bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiwavelength observations of NGC7027
Authors: Bains I. , Bryce M. , Pedlar A. , Muxlow T. W. B. , Thomasson P. , Mellema G.
Published: July 2016

We have made multi-wavelength observations of the young planetary nebula NGC 7027. The C-band continuum radio map shown in Figure 1 was obtained from the combination of MERLIN and VLA1 observations (M. Bryce et al., 1996). This map has the highest spatial resolution of any radio images of this object to date and has been compared with the HST archive picture of NGC7027, taken using WFPC2 with a 400 å wide F547N filter, to reveal the differences in the emission at the disparate wavelengths. The two maps, while being superficially different, show emission regions that are similar in size. The contours of radio brightness often coincide with prominent optical features.
Narrowband HST images of microstructures in Planetary Nebulae
Authors: Balick B. , Alexander J. , Hajian A. , Terzian Y. , Perinotto M. , Patriarchi P.
Published: July 2016

Hubble Space Telescope narrowband images of four PNe resolve the microstructures in four PNe known to contain FLIERs (e.g. Balick et al 1994). FLIERs are seen to fall into two morphological groups: very low ionization clumps of small knots with cometary-like tails, and sinewy transverse filaments with fainter extensions pointing outward from the nucleus. Generally speaking, FLIERs exhibit [NII]λ6584/Hα > 1. They are marginally detectable in Hα above the bright background of nebular emission, and all but invisible in [O III]λ5007A. In every case the star-facing side of the structure is on the order of a pixel in width (about 1015 cm). A decreasing ionization gradient is seen [O I]λ6300A, [S II]λ6717 + 31A, and [N II]λ6584A images.
A new deep imaging survey of Planetary Nebulae with known binary central stars
Authors: Bell S. A. , Pollacco D. L.
Published: July 2016

Binarity in central stars is often thought to be the most likely explanation for the bipolar and axisymmetric shapes seen in planetary nebulae. Theoretical computations show that low mass stellar companions — possibly even planets, merged nuclei and long period systems will also produce bipolar-shaped nebulae. As such all known short period binary central stars are expected to have an axisymmetric nebula surrounding them.
Models of Planetary Nebulae based on deprojection
Authors: Bremer Michael
Published: July 2016

Density distributions of four planetary nebulae have been calculated in cylindrical coordinates (r,z,ϕ) using the iterative deprojection algorithm by Bremer (1995). Narrowband filter CCD images of NGC 2346, NGC 6563, NGC 6826 and NGC 7009 in the Hα line (6562.8 å) were corrected for cosmic ray hits, background/foreground stars were removed, and the position angles PA of their symmetry axes were determined with a maximum correlation criterion. For NGC 6563, the axis was shifted manually to the south-east to put it on the central ridge (the PA was conserved). For deprojections in cylindrical coordinates, an inclination angle i (angle between the object axis and the line of sight) must be specified. Literature values based on optical spectra were available for NGC 2346 (Walsh 1983) and NGC 7009 (Preston and Willson 1990), for NGC 6563 and NGC 6826 lower limits were derived from deprojections.
Shaping bipolar and elliptical Planetary Nebulae: Rotation and magnetic field
Authors: García-Segura Guillermo , Langer Norbert , Różyczka Michał , Low Mordechai-Mark Mac , Franco José
Published: July 2016

We present hydrodynamical and magnetohydronynamical simulations for the formation and evolution of bipolar and elliptical planetary nebulae with two interacting winds. The models are performed under the hypothesis of a single central source, i.e. binary systems are not considered and a single initial wind function is used in our calculations. We explore various relevant parameters, including the effects of stellar rotation, ionizing radiation field and stellar magnetic field, and a catalogue of resulting shapes is generated.
Structure of selected Planetary Nebulae surrounding WR-type central stars
Authors: Górny S.K. , Gȩsicki K. , Acker A.
Published: July 2016

The main aim of this work was to confirm that expansion of planetary nebulae surrounding Wolf-Rayet type central stars is characterized by turbulent motions or strong variations of velocity in the radial direction relative to the nucleus. Such properties have already been found in Ml-25, M3-15 and Pel-1 by Gesicki & Acker (1995). We have analyzed the photoionization structure and velocity field of the NGC 40 - a planetary nebula with late type ([WC 8]) Wolf-Rayet nucleus. The spectra of Hα and [NII] lines have been obtained with the 1.5m telescope at the Observatoire de Haute-Provence. The spectrograph Aurelie with dispersion of 5Å/mm and a 3″ circular entrance was used. The method and the details of the applied computer codes are published in Gesicki et al. (1996).
3D photoionization models: the bipolar PN IC 4406
Authors: Gruenwald R. , Viegas S. M. , Broguière D.
Published: July 2016

A three-dimensional (3D) self-consistent photoionization code is developed in order to build more realistic models for asymmetrical and/or inhomogeneous photoionized nebulae. With these models the assumption of spherical or plane-parallel symmetry can be dropped and models with various geometries can be treated. The gaseous region is divided into numberous cubic cells, and the physical conditions in each cell are obtained taking into account the effect of the other cells in the optical depth and their contribution into the diffuse radiation. A model for IC 4406, which is a typical example of bipolar planetary nebula is presented. The model assumes a torus of dense material around the central star, as suggested in the literature. Its presence is confirmed by the model, in particular by the shape of the theoretical Hα + [NII] isophotal map. The chemical abundances required to explain the observed line intensities indicate that the chemical properties of this bipolar nebula are not characteristic of type I planetaries. A detailed paper will be published in Ap.J. (FAPESP, CNPq)
Deep imaging of type I PN
Authors: Hua C. T. , Dopita M. A.
Published: July 2016

Progress in developing theories concerning the evolution of the central star and the surrounding planetary nebula requires a large, uniform set of data (monochromatic images, isophotes) which CCD imaging of PN can supply at present (Kaler, 1985; Balick 1987). One of the unknown parameters remains the mass budget of the (PN + central star) system. As a matter of fact, existing inventories of the measured ionised mass in PN reveal a shortfall as compared with theory. Nonetheless, since the major portion of the total mass loss occurs in the earlier ejection phases, a main objective was to detect the faint brightness peripheral nebular emissions and to provide quantitative measurement when possible of the global ionised mass.
High dispersion spectra of Planetary Nebulae
Authors: Hyung S. , Aller L. H.
Published: July 2016

Determinations of the plasma diagnostics and chemical compositions of planetary nebulae require ultimately high dispersion spectra. For objects of high surface brightness the Hamilton Echelle Spectrograph at Lick Observatory is satisfactory for the region 3650–10100Å which involves the 168th to 56th echelle orders. For a slit width of 640 μm amounting to 1.15 arcsec at the Coude focus, the actual spectral resolution (FWHM) is about 0.2Å at 8850Å. The length of the slit is chosen as 4.0 arcsec. Hyung (1994) & Aller (1994) describe the observing procedure. Since the Hamilton echelle was designed primarily for star-like sources, it is not useful for extended low surface brightness PN. The earlier observations were obtained with an 800 × 800 chip that did not cover the echelle field, so several settings were needed. Later, we used a slower 2048 × 2048 chip which covered the whole field and was somewhat more efficient at longer wavelengths. The program has been completed and definitive measurements have obtained for NGC 2440, NGC 6543, NGC 6741, NGC 6818, NGC 7026, NGC 7662, and Hu 1-2. All of these PN display particularly rich, interesting spectra. Previously observed and published objects include IC 351, IC 418, IC 2149, IC 4997, NGC 6567, NGC 6572, NGC 6790, NGC 6886, NGC 7009, BD +30 3639, & Hubble 12. NGC 6884 is in press. Additional nebulae which are yet to be discussed are IC 4634, IC 4846, IC 5117, NGC 6210, & NGC 6803.
H2 kinematics in Planetary Nebulae
Authors: Kelly Douglas M. , Latter William B. , Hora Joseph L. , Woodward Charles E.
Published: July 2016

The evolution of planetary nebulae is controlled largely by hardening of the radiation field from the central star and by hydrodynamic interactions between the “fast wind” and the slower red giant wind. These processes also result in the heating and dissociation of H2 and in the production of H2 vibration–rotation lines in the near-infrared. Both mechanisms tend to produce high gas temperatures and, at high densities, a thermal population of states. Kinematic studies provide vital information on the geometry and expansion of the nebulae and offer a discriminant between shocked and photodissociated regions.
Recombination line abundances in NGC 6210
Authors: Kingsburgh R. L. , Komljenovic M. , López J. A. , Peimbert M.
Published: July 2016

We present abundances derived from echelle spectroscopy of the planetary nebula NGC 6210 from the forbidden, collisionally excited lines, and from the permitted, recombination lines. We have obtained spectra from 3 positions in the nebula: at the central star, and 6 and 12 arcseconds south of the central star. We find a discrepancy of a factor of 2 between the O2+/H+ ratio derived by the recombination lines and by the forbidden lines in each spatial position. This discrepancy may result from the presence of temperature fluctuations in NGC 6210, where the collisionally excited lines are exponentially weighted to regions of higher temperature. A value for the root-mean-square temperature fluctuation parameter t2(OIIabun)= 0.038+0.007–0.009 is derived for the central star spectrum, 0.040+0.006–0.013 for the 6 arcsecond offset, and 0.051+0.014–0.015 for the 12 arcsecond offset spectrum. Thus no significant variation in t2 is seen as a function of spatial position within the nebula. We have also estimated t2 by comparing the derived Balmer Jump temperature at the 6 arcsecond offset, Te(BaJ)= 7900+2400–1600K, with the temperature derived from the [O III] 5007/4363å ratio Te[O III]= 9370±100K at this position. This comparison suggest t2(BaJ)= 0.041±0.020, in agreement with the values for t2 as estimated from the recombination lines.
Investigating the near-IR properties of PN: Deep imaging of molecular hydrogen emission
Authors: Latter William B. , Hora Joseph L.
Published: July 2016

We present the first results of a deep near-infrared narrowband imaging study of several planetary nebulae. The data were acquired using the University of Hawaii 2.2m telescope on Mauna Kea and the “QUIRC” 1024 × 1024 array camera. With these sensitive high spatial resolution imaging data, we are able to explore in detail where H2 is found relative to the ionized region in planetary nebulae at various stages of evolution (See Figure 1, for an example). The objects were selected from previous studies to have evidence for extended emission from H2, and they are at several differing phases of central star evolution. The presence of molecules in the UV–flooded environment of a planetary nebula cannot be explained without highly non-spherical geometries and high densities, or clumping. Although there can be an ambiguity in the excitation mechanism (UV photons or shocks), the location of H2 emission identifies regions of the nebula with sufficient dust shielding and density for the survival of molecular species. The emission morphology also provides information that helps identify which excitation mechanism is most likely. When combined with data provided by other molecular studies, we can examine how the photodissociation region evolves through the circumstellar envelope as the planetary nebula tracks across the top of the HR diagram. We can also consider how morphological evolution of the nebula, through interacting winds and shocks, might provide the conditions necessary for molecular survival.
The global motions of the cometary knots in the Helix Planetary Nebula (NGC 7293)
Authors: Meaburn J. , Clayton C. A. , Bryce M. , Walsh J. R.
Published: July 2016

The nature and origin of the hundreds of ionized knots, with cometary tails, in the Helix planetary nebula are both being unravelled by recent observations. Healey and Huggins (1990, AJ, 100, 511), Meaburn et al (1992, MNRAS, 255, 177) and Walsh and Meaburn (1993, ESO Messenger, 73, 35) all showed, in various ways, that these knots have dense (106 cm–3), dusty, molecular cores with ionized arcs of gas on the surfaces pointing towards the ionizing star. This structure is confirmed in detail by the HST imagery of O'Dell and Handron (1996, ApJ, in press).
Multiwavelength kinematics of the PNe Humason 1–2 and NGC 7662
Authors: Ortega V. , Cuesta L. , Mampaso A. , Corradi R.L.M.
Published: July 2016

The conventional interpretation of the “Wilson effect”is based on the fact that, in a simple photoionization model of a thick shell in free expansion, the elements with a high ionization potential are found in the innermost part of the shell, which move slower than the outer regions where the low ionization ions are located. A real PN is however a much more complex object than in the picture above. For these reasons, we are carrying on a project aimed at studying in detail the Wilson effect in a large number of objects of different types. We present here preliminary results for two PNe, the bipolar nebula Hu 1-2 and the elliptical NGC 7662. Observation have been secured with the Utrecht Echelle Spectrograph placed at 4.2m William Herschel Telescope, (La Palma, Canary Islands). The spatial resolution is 0.36 arcsec, and the resolving power R=46000. The results are presented in Table 1. The increase of expansion velocity with decreasing potential is clearly seen except for Hydrogen. This ion is a quite peculiar case: although its ionization potential is quite low, this element behaves also as a high excitation atom since it has only one possible ionized state. Futhermore, as we have spatial resolution we can study this relation between velocity and ionization potential in different points of the nebula.
Ionization correction factors from an extensive grid of photoionization models of Planetary Nebulae
Authors: Rokach O. , Golovaty V.
Published: July 2016

Using a new photoionization code PAN (Yu. Malkov et al, this book) we have built a grid of 250 photoionization models for planetary nebulae (PN). The stellar evolutionary tracks for PN nuclei with M∗ = 0.566, 0.598, 0.644 and 0.8M⊙ are taken from the computations of the Blöcker (A&A, 299, 1995). On the L∗ – Teff diagram our grid covers whole region in which the PN nuclei are observed. The spectra of the central stars at λ ≤ 912 Å corresponded to non-LTE model atmospheres (R.E.S. Clegg and D. Middlemass, MNRAS, 228, 1987), corrected for presence of the stellar wind. The nebular shell was assumed to be spherically symmetric, and the profile of the radial gas density distribution in it was taken equal to the empirical approximate expression found from the analysis of isophotal maps of real PN (V. Golovaty and Yu. Malkov, Astron. Zh., 69, 1992). Each model was calculated for three choises of Mshell and each of them for two choises of shell expansion velosity −15 and 30 km/sec respectively. The relative elemental abundances were the same for all models: H:He:C:N:O:Ne:Mg:Si:S:Ar = 10000:1200:5.0:1.0:6.0:0.8:0.3:0.3:0.15:0.04 (by number of atoms).
Electron excitation of heavy elements in Planetary Nebulae
Authors: Schöning T. , Butler K.
Published: July 2016

Modern observational equipment makes it possible to identify extremely weak metal lines in deep surveys of the optical and near-IR region of the electromagnetic spectrum. In particular, collisionally excited lines from heavy ions (Z > 30) have been recently identified in the spectrum of NGC 7027 (Péquignot & Baluteau 1994). However, detailed quantitative analyses of the observed lines have not been feasible due to the lack of accurate collisional data for the heavy elements.
Expansion analyses on Planetary Nebulae
Authors: Tamura S. , Yadoumaru Y. , Shibata K. M. , Tajitsu A.
Published: July 2016

Since planetary nebulae(PNe) are defined as the expanding ionized gas surrounding hot central stars, the most important and fundamental subject is to study expansion characteristics. What and how can we determine a typical expansion velocity of individual nebula? In spite of great success of Perek and Kohoutek Catalog(1967) and a recent Strasbourg-ESO Catalogued 992), PNe researchers have suffered from the lack of sufficiently large samples of expansion measurements on various type of PNe.
A self-consistent photoionization-dust continuum-molecular line transfer model of NGC7027
Authors: Volk Kevin , Kwok Sun
Published: July 2016

A model to simulate the entire spectrum (1000 Å to 1 cm) of the high-excitation young planetary nebula NGC 7027 is presented. The ionized, dust, and molecular components of the object are modeled using geometric parameters obtained from visible, radio, infrared, and CO data. The physical processes considered include recombination lines of H and He, collisional excited lines of metals, bf and ff continuum radiations, two-photon radiation, dust continuum radiation, and molecular rotational and vibrational transitions. The dust component is assumed to be heated by a combination of direct starlight and the line and continuum radiation from the ionized nebula. The molecular component of the nebula is coupled to the dust component through the stimulated absorption of the dust continuum radiation. Specifically, we compare the predicted fluxes of the CO rotational lines and the 179.5 μm water rotational line to those observed by the Infrared Space Observatory satellite (Liu et al. 1996, A&A in press).
Giant emission features at large distances from PNe: A preliminary investigation
Authors: Zanin C. , Weinberger R.
Published: July 2016

“Senile” PNe are very old nebulae of extremely low surface brightness and large linear size; they offer e.g. the possibility of probing the conditions of the ISM also non-locally. We give three examples of huge nebulae in a preliminary inquire.

NGC 3242: An ESO Schmidt plate obtained in April 1996 shows the ‘wrapped’ morphology of the faint arc discovered by Deeming (1966, Astrophys. J. 146, 287) 11′ south-west of this PN. Probably this arc is part of a giant halo of very low surface brightness around NGC 3242, but up to now the detection of the halo is questionable. A spectrum of the filament obtained at Las Campanas shows [O iii]/Hα ∼ 5 compared with a value of ∼ 3 in the nebula (Perinotto et al. 1994, Astron. Astrophys. Supp., 107, 481). This high ratio is larger than that expected for the excitation class of NGC 3242, even larger than the maximum allowed for a photo-ionized nebula of more or less normal chemical abundance. Thus, due to the spectral characteristic and to the filamentary structure of the arc we suspect that shocks appear to play a role.
An empirical model of morphologies of Planetary Nebulae
Authors: Zhang C. Y. , Kwok S.
Published: July 2016

The variety of different morphologies of planetary nebulae (PNs) have always fascinated researchers in the field. Recent progress in CCD imaging techniques has resulted in a large number of homogeneous optical images of more than a few hundreds PNs (Balick 1987, Schwarz, Corradi and Melnick 1992). In addition, two major radio surveys using the Very Large Array (VLA) by Aaquist and Kwok (1990, 1991) and by Zijstra, Pottasch and Bignell (1989) have revealed detailed morphologies in the radio, including many compact star-like PNs. This treasure of data sets contains useful information about morphologies, density distributions, formation and evolution of PNs, yet to be fully explored.
Binary post-AGB stars
Authors: Waters L.B.F.M. , Waelkens C. , Van Winckel H.
Published: July 2016

Low and intermediate mass stars leave the Asymptotic Giant Branch (AGB) when the mass in their H-rich envelope is less than about 0.01 M⊙, and the high mass loss drops several orders of magnitude. The central star rapidly evolves to the left part of the HR diagram along a track of constant luminosity (e.g. Schönberner 1983). In principle the evolution of the central star to higher Teff and the expansion and cooling of the AGB remnant are easy to calculate. In practice several complicating factors arise which make it much more difficult to predict the morphology and properties of post-AGB stars, such as binarity, post-AGB mass loss and aspherical AGB mass loss. Binarity of post-AGB stars affects the morphology of the circumstellar environment, and it affects evolutionary timescales and surface chemical abundances of the components in the system. This review discusses some properties of binary post-AGB stars.
Pulsations of the Mira-type component in the Symbiotic Binary R Aqr
Authors: Chinarova L. L. , Andronov I. L. , Schweitzer E.
Published: July 2016

Time series analysis of the brightness variations of R Aqr is based on 1521 visual observations from the AFOEV database. The statistically significant number of harmonics for the mean phase curve is m = 5. The cycle-to-cycle variations of the phase curve are present. The most stable in phase is the maximum, for which no secular period variations detected, but a secondary cycle of P2 = 3955 ± 50d and amplitude (0.032 ± 0.005)P may be suggested.
OH/IR star color mimics with S(25) > 100 Jy
Authors: Lewis B. M.
Published: July 2016

O-rich circumstellar dust shells that do not exhibit 1612 MHz masers (Lewis 1992), despite appropriate IR colors and 1612 MHz sensitivity, are known as OH/IR star color mimics. Since previous studies of mimics depend on samples with a limited IR spectral type and color range, we use the data collected for poster III-8 to identify the mimics in an all-sky sample of bright IRAS sources with S(25) > 100 Jy and (60-25)μm < 0.0: this expands on Gaylard et al. (1989), and benefits from the greater quantity of maser data now and a wider IR color range.
Properties which cannot be explained by Planetary Nebulae's progenitors
Authors: Soker Noam
Published: July 2016

Stellar binary companions account for bipolar PNe (∼ 11% of all PNe1), and some ellipticalls (22%2). The rest of axisymmetrical PNe (40% to 60% of all PNe) are due to substellar objects (planets and brown dwarfs)3. This classification of axi symmetrical PNe suggests that substellar objects are commonly present within several × AU around main sequence stars, and that several substellar objects must be present around most main sequence stars3. Some substellar and low mass stellar companions will enter the primary envelope only as the primary reaches the upper AGB. Thus, the early mass loss episode will be spherical, leading to the formation of a spherical halo around an elliptical inner region. Gas giant planets and brown dwarfs close to the primary, will not allow Earth-like planets to have stable orbits. Systems with no Jupiter-like planets will allow Earth-like planets to be present. These stars will form spherical PNe (10%-20% of all PNe, including spherically ejected PNe that have been deformed by the ISM through which they move4). Systems with substellar objects at large separation, as Jupiter in the solar system, will also allow Earth-like planets to be present. These systems will form PNe with spherical halo. Therefore, life may have been present in planets around the central stars of round PNe and elliptical PNe with round halos.
Mass loss processes in hot evolved stars: Planetary Nebula nuclei in the large Magellanic Cloud
Authors: Bianchi L. , Vassiliadis E. , Dopita M. A.
Published: July 2016

As part of a broad study of stellar winds in different galaxies, to establish observational constraints on the influence of metallicity on the mass loss process, we investigate the winds of planetary nebula (PN) nuclei in the Large Magellanic Cloud. Theoretically, the radiation pressure mechanism implies a strong dependence of the wind acceleration on the element abundances. Observationally, model predictions have been tested using Pop. I stars in the Magellanic Clouds (Puls et al. 1996, A&A, 305, 171) and massive stars in the nearby galaxies M31, M33 and NGC 6822 (Bianchi et al. 1996, AJ, 111, 2303; Bianchi et al. 1996, in prep.). We now extend this investigation to low luminosity, evolved objects.
Planetary Nebulae in elliptical galaxies: Dynamical models for Centaurus A
Authors: Mathieu Anne , Dejonghe Herwig
Published: July 2016

We use planetary nebulae major- and minor-axis kinematics (Hui et al. 1995) of the dust-lane elliptical galaxy NGC 5128 (Centaurus A) to build triaxial dynamical models.
Planetary Nebulae in M31: Abundances, and comparison with bright Planetary Nebulae in the LMC
Authors: Richer M. G. , Stasińska G. , McCall M. L.
Published: July 2016

We have obtained spectra of 28 planetary nebulae in the bulge of M31 using the MOS spectrograph at the Canada-France-Hawaii Telescope. Typically, we observed the [O II] λ3727 to He I λ5876 wavelength region at a resolution of approximately 1.6 å/pixel. For 19 of the 21 planetary nebulae whose [OIII]λ5007 luminosities are within 1 mag of the peak of the planetary nebula luminosity function, our oxygen abundances are based upon a measured [OIII]λ4363 intensity, so they are based upon a measured electron temperature. The oxygen abundances cover a wide range, 7.85 dex < 12 + log(O/H) < 9.09 dex, but the mean abundance is surprisingly low, 12 + log(O/H)–8.64 ± 0.32 dex, i.e., roughly half the solar value (Anders & Grevesse 1989). The distribution of oxygen abundances is shown in Figure 1, where the ordinate indicates the number of planetary nebulae with abundances within ±0.1 dex of any point on the x-axis. The dashed line indicates the mean abundance, and the dotted lines indicate the ±1 σ points. The shape of this abundance distribution seems to indicate that the bulge of M31 does not contain a large population of bright, oxygen-rich planetary nebulae. This is a surprising result, for various population synthesis studies (e.g., Bica et al. 1990) have found a mean stellar metallicity approximately 0.2 dex above solar. This 0.5 dex discrepancy leads one to question whether the mean stellar metallicity is as high as the population synthesis results indicate or if such metal-rich stars produce bright planetary nebulae at all. This could be a clue concerning the mechanism responsible for the variation in the number of bright planetary nebulae observed per unit luminosity in different galaxies (e.g., Hui et al. 1993).
The chemical abundances of Planetary Nebulae in Centaurus-A (NGC 5128)
Authors: Walton N. A. , Walsh J. R. , Jacoby G. , Peletier R. F.
Published: July 2016

Abundances in early-type galaxies are measured from the analysis of stellar spectra (e.g. colour indices, Peletier et al, 1990). The presence of many planetary nebulae (PN) in early-type galaxies provides an independent measure of abundances for the old stellar population and allows the spread in abundances to be sampled at a range of galacto-centric distances. PN are feasible for this project since the nebular O, Ne and S abundances in most PN reflect that of the progenitor star.
Do Lensing Statistics Rule out a Cosmological Constant?
Authors: Chiba M. , Yoshii Y.
Published: July 2016

We present new calculations of the gravitational lensing statistics following recent revised knowledge of the luminosity function and internal velocity dispersion of E/S0 galaxies which work as effective lenses for background high-redshift QSOs. We show that the theoretical prediction of the lensing statistics is much smaller than previously expected. In sharp contrast with the earlier statistics supporting an Ω0 = 1 universe, the reported small lensing probability from the Hubble Space Telescope (HST) snapshot lens survey is in best agreement with a low-density, flat universe with Ω0 ≃ 0.2 and Ω0 + λ0 = 1. The age of this universe, combined with the HST measurement of a high value of the Hubble constant H0, can be reconciled with the age of the oldest globular clusters in the Milky Way (ApJ, 1997, Vol. 489, in press).
H0 from Distant Clusters of Galaxies Observed with ASCA
Authors: Furuzawa A. , Tawara Y. , Yamashita K. , Miyoshi S. , Matsuura M.
Published: July 2016

ASCA, Japanese X-ray Sattelite, can obtain the spatial distribution of density and temperature of the intracluster medium at the same time and greatly improve the accuracy for the derivation of the Hubble constant using the thermal Sunyaev-Zel'dovich effect. Table 1 shows the results of ASCA observations of 4 distant clusters of galaxies. The parameters of the density distribution were obtained assuming the β model.
Observations of the CMB on Scales of 2° to 15°
Authors: Davies R.D. , Davis R.J. , Wilkinson A. , Watson R.A. , Melhuish S.J. , Dicker S. , Veeraraghavan S. , Rebolo R. , Gutierrez C.M. , Hoyland R.J. , Lasenby A.N. , Hancock S. , Jones A.W. , Rocha G.
Published: July 2016

Beamswitching has been used at 10, 15 and 33 GHz to map the microwave background over the Declination range 30° to 45°, covering more than one steradian of the sky. The beamwidth is 5° and the beam-throw is ±8° at each frequency. The three data sets are used to separate Galactic emission from intrinsic CMB emission. For the scan at Dec = 40° the intrinsic fluctuation level is ΔTrms = 48+21−15 μK on a coherence scale of 4°; the equivalent analysis for a Harrison-Zeldovich model gives a power spectrum normalisation of Qrms = 22+10−6 μK. The value of the fluctuation amplitude calculated from the likelihood analysis of the two-dimensional data set is ΔTrms = 54 ± 13 μK at 10 GHz and 39+8−7 μK at 15 GHz.
CMB Anisotropies Produced by Nonlinear Voids
Authors: Sakai Nobuyuki , Yokoyama Jun'Ichi , Sugiyama Naoshi
Published: July 2016

Although the CMB anisotropy is an important probe of primordial fluctuations at recombination, which carries information on the cosmological parameters as well as the nature of dark matter, CMB photons are also affected gravitationally by nonlinear structures between recombination and the present epoch. In this paper, using Thompson & Vishniac's model [1], we investigate the effect of a void network on the CMB anisotropy in the Einstein-de Sitter background. In particular, we estimate both the Rees-Sciama effect [2] and the gravitational lensing effect (see, e.g., [3]).
Evolutionary Population Synthesis Models of Primeval Galaxies: A Critical Appraisal
Authors: Buzzoni A.
Published: July 2016

A recognized problem when searching for primeval galaxies at cosmological distances is a definition of a firm selection criterion (alternative to a direct but extremely time-demanding measure of z) to single out high-redshift candidates from the plethora of other more or less peculiar objects (i.e. AGN, starburst galaxies etc.) at lower distances.

The case of the HST “Deep Field” (HDF) observations (Williams et al. 1996) is especially relevant in this regard as galaxies up to z = 3.2 have been detected in the field (Steidel et al. 1996).
Measuring Galaxy Bias from the High-Order Correlation Functions
Authors: Jing Y.P.
Published: July 2016

In this talk, I will show how to determine the biasing factor b from the high-order moments of galaxies. The determination is based on the analytical modeling of primordial peaks and virialized halos and is independent of the currently unknown density parameter Ω0 and other cosmological parameters. The observed high-oder moments of the APM galaxies require that the biasing factor b be very close to 1, i.e. the optical galaxies are an unbiased tracer of the underlying mass distribution (on quasilinear scale). The theoretical argument can be easily generalized to the three-point correlation function and the bispectrum both of which can used as further observational tests to the important conclusion of b ≈ 1 drawn from the high-order moments. Finally I present our preliminary results of the three-point correlation functions for the Las Campanas Redshift Survey.
Cosmological Parameters from the X-Ray Evolution of Clusters
Authors: Bower R.G. , Kay S.T.
Published: July 2016

This poster paper presents an extension of the entropy-driven model of cluster evolution developed by Bower, 1997 (MN, 288, 355) in order to study the evolution of clusters in a low density universe. Our approach allows us to explicitly seperate the contributions from gravitational collapse and changes in the core entropy of the intracluster gas. Here, we apply the model to determine whether a preferred value of Ω0 is selected by currently available constraints (Figure 1). Measurements of the X-ray evolution of clusters cannot, by themselves, select out a particular cosmological model. An additional constraint on the effective power spectrum index (n) is required. This can either come from a measurement of the large-scale galaxy correlation function or from the shape of the present-day temperature function. A theoretical calculation of the Ω0 dependence of the power spectrum does not help break the inherent degeneracy.
Galaxy Luminosity Function based on the Press-Schechter Theory
Authors: Yoshida H. , Umemura M. , Yoshii Y.
Published: July 2016

We investigate the cosmological model dependence of galaxy luminosity function (GLF) obtained by the Press–Schechter (PS) prescription. We consider the power–law spectra as well as a CDM spectrum for primordial density fluctuations, assuming a variety of cosmological models. We do not consider any galaxy luminosity (chemical) evolution in this report.
Statistical Properties of Magnetic CP Stars
Authors: Bagnulo S.
Published: July 2016

Magnetic fields of chemically peculiar (CP) stars of the upper main sequence are characterised by a geometry organised at a large scale, permeating the entire photosphere, and with a typical strength of the order of 0.1–30 kG. Here I review the results obtained from statistical studies of the structures of the magnetic fields of CP stars, which are aimed at finding how magnetic strength and morphology are correlated with other stellar characteristics and with the star's evolutionary state.
Dynamical Atmospheres and Winds of AGB Stars
Authors: Höfner S. , Sandin C. , Aringer B. , Andersen A. C. , Jørgensen U.G. , Gautschy-Loidl R. , Nowotny W. , Hron J.
Published: July 2016

We summarize the current status of our latest generation of model atmospheres for pulsating asymptotic giant branch stars, discussing effects of non-grey radiative transfer, dust grain properties and drift between gas and dust on the atmospheric structures and wind characteristics. In addition, we give an overview of the resulting synthetic spectra and how they compare with observations.
Modelling the Mass Loss of Cool AGB Stars
Authors: Woitke Peter
Published: July 2016

The current status of modelling the wind driving mechanism of AGB stars is reviewed. Our present understanding of these winds is substantially guided by spherically symmetric, time-dependent models which reveal a complex interplay between stellar pulsation, hydrodynamics, small-scale waves, chemistry, dust formation and radiative transfer. The level of approximation used for the physical description of the various processes, and the degree of consistence in the models are crucial and different approaches lead to rather different results. Beside reviewing the frontiers of the present theoretical research on AGB star winds, this paper presents some new results concerning the cooling of the gas behind propagating shock waves in the outer atmosphere and the self-organisation of dust-forming gases (cloud formation) caused by a radiative/thermal instability of dust forming gases.
Infrared Observations of Galactic Planetary Nebulae
Authors: Preite-Martinez A.
Published: July 2016

Five months after the 1982 Symposium in London the InfraRed Astronomical Satellite (IRAS) was launched. Undoubtedly this has been the major event of the last five years in the infrared world, with a great impact in the field of Planetary Nebulae (PN) research (^).
Near Infrared Photometry of Compact Planetary Nebulae
Authors: Peña M. , Torres-Peimbert S.
Published: July 2016

The study of young planetary nebulae can provide information about the ejection process of the nebular material as well as on nebular evolution and the enrichment of the interstellar medium. The youngest PN are expected to be compact and very dense, they usually show signs of variability and IR excess due to the presence of warm dust which, in some cases, seems to be mixed with the ionized gas.
A VLA Radio Continuum Survey of Planetary Nebulae
Authors: Zijlstra A. , Pottasch S. R. , Bignell C.
Published: July 2016

With the Very Large Array it is now possible to make high resolution radio continuum maps with sensitivity less than a milliJansky in an observation of only 5 minutes. We have used this so-called snapshot capability to measure about 400 PN north of declination −35. Most of the measurements were carried out at 6 cm. Some of the stronger sources were observed at several frequencies. Most sources were detected, however many nebulae were too weak to map in detail. The resolution ranges from 1.5″ to 1′, depending on the size of the PN. The selected PN have sizes in the range from 4″ to 6′.
Expansion Velocities and Characteristics of Galactic Planetary Nebulae
Authors: Weinberger Ronald
Published: July 2016

An up-to-date account of expansion data and their interpretation is provided.- the importance of spatiokine-matical models is underlined; bipolar outflows appear to be characteristic of very young objects and prolate spheroids (including toroids and rings) seem to be a useful approximation for many PN.- High-velocity features are much more frequent than previously assumed.- Expansion velocities vs. linear radii diagrams for [OIII], HI, and [NII], based on a new catalogue show a broad, rather homogeneous distribution and thus are of limited value for studies of the dynamical evolution or formation mechanisms of PN - future investigations of these relations should be pursued separately for groups of PN with similar physical properties; a difference in the kinematical properties of B and C nebulae could, however, be confirmed.- Several recommendations for work in this area are added.
Multiple Shell Planetary Nebulae
Authors: Chu You-Hua
Published: July 2016

It has been shown in several independent investigations that the multiple-shell phenomenon is prevalent in planetary nebulae. Despite the common classification, the multiple shell planetary nebulae are a heterogeneous group of objects, as testified by the wide variety of their morphologies and physical structures. There are two types of double-shell structures that are seen frequently: one has an inner shell expanding supersonically into a faint, subsonically expanding halo, and the other has a bright attached envelope co-expanding with the inner shell. The physical structures and relative elemental abundances in the shells are reviewed, and their possible formation mechanisms are discussed.
Photoionization Models
Authors: Harrington J. Patrick
Published: July 2016

A recent comparison of the photoionization models generated by five independent codes run with the same density and stellar radiation shows substantial agreement. Problems are more likely to arise with the defining parameters: the density distribution should be based on observed images, and the ionizing radiation should be from model atmosphere calculations, which, however, are inadequate for stars with winds. Models can be improved by including dust and by incorporating, self-consistently, radiative transfer in optically thick lines. Future work may extend modeling to axially-symmetric objects, to the interface with the hot, shocked, stellar wind, and to the molecular component present around many nebulae.
Investigation of two Planetary Nebulae and their Angular Vicinity in Cygnus
Authors: Saurer W. , Weinberger R.
Published: July 2016

We present the results of an investigation of M1-79 and K3-82. Physical parameters like expansion velocities, spatial shapes, Zanstrahydrogen-temperatures, etc. were obtained by use of high resolution spectroscopy and CCD-images.

The two PN are medium excitation and exhibit usual expansion velocities. To find out the spatial shapes we utilized the simple model of a truncated spherical shell. A comparison between the theoretical intensity ratios from this model and the measurements is leading to the conclusion that both PN have the structure of a ring. K3-82 is seen pole-on, Ml-79 is seen edge-on.
Structure and Morphology of NGC6369
Authors: Chatterjee Tapan K. , Campos J.
Published: July 2016

NGC 6369 is a remarkable object, especially in the light of structure and morphology. We studied this object by taking many red plates (103aE), coupled with red filters (F29), of varying exposures using the Schmidt Telescope of the INAOE. The structure brought out by the analysis of the plates indicate that the object consists of a prolate disk sphaped ring nebula with a central hole and featuring huge plumes emanating out of the ring which engulf an outer envelope having a diameter about twice that of the ring. The striking feature of the plumes is that they emanate almost symmetrically out of the two prolate ends of the ring and curve out almost symmetrically along opposite directions.

A comparison of the structures of this object with the temporal evolution of the gas density in the numerical simulations of a purely gaseous self-gravitating polytropic ring is conducted. Features resembling the plumes of this object are found at a certain stage of the simulations. A careful comparison of the observed and computer generated features indicate a marked similarity in the sense that both, the observed and simulated ring appear to be similar to the cross section of a prolate spheroid at the ends of which emanate the plumes. This seems to confirm that the evolution of this object is consistent with its being a planetary nebula having the appearance of a prolate spheroid with a central hole, which is a basic observational feature of most planetary nebulae.
Deep Narrow Band Interference Filter Photographs of Selected Extended Planetary Nebulae
Authors: Rosado M. , Moreno M.
Published: July 2016

Narrow-band interference filter photographs in the light of Hα, [S II] (λ = 6717 and 6731 A). [N II] (λ = 6584 A) and [O III] (λ = 4363 A) of four extended PNs are shown. These photographs were obtained with a focal reducer and a single-stage image tube attached to the 2.1 m Cassegrain focus telescope of the Observatorio Astronómico Nacional at San Pedro Mártir, B.C.N. The exposure times were of one hour. For each photograph we have obtained a calibration by means of a step density wedge.
IRAS Observations of Extended Planetary Nebulae
Authors: Leene A. , Pottasch S. R.
Published: July 2016

The pointed observations made by the IRAS satellite have been analysed. In total 67 nebulae have been observed of which 10 proved to be resolved. The majority of the observations were carried out with the CPC and with the DSD macro of the survey array (Leene & Pottasch, 1987b). Further special deep maps were made of six nebulae (Leene & Pottasch, 1987a; Leene, 1987). Typical noise levels of the deep images are 0.03–0.1 MJy ster−1.

The distribution of emission around the central star confirms that the 12 and 25 μm emission are due to ionic line emission. This is very clear in the nebula NGC 7293 (Leene & Pottasch, 1987a) and in NGC 6853 (Zhang et al., 1987). The other nebulae (A7, A21, A31, A35 and NGC 1360) confirm these findings. The 12 μm emission is most likely due to the NeII (12.81 μm) or due to the SIV (10.52 μm) line. The 25 μm band shows a strong central contribution due to the OIV (25.87 μm) line and a halo of the SIII (18.68 μm) line.
Infrared Images and Line Profiles of Planetary Nebulae
Authors: Smith M. G. , Geballe T. R. , Aspin C. , Mclean I. S. , Roche P. F.
Published: July 2016

We present high spatial resolution infrared images of the planetary nebulae NGC 7027, M2-9, BD +30 3639, NGC 7099 and NGC 7662. These were taken through a selection of broad and narrow-band line and continuum filters (including a Fabry-Pérot interferometer) using the 2D infrared array “IRCAM” on the United Kingdom Infrared Telescope, UKIRT, in July 1987. Comparison is made with recently published high-resolution VLA radio maps (Basart and Daub 1987, Ap. J., 317, 412) and mid-IR Wyoming Infrared Telescope raster-scanning maps (Bentley et al.1984, Ap. J., 278, 665).
NGC 2899: An Evolved Bipolar Planetary Nebula
Authors: López J. A. , Falcón L. H. , Ruiz M. T. , Roth M.
Published: July 2016

NGC 2899 (PK 277-3°l, He 2-30, RCW 43) is a southern planetary nebula of fairly large angular size (∼2!6 × 1!4) and moderate high surface brightness. Its morphology strongly resembles a loose bipolar structure with conspicuous bright condensations of toroidal geometry placed along the minor axis, on each side of the central object.
High Resolution Long-Slit Spectroscopy of A78
Authors: Manchado A. , Pottasch S. R. , Mampaso A.
Published: July 2016

High spectral resolution bidimensional spectroscopy of A78 in the He II λ4686 A, H λ4861 A, [O III] λ4959 A and [O III] λ5007 A lines is reported, confirming the different morphology of the nebula in these lines. The resulting velocity maps suggest different episodes in the history of the nebula, with an external hydrogen-rich layer expanding at low velocity (35±10 km/s), showing little structure and extending from approximately 35 to 55 arcsec. The [O III] and the He II maps show, however, an inner shell with at least two different expansion velocities; 73 km/s and 41 km/s.
The Halos of NGC 6543 and NGC 6826
Authors: Manchado A. , Pottasch S. R. , Mampaso A.
Published: July 2016

Long slit low resolution (3.4 A) spectra of the planetary nebulae NGC 6543 and NGC 6826, obtained using the 2.5-m Isaac Newton Telescope (La Palma) with the Image Photon Counting System (IPCS), indicate different physical conditions in the outer halos than in the central zone, with an outward increase of electronic temperature. The estimated mass contained in these halos is considerably larger than the values of the inner nebulae.
CO in the Bipolar Nebula NGC 2346
Authors: Healy A. P. , Huggins P. J.
Published: July 2016

We report on observations of the J = 2-1 line of CO to study the distribution and kinematics of the molecular gas in the bipolar planetary nebula NGC 2346. The data were obtained with the National Radio Astronomy Observatory 12-m telescope whose beamsize (FWHM = 30″) partially resolves the CO emitting region. A map of the velocity integrated emission shows a roughly rectangular distribution, approximately 53″ × 34″, oriented along the minor axis of the optical nebula. The CO spectrum towards the central star system is strongly double peaked. The mapping data show that this results from two distinct regions which are offset south-east and north-west of the center with radial velocities which are, respectively, larger and smaller than that of the star system. Overall the CO data are consistent with an expanding and partially disrupted distribution of molecular gas around the waist of the optical nebula. Mass estimates confirm that a substantial amount of the matter ejected by the star system is still in molecular form.