scholarly journals Molecular studies of Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 141-149 ◽  
Author(s):  
Yong Zhang
Keyword(s):  
Molecular Species ◽  
Active Site ◽  
Planetary Nebula ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Diffuse Interstellar Bands ◽  
Diffuse Clouds ◽  
Complex Organic

AbstractCircumstellar envelopes (CEs) around evolved stars are an active site for the production of molecules. After evolving through the Asymptotic Giant Branch (AGB), proto-planetary nebula (PPN), to planetary nebula (PN) phases, CEs ultimately merge with the interstellar medium (ISM). The study of molecules in PNe, therefore, is essential to understanding the transition from stellar to interstellar materials. So far, over 20 molecular species have been discovered in PNe. The molecular composition of PNe is rather different from those of AGB and PPNe, suggesting that the molecules synthesized in PN progenitors have been heavily processed by strong ultraviolet radiation from the central star. Intriguingly, fullerenes and complex organic compounds having aromatic and aliphatic structures can be rapidly formed and largely survive during the PPN/PN evolution. The similar molecular compositions in PNe and diffuse clouds as well as the detection of C60+ in the ISM reinforce the view that the mass-loss from PNe can significantly enrich the ISM with molecular species, some of which may be responsible for the diffuse interstellar bands. In this contribution, I briefly summarize some recent observations of molecules in PNe, with emphasis on their implications on circumstellar chemistry.

scholarly journals Molecular lines in the envelopes of evolved stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 169-170 ◽  
Author(s):  
Yong Zhang ◽  
Sun Kwok ◽  
Dinh-V- Trung
Keyword(s):  
Planetary Nebula ◽  
Central Star ◽  
Molecular Ions ◽  
Stellar Winds ◽  
X Rays ◽  
Circumstellar Envelopes ◽  
Chain Molecules ◽  
Evolved Stars ◽  
Physical Environments ◽  
Molecular Lines

AbstractWe report a spectral line survey of the circumstellar envelopes of evolved stars at millimeter wavelengths. The data allow us to investigate the chemical processes in different physical environments and evolutionary stages. A total of more than 500 emission features (mostly rotational transitions of molecules) are detected in the survey. Our observations show that the sources in different evolutionary stages have remarkably different chemical composition. As a star evolves from AGB stage to proto-planetary nebula, the abundances of Si-bearing molecules (SiO, SiCC, and SiS) decrease, while the abundances of some long-chain molecules, such as CH3CN, C4H, and HC3N, increase. After further evolution to planetary nebula, the abundances of neutral molecules dramatically decrease, and the emission from molecular ions becomes more intense. These differences can be attributed to the changes of the role that dust, stellar winds, shock waves, and UV/X-rays from the central star play in different evolutionary stages. These results will provide significant constraints on models of circumstellar chemistry.

scholarly journals The spectra of evolved stars at 20–25 GHz: Tracing circumstellar chemistry during the asymptotic giant branch to planetary nebula transition

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Yong Zhang ◽  
Wayne Chau ◽  
Jun-ichi Nakashima ◽  
Sun Kwok
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Evolutionary Sequence ◽  
Frequency Range ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Line Survey ◽  
And Inversion

Abstract We report an unbiased radio line survey towards the circumstellar envelopes of evolved stars at the frequency range from 20 to 25 GHz, aiming to obtain a more complete unbiased picture of the chemical evolution in the final stages of stellar evolution. The observation sample includes the asymptotic giant branch (AGB) star IRC +10216, the proto-planetary nebulae (PPNs) CRL 2688 and CRL 618, and the young planetary nebula (PN) NGC 7027, representing an evolutionary sequence spanning about 10000 years. Rotational transitions from cyanopolyyne chains and inversion lines from ammonia are detected in the AGB star and PPNs, while the PN displays several recombination lines. The different spectral behaviors of these evolved stars clearly reflect the evolution of circumstellar chemistry during the AGB–PPN–PN transitions.

scholarly journals New models for the rapid evolution of the central star of the Stingray Nebula

2021 ◽  
Author(s):  
T M Lawlor
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Planetary Nebula ◽  
Rapid Evolution ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Initial Mass ◽  
Thermal Pulse ◽  
The Past ◽  
New Models

Abstract We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

scholarly journals A Speculation into the Origin of Neutral Globules in Planetary Nebulae: Could the Helix’s Comets Really be Comets?

1995 ◽  
Vol 12 (2) ◽  
pp. 170-173
Author(s):  
Grant Gussie
Keyword(s):  
Solar System ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Oort Cloud ◽  
Asymptotic Giant Branch ◽  
Neutral Gas ◽  
Red Giant ◽  
The Masses

AbstractA novel explanation for the origin of the cometary globules within NGC 7293 (the ‘Helix’ planetary nebula) is examined, namely that these globules originate as massive cometary bodies at large astrocentric radii. The masses of such hypothetical cometary bodies would have to be several orders of magnitude larger than those of any such bodies observed in our solar system in order to supply the observed mass of neutral gas. It is, however, shown that comets at ‘outer Oort cloud’ distances are likely to survive past the red giant and asymptotic giant branch evolutionary phases of the central star, allowing them to survive until the formation of the planetary nebula. Some observational tests of this hypothesis are proposed.

Millimetre Observations of Evolved Stars

1996 ◽  
Vol 13 (2) ◽  
pp. 185-186
Author(s):  
Jessica M. Chapman
Keyword(s):  
Mass Loss ◽  
Stellar Atmosphere ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
High Mass Loss ◽  
Transfer Momentum

Radio emission at centimetre and millimetre wavelengths provides a powerful tool for studying the circumstellar envelopes of evolved stars. These include stars on the asymptotic giant branch (AGB), post-AGB stars and a small number of massive M-type supergiant stars. The AGB stars and M-type supergiants are characterised by extremely high mass-loss rates. The mass loss in such an evolved star is driven by radiation pressure acting on grains which form in the outer stellar atmosphere. The grains are accelerated outwards and transfer momentum to the gas through grain–gas collisions. The outflowing dust and gas thus form an expanding circumstellar envelope through which matter flows from the star to the interstellar medium, at a typical velocity of 15 km s−1. For a recent review of circumstellar mass loss see Chapman, Habing & Killeen (1995).

scholarly journals The first water fountain in a planetary nebula

2012 ◽  
Vol 8 (S287) ◽  
pp. 230-234
Author(s):  
Olga Suárez ◽  
José Francisco Gómez ◽  
Philippe Bendjoya ◽  
Luis. F. Miranda ◽  
Martín. A. Guerrero ◽  
...  
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Survival Times ◽  
Jet Formation ◽  
Evolved Stars ◽  
Water Masers ◽  
First Time ◽  
Water Maser

AbstractWater fountains are evolved stars showing water masers with velocity spanning more than ~100 km/s. They usually appear at the end of the Asymptotic Giant Branch (AGB) phase or at the beginning of the post-AGB phase, and their masers trace the first manifestation of axisymmetric collimated mass-loss. For the first time, masers with water fountain characteristics have been detected towards a PN (IRAS 15103–5754), which might require a revision of the current theories about jet formation and survival times. IRAS 15103-5754 was observed using the ATCA interferometer at 22 GHz (both continuum and water maser). The main results of these observations are summarized here. The evolutionary classification of this object is also discussed.

scholarly journals Circumstellar spirals/shells/arcs: the message from binary stars

2016 ◽  
Vol 12 (S323) ◽  
pp. 199-206
Author(s):  
Hyosun Kim
Keyword(s):  
Mass Loss ◽  
Binary Stars ◽  
Planetary Nebula ◽  
Fossil Record ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Molecular Line ◽  
The Past ◽  
Recurrent Patterns

AbstractA consensus has grown in the past few decades that binarity is key to understanding the morphological diversities of the circumstellar envelopes (CSEs) surrounding stars in the Asymptotic Giant Branch (AGB) to Planetary Nebula (PN) phase. The possible roles of binaries in their shaping have, however, yet to be confirmed. Meanwhile, recurrent patterns are often found in the CSEs of AGB stars and the outer halos of PNe, providing a fossil record of the mass loss during the AGB phase. In this regard, recent molecular line observations using interferometric facilities have revealed the spatio-kinematics of such patterns. Numerical simulations of binary interactions producing spiral-shells have been extensively developed, revealing new probes for extracting the stellar and orbital properties from these patterns. I review recent theoretical and observational investigations on the circumstellar spiral-shell patterns and discuss their implications in linking binary properties to the asymmetric ejection events in the post-AGB phase.

scholarly journals GTC/CanariCam mid-IR imaging of the fullerene-rich planetary nebula IC 418

2016 ◽  
Vol 12 (S323) ◽  
pp. 150-154
Author(s):  
J. J. Díaz-Luis ◽  
D. A. García-Hernández ◽  
A. Manchado ◽  
P. García-Lario ◽  
E. Villaver ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Molecular Species ◽  
Formation Process ◽  
Planetary Nebula ◽  
Narrow Band ◽  
Major Constituent ◽  
Simultaneous Presence ◽  
Circumstellar Envelopes ◽  
Photochemical Processing ◽  
Circumstellar Environments

AbstractThe formation process(es) of fullerenes in space is still uncertain and several mechanisms have been proposed in the literature. In particular, the most accepted idea to explain the simultaneous presence of fullerenes and PAH-like emission in the H-rich circumstellar envelopes of PNe is that these molecular species may be formed from the photochemical processing of a carbonaceous compound with a mixture of aromatic and aliphatic structures, which should be a major constituent of their circumstellar envelopes. Here we present seeing-limited narrow-band mid-IR GTC/CanariCam images of the fullerene-containing PN IC 418. The narrow-band images cover the 9−13, 11.3, and 17.4 μm emission features (and their adjacent continua) in this extended PN. We study the relative sub-arcsecond spatial distribution of the nebula in these filters with the intention of getting some clues about the formation process of fullerenes in H-rich circumstellar environments.

scholarly journals Spectral analysis of the barium central star of the planetary nebula Hen 2−39

2019 ◽  
Vol 624 ◽  
pp. A1 ◽  
Author(s):  
L. Löbling ◽  
H. M. J. Boffin ◽  
D. Jones
Keyword(s):  
Mass Transfer ◽  
Spectral Analysis ◽  
Planetary Nebula ◽  
Central Star ◽  
Optical Spectra ◽  
Roche Lobe ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Echelle Spectrograph ◽  
Process Elements

Context. Barium stars are peculiar red giants characterized by an overabundance of the elements synthesized in the slow neutron-capture nucleosynthesis (s-process elements) along with an enrichment in carbon. These stars are discovered in binaries with white dwarf companions. The more recently formed of these stars are still surrounded by a planetary nebula. Aims. Precise abundance determinations of the various s-process elements, of further key elements that act as indicators for effectiveness of nucleosynthesis on the asymptotic giant branch and, especially, of the lightest, short-lived radionuclide technetium will establish constraints for the formation of s-process elements in asymptotic giant branch stars as well as mass transfer through, for example, stellar wind, Roche-lobe overflow, and common-envelope evolution. Methods. We performed a detailed spectral analysis of the K-type subgiant central star of the planetary nebula Hen 2−39 based on high-resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope using local thermodynamic equilibrium model atmospheres. Results. We confirm the effective temperature of Teff = (4350 ± 150) K for the central star of the planetary nebula Hen 2−39. It has a photospheric carbon enrichment of [C∕H] = 0.36 ± 0.08 and a barium overabundance of [Ba∕Fe] = 1.8 ± 0.5. We find a deficiency for most of the iron-group elements (calcium to iron) and establish an upper abundance limit for technetium (log ɛTc < 2.5). Conclusions. The quality of the available optical spectra is not sufficient to measure abundances of all s-process elements accurately. Despite large uncertainties on the abundances as well as on the model yields, the derived abundances are most consistent with a progenitor mass in the range 1.75–3.00 M⊙ and a metallicity of [Fe∕H] = −0.3 ± 1.0. This result leads to the conclusion that the formation of such systems requires a relatively large mass transfer that is most easily obtained via wind-Roche lobe overflow.

scholarly journals Vibrationally excited water emission at 658 GHz from evolved stars

2017 ◽  
Vol 609 ◽  
pp. A25 ◽  
Author(s):  
A. Baudry ◽  
E. M. L. Humphreys ◽  
F. Herpin ◽  
K. Torstensson ◽  
W. H. T. Vlemmings ◽  
...  
Keyword(s):  
Vibrational State ◽  
Line Emission ◽  
Central Star ◽  
Rotational Transition ◽  
Asymptotic Giant Branch ◽  
Time Variability ◽  
Vibrationally Excited ◽  
Physical Conditions ◽  
Evolved Stars ◽  
Water Layers

Context. Several rotational transitions of ortho- and para-water have been identified toward evolved stars in the ground vibrational state as well as in the first excited state of the bending mode (v2 = 1 in (0, 1, 0) state). In the latter vibrational state of water, the 658 GHz J = 11,0−10,1 rotational transition is often strong and seems to be widespread in late-type stars. Aims. Our main goals are to better characterize the nature of the 658 GHz emission, compare the velocity extent of the 658 GHz emission with SiO maser emission to help locate the water layers and, more generally, investigate the physical conditions prevailing in the excited water layers of evolved stars. Another goal is to identify new 658 GHz emission sources and contribute in showing that this emission is widespread in evolved stars. Methods. We have used the J = 11,0−10,1 rotational transition of water in the (0, 1, 0) vibrational state nearly 2400 K above the ground-state to trace some of the physical conditions of evolved stars. Eleven evolved stars were extracted from our mini-catalog of existing and potential 658 GHz sources for observations with the Atacama Pathfinder EXperiment (APEX) telescope equipped with the SEPIA Band 9 receiver. The 13CO J = 6−5 line at 661 GHz was placed in the same receiver sideband for simultaneous observation with the 658 GHz line of water. We have compared the ratio of these two lines to the same ratio derived from HIFI earlier observations to check for potential time variability in the 658 GHz line. We have compared the 658 GHz line properties with our H2O radiative transfer models in stars and we have compared the velocity ranges of the 658 GHz and SiO J = 2−1, v = 1 maser lines. Results. Eleven stars have been extracted from our catalog of known or potential 658 GHz evolved stars. All of them show 658 GHz emission with a peak flux density in the range ≈50–70 Jy (RU Hya and RT Eri) to ≈2000–3000 Jy (VY CMa and W Hya). Five Asymptotic Giant Branch (AGB) stars and one supergiant (AH Sco) are new detections. Three AGBs and one supergiant (VY CMa) exhibit relatively weak 13CO J = 6−5 line emission while o Ceti shows stronger 13CO emission. We have shown that the 658 GHz line is masing and we found that the 658 GHz velocity extent tends to be correlated with that of the SiO maser suggesting that both emission lines are excited in circumstellar layers close to the central star. Broad and stable line profiles are observed at 658 GHz. This could indicate maser saturation although we have tentatively provided first information on time variability at 658 GHz.

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