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Post Info TOPIC: Planetary nebulae


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RE: Planetary nebulae
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Title: Herschel observations of planetary nebulae
Author: Griet C. Van de Steene

This article presents an overview of the published results for planetary nebulae based on images and spectroscopy from the PACS, SPIRE, and HIFI instruments on board the Herschel satellite.

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Title: Central Stars of Planetary Nebulae
Author: David Jones

In this brief invited review, I will attempt to summarise some of the key areas of interest in the study of central stars of planetary nebulae which (probably) won't be covered by other speakers' proceedings. The main focus will, inevitably, be on the subject of multiplicity, with special emphasis on recent results regarding triple central star systems as well as wide binaries which avoid a common-envelope phase. Furthermore, in light of the upcoming release of Kepler's Campaign 11 data, I will discuss a few of the prospects from that data including the unique possibility to detect merger products.

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Title: Central stars of mid-infrared nebulae discovered with Spitzer and WISE
Author: V.V. Gvaramadze, A.Y. Kniazev

Searches for compact mid-IR nebulae with the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE), accompanied by spectroscopic observations of central stars of these nebulae led to the discovery of many dozens of massive stars at different evolutionary stages, of which the most numerous are candidate luminous blue variables (LBVs). In this paper, we give a census of candidate and confirmed Galactic LBVs revealed with Spitzer and WISE, and present some new results of spectroscopic observations of central stars of mid-IR nebulae.

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Planetary nebulae Central Stars
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Title: A Survey for hot Central Stars of Planetary Nebulae I. Methods and First Results
Author: Graham C. Kanarek, Michael M. Shara, Jacqueline K. Faherty, David Zurek, Anthony F.J. Moffat

We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for K_s \ge 14 Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebulae, and are likely to come from massive progenitor populations, and themselves be more massive than any sample of planetary nebulae known. Our survey has identified thousands of such candidates.

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Planetary nebula progenitors
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Title: Planetary nebula progenitors that swallow binary systems
Author: Noam Soker (Technion, Israel)

I propose that some irregular `messy' planetary nebulae owe their morphologies to triple-stellar evolution where tight binary systems are tidally and frictionally destroyed inside the envelope of asymptotic giant branch (AGB) stars. The tight binary system might breakup with one star leaving the system. In an alternative evolution, one of the stars of the brook-up tight binary system falls toward the AGB envelope with low specific angular momentum, and drowns in the envelope. In a different type of destruction process the drag inside the AGB envelope causes the tight binary system to merge. This releases gravitational energy within the AGB envelope, leading to a very asymmetrical envelope ejection, with an irregular and `messy' planetary nebula as a descendant. The evolution of the triple-stellar system before destruction can be in a full common envelope evolution (CEE) or in a grazing envelope evolution (GEE). Both before and after destruction the system might lunch pairs of opposite jets. One pronounced signature of triple-stellar evolution might be a large departure from axisymmetrical morphology of the descendant planetary nebula. I estimate that about one in six non-spherical PNe is shaped by one of these triple-stellar evolutionary routes.

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Title: On the distances of planetary nebulae 
Author: Haywood Smith Jr 

We reconsider calibration of statistical distance scales for planetary nebulae, examining precision and systematic error for various distance methods used as well as the scales themselves. A different calibration strategy, one based on precise trigonometric parallaxes by Harris et al. (2007), is presented. Most statistical scales have an overall scale error; in addition, all four tested show dependence of distance ratio [scale/actual] on nebular radius. Some methods used for calibration have systematic errors, and the extinction method is found to be mostly unreliable. Comparison of Hipparcos parallaxes for a few large planetaries with our "best estimate" distances for those confirms the overestimation of 2.5 found by Harris et al. for PHL 932. We suggest a possible connection with the smaller overestimation found by Melis et al. (2014) when testing Hipparcos parallaxes for some of the Pleiades. 

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Title: Rule or exception? Planetary nebulae around hot subdwarf stars
Authors: A. Aller (1), L.F. Miranda (1,2), A. Ulla (1), R. Oreiro (3), M. Manteiga (4), E. Pérez (1), C. Rodríguez-López (3) ((1) Departamento de Física Aplicada, Universidade de Vigo, Vigo, Spain, (2) Consejo Superior de Investigaciones Científicas, Madrid, Spain, (3) Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain, (4) Departamento de Ciencias de la Navegación y de la Tierra, Universidade da Coruña, A Coruña, Spain)

In this work, we present the first results of an ongoing survey to search for planetary nebulae (PNe) around hot subdwarf stars (sdOs). Deep images and intermediate-resolution long-slit spectra of RWT 152, the only confirmed PN+sdO system in the northern hemisphere, as well as preliminary results for other sdO+PN candidate are presented.

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Central Stars of Planetary Nebulae
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Title: A New Grid of Synthetic Spectra for the Analysis of [WC]-type Central Stars of Planetary Nebulae
Authors: Graziela R. Keller, James E. Herald, Luciana Bianchi, Walter J. Maciel, Ralph C. Bohlin

We present a comprehensive grid of synthetic stellar-atmosphere spectra, suitable for the analysis of high resolution spectra of hydrogen-deficient post-Asymptotic Giant Branch (post-AGB) objects hotter than 50000 K, migrating along the constant luminosity branch of the Hertzsprung-Russell diagram (HRD). The grid was calculated with CMFGEN, a state-of-the-art stellar atmosphere code that properly treats the stellar winds, accounting for expanding atmospheres in non-LTE, line blanketing, soft X-rays, and wind clumping. We include many ionic species that have been previously neglected. Our uniform set of models fills a niche in an important parameter regime, i.e., high effective temperatures, high surface gravities, and a range of mass-loss values. The grid constitutes a general tool to facilitate determination of the stellar parameters and line identifications and to interpret morphological changes of the stellar spectrum as stars evolve through the central star of planetary nebula (CSPN) phase. We show the effect of major physical parameters on spectral lines in the far-UV, UV, and optical regimes. We analyse UV and far-UV spectra of the central star of NGC 6905 using the grid to constrain its physical parameters, and proceed to further explore other parameters not taken in consideration in the grid. This application shows that the grid can be used to constrain the main photospheric and wind parameters, as a first step towards a detailed analysis. The full grid of synthetic spectra, comprising far-UV, UV, optical, and IR spectral regions, is available on-line.

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RE: Planetary nebulae
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Title: Testing the binary hypothesis for the formation and shaping of planetary nebulae
Authors: D. Douchin, O. De Marco, G. H. Jacoby, T. C. Hillwig, D. J. Frew, I. Bojicic, G. Jasniewicz, Q. A. Parker

There is no quantitative theory to explain why a high 80% of all planetary nebulae are non-spherical. The Binary Hypothesis states that a companion to the progenitor of a central star of planetary nebula is required to shape the nebula and even for a planetary nebula to be formed at all. A way to test this hypothesis is to estimate the binary fraction of central stars of planetary nebulae and to compare it with that of the main sequence population. Preliminary results from photometric variability and the infrared excess techniques indicate that the binary fraction of central stars of planetary nebulae is higher than that of the main sequence, implying that PNe could preferentially form via a binary channel. This article briefly reviews these results and current studies aiming to refine the binary fraction.

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A Planetary Nebula Gallery

pne_w11.jpg

This gallery shows four planetary nebulas from the first systematic survey of such objects in the solar neighbourhood made with NASA's Chandra X-ray Observatory. The planetary nebulas shown here are NGC 6543, also known as the Cat's Eye, NGC 7662, NGC 7009 and NGC 6826. In each case, X-ray emission from Chandra is coloured purple and optical emission from the Hubble Space Telescope is coloured red, green and blue.
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