Showing papers on "White dwarf published in 1974"
811 citations
114 citations
TL;DR: In this paper, it was shown that for a 1.00-solar-mass white dwarf it is impossible to achieve mass ejection without an energy generation of approximately 10 to the 16th ergs/g/sec.
Abstract: Results of a computation of a variety of evolutionary sequences involving thermonuclear runaways in the hydrogen-rich envelopes of 1.00-solar-mass carbon-oxygen white dwarfs. The evidence concerning the location of the outburst in the nova system is reexamined, and it is concluded that the white dwarf is the seat of the outburst. An order-of-magnitude argument is presented which indicates that for a 1.00-solar-mass white dwarf it is impossible to achieve mass ejection without an energy generation of approximately 10 to the 16th ergs/g/sec. A description is given of models with low nuclear enhancements that do not produce an outburst, although their evolution has certain implications for the cause of the dwarf-nova outburst. The results for models that produced a nova outburst are then presented, and on the basis of these results it is found possible to explain continuous ejection, Kukarkin and Parenago's (1934) relationship, and other gross features of the nova phenomena.
104 citations
52 citations
TL;DR: Spectroscopic, kinematic, and photometric data for some 200 LFT stars are presented in this paper, where eleven white dwarfs are found in the survey and two new candidates are added to a possible group of white dwarFS.
Abstract: Spectroscopic, kinematic, and photometric data for some 200 LFT stars are presented. Eleven white dwarfs are found in the survey and two new candidates are added to a possible group of white dwarfs. Most of the remaining stars are M dwarfs of the old-disk and halo populations. The kinematic differences between these populations are reflected in the spectral lines of the halo stars where [MIHi > - 1. Key words: large proper motions - nearby stars - white dwarfs - red dwarfs
45 citations
TL;DR: In this paper, a model for Cyg X-3 based on a short-lived phase in the evolution of a U Geminorum-type binary where rapid mass transfer and mass loss occurs is presented.
Abstract: Description of a model for Cyg X-3 based on a short-lived phase in the evolution of a U Geminorum-type binary where rapid mass transfer and mass loss occurs. X rays are generated by accretion on the white dwarf component, while both stars are enveloped in a thick stellar wind emanating from the red dwarf. Electron scattering in the cloud is responsible for the modulation of the X rays with the orbital period of 4.8 hours. Ultraviolet radiation and low-energy X rays absorbed in the cloud are reradiated in the optical and infrared, which, it is predicted, will display a 4.8-hr modulation in phase with the X-ray light curve. The X-ray absorption cutoff should also vary with phase, appearing at minimum energy when the source is at maximum light. The model also provides a framework in which certain aspects of the associated nonthermal radio source may be understood. Finally, it is suggested that the model may be applicable to Sco X-1 as well.
41 citations
TL;DR: In this paper, the evolution of the 0.5 solar mass white dwarfs is considered and four models of luminosity with.00355 solar luminosity, differing only in the initial abundances of C-12, N-14, and O-16, are presented.
Abstract: Consideration of the evolution of thermonuclear runaways in the hydrogen-rich envelopes of 0.5 solar mass carbon-oxygen white dwarfs. The larger radii of these stars, compared with the 1.00 solar mass white dwarfs, results in a lesser degree of degeneracy at the same depth in the star. Four models of luminosity with .00355 solar luminosity, differing only in the initial abundances of C-12, N-14, and O-16, are presented. The degree of enhancement required to produce mass ejection, and thereby a nova-type outburst, is greater than for the 1.00 solar mass model. Nevertheless, the evolution of the 0.5 solar mass model that ejected material is very similar to that of the 1.00 solar mass models, and it also ejects significant amounts of C-13, N-15, and O-17 into the interstellar medium. The 0.5 solar mass outburst is considerably less intense than the 1.00 solar mass outburst (even under optimum conditions), and this lower mass behavior is interpreted as associated with the observed outburst of the slowest novae.
36 citations
Journal Article•
TL;DR: In this paper, the plausibility of appreciable accretion of chemically fractionated matter after Hayashi-phase convection has terminated is discussed, and some possible observational consequences of enhanced surface heavy-element abundances are investigated.
Abstract: Stellar surface heavy-element abundances may be substantially higher than interior abundances if there is appreciable accretion of chemically fractionated matter after Hayashi-phase convection has terminated. The plausibility of appreciable accretion is discussed, and some possible observational consequences of enhanced surface heavy-element abundances are investigated. These consequences include a reduced solar neutrino flux, systematic variations in surface abundance along the main sequence and along the giant branch, and relatively low heavy-element abundances among planetary nebulas and white dwarfs and in the interstellar medium. There is marginal observational evidence in support of the hypothesis of enhanced stellar surface heavy-element abundances.
35 citations
32 citations
TL;DR: In this article, the plausibility of appreciable accretion of chemically fractionated matter after Hayashi-phase convection has terminated is discussed, and some possible observational consequences of enhanced surface heavy-element abundances are investigated.
Abstract: Stellar surface heavy-element abundances may be substantially higher than interior abundances if there is appreciable accretion of chemically fractionated matter after Hayashi-phase convection has terminated. The plausibility of appreciable accretion is discussed, and some possible observational consequences of enhanced surface heavy-element abundances are investigated. These consequences include a reduced solar neutrino flux, systematic variations in surface abundance along the main sequence and along the giant branch, and relatively low heavy-element abundances among planetary nebulas and white dwarfs and in the interstellar medium. There is marginal observational evidence in support of the hypothesis of enhanced stellar surface heavy-element abundances.
TL;DR: In this article, the main requirement is that the accreted hydrogen be mixed with comparable numbers of C-12 (or other alpha nuclei) before a runaway capture of protons takes place.
Abstract: Consideration of events by which both s- and r-process nucleosynthesis may occur on the surfaces of white-dwarf stars. The main requirement is that the accreted hydrogen be mixed with comparable numbers of C-12 (or other alpha nuclei) before a runaway capture of protons takes place. Subsequent events offer many possibilities for nucleosynthesis and stars of peculiar composition. A new mechanism for a surface s-process due to few-MeV protons is also described. Concluding comments concern cosmic gamma-ray bursts and the origin of anomalous low-energy galactic cosmic rays.
TL;DR: The spectrum of the white dwarf suspect, GD 90, was shown to contain broad Balmer lines with resolved Zeeman structure, which correspond to the calculated spectrum of hydrogen at 5 plus or minus 0.5 MG as discussed by the authors.
Abstract: The spectrum of the white dwarf suspect, GD 90, is shown to contain broad Balmer lines with resolved Zeeman structure. All the observed features correspond to the calculated spectrum of hydrogen at 5 plus or minus 0.5 MG. A region of approximately 20% of the observed stellar disk must be subject to a reasonably uniform field of this strength. The sigma components of the Zeeman patterns in H beta and H gamma are found to be circularly polarized, indicating that the field has a component directed along the line of sight. There is evidence for an additional stronger and less homogeneous field, as would be expected if the dominant 5 -MG region were at the equator of a dipolar field.
TL;DR: In this paper, the neutrino pair emission from thermally excited nuclear states may be significant in white dwarfs with central temperature ≲10 8° K, where weak neutral currents couple with the strengths suggested by recent experiments.
TL;DR: In this article, it was shown that due to degeneracy rather high Eddington-Vogt circulation velocities occur in cooling white dwarfs and that angular momentum is redistributed within a time scale short compared to the cooling time of the star.
Abstract: It is shown that due to degeneracy rather high Eddington-Vogt circulation velocities occur in cooling white dwarfs. The conclusion is that in fast rotating white dwarfs angular momentum is redistributed within a time scale short compared to the cooling time of the star. This might be important for the theory of very oblate rotating white dwarfs.
TL;DR: The number of white dwarfs in the Hyades cluster is compared with the number of stars expected to have died during the Iffetime of the cluster, in dffferent mass intervals above the present turnoff mass as discussed by the authors.
Abstract: The number of white dwarfs in the Hyades cluster is compared with the number of stars expected to have died during the Iffetime of the cluster, in dffferent mass intervals above the present turnoff mass. The uncertainties (mostly statistical, so not likely to be resolved) preclude the possibility of making a significant estimate of the upper mass limit for stars that die as white dwarfs. This limit is of theoretical importance in relation to such problems as carbon detonation and pulsar formation. Key words: white dwarfs - Hyades cluster - supernovae - stellar evolution
TL;DR: In this paper, the authors investigated the accretion flow onto white dwarfs by numerically integrating the full nonlinear hydrodynamic equations under the assumption of spherical symmetry to determine the short-term time-dependent behavior.
Abstract: The accretion flow onto white dwarfs is investigated by numerically integrating the full nonlinear hydrodynamic equations under the assumption of spherical symmetry to determine the short-term time-dependent behavior, to determine the effects on the flow when radial modes of oscillation of the star are excited, to see if X-rays are produced, and to determine the radiation spectrum. Some applications of the results to known X-ray sources are suggestive.