Ages of evolved low mass stars: Central stars of planetary nebulae and white dwarfs

AbstractWhile most of the low-mass stars stay hydrogen-rich on their surface throughout their evolution, a considerable fraction of white dwarfs as well as central stars of planetary nebulae have a hydrogen-deficient surface composition. The majority of these H-deficient central stars exhibit spectra very similar to massive Wolf-Rayet stars of the carbon sequence, i.e. with broad emission lines of carbon, helium, and oxygen. In analogy to the massive Wolf-Rayet stars, they are classified as [WC] stars. Their formation, which is relatively well understood, is thought to be the result of a (very) late thermal pulse of the helium burning shell. It is therefore surprising that some H-deficient central stars which have been found recently, e.g. IC 4663 and Abell 48, exhibit spectra that resemble those of the massive Wolf-Rayet stars of the nitrogen sequence, i.e. with strong emission lines of nitrogen instead of carbon. This new type of central stars is therefore labelled [WN]. We present spectral analyses of these objects and discuss the status of further candidates as well as the evolutionary status and origin of the [WN] stars.

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Planets, evolved stars, and how they might influence each other.

Proceedings of the International Astronomical Union ◽

10.1017/s174392131201099x ◽

2011 ◽

Vol 7 (S283) ◽

pp. 219-226 ◽

Cited By ~ 1

Author(s):

Eva Villaver

Keyword(s):

White Dwarfs ◽

Main Sequence ◽

Planetary Nebulae ◽

The Other ◽

Horizontal Branch ◽

Low Mass Stars ◽

Evolved Stars ◽

Low Mass ◽

Red Giant

AbstractOver the last 20 years planetary searches have revealed a wealth of systems orbiting stars on the main sequence. Most of these low-mass stars eventually will evolve into the Giant phases before entering the planetary nebulae (PNe) stage. In the last years, the presence of planets has also been discovered around more massive evolved stars, mostly, along the Red Giant but also along the Horizontal Branch. Moreover, disks have been found around White Dwarfs presumably formed by tidally disrupted asteroids. In all, there is evidence that an evolved (ing) star might influence the survival of planets. In this review I will try to summarize such evidence but furthermore I will present the other side of the story, that is, how the presence of a planet might alter the evolution of stars and with that the PN formation.

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Chemical Abundances of the Planetary Nebulae NGC 2392 and NGC 3242

International Astronomical Union Colloquium ◽

10.1017/s0252921100079240 ◽

2001 ◽

Vol 183 ◽

pp. 339-340

Author(s):

C.H. Wu ◽

J.Z. Li ◽

Z.W. Chang ◽

C.Y. Lin ◽

J.Y. Hu ◽

...

Keyword(s):

Planetary Nebulae ◽

Astronomical Observatory ◽

Chemical Compositions ◽

Chemical Abundances ◽

Low Mass Stars ◽

Preliminary Results ◽

Mass Distributions ◽

Low Mass ◽

Red Giant ◽

Central Stars

AbstractPlanetary nebulae represent the end product of the evolution of low mass stars with M < 8M⊙. The central stars have masses between 0.55 and 0.85M⊙. This means a large amount of material must have been distributed in the interiors of the PNe. The observed variations of the chemical compositions and mass distributions therefore carry important information about the nature of the associated AGB superwinds and Red Giant outflows. (Kwok et al, 1978) A program for comprehensive multiwavelength study of PNe has been initiated at NCU. One recent study has to do with the spectrographic observations of the planetary nebulae NGC 2392 and NGC 3242 using the 2.16 m telescope of the Beijing Astronomical Observatory. Some preliminary results are presented here.

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ISO-SWS spectra of Planetary Nebulae with low-mass [WC] central stars: a mixed C- and O-rich dust chemistry

Symposium - International Astronomical Union ◽

10.1017/s0074180900205810 ◽

1999 ◽

Vol 193 ◽

pp. 376-377

Author(s):

Patrick W. Morris ◽

L.B.F.M. Waters ◽

Douwe A. Beintema

Keyword(s):

Mass Loss ◽

Planetary Nebulae ◽

Low Mass ◽

Thermal Pulses ◽

Central Stars

The timing of PNe formation around low-mass WC stars is unsettled with respect to pulsations early in the post-AGB phase, or later thermal pulses (e.g., Tylenda & Gorny 1997). The chemistry of the dust in the nebulae can be used to trace the mass-loss history. Using ISO-SWS spectroscopy, the PNe BD+30°3639 [WC9] and He2–113 [WC11] have been identified by Waters et al. (1998) to exhibit emission from C-rich dust (PAHs) in the surrounding envelopes at λ 15 μm, while O-abundant silicate features are present at longer wavelengths. Figure 1 shows the PAH features, which include additional WCPNe observations to extend the range of stellar spectral subtypes.

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NLTE analysis of central stars of highly excited Planetary Nebulae

Symposium - International Astronomical Union ◽

10.1017/s0074180900130141 ◽

1997 ◽

Vol 180 ◽

pp. 132-132

Author(s):

T. Rauch ◽

J. Köppen ◽

R. Napiwotzki ◽

K. Werner

Keyword(s):

White Dwarfs ◽

State Of The Art ◽

Planetary Nebulae ◽

Evolutionary Status ◽

Agb Stars ◽

Spectral Analyses ◽

Central Stars

Very hot central stars (CSPN) of highly excited planetary nebulae (PN) display directly the formation of white dwarfs. Only a few of these CSPN have been analyzed so far due to their low brightness and thus, the interpretation of their evolutionary status is hampered by statistical incompleteness. In the last decade many spectral analyses of very hot post-AGB stars by means of state-of-the-art NLTE model atmospheres have been performed (e.g. Rauch et al. 1996; Werner & Rauch 1994; Rauch & Werner 1995) and our picture of post-AGB evolution has been improved.

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A High Resolution Far-UV Spectral Atlas of CSPNs and Hot White Dwarfs

Symposium - International Astronomical Union ◽

10.1017/s0074180900170214 ◽

1993 ◽

Vol 155 ◽

pp. 91-91

Author(s):

R.W. Tweedy

Keyword(s):

High Resolution ◽

White Dwarfs ◽

Planetary Nebulae ◽

Central Star ◽

Evolutionary Sequence ◽

Spectroscopic Analyses ◽

Spectroscopic Information ◽

The University ◽

Phd Thesis ◽

Central Stars

A high-resolution IUE spectral atlas of central stars of planetary nebulae and hot white dwarfs has been produced (part of Tweedy, 1991, PhD thesis from the University of Leicester, UK), and examples from it are shown here. It has been sorted into an approximate evolutionary sequence, based on published spectroscopic analyses, from the cool 28,000K young central star He 2–138, through the hot objects like NGC 7293 and NGC 246 at 90,000K and 130,000K respectively, down to 40,000K DA white dwarfs like GD 2, which is the chosen cutoff for this selection. Copies of a revised version of this atlas, which will include more recent spectroscopic information and also white dwarfs down to 35,000K – to include the Si III object GD 394 – will be sent to anyone who requests one.

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Helium Flashes Through the NCO Reaction

International Astronomical Union Colloquium ◽

10.1017/s0252921100093453 ◽

1988 ◽

Vol 108 ◽

pp. 57-58

Author(s):

K. Arai ◽

K. Kaminisi ◽

M. Hashimoto ◽

K. Nomoto

Keyword(s):

Fermi Energy ◽

White Dwarfs ◽

Threshold Energy ◽

Low Mass Stars ◽

Low Mass

It is generally accepted that the helium flash occurs when the 3α reaction commences in the degenerate helium core of low mass stars. In this core, original CNO isotopes have been converted into 14N and the electron Fermi energy becomes large enough to approach the threshold energy for e-capture on 14N. Hence Kaminisi et al. (1975) have pointed out that in these circumstances the 14N(e−, v)14C(α,γ)18O (NCO) reaction may play an important role for igniting the helium flash.We, therefore, examine the effects of the NCO reaction on the evolution of low mass stars. A key ingredient of the NCO reaction is that the density reaches the threshold for e-capture (ρth≃ 106 g cm−3). Evolutionary sequences are presented for the cases of accreting helium white dwarfs (Hashimoto et al. 1986) and a 0.7 M⊙, Population II star ascending the giant branch.

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Neutron Star Formation in Theoretical Supernovae — Low Mass Stars and White Dwarfs —

Symposium - International Astronomical Union ◽

10.1017/s0074180900160905 ◽

1987 ◽

Vol 125 ◽

pp. 281-303

Author(s):

Ken'ichi Nomoto

Keyword(s):

Neutron Stars ◽

White Dwarfs ◽

Binary Systems ◽

Crab Nebula ◽

Close Binary ◽

Low Mass Stars ◽

Supernova Explosions ◽

Low Mass ◽

Strongly Degenerate ◽

The Crab Nebula

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O+Ne+Mg cores is discussed. For the 10–13 M⊙ stars, behavior of off-center neon flashes is crucial. The 8–10 M⊙ stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. We also examine the conditions for which neutron stars form from accretion-induced collapse of white dwarfs in close binary systems.

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Appendix A: A Catalog of Hydrogen-Deficient Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100091077 ◽

1985 ◽

Vol 87 ◽

pp. 498-506

Author(s):

J.S. Drilling ◽

P.W. Hill

Keyword(s):

Data Base ◽

White Dwarfs ◽

Planetary Nebulae ◽

Basic Data ◽

Complete List ◽

Central Stars

The following four tables were originally presented as part of the paper entitled ‘Basic Data on Hydrogen-Deficient Stars’ by J. S. Drilling, which appears earlier in this volume. A number of corrections and additions have been made by the participants, mostly by P. W. Hill using the SIMBAD data base. A much improved version of the catalog therefore follows. Helium-rich central stars of planetary nebulae, helium-rich white dwarfs, and Wolf-Rayet stars are not included. A complete list of helium-rich central stars is given by Mendez et al. elsewhere in this volume.

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White Dwarfs and Planetary Central Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900139166 ◽

1989 ◽

Vol 131 ◽

pp. 545-554

Author(s):

James Liebert

Keyword(s):

White Dwarf ◽

White Dwarfs ◽

High Surface ◽

Planetary Nebulae ◽

Hydrogen Atmosphere ◽

Surface Gravity ◽

Surface Hydrogen ◽

Central Stars

Studies of hot white dwarf samples constrain the properties and evolution of planetary nuclei and the nebulae. In particular, the white dwarf and planetary nebulae formation rates are compared. I discuss the overlap of the sequences of white dwarfs having hydrogen (DA) and helium-rich (DO) atmospheres with known central stars of high surface gravity. There is evidence that the hydrogen atmosphere nuclei have “thick” outer hydrogen layers (≳ 10−4 M⊙), but that DA white dwarfs may have surface hydrogen layers orders of magnitude thinner. Finally, a DA planetary nucleus is discussed (0950+139) which has undergone a late nebular ejection; this object may be demonstrating that a hydrogen layer can be lost even after the star has entered the white dwarf cooling sequence.

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