bluuebunny/crossref_metadata_2025 huggingface dataset:
A 2μm narrow-band survey for emission-line stars in the inner Galaxy
Authors: Blum Robert D. , Damineli Augusto
Published: July 2016

We have begun a search for emission-line stars toward the inner Galaxy using narrow-band photometry centered on the emission lines of He I 2.06μm, C IV 2.08μm, H I Brγ 2.166μm and He II 2.189μm. The census of Wolf-Rayet and other emission-line stars in the Galaxy is incomplete, owing to the large extinction at optical and shorter wavelengths toward the inner Galaxy. However, these massive, evolved stars are bright and can be detected at large distances in the near infrared.
A kinematical search for Wolf-Rayet nebulae in the irregular galaxy IC 10
Authors: Bullejos Almudena , Rosado Margarita , Georgiev Leonid N. , Esteban César , Borissova J.H.
Published: July 2016

In this work we report the search for nebulosities associated with the candidate Wolf-Rayet stars listed in Massey el al (1992) in the irregular galaxy IC 10, based upon Hα, [S II], and [O III] direct images and imaging Fabry-Pérot spectroscopy. Approximately 95% of the WR candidate stars we analyzed are found within nebulae. For most of these nebulae, we find broad wings on their Hα radial-velocity profiles. For some of the nebulae, the Hα velocity profiles are broadened with a typical velocity difference of 80–100 kms1.
Effects of the hot stellar component on derived physical parameters of the Carina Nebula
Authors: Robledo-Rella Víctor , Peña Miriam
Published: July 2016

Studies of extragalactic (un-resolved) H II regions, usually rely on assumptions about the underlying stellar absorption to estimate the reddening corrections needed to derive physical conditions of the ionized gas and to infer parameters of the ionizing stars (Robledo-Rella & Firmani 1990). We have addressed the problem of estimating quantitatively the effects of the hot star spectra on derived physical (nebular and stellar) parameters of galactic H II regions.
The IMF and star-formation history of the ionizing cluster of 30 Doradus
Authors: Selman Fernando J. , Melnick Jorge , Bosch Guillermo L. , Terlevich Roberto J.
Published: July 2016

A new method is used to determine masses, ages, and reddening for the stars of the starburst cluster NGC 2070 in 30 Doradus. The data are consistent with a star-formation rate which increases exponentially with a characteristic rise time of 1.7 Myr, independent of mass, starting 7 Myr ago. The IMF is consistent with a single power law IMF with Salpeter slope over the whole 3 M⊙ < M < 120 M⊙ range investigated, with evidence for flattening for the innermost radial bin.
The environments of Wolf-Rayet stars in M 31
Authors: Walterbos René A.M. , Bransford Mark A. , Thilker David A. , King Nichole L.
Published: July 2016

We have conducted a systematic search for nebulae surrounding Wolf-Rayet stars in M31, where 28 objects are found.
Synthesis models for starburst populations with Wolf-Rayet stars
Authors: Leitherer Claus
Published: July 2016

The prospects of utilizing Wolf-Rayet populations in starburst galaxies to infer the stellar content are reviewed. I discuss which WR star features can be detected in an integrated stellar population. Specific examples are given where the presence of WR stars can help understand galaxy properties independent of the O-type star population. I demonstrate how populations with small age spread, such as super star clusters, permit observational tests to distinguish between single-star and binary models to produce WR stars. Different synthesis models for WR populations are compared. Predictions for WR properties vary dramatically between individual models. The current state of the models is such that a comparison with starburst populations is more useful for improving WR atmosphere and evolution models than for deriving the star-formation history and the initial mass function.
A new Wolf-Rayet galaxy with a Seyfert nucleus
Authors: Cid Fernandes Roberto , Lacerda R. Rodrigues , Schmitt Henrique R. , Bergmann Thaisa Storchi
Published: July 2016

We report the detection of a WR feature in the nuclear spectrum of the Seyfert 2 galaxy Mrk 1210. The growing list of WR/Seyfert galaxies strengthens the evidence for a connection between nuclear activity and star-formation.
Two-dimensional spectroscopy of the Wolf-Rayet galaxy NGC 4861
Authors: García-Lorenzo Begoña , Mediavilla E. , Arribas S.
Published: July 2016

We have obtained two-dimensional spectroscopy of the central ∼10″ × 12″ of the Wolf-Rayet galaxy NGC 4861. We have carried out a preliminary analysis of the data, deriving continua at different wavelengths, and emission-line intensity maps (HeI λ4471, HeII λ4686, Hβ, [O III]λ4959, 5007) directly from the observed spectra.
Wolf-Rayet stars in I Zw 18
Authors: Legrand Francoid , Kunth Daniel , Roy Jean-René , Mas-Hesse J. Miguel , Walsh Jeremy R.
Published: July 2016

Wolf-Rayet stars have been detected in the NW region of the metal–poor starburst galaxy I Zw 18. The integrated luminosity and FWHM of the bumps at 4650 Å and 5808 Å are consistent with the presence of a few individual stars of WC4 or WC5 type. The unexpected presence of WC stars in such a low-metallicity galaxy could, however, be explained by high mass loss rates, or alternatively favor a binary channel for WR formation. WC stars could also account for the strong and narrow He II 4686Å emission line which peaks co-spatially with the WR bump emission (see Schaerer 1996).
An X-ray survey of Wolf-Rayet galaxies
Authors: Stevens Ian R. , Strickland David K.
Published: July 2016

We report on an ongoing survey of the X-ray properties of Wolf-Rayet galaxies. The current sample now has 14 detections, as well as a number of upper-limits. WR galaxies have soft thermal X-ray spectra with properties consistent with an origin from superbubbles in a young starburst.
The chemical evolution of dwarf starburst galaxies
Authors: Matteucci Francesca , D'Ercole Annibale
Published: July 2016

We will review the most popular models for the chemical evolution of some starburst galaxies, in particular dwarf irregular galaxies. These galaxies are relatively simple and unevolved objects with low metallicities and large gas contents, suggesting that they are either young or have undergone discontinuous star formation activity. Some dwarf irregulars are starburst galaxies currently experiencing an intense star formation event and they are known as blue compact galaxies or extragalactic H II regions. We will discuss the effects of the presence of dark matter halos together with stellar energetics (stellar winds and supernovae) on the development of a galactic wind in these systems. Particular emphasis will be given to the role of massive stars in driving the thermal and chemical evolution of the gas, in particular to type II supernovae. A comparison between different model predictions for abundances and abundance ratios will be used to impose constraints on the star formation history and on the amount of dark matter, which we found to be extremely important in these systems.
Evolution of the ISM in starbursting dwarf galaxies
Authors: Brighenti Fabrizio , D'Ercole Annibale
Published: July 2016

We present a 2D-hydrodynamical simulation of the gas flow generated by a starburst in a dwarf galaxy. We focus in particular on the ejection efficiency both of the ISM and of the metals produced during the burst. It turns out that while the galaxy is able to retain most of the ISM, a significant fraction of the metals is lost, supporting the differential wind scenario. A new burst may occur after ∼ 0.5-1 Gyr, when the central gas surface density approaches the critical value, during the post starburst gas replenishment.
Starburst galaxy NGC 7673: a minor merger remnant
Authors: Homeier Nicole L. , Gallagher John S.
Published: July 2016

We investigate the kinematics of the luminous starburst galaxy NGC 7673 = Mrk 325, a nearby example of a ‘clumpy irregular galaxy’. Images with the WIYN 3.5m telescope reveal outer wisps associated with mergers, and we suggest NGC 7673 is the survivor of a minor merger. DensePak spectroscopy of the Hα kinematics shows that the H II regions are confined to a rotating disk. The Hα emission line velocity field indicates that although there is widespread star formation across the inner disk, it is still rotating smoothly. The Hα emission profiles over the brightest regions of the galaxy have two components: narrow, FWHM ≈ 50kms−1 lines, and broad, FWHMW ≈ 150 km s−1 lines. The width of the narrow lines is likely due to a combination of averaging effects, stellar winds and SNRs, and possibly gravitational motions within the disk. The origin of the broad component, which eclipses the narrow component in flux over much of the galaxy's inner regions, is still unclear. We may be looking at turbulent gas encased in bubbles carved out by massive stars and their descendants, or possibly some localized outflows from the disk.
Metallicity dependence of starburst spectra
Authors: Traat Peeter
Published: July 2016

The impact of chemical composition on the spectrum of stellar population formed in the starburst is studied. The range of metallicities Z = 0.0001–0.05–0.1 covers all the compositions observed; depending on age, wavelength region and IMF, the UV-fluxes differ between extreme compositions at least ten-fold or more. Independent of age, UV-fluxes shortwards of the Balmer jump monotonically decline with the growth of metallicity. The optical IR wavelenght region are also influenced, with fluxes at λ > 1 μm differing typically factors 10–50. In the IR the actually brightest emitting composition gets reversed with age.
Lunar Accretion from an Impact-Generated Disk
Authors: Kokubo Eiichiro , Ida Shigeru
Published: July 2016

We investigate the evolution of a circumterrestrial disk of debris generated by a giant impact on the Earth and the dynamical characteristics of the moon accreted from the disk by using N-body simulation. We find that in most cases the disk evolution results in the formation of a single large moon on a nearly circular orbit close to the equatorial plane of the initial disk just outside the Roche limit. The efficiency of incorporation of disk material into a moon is 10-55%, which increases with the initial specific angular momentum of the disk. These results hardly depend on the initial condition of the disk as long as the disk mass is a few times the present lunar mass and most disk mass exists inside the Roche limit.
The Inner Structure of Cold Dark Matter Halos
Authors: Navarro Julio F.
Published: July 2016

I report on recent progress in our understanding of the structure of CDM halos, and in particular of the inner mass profile of galaxy-sized systems. Numerical simulations have consistently shown that the density profiles of CDM halos steepen monotonically from the center outwards, with slopes shallower than isothermal near the center and steeper than isothermal near the virial radius. Ongoing debate centers on the precise radial dependence of the logarithmic slope, as well as on whether it approaches a well defined asymptotic central value. The latest high-resolution simulations suggest that the circular velocity profile is well approximated by the model proposed by Navarro, Frenk & White (NFW). On the other hand, the radial dependence of the slope of the density profile differs modestly, but significantly, from the model proposed by NFW. As a result, NFW fits tend to underestimate the density at radii just inside the scale radius. Rather than implying a very steep (ρ ∝ r-1.5) inner divergent slope, I argue that the data is actually best represented by a model where the density profile becomes increasingly shallow with radius, with little sign of approach to a well-defined asymptotic value. A model where the phase-space density profile is a power law accounts well for these results and suggests that the innermost slope may be as shallow as ρ ∝ r-0.75. These conclusions are supported by a thorough numerical convergence study that elucidates the effect of numerical parameters such as the timestep, gravitational softening, and particle number, on the mass profile of simulated dark matter halos.
A Special-purpose Computer for Molecular Dynamics Simulations: MDM
Authors: Narumi Tetsu
Published: July 2016

We developed a special-purpose computer for molecular dynamics simulations, which we call Molecular Dynamics Machine (MDM). MDM accelerates the Coulomb and van der Waals force calculation with the Ewald method. It is composed of three parts: MDGRAPE-2, WINE-2 and a host computer. MDGRAPE-2 accelerates the real-space part of the Coulomb and van der Waals forces. WINE-2 accelerates wavenumber-space part of the Coulomb force. The host computer performs other calculations. The peak performance is 78 Tflop/s. It can also be used for cosmological, Smoothed Particle Hydrodynamics, and vortex dynamics simulations.
Long-term integration error of KS regularized orbital motion
Authors: Arakida Hideyoshi , Fukushima Toshio
Published: July 2016

We show the effectiveness of the KS regularization and the method of variation of parameter for integrating of the perturbed two body problems.
Warped Accretion Discs
Authors: Chakrabarty D. , Murray J. , Wynn G.A. , King A.R.
Published: July 2016

In this article we report the results of our numerical investigation of warped accretion discs in binary stellar systems. We perform complete 3-D hydrodynamic simulations of binary discs. The disc is rendered unstable to the warp mode under the action of the magnetic field of the companion star in the binary. The disc thus warped is noted to undergo retrograde precession with a precession period just slightly less than the binary period. This small difference in periods can explain the phenomenon of negative superhumps observed in a number of binaries. Besides the modal analysis based on Fourier transforms, warps were also studied by a simple and robust technique that we developed; this is based on an analysis of the azimuthal distributions of particles that lie above and below the mid-plane of the disc.
Cold Dark Matter Substructure and the Heating of Galactic Disks
Authors: Font Andreea S. , Navarro Julio F.
Published: July 2016

We investigate recent suggestions that substructure in cold dark matter (CDM) halos has potentially destructive effects on galactic disks. N-body simulations of disk/bulge models of the Milky Way, embedded in a dark matter halo with substructure similar to that found in cosmological simulations, show that tides from substructure halos play only a minor role in the dynamical heating of the stellar disk. This suggests that substructure might not preclude CDM halos from being acceptable hosts of thin stellar disks.
Monte Carlo Simulations of Million Body Star Clusters
Authors: Giersz Mirek
Published: July 2016

The first results of Monte Carlo simulations of the evolution of tidally limited, multi-mass million star clusters with stellar evolution and dynamically formed binaries are presented.
Are cosmological N-body simulations reliable on scales below the mean separation length of particles?
Authors: Hamana Takashi , Yoshida Naoki , Suto Yasushi
Published: July 2016

We critically examine the reliability of clustering below the mean separation length of particles in cosmological high-resolution N-body simulations. The particle discreteness effect imposes two fundamental limitations on those scales; the lack of the initial fluctuation power and the finite mass resolution. We address this problem applying the dark matter halo approach which makes us possible to examine separately how those two limitations affect the simulation results at later epochs. We find that the reliability of the simulations on scale below the mean particle separation is primarily determined by the mass of particles. Since the small scale matter clustering is dominated by the matter in a virialized halo, it is naturally expected that the small scale clustering becomes unreliable when the characteristic nonlinear mass for gravitationally collapsed objects at that time becomes smaller than the particle mass. This is confirmed by a detailed comparison with three major cosmological simulations. The characteristic mass, MNL(z), is approximately given by the condition σ(MNL, z) = 1. This mass scale should be much larger than the simulation particle mass mpart so as to reproduce the proper amplitude of the small scale clustering. This requirement can be translated to the criterion for the critical redshift zcrit when simulations reasonably resolve the clustering on scales below the mean separation: MNL(zcrit) = nhalompart, where we introduce a fudge factor, nhalo, of around ten. We conclude that at z > zcrit high-resolution N-body simulations are not reliable on scales below the mean particle separation. Although it is not obvious if the opposite is true at z < zcrit, our detailed comparison suggests that it is indeed the case at least as far as the two-point correlation functions of the matter are concerned. The detail discussions are presented in Hamana, Yoshida & Suto (2001).
Radiation-Hydrodynamical Simulations of Primordial Galaxy Formation in the UV Background
Authors: Kitayama Tetsu , Susa Hajime , Umemura Masayuki , Ikeuchi Satoru
Published: July 2016

We study the effects of the ultraviolet background radiation (UVB) on the formation of primordial galaxies, solving self-consistently radiative transfer of photons, non-equilibrium H2 chemistry, and one-dimensional hydrodynamics. The cut-off scale of collapse is shown to drop significantly compared to previous optically thin predictions, due to both self-shielding of the gas and H2 cooling. For plausible radiation intensities and spectra, the collapsing gas can cool efficiently to temperatures well below 104K before rotationally supported. Our results imply that star formation can take place in low-mass objects collapsing in the UVB.
Origin of the galaxy morphology
Authors: Nakasato N.
Published: July 2016

In the current most plausible Cold Dark Matter (CDM) cosmology, larger halos increase their mass by the progressive mergers of smaller clumps. Due to these progressive merger events, galaxies have formed and evolved. Such merger events could trigger star bursts depending on mass of a merging object. In other words, star formation history reflects the strength of the interaction between a galaxy and merging objects. Also, a several merger events strongly affect the development of the morphology of galaxies as assumed in semi-analytic models. In the most advanced semi-analytic models, N-body simulations of dark matter particles are used to obtain the merging history of halos. By combining the description of radiative cooling, hydrodynamics and star formation with the obtained merging history, such models successfully have explained the various qualitative predictions. Here, we show the results of similar approach but using a fullly numerical model. In contrast to the semi-analytic models, we use our high resolution Smoothed Particle Hydrodynamics (SPH) models. With our SPH code, we try to tackle the problem of the galaxy morphology. We have done a several handful high-resolution SPH simulations and analyzed the merging history of such models. Accordingly, we can see the relation between the obtained morphology and the merging history or other physical properties of the model.
The relaxation time in spherical galaxy simulations
Authors: Namboodiri P. M. S.
Published: July 2016

The relaxation time of a spherical galaxy with various density distributions has been evaluated using numerical simulations. The results indicate that the relaxation time is weakly dependent on the density of the galaxies in these simulations.
Supernova Feedback in SPH Simulations of Galaxies
Authors: Pelupessy Inti , Icke Vincent , van der Werf Paul
Published: July 2016

We report on the development of a N-body/SPH code for galaxy interactions, with particular emphasis on SN feedback implementations. We show that current methods of SN feedback probably need simulations with > 105– 106gas particles per galactic disk to be able to realistically describe galactic fountains and superwinds.
Historical Remarks on the Spectroscopic Analysis of Planetary Nebulae
Authors: Aller Lawrence H. , Hyung Siek
Published: July 2016

To record the spectral lines of stars and nebulae, photographic photometry was routinely used in the early 1900s, to be later replaced by methods employing more advanced detectors. We review the progress of planetary nebular spectroscopic studies, i.e. from the early photographic photometry, through to the 1950s photoelectric scanner observations, and finally to recent charge-coupled-device spectroscopy.
The Edinburgh/AAO/Strasbourg Catalogue of Galactic Planetary Nebulae
Authors: Parker Q. A. , Hartley M. , Russeil D. , Acker A. , Ochsenbein F. , Morgan D. H. , Beaulieu S. , Morris R. , Phillipps S. , Cohen M.
Published: July 2016

We report on version 1.0 of the Edinburgh/AAO/Strasbourg catalogue of new and possible Planetary Nebulae (PN) distributed via cdrom at this meeting. We provide accurate positions, designations, images and other descriptive parameters for the PN. In future releases this will be supplemented by inclusion of spectra and related material such as line ratios, velocities etc.

The 900+ PN have been discovered solely from visual scrutiny of narrow-band exposures taken for the AAO/UKST H-alpha survey of the Southern Galactic Plane. Most have classic PN-type morphologies (i.e. bi-polar, rings, shells or ovals). SuperCOSMOS data will soon supersede our visual scanning but it proved an effective preliminary technique to identify candidate PN on the basis of morphology, isolation and identification as an H-alpha nebulosity. We already have confirmatory spectroscopy for ~ 700 objects. Much of our new sample are of very low surface brightness, with no obvious central star, and so have remained undetected in previous surveys. They are revealed here due to the excellent depth, resolution, coverage and uniformity of the H-alpha survey. Many PN are also well extended. The average angular size is 51″ with the median of 27″ but examples extend to several arcminutes. This may indicate many are in a highly evolved state where the central star has faded from easy optical detection and the nebula itself is dissipating into the ambient ISM. Large numbers of candidate PN have also been found in the Galactic Bulge region, most of which have been confirmed via UKST FLAIR/6dF MOS spectroscopy (Parker et al, in preparation and these proceedings).

By version 2.0 (release in 2002) we will have doubled the number of Galactic PN accrued from all sources over the last 75 years. This new catalogue should have a profound impact on many aspects of PN research.
New Emission Line Planetary Nebulae Nuclei in the Direction of the Galactic Center
Authors: Górny S.K. , Siódmiak N.
Published: July 2016

We have discovered new Wolf-Rayet type and weak emission-lines nuclei of the planetary nebulae in the Galactic center.
H 2–12, a Misidentified Planetary Nebula in Kepler's SNR
Authors: Riesgo-Tirado H. , López J. A.
Published: July 2016

H 2–12 (PN 004.5+06.8) is classified as a true or probable planetary nebula (Acker et al. 1992). We obtained narrow-band imagery and long-slit echelle spectra from several positions across H 2–12. It is shown that H 2–12 is associated with one of the brightest condensations located at the periphery of Kepler's SNR. Thus, H 2–12 should be noted as a misclassified PN.
New WR Central Stars of PNe identified on the AAO/UKST Hα Survey
Authors: Morgan D. H. , Parker Q. A.
Published: July 2016

Candidate central stars can be seen in some (≤10%) of the many (~1000) new planetary nebulae found during scans of the AAO/UKST Hα survey of the Milky Way (Parker et al. 2002). Spectroscopic observations have identified seven with Wolf-Rayet emission features, thereby adding significantly to the 56 [WR] central stars already known (Jeffery et al. 1996). Two of these are late-type stars – [WC8] and [WC9-10], and four are early-type around [WC4] or possibly [WO4]. Two of the early-type stars have unusual strong emission features near 4610Å which may be attributed to [N V] and could be indicative of enhanced nitrogen in their atmospheres and unusual stellar evolution. The seventh star is of the [WN] sequence and, if confirmed, would be the only known [WN] central star in the Galaxy. Its surrounding circular nebula has emission lines with expansion velocities exceeding 150 km/s suggesting that the object may not a conventional planetary nebula. The possibility that it is a Population I star with a ring nebula, although looking increasingly less likely, cannot be finally ruled out at this stage. Full details of the [WC] stars have been given by Morgan, Parker, & Russeil (2001) and Parker & Morgan (2002). The candidate [WN] star is described by Morgan & Parker (2002).
The Central Stars Parameters and the Distances to Galactic Planetary Nebulae
Authors: Sharova O. I.
Published: July 2016

In our paper (Sharova, 1995) a method of determining the distances to galactic planetary nebulae has been based on the recently established (Sharova, 1992) regression relationship between the central stars radius and the temperature. Now our scale is compared to 18 other scales, in four of which the central stars parameters also are used, instead of nebulae ones. The scale distance estimations DS are compared with independently known individual distance D. The values log(DS/D) and their dependence on radius of the nebulae are analysed. Each scale is described by two parameters: a geometrical average value < log DS/D > and the relation ρ/ρc, where ρ is the correlation coefficient for log DS/D — log RN, and ρc is its critical value. If ρ/ρc > 1, the correlation is significant with the confidence probability 95%. For example we obtained the following results: ρ/ρc = 0.153, 0.494, 2.126, 2.228; < DS/D >=0.999, 2.145, 2.126, 1.414 for our scale and for widely known MKH, CKL, VdSZ scales respectively. By both criteria our scale achieves better agreements, on average, with individual estimations of distances than others.
OH/IR Star “Death” Statistics
Authors: Lewis B. M.
Published: July 2016

Four dead OH/IR stars are identified in a complete Arecibo sample of OH/IR stars, together with one in the process of dying.
Fe-Deficiency in H-Deficient Post-AGB Stars Due to n-Capture Nucleosynthesis
Authors: Herwig Falk , Lugaro Maria , Werner Klaus
Published: July 2016

H-deficient post-AGB objects, e.g. PG1159 type star K1-16 and born-again AGB star Sakurai's object, have been reported to be significantly iron-deficient. We find that the iron deficiencies expected due to neutron-capture nucleosynthesis during either the progenitor AGB evolution and/or the neutron burst that occurs as a result of the rapid burning of protons during a post-AGB He-flash are generally in line with observations.
H- and He-burning Central Stars and the Evolution to White Dwarfs
Authors: Blöcker T.
Published: July 2016

The structure and evolution of central stars of planetary nebulae (CSPNe) is reviewed. CSPNe represent the rapid transitional stage between the Asymptotic Giant Branch (AGB) and the white-dwarf domain. It is shown that the whole evolution off the AGB through the central-star regime depends on the evolutionary history. The detailed evolution into a white dwarf is controlled by the internal stellar structure which, in turn, is determined by the duration of the preceding AGB evolution and therefore by the AGB mass-loss history. The evolution of hydrogen-deficient central stars has been a matter of debate since many years. Convective overshoot appears to be a key ingredient to model these objects. Various thermal-pulse scenarios with inclusion of overshoot are discussed, leading to surface abundances in general agreement with those observed for Wolf-Rayet central stars.
Quasi-Periodic Shells Around Post-AGB Stars and PNe
Authors: Simis Yvonne
Published: July 2016

In a previous paper (Simis, Icke, & Dominik 2001, hereafter SID2001), it was shown that the concentric, quasi-periodic shells around IRC +10216 seem to originate on the AGB, as an instability in the wind. In this contribution a grid of model calculations is used to investigate the formation mechanism further. Comparing the calculations leads to the conclusion that mass loss variability on the AGB, and hence the formation of shells, is more likely to occur for relatively high stellar mass and temperature, and low luminosity than for lower mass and temperature and higher luminosity.
Interpreting the Evolving Clumpy Shell Structure of IRC +10216 in Terms of Time Dependent Dust Shell Models
Authors: Winters J. M. , Blöcker T. , Hofmann K.-H. , Weigelt G.
Published: July 2016

The prototypical dust-enshrouded carbon Mira IRC +10216 is known to exhibit intrinsic changes on a time scale of the order of only a few years as revealed, e.g., by CO infrared line profiles (Winters et al. 2000a), its infrared light curves, and by high spatial resolution monitoring in the infrared (Osterbart et al. 2000; Tuthill et al. 2000). In particular, the infrared light curves indicate a possible periodicity on a ≈ 20 yr time scale, i.e. that a recurrent phenomenon might lead to the observed variations. Such multi-periodicity time scales of several (≈ 10) stellar pulsation periods are predicted by consistent hydrodynamical models which include a proper treatment of dust formation (e.g. Winters et al. 2000b). In these models discrete dust layers form in time intervals which are several times longer than the typical pulsation period of an AGB star (Fleischer, Gauger, & Sedlmayr 1995; Höfner, Feuchtinger, & Dorfi 1995).
The Dynamical Gas Evolution of Low-and Intermediate-Mass Stars: PN Formation
Authors: Villaver Eva , Manchado Arturo , García-Segura Guillermo
Published: July 2016

Planetary nebula (PN) formation is intimately linked to stellar evolution. The stellar wind during the AGB and post-AGB stages depends on the progenitor mass and determines, together with the radiation field of the star, the structure and evolution of PNe. We summarize the results of the PhD thesis of E. Villaver, where we combined the results of stellar evolution with a numerical code to study the PN formation process.
Central Stars of Young Planetary Nebulae - A New Class of Variables
Authors: Handler G.
Published: July 2016

A new class of variable star is proposed. These are variable central stars of young Planetary Nebulae exhibiting roughly sinusoidal (semi)regular photometric and/or radial velocity variations with time scales of several hours. Fourteen of these objects have been identified. Their temperatures are between 25000 and 50000 K and most show hydrogen-rich spectra. The most likely reason for the variability is stellar pulsation. Another possibility would be variable stellar mass loss, but in that case the mechansism causing it must be different from that operating in massive O stars. We speculate that it actually is the stellar pulsations which cause mass loss mdulations.
The “21” μm and “30” μm Emission Features in Planetary Nebulae with Wolf-Rayet Central Stars
Authors: Hony Sacha , Waters L.B.F.M. , Tielens A.G.G.M.
Published: July 2016

We present mid infrared spectra of two planetary nebulae with H poor central stars that exhibit the “21” and “30” μm emission features. These features are found in carbon rich dust surroundings. The presence of these features shows that these sources have suffered an extended period of carbon rich mass loss before becoming H poor. We discuss the occurrence of both O-rich and C-rich dust in the sample of planetary nebulae observed with the Infrared Space Observatory.
ISO–SWS spectra of [WR] planetary nebulae
Authors: Szczerba Ryszard , Volk Kevin , Górny Sławomir K.
Published: July 2016

We have analyzed Infrared Space Observatory Short Wavelength Spectrometer (ISO–SWS) observations for 16 Wolf–Rayet ([WR]) planetary nebulae (PNe) with the aim of identifying the dust features present in this group of objects. We have found that Polycyclic Aromatic Hydrocarbon (PAH) molecular bands (which are present in most of the observed [WR] PNe) are more frequent than crystalline silicate features.
Carbonates in Planetary Nebulae
Authors: Kemper F. , Waters L. B. F. M. , de Koter A. , Jäger C. , Henning Th. , Molster F. J. , Barlow M. J. , Lim T.
Published: July 2016

We report the discovery of carbonates in the Planetary Nebulae NGC 6302 and NGC 6537 (Kemper et al. 2002). In the ISO LWS spectra far-infrared features have been identified with calcite and dolomite by comparison with laboratory spectra of these minerals. This is the first time that carbonates have been identified outside the solar system. In a follow-up study (Kemper et al., in prep.) a detailed analysis of the mineral composition of the dust in NGC 6302 is presented.
IR Spectroscopy and Imaging of IRAS 16342-3814
Authors: Dijkstra C. , Waters L. B. F. M. , Kemper F. , de Koter A. , Hony S. , Dominik C. , Zijlstra A. , Matsuura M.
Published: July 2016

The late stages of stellar evolution of stars with low or intermediate mass (1 M⊙ to 8 M⊙) are characterized by extensive mass loss, which can be traced in their circumstellar environment. Here we consider the case of IRAS 16342-3814, a bipolar proto planetary nebula which shows very high velocity (~ 50 km s-1) OH maser emission (Sahai et al. 1999). We present the complete Infrared Space Observatory (ISO) spectrum and an infrared TIMMI2 Q-band image of this source. Based on these data we discuss the composition and geometry of the circumstellar dust in IRAS 16342-3814.
Could SiC A+B grains have originated in a post-AGB thermal pulse?
Authors: Herwig Falk , Amari Sachiko , Lugaro Maria , Zinner Ernst
Published: July 2016

The carbon and nitrogen isotopic ratios of pre-solar SiC grains of type A+B suggest a proton-limited nucleosynthetic process as encountered, for instance, during the very late thermal pulse of post-AGB stars. We study the nuclear processes during this phase and find carbon and nitrogen isotopic ratios which can reproduce those of A+B grains. These results are still preliminary because they depend on uncertain factors such as the details of mixing during the post-AGB thermal pulse, the rates of some nuclear reactions, and the assumptions on mixing during the progenitor AGB phase.
Silicon Carbide as the Carrier of the 21μm Feature
Authors: Speck A. K. , Hofmeister A. M.
Published: July 2016

Some proto-planetary nebulae (PPNe) exhibit an enigmatic feature in their infrared (IR) spectra at ~21 μm. PPNe which display this feature are all C-rich and all show evidence for s-process enhancements in their photospheres, indicative of efficient dredge-up during the ascent of the asymptotic giant branch (AGB). Furthermore, this 21 μm feature is not seen in the spectra of either the precursors to PPNe, the AGB stars, or the successors of PPNe, planetary nebulae (PNe). However the 21 μm feature has been seen in the spectra of PNe with Wolf-Rayet central stars. Therefore the carrier of this feature is unlikely to be a transient species that only exists in the PPNe phase. It is more likely that the physical conditions in the AGB stars and PNe conspire against the observation of an IR feature at 21 μm. This feature has been attributed to various molecular and solid state species, none of which satisfy all constraints, although TiC and PAHs have seemed the most viable.
Bi-abundance Photoionization Models for Planetary Nebulae
Authors: Péquignot D. , Liu X.-W. , Barlow M. J. , Storey P. J. , Morisset C.
Published: July 2016

A new class of planetary nebulae, in which abundances derived from optical recombination lines (ORL) seem to be much larger than those derived from collisionally excited lines (CEL) by up to one or two orders of magnitude is now well identified (Liu, these proceedings and references therein).

Photoionization models including two components, one highly enriched in C, N, O, Ne and deficient in H and the other one of more usual composition, can account for most of the numerous spectroscopic data available from UV to far-IR in two of the best observed, most extreme examples, namely NGC 6153 and M142 (Péquignot et aI., 2002, and in preparation). The few discrepancies left can generally be understood in terms of inaccuracy of the observations (calibration of infrared line fluxes relative to the optical) and some atomic data, particularly in the unusual conditions prevailing in the H-deficient component.
Sulfur, Chlorine & Argon Abundances in Galactic PNe
Authors: Kwitter Karen B. , Henry Richard B.C.
Published: July 2016

We report first results from our extensive study of S, Cl and Ar abundances in a large sample (>60) of primarily Type II planetary nebulae (PNe) in the Galaxy (see Kwitter & Henry 2001, ApJ, 562, 804). Ratios of S/O, Cl/O, and Ar/O constitute important tests of differential nucleosynthesis of these elements and serve as strict constraints on massive star yield predictions. The use of PNe to measure the original stellar abundances of S, Cl, and Ar is possible because PN progenitors, intermediate-mass stars between 1 and 8M⊙, lack sufficient mass to synthesize these elements. Therefore, their abundances measured in the nebulae at present reflect accurately the original stellar abundances.

Here we present results from new ground-based optical spectra of planetary nebulae extending from 3600–9600Å. The observed spectral range includes the strong near-infrared lines of [S III] λλ9069,9532, which allowed us to extensively test their effectiveness as an indicator of S++. We find that the S++ abundances derived from these lines are quite consistent with those derived from the λ6312 line when the latter is well measured. In addition, we find that the atmospheric absorption affecting the near-infrared lines can be minimized by using in the calculation whichever of the pair is less affected: if the observed ratio of λ9532/λ9069 exceeds 2.48, the theoretical value, we use λ9532; if we observe a ratio <2.48, we use λ9069 instead. We also introduce a new, model-tested ionization correction factor for sulfur that includes the latest atomic data and the effects of matter-boundedness.

For the northern subsample we find the following averages: S/O=1.2E-2±0.71E-2, Cl/O=3.3E-4±1.6E-4, Ar/O=5.0E-3±1.9E-3.

Subsequent papers in this series will present the full analysis and compare our derived abundances of S, Cl, and Ar with nucleosynthesis predictions from massive stars. (A companion paper in this volume by Milingo, Henry & Kwitter discusses the southern subset observed at CTIO; see also Milingo, J.B., Kwitter, K.B., Henry, R.B.C., & Cohen, R.E. 2002, ApJS, in press; Milingo, J.B., Henry, R.B.C., & Kwitter, K.B. 2002, ApJS, 2002, in press.)
Far-Ultraviolet Spectra of Planetary Nebulae
Authors: Sonneborn George
Published: July 2016

The Far Ultraviolet Spectroscopic Explorer (FUSE)> satellite provides a unique opportunity to obtain high-resolution far-UV spectra of a wide variety of astronomical objects, including planetary nebulae. Most FUSE observations of PNe to date have concentrated on the hot central star, providing a very effective way to study the atmosphere of the central star, the surrounding nebula through the absorption features from circumstellar gas. FUSE has found evidence of hot molecular hydrogen in several planetary nebulae, including M27 and BD+30° 3639. Central star spectra also reveal new information about stellar winds, mass loss, and photospheric abundances.
XMM-Newton Detection of Extended X-ray Emission from the Saturn Nebula
Authors: Guerrero Martín A. , Gruendl Robert A. , Chu You-Hua
Published: July 2016

XMM-Newton EPIC observations of the planetary nebula NGC 7009, the Saturn Nebula, have detected extended X-ray emission from its central cavity. The diffuse X-ray emission must originate in the shocked fast stellar wind. Spectral analyses show that the temperature of the hot gas is 1.7 x 106 K. The RMS density derived from the volume emission measure is a few tens H-atom cm-3. The hot gas does not appear over-pressurized with respect to the nebular shell. The Saturn Nebula may represent an evolutionary stage at which the dynamic effects of the hot gas in the central cavity on the cold nebular shell starts to decline due to the diminishing strength of the fast stellar wind and the expansion of the central cavity.
Hot Haloes of Planetary Nebulae
Authors: Tylenda Romuald
Published: July 2016

We present model results of time-dependent ionization of a nebula with a halo. Fast transition of the ionization front across the halo causses its heating well above the equilibrium temperature. For a long time after this event the halo is observed as hotter than the main inner nebula, in agreement with observations of some planetary nebulae.
Density of Low-ionization Structures in PNe
Authors: Gonçalves Denise R. , Corradi Romano L.M. , Mampaso Antonio , Campos Cristina
Published: July 2016

We have recently completed a comprehensive analysis of the morphological and kinematical properties of ~ 50 PNe which are known to possess low-ionization (micro)structures (LISs; Gonçalves et al. 2001). This study has shown that density is a crucial parameter for distinguishing among several physical processes responsible for their formation and evolution.

We are at present analysing long-slit, medium-resolution optical spectra of 18 PNe in order to determine the physical parameters of the LISs and their environments. These data were obtained with the 1.5 m Danish (ESO) and the 2.5 m Isaac Newton (ORM) telescopes.

Here we show the first results of this survey, presenting the density variation of NGC 7009 and comparing it with the derived densities of K 4-47 and Wray 17-1.
High Velocity Flow Suggested by Wing Components of the Hα Line Profiles in the Selected Planetary Nebulae
Authors: Tamura S. , Otsuka M. , Tajitsu A.
Published: July 2016

This is a short report on the study of internal motions of selected Planetary nebulae. We have studied this subject with both high (4 or 8 Å/mm) and intermediate (20 Å/mm) dispersion spectrographs. During the course of this work we noticed the existence of a high velocity gas flow distinct from the well known expanding gas, but with smaller velocities than stellar winds (Yadoumaru & Tamura 1994 on Abell 30; Otsuka & Tamura, 2001 on H 4-1). We present subsequent results obtained with the intermediate dispersion spectrograph about 10 selected planetary nebulae. The analyses were made by multiple Gaussian method on the emission line profiles of Hα. High velocity gas flows were recognized by a weak broad wing component.
The Most Oxygen-Poor Planetary Nebula
Authors: Richer Michael G. , Tovmassian Gaghik , Stasińska Grażyna , Gutierrez Carlos , Veillet Christian
Published: July 2016

PNG135.9+55.9 is a halo planetary nebula recently discovered among the objects from the Second Byurakan Survey. Based upon our first observations, a photoionization model analysis shows that the oxygen abundance in the nebula must be extremely low, probably 10-2–10-3 of the solar value. This finding has strong implications on our understanding of the formation of planetary nebulae, of mixing processes in the stellar progenitors and of the evolution of the Galactic halo.
Extragalactic Planetary Nebulae as Mass Tracers: Observational Aspects
Authors: Arnaboldi Magda
Published: July 2016

Planetary nebulae observed in our Milky Way galaxy and in the galaxies of the Local Group do impress us for their morphologies and complexities. But when we look at planetary nebulae outside the Local Group, all this must be forgotten, as they become unresolved and merely points of green light. This paper will review how these green spots of light can be used as probes of the mass distribution and dynamics of elliptical galaxies and nearby clusters.
Overcoming Systematic Errors in the Spectrophotometry of Extragalactic Planetary Nebulae with 3D Spectroscopy
Authors: Becker Thomas , Böhm Petra , Roth Martin M. , Schönberner Detlef , Soffner Till
Published: July 2016

Using Hα Fabry-Pérot images of the central 7 arcmin of M31 we demonstrate the amount of filamentary gaseous emission of the ISM in the bulge of this galaxy, which, along with the high surface brightness in the continuum, is known to cause serious problems for the spectrophotometry of PNe in this region. From pioneering work in the Magellanic Clouds and M31 the observational difficulties have been known for some time. We present first observations of PNe in the bulge of M31 obtained with Integral Field Spectroscopy (3D), a method which is shown to be capable of providing superior background subtraction accuracy, compared to conventional slit spectroscopy. Data were secured with MPFS at the Selentchuk 6m telescope, and during a commission run of PMAS at Calar Alto. It is shown how the spatial information obtained from the 3D technique is used to correct for systematic errors in the measurement of emission line intensities which have been reported in the literature.
Infrared Spectra of Brown Dwarf Candidates in Taurus
Authors: Magazzù A. , Dougados C. , Licandro J. , L. Martín E. , Magnier E. A. , Ménard F.
Published: July 2016

We have obtained low resolution infrared spectra of 21 brown dwarf candidates, selected from a survey performed at the Canada-France-Hawaii Telescope. The spectra were obtained at the Telescopio Nazionale Galileo (La Palma), using the NICS spectrometer in the Amici configuration, which allows to observe the range 0.85–2.45 μm in a single shot. The bands shown by most of the spectra confirm that we are dealing with low effective temperature objects. Preliminary results of spectral classification are presented.
A Large, Deep Survey of the Taurus Dark Clouds
Authors: Osborne S. L. , Jameson R. F. , Dobbie P. D. , L. Martín E.
Published: July 2016

Preliminary results from a deep R, I and Z band survey of ~ 6 square degrees of the Taurus Dark Cloud region are presented. 186 potential brown dwarfs have been unearthed, with seven having follow-up spectroscopic data. The spectra reveal three mid/late-type M dwarfs, of which two show weak Hα emission. If these objects are members of the TDC region, theoretical models suggest masses in the range 10 – 20 MJ.
The Substellar Population in IC 348
Authors: Luhman K. L.
Published: July 2016

I present the latest results in a continuing effort to spectroscopically identify the substellar members of the young cluster IC 348. I have combined new images at I and Z with IR photometry from previous studies and from 2MASS and selected candidate members of the cluster across a larger area and at lower masses than probed in previous surveys. After observing these candidates with spectroscopy, the latest census for IC 348 contains 234 members with spectral types, 22 of which are later than M6 and thus are probably substellar. Individual masses of cluster members are estimated by combining their positions on the Hertzsprung-Russell (H-R) diagram with theoretical evolutionary models. From an extinction-limited sample of members (AV ≤ 4), I construct an IMF for IC 348 that should be complete down to 0.02 M⊙. This IMF is compared to a similarly derived mass function for Taurus by Briceño et al. (2002); these data provide clear evidence for a variation of the IMF with star-forming conditions.
The Substellar Population in σ Orionis
Authors: Zapatero Osorio M. R. , Barrado y Navascués D. , J. S. Béjar V. , Rebolo R. , Caballero J. A. , Martín E.L. , Mundt R. , Eislöffel J.
Published: July 2016

The σ Orionis cluster (~3 Myr, 350 pc) is an ideal site to investigate the early evolution of substellar (brown dwarf and planetary mass) objects. To date, the cluster photometric and spectroscopic sequence of free-floaters is known for a wide mass range from 1 M⊙ down to roughly 3 MJup. The substellar domain covers spectral types that go from mid-M classes to the recently defined “methane” T-types, i.e., surface temperatures between ~3000K and 800 K. We derive a rising initial substellar mass function in the mass interval of 150–5 MJup (dN/dM ~ M-α, with α = 0.9 ± 0.4). We also find evidence for a extension of this mass function toward lower masses down to 2–3 MJup. This indicates that the population of isolated planetary mass objects with masses below the deuterium burning threshold is rather abundant in the cluster.