bluuebunny/crossref_metadata_2025 huggingface dataset:
Mainline and water maser observations of OH/IR stars in the Arecibo sky
Authors: Lewis B. M.
Published: July 2016

A complete sample of color selected IRAS sources with S(25) ≥ 2 Jy in the Arecibo sky and(0° ≤ δ ≤ 37°) was examined previously for 1612 MHz masers. The resulting set of OH/IR stars has now been searched for mainline OH masers at Arecibo (Lewis 1997) and for 22 GHz water masers at Effelsberg (Engels & Lewis 1996). The high overall detection rate of 61.6% for the mainlines and 54.8% for water is partly a result of deployed sensitivity, and partly due to the many blue objects in the sample. But the detectability of both masers improves when S(25)> 20 Jy, as the accompanying tables show. Still the bluest objects exhibit higher (usually ≥80%) detection rates, while there is a clear decrease in detections from redder shells: this decrease begins circa (25–12) μm=–0.55 for mainline masers, and abruptly circa (25–12) μm = −0.35 for water. These trends adhere to the descriptive sequence of the chronological scenario for masers in circumstellar shells, though a few proto planetary nebulae and very red OH/IR stars have water masers and a few mainline masers are detected in shells with (25-12) μm ≥ −0.2.
Cycle-to-cycle changes in the Mira-type star RT Cyg
Authors: Marsakova V. I. , Andronov I. L. , Schweitzer E.
Published: July 2016

The moments of 82 maxima and 76 minima are used for the correlation analysis of the characteristics of the individual cycles. 5 not trivial correlations were found. The characteristic time of the secular decrease of the period is |P/P| = (23.4 ± 4.3) · 103 yrs, but decade–scale and cycle–to–cycle variations are also present.
Radio and optical observations at high spatial and spectral resolution of compact young Planetary Nebulae
Authors: Miranda L. F. , Torrelles J. M. , Eiroa C.
Published: July 2016

We present VLA-A radio continuum at 3.6 cm and H92α observations, and optical long-slit spectra at high spectral and spatial resolution of the compact Planetary Nebulae (PNs) Hu 2-1, IC 4997, IC 5117 and NGC 6884. The radio continuum maps show the subarcsecond structure of the PNs in detail. From the optical spectra, the basic kinematical properties can be deduced. The H92α emission line, spatially and spectrally resolved in IC 5117 and Hu 2-1, allows us to observe the kinematics of the PNs in spatial scales of ∼ 0.3″. By combining the radio and optical data, it is possible to identify the components present in the nebulae, to deduce their spatio-kinematical structure, and to obtain estimates for the electron density and temperature, ionized masses and kinematical ages. All this information permits to impose constraints about the mass ejection processes involved in the formation of PNs and when they have occurred.
The chemical composition of IRAS 05341+0852: a post-AGB F supergiant with 21 μm emission
Authors: Reddy B. E. , Parthasarathy M. , Gonzalez G. , Bakker E. J.
Published: July 2016

An abundance analysis of the photosphere of the F-type Post-AGB candidate IRAS 05341-+0852 is presented. It shows that the star is metal-poor ([Fe/H]=–1.0) and carbon-rich (C/0≈2.2). Carbon, nitrogen, oxygen, silicon, and possibly lithium and aluminum are found to be over abundant. Most importantly this star has large overabundance of s-process elements which are as follows: [Y/Fe]= 1.80, [Ba/Fe]= 2.58, [La/Fe]= 2.86, [Ce/Fe]= 2.95, [Pr/Fe]= 2.27, [Nd/Fe]= 1.97, and [Sm/Fe]= 0.86. The overabundances of s-process elements and carbon in IRAS 05341+0852 is direct evidence for the association of s-process enhancements with shell-flashes and dredge-up. These are likely responsible for the increase in C/O. The possible overabundance of Li ([Li/Fe]≤2.5) and Al ([Al/Fe]≤ 1.1) in IRAS 05341+0852 could indicate that there was Hot Bottom Burning (HBB), where the base of the convective envelope is hot enough for nucleosynthesis to occur (Lattanzio 1993). HBB has been suggested as the mechanism responsible for the production of Li in the Li-rich AGB stars discovered by Smith and Lambert (1989). In fact these are bright AGB stars which are oxygen-rich rather than carbon-rich. Recent calculations by Sackmann and Boothroyd (1992) showed that Li-rich and O-rich AGB stars are the result of HBB. In the HBB models temperatures of the order of 0.5–1 × 108 K are encountered at the base of the convective envelope (Blöcker and Schönberner 1991). This is hot enough for the reaction 25Mg(p,γ) 26 Al resulting in the production of Al.
Hubble Space Telescope and ground-based optical imaging of the Proto-Planetary Nebula M1-92
Authors: Trammell Susan R. , Goodrich Robert W.
Published: July 2016

We present HST and ground-based images of the bipolar proto-planetary nebula M1-92. Trammell et al. (1993) studied Ml-92 using spectropolarimetry and concluded that the continuum emission is reflected from the inner regions of the object, the forbidden lines are formed locally in the bipolar lobes, and the permitted lines are partially reflected and partially formed in the bipolar lobes. The emission produced in the lobes of Ml-92 is indicative of shock heating, Vs = 60–100 km s–1. Shock emission dominates the optical line spectra of the lobes of M1-92 and is a powerful probe into the properties of the mass loss occurring between the AGB and PN phases of evolution.
The structure of the molecular envelope around CRL 2688
Authors: Yamamura I. , Deguchi S. , Kasuga T.
Published: July 2016

We have observed CRL 2688 (the Egg nebula) in the 13CO J = 1–0 and CS J = 1–0 and 2–1 lines by the Nobeyama Millimeter Array with a resolution of about 4″. The 13CO velocity channel maps show that emission consists of three components; a spherical core, an extended envelope, and a bipolar high-velocity component (Yamamura et al. 1995).A spherical shape of the core despite of the maximum optical depth of about the unity indicates that the disk-like structure, expected from the shape of the bipolar nebula, is smaller than the present beam size (corresponding to about 6 × 1016cm at 1kpc). The combined maps made from the data by the NMA and the Nobeyama 45-m telescope show that emission spreads towards the south of the center more then the opposite direction.
A survey for new PN in the southern galactic bulge
Authors: Beaulieu Sylvie F. , Dopita Michael A. , Freeman Kenneth C. , Kalnajs Agris J.
Published: July 2016

We present the results of a deep and uniform narrow-band Hα imaging survey for planetary nebulae (PNe) in the southern galactic bulge. The goal of this survey was to obtain a sample of bulge tracers which is being used to study the dynamics of the Milky Way bulge (Beaulieu, 1996).
Abundances for a large sample of galactic Planetary Nebulae
Authors: Golovaty V. V. , Malkov Yu.F.
Published: July 2016

We present a database on the chemical composition of 200 planetary nebulae (PNe) in our Galaxy. Abundances of He, C, N, O, Ne, Mg, Si, S, and Ar are found for 175, 64, 190, 200, 170, 13, 40, 173, and 187 PNe respectively. The abundances for all PNe are obtained with the same atomic data and by the same method of abundance determination, so the database is highly homogeneous. The method of the determination of nebular abundances based on a photoionization model grid is described by Golovaty et al. (1993). Observational data have been compiled from 105 papers published in 1976–1994. For most of PNe in our sample, the distances and central star masses are determined as well (Malkov, this volume).
What we can say about PN if their luminosity function distances are correct
Authors: Jacoby George H.
Published: July 2016

I review the arguments favoring the high reliability of the PNLF method. Agreement with Cepheid distances is better than 8%, and consistency for multiple PNLF distances within clusters is even better. Agreement between Cepheid distances to spirals and PNLF distances to ellipticals within the same cluster also is excellent. In order for the PNLF method to work despite the vast diversity of properties seen among PN, several factors must operate. Most importantly, the progenitors of the bright extragalactic PN probably have ages less than ∼10 Gyrs. Also, very young PN must either be absent from the bright extragalactic samples or must have lower luminosities than suggested by their predicted central star masses. The latter may be due to internal dust, nitrogen enrichment that competes with oxygen for ionizing photons, and/or a tendency for massive PN to be optically thin to ionizing radiation. In addition, models that reproduce observed PNLFs rely on theoretical evolutionary tracks of central stars, and so these tracks also must be reasonably correct. PNLF observations suggest, however, that the slope of the initial-to-final mass relation is shallower than the Weidemann (1987) relation.
The Cosmological Parameters H0 and Ω0
Authors: Tully R. Brent
Published: July 2016

The first section discusses a recalibration of the luminosity–linewidth technique and its use in a determination of H0. The recalibration introduces (i) new cluster calibration data, (ii) new corrections for reddening as a function of inclination, and (iii) a new zero-point calibration using 13 galaxies with distances determined via the cepheid period–luminosity method. It is found that H0 = 82 ± 16 km s−1 Mpc−1 (95% confidence).
Determination of Cosmological Parameters by Cosmic Microwave Background
Authors: Sugiyama Naoshi
Published: July 2016

After the sensational discovery of Cosmic Microwave Background (CMB) anisotropies by Differential Microwave Radiometer (DMR) boarded on the Cosmic Background Explore (COBE) (Smoot et al. 1992), the number of observational data of temperature fluctuations have been rapidly increasing (see e.g., White, Scott and Silk 1994) together with the understanding of physical processes of evolution of CMB anisotropies. Nowadays, CMB anisotropies are becoming one of the key observational object in the modern cosmology. CMB anisotropies provide us direct information at last scattering surface, i.e., redshift z ≈ 1000. Since the shape of the angular power spectrum of CMB anisotropies is highly sensitive to geometry of the universe, cosmological models and cosmological parameters, i.e., density parameter Ω0, Hubble constant h which is normalized by 100km/s/Mpc, cosmological constant Λ, baryon density ΩB and so on, CMB anisotropies are expected to be a new tool to understand our universe. Moreover, we can obtain information of thermal history of the universe after recombination (through the formation of secondary fluctuations and damping of primary fluctuations), physics of clusters of galaxies (through the Sunyaev-Zeldovich effect) and non-linear structure of the universe (through the gravitational lensing effect) from CMB anisotropies.
The Formation and Evolution of Galaxies: Perspectives on the Origin of the Hubble Sequence
Authors: Ellis R.S.
Published: July 2016

I review recent observational progress concerning the evolution of the morphological distribution of galaxies in the rich cluster environment and in the faint field population. By coupling HST imagery with ground-based spectroscopic diagnostics, evidence accumulates that galaxy morphology can be a transient phenomenon reflecting various changes in the star formation rate. Possible physical processes responsible for these changes are discussed. Future progress in understanding them will depend on securing 2-D spectroscopic data for representative systems.
Galaxy Evolution Probed by Mid-Infrared Deep Surveys
Authors: Taniguchi Y.
Published: July 2016

We discuss the formation and evolution of galaxies in view of recent mid-infrared deep surveys made using Infrared Space Observatory. A special interest is addressed to finding reddened massive populations at high redshifts.
Multicolor Luminosity Function of Field Galaxies
Authors: Brunello A. , Saracco P. , Garilli B. , Maccagni D. , Chincarini G.
Published: July 2016

The aim of this programme is to determine the luminosity function of field galaxies in different bands for a unique sample. From the ESP [1] redshift survey of 3344 bj ≤ 19.4 galaxies, we have extracted a fair subsample and obtained multicolor photometry for 354 (11%) galaxies in the V, R (Johnson) and i (Gunn) filters and for 148 (4%) in the K′ band. Errors on the total magnitudes are smaller than 0.1 in all bands. In order to obtain absolute magnitudes, we applied k-corrections [2] after deriving a rough morphological classification based on color information. Here we present a by product of this programme: the determination of the color-luminosity relationship. The figure shows how the rest-frame Bj-K' color is strongly related to the absolute i magnitude while such correlation is not present using optical colors. If we assume Mi is a good mass tracer, the figure indicates that bluer galaxies are the less massive ones.
Evolutionary and Cosmological Corrections for High Redshift Galaxies
Authors: Möller C.S. , Alvensleben U. Fritze-v. , Fricke K.J.
Published: July 2016

We calculate the evolution of high redshift galaxies by spectral type with our unified chemically consistent spectrophotometric evolution code. This model takes into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary tracks, color calibrations and spectra (Möller et al. 1997).

We analyse how the consideration of a realistic metallicity distribution affects the evolutionary and cosmological corrections in various bands as a function of redshift. For various spectral types of galaxies and various cosmological parameters we present the color and magnitude evolution as a function of redshift and compare them with observations.
Void Hierarchy in the Northern Local Void
Authors: Lindner U. , Fricke K.J. , Einasto J. , Einasto M.
Published: July 2016

Empirical studies of the Large–Scale Structure in the nearby Universe come in two complementary modes, namely the investigation of either the distribution of luminous matter or voids: (i) The description of the galaxy and cluster distribution employs correlation functions, clustering analysis, topological methods, et cetera. (ii) The investigation of the empty regions between systems of galaxies uses void probability functions, mean diameters of voids, the compilation of void catalogues, and so forth.
Gravitational Lensing in the Clumpy Universe
Authors: Asada Hideki
Published: July 2016

Most of methods to determine the cosmological parameters by using the gravitational lensing are based on the following three typical observations; (1) the image separation, (2) the lensing statistics and (3) the time delay. For the accurate estimation of the cosmological parameter, it is of great importance to clarify the relation between the observation in the realistic universe and the determination of the cosmological parameters. In particular, it has been discussed by many authors that inhomogeneities of the universe may affect the cosmological tests.
Probing Density Fluctuations in the Universe with the FIRST Radio Survey
Authors: Cress C.M.
Published: July 2016

We compare the angular correlation function measured for FIRST sources (Becker et al., Cress et al.) with COBE-normalized CDM-model predictions (Cress & Kamionkowski). We note that uncertainties in the z-distribution do not affect the predictions dramatically and that the effects of non-linear evolution of the power spectrum are significant for θ<∼20′. We find the CF at larger angles to be sensitive to clustering of nearby sources. The smaller angle measurements, when combined with results from other surveys (Loan et al., Rengelink et al.) indicate that the bias required for the data to fit CDM models increases as the surveys probe deeper. We also point the reader to Refregier et al. for information on the use of weak lensing of FIRST sources in probing foreground mass.
Multiscale Comparison of Potent and IRAS
Authors: Haines Paul , Ellis G.F.R.
Published: July 2016

We compare the density fields from POTENT and IRAS. We vary the smoothing scale, and use a non-parametric test to obtain a value for the linear bias parameter b, as a function of offset c, which arises because the normalisation volumes for the two samples are different (Dekel et al., 1993). The smoothed fractional overdensities are related by δP = δI/b + c.
The Angular Correlation Function of Faint Galaxies during the Decreasing Correlation Period
Authors: Ogawa Tomoya , Roukema Boudewijn F. , Yamashita Kazuyuki
Published: July 2016

During the period of galaxy formation, many small-length-scale perturbations superimposed on high-amplitude large-length-scale perturbations should have their overdensities boosted into the non-linear regime, while small-scale perturbations in other regions remain linear. The formation of the first galaxies in discrete, high overdensity regions may lead to an initial amplitude of the spatial correiatio? function of galaxies, ξ0, much higher than that expected from linear fluctuation theory. This initially high “bias” would consequently decrease to the near-unity values expected from local observations. Such a Decreasing Correlation Period (DCP) is detected in N-body simulations under certain conditions by several authors; Roukema
(1993), Brainerd & Villumsen (1994), Roukema et al. (1997) and unpublished simulations by one of us (Yamashita).
Galaxy Distribution in Clusters of Galaxies
Authors: Okamoto T. , Yachi S. , Habe A.
Published: July 2016

Galaxy distribution in clusters maybe affected by dynamical evolution of clusters and merging process of their member galaxies. In oreder to studey the effect, we study formation and evolution of galaxies in clusters by using N-body simulation. To identify galaxy size dark halos, we use the adaptive friends-of-friends algorithm (van Kampen 1995) at several red-shifts. At the same time, we treat galaxy merging and dark matter accretion to the galaxies by using the simple merging model. In this model we assume that galaxies have the merging cross section proportional to and if they encounter in small relative velocity (< Vmerge), they merge into one galaxy.
Are there Ghost Images of the Coma Cluster at other Redshifts?
Authors: Roukema Boudewijn F.
Published: July 2016

The topology of the Universe is a fundamental property of our Universe according to Friedmann-Lemaître models[3, 9, 7], but has not yet been reliably measured. As pointed out by Sato[12], the Universe may be finite even though flat or negatively curved: infinite volume of a hypersurface.
Theoretical and Observational Implications of a Super-Horizon-Scale Inhomogeneous Cosmological Model
Authors: Tomita K.
Published: July 2016

We discuss the theoretical and observational implications of an inhomogeneous cosmological model consisting of three regions: the inner low-density homogeneous region, the self-similar (or partially similar) inhomogeneous region and the outer nearly flat homogeneous region. When we assume Einstein's gravitational theory without cosmological constant, the standard inflation theory, and the observational fact of local low density around us, this model is found to be reasonable. The boundary between the inner region and the self-similar region is assumed to be in a spherical shell corresponding to the epoch of redshift z = 1.5–2.0, when the numbers of QSOs and Ly α clouds changed rapidly.
Type-Specific Luminosity Functions of Nearby Clusters of Galaxies
Authors: Yagi M. , Shimasaku K. , Yasuda N. , Doi M. , Okamura S. , Kashikawa N. , Sekiguchi M.
Published: July 2016

We study the total luminosity function (LF) and the type-specific LF of 7 nearby clusters of galaxies (A1060, S805, A2063, A1736, A1644, A1631, and A754) using the R-band image (1.0 × 0.5 deg2) taken with our mosaic CCD camera mounted on 1-m telescope at the Las Campanas Observatory.
New Evidence for Non-Cosmological Redshift
Authors: Chu Yaoquan , Zhu Xingfen
Published: July 2016

Recently Arp (1997) has published a list of x-ray emitting blue stellar objects (BSO) around 24 Seyfert galaxies. Herewith we present our optical identification of 5 BSOs in the field NGC3516 obtained on April 4-5, 1997 using the 2.16m telescope at Xinlong Station, Beijing Astronomical Observatory. One of the objects Q1107+7232 with z=2.10 (θ = 4.34′, θ is the angular distance from the center of NGC3516) is already listed in the Hewitt-Burbidge Catalog (1993). We find the other four objects are all quasars: Q1108+7226 with z=0.328 (θ = 11.23′); Q1106+7244, z=0.690 (θ = 10.23′); Q1105+7242, z=0.930, (θ = 10.990; QH05+7238, z=1.399 (θ = 7.42′) Q1107+7232, z=2.10 (θ = 4.34′)
Observational Physics of Mirror World
Authors: Bochkarev N.G. , Khlopov M. Yu.
Published: July 2016

Mirror (shadow) particles are required to restore symmetry between left- and right-handed coordinate systems. If mirror world exists, it has been born at the same time as the ordinary world and has the same evolution (in the case of the shadow world - broken mirror symmetry, the evolution and structure of the shadow world does not correspond with the observed world). Mirror world is a kind of dark matter. According to Bahcall (1984) local dark matter has a density approximately equal to the density of observed (ordinary) matter.
Decaying Cosmological Constant and the Choice of a Conformal Frame
Authors: Fujii Yasunori
Published: July 2016

A solution of the cosomlogical constant problem seems to come from a version of the scalar-tensor theory of gravity, which is characterized by a “nonminimal coupling“ in place of the standard Einstein-Hilbert action, where ɸ is the scalar field while ξ a constant. One then encounters an inherent question never fully answered: How can one single out a right conformai frame?
Formation of Topological Defects during Preheating
Authors: Kasuya S. , Kawasaki M.
Published: July 2016

Recent investigations revealed that the explosive decay of the inflaton field takes place in the first stage of reheating due to the effect of parametric resonance (Kofman et al., 1994). One of surprising possibilities of the non-thermal fluctuations (created particles) during preheating is the symmetry restoration which may lead to the formation of topological defects (Kofman et al., 1996; Tkachev, 1996).
The Current Status in the Modelling of Stellar Atmospheres
Authors: Gustafsson Bengt
Published: July 2016

The old question whether models of stellar atmospheres are wrong, adequate, or even overelaborated, is discussed with a number of examples from contemporary research as a background. A simple quality classification scheme for models of different types is presented. It is concluded that, in spite of rapid recent progress, we are far from having fully satisfactory theoretical representations of stellar atmospheres. Reasons for continuing the efforts to reach a higher degree of physical consistency in model atmosphere work are discussed.
Observational Evidence for the Stratification of Chemical Abundances in Stellar Atmospheres
Authors: Ryabchikova T. , Wade G. A. , Leblanc F.
Published: July 2016

We present spectroscopic and photometric observational evidence for abundance stratification in stellar atmospheres. Attention is given to chemically peculiar (Ap) stars in which magnetic fields stabilize the atmosphere, allowing diffusion processes to establish abundance stratification during the early stages of star's life. The results of recent empirical modelling of chemically stratified atmospheres are briefly discussed, and a comparison is given with the predictions of self-consistent atmospheric models which include radiative diffusion.

The importance of abundance stratification analysis is demonstrated for rapidly oscillating (roAp) stars in which the amplitudes of the radial velocity pulsations are different for the lines of different elements in different ionization stages. We also demonstrate that chemical stratification has important effects on the Zeeman Stokes IQUV profiles of Ap stars, indicating that stratification must be taken into account in detailed modelling of their magnetic fields.
Radio Images of Planetary Nebulae
Authors: Terzian Yervant
Published: July 2016

The continuum radio spectra of planetary nebulae are discussed, and the structure of these objects is examined from the observed aperture synthesis brightness distributions determined with the Very Large Array. The use of radio observations in determining distances to planetary nebulae is examined. The detection of atomic neutral hydrogen at λ21 cm associated with planetary nebulae, as well as the associated CO and OH components are discussed. An upper limit, of the nebular magnetic field associated with the neutral material, of 1mG is reported for NGC 6302.
New and Misclassified Planetary Nebulae
Authors: Kohoutek L.
Published: July 2016

75 objects have been classified as new planetary nebulae since 1982. They are summarized in Table 1 which gives the designations, names, coordinates and references to the discovery. In the list of misclassified PN (Table 2) 41 objects have been included; Table 3 presents objects with incorrect identification in CGPN. The main properties of a PN and of its nucleus are given in a summary which can be useful for a correct classification of planetaries.
The Probable Low Excitation Planetary Nebula M3-44
Authors: Gutiérrez-Moreno A. , Moreno H. , Cortés G.
Published: July 2016

The Hα emission object M3-44 was observed photographically and spectroscopically. Photographs were obtained in the visual region, in [0 III] λ5007, and in Hα. The visual image is faint and has almost stellar aspect; the object is not visible in [0 III], but the Hα image is very intense, with a diameter of the order of 5″.
Optical and Infrared Observations of the Peculiar Planetary Nebula He2-442
Authors: Arkhipova V.P. , Yesipov V.F. , Yudin B.F.
Published: July 2016

Infrared observations of He2-442 carried out at Crimean Station of Sternberg Institute during 1984–1986 revealed that in the past ten years the 1–10 μm flux has decreased by factor ∼ 2.4, the colour temperature determined from (K-L) index has decreased by ∼ 300 K, and the infrared energy distribution has been changed also essentially. However, the definite cool star features, for example, Mira-like variability was not yet recorded.
Nebular Density Distributions; A Critical Look
Authors: Kirkpatrick Ronald C.
Published: July 2016

The symmetry of planetary nebulae demands an explanation. Underlying previous attempts to explain these objects is the inferred density distribution based on spatio-kinematic models such as those of Weedman (1968), Reay et al. (1983) and others. Although some observations suggest a linear velocity-radius relationship for planetaries, plausible hypothetical examples may be constructed which greatly violate a linear relationship, and hydrodynamic theory (Schmalz 1986) suggests it may not hold even when observations may be most easily interpreted as supporting a linear relationship. Therefore, an independent assessment of the nebular density distribution is needed.
Kinematics of Abell 30
Authors: Jacoby George H. , Chu You-Hua
Published: July 2016

Abell 30 is a remarkable PN with a H-depleted core. Four bright knots have been identified in the [O III] line (Jacoby 1979). The previous kinematic study has shown that J1 and J3 form a pair expanding at radial velocities of ±25 km/s with respect to the central star, and J4 has a radial velocity of −22 km/s (Reay, Atherton, and Taylor 1983).
Emission Line Profiles in the Planetary Nebulae IC 4593 and NGC 6153
Authors: Banerjee D.P.K. , Anandarao B. G.
Published: July 2016

The Planetary Nebulae IC 4593 and NGC 6153 are two rather compact objects not well studied. The nebula IC 4593 is about 12 arcsec in diameter and has a central star of Type 07 f; while the southern nebula NGC 6153 is about 22 arcsec in diameter and its central star is faint and of unknown spectral type. Using a high-resolution scanning Fabry-Pérot spectrometer we have made profile measurements of emission lines Hα λ6563 A, [O III] λ5007 A, and [N II] λ6584 A in the central regions of these two nebulae. We have found expansion velocities for IC 4593 of 40 km s−1 in [N II] and 16 km s−1 in [O III]. In the case of NGC 6153, we have obtained expansion velocities of 15 km s−1 in [N II] and 13 km s−1 in [O III] line. The profiles in Hα in both the nebulae dis not show a double peaked feature due to the larger thermal broadening. In the case of IC 4593, both [O III] and [N II] profiles showed complex structures. These results and their interpretation will be discussed.
A New Study of Some Galactic Planetary Nebulae
Authors: Meatheringham Stephen J. , Wood Peter R. , Faulkner D. J.
Published: July 2016

Expansion velocities ([O III], [O II], and He II) have been measured for a sample of 64 Southern Planetary Nebulae (PN). The ratio of [O III] to [O II] expansion velocities is used to derive a typical ionized shell thickness of order ΔR/Rneb ≍ 0.12. Nebular electronic densities have been determined from the [O II]λλ3727, 3729 A doublet for 23 of these objects. These data are compared with previously published values. The Dopita et al. (1987) distance scale for Magellanic Cloud PN based on a correlation between observable nebular parameters is used to derive distances to 32 Galactic nebulae. These distances are compared with published values, and lead to the conclusion that the Dopita et al., Daub (1982) and Maciel (1984) distance scales agree well, but that the Shklovsky (1956) method yields distances that are too large. Nebular ionized masses are also calculated for a subset of 30 objects.
Spectroscopic Investigations of Halos of Planetary Nebulae
Authors: Bässgen M. , Bässgen G. , Grewing M. , Cerrato S. , Bianchi L.
Published: July 2016

Different ESO-telescopes with medium resolution spectrographs and CCD-detectors were used to look for emission from extended halos around Planetary Nebulae. In three out of four cases the search was successful. The ratio Rhalo/Rneb ranges from 2 to about 10. Assuming that the halos have been produced by the winds of the Red Giant progenitor stars, we determine Ṁ/VAGB of these progenitors, using the measured Hα- and Hβ-fluxes. These values scatter in a relatively narrow range around 2‥5 · 10−7 (M⊙/y)/(km/s). In some objects emission line fluxes were measured at two ore more radial distances and radial density profiles were derived from them. These are in good agreement with the expected n∼r−2 density law expected for a freely expanding wind.
Molecular Hydrogen Emission from Cold Condensations in NGC 2440
Authors: Reay N. K. , Walton N. A. , Atherton P. D.
Published: July 2016

We report observations of the v = 1-0 S(1) line of molecular hydrogen in the high excitation Planetary Nebula NGC 2440. The emission is particularly strong at the positions of the two bright condensations which lie well within the H II region and close to the position of the very hot T = 350,000 K central star. The emission is consistent with an excited molecular hydrogen mass of 2–4 × 10−5 M⊙ in the condensations, and we estimate the total mass of excited molecular hydrogen associated with the H II region to be 6 × 10−3 M⊙. We show that the radiation pressure from the central star is insufficient to excite the S(1) line emission. We also show that a stellar wind driven shock would imply a mass loss rate of 3 × 10−7 M⊙ yr−1 if we adopt a wind velocity of 2000 km s−1.
The Systematics and Distribution of Molecular Hydrogen in Planetary Nebulae
Authors: Payne P. W. , Storey J.W.V. , Webster B. L. , Dopita M. A. , Meatheringham S. J.
Published: July 2016

The infrared S(1) line of molecular hydrogen has been searched for in twenty-two planetary nebulae using the imaging mode of the Anglo-Australian Telescope. The line was detected and mapped in eleven objects. It has been demonstrated that all those with strong excited molecular hydrogen belong to a subclass of the Type I planetary nebulae, morphologically consisting of an equatorial toroid with faint bipolar extensions. Furthermore, nearly all planetaries with these characteristics have strong molecular hydrogen. The molecular line ratios in the 2.0 to 2.5 micron window are consistent with shock excitation. The observations suggest that the morphology of these planetaries has been controlled by a fast stellar wind interacting with a disc of gas concentrated in the equatorial plane.
OH Maser Emission from Young Planetary Nebulae
Authors: Zijlstra A. , Pottasch S. R. , te Lintel P. , Bignell C.
Published: July 2016

OH/IR stars are now generally accepted to be progenitors of planetary nebulae. We have carried out a project to try to find objects in the transition phase between OH/IR stars and PN. Transition objects should be characterized by having both continuum radio emission and a 1612 MHz OH maser line. The continuuum emission would indicate that the central star has become hot enough to ionize part of the envelope, while the OH maser indicates that a large part of the envelope is still neutral. Only one such object was known, namely Vy 2-2.
N/O Abundances in Planetary Nebulae from Far-Infrared Line Observations
Authors: Dinerstein Harriet L. , Werner Michael W.
Published: July 2016

Measurements of the [O III] 52, 88 μm and [N III] 57 μm fine-structure emission lines have been obtained for nine planetary nebulae, using the facility far-infrared array spectrometer on NASA's Kuiper Airborne Observatory. The N++/O++ ratios determined from these observations range by more than an order of magnitude among the sample. Using recent improved values for the atomic parameters, we find that the N++/O++ ratios agree fairly well with values of N+/O+ determined from optical lines in the same objects. The highest N++/O++ values, found for the extreme “Type I” nebulae NGC 2440 and NGC 6302, are approximately unity. These results imply that the synthesis and mixing of nitrogen must be extremely efficient in the progenitor stars of some planetary nebulae, and that these nebulae are significant sources of nitrogen to the interstellar medium. The local electron densities derived from the intensity ratios of the two [O III] lines are generally lower than values in the literature determined from small-beam optical observations of other ions, such as [O II]. This effect can be understood in terms of the presence of clumpy structure in the nebula, since the far-infrared lines have fairly low critical densities for collisional de-excitation and therefore are preferentially emitted from low-density gas.
The Spatial Distribution of Line Ratio O III/O II in High Excitation Planetary Nebulae
Authors: Noriega-Crespo A. , McCall M.
Published: July 2016

Previous attempts to model the integrated line ratio [O III] 5007 A/[O II] 3727 A for high excitation planetary nebulae (Che and Köppen 1983) have suggested that the charge exchange coefficient (k) for the reaction

could be 10 times smaller than the predicted theoretical value. The influence of other factors that may contribute to differences in the O III/O II ratio, such as the ionizing spectrum and the nebular gas density distribution, seem to be relatively small in the high excitation nebulae.
Magnitudes, Spectra, and Temperatures of Planetary Nuclei
Authors: Kaler James B.
Published: July 2016

The purpose of this review is to examine the fundamental observational parameters of the central stars of planetary nebulae, namely their apparent magnitudes and gross spectral characteristics, and how these relate to the derivation or estimation of effective temperatures.
Wind Features and Wind Velocities
Authors: Grewing Michael
Published: July 2016

Fast winds have been detected in the spectra of many nuclei of planetary nebulae (PNNi). The wind velocities range from about 600 km/s to roughly 4000 km/s. While these winds add little to the mass of the nebular shells they may significantly effect their internal kinematics.

By studying the emission from the faint outer envelopes of PNe one can infer also the wind properties of the progenitors of the current nuclei. This will in the end allow to test quantitatively current models of the origin of PNe.
Mass Loss Rates in Central Stars of Planetary Nebulae
Authors: Perinotto M.
Published: July 2016

Central stars of planetary nebulae (PNCS) frequently exhibit fast winds (cf. Cerruti-Sola and Perinotto, 1985; C.P. and Grewing, this volume). They may be important for the structure of the whole nebula as well as for the evolution of the central star. Their speed is typically two orders of magnitude higher than that of the classical optically visible nebula, which in turn expands a few times faster than the most external winds detected in few cases in the radio domain.

I review here the status of art in the determination of the mass loss rates (M) associated with these fast winds. I restrict myself to the ‘observational’ determinations. Only at the end I will say something about the predictions of multi-scattering line radiation wind driven theory in connection with one best studied object: N6C 6543. This allows one to conclude that this theory may be the right explanation also for these winds.
Temperatures and Luminosities of Planetary Nebulae Nuclei
Authors: Bianchi Luciana , Recillas Elsa , Grewing Michael
Published: July 2016

The location of Planetary Nebulae Nuclei (PNNi) on the H-R diagram is a very important clue to understand the evolution of these objects.
Broad Baseline Flux Distribution of Planetary Nuclei
Authors: Heap Sara , Torres Ana V.
Published: July 2016

We have analyzed the flux distributions of 13 planetary nuclei (NPN) spanning the full range of spectral classes known among central stars, except white dwarfs (see Table 1). We combined low-dispersion spectra from the IUE archives with absolute spectrophotometry scans taken by Dr. P. Massey at Kitt Peak with the Intensified Reticon Scanner (IRS) to obtain flux distributions covering the wavelength range λλ1150–7200 at ∼ 7 A resolution. In order to get the intrinsic stellar energy distributions, we first corrected the observed fluxes for interstellar extinction, and then subtracted out the nebular fluxes, which we estimated from the Hβ flux on the IRS observations and from the nebular temperature, density and helium ionic abundances. Finally, we fitted blackbody curves to the stellar continua.
Echelle Spectra of a Large Sample of Planetary Nebula Nuclei
Authors: McCarthy James K.
Published: July 2016

We have undertaken at Palomar Observatory to obtain high resolution spectra of a large sample of planetary nebula nuclei (PNN) in order to systematically investigate their spectral morphologies and then to derive temperatures and surface gravities by comparing absorption line profiles to model atmospheres. We have taken as our sample all those central stars of planetary nebulae within 1.3 kpc of the sun according to the distance determinations of Daub (Ap, J., 260, 612, 1982); of the 94 objects in this unbiased sample, 64 are in the sky visible from Palomar and 33 have central stars bright enough to be observed at a resolution of 5 000 with an “echellette” spectrograph on the 5-m Hale telescope, leaving 7 PNN (11% of the northern sample of 64 PNN) which are too faint to be observed at present.
A Survey of Planetary Nebulae in the SMC and M31
Authors: Meyssonnier N. , Azzopardi M. , Lequeux J. , Gathier R.
Published: July 2016

Our general method for finding planetary nebulae (PN) is to make wide field objective-prism or objective-grating low-dispersion spectra on photographic plates, PN stand up amongst other emission-line objects either as Hα + [N II] 6548-6583 A emitters or as [O III] 50007 A emitters with faint or no continuum, higher-resolution spectroscopy is used for confirming a selection of candidates.
N 66: A High Excitation N Rich Planetary Nebula in the LMC
Authors: Peña M. , Ruiz M. T.
Published: July 2016

Spectrophotometry data of the planetary nebula N 66 (WS 35) has been obtained with the CTIO 4-m telescope equipped with an R-C spectrograph and a 2D-Frutti detector. The spectral range between 3700 A and 6800 A was covered at 4 A resolution.
OH/IR Stars and other IRAS Point Sources as Progenitors of Planetary Nebulae
Authors: Habing H. J. , te Lintel Hekkert P. , van der Veen W.E.C.J.
Published: July 2016

We briefly review the history of the search for progenitors of planetary nebulae starting with Shklovsky's (1956) paper. The inner structure of AGB stars (the likely progenitors) is sketched. The (l, b) distributions and the (l, V) distributions (V is the centre of mass radial velocity) of OH/IR stars and of planetary nebulae are compared; it is concluded that, grosso modo, both types of objects belong to the same galactic population and that most OH/IR stars develop ultimately into planetary nebulae. From a comparison of the properties of OH/IR stars and of Mira variables it is concluded that both are AGB stars with the OH/IR stars having developed from Mira variables. Most OH/IR stars are long period variables but the few that are not are probably transition cases -no longer AGB stars and very early planetary nebulae. It is argued that the IRAS catalog contains a large number of AGB stars without (detected) OH maser emission, but otherwise similar to OH/IR stars. An evolutionary sequence is presented from Mira's to oxygen-rich planetary nebulae. Some speculations are added on the formation of carbon stars and carbon-rich planetary nebulae.
Models of Planetary Nebulae: Generalisation of the Multiple Winds Model
Authors: Kahn F. D.
Published: July 2016

According to the multiple winds model a planetary nebula forms as the result of the interaction of a fast wind from the central star with the superwind that had previously been emitted by the progenitor star. The basic theory which deals with the spherically symmetrical case is briefly summarised. Various improvements are then considered in turn. A better history is clearly needed of the way that the central star becomes hotter, it is unrealistic to make the assumption that the superwind is spherically symmetrical, and finally there are likely to be important instabilities at some of the interfaces in the PN, notably that between the shocked superwind and the HII layer. These changes in the theoretical description produce a better understanding of the conditions in the outer parts of a PN and of the nature of its general shape, and they should lead to an explanation for the occurrence of high speed motions, and of highly ionized species and high excitation spectral lines.
The Optically Resolved Planetary Nebula/OH Maser Vy 2-2
Authors: Falomo R. , Sabbadin F.
Published: July 2016

Vy 2-2 is, to our knowledge, the only planetary nebula exhibiting OH emission, indicating that it is a very young PN still enveloped by the neutral shell of the progenitor AGB star.
New IR-Observations of Post AGB Stars and Proto-Planetary Nebulae
Authors: van der Veen W.E. , Habing H. J. , Geballe T. R.
Published: July 2016

A sample was selected from the IRAS Point Source Catalogue based on the following selection criteria: very red (“cold”) IRAS-colours: roughly F25/F12 > 2.5 and F60/F25 < 1.2; and low IR-variability: VAR < 30. These non-variable IR-sources may be stars that have evolved beyond the AGB (Asymptotic Giant Branch); a large fraction (40%) is associated with known planetary nebulae (Van der Veen and Habing, 1987, Astron. Astrophys., in press). To determine the nature of the other 60% additional observations were made mainly in the infrared: 1–13 μm, during 4 observing runs: ESO (La Silla, Chile) in July 1986 and June 1987; UKIRT (Hawaii) in August 1986 and June 1987. A total number of 58 sources was observed. A summary of the observations: -IR broad band photometry at 1.2, 1.6, 2.2, 3.8 and 4,6 μm for all 58 sources. -IR broad band photometry at 8.4, 9.7 and 12.8 μm for 19 sources. -IR small band photometry for 4 sources in the ranges 2–2.5 μm and 3–3.5 μm. -IR spectroscopy for 10 sources in the ranges 2–2.5 μm and 3–3.5 μm, -V, R, I observations (0.55, 0.7 and 0.9 μm) for 5 sources associated with a star of visual magnitude 8–9. These observations were carried out by D. de Winter (Amsterdam) with the 0.5-m ESO telescope at La Silla (Chile). -Walraven photometry (0.32, 0.36, 0.38, 0.43 and 0.54 μm) for 21 stars brighter than V = 15 and within 10“ from the IRAS position. These observations were carried out by M. van Haarlem (Leiden) with the 0.9-m Dutch telescope at La Silla (Chile).
New OH/IR Stars: Proto-Planetary Nebulae?
Authors: Eder J. , Lewis B. M. , Terzian Yervant
Published: July 2016

The IRAS infrared colors, (60 - 25)μm and (25 - 12)μm, allow efficient identification of Type II OE/IR stars. We present Arecibo1 OH (1612 MHz) observations of 474 IRAS point sources chosen to define the exact regions of the two-color diagram occupied by OH/IR stars. Our observations are complete within the boundary regions of the two-color locus and within the region, 16h right ascension < 22h, 0° < declination < 37°. The sensitivity of the Arecibo telescope allows the identification of many weak sources that would not have been detected by previous surveys and the weak end of the masing phenomenon has been studied for the first time.
Direct Evidence for a Bipolar Stellar Wind in NGC 2392
Authors: O'Dell C.R.
Published: July 2016

Very high spectral resolution slit spectra have been used to investigate the kinematic structure of the double shell planetary nebula NGC 2392, the Eskimo Nebula. Each shell produces a spectrum corresponding to the projected radial velocity, a pattern which varies according to the position angle of the spectrograph's entrance slit. Multiple slit observations were used to determine that the inner shell is an incomplete prolate spheroid pointed almost at the observer and missing the tip ends. The outer shell is nearly spherical and more uniform.
A New Method for Observational Testing of the Planetary Nebulae Nuclei Evolution
Authors: Szczerba R.
Published: July 2016

Planetary nebulae (PNe) are very useful as a tool for testing the theory of stellar evolution. The most widely applied method in this respect is the Hertzsprung-Russell (H-R) diagram. However, the observed positions of planetary nebulae nuclei (PNNi) on the H-R diagram are subject to large uncertainties, mostly due to inaccurate distances to them. On the other hand, the (absolute visual magnitude, age)-diagram also is not free of this problem. Therefore, an attempt has been done to develop a new method which is distance-independent. For comparison between theory and observations we propose the I (Hell λ 4686) /I(H β) versus log [I(H β, PN)/IC (H β, PNN)] diagram. Both ratios reflect the evolutionary status of the central star and the surrounding nebula. Consequently, such diagram is a valuable tool for studying common evolution of the PNN-PN system.
White Dwarfs and Planetary Central Stars
Authors: Liebert James
Published: July 2016

Studies of hot white dwarf samples constrain the properties and evolution of planetary nuclei and the nebulae. In particular, the white dwarf and planetary nebulae formation rates are compared. I discuss the overlap of the sequences of white dwarfs having hydrogen (DA) and helium-rich (DO) atmospheres with known central stars of high surface gravity. There is evidence that the hydrogen atmosphere nuclei have “thick” outer hydrogen layers (≳ 10−4 M⊙), but that DA white dwarfs may have surface hydrogen layers orders of magnitude thinner. Finally, a DA planetary nucleus is discussed (0950+139) which has undergone a late nebular ejection; this object may be demonstrating that a hydrogen layer can be lost even after the star has entered the white dwarf cooling sequence.