Relevant bibliographies by topics / General — white dwarfs — X-rays

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Academic literature on the topic 'General — white dwarfs — X-rays'

Author: Grafiati
Published: 4 June 2025
Last updated: 23 June 2025

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Journal articles on the topic "General — white dwarfs — X-rays"

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Lima, I. J., G. J. M. Luna, K. Mukai, et al. "Symbiotic stars in X-rays." Astronomy & Astrophysics 689 (September 2024): A86. http://dx.doi.org/10.1051/0004-6361/202449913.

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White dwarf symbiotic binaries are detected in X-rays with luminosities in the range of 1030–1034 ergs s−1. Their X-ray emission arises either from the accretion disk boundary layer, from a region where the winds from both components collide, or from nuclear burning on the surface of the white dwarf (WD). In our continuous effort to identify X-ray-emitting symbiotic stars, we studied four systems using observations from the Neil Gehrels Swift Observatory and XMM-Newton satellites in X-rays and from Transiting Exoplanet Survey Satellite (TESS) in the optical. The X-ray spectra were fit with absorbed optically thin thermal plasma models that are either single- or multitemperature with kT < 8 keV for all targets. Based on the characteristics of their X-ray spectra, we classified BD Cam as possible β-type, V1261 Ori and CD −27 8661 as δ-type, and confirmed NQ Gem as β/δ-type. The δ-type X-ray emission most likely arises from the boundary layer of the accretion disk, while in the case of BD Cam, its mostly soft emission originates from shocks, possibly between the red giant and WD and disk winds. In general, we find that the observed X-ray emission is powered by accretion at a low accretion rate of about 10−11 M⊙ yr−1. The low ratio of X-ray to optical luminosities, however indicates that the accretion-disk boundary layer is mostly optically thick and tends to emit in the far or extreme UV. The detection of flickering in optical data provides evidence of the existence of an accretion disk.
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Ögelman, H., J. Krautter, and K. Beuermann. "Exosat Observations of X-Rays from Classical Novae during Outburst Stage." International Astronomical Union Colloquium 93 (1987): 279. http://dx.doi.org/10.1017/s0252921100104981.

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AbstractThe initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime of EXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984 # 1 (PW Vul), and two observations of Nova Vulpeculae 1984 # 2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to ~ 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is ~ 2 to 3 years, which leads to the conclusion that the burned envelope mass Mburn should be of the order of . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9 M⊙, core luminosity of ~ 2 × 104L⊙, and envelope mass of 10−6M⊙, can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have ≥ 1.1 M⊙ core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind with Ṁ ≤ 5 × 10−7M⊙yr−1 appears to be necessary. The few observations of Nova Vulpeculae 1984 # 1 and Nova Vulpeculae 1984 # 2 , during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.
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Balman, S. "Inner Disk Structure of Dwarf Novae in the Light of X-Ray Observations." Acta Polytechnica CTU Proceedings 2, no. 1 (2015): 116–22. http://dx.doi.org/10.14311/app.2015.02.0116.

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Diversity of the X-ray observations of dwarf nova are still not fully understood. I review the X-ray spectral characteristics of dwarf novae during the quiescence in general explained by cooling flow models and the outburst spectra that show hard X-ray emission dominantly with few sources that reveal soft X-ray/EUV blackbody emission. The nature of aperiodic time variability of brightness of dwarf novae shows band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break (1-6 mHz) indicates inner disk truncation of the optically thick disk with a range of radii (3.0-10.0)×109 cm. The RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence reveal that the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. A preliminary analysis of SU UMa indicates a similar behaviour. In addition, I find that the outburst spectra of WZ Sge shows two component spectrum of only hard X-ray emission, one of which may be fitted with a power law suggesting thermal Comptonization occuring in the system. Cross-correlations between the simultaneous UV and X-ray light curves (XMM −Newton) of five DNe in quiescence show time lags in the X-rays of 96-181 sec consistent with travel time of matter from a truncated inner disk to the white dwarf surface. All this suggests that dwarf novae and other plausible nonmagnetic systems have truncated accretion disks indicating that the disks may be partially evaporated and the accretion may occur through hot (coronal) flows in the disk.
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Mukhopadhyay, Banibrata, and Mukul Bhattacharya. "Formation, Possible Detection and Consequences of Highly Magnetized Compact Stars." Particles 5, no. 4 (2022): 493–513. http://dx.doi.org/10.3390/particles5040037.

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Over the past several years, there has been enormous interest in massive neutron stars and white dwarfs due to either their direct or indirect evidence. The recent detection of gravitational wave event GW190814 has confirmed the existence of compact stars with masses as high as ∼2.5–2.67 M⊙ within the so-called mass gap, indicating the existence of highly massive neutron stars. One of the primary goals to invoke massive compact objects was to explain the recent detections of over a dozen Type Ia supernovae, whose peculiarity lies with their unusual light curve, in particular the high luminosity and low ejecta velocity. In a series of recent papers, our group has proposed that highly magnetised white dwarfs with super-Chandrasekhar masses can be promising candidates for the progenitors of these peculiar supernovae. The mass-radius relations of these magnetised stars are significantly different from those of their non-magnetised counterparts, which leads to a revised super-Chandrasekhar mass-limit. These compact stars have wider ranging implications, including those for soft gamma-ray repeaters, anomalous X-ray pulsars, white dwarf pulsars and gravitational radiation. Here we review the development of the subject over the last decade or so, describing the overall state of the art of the subject as it stands now. We mainly touch upon the possible formation channels of these intriguing stars as well as the effectiveness of direct detection methods. These magnetised stars can have many interesting consequences, including reconsideration of them as possible standard candles.
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MIRZA, BABUR M. "GRAVITOMAGNETIC RESONANCE SHIFT DUE TO A SLOWLY ROTATING COMPACT STAR." International Journal of Modern Physics D 13, no. 02 (2004): 327–33. http://dx.doi.org/10.1142/s0218271804004463.

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The effect of a slowly rotating mass on a forced harmonic oscillator with two degrees of freedom is studied in the weak field approximation. It is found that according to the general theory of relativity there is a shift in the resonant frequency of the oscillator which depends on the density and rotational frequency of the gravitational source. The proposed shift is quite small under normal physical situations however it is estimated that for compact X-ray sources such as white dwarfs, pulsars and neutron stars the shift is quite appreciable.
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Jinzhong, Liu, and Zhang Yu. "A binary population synthesis study on gravitational wave sources." Proceedings of the International Astronomical Union 11, A29B (2015): 365–66. http://dx.doi.org/10.1017/s1743921316005548.

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AbstractGravitational waves (GW) are a natural consequence of Einstein's theory of gravity (general relativity), and minute distortions of space-time. Gravitational Wave Astronomy is an emerging branch of observational astronomy which aims to use GWs to collect observational data about objects such as neutron stars and black holes, about events such as supernovae and about the early universe shortly after the big bang.This field will evolve to become an established component of 21st century multi-messenger astronomy, and will stand shoulder-to-shoulder with gamma-ray, x-ray, optical, infrared and radio astronomers in exploring the cosmos. In this paper, we state a recent theoretical study on GW sources, and present the results of our studies on the field using a binary population synthesis (BPS) approach, which was designed to investigate the formation of many interesting binary-related objects, including close double white dwarfs, AM CVn stars, ultra-compact X-ray binaries(UCXBs), double neutron stars, double stellar black holes. Here we report how BPS can be used to determine the GW radiation from double compact objects.
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Oks, Eugene. "Review of recent advances in the analytical theory of Stark broadening of spectral lines in plasmas: applications to laboratory discharges and astrophysical plasmas." Journal of Physics: Conference Series 2439, no. 1 (2023): 012009. http://dx.doi.org/10.1088/1742-6596/2439/1/012009.

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Abstract We present an overview of latest advances in the analytical theory of Stark broadening of spectral lines and their applications to various types of laboratory and astrophysical plasmas. They include: 1) in-depth study of intra-Stark spectroscopy in the x-ray range in relativistic laser-plasma interactions; 2) effect of diamagnetism on the number of observable hydrogen lines in plasmas; 3) influence of magnetic-field-caused modifications of trajectories of plasma electrons on the width of hydrogen/deuterium spectral lines: applications to white dwarfs; 4) Stark broadening of hydrogen/deuterium spectral lines by a relativistic electron beam: analytical results and applications to magnetic fusion; 5) counterintuitive dependence of the dynamical Stark width of hydrogenic spectral lines on the electron density.
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Melrose, DB, and WEP Padden. "Comptonisation of Radiation Below the Cyclotron Frequency in a Strong Magnetic Field." Australian Journal of Physics 39, no. 6 (1986): 961. http://dx.doi.org/10.1071/ph860961.

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We present new equations describing the Thomson scattering of the o-mode and z-mode in a strongly magnetised plasma, valid below the fundamental cyclotron frequency. Scattering by nonrelativistic thermal electrons leads to a frequency diffusion equation for the more strongly scattered o-mode and this equation is effectively the Kompaneets equation with cross section 2/ 15th of the Thomson' cross section. Transfer of the photons tends to be dominated by the less strongly scattered z-mode; an o-mooe photon is scattered occasionally into a z-mode photon, which then diffuses rapidly due to its large mean free path before being scattered back into an o-mode photon. Our results should have applications in X-ray pulsars and 'Y-ray burst sources, as well as magnetic white dwarfs occurring in cataclysmic variables.
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Antokhina, E. A., and I. I. Antokhin. "DETERMINATION OF THE CLOSE BINARY SYSTEMS PARAMETERS BY SYNTHESIS METHODS: FROM WHITE DWARFS TO WOLF–RAYET STARS AND BLACK HOLES." Астрономический журнал 100, no. 9 (2023): 772–84. http://dx.doi.org/10.31857/s0004629923090013.

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Synthesis methods for light and radial velocity curves are currently one of the main tools for studying close binary systems (CBS). The paper gives a brief overview of the history and development of the methods and their implementations at the SAI MSU, where a set of computer programs has been created to analyze observations of various types of CBS. As a demonstration, we present the results of the analysis by our algorithms of three interesting CBSs at different evolutionary stages. An analysis of the unusual light curves of the recently discovered pre-cataclysmic binary GPX-TF16E-48 was performed using the Roche model with spots on the normal star. The X-ray light curves of the microquasar SS433 were analyzed in a model with a precessing accretion disk. Thanks to the photometric data obtained from space, the highly elliptical Wolf–Rayet binary WR22 was studied in the Roche model accounting for the absorption in the powerful wind of the Wolf–Rayet star. As a result of this detailed analysis of the light curves and involving spectroscopic information, the parameters of the CBSs and their components were found. The paper is based on a talk presented at the astrophysical memorial seminar “Novelties in Understanding the Evolution of Binary Stars”, dedicated to the 90th anniversary of Professor M.A. Svechnikov.
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Wang, Joan Jing, and Hsiang-Kuang Chang. "Can SGRs/AXPs Originate from Neutron Star Binaries?" Physics Research International 2014 (August 21, 2014): 1–8. http://dx.doi.org/10.1155/2014/375624.

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Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are two groups of enigmatic objects, which have been extensively investigated in past few decades. Based on the ample information about their timing behaviors, spectra, and variability properties, it was proposed that SGRs/AXPs are isolated neutron stars (NSs) with extremely strong magnetic fields, the so-called magnetars. Nonetheless, some alternative models are probably equally convincing such as those proposing that they are accreting NSs with a fall-back disk or rotation-powered magnetized and massive white dwarfs. The nature and nurture of SGRs/AXPs remain controversial. In this paper, we propose that SGRs/AXPs can, alternatively, originate from normal NSs in binary systems, which resorts to the reexplosion of normal NS induced by instant contraction of the massive star envelope in a Thorne-Żytkow object (TZO). The spin-period clustering is due to either the brake of a slowly rotating envelope or the frictional drag during the common-envelope phase.
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Book chapters on the topic "General — white dwarfs — X-rays"

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Werner, K. "White Dwarfs." In The Universe in X-Rays. Springer Berlin Heidelberg, 2008. http://dx.doi.org/10.1007/978-3-540-34412-4_11.

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Atkinson, Martin E. "Radiological anatomy of the oral cavity." In Anatomy for Dental Students. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199234462.003.0040.

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The radiographs most frequently taken in general dental practice are of the teeth and their immidiate supporting tissues for detection of dental caries or assessment of bone loss in periodontal disease. Intraoral radiographs are taken by placing the X-ray-sensitive film or receptor in the mouth close to the teeth being investigated. Extraoral radiographs use larger films or receptors positioned externally and produce a view of the entire dentition and its supporting structures on a single film; they are used to ascertain the state of development of the dentitions prior to orthodontic treatment, for example. Dental panoramic tomographs (DPTs) are the most frequent extraoral radiographs. A radiograph is a negative photographic record. Dense structures such as bone are designated as radio-opaque; they absorb some X-rays and appear white on radiographs. More X-rays pass through less dense radiolucent structures such as air-filled cavities which show up as black areas. The contrast between different tissues of the structures which the X-ray beam passes through is determined by their radiodensity which, in turn, is largely due to their content of metallic elements. Calcium and iron are the prevalent heavy metals in the body. Calcium is combined with phosphate to form hydroxyapatite crystals in bones and mineralized tissues in teeth. Iron is present in haemoglobin in blood, but only large concentrations of blood, such as those found within the heart chambers, show up on X-rays. In sequence from densest to most lucent, the radiodensity of the dental and periodontal tissues are: enamel, dentine, cementum, compact bone, cancellous bone, demineralized carious enamel and dentine, dental soft tissues such as pulp and periodontal ligament, and air; gold and silver–mercury amalgam metallic restorative materials are even denser than enamel. A radiograph is a two-dimensional representation of a three-dimensional situation. The orientation of anatomical structures relative to the X-ray beam is a major factor determining their appearance on the film. For example, a beam travelling through the long axis of a radiodense structure will produce a whiter image on the film than one passing through its shorter axis because more X-rays are absorbed; the structure will also have a different shape.
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Conference papers on the topic "General — white dwarfs — X-rays"

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Mukhopadhyay, Banibrata, and A. R. Rao. "Soft gamma-ray repeaters and anomalous X-ray pulsars as highly magnetized white dwarfs." In Proceedings of the MG14 Meeting on General Relativity. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813226609_0580.

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Caceres, Diego L., and Jorge A. Rueda. "On the spin-down and X-ray luminosity of anomalous X-ray pulsars and soft gamma repeaters as white dwarfs." In Proceedings of the MG14 Meeting on General Relativity. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813226609_0583.

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Hayashi, Takayuki. "White dwarf mass estimation with X-ray observation." In Proceedings of the MG14 Meeting on General Relativity. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813226609_0201.

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Traulsen, Iris, Klaus Reinsch, Klaus Werner, and T. Rauch. "Accretion onto selected magnetic white dwarfs as seen in X-rays." In 17TH EUROPEAN WHITE DWARF WORKSHOP. AIP, 2010. http://dx.doi.org/10.1063/1.3527828.

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Borges, Sarah V., Claudia V. Rodrigues, Jaziel G. Coelho, Manuel Malheiro, and Manuel Castro. "A white dwarf accretion model for the anomalous X-ray pulsar 4U 0142+61." In Proceedings of the MG15 Meeting on General Relativity. WORLD SCIENTIFIC, 2022. http://dx.doi.org/10.1142/9789811258251_0316.

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Kholtygin, A., I. Yakunin, E. Ryspaeva, and D. Mokshin. "A nature of the X-ray and optical emission from gamma Cassiopeia stars." In Modern astronomy: from the Early Universe to exoplanets and black holes. Special Astrophysical Observatory of the Russian Academy of Sciences, 2024. https://doi.org/10.26119/vak2024.063.

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To test the origin of the X-ray and optical emission from the $\gamma$ Cas-type stars, we analyzed their optical spectra obtained on the 6-m telescope BTA, the 1.25-m telescope of the Crimean station of the State Astronomical Institute (SAI, Moscow), the 2.5-m telescope SAI25 of SAI, and the photometric TESS light curves. We compare the optical variability of the $\gamma$ Cas-type stars with variations of their X-ray luminosity. An overlap between the periods of line profile variations in the spectra of $\gamma$ Cas stars and the variations in their X-ray brightness allows us to assume that a significant fraction of X-rays emits from the same place where the optical radiation comes from. The $\gamma$ Cas-type stars HD 45314, HD 45995 and NGC 6649 9 demonstrate the ultrafast X-ray brightness variations with the periods of about 50–90 seconds, which may be the rotation periods of white dwarfs components of binary systems. Thus, we can assume that at least for these stars the X-ray emission goes partly due to accretion onto rapidly rotating white dwarfs. The anomalously hard X-ray emission from the $\gamma$ Cas stars can be interpreted by assuming that the contribution of non-thermal X-ray emission is generated as a result of a reconnection of the local magnetic field lines of the Be star and its decretion disk.
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