scholarly journals White Dwarfs and Planetary Central Stars

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.

scholarly journals Implications of White-Dwarf Crystallization for the Chemical Composition of the Planetary Nuclei

1968 ◽  
Vol 34 ◽  
pp. 425-427
Author(s):  
H.M. Van Horn
Keyword(s):  
Chemical Composition ◽  
White Dwarf ◽  
White Dwarfs ◽  
Planetary Nebulae ◽  
Considerable Importance ◽  
Central Stars

It now seems to be reasonably well-established that the central stars of planetary nebulae evolve directly into white dwarfs. Evidently a knowledge of the chemical composition of the white dwarfs would therefore be of considerable importance in helping to identify the point in the evolution at which the mechanism responsible for expulsion of the nebular shell becomes operative. For this reason I would like to present some evidence which provides a direct suggestion for the internal composition of some of the white dwarfs and to examine briefly the implications of this suggestion for the relation between the planetary nuclei and the white dwarfs.

scholarly journals IUE Observations of Central Stars

1983 ◽  
Vol 103 ◽  
pp. 375-390
Author(s):  
Sara R. Heap
Keyword(s):  
White Dwarf ◽  
Spectral Properties ◽  
White Dwarfs ◽  
Planetary Nebulae ◽  
Hot Stars ◽  
Gravitational Settling ◽  
Ultimate Fate ◽  
Central Stars

Despite similar evolutionary histories and a common ultimate fate as white dwarfs, central stars of planetary nebulae have surprisingly diverse spectral properties. Their visual spectral types encompass all varieties known for hot stars, including Wolf-Rayet, O and Of, subdwarf O, white-dwarf, and continuous (Aller 1968, 1976), and O VI-emission types (Smith and Aller 1969, Heap 1982). Their spectroscopic temperatures range from less than 30,000°K (e.g. He 2-138, Mendez and Niemela 1979; the WC 11 stars, Houziaux and Heck 1982) to upwards to 150,000°K or more (e.g. NGC 246, Heap 1975; Abell 30, Greenstein 1981). Their atmospheres range from demonstrably helium- and carbon-rich (e.g. the WR stars, Barlow and Hummer 1982, Benvenutı et al. 1982) to apparently normal (e.g. the Of stars, Heap 1977a,b), to helium-poor (e.g. the nascent white dwarfs in Abell 7 and NGC 7293, where gravitational settling appears to have already taken effect, Mendez et al. 1981).

scholarly journals Catalogue of the central stars of planetary nebulae

2020 ◽  
Vol 640 ◽  
pp. A10
Author(s):  
W. A. Weidmann ◽  
M. B. Mari ◽  
E. O. Schmidt ◽  
G. Gaspar ◽  
M. M. Miller Bertolami ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Late Stage ◽  
Planetary Nebulae ◽  
Surface Gravity ◽  
Physical Parameters ◽  
Evolutionary Models ◽  
Pertinent Information ◽  
Central Stars ◽  
Statistical Improvement ◽  
Magnitude Estimates

Planetary nebulae represent a potential late stage of stellar evolution, however, their central stars (CSPNe) are relatively faint and, therefore, pertinent information is available for merely < 20% of the Galactic sample. Consequently, the literature was surveyed to construct a new catalogue of 620 CSPNe featuring important spectral classifications and information. The catalogue supersedes the existing iteration by 25% and includes physical parameters such as luminosity, surface gravity, temperature, magnitude estimates, and references for published spectra. The marked statistical improvement enabled the following pertinent conclusions to be determined: the H-rich/H-poor ratio is 2:1, there is a deficiency of CSPNe with types [WC 5-6], and nearly 80% of binary central stars belong to the H-rich group. The last finding suggests that evolutionary scenarios leading to the formation of binary central stars interfere with the conditions required for the formation of H-poor CSPN. Approximately 50% of the sample with derived values of log L⋆, log Teff, and log g, exhibit masses and ages consistent with single stellar evolutionary models. The implication is that single stars are indeed able to form planetary nebulae. Moreover, it is shown that H-poor CSPNe are formed by higher mass progenitors. The catalogue is available through the Vizier database.

scholarly journals Some Properties of Hot, High-Gravity, Pure Helium Atmospheres

1979 ◽  
Vol 53 ◽  
pp. 125-129
Author(s):  
F. Wesemael ◽  
H.M. Van Horn
Keyword(s):  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
Model Atmosphere ◽  
Surface Gravity ◽  
High Gravity ◽  
Pure Helium

Model atmosphere analyses of white dwarf spectra have contributed significantly to our understanding of the properties of degenerate stars.: In particular, the pioneering investigations of Bues (1970), Strittmatter and Wickramasinghe (1971) and Shipman (1972) have provided the first reliable determinations of the effective temperature and surface gravity of these objects (see Shipman 1979 and Weidemann 1978 for recent results). We now know with certainty that the hydrogen-rich white dwarf sequence extends at least over the range Te ∽ 6000 – 60.000K. In contrast, the hottest identified helium-rich white dwarfs seem to reach Te ~ 25.000K only, a puzzling result since the progenitors of DB white dwarfs should presumably also be helium-rich.

scholarly journals Evolutionary Tracks for Central Stars of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 463-472 ◽  
Author(s):  
Detlef Schönberner
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Helium Burning ◽  
Hydrogen Burning ◽  
Stellar Envelope ◽  
Thermal Pulse ◽  
Pulse Cycle ◽  
Central Stars

Our understanding of the evolution of Central Stars of Planetary Nebulae (CPN) has made considerable progress during the last years. This was possible since consistent computations through the asymptotic giant branch (AGB), with thermal pulses and (in some cases) mass loss taken into account, became available (Schönberner, 1979, 1983; Kovetz and Harpaz, 1981; Harpaz and Kovetz, 1981; Iben, 1982, 1984; Wood and Faulkner, 1986). It turned out that the evolution depends very sensitively on the inital conditions on the AGB. More precisely, the evolution of an AGB remnant is a function of the phase of the thermal-pulse cycle during which this remnant was created on the tip of the AGB by the planetary-nebula (PN) formation process (Iben, 1984, 1987). This was first shown by Schönberner (1979), and then fully explored by Iben (1984). In short, two major modes of PAGB evolution to the white dwarf stage are possible, according to the two main phases of a thermally pulsing AGB star: the hydrogen-burning or helium-burning mode. If, for instance, the PN formation, i.e. the removal of the stellar envelope by mass loss, happens during a luminosity peak that follows a thermal pulse of the helium-burning shell, the remnant leaves the AGB while still burning helium as the main energy supplier (Härm and Schwarzschild, 1975). On the other hand, PN formation may also occur during the quiescent hydrogen-burning phase on the AGB, and the remnant continues then to burn mainly hydrogen on its way to becoming a white dwarf.

scholarly journals An imaging and spectroscopic survey of the Abell Planetary Nebulae

1997 ◽  
Vol 180 ◽  
pp. 287-287
Author(s):  
N. A. Walton ◽  
J. R. Walsh ◽  
G. Dudziak
Keyword(s):  
White Dwarf ◽  
Surface Brightness ◽  
Planetary Nebulae ◽  
Central Star ◽  
Large Size ◽  
Low Surface Brightness ◽  
Thermal Pulses ◽  
Central Stars

The Abell catalogue of planetary nebulae (PN) are distinguished by their large size, low surface brightness and generally faint central stars. They are thought to be old PN approaching the White Dwarf cooling track. A number have evidence for late thermal pulses (H-poor ejecta near the central star, e.g. A78) and binary central stars.

scholarly journals NLTE analysis of central stars of highly excited Planetary Nebulae

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.

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

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.

scholarly journals Models for Nuclei of Planetary Nebulae and for Ultraviolet Stars

1974 ◽  
Vol 59 ◽  
pp. 113-114
Author(s):  
J. Katz ◽  
R. Malone ◽  
E. E. Salpeter
Keyword(s):  
Surface Temperature ◽  
Total Mass ◽  
High Surface ◽  
Planetary Nebulae ◽  
Red Giants ◽  
High Luminosity ◽  
Stages Of Development ◽  
Initial Carbon ◽  
High Surface Temperature ◽  
Central Stars

A series of stellar models were evolved, all with a total mass of 0.65 M⊙, an initial carbon-oxygen core of mass 0.60 M⊙, an intermediate helium mantle and an outer hydrogen-rich envelope with mass varying from case to case. Although the most hydrogen-rich cases resulted in red giants, cases with ≲ 0.01 M⊙ in the hydrogen envelope evolved at high surface temperature. The early stages of development of these models are similar to observed central stars of planetary nebulae. The later stages (when the nebula should be very thin optically) still have a high luminosity; the relevance to ‘ultraviolet stars’ will be discussed.

scholarly journals Stellar wind models of central stars of planetary nebulae

2020 ◽  
Vol 635 ◽  
pp. A173 ◽  
Author(s):  
J. Krtička ◽  
J. Kubát ◽  
I. Krtičková
Keyword(s):  
Mass Loss ◽  
White Dwarf ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Terminal Velocity ◽  
Asymptotic Giant Branch ◽  
Central Stars ◽  
Loss Rates

Context. Fast line-driven stellar winds play an important role in the evolution of planetary nebulae, even though they are relatively weak. Aims. We provide global (unified) hot star wind models of central stars of planetary nebulae. The models predict wind structure including the mass-loss rates, terminal velocities, and emergent fluxes from basic stellar parameters. Methods. We applied our wind code for parameters corresponding to evolutionary stages between the asymptotic giant branch and white dwarf phases for a star with a final mass of 0.569 M⊙. We study the influence of metallicity and wind inhomogeneities (clumping) on the wind properties. Results. Line-driven winds appear very early after the star leaves the asymptotic giant branch (at the latest for Teff ≈ 10 kK) and fade away at the white dwarf cooling track (below Teff = 105 kK). Their mass-loss rate mostly scales with the stellar luminosity and, consequently, the mass-loss rate only varies slightly during the transition from the red to the blue part of the Hertzsprung–Russell diagram. There are the following two exceptions to the monotonic behavior: a bistability jump at around 20 kK, where the mass-loss rate decreases by a factor of a few (during evolution) due to a change in iron ionization, and an additional maximum at about Teff = 40−50 kK. On the other hand, the terminal velocity increases from about a few hundreds of km s−1 to a few thousands of km s−1 during the transition as a result of stellar radius decrease. The wind terminal velocity also significantly increases at the bistability jump. Derived wind parameters reasonably agree with observations. The effect of clumping is stronger at the hot side of the bistability jump than at the cool side. Conclusions. Derived fits to wind parameters can be used in evolutionary models and in studies of planetary nebula formation. A predicted bistability jump in mass-loss rates can cause the appearance of an additional shell of planetary nebula.

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