scholarly journals Born-again AGB stars: Starting point of the H-deficient post-AGB evolutionary sequence?

1999 ◽  
Vol 191 ◽  
pp. 493-498 ◽  
Author(s):  
K. Werner ◽  
S. Dreizler ◽  
T. Rauch ◽  
L. Koesterke ◽  
U. Heber
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars ◽  
Evolutionary Sequence ◽  
Starting Point ◽  
Born Again

We discuss the origin of hot hydrogen-deficient post-AGB stars. Evidence is growing that the “born-again AGB star scenario” as a consequence of a late He shell flash cannot explain the diverse observations. Analyses of the stars and their associated planetary nebulae suggest that the H-deficiency is not formed during the second post-AGB phase but already while the star is still on the AGB. There are even hints that the H-deficiency can occur before the first departure from the AGB.

scholarly journals Spectral analysis of the O(He)-type central stars of the planetary nebulae K 1-27 and LoTr 4

2011 ◽  
Vol 7 (S283) ◽  
pp. 482-483
Author(s):  
Nicole Reindl ◽  
Ellen Ringat ◽  
Thomas Rauch ◽  
Klaus Werner ◽  
Jeffrey. W. Kruk
Keyword(s):  
Spectral Analysis ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Evolutionary Sequence ◽  
Preliminary Results ◽  
Pure Helium ◽  
R Coronae Borealis Stars ◽  
Central Stars

AbstractThe four known O(He) stars are the only amongst the hottest post-AGB stars whose atmospheres are composed of almost pure helium. Thus, their evolution deviates from the hydrogen-deficient post-AGB evolutionary sequence of carbon-dominated stars like e.g. PG 1159 stars. The origin of the O(He) stars is still not explained. They might be either post-early AGB stars or the progeny of R Coronae Borealis stars. We present preliminary results of a non-LTE spectral analysis based on FUSE and HST/COS observations.

OH/IR Stars and other IRAS Point Sources as Progenitors of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 359-380 ◽  
Author(s):  
H. J. Habing ◽  
P. te Lintel Hekkert ◽  
W.E.C.J. van der Veen
Keyword(s):  
Planetary Nebulae ◽  
Point Sources ◽  
Agb Stars ◽  
Evolutionary Sequence ◽  
Centre Of Mass ◽  
Long Period ◽  
Mira Variables ◽  
Ir Stars ◽  
Galactic Population ◽  
History Of

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.

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 New detections of H2O masers in planetary nebulae and post-AGB stars using the Robledo-70 m antenna

2007 ◽  
Vol 467 (3) ◽  
pp. 1085-1091 ◽  
Author(s):  
O. Suárez ◽  
J. F. Gómez ◽  
O. Morata
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars

scholarly journals Near–Infrared Imaging of Proto-Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 340-340 ◽  
Author(s):  
R.E.S. Clegg ◽  
N. A. Walton ◽  
M.J. Barlow
Keyword(s):  
Molecular Hydrogen ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Preliminary Results ◽  
Near Ir ◽  
Intermediate Mass Stars ◽  
Hydrogen Lines

It is not really known how low and intermediate mass stars eject mass to form PNs. We present preliminary results from a programme of near–IR imaging, in which we study a sequence of objects, from extreme AGB stars through proto–planetaries to young, compact PNs. We aim to study the sequence of morphologies, to see where the onset of bipolar shaping occurs, and to use the IR molecular hydrogen lines to map neutral regions around ionized nebulae.

scholarly journals Abundance Analysis of the J4 Equatorial Knot of the Born-again Planetary Nebula A30

2022 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Jordan Simpson ◽  
David Jones ◽  
Roger Wesson ◽  
Jorge García-Rojas
Keyword(s):  
Binary System ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Upper Limit ◽  
Chemical Segregation ◽  
Born Again ◽  
Physical And Chemical

Abstract A30 belongs to a class of planetary nebulae identified as “born-again”, containing dense, hydrogen-poor ejecta with extreme abundance discrepancy factors (ADFs), likely associated with a central binary system. We present intermediate-dispersion spectroscopy of one such feature—the J4 equatorial knot. We confirm the apparent physical and chemical segregation of the polar and equatorial knots observed in previous studies, and place an upper limit on the ADF for O2+ of 35, significantly lower than that of the polar knots. These findings further reinforce the theory that the equatorial and polar knots originate from different events.

Formation Rates of AGB Stars and Planetary Nebulae

1997 ◽  
pp. 411-411
Author(s):  
R. Ortiz ◽  
W. J. Maciel
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars

scholarly journals The Ionization of Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 190-204 ◽  
Author(s):  
Robert E. Williams
Keyword(s):  
Ionizing Radiation ◽  
Emission Line ◽  
Radiation Field ◽  
Planetary Nebulae ◽  
Model Atmosphere ◽  
Evolutionary Sequence ◽  
Lyman Continuum ◽  
The Mean ◽  
Central Stars

The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Böhm and Deinzer. Emission-line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.

scholarly journals Light and velocity variability in Proto-Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 351-351
Author(s):  
Bruce J. Hrivnak ◽  
Wenxian Lu
Keyword(s):  
Physical Properties ◽  
Radial Velocity ◽  
Planetary Nebulae ◽  
Agb Stars

We have been carrying out a program of monitoring light and velocity variability in proto-planetary nebulae (PPN). Variability might arise due to binarity or pulsation. Many planetary nebulae display a bipolar shape, and it is suggested that this is caused by binarity. This can be investigated in PPN, particularly by radial velocity studies of those of spectral types F and G. Pulsation is known to exist in other types of post-AGB stars, and can be a means to learn more about the physical properties of the stars. No previous study of a sample of PPN has been published.

scholarly journals Infrared studies of post-AGB stars and PNe

2016 ◽  
Vol 12 (S323) ◽  
pp. 28-31
Author(s):  
Kyung-Won Suh
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars ◽  
Spectral Evolution ◽  
Large Sample ◽  
Infrared Studies

AbstractWe present infrared two color diagrams (2CDs) for a large sample of AGB stars, post-AGB stars, and planetary nebulae (PNe) to study their spectral evolution in infrared bands. We discuss possible evolutionary tracks from AGB stars to PNe on the 2CDs. We use catalogs from the available literature for the sample of AGB stars, post-AGB stars, and PNe in our Galaxy.

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