Showing papers on "White dwarf published in 1986"
TL;DR: The separation of high-mass pulsators into three clearly defined groups enables some of the properties of a pulsator to be predicted if only a few of its parameters are known as mentioned in this paper.
Abstract: High mass X-ray pulsators are shown to be divisible into three distinct groups on the basis of their observational properties: 1) the Be star systems, 2) non-Be star systems with long pulse periods, (~102 — 103 s), and 3) non-Be star systems with short pulse periods (~100 — 101 s). Differences in mass transfer processes between the groups are invoked to account for the different properties. The separation of high mass pulsators into three clearly defined groups enables some of the properties of a pulsator to be predicted if only a few of its parameters are known. Because of this the optical counterparts of the X-ray sources H0850-42, OAO1653-40 and 1E1048.1-5937 are predicted to be either Be stars or, much less likely, low mass binaries. The orbital (Po) and spin (Ps) periods of the short period systems may be anti-correlated, a phenomenon which is also exhibited by the intermediate polar white dwarf binaries. For the long period systems there is no strong relationship between Po and Ps as there is for the Be star systems. It is shown that for the Be star systems this relationship cannot be accounted for by accretion from a stellar wind if there is equality between the Alfven and corotation radii of the neutron stars in these systems. However, accretion from a non-expanding atmosphere is not excluded. The lack of any correlation between Ps and Po for the supergiant systems is attributed to the low angular momentum of accreted matter. The Be star systems, however, probably accrete significant angular momentum which can result in an accretion disk.
313 citations
TL;DR: In this paper, a nouvelle methode de calcul a deux dimensions for obtenir les structures d'etoiles en rotation rapide and de disques gazeux.
Abstract: On formule une nouvelle methode de calcul a deux dimensions pour obtenir les structures d'etoiles en rotation rapide et de disques gazeux
258 citations
TL;DR: In this paper, the origin of magnetized neutron stars in binaries and the 1.55 ms pulsar was examined in terms of the magnetic field decay model for radio pulsars with a decay time scale of order 5 x 10 to the 6th yr over 7-10 e-foldings.
Abstract: The origin of magnetized neutron stars in binaries and the 1.55 ms pulsar is examined in terms of the magnetic field decay model for radio pulsars with a decay time scale of order 5 x 10 to the 6th yr over 7-10 e-foldings. Observational data of pulsing X-ray sources, nonpulsing X-ray sources, and binary radio pulsars are analyzed. Evolutionary scenarios for Her X-1, MXB 1730-335, 4U 1626-67, GX 1 + 4, 1E 2259 + 59, and long-period binary pulsars are described. The data reveal that: magnetic field strengths for accretion-powered X-ray pulsars in massive binaries and rotation-powered radio pulsars in short-period binaries support the formation of these neutron stars by core collapse following the Fe photodisintegration phase of a He-core remnant that resulted from mass transfer; however, the magnetic field strengths for neutron stars, low-mass X-ray binaries, and in wide radio pulsar binaries are explained if the magnetized neutron stars were formed less than 10 to the 8th years ago by accretion-induced collapse of a massive white dwarf. It is noted that with these two formation models all observations of the magnetic fields of neutron star in binaries are consistent with one single-field decay time scale consistent with one single-fieldmore » decay time scale down to a surface field strength of less than or equal to 3 x 10 to the 9th G. 108 references.« less
234 citations
TL;DR: In this paper, the effects of mass and angular momentum losses during a nova eruption are investigated by simulation in the context of a new nova evolution model, and the results of these simulations are used to demonstrate the consistency of variable MTR in resolving the MTR discrepancy.
Abstract: The effects of mass and angular momentum losses during a nova eruption are investigated by simulation in the context of a new nova evolution model. It is argued that surveys for cataclysmic variables (CVs) are very incomplete and that the local space density of CVs could well be 0.0001/cu pc. It is shown that the competing effets of mass and angular momentum loss usually increase the separation of a red and white dwarf during a nova eruption. The reasons why old novae remain bright for about a century after eruption and why they reduce the mass transfer rate (MTR) and eventually go into a state of hibernation for a thousand to a million years, eventually reviving as dwarf novae or novalike variables, are discussed. The results of these simulations are used to demonstrate the consistency of variable MTR in resolving the MTR discrepancy. 43 references.
220 citations
01 Jan 1986
TL;DR: The separation of high-mass pulsators into three clearly defined groups enables some of the properties of a pulsator to be predicted if only a few of its parameters are known as mentioned in this paper.
Abstract: High mass X-ray pulsators are shown to be divisible into three distinct groups on the basis of their observational properties: 1) the Be star systems, 2) non-Be star systems with long pulse periods, (~102 — 103 s), and 3) non-Be star systems with short pulse periods (~100 — 101 s). Differences in mass transfer processes between the groups are invoked to account for the different properties. The separation of high mass pulsators into three clearly defined groups enables some of the properties of a pulsator to be predicted if only a few of its parameters are known. Because of this the optical counterparts of the X-ray sources H0850-42, OAO1653-40 and 1E1048.1-5937 are predicted to be either Be stars or, much less likely, low mass binaries. The orbital (Po) and spin (Ps) periods of the short period systems may be anti-correlated, a phenomenon which is also exhibited by the intermediate polar white dwarf binaries. For the long period systems there is no strong relationship between Po and Ps as there is for the Be star systems. It is shown that for the Be star systems this relationship cannot be accounted for by accretion from a stellar wind if there is equality between the Alfven and corotation radii of the neutron stars in these systems. However, accretion from a non-expanding atmosphere is not excluded. The lack of any correlation between Ps and Po for the supergiant systems is attributed to the low angular momentum of accreted matter. The Be star systems, however, probably accrete significant angular momentum which can result in an accretion disk.
216 citations
TL;DR: In this paper, the authors present nouvelles estimations des echelles de temps de diffusion des elements lourds dans les naines blanches.
Abstract: On presente de nouvelles estimations des echelles de temps de diffusion des elements lourds dans les naines blanches
205 citations
148 citations
135 citations
TL;DR: In this article, optical and X-ray observations of the ultrashort period cataclysmic variable SW UMa are reported, and the photometric observations reveal the presence of a hump in the light curve occurring at an orbital phase which is consistent with the phase at which the region of enhanced line emission is most favorably seen.
Abstract: Time-resolved X-ray and optical photometric and optical spectroscopic observations of the ultrashort period cataclysmic variable SW UMa are reported. The spectroscopic observations reveal the presence of an s-wave component which is almost in phase with the extreme line wings and presumably the white dwarf. This very unusual phasing in conjunction with the available optical and X-ray data seems to indicate that a region of enhanced emission exists on the opposite side of the disk from the expected location of the hot spot. The photometric observations reveal the presence of a hump in the light curve occurring at an orbital phase which is consistent with the phase at which the region of enhanced line emission is most favorably seen. Changes in the hump amplitude are seen from night to night, and a 15.9 min periodicity is evident in the light curve. The optical and X-ray periodicities suggest that SW UMa is a member of the DQ Her class of cataclysmic variables.
127 citations
TL;DR: In this paper, a new bound on the Yukawa coupling to electrons of g −13 was established for invisible axions, corresponding to a Peccei-Quinn scale of v > 1 × 10 9 9 GeV corresponding to m a −2 eV.
TL;DR: In this paper, the optical counterparts of two binary pulsar systems were found to be white dwarfs and the existence of a cool and therefore old white dwarf in the 0655+64 system contradicts the standard hypothesis of exponential decay of magnetic fields in neutron stars.
Abstract: We report the discovery of the optical counterparts of two binary pulsar systems-0655+64 and 0820+02. In accordance with stellar evolution scenarios we find the optical counterparts to be white dwarfs. The existence of a cool and therefore old white dwarf in the 0655+64 system contradicts the standard hypothesis of exponential decay of magnetic fields in neutron stars. We resolve this contradiction by hypothesizing that the magnetic field in neutron stars consists of two components-an exponentially decaying field and a steady field. The former probably resides in the crust and the latter perhaps in the core: The consequences of this hypothesis for the lifetimes of millisecond pulsars, binary pulsars, and galactic bulge X-ray sources are discussed.
TL;DR: In this paper, the number of comets in orbit around other single stars in clouds similar to the one present in our own solar system is constrained directly, and this in turn constrains the presence of the comets around main-sequence stars.
Abstract: It is shown how to obtain interesting limits on the number of comets in orbit around other single stars in clouds similar to the one present in our own solar system. The number of comets around white dwarf stars is constrained directly, and this in turn constrains the presence of comets around main-sequence stars. If a white dwarf possesses a cloud of comets similar to the Oort cloud, it will occassionally accrete a comet. The accretion of a comet may add enough heavy elements to the atmosphere of the white dwarf to produce a recognizable spectral signature; it is suggested that the calcium reported in the white dwarf G 74-7 is due to recent comet accretion. This signature will persist until sedimentation has removed the heavy elements from the atmosphere; the mean time between accretion events is comparable to the sedimentation time for cool DA stars, so this signature should be frequently observed if cometary systems are common. The possibility that cometary systems greater than or approximately equal to 3 times more massive than the Oort cloud are present around most white dwarf stars are excluded and how this limit can be improved is indicated. It is shown that a star keeps most of its comets during the vigorous mass loss phase prior to the appearance of the white dwarf star. Thus, the constraints obtained here may be applied to the main-sequence progenitors of the white dwarfs.
TL;DR: In this paper, an M7-III star named CH Cyg was observed to undergo periods of brightening in the blue-violet continuum at irregular intervals of a few years.
Abstract: CH Cyg is an M7 III star that is known to undergo periods of brightening in the blue-violet continuum at irregular intervals of a few years1–3. During the active phase, the spectrum also exhibits strong Balmer emission and emission lines from He I, Fe II and various forbidden transitions, giving it the appearance of a symbiotic star. As part of a monitoring programme on symbiotic stars, observations with the National Radio Astronomy Observatory Very Large Array (VLA) have been made on CH Cyg over the past year at intervals of a few months. During the period April 1984 to May 1985 this monitoring revealed a strong radio outburst coincident with the production of a multi-component jet, and a comparison of high-resolution maps at two epochs separated by 75 days shows that the jet is expanding at a rate of 1.1 arc s yr−1. The onset of the radio outburst coincides in time with a remarkable decline in the visual brightness of the star. The luminosity of the star during the optically active state and the energetics of the mass loss suggest that the outburst is the result of accretion at, or near, the Eddington limit onto the surface of a white dwarf.
TL;DR: In this article, the energy distributions for 12 hot, helium-atmosphere DB white dwarfs, including the four known pulsating stars which define an empirical DB instability strip, are presented.
Abstract: Ultraviolet energy distributions are presented for 12 hot, helium-atmosphere DB white dwarfs, including the four known pulsating stars which define an empirical DB instability strip. The UV spectrophotometry is reported, and the energy distributions are matched with two separate grids of DB model atmosphere calculations, so that effective temperature estimates may be derived. The sources of uncertainty in the UV temperature fits are assessed, and a comparison with estimates from optical data is made.
TL;DR: Evaluation des amplitudes and des phases des composantes de Fourier de la courbe de lumiere du modele standard d'une polaire intermediaire as discussed by the authors.
Abstract: Evaluation des amplitudes et des phases des composantes de Fourier de la courbe de lumiere du modele standard d'une polaire intermediaire
TL;DR: In this paper, the properties of a binary component which fills its Roche lobe after becoming a giant with a degenerate helium core of about 0.3 solar mass are analyzed, and an equation of state is defined that accounts for Coulomb forces, liquification and crystallization, as well as gravitation and chemical diffusion during cooling phases.
Abstract: The properties of a binary component which fills its Roche lobe after becoming a giant with a degenerate helium core of about 0.3 solar mass are analyzed. An equation of state is defined that accounts for Coulomb forces, liquification and crystallization, as well as gravitation and chemical diffusion during cooling phases. The mass loss is so fast that the companion overflows its Roche lobe and transferred matter forms a common envelope around both stars, with mass lost by transfer out of the system. Hydrogen flames occur when the object is compact and forced to refill the Roche lobe and when hydrogen has diffused outward to high temperature regions. A cooling curve is established and used to generate a number-magnitude distribution function of helium dwarfs. 48 references.
TL;DR: In this paper, the discovery and study of a PG white dwarf which shows strong linear and circular polarization modulated with a rotation period of 3 hr 24 min is reported. But the star is more highly magnetic than even Grw +70 deg 8247, with absorption components of hydrogen in its optical and UV spectra corresponding to fields from 200 to more than 500 MG.
Abstract: The discovery and study of a PG white dwarf which shows strong linear and circular polarization modulated with a rotation period of 3 hr 24 min is reported. The new star, PG 1031 + 234, is more highly magnetic than even Grw +70 deg 8247, with absorption components of hydrogen in its optical and UV spectra corresponding to fields from 200 to more than 500 MG. An asymmetric dependence of polarization on rotational phase shows that the surface field structure on the star is more complex than a simple centered dipole. The basic observational features can be well reproduced by a rotating star containing an oblique centered dipole punctuated near its magnetic equator by a high-field spot containing primarily radial field lines.
TL;DR: A survey for ultraviolet-excess objects has been performed for over about 1000 sq deg of the Galactic plane as discussed by the authors, and over 70 white dwarfs and subdwarfs were identified from the survey plates, and these objects were analyzed statistically to determine scale heights and space densities.
Abstract: A survey for ultraviolet-excess objects has been performed for over about 1000 sq deg of the Galactic plane. Photographic blue and ultraviolet plates were obtained to select ultraviolet-excess candidates, and spectroscopic observations were used to determine the nature of those objects. Over 70 white dwarfs and subdwarfs were identified from the survey plates, and these objects were analyzed statistically to determine scale heights and space densities. The sample was complete to B = 15.3 mag, with the space density of white dwarfs for Mv of less than 12.25 equal to 0.72 + or 0.25/1000 cu pc, slightly higher than that from the Palomar-Green survey. The average absolute magnitude determined for both the subdwarf O and the subdwarf B stars was considerably fainter than previous determinations, while the scale height for the subdwarfs was lower than earlier suggested values. The space density for the subdwarf O stars is about 7 x 10 to the -7th/cu pc, while the value for the subdwarf B stars is about 2 x 10 to the -6th/cu pc, both values considerably higher than previous estimates. The space densities can be used to place evolutionary constraints on these objects.
TL;DR: In this paper, the radial velocity variations are detected for the carbon star G77-61 with a binary period of 245 days, and the most straightforward evolutionary hypothesis is that this star has an extremely metal-poor composition, and that it accreted a small amount of carbon-rich material when the now-unseen primary was at maximum radius.
Abstract: In the present study of astrometric, photometric, and spectrophotometric data for the low luminosity carbon star G77-61, radial velocity variations are detected which have a binary period of 245 days. The unseen companion is probably a cool white dwarf of much higher mass than the visible object. The most straightforward evolutionary hypothesis is that this star has an extremely metal-poor composition, and that it accreted a small amount of carbon-rich material when the now-unseen primary was at maximum radius. This may have inverted the C/O abundance of the secondary without achieving common envelope evolution and a sorter period.
Journal Article•
TL;DR: In this article, the authors discuss the nucleosynthesls results of those carbon deflagratlon supernovae in detail, and special emphasis is given to the discussion of burning conditions.
Abstract: There Is Increasing evidence that Type supernovae (SN I) are the main producers of Iron-peak elements In the Galaxy. In addition observations of SN I also Indicate the existence of appreciable amounts of Intermediate elements like O. Mg. SI. S. and Ca In the outer layers of the exploding star. Such an abundance pattern can be produced by carbon deflagratlon models of accreting carbon-oxygen white dwarfs In binary systems or stars on the asymptotic giant branch (AGB) which Ignite central carbon burning explosively. The present study discusses the nucleosynthesls results of those carbon deflagratlon supernovae In detail. Special emphasis Is given to the discussion of burning conditions and corresponding nucleosynthesls products. The overproduction of 54Fe+58NI. mentioned In earlier publications. Is stili existing. Assuming that SN I which contributed to the abundances In the solar system. originated from white dwarfs with a metaillcity range O. 1
01 Dec 1986
TL;DR: The role of Binaries in Globular Cluster Evolution is discussed in this article, where the evolution of X-Ray Binaries and the formation of Neutron Stars are discussed.
Abstract: The Role of Binaries in Globular Cluster Evolution.- Common Envelope Evolution.- Origin and Evolution of X-Ray Binaries in Globular Clusters.- A Note on the Nature of the Secondaries in Ultra-Compact Binaries.- Wind Fed X-Ray Binaries.- The Three Types of High Mass X-Ray Pulsator.- Orbital Period Changes in Massive X-Ray Binaries.- From Wide to Close Binaries?.- Evolution of Close Binaries and the Formation of Neutron Stars.- Quasi-Periodic Oscillations in GX 5-1 and SCO X-1.- Quasi-Periodic Oscillations in the X-Ray Flux of CYG X-2 and Their Relation to the Source Spectra.- Quasi-Periodic Oscillations as a Probe of Galactic-Bulge X-Ray Sources.- On the Nature of the Quasiperiodic Oscillations of Low Mass X-Ray Binaries.- The Duration of the Detached Phase in Low-Mass X-Ray Binaries in which the Neutron Star was Formed by Accretion-Induced Collapse of a White Dwarf.- Some Remarks on Classifications of Low-Mass X-Ray Binaries.- Two Spectral Components and Their Luminosity-Related Changes of Low-Mass Binary X-Ray Sources.- The Evolution of Low Mass Binary Systems.- Eclipse of a Bright Spot in the Disk of Her X-1.- The Orbital Periods of the Low Mass X-Ray Binaries.- Exosat Observations of the 35-Day Cycle of Her X-1 Evidence for Neutron Star Precession.- Timing Analysis of the Galactic Bulge X-Ray Source GX 17+2.- On the Evolution of Her X-1.- Do Neutron Star Magnetic Fields Decay?.- Secular Evolution of Cataclysmic Binaries.- The Evolution of Magnetic Cataclysmic Variables.- Variability of Apparent Radii in the Decay Part of Type I X-Ray Bursts.
Journal Article•
TL;DR: Analyse de 96 heures de photometrie a haute vitesse de la variable pulsante PG 1159-035, obtenues de 1979 a 1984 as discussed by the authors.
Abstract: Analyse de 96 heures de photometrie a haute vitesse de la variable pulsante PG 1159-035, obtenues de 1979 a 1984
01 Jan 1986
TL;DR: In this paper, the present status of observations of compact X-ray sources with emphasis on the aspects related to radiation hydrodynamics, based on the recent observational results, in particular those from the Japanese Xray astronomy sa te l l i te Tenma.
Abstract: This paper reviews the present status of observations of compact X-ray sources with emphasis on the aspects related to radiation hydrodynamics, based on the recent observational results, in part icular those from the Japanese X-ray astronomy sa te l l i te Tenma. The main feature of Tenma is a large-area gas sc in t i l l a t i on proportional counters (GSPC) with energy resolution twice that of ordinary proportional counters, which can yield information on energy spectrum superior in qual i ty to previous results. We shall deal here only with those galactic X-ray sources in which the compact object is a neutron star or possibly a black hole, and exclude white dwarf sources.
TL;DR: In this article, the authors observed about 140 white dwarfs on eight nights in 1982, with about 10,000 to 30,000 photons/pixel being detected near the central wavelengths of the double CCD camera used.
Abstract: Despite their relatively high stability and slow evolution, white dwarfs are subject to important changes as they cool, since little material is required to contaminate an atmosphere that is only a few meters thick. With an eye to these complexities, about 140 white dwarfs were observed on eight nights in 1982, with about 10,000 to 30,000 photons/pixel being detected near the central wavelengths of the double CCD camera used. Steep Balmer decrements are noted to occur in the cooler degeneration due to increasing He/H ratio. The predominance of non-DA stars as late evolutionary stages prompts questions as to the fate of the accreted and residual H in postasymptotic giant branch evolution. No definitive theoretical argument is found to explain how most of the residual hydrogen is destroyed. 51 references.
01 Jan 1986
TL;DR: In this paper, a long duration Type II supernova model was proposed based on repeated encounter with the electron-positron pair instability in stars heavier than about 60 M⊙.
Abstract: Presupernova models of massive stars are presented and their explosion by “delayed neutrino transport” examined. A new form of long duration Type II supernova model is also explored based upon repeated encounter with the electron-positron pair instability in stars heavier than about 60 M⊙. Carbon deflagration in white dwarfs is discussed as the probable explanation of Type I supernovae and special attention is paid to the physical processes whereby a nuclear flame propagates through degenerate carbon.
TL;DR: On suit l'evolution complete d'une etoile de population I et de masse initiale 3M○. jusqu'a son refroidissement final.
Abstract: On suit l'evolution complete d'une etoile de population I et de masse initiale 3M○. jusqu'a son refroidissement final
TL;DR: In this article, the existence of a degenerate dwarf as a companion for gamma Cas instead of a neutron star was suggested, and the lack of luminosity from the white dwarf companion is attributed to a nonspherical mass loss from the primary.
Abstract: The X-ray source gamma Cassiopeiae was observed with the X-ray astronomy satellite Tenma A strong iron line was observed at 68 keV with an intensity of 280 eV equivalent width as is expected from a highly ionized plasma The strength of the iron line at 68 keV and the existence of a thin thermal plasma are in conflict with models that require a neutron star as the X-ray source From many of the X-ray binaries with a neutron star, only a weak ionized iron line (less than 50 eV at 67 keV) or strong reprocessed iron line (64 keV) has been observed with Tenma This Letter suggests the possible existence of a degenerate dwarf as a companion for gamma Cas instead of a neutron star The lack of luminosity from the white dwarf companion is attributed to a nonspherical mass loss from the primary 23 references