. Although work on atmospheric models is addressing the treatment of dust, and is increasing the completeness of molecular opacity linelists, the effective temperatures of L and T dwarfs cannot be derived confidently from the modelled spectral energy distributions. However, because the radii of brown dwarfs older than 0.1 Gyr vary little with mass, measurements of intrinsic luminosity (i.e. total integrated flux and parallax) accurately determine effective temperature. Using this method we find a well constrained relationship between the effective temperatures of L and T dwarfs and spectral type, but with temperature nearly constant from L7 to T4. More work is required to determine the uniqueness of this relationship and to constrain the masses and ages of brown dwarfs.
Evolution of Brown Dwarf Atmospheres: Investigating Physical Parameters from Near-IR Spectra
Authors: Gorlova Nadya , Meyer Michael R. , Liebert Jim , Rieke George H.
Published: July 2016

We obtained near–infrared spectra of a sample of very low mass objects as a function of age in order to investigate the temperature and surface gravity sensitivity of several features in the J– and K–bands.
Methane and the Spectra of T Dwarfs
Authors: Homeier Derek , Hauschildt Peter H. , Allard France
Published: July 2016

We have updated our PHOENIX model atmospheres and theoretical spectra for ultracool dwarfs with new opacity data for methane based on line strength predictions with the STDS software. By extending the line list to rotational levels of J = 40 we can significantly improve the shape of the near-IR absorption features of CH4, and in addition find an enhanced blanketing effect, resulting in up to 50% more flux emerging in the J band than seen in previous models, which may thus contribute to the brightening in J and blue IR colors observed in T dwarfs.
Middle-Infrared Observations of DENIS J0255-4700
Authors: Creech-Eakman Michelle , Serabyn Eugene , Orton Glenn S. , Hayward Thomas L.
Published: July 2016

The first infrared photometry of an L-type brown dwarf, DENIS J0255-4700, includes N-band and narrow-band 8.8-μm detections, with upper limits in narrow-band 10.3 and 11.7 μm. Model-independent blackbody fits of existing data yield Teff = 1250 – 1750 K, with models favoring the lower end of that range. Dusty atmospheric models by Allard, Burrows and Marley which match the near-infrared photometry are not completely consistent with our mid-infrared photometry.
Testing for Photometric Variability at the L/T Boundary
Authors: Enoch Melissa L. , Brown Michael E. , Burgasser Adam J.
Published: July 2016

We construct Ks-band light curves for nine field L and T brown dwarfs using the Palomar 60 inch Telescope. Results of a robust statistical analysis indicate that about half the targets show significant evidence for variability. Two of these variable targets have marginally significant peaks in the Lomb-Scargle periodogram. The phased light curves show evidence for periodic behavior on timescales of about 1.5 and 3.0 hours.
High Dynamic Range and the Search for Planets
Authors: Tokunaga A. T. , Ftaclas C. , Kuhn J. R. , Baudoz P.
Published: July 2016

General arguments for optimized coronagraphy in the search for planets are presented. First, off-axis telescopes provide the best telescopic platforms for use with coronagraphy, and telescope fabrication technology now allows the fabrication of such telescopes with diameters of up to 6.5 m. We show that in certain circumstances a smaller telescope with an off-axis primary has a signal-to-noise advantage compared with larger Cassegrain telescopes. Second, to fully exploit the advantages of the coronagraph for suppressing stray light, it is necessary to use a high Strehl ratio adaptive optics system. This can be best achieved initially with modest aperture telescopes of 3–4 m in diameter. Third, application of simultaneous differential imaging and simultaneous polarimetric techniques are required to reach the photon-limit of coronagraphic imaging. These three developments, if pursued together, will yield significant improvements in the search for planets.
Prospecting for Brown Dwarfs in Space Infrared Telescope Facility (SIRTF) Legacy Science Datasets
Authors: Padgett D. , O'Linger J. , Stapelfeldt K.
Published: July 2016

We discuss the prospects for brown dwarf detections in the field and in star-forming regions using data from the SIRTF Legacy Science Programs. We concentrate in particular on the SIRTF Wide-area InfraRed Extragalactic survey (SWIRE) and “From Cores to Disks” program (c2d). The SWIRE program will map up to 70 square degrees of high galactic latitude sky, providing wavelength coverage from 3.6 to 160 μm. SWIRE's estimated 5σ sensitivity of 10 microJy at 4.5 μm and its relatively large areal coverage will make it uniquely sensitive to the population of extremely cool (T ≤ 600 K) field brown dwarfs thus far undetected in other surveys. The “c2d” program will map up to 20 square degrees in nearby (d ≤ 300 pc) star-forming molecular clouds over the wavelength range 3.6 – 70 microns, potentially detecting young brown dwarfs down to a few MJupiter. Taken together, these two SIRTF datasets will offer a unique opportunity to take a census of the low mass/temperature members of the brown dwarf population.
Searching for Ultracool Companions with NICI
Authors: Ftaclas C. , Martín E. L. , Toomey D.
Published: July 2016

We present to the brown dwarf community the Near Infrared Coronographic Imager (NICI), which is being built for installation in 2005 on the Gemini South Telescope. NICI's dual channel architecture and dedicated AO system are designed to permit deep circumstellar discrimination of faint sources where some spectral key can be used to get a simultaneous estimate of the background. One of the principal science goals of NICI is to search for ultracool companions to stars and brown dwarfs.
Surveying the Solar Neighborhood for Brown Dwarf Companions with the ECLIPSE Discovery Mission
Authors: Stapelfeldt Karl
Published: July 2016

The proposed Eclipse Discovery mission is an optical space telescope designed to provide a thousandfold reduction in scattered light near bright stars in comparison to any Hubble Space Telescope instrument. A survey of 500 single stars within 15 pc can detect companions with absolute z magnitude of 22 at separations > 10 AU in most of the targets. Spectrophotometry of CH4 and H2O bands between 0.8-1.0 μm can be used to derive the effective temperatures of the objects. The ECLIPSE brown dwarf survey would directly measure the luminosity function of brown dwarf companions down to ~20 Jupiter masses, providing a crucial comparison with field objects.
Nomenclature: Brown Dwarfs, Gas Giant Planets, and ?
Authors: Boss Alan P. , Basri Gibor , Kumar Shiv S. , Liebert James , Martín Eduardo L. , Reipurth Bo , Zinnecker Hans
Published: July 2016

The question of what sort of guidelines should be used to classify substellar mass objects was considered and debated during an evening panel discussion at the IAU 211 Symposium on Brown Dwarfs.
Massive star abundances in the Galaxy and the Magellanic Clouds
Authors: Smartt Stephen J.
Published: July 2016

The use of photospheric abundances in OB-type main-sequence stars and A and B-type supergiants as probes of rotation and evolutionary status is reviewed. The abundances of CNO and boron can be compared quantitatively with stellar evolutionary calculations. In particular the abundance ratios of N/O and N/C can be derived in blue supergiants to determine if they are consistent with the stars having gone through a red supergiant phase and dredge-up of core material to the surface. The results from several different studies are reviewed and compared. For blue supergiant stars in the mass-range 5-80 M⊙ the situation appears consistent — there is no evidence for stars of any mass having undergone blue-loops in the HR diagram. The stellar samples show significant signs of having N enriched atmospheres, and the quantitative values are consistent with stellar evolutionary calculations which invoke turbulent diffusive mixing while massive stars are on the main-sequence. Results on the interesting blue supergiant Sher 25 are presented, and linked to Sk-69°202; the B3Ia progenitor of SN 1987A. A spectacular ejection nebula surrounds Sher 25, much like that which was ejected by Sk–69°202 during its final stages of evolution. Both of these were thought to have been formed during a mass-loss event when the stars were in the red supergiant phase. The CNO abundances derived in Sher 25 suggest the nebula was ejected during the blue supergiant phase, and that rotation can explain the N-enrichment found in the stellar photosphere.
Overloaded and fractured stellar winds
Authors: Feldmeier Achim , Oskinova Lida M. , Hamann Wolf-Rainer , Owocki Stanley P.
Published: July 2016

We discuss the connection between wind overloading and discrete absorption components in P-Cygni line profiles from O-type stars. Overloading can create horizontal plateaus in the radial wind speed that cause the extra absorption in the line profile. The upstream propagation speed of these velocity plateaus is analyzed. The second part of the paper deals with X-ray emission from O-type stars. X-ray line profiles observed with Chandra and XMM-Newton are often symmetric, contrary to what is expected for lines from a homogeneous wind. We discuss the influence on line symmetry of photon escape channels in a strongly clumped wind.
Dust formation as a diagnostic of Wolf-Rayet winds
Authors: Williams Peredur M. , van der Hucht Karel A. , Morris Patrick W. , Marang Fred
Published: July 2016

Dust formation by Wolf-Rayet stars is a powerful diagnostic of exceptional activity in their winds. Observed behaviour ranges from stars which make dust continually (e.g., WR 104, WC9d+B0.5V) to those which make dust for short episodes at periodic intervals (e.g., WR 140, WC7pd+04-5). In both examples, dust formation is related to colliding WR and OB stellar winds in binary orbits. We have been using IR photometry primarily from the SAAO and ESO and spectroscopy with ISO-sws to investigate systems having intermediate properties (WR 98a, WC8-9vd+?) or more complex behaviour (WR 48a, WC8ed+?).
X-ray observations of massive colliding wind binaries
Authors: Corcoran Michael F.
Published: July 2016

Massive stars in binary systems can generate X-ray emission in the region between the two stars where stellar winds collide. Colliding wind X-ray emission acts as an in-situ probe of important wind parameters like mass-loss rates, chemical abundances, wind velocities, and possibly magnetic field strengths. Variations in observed colliding-wind X-ray emission can be produced by the changing line-of-sight to the colliding wind region as the stars move in orbit and/or the changing emission measure of the shocked gas in the wind collision zone produced if the separations between the two stars change. X-ray variability depends on the wind and orbital parameters and so can in principal allow the direct measurement of mass functions even for low inclination systems and provide a connection between the stellar and wind parameters. X-ray emission from colliding wind systems can thus be used to refine our understanding of the evolutionary state of massive stars and to help test evolutionary models. We discuss recent advances in defining the X-ray spectral and temporal signatures of colliding wind X-ray emission using ROSAT, ASCA, RXTE, Chandra and XMM-Newton data.
Gamma-ray production in selected Wolf-Rayet binaries
Authors: Benaglia Paula , Romero Gustavo E.
Published: July 2016

In the colliding wind region of early-type binaries, electrons can be accelerated up to relativistic energies, as demonstrated by the detection of non-thermal radio emission from several WR+OB systems. The particle acceleration region is exposed to strong photon fields, and inverse-Compton cooling of the electrons could result in a substantial high-energy non-thermal flux. We present here preliminary results of a study of the binaries WR 140, WR 146, and WR 147 in the light of recent radio and γ-ray observations. We show that under reasonable assumptions WR 140 can produce the γ-ray flux from the GRO-egret source 3EG J 2022+4317. WR 146 and WR 147 are below the detection threshold.
Insights into Wolf-Rayet WC9 stars from spectroscopy
Authors: Eenens Philippe , Corral Luis J.
Published: July 2016

We present new spectroscopic observations of WC9 stars. As predicted by Williams & van der Hucht (2000), O ii lines are weak in the dust-free star WR88, which also shows a high ionization. Spectral variability is detected in WR 106 and WR 121. These findings are briefly discussed in terms of the conditions for dust formation in Wolf-Rayet winds.
Hydrodynamic model atmospheres for hot stars
Authors: Gräfener Götz , Hamann Wolf-Rainer
Published: July 2016

Recent non-LTE models for expanding atmospheres, accounting for iron group line-blanketing and clumping, show a radiative acceleration which supplies a large part of the driving force of WR and O star winds. Aiming at the calculation of fully consistent wind models, we developed a method to include the solution of the hydrodynamic equations into our atmosphere code, taking into account the radiation pressure from the CMF radiation transport. In the present work we discuss the resulting wind acceleration for ‘standard’ WR and O-type star model atmospheres, and present a hydrodynamically consistent non-LTE model for the O4I(n)f star ζ Pup. In addition we demonstrate the effect of clumping on the radiative acceleration.
Wind inhomogeneities in [Wc] central stars of planetary nebulae
Authors: Grosdidier Yves , Moffat Anthony F.J. , Acker Agnès
Published: July 2016

In the present poster paper, we summarize the observational spectroscopic evidence for wind clumping originating in some [WC8-10] and [WO4] central stars of planetary nebulae. Specifically, we concentrate on the C iii λ5696 and C iv λλ5801/12 emission-line variability observed for well-known planetary nebula nuclei.
Line-blanketing effects in atmospheres of O-type stars
Authors: Martins Fabrice , Schaerer Daniel
Published: July 2016

Line-blanketing effects in atmospheres of O-type stars are studied based on models computed with the non-LTE spherically expanding code cmfgen (Hillier & Miller 1998). We show that the inclusion of metals leads to a reduction of the effective temperature scale by ~ 1500 K at spectral type O9.5, up to ~ 4000 K at spectral type O3. This change of the Teff scale implies a reduction of the luminosity by ~0.1 dex and a decrease of the ionising flux by ~ 50% for a given spectral type.
High-resolution spectroscopy of two LBV cycles of HR Car
Authors: Szeifert Thomas , Kaufer Andreas , Crowther Paul A. , Stahl Otmar , Sterken Chris
Published: July 2016

Luminous Blue Variables (LBVs or S Dor Variables) are showing characteristic variability of very long timescales of a decade and more. During their expansion and contraction phases, they move across a wide part of the H-R diagram with dramatic changes of their stellar wind characteristics, radius and temperature. We present results of our long-term spectroscopic monitoring campaigns for the galactic star HR Car with optical spectra taken over 13 years and two minimum and maximum phases observed during this time.
On the evolution of massive close binaries
Authors: Langer Norbert , Wellstein Stephan , Petrovic Jelena
Published: July 2016

We discuss which fraction of the matter flowing to the companion during a Roche lobe overflow phase can actually be accreted by the secondary star. Employing new evolutionary models for massive close binaries which include the effects of rotation for both components as well as angular momentum accretion and spin-orbit coupling, we propose a physical model to calculate the accretion efficiency in Case A and B systems. We provide examples showing that both cases, high and low accretion efficiency, do occur within these models, as it seems required by observed post-mass transfer systems. Furthermore, we discuss late evolutionary stages of such binaries, with emphasis on the formation of compact objects: what are their spin rates, which systems can produce black holes, which gamma-ray bursts?
Influence of radiation pressure and wind momentum on mass transfer in massive binaries
Authors: Dessart Luc , Petrovic Jelena , Langer Norbert
Published: July 2016

We perform radiation hydrodynamics simulations of mass transfer in close and massive binary systems, focusing especially on the impact of radiation pressure and wind momentum from the two luminous stars that compose the system. We find that for the large mass transfer rates important for the evolution of such binary systems (of the order of 10–3M⊙yr–1), the light and wind momenta are too low to affect the behaviour of the dense gas stream ejected by the Roche Lobe filling component. In particular, the presence of a wind-wind collision between the two stars has no effect on the gas stream dynamics.
Nebular diagnostics of hot star atmospheres
Authors: Stasińska Grazyna , Schaerer Daniel , Zeippen Claude J.
Published: July 2016

The ionization structure of nebulae depends on the spectral energy distribution of the ionizing stars. Therefore nebulae are potential tools to check the validity of the energy distribution predicted by stellar atmosphere models. However, the problem is complicated by the fact that the ionization structure also depends on the nebular density distribution and that the predictions of photo-ionization models strongly rely on atomic physics computations, which bear their own uncertainties.
Massive stars and the creation of our Galactic Center
Authors: Figer Donald F.
Published: July 2016

Our Galactic Center hosts over 10% of the known massive stars in the Galaxy. The majority of these stars are located in three particularly massive clusters that formed within the past 5 Myr. While these clusters are extraordinary, their formation repesents about half of the total inferred star-formation rate in the Galactic Center. There is mounting evidence that the clusters are just present-day examples of the hundreds of such similar clusters that must have been created in the past, and whose stars now comprise the bulk of all stars seen in the region. I discuss the massive stellar content in the Galactic Center and present a new analysis that suggests that effects of continuous star-formation in the Galactic Center can be seen in the observed luminosity functions newly-obtained HST-nicmos and Gemini-ao data.
Radio observations of Galactic Center massive stars
Authors: Lang Cornelia C.
Published: July 2016

High-resolution multi-frequency observations made with the VLA have revealed the presence of stellar winds in two of the three known massive stellar clusters at the Galactic Center (GC). At a distance of only 8.0 kpc, we are able to resolve radio sources associated with individual near-infrared sources known to be losing mass at high rates. Herein, I discuss the spectral and spatial properties of the radio sources and their near-infrared counterparts, their inferred mass-loss rates, variability and the prospects for detecting stellar winds sources in the Central Cluster, near the supermassive blackhole SgrA*. Such massive clusters as these three GC clusters have a profound impact on the interstellar medium, as evidenced by radio and X-ray observations of the surrounding regions.
Synthetic UV spectra of starburst regions with massive close binaries
Authors: Belkus Houria , Van Bever Joris , Vanbeveren Dany , van Rensbergen Walter
Published: July 2016

We present the evolution of synthetic ultraviolet spectra of starburst regions having a significant fraction of binaries. The population synthesis program uses an extended library of stellar evolutionary tracks of single stars and binaries computed with the most recent stellar wind mass loss rates during RSG, LBV and WR stages. In the case of binaries we account in detail for the effects of Roche lobe overflow, mass transfer and mass accretion, common envelope evolution, the spiral-in process, asymmetric kicks to neutron stars as a result of their supernova explosion, etc. The most important synthesized line profiles are those of Si iv λ1400 and C iv λ1550, two P-Cygni lines prominent in O-type stars. The main effect of the close binaries is to extend the UV bright lifetime of the starburst due to the appearance of accretion stars. But more importantly, our computations show that a spectrum of a single star model of about 6 Myr old is effectively undistinguishable from that of a binary rich model of about 10 Myr old. This indicates a possible age degeneracy, reminiscent of the influence of binaries on the commonly used optical age indicator WHβ.
Resolved and unresolved populations: statistics and synthesis models
Authors: Cerviño Miguel
Published: July 2016

In this contribution, I present 90%-confidence limits on diagnostic diagrams of Wλ(WR-bump) and L(WR-bump)/L(Hβ) ratio vs.Wλ(Hβ) resulting from evolutionary synthesis models that include the statistical dispersion due to finite stellar populations in real star forming regions.
Triggered massive star formation in the open cluster NGC 1893
Authors: Marco Amparo , Negueruela Ignacio
Published: July 2016

We have carried out a search for emission line pre-main sequence (PMS) stars in the area of the star-forming young open cluster NGC 1893 by means of slitless spectroscopy. We find 19 emission line stars with spectral types spanning the range from early B-type to G-type. All the PMS stars are confined to two small regions: the outer rim of the molecular cloud associated with the H ii region IC 410 and the vicinity of the bright emission cometary nebulae Sim 129 and Sim 130. The overall spatial distribution of PMS stars strongly suggests, that present day star formation in NGC 1893 is triggered by the O-type stars in the cluster.
Recent progress in understanding the hot and warm gas phases in the halos of star-forming galaxies
Authors: Strickland David K. , Heckman Timothy M. , Colbert Edward J.M. , Hoopes Charles G. , Weaver Kimberley A.
Published: July 2016

In this contribution we present a few selected examples of how the latest generation of space-based instrumentation — NASA's Chandra X-ray Observatory and the Far-Ultraviolet Spectroscopic Explorer (FUSE) — are finally answering old questions about the influence of massive star feedback on the warm and hot phases of the ISM and IGM. In particular, we discuss the physical origin of the soft thermal X-ray emission in the halos of star-forming and starburst galaxies, its relationship to extra-planar Hα emission, and plasma diagnostics using FUSE observations of O vi absorption and emission.
Dispersal of massive star products and consequences for galactic chemical evolution
Authors: Oey M. S.
Published: July 2016

The processes that disperse the products of massive stars from their birth sites play a fundamental role in determining the observed abundances. I discuss parameterizations for element dispersal and their roles in chemical evolution, with an emphasis on understanding present-day dispersion and homogeneity in metallicity. Turbulence dominates mixing processes, with characteristic timescales of order 108 yr, implying significant dilution of metals into the ISM. This permits a rough estimate of the metallicity distribution function of enrichment events. Many systems, including the Milky Way and nearby galaxies, show metallicity dispersions that as yet appear consistent with pure inhomogeneous evolution. There are also systems like I Zw 18 that show strong homogenization, perhaps tied to small galaxy size, high star formation rate, and/or superwinds.
The interstellar medium local to HD 10125 (O9.7II)
Authors: Cichowolski Silvina , Arnal E. Marcelo , Cappa Cristina E. , Pineault Sergey , St-Louis Nicole
Published: July 2016

The structure and dynamics of the interstellar medium (ISM) are strongly affected by the action of massive stars. They deposit in the ISM a huge number of ionizing photons and transfer to it vast amounts of mechanical energy via their powerful stellar winds. As a consequence, massive stars create what is known as an interstellar bubble, i.e., a minimum in the gas distribution characterized by a low volume density and a high temperature, surrounded by an expanding envelope (Weaver et al. 1977). The star should be seen projected onto, or close to, the centre of the H i minimum.
An X-ray survey of Wolf-Rayet stars in the Magellanic Clouds
Authors: Guerrero Roncel Martín A. , Chu You-Hua
Published: July 2016

We have used archival Chandra-acis observations to search for X-ray emission from WR stars in the Magellanic Clouds (MCs), where the low interstellar absorption and known distances make it easy to compare X-ray luminosities with spectral types and binary status of WR stars. We have detected X-ray emission from ~20 WR stars in the MCs with X-ray luminosities of 6.6×1032-1.4×1035 ergs s–1. The analysis of the X-ray spectra of the brightest sources indicates that the X-ray emitting gas has temperatures ≥ 1.0×107 K, as expected in colliding winds. We will compare these results with the binary status of the WR stars to determine the amounts of the X-ray emission produced in the colliding winds for WR stars in binary systems and to assess the X-ray emission from single WR stars.
A search for Beta Cephei stars in LMC and SMC
Authors: Kjeldsen H. , Baade D.
Published: July 2016

The β Cephei instability is believed to be caused by the κ-mechanism. Model calculations, based on revised metal opacities, show this mechanism to be strongly sensitive to metallicity (e.g., Dziembowski, W. A. & Pamyatnykh, A. A., 1993: MNRAS, 262, 204). It appears that [Fe/H] must be larger than the solar value in order to drive the β Cephei pulsations. For this reason, the models predict that no β Cephei stars should be found in the Magellanic Clouds. Balona (1992: MNRAS, 256, 425; 1992: ASP Conf. Ser., Vol. 30, 155; 1993: MNRAS, 260, 795) has tested this prediction by observing three young clusters in the SMC and LMC (NGC 330, NGC 2004 and NGC 2100). He found no β Cephei stars down to a magnitude of V ≈ 16; the threshold for detection of variability on time-scales of a few hours was 10 mmag. Most Galactic β Cephei stars have amplitudes greater than this, but we might expect β Cephei stars in the Magellanic Clouds (if they exist) to have smaller amplitudes, due to the different environment. To test this, we have observed two young clusters NGC 371 (SMC) and NGC 2122 (LMC) with high sensitivity.
Amplitude Variations in Rotationally Split Multiplets
Authors: Buchler J. Robert , Goupil Marie-Jo , Serre Thierry
Published: July 2016

We have extended a formalism that was developed for radial pulsators (Buchler & Goupil 1984) to the nonradial ones (Goupil & Buchler 1993). For an ℓ = 1 triplet, for example, the modal amplitudes satisfy the nonlinear amplitude equations
Line Profile Variations in Be Stars
Authors: Gies Douglas R.
Published: July 2016

The periodic variations in the photospheric lines of Be stars could result from rotation or nonradial pulsations (NRP). Here I review the spectroscopic results on ten Be stars which have been targeted in recent multiwavelength campaigns. Most of the stars display variability consistent with an l = –m = 2 NRP mode with periods on the order of a day, and the associated light curves are consistent with the pulsation periods, amplitudes, and phases derived from spectroscopy. The variability is strongest in the line wings which only agrees with the NRP prediction that horizontal motions should exceed vertical motions for g-mode pulsations. High frequency, non-periodic variations are also observed, but I argue that these are of circumstellar origin and do not represent high-order NRP. The NRP periods are also found in variations of the Hβ emission line but these probably result from photospheric and not disk variations. However, the same periods occur in the C IV λ1550 P Cygni line, which strongly suggests that NRP modulates the local stellar wind.
Seismology of southern Be stars
Authors: Janot-Pacheco Eduardo , Leister Nelson Vani
Published: July 2016

We have started in 1990 a search for moving bumps in the HeI λ 667.8 nm of mainly southern, bright Be stars. The objects of our sample have been selected on the basis of photometric variability (Cuypers et al., 1989). High resolution (R≥ 30,000), high signal-to-noise ratio (S/R≥ 300) spectroscopic observations have been performed at the brazilian Laboratório Nacional de Astrofísica with a CCD camera attached to the coudé spectrograph of the 1.60 m telescope (e.g. Table I). Several hundred spectra have been taken during the last three years. Photometric observations simultaneous with spectroscopy were made on the same site in July 1992 with a two-channel photometer (Stromgren b filter) and a CCD camera (Johnson B filter) installed at two 0.60 m telescopes. The idea is try to disentangle the controversy between NRP and RM models with the help of simultaneous spectroscopy and photometry.
A survey of line profile variations in non-emission line B0–B5 III–V stars
Authors: Fieldus M. S. , Bolton C. T.
Published: July 2016

Some investigators have attributed the photometric and spectral line profile variations (lpv) that are common among the B stars to nonradial pulsation while others have attempted to explain them by rotation of photospheric or circumstellar structures with respect to our line of sight. One of the problems in resolving this debate has been our lack of knowledge of how these variations depend on fundamental stellar characteristics. Surveys of lpv have covered the Be and a few Bn stars (D. Penrod, unpublished), the O stars (Fullerton 1990), and B8-B9.5 main sequence stars (Baade 1989), but noone has carried out a systematic search for lpv among the near main sequence, non-emission line early- and mid-B stars. This paper describes preliminary results from such a survey.