On the frequency of planetary nebula nuclei powered by helium burning and on the frequency of white dwarfs with hydrogen-deficient atmospheres

1984 ◽  
Vol 277 ◽  
pp. 333 ◽  
Author(s):  
I., Jr. Iben
Keyword(s):  
Planetary Nebula ◽  
White Dwarfs ◽  
Helium Burning

The Chemical Composition of White Dwarfs as a Test of Convective Efficiency during Core Helium Burning

2003 ◽  
Vol 583 (2) ◽  
pp. 878-884 ◽  
Author(s):  
Oscar Straniero ◽  
Inmaculada Dominguez ◽  
Gianluca Imbriani ◽  
Luciano Piersanti
Keyword(s):  
Chemical Composition ◽  
White Dwarfs ◽  
Helium Burning

scholarly journals Asteroseismological Probing of the Thermal Evolution of White Dwarf Stars

1992 ◽  
Vol 9 ◽  
pp. 643-645
Author(s):  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Thermal Evolution ◽  
Sequence Evolution ◽  
Helium Burning ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
Low Mass

AbstractIt is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of helium burning, mostly carbon and oxygen. The exact proportions of C and 0 are unknown because of uncertainties in the nuclear rates of helium burning.

scholarly journals From Planetary Nebula nuclei to white dwarfs: The impact of evolutionary envelope masses

1997 ◽  
Vol 180 ◽  
pp. 389-389 ◽  
Author(s):  
T. Blöcker ◽  
F. Herwig ◽  
T. Driebe ◽  
H. Bramkamp ◽  
D. Schönberner
Keyword(s):  
Planetary Nebula ◽  
Total Mass ◽  
White Dwarfs ◽  
Stellar Mass ◽  
Asymptotic Giant Branch ◽  
The Masses ◽  
The Impact

It is well known that the evolution of white dwarfs (WDs) depends sensitively on the question whether they have “thin” or “thick” envelopes of H and He (see Wood 1995). Standard evolutionary caluclations (e.g. Paczynksi 1971) show that at the tip of the Asymptotic Giant Branch the envelope masses are tightly correlated with the mass of the hydrogen exhausted core (≈ total mass). Accordingly, the masses of hydrogen, MH, and helium, MHe, on top of the degenerate C/O interiors decrease by orders of magnitudes with increasing stellar mass. In contrast, many applications of WD calculations consider only single values of qH,He = log(MH,He/M∗) asuming either “thick” or “thin” envelopes.

scholarly journals The Status of the Absolute Calibration of Stellar Fluxes Between 912 and 1200 Å

1985 ◽  
Vol 111 ◽  
pp. 479-483
Author(s):  
R. S. Polidan ◽  
J. B. Holberg
Keyword(s):  
Planetary Nebula ◽  
White Dwarfs ◽  
Main Sequence ◽  
Absolute Calibration ◽  
Energy Distributions ◽  
B Stars ◽  
The Status ◽  
The Absolute ◽  
Flux Calibration

Recent results have shed new light on the status of the calibration of absolute stellar fluxes between 912 and 1200 Å. Observations of hot white dwarfs, subdwarfs and planetary nebula nuclei with the Voyager ultraviolet spectrometers provide evidence that the current calibration agrees very well with extrapolations of IUE energy distributions shortwards of 1200 Å. Voyager observations of main sequence B-stars used as flux calibration sources have revealed that many are variable in brightness in the 912–1200 Å region. We conclude there is no current observational motivation for any revision of the 912 to 1200 Å calibration described by Holberg et al. (1982).

The Effect of CNO Metal Abundances on the Soft X-Ray Emission from He Rich White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 202-205
Author(s):  
M.A. Barstow
Keyword(s):  
Effective Temperature ◽  
Planetary Nebula ◽  
White Dwarfs ◽  
X Ray ◽  
Metal Abundances

AbstractPredicted soft X-ray fluxes for model atmospheres containing varying concentrations of CNO metals are compared with those observed by EXOSAT for the planetary nebula nucleus K1-16. An effective temperature in the range ≈ 125000 − 180000K is determined for K1-16 and a limit on the concentration of CNO in the atmosphere (between 0.02 and 20 ×solar relative to He) obtained. Some comments on the application of the models to the apparently metal rich star H1504+65 are included.

scholarly journals Model Planetaries with rapidly evolving central stars: A case for FG Sge

1997 ◽  
Vol 180 ◽  
pp. 391-391
Author(s):  
K. Kifonidis ◽  
D. Schönberner
Keyword(s):  
White Dwarfs ◽  
Central Star ◽  
Frequency Of Occurrence ◽  
Helium Burning ◽  
Temporary Growth ◽  
Red Giant ◽  
Born Again ◽  
Thermal Pulses ◽  
Central Stars

Ever since the pioneering work of Schönberner (1979, A&A, 79, 108) and Iben (1984, ApJ, 277, 333) who showed that the evolution of post-AGB remnants might be affected by late thermal pulses of the helium-burning shell, resulting in a temporary growth of these objects to red giant dimensions, many attempts were made to explain a number of puzzling objects, among them the well-known variable central star FG Sge as well as the R CrB and PG 1159 stars, by this so-called “born-again AGB” scenario (Iben et al. 1983, ApJ, 264, 605; Iben & MacDonald 1995, in: White Dwarfs, Springer, p. 48). However, it is still not clear if the frequency of occurrence of such events is high enough as to be consistent with the number of born-again candidates. This is due to the very short evolutionary timescales during the pulse and the character of the post-pulse evolution which resembles the first post-AGB phase and makes it difficult for an observer to distinguish such objects from “normal” central stars.

scholarly journals From Planetary Nebulae to White Dwarfs: Constraints from the Asteroseismology of the Pulsating Planetary Nebula Central Star RXJ 2117+3412

2002 ◽  
Vol 185 ◽  
pp. 610-611
Author(s):  
P. Moskalik ◽  
G. Vauclair
Keyword(s):  
Planetary Nebula ◽  
White Dwarfs ◽  
Planetary Nebulae ◽  
Central Star

AbstractWe summarize the results of an asteroseismological study of the pulsating planetary nebula central star RXJ 2117+3412.

scholarly journals Suzaku Reveals Helium-burning Products in the X-Ray-emitting Planetary Nebula BD +30 3639

2006 ◽  
Vol 647 (2) ◽  
pp. L131-L134 ◽  
Author(s):  
M. Murashima ◽  
M. Kokubun ◽  
K. Makishima ◽  
J. Kotoku ◽  
H. Murakami ◽  
...  
Keyword(s):  
Planetary Nebula ◽  
Helium Burning ◽  
X Ray

scholarly journals Effects of rotation on the helium burning shell source in accreting white dwarfs

2004 ◽  
Vol 425 (1) ◽  
pp. 217-228 ◽  
Author(s):  
S.-C. Yoon ◽  
N. Langer ◽  
S. Scheithauer
Keyword(s):  
White Dwarfs ◽  
Helium Burning ◽  
Effects Of Rotation
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