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Articles de revues sur le sujet « X-rays: star »

Auteur : Grafiati

Publié le 9 mars 2023

Mis à jour le 31 juillet 2025

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1

Vilhu, O., T. R. Kallman, K. I. I. Koljonen, and D. C. Hannikainen. "Wind suppression by X-rays in Cygnus X-3." Astronomy & Astrophysics 649 (May 2021): A176. http://dx.doi.org/10.1051/0004-6361/202140620.

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Context. The radiatively driven wind of the primary star in wind-fed X-ray binaries can be suppressed by the X-ray irradiation of the compact secondary star. This causes feedback between the wind and the X-ray luminosity of the compact star. Aims. We aim to estimate how the wind velocity on the face-on side of the donor star depends on the spectral state of the high-mass X-ray binary Cygnus X-3. Methods. We modeled the supersonic part of the wind by computing the line force (force multiplier) with the Castor, Abbott & Klein formalism and XSTAR physics and by solving the mass conservation a

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Brorby, M., and P. Kaaret. "X-rays from Green Pea analogues." Monthly Notices of the Royal Astronomical Society 470, no. 1 (2017): 606–11. http://dx.doi.org/10.1093/mnras/stx1286.

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Abstract X-ray observations of two metal-deficient luminous compact galaxies (LCG; SHOC 486 and SDSS J084220.94+115000.2) with properties similar to the so-called Green Pea galaxies were obtained using the Chandra X-ray Observatory. Green Pea galaxies are relatively small, compact (a few kpc across) galaxies that get their green colour from strong [O iii] λ5007 Å emission, an indicator of intense, recent star formation. These two galaxies were predicted to have the highest observed count rates, using the X-ray luminosity–star formation rate (LX–SFR) relation for X-ray binaries, from a statisti

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Nagase, Fumiaki. "Photoionized Plasmas in X-Ray Binary Pulsars: ASCA Observations." Symposium - International Astronomical Union 188 (1998): 101–4. http://dx.doi.org/10.1017/s0074180900114524.

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Massive X-ray binary pulsars have often evolved early-type companion stars which emanate strong stellar winds. X-rays emitted from the accreting neutron star irradiate and ionize the surrounding stellar wind, thus forming a photoionized sphere surrounding the neutron star. The photoionization structure of matter surrounding the neutron star was calculated by Hatchett and McCray (1977) and McCray et al. (1984), for Cen X-3 and Vela X-1 respectively.

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Watson, A. "ASTROPHYSICS:Z Mimics X-rays From Neutron Star." Science 286, no. 5447 (1999): 2059. http://dx.doi.org/10.1126/science.286.5447.2059.

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Kaspi, Victoria M. "The Neutron Star Zoo." Proceedings of the International Astronomical Union 13, S337 (2017): 3–8. http://dx.doi.org/10.1017/s1743921317010390.

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AbstractSince their discovery 50 years ago, neutron stars have continually astonished. From the first-discovered radio pulsars to the powerful “magnetars” that emit sudden bursts of X-rays and γ-rays, from the so-called Isolated Neutron Stars to Central Compact Objects, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to cement an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I briefly survey the disparate neutron star classes, describe their pr

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Babel, J. "Diffusion, Winds and X-Rays from Magnetic Stars." Highlights of Astronomy 11, no. 2 (1998): 674–75. http://dx.doi.org/10.1017/s1539299600018426.

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AbstractWe propose a self-consistent approach of the CP star phenomenon and try to solve simultaneously the problems of abundance spots, wind and X-ray emission from these stars. We also discuss the periodic X-ray emission from the 07V star θ1 Orionis C and its link with Bp stars.

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Fabian, A. C., and P. A. Thomas. "X-Rays from Elliptical Galaxies." Symposium - International Astronomical Union 127 (1987): 155–65. http://dx.doi.org/10.1017/s0074180900185146.

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X-ray observations have shown that early-type galaxies contain a hot interstellar medium. This implies that the galaxies have a) a low supernova rate; b) high total gravitational binding masses and c) continuous star formation. Much of the gas in isolated galaxies is probably due to stellar mass-loss. The details of its behaviour are complex.

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Kumagai, S. "X-Rays and γ-Rays from SN 1987A". International Astronomical Union Colloquium 145 (1996): 173–81. http://dx.doi.org/10.1017/s0252921100008046.

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Theoretical light curves and spectra of X-rays and γ-rays from SN 1987A are calculated by the Monte Carlo method, based on a model built up from the early observations of neutrinos and optical light. Comparison of the predicted radiation with observational results obtained later confirms the radiation mechanism of supernovae: γ-rays are emitted in the decays of radioactive 56Co and X-rays are generated by the Compton degradation of these γ-rays. It also suggests that large scale mixing occurred and clumpy structure was formed inside the ejecta. These findings lead us to construct the model wit

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Wolk, Scott J., Ignazio Pillitteri, and Katja Poppenhaeger. "Observed effects of star-planet interaction." Proceedings of the International Astronomical Union 11, S320 (2015): 382–87. http://dx.doi.org/10.1017/s1743921316000272.

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AbstractSince soon after the discovery of hot Jupiters, it had been suspected that interaction of these massive bodies with their host stars could give rise to observable signals. We discuss the observational evidence for star-planet interactions (SPI) of tidal and magnetic origin observed in X-rays and FUV. Hot Jupiters can significantly impact the activity of their host stars through tidal and magnetic interaction, leading to either increased or decreased stellar activity – depending on the internal structure of the host star and the properties of the hosted planet. In HD 189733, X-ray and F

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Nomoto, Ken’ichi, and Sachiko Tsuruta. "Thermal Radiation from a Neutron Star in SN 1987A." International Astronomical Union Colloquium 108 (1988): 448–49. http://dx.doi.org/10.1017/s0252921100094367.

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The supernova 1987A in the Large Magellanic Cloud has provided a new opportunity to study the evolution of a young neutron star right after its birth. A proto-neutron star first cools down by emitting neutrinos that diffuse out of the interior within a minutes. After the neutron star becomes transparent to neutrinos, the neutron star core with > 1014 g cm−3 cools predominantly by Urca neutrino emission. However, the surface layers remain hot because it takes at least 100 years before the cooling waves from the central core reach the surface layers (Nomoto and Tsuruta 1981, 1986, 1987).From

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Kii, Tsuneo. "X-Ray Polarizations from Accreting Strongly Magnetized Neutron Stars: Case Studies for the X-Ray Pulsars 4U 1626–67 and Hercules X-1." Publications of the Astronomical Society of Japan 39, no. 5 (1987): 781–800. https://doi.org/10.1093/pasj/39.5.781.

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Abstract The linear polarization of X-rays from an accreting neutron star with a strong magnetic field of 1012 – 1013 G is calculated to investigate a possibility of observing the polarization of X-rays. Two binary X-ray pulsars, 4U 1626–67 and Her X-1, are considered as examples. The polarization degree is expected to be larger than 10 % for some pulse phases. The result suggests a feasibility of detecting the X-ray polarization from X-ray binary pulsars with techniques available at present.

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Tsuboi, Yohko. "X-Rays From Class 0/I Protostars." Symposium - International Astronomical Union 221 (2004): 247–56. http://dx.doi.org/10.1017/s007418090024165x.

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In the last decade, our interest moved significantly to the youngest stellar phase, “protostars”. Evidence for infalls and outflows are implying violent star-forming activities close vicinity of the protostar itself. However, due to the very high extinction in optical and near-infrared band or even in soft X-ray band, we had no tool to access the star itself. In such situation, Chandra X-ray Observatory, with the high transparency in the hard X-ray band and the superior spatial resolution, are beginning to reveal X-ray emitting phenomena deep inside the protostellar cores. In this paper, the h

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Poppenhaeger, Katja, Benjamin T. Montet, Julián D. Alvarado-Gómez, Elsa Palumbo, and Adina D. Feinstein. "X-Ray and Optical Observations of the Young M Dwarf Dipper Star TIC 234284556." Research Notes of the AAS 7, no. 9 (2023): 200. http://dx.doi.org/10.3847/2515-5172/acfd9d.

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Abstract We observed TIC 234284556 in X-rays and in the optical with XMM-Newton to study the recurring dip previously seen in TESS observations. The dip did not appear during our observation. We detect X-ray flares and anti-correlated rotational modulation in X-rays and in the optical.

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Montmerle, Thierry. "The Quest for X-Rays from Protostars." Symposium - International Astronomical Union 188 (1998): 17–20. http://dx.doi.org/10.1017/s0074180900114330.

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The field of low-mass star formation and early evolution has made rapid progress in recent years, thanks in particular to observations in the IR and mm ranges. The current evolutionary scheme calls for two main stages, themselves divided into two substages (e.g., André & Montmerle 1994): (i) protostars, comprizing the newly discovered so-called “Class 0 sources”, detected mostly or only in the mm range, which are young protostars with estimated ages ~ 104 yrs, and “Class I sources”, visible in the near- to mid-IR, which are evolved protostars with estimated ages ~ 105 yrs; (ii) T Tauri sta

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Bard, Christopher, and Richard Townsend. "X-rays From Centrifugal Magnetospheres in Massive Stars." Proceedings of the International Astronomical Union 9, S307 (2014): 449–50. http://dx.doi.org/10.1017/s1743921314007352.

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AbstractIn the subset of massive OB stars with strong global magnetic fields, X-rays arise from magnetically confined wind shocks (Babel & Montmerle 1997). However, it is not yet clear what the effect of stellar rotation and mass-loss rate is on these wind shocks and resulting X-rays. Here, we present results from a grid of Arbitrary Rigid-Field Hydrodynamic simulations (ARFHD) of a B-star centrifugal magnetosphere with an eye towards quantifying the effect of stellar rotation and mass-loss rate on the level of X-ray emission. The results are also compared to a generalized XADM model for X

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Luna, Gerardo J. M., J. L. Sokoloski, and Roberto D. D. Costa. "X-rays from the Symbiotic Star RX Pup." Astrophysics and Space Science 304, no. 1-4 (2006): 283–85. http://dx.doi.org/10.1007/s10509-006-9131-y.

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Rueda, J. A., Liang Li, R. Moradi, R. Ruffini, N. Sahakyan, and Y. Wang. "On the X-Ray, Optical, and Radio Afterglows of the BdHN I GRB 180720B Generated by Synchrotron Emission." Astrophysical Journal 939, no. 2 (2022): 62. http://dx.doi.org/10.3847/1538-4357/ac94c9.

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Abstract Gamma-ray bursts (GRBs) are systems of unprecedented complexity across all the electromagnetic spectrum, including the radio, optical, X-rays, gamma rays in the MeV and GeV regimes, as well as ultrahigh-energy cosmic rays, each manifested in seven specific physical processes with widely different characteristic evolution timescales ranging from 10−14 s to 107 s or longer. We here study the long GRB 180720B originating from a binary system composed of a massive carbon-oxygen (CO) star of about 10M ⊙ and a companion neutron star (NS). The gravitational collapse of the CO star gives rise

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Mereghetti, S., and T. Belloni. "ROSAT observation of the HII region RCW 49 Possible discovery of a new Wolf-Rayet ring nebula." Symposium - International Astronomical Union 163 (1995): 76–77. http://dx.doi.org/10.1017/s0074180900201691.

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We have observed the southern HII region RCW 49 with the ROSAT PSPC instrument. Part of the diffuse X-ray and optical emission present in this region might be associated with the X-ray selected WR star Th35-42 (WR20c). The young star cluster Westerlund 2 (which contains WR20a) is seen in X-rays as a centrally peaked, resolved source, surrounded by fainter diffuse emission.

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Papavasileiou, Theodora, Odysseas Kosmas, and Ioannis Sinatkas. "Radiation Emission and Absorption by Astrophysical Jets from XRBs." HNPS Advances in Nuclear Physics 29 (May 3, 2023): 107–12. http://dx.doi.org/10.12681/hnpsanp.4890.

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High-energy particles and radiation such as protons, pions, muons, neutrinos and gamma-ray photons are known to emit from collimated outflows of magnetized astrophysical plasma known as jets. They are being ejected by Active Galactic Nuclei or X-ray binary systems consisting of a companion star accreting mass onto a black hole or a neutron star. Our work focuses on the calculation of the produced particle energy distributions and mainly on the intensity of gamma-rays. We apply this model to prominent examples of Black Hole XRBs such as Cygnus X-1, SS 433, GRS 1915+105, etc. We also study and w

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Hurley, Kevin. "Cosmic Gamma-Ray Bursts: The Big Picture." International Astronomical Union Colloquium 192 (2005): 433–39. http://dx.doi.org/10.1017/s0252921100009519.

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SummaryA “typical” GRB occurs in a star-forming region of a galaxy at a redshift z~1. In currently popular models, it is caused by the collapse of a massive star which has exhausted its nuclear fuel supply. The star collapses to a black hole threaded by a strong magnetic field, and possibly fed by an accretion torus. Through a variety of processes, electrons are accelerated and gamma-rays, X-rays, optical light, and radio emission ensue, with durations from seconds to years. In this talk, I will review the general observational properties of bursts, their afterglows and host galaxies, and some

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Ruderman, M. "Neutron Star Powered Accelerators." Symposium - International Astronomical Union 195 (2000): 463–71. http://dx.doi.org/10.1017/s0074180900163508.

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Neutron stars can be the underlying source of energetic particle acceleration in several ways. The huge gravitational-collapse energy released in their birth, or the violent fusion at the end of the life of a neutron-star binary, is the energy source for an accelerator in the surrounding medium far from the star. This would be the case for: (a) cosmic rays from supernova explosions with neutron-star remnants; (b) energetic radiation from “plerions” around young neutron stars (e.g., the Crab Nebula, see Pacini 2000); and (c) “afterglow” and γ-rays of cosmic Gamma-Ray Burst (GRB) sources with po

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Wolk, Scott J., Ignazio Pillitteri, and Katja Poppenhaeger. "Observable Impacts of Exoplanets on Stellar Hosts – An X-Ray Perspective." Proceedings of the International Astronomical Union 12, S328 (2016): 290–97. http://dx.doi.org/10.1017/s1743921317004161.

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AbstractSoon after the discovery of hot Jupiters, it was suspected that interaction of these massive bodies with their host stars could give rise to observable signals. We discuss the observational evidence for star-planet interactions (SPI) of tidal and magnetic origin observed in X-rays. Hot Jupiters can significantly impact the activity of their host stars through tidal and magnetic interaction, leading to either increased or decreased stellar activity – depending on the internal structure of the host star and the properties of the hosted planet. We provide several examples of these interac

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Smith, Myron A., та R. Lopes de Oliveira. "Do the γ Cas X-rays come from the Be Star?" Proceedings of the International Astronomical Union 6, S272 (2010): 428–29. http://dx.doi.org/10.1017/s1743921311011057.

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Rivera, Gabriela Calistro. "Panchromatic characterisation of accreting black holes in dusty star-forming galaxies." Proceedings of the International Astronomical Union 15, S356 (2019): 26. http://dx.doi.org/10.1017/s1743921320002537.

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AbstractAlthough AGN do not typically dominate the bolometric emission of dusty star forming galaxies, large AGN fractions (sometimes > 40%) have been observed in various sub-millimeter surveys. These diagnostics have been however mostly based on X-ray counterpart selections and a complete multiwavength census of the fraction of AGN hosts is needed. I will present new advances in the modelling of panchromatic spectral energy distributions (SEDs) of active galactic nuclei (AGN), based on our publicly available code AGNfitter (Calistro-Rivera et al.2016). AGNfitter implements a fully Bayesian

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Bogdanov, Slavko. "X-rays from Radio Millisecond Pulsars." Proceedings of the International Astronomical Union 13, S337 (2017): 116–19. http://dx.doi.org/10.1017/s1743921317011553.

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AbstractThe Galactic population of rotation-powered (aka radio) millisecond pulsars (MSPs) exhibits diverse X-ray properties. Energetic MSPs show pulsed non-thermal radiation from their magnetospheres. Eclipsing binary MSPs predominantly have X-ray emission from a pulsar wind driven intra-binary shock. Typical radio MSPs emit X-rays from their heated magnetic polar caps. These thermally emitting MSPs offer the opportunity to place interesting constraints on the long sought after dense matter equation of state, making them important targets of investigation of the recently deployed Neutron Star

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Oskinova, Lidia. "X-raying massive stars and their feedback near and far." Proceedings of the International Astronomical Union 18, S361 (2022): 479–84. http://dx.doi.org/10.1017/s1743921322003404.

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AbstractMassive stars emit X-rays. Despite modest X-ray luminosities of single hot massive stars, the ongoing large observing campaigns combining X-ray and UV spectroscopy provide a tomographic view of stellar winds. It is now established that X-ray radiation is modulated with stellar rotation and shows the same period as discrete absorption components (DACs) in the UV resonance lines. The latter are associated with corotating interaction regions (CIRs) in stellar winds, therefore the mechanisms responsible for generation of X-rays and CIRs appear to be physically linked. Binary massive stars

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Betancourt Kamenetskaia, Boris, Anja Brenner, Alejandro Ibarra, and Chris Kouvaris. "Proton capture in compact dark stars and observable implications." Journal of Cosmology and Astroparticle Physics 2023, no. 10 (2023): 027. http://dx.doi.org/10.1088/1475-7516/2023/10/027.

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Abstract Asymmetric dark matter under certain conditions could form compact star-like objects, which can be searched either through gravitational lensing or by observation of gravitational waves from binaries involving such compact objects. In this paper we analyze possible signatures of such dark stars made of asymmetric dark matter with a portal to the Standard Model. We argue that compact dark stars could capture protons and electrons from the interstellar medium, which then accumulate in the core of the dark star, forming a very hot gas that emits X-rays or γ-rays. For dark matter paramete

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Swartz, Douglas A., Jeremy J. Drake, Ronald F. Elsner, et al. "The Herbig Ae Star HD 163296 in X‐Rays." Astrophysical Journal 628, no. 2 (2005): 811–16. http://dx.doi.org/10.1086/429984.

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LaMassa, Stephanie M., T. M. Heckman, and A. Ptak. "DISENTANGLING AGN AND STAR FORMATION IN SOFT X-RAYS." Astrophysical Journal 758, no. 2 (2012): 82. http://dx.doi.org/10.1088/0004-637x/758/2/82.

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Robrade, J., and J. H. M. M. Schmitt. "Altair – the “hottest” magnetically active star in X-rays." Astronomy & Astrophysics 497, no. 2 (2009): 511–20. http://dx.doi.org/10.1051/0004-6361/200811348.

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Oskinova, Lidia M., Vasilii V. Gvaramadze, Götz Gräfener, Norbert Langer, and Helge Todt. "X-rays observations of a super-Chandrasekhar object reveal an ONe and a CO white dwarf merger product embedded in a putative SN Iax remnant." Astronomy & Astrophysics 644 (December 2020): L8. http://dx.doi.org/10.1051/0004-6361/202039232.

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The merger of two white dwarfs (WDs) is a natural outcome of the evolution of many binary stars. Recently, a WD merger product, IRAS 00500+6713, was identified. IRAS 00500+6713 consists of a central star embedded in a circular nebula. The analysis of the optical spectrum of the central star revealed that it is hot, hydrogen, and helium free, and it drives an extremely fast wind with a record breaking speed. The nebula is visible in infrared and in the [O III] λ5007 Å line images. No nebula spectroscopy was obtained prior to our observations. Here we report the first deep X-ray imaging spectros

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Green, Samuel, Jonathan Mackey, Thomas J. Haworth, Vasilii V. Gvaramadze, and Peter Duffy. "Thermal emission from bow shocks." Astronomy & Astrophysics 625 (April 29, 2019): A4. http://dx.doi.org/10.1051/0004-6361/201834832.

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The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60°2522. The young dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We ran 2D hydrodynamic simulations to model the interaction of the wind of the central star with the interstellar medium (ISM). The models cover a range of possible ISM number densities of n = 50−200 cm−3 and stellar velocities of v* = 20−40 km s−1. Synthetic Hα and 24 μm emission maps predict the same apparent spherical bubb

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Oskinova, L. M., R. Ignace, and D. P. Huenemoerder. "X-ray diagnostics of massive star winds." Proceedings of the International Astronomical Union 12, S329 (2016): 151–55. http://dx.doi.org/10.1017/s1743921317002952.

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AbstractObservations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-

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Owen, Ellis R., Kinwah Wu, Xiangyu Jin, Pooja Surajbali, and Noriko Kataoka. "Starburst and post-starburst high-redshift protogalaxies." Astronomy & Astrophysics 626 (June 2019): A85. http://dx.doi.org/10.1051/0004-6361/201834350.

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Quenching of star-formation has been identified in many starburst and post-starburst galaxies, indicating burst-like star-formation histories (SFH) in the primordial Universe. Galaxies undergoing violent episodes of star-formation are expected to be rich in high energy cosmic rays (CRs). We have investigated the role of these CRs in such environments, particularly how they could contribute to this burst-like SFH via quenching and feedback. These high energy particles interact with the baryon and radiation fields of their host via hadronic processes to produce secondary leptons. The secondary p

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Sidoli, Lara, and Adamantia Paizis. "Investigating High Mass X-ray Binaries at hard X-rays with INTEGRAL." Proceedings of the International Astronomical Union 14, S346 (2018): 178–86. http://dx.doi.org/10.1017/s1743921319001145.

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AbstractThe INTEGRAL archive developed at INAF-IASF Milano with the available public observations from late 2002 to 2016 is investigated to extract the X-ray properties of 58 High Mass X-ray Binaries (HMXBs). This sample consists of sources hosting either a Be star (Be/XRBs) or an early-type supergiant companion (SgHMXBs), including the Supergiant Fast X-ray Transients (SFXTs). INTEGRAL light curves (sampled at 2 ks) are used to build their hard X-ray luminosity distributions, returning the source duty cycles, the range of variability of the X-ray luminosity and the time spent in each luminosi

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Owocki, Stan P., Atsuo T. Okazaki та Gustavo Romero. "Modeling TeV γ-rays from LS 5039: an active OB star at the extreme". Proceedings of the International Astronomical Union 6, S272 (2010): 587–92. http://dx.doi.org/10.1017/s1743921311011471.

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AbstractPerhpas the most extreme examples of “Active OB stars" are the subset of high-mass X-ray binaries – consisting of an OB star plus compact companion – that have recently been observed by Fermi and ground-based Cerenkov telescopes like HESS to be sources of very high energy (VHE; up to 30 TeV!) γ-rays. This paper focuses on the prominent γ-ray source, LS5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical (e ≈ 0.24) orbit with its companion, assumed here to be a black-hole or unmagnetized neutron star. Using 3-D SPH simulations of the Bondi-Hoyle accretion

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Hoshi, Reiun. "Disk Accretion onto a Weakly Magnetized Neutron Star." Publications of the Astronomical Society of Japan 36, no. 4 (1985): 785–97. https://doi.org/10.1093/pasj/36.4.785.

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Abstract The structure of an accretion disk surrounding a weakly magnetized neutron star is investigated in a framework of the conventional α-model. We assume that the surface magnetic fields are so weak that the accretion disk extends down to the neutron star surface. We have found that the innermost region of the disk is optically thin. X-rays emerge from the inner portion of the optically thick disk which is located outside the optically thin inner region and from the neutron star surface. Observed spectra of several bright bulge sources (low-mass X-ray binaries) with the SPC detectors aboa

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Harding, A. K., J. J. Barnard, F. W. Stecker, and T. K. Gaisser. "Production and Interaction of High Energy Neutrinos in Close X-ray Binaries." Symposium - International Astronomical Union 125 (1987): 552. http://dx.doi.org/10.1017/s0074180900161376.

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Reports of air showers with E > 1015 eV from Cygnus X-3, LMC X-4, Vela X-1 and Hercules X-1 have been interpreted as requiring production of neutral secondaries by cosmic rays accelerated by the compact partner in these systems. If neutral pions are the source of photons that produce the observed air showers, then charged pions must also be produced, and they will give rise to neutrinos. We consider limits that may be placed on binary systems like Cygnus X-3 in which a neutron star is a strong source of ultra-high energy (UHE) particles that produce photons, neutrinos and other secondary pa

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Washinoue, Haruka, Shinsuke Takasao, and Kenji Furuya. "Effect of Time-varying X-Ray Emission from Stellar Flares on the Ionization of Protoplanetary Disks." Astrophysical Journal 976, no. 1 (2024): 25. http://dx.doi.org/10.3847/1538-4357/ad7fdf.

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Abstract X-rays have significant impacts on cold, weakly ionized protoplanetary disks by increasing the ionization rate and driving chemical reactions. Stellar flares are explosions that emit intense X-rays and are the unique source of hard X-rays with an energy of ≳10 keV in the protoplanetary disk systems. Hard X-rays should be carefully taken into account in models as they can reach the disk midplane as a result of scattering in the disk atmospheres. However, previous models are insufficient to predict the hard X-ray spectra because of simplifications in flare models. We develop a model of

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Nazé, Yaël, Gregor Rauw, Myron A. Smith, and Christian Motch. "Deciphering hard disks." Proceedings of the International Astronomical Union 18, S361 (2022): 319–20. http://dx.doi.org/10.1017/s1743921322003003.

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AbstractSome Be stars were found to emit very bright and extremely hard thermal X-rays. This so-called γ Cas -star category is rapidly growing, showing that the phenomenon is far from being uncommon and its consequences on Be population feedback should be examined. The origin of this X-ray peculiarity is however much debated. In this contribution, we review the most recent observational clues and derive constraints on the cause of the phenomenon: properties of these stars (multiplicity status, photometric variability), X-ray reaction to disk changes, impact of stripped-star companions on the X

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Feigelson, Eric D., Philip J. Armitage, and Konstantin V. Getman. "Protoplanetary disks and hard X-rays." Proceedings of the International Astronomical Union 5, H15 (2009): 744. http://dx.doi.org/10.1017/s1743921310011312.

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The physics of protoplanetary disks and the early stages of planet formation is strongly affected by the level of ionization of the largely-neutral gas (Armitage 2009; Balbus 2009). Where the ionization fraction is above some limit around ~ 10−12, the magnetorotational instability (MRI) will ensue and the gas will become turbulent. The presence or absence of disk turbulence at various locations and times has profound implications for viscosity, accretion, dust settling, protoplanet migration and other physical processes. The dominant source of ionization is very likely X-rays from the host sta

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Shu, Frank H., and Hsien Shang. "Protostellar X-Rays, Jets, and Bipolar Outflows." Symposium - International Astronomical Union 182 (1997): 225–39. http://dx.doi.org/10.1017/s0074180900061672.

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We review the theory of x-winds in young stellar objects (YSOs). In particular, we consider how a model where the central star does not corotate with the inner edge of the accretion disk may help to explain the enhanced emission of X-rays from embedded protostars. We argue, however, that the departure from corotation is not large, so a mathematical formulation that treats the long-term average state as steady and axisymmetric represents a useful approximation. Magnetocentrifugally driven x-winds of this description collimate into jets, and their interactions with the surrounding molecular clou

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Rankin, John, Vadim Kravtsov, Fabio Muleri, et al. "X-Ray Polarimetry as a Tool to Constrain Orbital Parameters in X-Ray Binaries." Astrophysical Journal 962, no. 1 (2024): 34. http://dx.doi.org/10.3847/1538-4357/ad1991.

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Abstract X-ray binary systems consist of a companion star and a compact object in close orbit. Thanks to their copious X-ray emission, these objects have been studied in detail using X-ray spectroscopy and timing. The inclination of these systems is a major uncertainty in the determination of the mass of the compact object using optical spectroscopic methods. In this paper, we present a new method to constrain the inclination of X-ray binaries, which is based on the modeling of the polarization of X-rays photons produced by a compact source and scattered off the companion star. We describe our

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Gregory, S. G., K. Wood, and M. Jardine. "Why are accreting T Tauri stars less luminous in X-rays than non-accretors?" Proceedings of the International Astronomical Union 3, S243 (2007): 163–70. http://dx.doi.org/10.1017/s1743921307009520.

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AbstractAccreting T Tauri stars are observed to be less luminous in X-rays than non-accretors, an effect that has been detected in various star forming regions. To explain this we have combined, for the first time, a radiative transfer code with an accretion model that considers magnetic fields extrapolated from surface magnetograms obtained from Zeeman-Doppler imaging. Such fields consist of compact magnetic regions close to the stellar surface, with extended field lines interacting with the disk. We study the propagation of coronal X-rays through the magnetosphere and demonstrate that they a

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Kosmas, Odysseas, Theodora Papavasileiou, and Theocharis Kosmas. "Integral Fluxes of Neutrinos and Gamma-Rays Emitted from Neighboring X-ray Binaries." Universe 9, no. 12 (2023): 517. http://dx.doi.org/10.3390/universe9120517.

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Astrophysical plasma ejections (jets) are formed and powered by black holes that accrete material from their companion star in binary systems. Black hole X-ray binary systems constitute potential powerful galactic and extragalactic neutrino and gamma-ray sources. After being accelerated to highly relativistic velocities and subjected to various energy-consuming interactions, the lepto-hadronic content of the jets produces secondary particles such as pions and muons that decay to gamma-ray photons and neutrinos heading towards the Earth. In this work, we employ a jet emission model in order to

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MacFarlane, J. J. "Effects of X-rays on the ionization state of Be star winds." Symposium - International Astronomical Union 162 (1994): 202–3. http://dx.doi.org/10.1017/s0074180900214848.

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It is important to understand the ionization state of Be star winds for several reasons, including: (1) if known, mass loss rates can be determined from UV P Cygni profiles; (2) the radiation line driving force which accelerates the winds depends on the ionization distribution; and (3) analysis of line profiles, in conjunction with polarization data, can help assess the credibility of various hypotheses for the assymetric nature of Be star winds.

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Hamaguchi, Kenji, Hiroshi Murakami, Katsuji Koyama, and Shiro Ueno. "X-Ray Valiabilities from Protostars in the RCrA Molecular Cloud." Symposium - International Astronomical Union 188 (1998): 234–35. http://dx.doi.org/10.1017/s0074180900114913.

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R CrA molecular cloud, at a distance of 130pc(Marraco, Rydgren 1981), is one of the active low-to-middle mass star forming regions. The core of this cloud, named Coronet, contains five protostar candidates. In 1994, we observed the Coronet Cluster using the X-ray satellite ASCA, and discovered hard X-rays from protostar candidates(Koyama et al. 1996).

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Spaans, Marco, Aycin Aykutalp, and Seyit Hocuk. "The impact of metallicity and X-rays on star formation." Proceedings of the International Astronomical Union 6, S270 (2010): 507–10. http://dx.doi.org/10.1017/s1743921311000895.

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AbstractStar formation is regulated through a variety of feedback processes. In this study, we treat feedback by metal injection and a UV background as well as by X-ray irradiation. Our aim is to investigate whether star formation is significantly affected when the ISM of a proto-galaxxy enjoys different metallicities and when a star forming cloud resides in the vicinity of a strong X-ray source. We perform cosmological Enzo simulations with a detailed treatment of non-zero metallicity chemistry and thermal balance. We also perform FLASH simulations with embedded Lagrangian sink particles of a

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Kluźniak, W., M. Ruderman, J. Shaham, and M. Tavani. "Low Energy Galactic Center Gamma Rays from Low Mass X-Ray Binaries." Symposium - International Astronomical Union 136 (1989): 627–32. http://dx.doi.org/10.1017/s0074180900187121.

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The hard X-ray and low energy γ-ray emission from the galactic center region (GCR) has four components: a power-law continuum between 20/50 keV and 200/300 keV with a power-law photon index β in the range ~ 2.5 to ~ 3.1; a harder spectrum with β ~ 1.–1.5 between 200/300 keV and ~ 511 keV; a narrow electron-positron annihilation line at 511 keV, reported to disappear in less than < 1/2 yr, although the temporal variation is controversial; and an equally variable continuum emission between 511 keV and several MeV (“MeV bump”). All four have luminosities 1037–1038 erg s−1, if they are located

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Argiroffi, C., A. Maggio, T. Montmerle, et al. "V4046 Sgr: X-rays from accretion shock." Proceedings of the International Astronomical Union 9, S302 (2013): 46–47. http://dx.doi.org/10.1017/s1743921314001690.

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AbstractWe present results of the X-ray monitoring of V4046 Sgr, a close classical T Tauri star binary, with both components accreting material. The 360 ks long XMM observation allowed us to measure the plasma densities at different temperatures, and to check whether and how the density varies with time. We find that plasma at temperatures of 1–4 MK has high densities, and we observe correlated and simultaneous density variations of plasma, probed by O VII and Ne IX triplets. These results strongly indicate that all the inspected He-like triplets are produced by high-density plasma heated in a

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