Showing papers on "White dwarf published in 1976"
TL;DR: In this article, a study of some aspects of the binary pulsar PSR 1913+16 is presented in the light of recently reported observational results, and a test based on the detection of orbital period changes due to gravitational radiation is examined.
Abstract: A study of some aspects of the binary pulsar, PSR 1913+16, is presented in the light of recently reported observational results. If the companion to the pulsar gives a Newtonian contribution to the observed apsidal motion (a helium star or a rotating white dwarf), then it will probably be observable: the former either optically or through the dispersive effects of a stellar wind, and the latter through a secular change in the observed inclination of the orbit. If alternatively the companion behaves dynamically as a point mass (apsidal motion caused solely by general relativity), observations of the O (..nu../c)/sup 2/ frequency shift will furnish a measurement of the masses of the components. In addition, with a tenfold improvement in timing accuracy, the post-Newtonian corrections to the Keplerian ellipse and the effects of aberration could in principle be measured. This would then provide a determination of the orientation of the pulsar spin axis and allow the observation of geodetic spin precession to become a test of general relativity. We also examine the test based on the detection of orbital period changes due to gravitational radiation.Possible evolutionary histories are discussed. The most probable present system consists of two neutron stars, the endmore » result of an X-ray binary phase followed by a double core star phase. In this scenario the long timing age and short period of PSR 1913+16 are shown to be interrelated if the pulsar was the first neutron star formed. To show that other companions are not ruled out on evolutionary grounds, we construct alternate histories leading to either He star, white dwarf, or black hole companions. (AIP)« less
226 citations
TL;DR: In this paper, a simple angular momentum argument is presented to show that if the absence of thermal equilibrium solutions for contact binary components prevents the growth of deep common envelopes, the mass ratio (secondary/primary) decreases on an evolutionary time scale until the secondary is completely dissipated, during the primary's initial ascent of the giant branch.
Abstract: A simple angular momentum argument shows that, if the absence of thermal equilibrium solutions for contact binary components prevents the growth of deep common envelopes, the mass ratio (secondary/primary) decreases on an evolutionary time scale until the secondary is completely dissipated, during the primary's initial ascent of the giant branch. If simultaenous thermal equilibrium for both components exists at some stage, the binary may overflow its outer critical surface, dissipating its orbital angular momentum in an ''excretion'' disk. Homogeneous evolution of the primary is observationally excluded.Gravitational radiation can significantly affect the evolution of a moderate- or low-mass system, but dominates only in the lowest-mass binaries. Considerations of thermal stability suggest that a contact system cannot survive as a binary beyond the main-sequence stage. Large-scale angular momentum loss as the primary attempts to cross the Hertzsprung gap renders the remnant indistinguishable from an ordinary single star. Angular momentum losses in a stellar wind during giant branch and asymptotic giant branch evolution are sufficient to prevent rotational instability of the degenerate core or white dwarf remnant. (AIP)
187 citations
TL;DR: In this article, a review of the observations that bear most directly on the structure of cataclysmic variables at minimum light are reviewed. Sections include: the basic model, masses, the structures of the disk, the rapid oscillations, and the source of the eruptions.
Abstract: The cataclysmic variables are usually divided into the following four classes: novae; recurrent novae; dwarf novae, which are subclassified as U Geminorum stars or Z Camelopardalis stars; and novalike variables. Those observations that bear most directly on the structure of cataclysmic variables at minimum light are reviewed. Sections include: the basic model; masses; the structure of the disk; the rapid oscillations; and the source of the eruptions. 5 figs., 4 tables, 133 refs. (GHT)
117 citations
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54 citations
TL;DR: In this paper, the authors used a grazing-incidence telescope during the Apollo-Soyuz mission to observe EUV emission from an extrasolar object which were made with a NASA X-ray source in Coma Berenices.
Abstract: Results are reported for observations of EUV emission from an extrasolar object which were made with a grazing-incidence telescope during the Apollo-Soyuz mission. The total energy flux in the spectral band between 170 and 620 A is estimated to be approximately 4 by 10 to the -9th power erg/sq cm per sec. It is shown that the data support the identification of the EUV object with the ultrasoft X-ray source in Coma Berenices. The source of both emissions is suggested to be the hot white dwarf HZ 43, located at right ascension 13 hr 43 min and declination +29 deg 22 min (1950). The temperature of HZ 43 is estimated as 110,000 K, giving it the highest temperature of any known white dwarf.
51 citations
TL;DR: The present state of empirical knowledge about neutron-star masses is reviewed in this article, where it is shown how the mass function of a pulsar-containing binary system can be inferred from measurements of the pulsation period and the projected semimajor axis of the PSR orbit plus independent information concerning the inclination of the orbital plane, the mass of the companion star, or both.
Abstract: The present state of empirical knowledge about neutron-star masses is reviewed. It is shown how the mass function of a pulsar-containing binary system can be inferred from measurements of the pulsation period and the projected semimajor axis of the pulsar orbit plus independent information concerning the inclination of the orbital plane, the mass of the companion star, or both. Relevant observational properties, the type of information used to constrain the pulsar mass, and the range of allowable pulsar masses are summarized for the binary systems 3U 0900-40, Cen X-3, SMC X-1, Her X-1, and PSR 1913+16. It is found that as long as the general theory of relativity is correct, neutron-star masses should range from about 1.4 to 1.9 solar masses if the companion is a normal white dwarf or should be less than about 1.9 solar masses if the companion is some other object. It is concluded that these mass estimates are entirely consistent with the predictions of nuclear physics theory.
41 citations
TL;DR: In this paper, the authors interpret the behavior of T CrB in terms of accretion in a binary system and show that the mass of the blue component is clearly greater than the Chandrasekhar limit, even though the blue components of common novae are widely believed to be white dwarfs.
Abstract: THE recurrent nova T CrB has long been regarded as an anomaly among cataclysmic variables. It is a binary system consisting of an M3III giant and a blue companion1. From the radial velocity curves, Kraft2 found component masses of ≥ 3.7M⊙ and ≥ 2.6M⊙, respectively, later revised downwards to 2.6M⊙ and 1.9M⊙ by Paczynski3. Nevertheless, the mass of the blue component is clearly greater than the Chandrasekhar limit, even though the blue components of common novae are widely believed to be white dwarfs. The binary period, 227.5 d, is > 300 times longer than that of GK Per3, the longest period known among the remaining cataclysmic variables, and in stark contrast with the 0.0567-d period of WZ Sge, the only other recurrent nova of known binary period. Warner4 has suggested, however, that T CrB is typical of the majority of recurrent novae. In this paper we interpret the behaviour of T CrB in terms of accretion in a binary system.
36 citations
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TL;DR: In this article, objects that have already been detected as discrete soft x-ray sources are reviewed, including supernova remnants, a recurrent nova, flare stars, the coronas of nearby stars, SS Cygni, a white dwarf, and a soft component of emission from binary xray stars.
Abstract: Objects that have already been detected as discrete soft x-ray sources are reviewed. They include supernova remnants, a recurrent nova, flare stars, the coronas of nearby stars, SS Cygni, a white dwarf, and a soft component of emission from binary x-ray stars. A brief mention is made of those aspects of the diffuse cosmic soft x-ray background that may be related to the discrete sources. 10 figs., 3 tables, 177 refs. (GHT)
TL;DR: The detection of a second EUV (100-1000 A) probable white dwarf star with the EUV telescope aboard the Apollo Soyuz mission is reported in this article, where a grid of LTE pure-hydrogen, high-surface-gravity model atmospheres is used, in combination with EUV data and optical spectrophotometry, to derive the stellar parameters, yielding an effective temperature of 60,000 K, a radius of 17,000 km at 100 pc, and a luminosity of 7(d/100 pc) squared solar luminosities.
Abstract: The detection of a second EUV (100-1000 A) probable white dwarf star with the EUV telescope aboard the Apollo Soyuz mission is reported. The positional error box includes Feige 24, a binary system consisting of a very blue white dwarf and a dMe star. A grid of LTE pure-hydrogen, high-surface-gravity model atmospheres, is used, in combination with the EUV data and optical spectrophotometry, to derive the stellar parameters, yielding an effective temperature of 60,000 K, a radius of 17,000 km at 100 pc, and a luminosity of 7(d/100 pc) squared solar luminosities. The Feige 24 models appear to rule out white dwarfs with pure hydrogen atmospheres if the interstellar helium abundance and ionization are not anomalous.
TL;DR: In this paper, it was shown that a stationary star, consisting of a viscous heat-conducting general-relativistic fluid, must be axisymmetric.
Abstract: The final state of thermonuclear evolution of a star may consist of either a black hole or an ''ordinary'' star such as a white dwarf or neutron star. For the case of black holes, a great deal is known about the structure of this final stationary state; in particular, Hawking has shown that stationary black holes are axisymmetric. An extension of this result is presented which includes the ''ordinary'' final state of stars. It is shown that a stationary star, consisting of a viscous heat-conducting general-relativistic fluid, must be axisymmetric. For this proof, the star is assumed to be embedded in an asymptotically Minkowskian spacetime manifold. The functions which describe the geometry and the fluid of the star are assumed to satisfy certain smoothness conditions. (AIP)
TL;DR: In this paper, a simple two-component model for a white dwarf star has been constructed, and its properties have been examined for arbitrary central densities for typical white dwarf densities, the internal electric field is quite small and other characteristics are almost identical to those calculated by the Chandrasekhar classical white dwarf model.
Abstract: A previously developed method for making the Einstein-Maxwell equations determinate for a static, multicomponent fluid also permits the calculation of the macroscopic electric field in such a body. As a practical application of these equations, a simple, two-component model for a white dwarf star has been constructed, and its properties have been examined for arbitrary central densities. It is found that, for typical white dwarf densities, the internal electric field is quite small and other characteristics are almost identical to those calculated by the Chandrasekhar classical white dwarf model. For very large central densities, however, internal fields can be quite large, with a general correlation between large mass densities and large charge densities. (AIP)
Journal Article•
TL;DR: In this article, it was shown that the contribution to the ionization of the interstellar medium due to planetary nebulae is from one or two orders of magnitude smaller than that due to O stars.
Abstract: It is found that the contribution to the ionization of the interstellar medium due to planetary nebulae is from one or two orders of magnitude smaller than that due to O stars. The mass return to the interstellar medium due to planetary nebulae is investigated, and the birth rate of white dwarfs and planetary nebulae are compared. Several arguments are given against the possibility that the infrared sources detected by Becklin and Neugebauer in the direction of the galactic center are planetary nebulae. (AIP)
TL;DR: In this article, the evolution of a binary system with components of 10M and 8M was studied, and it was found that after the end of core helium burning, a second stage of mass transfer from the primary occurs, which is prohibited by the large neutrino losses in the degenerated core.
Abstract: The evolution of a binary system with components of 10M⊙ and 8M⊙ is computed through a case B of mass exchange. It is found that after the end of core helium burning, a second stage of mass transfer from the primary occurs. Carbon ignition is prohibited by the large neutrino losses in the degenerated core. The primary remnant, a 1.12M⊙ star, ends as a white dwarf. A comparison with the 10M⊙ single evolution is made.
TL;DR: The soft x-rays observed from the Sirius system can be readily explained as thermal emission originating from deep layers of the atmosphere of the white-dwarf star Sirius B, as long as the atmosphere is helium-and metal-poor as discussed by the authors.
Abstract: The soft x-rays observed from the Sirius system can be readily explained as thermal emission originating from deep layers of the atmosphere of the white-dwarf star Sirius B, as long as the atmosphere of Sirius B is helium- and metal-poor. (AIP)
TL;DR: In this article, a simplified model of galactic star formation predicts that the local death rate of stars with main-sequence masses between 1 and 5 M/sub sun/ is 2.
Abstract: We reexamine the planetary nebulae in the greater solar neighborhood and find the local number density to be about 80 kpc/sup -3/ and a local birth (and death) rate of some 4--6 x 10/sup -3/ kpc/sup -3/ yr/sup -1/. For the corresponding whole-galaxy figures we adopt tentatively a total planetary population of about 38,000 +- 12,000 and a production rate of 2 or 3 per year. A simplified model of galactic star formation predicts that the local death rate of stars with main-sequence masses between 1 and 5 M/sub sun/ is 2--3 x 10/sup -3/ kpc/sup -3/ yr/sup -1/; and Weidemann's statistics and cooling times for white dwarfs yield a comparable production rate for those objects of 2--5 x 10/sup -3/ kpc/sup -3/ yr/sup -1/. These several local rates, derived from entirely different sets of data, are all comparable and therefore reinforce the widely held idea that planetary nebulae are cosmically evanescent episodes between the main-sequence and white-dwarf stages in the evolution of all or most modestly massive stars.The model of star formation also predicts that the local death rate of stars with main-sequence masses greater than 5 M/sub sun/ is a few times 10/sup -4/ kpc/sup -3/ yr/sup -1/,more » in rough agreement with current estimates of the local production rate of supernovae and of pulsars. We suggest that neutron stars of all ages up to the age of the Galaxy may account for a modest fraction of the local mass density required by the Oort limit.We also explore the planetary nebulae far from the galactic plane and suggest that there are no more than about 100 such systems in the halo of the Galaxy. With the unproved assumption that halo planetaries are physically comparable to those in the disk, we are able to calculate an approximate upper limit to the mass of the halo of 2--5 x 10/sup 9/ M/sub sun/, or 1--3 percent of the conventionally accepted mass of the Galaxy. (AIP)« less
TL;DR: In this article, a variety of data are presented concerning the spectrum, distance, temperature, and evolutionary state of the hot white dwarf HZ 43, the first extrasolar object to be detected in the EUV band.
Abstract: A variety of data are presented concerning the spectrum, distance, temperature, and evolutionary state of the hot white dwarf HZ 43, the first extrasolar object to be detected in the EUV band. The data include spectrophotometry of the star and its red dwarf companion (HZ 43B), a trigonometric parallax for the star, its tangential velocity, and results of soft X-ray and EUV observations. The main conclusions are that: (1) the spectrum of HZ 43A is that of a hot DAwk star, (2) HZ 43B is a dM3.5e star, (3) the distance of the system is about 65 pc, (4) the tangential velocity is not atypical of white dwarfs, and (5) the stellar energy distribution of HZ 43A is well fitted by a black body with an effective temperature of approximately 110,000 K. Evolutionary implications of the existence of an object as hot as HZ 43A are briefly considered, and it is suggested that the progenitors of hot DA stars must include objects hotter than spectral type sdB, with logical possibilities being nuclei of planetary nebulae and sdO stars.
TL;DR: In this article, it is proposed that the nearly constant bolometric luminosity of FH Ser originates in the non-degenerate hydrogen burning region at the bottom of the hydrogen-rich envelope which remains after the primary ejection.
Abstract: A variety of observations of novae are discussed in light of theoretical models. It is proposed that the nearly constant bolometric luminosity of FH Ser originates in the nondegenerate hydrogen-burning region at the bottom of the hydrogen-rich envelope which remains after the primary ejection. The shift of the wavelength of peak emission from the visual to shortward of the ultraviolet is caused by the decrease of the photospheric radius of the remnant envelope as the bolometric luminosity stays nearly constant. The oscillations in the light curve of GK Per during the transition stage can be explained by a pulsation of the remnant envelope when it is larger than the semimajor axis of the binary system. The CNO overabundances in novae reported by various observers are strongly suggestive of the proposed nova mechanism. Implications of the upper limits on C-13 and N-15 found in DQ Her are discussed.
TL;DR: In this paper, luminosity functions in terms of bolometric magnitudes are constructed for M67 and for two samples of old-disk field giants, compared with theoretical rates of evolution on the giant branch.
Abstract: Luminosity functions in terms of bolometric magnitudes are constructed for M67 and for two samples of old-disk field giants. These are compared with theoretical rates of evolution on the giant branch. M67 has too few stars to give a useful comparison. The field giants show good agreement with theory, and the number of stars at the ''clump'' suggests that core helium-burning is prolonged by overshoot with semiconvective mixing. The fuel consumption derived from the luminosity functions is consistent with core helium ignition at the theortically predicted core mass, and with a final core mass in agreement with observed white dwarf masses. Data are needed for a larger complete sample of field giants for the luminosity function to be better determined. Further details, especially for the variable M giants at the top of the giant branch, are needed for population syntheses of elliptical galaxies. (AIP)
TL;DR: The results to date of a Southern Hemisphere search for new members of the ZZ Ceti class of variable stars are presented in this paper, where BPM 31594 was found to be variable and is a probable member of this class.
Abstract: The results to date of a Southern Hemisphere search for new members of the ZZ Ceti class of variable stars are presented. BPM 31594 was found to be variable and is a probable member of this class. This star exhibited a change in period by a factor of 2 in one day, and this change is discussed with respect to mode changes in nonradially oscillating white dwarf models. It is found that mode changes do not easily give a factor of 2 change in the observed period. (AIP)
TL;DR: If the gravitational constant decreases with time at a constant rate, there is a maximum possible age and a minimum possible luminosity for each white dwarf mass as discussed by the authors, which is compatible with the present values of these age and luminosity limits.
Abstract: If the gravitational constant decreases with time at a constant rate, there is a maximum possible age and a minimum possible luminosity for each white dwarf mass. White dwarfs older and fainter than these limits would, in the past, have exceeded the white dwarf mass limit and have become supernovae.The rate of change of the gravitational constant G/G= (-7.5 +- 2.7) x 10/sup -11/ year/sup -1/ recently reported by Van Flandern is compatible with the present values of these age and luminosity limits. (AIP)
Journal Article•
Journal Article•
TL;DR: In this paper, the photometric properties of R548 were investigated and it was shown that both frequencies vary in amplitude and in phase, and that the amplitude and phase variations are strictly periodic with periods near 11/2 days.
Abstract: R548 is a DA white dwarf which varies in luminosity. Two low-amplitude frequencies are simultaneously present in its light curve, one at 213 s and one at 274 s. We present the results of an extensive investigation of the photometric properties of R548. We demonstrate that both frequencies vary in amplitude and in phase, and that the amplitude and phase variations are strictly periodic, with periods near 11/2 days. The net effect is that the light curve of R548 is predictable to within 0.001 mag in amplitude and to about 10 s in time. We show that the variations of R548 are consistent with nonradial g-mode pulsations. (AIP)
TL;DR: In this article, the stellar masses and the angle of inclination for the PSR 1913+16 system were determined in terms of the observable periastron advance and second-order relativistic effects, for the cases (a) in which classical contributions to the apsidal motion are negligible, and (b) in case b, the companion is a helium main-sequence star.
Abstract: The stellar masses and the angle of inclination are determined for the system containing PSR 1913+16 in terms of the observable periastron advance and second-order relativistic effects, for the cases (a) in which classical contributions to the apsidal motion are negligible, and (b) in which the companion is a helium main-sequency star. In case b, the apsidal motion constant is calculated from models of such stars. Depending on the values found for the observable parameters, it may be possible to distinguish between cases a and b. The further uncertainty in the mass determination which arises if the companion is a rapidly rotating degenerate dwarf or helium main-sequence star is discussed. Black holes, neutrons stars, degenerate dwarfs, and helium main-sequence stars remain viable candidates for the companion at present. (AIP)
TL;DR: The original spectrograms plus newly acquired ones have been remeasured and analyzed along with numerous standard stars to provide a more definitive orbit solution and center-of-mass radial velocity for this important binary.
Abstract: The original spectrograms plus newly acquired ones have been remeasured and analyzed along with numerous standard stars to provide a more definitive orbit solution and center-of-mass radial velocity for this important binary. Evidence from the Ca ii emission lines suggests that a chromospheric ''event'' may have been observed which is related to mass exchange. (AIP)