scholarly journals ISO Spectra of Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 303-304 ◽  
Author(s):  
Kevin Volk ◽  
Sun Kwok
Keyword(s):  
Chemical Composition ◽  
Dust Emission ◽  
Planetary Nebulae ◽  
Emission Feature ◽  
Significant Fraction ◽  
Energy Output ◽  
Agb Stars ◽  
Dust Component

It has been well known since the IRAS mission that dust emission represents a significant fraction of the energy output from PNe (Zhang & Kwok 1991). Although the dust component in PNe was long thought to be due to the remnants of the envelopes of AGB stars (Kwok 1982), we now know that dust in PNe has a much richer chemical composition. In addition to amorphous silicates and SiC features commonly seen in AGB stars, PNe have been found to have strong aromatic infrared features (Russell et al. 1977), crystalline silicate features (Waters et al. 1997), and an unidentified emission feature at 30 μm (Forrest et al. 1981). In this paper, we show the ISO spectra of a number of PNe illustrating the diverse dust chemistry in PNe.

scholarly journals Morpho-Kinematics of the Circumstellar Environments around Post-AGB Stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 520-521
Author(s):  
Toshiya Ueta ◽  
Hideyuki Izumiura ◽  
Issei Yamamura ◽  
Masaaki Otsuka
Keyword(s):  
Dust Emission ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Emission Properties ◽  
Circumstellar Shell ◽  
Circumstellar Environments ◽  
Co Gas

AbstractWe observed two proto-planetary nebulae, HD 56126 representing a source with an elliptical circumstellar shell, and IRAS 16594−4656 representing a source with a bipolar circumstellar shell, with ALMA in the 12CO and 13CO J=3−2 lines and neighboring continuum to see how the morpho-kinematics of CO gas and dust emission properties in their circumstellar environments differ.

scholarly journals On the Origin of the 21 Micron Feature in Post-AGB Stars

1999 ◽  
Vol 191 ◽  
pp. 297-302 ◽  
Author(s):  
Sun Kwok ◽  
Kevin Volk ◽  
Bruce J. Hrivnak
Keyword(s):  
Planetary Nebulae ◽  
Emission Feature ◽  
Asymptotic Giant Branch ◽  
Agb Stars

The unidentified emission feature at 21 μm is now observed in 12 sources, all being objects in transition between the asymptotic giant branch and planetary nebulae phases. The relations between the 21 μm and other emission features, such as the PAH features and the broad 30 μm feature, and the possible origins of the 21 μm feature are discussed.

scholarly journals Unidentified Species in Envelopes around Carbon Stars

2013 ◽  
Vol 9 (S297) ◽  
pp. 219-222
Author(s):  
B. W. Jiang ◽  
A. Li ◽  
K. Zhang ◽  
J. M. Liu ◽  
J. Gao ◽  
...  
Keyword(s):  
Ir Spectra ◽  
Emission Spectrum ◽  
Single Photon ◽  
Dust Emission ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Carbon Stars ◽  
Unidentified Species ◽  
Ir Emission

AbstractThe infrared (IR) spectra of many evolved carbon-rich stars exhibit two prominent dust emission features peaking around 21μm and 30μm, with the former exclusively seen in proto-planetary nebulae (PPNe), while the latter seen in a much wider range of objects, including AGB stars, PPNe and planetary nebulae (PNe). The 30μm feature is seen in all the 21μm sources, but no correlation is found between these two features. Over a dozen carrier candidates have been proposed for the 21μm feature, but none of them has been widely accepted and the nature of the 21μm feature remains a mystery. The carrier of the 30μm feature also remains unidentified. MgS dust, once widely accepted as a valid carrier, was ruled out because of the sulfur budget problem. In this work we examine nano-sized FeO dust as a carrier for the 21μm feature. We calculate the IR emission spectrum of FeO nanodust which undergoes single-photon heating in PPNe. It is found that the 21μm feature emitted by FeO nanodust is too broad to explain the observed feature. For the 30μm feature, we argue that graphite could be a viable carrier. Graphite, provided its d.c. conductivity σd.c. exceeds ~100ohm−1cm−1, exhibits a pronounced band at 30μm.

scholarly journals AGB stars and galactic dynamics

1999 ◽  
Vol 191 ◽  
pp. 500-510 ◽  
Author(s):  
H. Dejonghe ◽  
K. Van Caelenberg
Keyword(s):  
Chemical Composition ◽  
Stellar Population ◽  
Milky Way ◽  
Planetary Nebulae ◽  
Line Of Sight ◽  
Galactic Dynamics ◽  
Stellar Systems ◽  
Agb Stars ◽  
Dynamical Models ◽  
Ir Stars

AGB stars, seen as a stellar population, can be used to probe the dynamical state of galaxies. The relevant data are mostly positions and line-of-sight velocities, sometimes together with information on chemical composition and/or age. As of now, dynamical models have been made for OH/IR stars and Planetary Nebulae. Other candidates are C stars, S stars, and Miras. We review the methods used and the results obtained so far, for the Milky Way and for (relatively nearby) extragalactic stellar systems.

scholarly journals Theoretical abundances in Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 257-257
Author(s):  
Paola Marigo
Keyword(s):  
Chemical Composition ◽  
Mass Loss ◽  
Analytical Model ◽  
Planetary Nebulae ◽  
Stellar Winds ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Thermal Pulse ◽  
Intermediate Mass Stars

A semi-analytical model has been constructed to calculate the TP-AGB evolution of low-and intermediate-mass stars (Marigo et al. 1996), starting from the first thermal pulse until the complete ejection of the envelope by stellar winds. We estimate the changes in the chemical composition of the envelope due to different processes: (i) the intershell nucleosynthesis and convective dredge-up; (ii) envelope burning in the most massive AGB stars (M ≥ 3–4M⊙); (iii) mass loss by stellar winds.

scholarly journals Quantitative Spectral Analysis of hot Post-AGB Stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 356-357
Author(s):  
Daniel R. Costa-Mello ◽  
Simone Daflon ◽  
Claudio B. Pereira
Keyword(s):  
Spectral Analysis ◽  
Chemical Composition ◽  
High Resolution ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Quantitative Spectral Analysis ◽  
Luminous Objects

AbstractPost-AGB (PAGB) stars are luminous objects of low and intermediate mass in a final and short stage of evolution in the transition between AGB stars and planetary nebulae (PNe). In this work we present a quantitative spectral analysis of some hot PAGBs based on high resolution spectra. The stellar parameters and chemical composition were obtained from the synthesis of non-LTE spectra.

scholarly journals Aromatic, aliphatic, and the unidentified 21 micron emission features in proto-planetary nebulae

2008 ◽  
Vol 4 (S251) ◽  
pp. 213-214 ◽  
Author(s):  
Bruce J. Hrivnak ◽  
Kevin Volk ◽  
T. R. Geballe ◽  
Sun Kwok
Keyword(s):  
Planetary Nebulae ◽  
Emission Feature ◽  
Agb Stars ◽  
New Feature ◽  
Simple Molecules

AbstractAromatic features at 3.3, 6.2, 7.7, 8.6, 11.3 μm are observed in proto-planetary nebulae (PPNe) as well as in PNe and H ii regions. Aliphatic features at 3.4 and 6.9 μm are also observed; however, these features are often stronger in PPNe than in PNe. These observations suggest an evolution in the features from simple molecules (C2H2) in AGB stars to aliphatics in PPNe to aromatics in PNe. In the same carbon-rich PPNe, a strong, broad, unidentified 21 μm emission feature has been found. We will present recent observations of the aromatic, aliphatic, and 21 μm emission features, along with C2H2 (13.7 μm) and a new feature at 15.8 μm, and discuss correlations among them and other properties of these PPNe.

scholarly journals On the inorganic carriers of the 21 micron emission feature in post-AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 215-216
Author(s):  
Ke Zhang ◽  
Biwei Jiang ◽  
Aigen Li
Keyword(s):  
Planetary Nebulae ◽  
Emission Feature ◽  
Observational Constraints ◽  
Agb Stars ◽  
Emission Power ◽  
Lower Strength ◽  
General Acceptance ◽  
Impurity Atoms

AbstractThe mysterious 21 μm emission feature seen in only 12 C-rich proto-planetary nebulae (PPNe) remains unidentified since its discovery in 1989. Over a dozen materials have been suggested as the carrier candidates while none of them has received general acceptance. We investigate the inorganic carrier candidates by applying the observational constraints of the feature strength and associated features. It is found that: (1) three candidates, TiC clusters, fullerenes with Ti impurity atoms, and SiS2, are not abundant enough to account for the emission power of the 21 μm band, (2) five candidates, doped-SiC, SiO2-mantled SiC dust, carbon and silicon mixtures, Fe2O3, and Fe3O4, all show associated features which are either not detected in the 21 μm sources or detected but with a much lower strength, and (3) FeO, which satisfies the abundance constraints, does not display any associated features which are not seen in the 21 μm sources. Moreover, FeO is more likely to survive in the C-rich environment than Fe2O3and Fe3O4. Thus FeO seems to be the most plausible one among the inorganic carrier candidates.

scholarly journals The Chemical Composition of Cometary Nuclei

1972 ◽  
Vol 45 ◽  
pp. 265-270
Author(s):  
L. M. Shul'man
Keyword(s):  
Chemical Composition ◽  
Cosmic Rays ◽  
Organic Molecules ◽  
Solid Phase ◽  
Critical Concentration ◽  
Energy Output ◽  
Time Interval ◽  
Nuclear Surface ◽  
Solar Cosmic Rays ◽  
Cometary Nuclei

The probable parent-molecules of radicals such as C3 and N2+ are discussed, and it is concluded that cometary nuclei may contain complicated organic molecules, such as C3H4, CH2N2, and C4H2. It is suggested that these molecules are formed by radiation synthesis in solid phase. In a time interval of order 107 to 109 yr bombardment from cosmic rays would be expected to transform the chemical composition to a depth of 1 m. Solar cosmic rays do not penetrate as far, and as a result the surface layer of the nucleus can be enriched with unsaturated hydrocarbons. After a critical concentration of this explosive material is reached a further burst of solar cosmic rays can initiate an explosion and thus an outburst in the comet's brightness. This mechanism is the only one advanced to date that can explain the synchronism of the energy output over the whole nuclear surface.

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