scholarly journals Chemical Enrichment and Central Star Properties

1993 ◽  
Vol 155 ◽  
pp. 572-572
Author(s):  
C.Y. Zhang
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Physical Processes ◽  
Chemical Abundances ◽  
Core Mass ◽  
Chemical Enrichment ◽  
The Core ◽  
Stellar Temperature ◽  
Independent Parameters

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

scholarly journals Planetary Nebula Evolution Traced by Distance-Independent Parameters

1993 ◽  
Vol 155 ◽  
pp. 480-480
Author(s):  
C.Y. Zhang ◽  
S. Kwok
Keyword(s):  
Physical Properties ◽  
Mass Distribution ◽  
Planetary Nebula ◽  
Strong Support ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolution Model ◽  
The Core ◽  
Independent Parameters ◽  
Central Stars

Making use of the results from recent infrared and radio surveys of planetary nebulae, we have selected 431 nebulae to form a sample where a number of distance-independent parameters (e.g., Tb, Td, I60μm and IRE) can be constructed. In addition, we also made use of other distance-independent parameters ne and T∗ where recent measurements are available. We have investigated the relationships among these parameters in the context of a coupled evolution model of the nebula and the central star. We find that most of the observed data in fact lie within the area covered by the model tracks, therefore lending strong support to the correctness of the model. Most interestingly, we find that the evolutionary tracks for nebulae with central stars of different core masses can be separated in a Tb-T∗ plane. This implies that the core masses and ages of the central stars can be determined completely independent of distance assumptions. The core masses and ages have been obtained for 302 central stars with previously determined central-star temperatures. We find that the mass distribution of the central stars strongly peaks at 0.6 M⊙, with 66% of the sample having masses <0.64 MM⊙. The luminosities of the central stars are then derived from their positions in the HR diagram according to their core masses and central star temperatures. If this method of mass (and luminosity) determination turns out to be accurate, we can bypass the extremely unreliable estimates for distances, and will be able to derive other physical properties of planetary nebulae.

scholarly journals Chemical abundances and metallicity of Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 291-291
Author(s):  
C. Y. Zhang ◽  
S. Kwok
Keyword(s):  
Planetary Nebulae ◽  
Chemical Abundances ◽  
Core Mass ◽  
The Core ◽  
Theoretical Predictions

Confrontations of the dredge-up theory with observed patterns of chemical abundances of planetary nebulae (PNs) have been carried out by many authors (see, e.g., Kaler & Jacoby 1990, 1991; Stasińska & Tylenda 1990). Although these studies suggest that the observational abundance ratios of PNs can qualitatively be explained by the current dredge-up theory, scatters around the theoretical predictions in their diagrams are always large. This has led Ratag (1991) to conclude that there is no correlation at all between the nebular abundances and the core mass of CSPNs (see also Pottasch 1993).

scholarly journals Historical overview of planetary nebulae research

2011 ◽  
Vol 7 (S283) ◽  
pp. 1-8
Author(s):  
Sun Kwok
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Evolutionary Status ◽  
Complex Molecules ◽  
Chemical Enrichment ◽  
Star Studies ◽  
The Galaxy ◽  
Underlying Causes

AbstractPlanetary nebulae (PNs) were first discovered over 200 years ago and our understanding of these objects has undergone significant evolution over the years. Developments in astronomical optical spectroscopy and atomic physics have shown that PNe are gaseous objects photoionized by UV radiation from a hot central star. Studies of the kinematics of the nebulae coupled with progress in theories of stellar evolution have led to the identification that PNe are evolved stars and progenitors of white dwarfs. Development of infrared and millimeter-wave technology in the 1970s made us realize that there is significant amount of neutral matter (molecules and dust) in PNe. The link of PNe to the stellar winds from their progenitor asymptotic giant branch (AGB) stars and subsequent dynamical interactions are now believed to be the underlying causes of the morphological structures of PNe. The role of PNe as prolific molecular factories producing complex molecules and organic solids has significant implications on the chemical enrichment of the Galaxy.In this paper, we discuss the misconceptions and errors that we have encountered in our journey of understanding the nature of PN. The various detours and dead ends that had happened during our quest to pin down the evolutionary status and causes of nebulae ejection will be discussed. As there are still many unsolved problems in PN research, these lessons of history have much to offer for future progress in this field.

The real time evolution of post-AGB stars

2019 ◽  
Vol 15 (S357) ◽  
pp. 154-157
Author(s):  
Marcin Hajduk
Keyword(s):  
Real Time ◽  
Time Evolution ◽  
Planetary Nebulae ◽  
Theoretical Models ◽  
Central Star ◽  
Maximum Temperature ◽  
Additional Parameter ◽  
Agb Stars ◽  
The Real ◽  
Hr Diagram

AbstractEvolution of post-AGB stars is extremely fast. They cross the HR diagram vertically on a timescale of hundreds to some ten thousands of years to reach maximum temperature in their lifetime. This is reflected in an increasing excitation of planetary nebulae on a timescale of years and decades. Since evolutionary timescale of post-AGB stars is very sensitive to their mass, observed changes can be used to determine model dependent central star masses. If an additional parameter is determined (e.g. luminosity or dynamic age), the observed evolution of planetary nebulae can be utilized for observational verification of theoretical models.

The relation between chemical enrichment and core mass in planetary nebulae

1990 ◽  
Vol 362 ◽  
pp. 491 ◽  
Author(s):  
James B. Kaler ◽  
George H. Jacoby
Keyword(s):  
Planetary Nebulae ◽  
Core Mass ◽  
Chemical Enrichment

scholarly journals The population of planetary nebulae near the Galactic Centre: chemical abundances

2016 ◽  
Vol 12 (S323) ◽  
pp. 339-340
Author(s):  
M. Mollá ◽  
O. Cavichia ◽  
R. D. D. Costa ◽  
W. J. Maciel
Keyword(s):  
Luminosity Function ◽  
Planetary Nebulae ◽  
Galactic Centre ◽  
Physical Parameters ◽  
Chemical Compositions ◽  
Galactic Bulge ◽  
Chemical Abundances ◽  
Chemical Enrichment ◽  
History Of ◽  
Low Dispersion

AbstractIn this work, we report physical parameters and abundances derived for a sample of 15 high extinction planetary nebulae located in the inner 2° of the Galactic bulge, based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman spectrograph. The new data allow us to extend our database including older, weaker objects that are at the faint end of the planetary nebulae luminosity function. The data provide chemical compositions for PNe located in this region of the bulge to explore the chemical enrichment history of the central region of the Galactic bulge. The results show that the abundances of our sample are skewed to higher metallicities than previous data in the outer regions of the bulge. This can indicate a faster chemical enrichment taking place at the Galactic centre.

scholarly journals IFU Spectroscopy of Southern Planetary Nebulae V: Low-Ionisation Structures

2017 ◽  
Vol 34 ◽  
Author(s):  
A. Ali ◽  
M. A. Dopita
Keyword(s):  
Emission Line ◽  
Planetary Nebulae ◽  
Central Star ◽  
Chemical Compositions ◽  
Physical Analysis ◽  
Type I ◽  
High Excitation ◽  
Chemical Abundances ◽  
Physical Conditions ◽  
Integral Field Spectroscopy

AbstractIn this fifth paper of the series, we examine the spectroscopy and morphology of four southern Galactic planetary nebulae Hen 2-141, NGC 5307, IC 2553, and PB 6 using new integral field spectroscopy data. The morphologies and ionisation structures of the sample are given as a set of emission-line maps. In addition, the physical conditions, chemical compositions, and kinematical characteristics of these objects are derived. The results show that PB 6 and Hen 2-141 are of very high excitation classes and IC 2553 and NGC 5307 are mid to high excitation objects. The elemental abundances reveal that PB 6 is of Type I, Hen 2-141 and IC 2553 are of Type IIa, and NGC 5307 is of Type IIb/III. The observations unveil the presence of well-defined low-ionisation structures or ‘knots’ in all objects. The diagnostic diagrams reveal that the excitation mechanism of these knots is probably by photoionisation of dense material by the nebular central stars. The physical analysis of six of these knots show no significant differences with their surrounding nebular gas, except their lower electron densities. In spite of the enhancement of the low-ionisation emission lines of these knots, their chemical abundances are nearly comparable to their surrounding nebulae, with the exception of perhaps slightly higher nitrogen abundances in the NGC 5307 knots. The integrated spectrum of IC 2553 reveals that nearly all key lines that have led researchers to characterise its central star as a weak-emission line star type are in fact of nebular origin.

scholarly journals Abundances in Local Group Planetary Nebulae

1995 ◽  
Vol 10 ◽  
pp. 480-482
Author(s):  
James B. Kaler
Keyword(s):  
Local Group ◽  
Initial Conditions ◽  
Planetary Nebulae ◽  
Magellanic Clouds ◽  
Chemical Compositions ◽  
Core Mass ◽  
Know How ◽  
Chemical Enrichment ◽  
Clear Link ◽  
The Galaxy

We are able to measure the chemical compositions of hundreds of planetary nebulae in our own Galaxy and in the Magellanic Clouds. Why, therefore, do we need to expend the effort to observe much more difficult targets in other Local Group galaxies? A severe lack of distances does not allow us to place Galactic planetary nuclei on the log L-log T plane with any degree of accuracy, so we cannot properly examine composition differences relative to core mass and state of evolution. We can perform such tasks for Magellanic Cloud objects, but do not know how the Clouds’ low-metallicities affect the results, and thus do not know how this sample of planetaries relates to the nebulae in our own system. We know, for example, that in the Clouds, nitrogen enrichment begins above a core mass of about 0.68 M⊙ (Kaler and Jacoby 1990), but other than a clear link between core mass and chemical enrichment in the Galaxy, do not know at what point it becomes important. To study such relationships, we therefore have to go to other galaxies with a variety of initial conditions for which distances are secure, namely those of the Local Group.

scholarly journals Improved synthetic TP-AGB models

1999 ◽  
Vol 191 ◽  
pp. 53-58
Author(s):  
P. Marigo
Keyword(s):  
Mass Range ◽  
Magellanic Clouds ◽  
Agb Stars ◽  
Carbon Stars ◽  
Core Mass ◽  
The Core ◽  
Extensive Analysis ◽  
Luminosity Functions ◽  
New Treatment ◽  
Analytical Relations

We present recent improvements and results of an extensive analysis of the TP-AGB phase performed by means of a synthetic model (Marigo 1998a, b; Marigo et al. 1998a, b). The improvements concern: i) the use of a homogeneous and accurate set of analytical relations (Wagenhuber & Groenewegen 1998); ii) a new treatment of envelope burning in the most massive TP-AGB stars (M > 3.5M⊙) to account for the possible break-down of the core mass-luminosity relation; iii) a better treatment of the third dredge-up to infer if and when the process takes place.Extensive calculations of synthetic TP-AGB models have been carried out over the mass range (0.8M⊙ ÷ 5M⊙) and for three sets of initial metallicity (Z = 0.019, Z = 0.008, Z = 0.004). The formation of carbon stars is investigated addressing the following issues: a) the reproduction of the observed luminosity functions of carbons stars in both Magellanic Clouds, and b) the formation of very bright and optically obscured carbon stars.

scholarly journals Stellar yields and abundances: new directions from planetary nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 86-94
Author(s):  
Maria Lugaro ◽  
Amanda I. Karakas ◽  
Marco Pignatari ◽  
Carolyn L. Doherty
Keyword(s):  
Noble Gas ◽  
Planetary Nebulae ◽  
Central Star ◽  
High Energy ◽  
Type I ◽  
Agb Stars ◽  
Capture Process ◽  
New Directions ◽  
Energy Environment ◽  
Central Stars

AbstractPlanetary nebulae retain the signature of the nucleosynthesis and mixing events that occurred during the previous AGB phase. Observational signatures complement observations of AGB and post-AGB stars and their binary companions. The abundances of the elements heavier than iron such as Kr and Xe in planetary nebulae can be used to complement abundances of Sr/Y/Zr and Ba/La/Ce in AGB stars, respectively, to determine the operation of theslowneutron-capture process (thesprocess) in AGB stars. Additionally, observations of the Rb abundance in Type I planetary nebulae may allow us to infer the initial mass of the central star. Several noble gas components present in meteoritic stardust silicon carbide (SiC) grains are associated with implantation into the dust grains in the high-energy environment connected to the fast winds from the central stars during the planetary nebulae phase.

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