bluuebunny/crossref_metadata_2025 huggingface dataset:
A Systematic Study of IRAS Selected Proto-Planetary Nebula Candidates III. The Northern Sources
Authors: Hu Jingyao
Published: July 2016

We have selected a PPN candidates sample from IRAS color-color diagram. The selected criteria, the objects list of whole sample and photometric and spectroscopic observational results for southern objects have been published (paper I, Hu et al, 1993), and CO and OH maser observations for the total sample are published in 1994 (paper II, Hu et al, 1994). The 20 northern objects were observed. The optical photometric observations were taken at the J. Kapteyn telescope with CCD camera, infrared photometric observations were obtained with 1.26 meter infrared telescope at Xinglong station, Beijing Observatory, and spectroscopic observational observations were carried out using the FOS attached on the 2.5 meter Issac Newton telescope in 1989; in 1996 and 2001 we re-observed these objects using 2.16 m telescope and OMR spectroscopy at Xinglong station, Beijing Observatory. We have not found any variations between two epochs for most objects in their optical spectra except IRAS 19367+2458. The spectra we obtained in 1989 IRAS 19367+2458 is a planetary nebula with [WC] core star (Hu and Dong, 1992), but in our spectra obtained in 1996 and 2001 it is a M-type star. There are two possibilities: 1. We made mistakes of identification, if so, where is the planetary nebula? 2. It varies, but we can not find any difference in the spectra obtained in 1996 and 2001. The question is still open, more observations are needed in the future.
2-D Radiation Transfer Model of Non-Spherically Symmetric Dust Shell in Proto-Planetary Nebulae
Authors: Su Kate Y. L. , Volk Kevin , Kwok Sun
Published: July 2016

Resent high-resolution optical imaging has directly revealed reflection nebulosity around proto-planetary nebulae (PPNs), the transition objects between asymptotic giant branch (AGB) stars and planetary nebulae (Sahai et al. 1998, Su et al. 1998, Ueta et al. 2000, Su et al. 2001). The existence of bipolar nebulae observed in the PPN phase suggests the presence of asymmetry in the AGB circumstellar dust shell. In order to model these objects, a self-consistent radiation transfer model is necessary. As a first attempt, we construct an approximate two-dimensional dust radiative transfer model to simultaneously fit the spectral energy distribution (SED) and images of a centrally-heated dust envelope.
Magnetic Field in the Proto-Planetary Nebula OH17.7–2.0
Authors: Bains Indra , Gledhill Tim , Yates Jeremy , Richards Anita
Published: July 2016

We have used radio observations of OH masers in proto-planetary nebula (PPN) candidates to probe the magnetic field structure of these objects. Here we present the first results of our study, concerning the PPN OH17.7–2.0.
Observed Evolution of the Nebulae and Central Stars
Authors: Tylenda Romuald
Published: July 2016

Several points involved in observational studies of evolution of planetary nebulae and their central stars are discussed. It concerns observed masses of nebulae and central stars, nature of H-deficient central stars, role of time-dependent ionization in the nebular haloes, and a recent discovery of strong enrichements in some planetary nebulae.
Radiation Driven Atmospheres of O-type stars: Constraints on the Mass–Luminosity Relation of Central Stars of Planetary Nebulae
Authors: Pauldrach A.W.A. , Hoffmann T.L. , Méndez R.H.
Published: July 2016

Recent advances in the modelling of stellar winds driven by radiation pressure make it possible to fit many wind-sensitive features in the UV spectra of hot stars, opening the way for a hydrodynamically consistent determination of stellar radii, masses, and luminosities from the UV spectrum alone. It is thus no longer necessary to assume a theoretical mass–luminosity relation. As the method has been shown to work for massive O stars, we are now able to test predictions from the post-AGB evolutionary calculations quantitatively for the first time. Here we present the first rather surprising consequences of using the new generation of model atmospheres for the analysis of a sample of central stars of planetary nebulae.
Calculation of Synthetic Ionizing Spectra for Planetary Nebulae
Authors: Rauch Thomas
Published: July 2016

We present a new grid (solar and halo abundance ratios) of state-of-the-art fully line-blanketed NLTE model atmospheres which covers the parameter range of central stars of planetary nebulae. The grid is available at the WWW.
WR Central Stars
Authors: Hamann Wolf-Rainer , Gräfener Götz , Koesterke Lars
Published: July 2016

Wolf-Rayet type central stars have been analyzed with adequate model atmospheres. The obtained stellar parameters and chemical abundances allow for a discussion of their evolutionary origin.
Abundances of [WC] Central Stars of PN and the Double Dust Chemistry Problem
Authors: De Marco Orsola
Published: July 2016

The chemical abundances of Wolf-Rayet ([WC]) central stars are reviewed. Although the evolutionary connection between cooler (late) and hotter (early) [WC] central stars and PG1159 central stars is now on solid ground, several issues still remain. In particular, hydrogen and oxygen abundances, that could provide a way of discriminating between different evolutionary channels, are affected by large uncertainties. Following the ground-breaking discovery that cool [WC] central stars harbor hot carbon- as well as hot oxygen-rich dust, current theories of their origin have been put in serious doubt. Observations of three cool [WC] central stars are presented here which, while confirming the deficiency of our theoretical understanding, hint at the possibility of alternative scenarios, such as dust-storing disks.
The Weak Emission Line Stars
Authors: Fogel Jeffrey , De Marco Orsola , Jacoby George
Published: July 2016

In this paper, we study the evolution of the weak emission line central stars of planetary nebula (WELS), which are similar to the H-deficient Wolf-Rayet central stars except for systematically weaker emission lines. Our attempts at finding an evolutionary sequence for the WELS similar to what was established for Wolf-Rayet central stars, were unsuccessful. No correlation was found between any of the analysed quantities: emission and absorption line fluxes or stellar and nebular parameters from the literature. It does appear, however, that WELS have intermediate stellar temperatures (30–80 kK), and do not reside in the middle of Type I planetary nebulae, possibly indicating lower mass precursors.
Wind Inhomogeneities in [WC] Central Stars: From Late-to Early-Type Nuclei
Authors: Acker A. , Grosdidier Y.
Published: July 2016

In Grosdidier et al. (2000, 2001), wind fluctuations were described for five [WC 8–10] stars. In this poster we present new results discussing the case of the hotter subtype [WO 4] (Grosdidier & Acker 2002). Specifically, we concentrate on the CIVλλ5801/12 emission-line variability observed for NGC 1501 and NGC 6751 (see also Acker & Durand, these proceedings). Main results: NGC 1501: The OVλ5590 and CIVλλ5801/12 emission lines as well as the CIV/CIII complex around 5690Å are variable at the 1% level. The amplitudes of the variations range from about 5% (OV), up to 7% (CIV) of the adjacent continuum flux. The HeIλ5876 is also found to be variable; NGC 6751: For this star, significant variability at the 1% level is detected for the CIVλλ5801/12 emission line only. Note that the variations are quite huge since they span 6–10% of the adjacent continuum flux. Small variations are seen around the line centre but they are essentially located in the red and blue wings of the line, the latter showing the largest level of variability. Generally, the amplitudes of the variations in [WO 4] central stars range up to 10% of the adjacent continuum flux, over timescales of hours, or days. This result is essentially the same than that found for [WC]-late type stars. We expect strong, hydrogen-deficient [WC] winds to be extreme examples for central stars of PN, so that any fine structure found in [WC] winds may apply to all winds of central stars of PN, much as one is finding now that weak, massive O-star winds also show the same fine structure as massive WR winds. The consequences of clumping in hot-star winds are manifold, including substantial constraints on the effective mass-loss rates, and their possible impact on the surrounding nebula itself (Acker et al. 2002). On the whole, the winds of all [WC] central stars are significantly stochastically variable on relatively short time-scales. This supports a turbulent origin.
High resolution molecular hydrogen imaging of the Ring Nebula
Authors: Speck A. K. , Meixner M. , Knezek P. , Jacoby G. H.
Published: July 2016

The relative morphologies and structures of molecular and ionized gas emission from planetary nebulae (PNe) allow a better understanding of the nature and evolution of these objects. The classical paradigm for the structure of PNe is that of an ionized gas bubble bounded by neutral gas and molecules. However, it has been shown that molecular gas exists within ionized regions, leading to a re-evaluation of the classic structure. In the Helix Nebula (NGC 7293) dense condensations known as cometary knots are known to exist in the main ionized nebula. The molecules in these knots are shielded from the ionizing radiation and thus survive within the ionized zone. Another PN in which H2 emission is seen to originate from within the ionized nebula in NGC 6720 (the Ring Nebula).
Molecular Hydrogen Emission from the Cometary Globules in the Helix Nebula (NGC 7293)
Authors: Walsh J. R. , Ageorges N.
Published: July 2016

The discovery of many dense, dusty condensations in the Helix Nebula, NGC 7293, by Meaburn et al. (1992) was the first direct evidence of the real inhomogeneity of the medium of a planetary nebula. On account of the small distance of the Helix nebula from the Sun (~200pc), the knots (cometary globules) can be resolved from the ground and studied in detail from HST imaging (O'Dell & Handron, 1996). The condensations typically have a projected diameter of <2″ and hence sizes of <6 x 1015 cm. The condensations consist of a dusty core, visible as absorption against the background high ionization central region of the nebula for the foreground globules, and with a bow-shaped ionization front, strong in low ionization emission. The emission is displaced in the direction towards the central star, often with an outwardly-directed radial tail.
The Chemistry of CRL 618
Authors: Woods Paul M. , Millar T. J. , Zijlstra Albert A. , Herbst E.
Published: July 2016

We present a chemical model of the central torus around CRL 618 in order to confirm that long-chained hydrocarbons and benzene are formed at detectable abundances. We reproduce the observed abundances of these molecules comparatively well. We infer from our calculations that CRL 618 must be a young PPN, with a post-AGB age of approximately 600 yr.
The Temperature Structure of Dusty Planetary Nebulae
Authors: Stasińska Graẓyna , Szczerba Ryszard
Published: July 2016

We have computed photoionization models of planetary nebulae containing dust. Photoelectric heating by small grains has an important effects on the temperature structure of the nebulae and could solve a number of problems that have found no satisfactory solution so far.
Atomic Processes in Planetary Nebulae
Authors: Nahar Sultana N.
Published: July 2016

A hot central star illuminating the surrounding ionized H II region usually produces very rich atomic spectra resulting from basic atomic processes: photoionization, electron-ion recombination, bound-bound radiative transitions, and collisional excitation of ions. Precise diagnostics of nebular spectra depend on accurate atomic parameters for these processes. Latest developments in theoretical computations are described, especially under two international collaborations known as the Opacity Project (OP) and the Iron Project (IP), that have yielded accurate and large-scale data for photoionization cross sections, transition probabilities, and collision strengths for electron impact excitation of most astrophysically abundant ions. As an extension of the two projects, a self-consistent and unified theoretical treatment of photoionization and electron-ion recombination has been developed where both the radiative and the dielectronic recombination processes are considered in an unified manner. Results from the Ohio State atomic-astrophysics group, and from the OP and IP collaborations, are presented. A description of the electronic web-interactive database, TIPTOPBASE, with the OP and the IP data, and a compilation of recommended data for effective collision strengths, is given.
A Deep UV-Blue Planetary Nebula Template Spectrum from NGC 7027
Authors: Walsh J. R. , Péquignot D. , Morisset C. , Storey P. J. , Sharpee B. , Baldwin J. , van Hoof P. A. M. , Williams R. E.
Published: July 2016

NGC 7027 is justifiably THE template spectrum for PNe. Its vast range of emission species – from molecular and neutral to ions with ionization potential > 120eV – its high surface brightness and accessibiliy for northern observatories make it the PN laboratory of choice. However the quality of the spectra from the UV to the IR is mixed, many line fluxes and identifications still remaining unchecked from photographic or image tube spectra. Very deep spectra of NGC 7027 (emission line strengths <10-4 of Hβ) in the 0.65 to 1.05μm region (Baluteau et al. 1995) showed the presence of many faint emission lines. Pequignot & Baluteau (1994) showed that heavy elements from the 4th, 5th and 6th rows of the Periodic Table have much higher abundances than Solar, confirming the synthesis of neutron capture elements in low mass stars and providing new constraints on stellar evolution theory.
Probing the Dark Secrets of PNe with ORLs
Authors: Liu X.-W.
Published: July 2016

There are two long-standing problems in nebular astrophysics: a) The dichotomy of abundance determinations whereby heavy element abundances relative to hydrogen from collisionally excited lines (CELs) are systematically lower than those from (much fainter) optical recombination lines (ORLs), a discrepancy that can be traced back to Wyse (1942) and Aller & Menzel (1945) who pioneered the ORL method; and b) The dichotomy of temperature determinations whereby Te derived from the collisionally excited [O III] forbidden line ratio is systematically higher than that derived from Balmer jump of the H I recombination spectrum, a discrepancy first discovered by Peimbert (1971) and attributed to temperature fluctuations in the nebula (Peimbert 1967). Thanks to the rapid progress in detector technology and recombination theory for multi-electron systems, significant progress has been made in recent years in our understanding of these two fundamental problems, which could potentially affect the derivation of abundances for a wide range of photoionized nebulae, both galactic and extragalactic. Both types of dichotomy are found to be real and are most likely caused by astrophysical effects rather than uncertainties in observations or in the basic atomic physics. The two problems are shown to be related and can be explained by assuming that PNe contain a small mass of extremely cold (Te ~ 103 K) inclusions, highly enriched in helium and heavy elements, embedded in diffuse material of “normal” abundances (~ solar) and temperature (Te ~ 104 K). The existence and nature of such H-deficient inclusions in PNe remains a mystery. A recent review on this subject is given by Liu (2002).
Far-Infrared Atomic Lines: PDRs or Shocks?
Authors: Meixner Margaret , Fong David , Sutton Edmund C. , Castro-Carrizo Arancha , Bujarrabal Valentín , Latter William B. , Tielens Alexander , Kelly Douglas M. , Barlow Michael J.
Published: July 2016

The relative role of the stellar radiation field, the stellar outflows and the interstellar radiation field (ISRF) in transforming the molecular ejecta into atomic gas was the subject of our ISO LWS and SWS spectroscopy study of 24 evolved stars which span the range from AGB stars to proto-planetary nebulae (PPNs) and PNs. The far-infrared (FIR) atomic fine-structure lines are powerful probes of the warm atomic gas in photodissociation regions (PDRs) and shocks. This paper summarizes and compares the ISO spectroscopy studies of carbon-rich (C-rich) and oxygen-rich (O-rich) evolved stars, published by Fong et al. (2001) and Castro-Carrizo et al. (2001), respectively. We find that photodissociation, not shocks, is responsible for the chemical change from molecular to atomic gas.
Accurate Abundances Determination of Planetary Nebulae
Authors: Salas J. Bernard , Pottasch S. R. , Wesselius P. R. , Marigo P.
Published: July 2016

Accurate chemical abundances for the following planetary nebulae (PNe); NGC 6537, He 2-111, NGC 6302, NGC 6445, NGC 6741, NGC 7027, NGC 7662, NGC 2440 and NGC 5315 have been derived using data from the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). Optical data from the literature has also been used. These work has been published by Pottasch et al. (2001), Bernard Salas et al. (2001 and 2002). In particular, the use of the ISO data has reduced the need for ionization correction factors. Furthermore, infrared data avoid or reduce many problems when deriving these abundances, namely: temperature fluctuations in the nebula, and extinction corrections. The electron temperature (Te) and density of the PNe has been derived. For those PNe in which the Te has been derived for several ions a trend with the ionization potential is present. Ions with high stages of ionization give higher Te, probably because they are formed close to the central star. The chemical abundances measured in these PNe give some hint of the nucleosynthesis and mixing processes experienced by their progenitor stars. In this view, a preliminary comparison with synthetic TP-AGB models is made (Bernard Salas et al. (in prep.)). NGC 7027, NGC 6741, NGC 2440, and NGC 6445 are consistent with the occurrence of the 3rd dredge-up due to both C12 and He4 enrichment. NGC 6537, NGC 6302, and He 2-111 are likely to have stellar progenitors experiencing hot bottom burning due to the low C12 and high N14 abundances.
Chemical Abundances of Planetary Nebulae Towards the Galactic Anticenter
Authors: Costa Roberto D.D. , Maciel Walter J. , Uchida Monica M.M.
Published: July 2016

We report the results of spectrophotometric determinations of chemical abundances for a planetary nebulae sample located outside the solar circle, with galactocentric distances between 8 and 14 kpc. Our results show a decreasing gradient for R>10 kpc and a possible dependence of the gradient with the age of the progenitors (Work supported by FAPESP).
A Spatially Resolved Spectroscopic Study of NGC 7009
Authors: Luo S.-G. , Liu X.-W.
Published: July 2016

Liu et al. (1995) and Luo, Liu & Barlow (2001) determined the CNONe abundances in NGC 7009 using optical recombination lines (ORLs) and found that they are all approximately a factor of five higher than the corresponding values derived from collisionally excited lines (CELs). We have obtained new deep high resolution long-slit spectra of NGC 7009. The data have been used to map the electron temperature, density and element abundances across the nebula, using both CELs and ORLs. While the electron temperature derived from the [O III] forbidden line ratio, Te([O III]), is found to be largely constant, that derived from Balmer jump of H I recombination spectrum, Te(BJ), shows large amplitude complicated variations. The ratios of the heavy element abundances derived from ORLs to those deduced from CELs are found to be correlated with the difference between the difference between Te([O III]) and Te(BJ) – a relation previously known to exist from analyses of the integration spectra of individual nebulae (Liu et al. 2001).
CFHT Fabry-Perot 2D Spectroscopy in Hα of the Planetary Nebula NGC 40: Universal Multifractal Analysis and Turbulent Status
Authors: Grosdidier Y. , Acker A. , Blais-Ouellette S. , Joncas G. , Moffat A.F.J.
Published: July 2016

Using CFHT/SIS Fabry-Perot interferograms of the planetary nebula NGC 40, we present an investigation of the statistical properties of fluctuating gas motions using structure functions traced by Hα emission-line centroid velocities (Grosdidier et al. 2002). We consider the structure functions 〈|Δv(r)|p〉 of order p, i.e. the spatially averaged moments of order p of the spatial velocity increments at projected spatial scale r of NGC 40's velocity field. In this poster, we test for i) Structure-function scaling related to turbulence in the nebula, 〈|Δv(r) |p〉 ~ rχ(p),ϛ and ii) Nonlinearity of the observed scaling exponents χ(p)s, as expected for intermittent turbulent flows. The first order structure function is indeed found to scale at the smallest scales with χ(1) = H ≈0.68. This value is larger than the value expected in the case of incompressible or compressible turbulence, for which one would obtain H = 1/3 or 1/2, respectively. This result suggests that the Hα layer is thick compared to the projected spatial separations (O'Dell & Castañeda 1987, and references therein). We can give a more quantitative description of the turbulent status of the PN NGC 40 through the examination of the structure function for different orders. Additionally we can discuss the nature of the turbulence in terms of Universal Multifractals, a continuous-scale limit of multiplicative cascades (Schertzer & Lovejoy 1987) and derive the level of intermittency in the nebula. The function χ(p) is indeed found to be nonlinear and well reproduced with the following Universal Multifractal parameters: α ≈ 1.90–2 (the field is highly multifractal with a gaussian generator) and C1 ≈ 0.08 (the field suffers significant intermittency, which is incompatible with monofractal additive stochastic models usually introduced in similar studies): ϛ(p) = p × H − C1(pα - p)/(α - 1). Fig. 1 shows the hierarchy of exponents χ(p) along with its best Universal Multifractal fit. Our results on the Wolf-Rayet ring nebula M 1–67 (Grosdidier et al. 2001) led to the same level of multifractality (α ≈ 1.9) but with smaller intermittency (C1 ≈ 0.04). Preliminary results on the Orion nebula (Grosdidier 2002) reveal a turbulent status relatively similar to that of the PN NGC 40. On the whole, such a study provides a way to quantify turbulence in PN, and more generally in other HII regions (with potential implications for the estimation of temperature fluctuations) and give insight on astrophysical turbulence for its own sake.
X-ray and UV Views of Hot Gas in Planetary Nebulae
Authors: Chu You-Hua , Guerrero Martín A. , Gruendl Robert A.
Published: July 2016

The interior of a planetary nebula (PN) is expected to be filled with shocked fast wind from the central star. This hot gas plays the most important role in the dynamical evolution of the PN; however, its physical conditions are not well-known because useful X-ray and far-UV observations were not available until the advent of Chandra, XMM-Newton, and FUSE. This paper reviews X-ray observations of the hot gas in PN interiors and far-UV observations of the interfaces between the hot gas and the dense nebular shells.
The Correlation of PN Morphology and Parameters
Authors: Manchado Arturo
Published: July 2016

The morphology of a complete sample of 255 northern planetary nebulae (PNe) was studied and correlated with the nebular parameters. PNe were classified according to the following scheme: round (R, 25%), elliptical (E, 58% of the sample), and bipolar (B, 17%). Bipolars include the quadrupolar subsample. A subclass of pointsymmetric and multiple shell PNe was also found. Nine per cent of ellipticals and 46% of bipolars were found to be pointsymmetric. Thirty-five per cent of the round and 22% of the elliptical PNe were found to be multiple shell PNe (MSPNe). Galactic latitude was found to be different for each morphological class (|b| = 8°, 5° and 2° for types R, E, and B, respectively). Galactic height was also found to vary: 〈z〉 = 647, 276, and 100 pc for categories R, E, and B, respectively. Segregation according to the chemical abundances was also found, with helium abundances of 0.10, 0.12, and 0.14 and N/O of 0.21, 0.31, and 1.33 for types R, E, and B, respectively. Both galactic distribution and chemical abundances point to a different stellar population for each morphological class, the round and bipolar types being the result of low and high stellar mass progenitor evolution, respectively.
MHD Models of Planetary Nebulae: Review
Authors: García-Segura Guillermo
Published: July 2016

When we discuss about MHD effects in planetary nebulae (PNe), there naturally arises a basic question: which magnetic field do we study? One possibility is the ISM magnetic field (e.g. Heiligman 1980), even more if we are concerned with moving PNe (e.g. Soker & Dgani 1997). The next possibility is the internal or stellar magnetic field (Gurzadian 1962). It is important to start this review by quoting Aller (1958): “It has been pointed out by Minkowski and others that the structural appearance of many planetary nebulae strongly suggest the presence of magnetic fields. It seems unlikely that such magnetic fields are produced ab initio in the nebular shell. Rather, they must have existed in the outer envelope of the parent star. Certain red giants stars with magnetic fields may evolve in such a way that the expansion of the shell is largely governed by the presence of such a field. Magnetic effects may actually be more important than gas pressure differentials and radiation pressure in controlling the evolution of a planetary nebula”.
Cyclotron Radiation: a Jet-Driving Mechanism in Magnetized PN Nuclei
Authors: Serber A. V.
Published: July 2016

We claim that cyclotron radiation at the electron gyrofrequency ωB is an efficient mechanism capable of driving highly collimated bipolar jets in magnetized nuclei of planetary nebulae.
Radiatively Driven Winds and the Formation of Bipolar Planetary Nebulae
Authors: Dwarkadas Vikram V. , Owocki Stanley
Published: July 2016

We study the role of radiatively driven winds in the formation of PNe. The modulation of these winds due to stellar rotation, and Von Zeipel gravity darkening, are both considered. Rotation produces a wind that is faster at the poles but denser at the equator. The Von Zeipel effect, which states that the stellar flux is proportional to the effective surface gravity, results in the inverse density distribution, giving a wind that is both faster and denser at the poles. Both these effects produce bipolar nebulae for large rotational velocities of the star.
New Insight on Hubble 4
Authors: Rabaça Carlos R. , Cuisinier François , Lorenz-Martins Silvia , Epitácio Pereira Daniel N. , Gonçalves Denise R. , Lastennet Erwan
Published: July 2016

We started a program of identification of faint structures in PNe on HST archive images, based on the “à trous” wavelet transform (Starck et al. 1998). Using this technique, an image is decomposed in a new set of N images, each with the same number of pixels as the original one, but containing only the structures of a characteristic scale size (going from one image to the next, the characteristic scale vary by a factor of two). The original image c0 can be expressed as the sum of all wavelet scales plus a residual smoothed array cN by C0(x, y) = CN(x, y) + Σj=1Nwj(x, y).
The Jets of NGC 6543
Authors: Francis B. P. , Bryce M. , Graham M. F. , Holloway A. J. , López J.A.
Published: July 2016

High spectral resolution observations of the high speed jets of NGC 6543 are presented. When deprojected, these give velocities of Vsouth = -82.0 km s-1 and Vsouth = 63.8 km s-1.
The Riddle of the Red Rectangle
Authors: Icke Vincent
Published: July 2016

I reconsider my study (Icke 1981) of the hydrodynamic mechanism that is responsible for the shape of the Red Rectangle. The density of this nebula is so high, and the central star(s) so cool, that momentum driven outflow is almost guaranteed. Focusing of a spherically symmetric stellar wind through an inner shock creates a biconical pattern that may be responsible for the characteristic X-shape of the outer nebula. I compute the evolution of periodic biconical outflow. Observations made available to me by Van Winckel can thus be modeled in great detail. Features that I initially thought to be problematic for my interpretation, such as the occurrence of intersecting shocks on the symmetry axis, turned out to be present on closer inspection of the Hα image.
Sh 2-68 – A Planetary Nebula Leaving it's Mark on the Interstellar Medium
Authors: Kerber F. , Guglielmetti F. , Mignani R. , Roth M.
Published: July 2016

Using Hα images from the Southern H-Alpha Sky Survey Atlas (SHASSA) we have discovered a “cometary tail” of ionized matter extending at least 30 arcmin from the main body of the planetary nebula Sh 2-68 (PN G030.6+06.2). This tail is aligned with the proper motion of the central star and is obviously a contrail of material left behind by Sh 2-68 moving in a Galactic Disk orbit. The tail's existence is a direct confirmation of Sh 2-68's interaction with the interstellar medium (ISM) and highlights the possibly important role of the ISM's magnetic field.
Semi-dynamic Modeling of Shell Formation for V4334 Sgr (Sakurai): An Online Probe for Early PNe Evolution?
Authors: Kimeswenger Stefan
Published: July 2016

The central star V4334 Sgr (Sakurai's Nova) of the planetary nebula PN G010.4+04.4 underwent in 1995–1996 the rare event of a very late helium flash shell burning. The rapid formation of a dust shell allows a precise model, basing on the dust formation history instead of the commonly used average dust formation rate and mass loss. The model applies a complete dust grain size distribution, and transiently heated grains. Only the fitting of the visual light curve gives already the complete spectral energy distribution (SED) model. No adjustment with the infrared data points is needed.
A Detailed Kinematical Study of the Point-Symmetric Planetary Nebula IC4634
Authors: Toledano O. , Riesgo-Tirado H. , Lopez J. A. , Meaburn J. , Bryce M. , Holloway A. J.
Published: July 2016

IC 4634 is a planetary nebula with a striking point-symmetric morphology. Strings of line-emitting knots, particularly bright in [N II] emerge from its bright Hα core. These strings bend in opposite directions on either side of the nucleus. We have obatined sub-arcsecond monochromatic imagery that neatly reveals its main morphological components. Additionally, we also present a comprehensive kinematic mapping of the nebula, consisting of several long-slit echelle positions across the main components of the nebula.
Expansion Velocities From Different Ions of Planetary Nebulae with [WC]-Type Central Stars
Authors: Medina Selene , Peña Miriam
Published: July 2016

High resolution spectroscopic data of a sample consisting of 24 planetary nebulae (PNe) with WR-type nuclei ([WC]) from the list of Tylenda et al. (1993) plus 1 late-[WC] presented by De Marco et al. (2001), and 7 PNe with weak emission line stars (WELS) nuclei listed in Tylenda et al. (1993) are analyzed. The data were collected using the 2.1 m telescope at the Observatorio Astronómico Nacional, San Pedro Mártir, México and were used to determine the expansion velocity (Vexp) of the gaseous component in each sample object in the following ions: [N II]λA6584, [O II]λ3729, [O III]λA5007, Hβ, HeI λ5876, and HeII λ4686. A sample of 8 non-WR type (typical) PNe were observed as a controlo sample. All observational data were systematically gathered using the REOSC Echelle Spectrograph on 1995 July 29–31, 1996 June 14–17, 1997 August 3–4, 1998 December 11–14, 1999 October 4–7, and 2000 November 1–3. In order to take the highest Vexp of the gesous component in each ion, it was taken the half width of the line at one tenth of the maximum intensity when the line featured either a single Gaussian profile or a Gaussian with extended wings profile. For two-peaks profiles, Vexp was measured taking into account both the peak-to-peak displacement and the HW of the lines.
First Results From the Local Group Census: Planetary Nebulae in Sextans B
Authors: Corradi R.L.M. , Magrini L. , Walton N. A. , Zijlstra A. A. , Walsh J. R. , Perinotto M. , Pollacco D. L. , Lennon D. J. , Greimel R.
Published: July 2016

The Local Group Census is a narrowband survey of all the galaxies of the Local Group (LG) with Dec ≥ −30°, being carried out as part of the Isaac Newton Group's Wide Field Survey programme. Observations are being obtained with the Wide Field Camera at the 2.5m Isaac Newton telescope, equipped with a mosaic of four 2k x 4k EEV CCDs covering a field of view of 34′ x 34′.
Planetary Nebulae in the Magellanic Clouds: Probing Stellar Evolution and Populations
Authors: Stanghellini Letizia
Published: July 2016

This review contains: (1) the scientific motivations for studying Planetary Nebulae in the Magellanic Clouds; (2) a review of this field of study, from the origins to the most recent results, focusing on the papers that have been published since the last IAU Symposium on Planetary Nebulae; (3) a review of the Hubble contribution to the field, from the early results to our own Magellanic Cloud Planetary Nebula program.
Spectral Analysis of the LMC [WC] Star SMP 61
Authors: Gräfener G. , Hamann W.-R. , Peña M.
Published: July 2016

HST UV and optical spectra of the early-type [WC] star SMP 61 in the LMC are analyzed by means of line blanketed non-LTE models for expanding atmospheres. The known distance to the LMC allows a reliable determination of the stellar parameters. The low iron surface abundance of the object possibly indicates a preceding evolution through a very late thermal pulse (VLTP).
Studies of the Planetary Nebulae in NGC 5128
Authors: Walsh J. R. , Jacoby G. H. , Peletier R. F. , Walton N. A.
Published: July 2016

As the nearest large elliptical galaxy, NGC 5128 is ideal for planetary nebula studies. Its size, favourable aspect, small distance and reddening allow low mass stellar evolution in a whole galaxy to be surveyed. The surface density and properties of the PN can be compared with stars of various ages, metallicities and components (bulge, halo). The PN provide the α-element abundances whilst stellar photometry is calibrated against Fe/H; applied to the same stellar population, the PN abundances can be related to those of the stars. Gradients and non-radial trends in the abundance can be mapped using spectral observations of a large number of PN, allowing star formation history to be studied.
A Search for Intra-group Planetary Nebulae in the M81 Group
Authors: Feldmeier John J. , Durrell Patrick R , Ciardullo Robin , Jacoby George H.
Published: July 2016

We present the initial results from an [O III] λ 5007 survey for intra-group planetary nebulae in the M 81 group of galaxies. A total of 0.36 square degrees of the survey have been analyzed thus far, and a total of four intra-group candidates have been detected. These data allow us to probe the physics of galaxy interactions in small groups, and give us an upper limit for the density of intracluster starlight. We find that the M 81 group has less than 3% of its stars in an intra-group component; this is much less than the fraction seen in richer galaxy clusters.
Theoretical Aspects of Galaxy Dynamics Using Planetary Nebulae
Authors: Mathieu Anne
Published: July 2016

The dynamics of the outer regions of elliptical galaxies is still poorly known. Their lack of gas means that it is not possible to use the usual optical and 21cm emission lines to determine the kinematics out to large radii, and the faintness of their stellar body means that data calculated using absorption lines are limited to the inner part of the galaxy. It is only by measuring the kinematics out to several optical scalelengths that one gets any unambiguous measure of the dark halo properties (Kent 1986).
The Stellar and Dark Matter Halo of NGC 5128
Authors: Peng Eric , Ford Holland , Freeman Kenneth
Published: July 2016

Extragalactic planetary nebulae (PNe) and globular clusters (GCs) are complementary tools for obtaining kinematic information on stellar populations in the outer halos elliptical galaxies. NGC 5128, as the nearest large elliptical (D ~ 3.5 Mpc), is an excellent galaxy for halo studies. We have now identified a total of 1140 PNe, and possess radial velocities for 736 PNe at distances out to 80 and 50 kpc along the photometric axes. There is clear evidence for kinematic axis twisting (triaxiality) in the PNe velocity field. The mass of NGC 5128 continues to rise out to 80 kpc, where M(< 80 kpc) ~ 6.4 x 1011M⊙ with M80/LB ~ 20. We also conducted a new survey for GCs out to 50 and 30 kpc, and now have radial velocities for 188 GCs (125 new). Both the red and blue GC systems exhibit rotation. The red (metal-rich) GCs share a misaligned kinematic axis with the PNe. The success of this survey bodes well for future galaxy halo studies.
Formation of Planetary-Mass Brown Dwarfs in Magnetic Molecular Clouds
Authors: P. Boss Alan
Published: July 2016

Searches for very low mass objects in young star clusters have uncovered evidence for free-floating objects with inferred masses possibly as low as 5 to 15 Jupiter masses (MJup), similar to the masses of several extrasolar planets. We show here that the process which forms single and multiple protostars, namely collapse and fragmentation of molecular clouds, might be able to produce self-gravitating objects with initial masses less than ˜ 1MJup. Models are calculated with a three dimensional, finite differences code which solves the equations of hydrodynamics, gravitation, and radiative transfer in the Eddington and diffusion approximations. Magnetic pressure is added to the gas pressure, magnetic tension is approximated by gravity dilution once collapse is well underway, and ambipolar diffusion is treated approximately as well. Initially oblate clouds fragment into multiple protostar systems containing a small number (of order four) of fragments. If such fragments can be ejected from an unstable quadruple protostar system, prior to gaining significantly more mass, protostellar collapse might then be able to explain the formation of free-floating objects with masses below 13MJup. These objects might then be best termed “sub-brown dwarfs”.
The Formation Mechanism and Resulting Properties of Brown Dwarfs
Authors: R. Bate Matthew , A. Bonnell Ian , Bromm Volker
Published: July 2016

We present results from the most complex hydrodynamical star formation calculation performed to date. It follows the collapse and fragmentation of a large-scale turbulent molecular cloud to form dozens of stars and brown dwarfs. It resolves all fragmentation down to the opacity limit, binary stars with separations as small as 1 AU, and circumstellar disks with radii down to ≈ 10 AU. In this proceedings, we examine the formation mechanism of the brown dwarfs and compare the initial mass function and the properties of the brown dwarfs with observations.
Brown Dwarf Companion Frequencies and Dynamical Interactions
Authors: F. Sterzik Michael , H. Durisen Richard
Published: July 2016

Numerical simulations are used to explore how gravitational interactions within young multiple star systems may determine the binary properties of brown dwarfs. We compare different scenarios for cluster formation and decay and find that brown dwarf binaries, although possible, generally have a low frequency. We also discuss the frequencies of brown dwarf companions to normal stars expected from these models.
Optical Spectroscopy of Young Brown Dwarfs in Orion
Authors: C. Riddick Fiona , F. Roche Patrick , W. Lucas Philip
Published: July 2016

Red spectra of a sample of low-mass stars and brown dwarfs in the Orion Trapezium cluster are discussed. They show late-type spectral characteristics confirming cluster membership and some show evidence of circumstellar activity.
The First Young Brown Dwarf in the Serpens Cloud
Authors: Monin Jean-Louis , Caux Emmanuel , Klotz Alain , Lodieu Nicolas
Published: July 2016

We report the discovery of the first young brown dwarf in the Serpens cloud (BD-Ser 1). It is obscured by more than ten magnitudes of visual absorption as indicated by near infrared (NIR) photometric survey at the NTT and confirmed by NIR spectroscopy at the VLT. We estimate the mass of this brown dwarf to be M ~ 0.05 M⊙ and its age to be ~ 3.5 Myr. Available NIR indices in the literature (designed for field brown dwarfs) fail to provide its current spectral type but using a model they correctly determine its future spectral type to be T. This is the first young brown dwarf ever found deeply embedded in the Serpens star formation region
Very Low Mass Stars and Brown Dwarfs in Taurus
Authors: White Russel , Basri Gibor
Published: July 2016

We present high resolution optical spectra obtained with the Keck I telescope of low mass T Tauri stars and brown dwarfs in the Taurus star forming region. Based on the inferred photospheric and circumstellar properties, we conclude that objects in Taurus with masses as low as 50 Jupiters form and evolve in the same way as higher-mass T Tauri stars, but with smaller disks and shorter disk lifetimes.
Brown Dwarfs in the Alpha Persei Cluster
Authors: Stauffer John R. , y Navascués David Barrado , Bouvier Jerome , Lodieu Nicholas , McCaughrean Mark
Published: July 2016

We have obtained a new, deep, wide-field optical imaging survey of the young Alpha Persei cluster which reveals a well-populated lower main sequence extending into the substellar mass regime. Subsequent infrared photometry confirms that most of the candidate brown dwarfs are indeed likely to be cluster members, with a predicted minimum mass of order 0.035 solar masses. We have combined the new candidate list with previous member catalogs to derive an IMF for Alpha Per; the slope of the IMF at the low mass end is α ~ 0.66. The Alpha Per IMF slope is thus very similar to that found in the Pleiades.
A Deep Large Scale Survey for Intermediate Age Brown Dwarfs in the Praesepe Cluster
Authors: J. Chappelle R. , Pinfield D. J. , Steele I. A.
Published: July 2016

We present a 1.4 square degree survey of the Praesepe open cluster complete to I = 21.3 and Z = 20.2. This corresponds to masses down to 0.06M⊙ and 0.075M⊙ for an assumed cluster age of 1.0 or 0.5 Gyrs respectively. Over fifty new Praesepe candidate members have been discovered with masses less than 0.25M⊙. We discuss plans to establish proper motions of identified Praesepe candidates, and to measure NIR photometry of our candidates.
Brown Dwarf and Low-Mass Star Sequences in the Pleiades and Praesepe
Authors: Pinfield D. J. , Dobbie P. D. , Jameson R. F.
Published: July 2016

We present new infrared photometry of Pleiades and Praesepe sources, and define the cluster sequences in colour magnitude and 2-colour diagrams. We identify non-members and unresolved binaries, and discuss the clusters binary fractions.
A Census of Brown Dwarf Binaries
Authors: Brandner Wolfgang , Bouy Hervé
Published: July 2016

Brown dwarf binary systems offer the unique opportunity to measure some of the underlying physical characteristics, like, e.g., the mass. In addition, the individual components of brown dwarf binaries are expected to be coeval and have the same chemical composition. This provides crucial constraints on any (evolutionary) model by greatly reducing the number of free parameters. Finally, brown dwarf binary statistics should shed light on the origin of brown dwarfs and possible formation mechanisms and environments. We summarize on-going surveys for brown dwarf binaries, and present first results of follow-up studies.
Detection of Nine M8.0–L0.5 Binaries: The Very Low Mass Binary Population and Its Implications for Brown Dwarf Formation Theories
Authors: Close Laird M. , Siegler Nick , Freed Melanie
Published: July 2016

Use of the highly sensitive Hōkūpa'a/Gemini curvature wave-front sensor has allowed for the first time direct adaptive optics (AO) guiding on very low mass (VLM) stars with SpT=M8.0–L0.5. A survey of 39 such objects detected 9 VLM binaries (7 of which were discovered for the first time to be binaries). Most of these systems (55%) are tight (separation < 5 AU) and have similar masses (ΔKs< 0.8 mag; 0.85 <q< 1.0). However, 2 systems (LHS 2397a, and 2M2331016-040618) have large ΔKs> 2.38 mag and consist of a VLM star orbited by a much cooler L6.5–L8.5 brown dwarf companion. Based on our initial flux limited (Ks< 12 mag) survey of 39 M8.0–L0.5 stars (mainly from the sample of Gizis et al. 2000) we find a binary fraction in the range 19±7% for M8.0–L0.5 binaries with separations > 2.6 AU. This is slightly less than the 32 ± 9% measured for more massive (M0–M4) stars over the same separation range (Fischer & Marcy 1992). It appears M8.0–L0.5 binaries (as well as L and T dwarf binaries) have a much smaller semi-major axis distribution peak (~ 4 AU) compared to more massive M and G stars which have a broad peak at larger ~ 30 AU separations. We also find no VLM binaries (Mtot< 0.18M⊙) with separations > 20 AU. We find that a velocity “kick” of ~ 3 km/s can reproduce the observed cut-off in the semi-major axis distribution at ˜ 20 AU. This kick may have been from the VLM system being ejected from its formation mini-cluster.
Discovery of a Tight Brown Dwarf Companion to the Low Mass Star LHS 2397a
Authors: Freed Melanie , M. Close Laird , Siegler Nick
Published: July 2016

Using the adaptive optics system, Hōkūpa'a, at Gemini-North, we have directly imaged a companion around the UKIRT faint standard M8 star, LHS 2397a (FS 129) at a separation of 2.96 AU. Near-Infrared photometry obtained on the companion has shown it to be an L7.5 brown dwarf and confirmed the spectral type of the primary to be an M8. We also derive a substellar mass of the companion of 0.068M⊙, although masses in the range (0.061 – 0.069) are possible, and the primary mass as 0.090M⊙ (0.089 – 0.094). Reanalysis of archival imaging from HST has confirmed the secondary as a common proper motion object. This binary represents the first clear example of a brown dwarf companion within 4 AU of a low mass star, and should be the first L7.5 to have a dynamical mass. As part of a larger survey of M8-M9 stars, this object may indicate that there is no “brown dwarf desert” around low mass primaries.
Near-Infrared Adaptive Optics Spectroscopy of Binary Brown Dwarfs HD 130948B and HD 130948C
Authors: Goto M , Tokunaga A.T. , Cushing M. , Potter D. , Kobayashi N. , Takami H. , Takato N. , Terada H. , Hayano Y. , Iye M. , Gaessler W. , Saint-Jacques D.J.
Published: July 2016

We present near-infrared spectroscopy of low-mass companions in the HD 130948 system (Goto et al. 2002a). Adaptive optics on the Subaru Telescope allowed for spectroscopy of the individual components of the 0″.13 binary system. Based on a direct comparison with a series of template spectra, we determined the spectral types of HD 130948B and C to be L4 ± 1. We find they are most likely a binary brown dwarf system.
CHAOS: The Cornell High-Order Adaptive Optics Survey for Brown Dwarfs
Authors: Carson Joseph , Eikenberry Stephen , Brandl Bernhard , Wilson J. C. , Hayward T. L.
Published: July 2016

The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.

Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.

While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary system HD150451AB. Forty seven parsecs from earth, the candidate indicated a projected orbital separation of 280 AU.