Navegando por Assunto "Magnetic variable stars"

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    Breaking the Degeneracy in Magnetic Cataclysmic Variable X-Ray Spectral Modeling Using X-Ray Light Curves
    (IOP science) Belloni, Diogo; Rodrigues, Claudia Vilega; Schreiber, Matthias R.; Castro, Manuel; Costa, Joaquim Eduardo Rezende; Hayashi, Takayuki; Lima, Isabel de Jesus; Luna, Gerardo Juan Manuel; Martins, Murilo; Oliveira, Alexandre Soares de; Parsons, Steven G.; Silva, Karleyne Medeiros Gomes da; Stecchini, Paulo Eduardo; Stuchi, Teresa de Jesus; Zorotovic, Monica
    We present an analysis of mock X-ray spectra and light curves of magnetic cataclysmic variables using an upgraded version of the 3D cyclops code. This 3D representation of the accretion flow allows us to properly model total and partial occultation of the postshock region by the white dwarf as well as the modulation of the X-ray light curves due to the phase-dependent extinction of the preshock region. We carried out detailed postshock region modeling in a four-dimensional parameter space by varying the white dwarf mass and magnetic field strength as well as the magnetosphere radius and the specific accretion rate. To calculate the postshock region temperature and density profiles, we assumed equipartition between ions and electrons; took into account the white dwarf gravitational potential, the finite size of the magnetosphere, and a dipole-like magnetic field geometry; and considered cooling by both bremsstrahlung and cyclotron radiative processes. By investigating the impact of the parameters on the resulting X-ray continuum spectra, we show that there is an inevitable degeneracy in the four-dimensional parameter space investigated here, which compromises X-ray continuum spectral fitting strategies and can lead to incorrect parameter estimates. However, the inclusion of X-ray light curves in different energy ranges can break this degeneracy, and it therefore remains, in principle, possible to use X-ray data to derive fundamental parameters of magnetic cataclysmic variables, which represents an essential step toward understanding their formation and evolution.
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    Search for Magnetic Accretion in SW Sextantis Systems
    (IOP science) Lima, Isabel de Jesus; Rodrigues, Claudia Vilega; Lopes, Carlos Eduardo Ferreira; Szkody, Paula; Jablonski, Francisco José; Oliveira, Alexandre Soares de; Silva, Karleyne M. G.; Belloni, Diogo; Palhares, Matheus Soares; Shugarov, Sergey; Baptista, Raymundo; Almeida, Leonardo Andrade de
    SW Sextantis systems are nova-like cataclysmic variables that have unusual spectroscopic properties, which are thought to be caused by an accretion geometry having part of the mass flux trajectory out of the orbital plane. Accretion onto a magnetic white dwarf is one of the proposed scenarios for these systems. To verify this possibility, we analyzed photometric and polarimetric time-series data for a sample of six SW Sex stars. We report possible modulated circular polarization in BO Cet, SW Sex, and UU Aqr with periods of 11.1, 41.2, and 25.7 minutes, respectively, and less significant periodicities for V380 Oph at 22 minutes and V442 Oph at 19.4 minutes. We confirm previous results that LS Peg shows variable circular polarization. However, we determine a period of 18.8 minutes, which is different from the earlier reported value. We interpret these periods as the spin periods of the white dwarfs. Our polarimetric results indicate that 15% of the SW Sex systems have direct evidence of magnetic accretion. We also discuss SW Sex objects within the perspective of being magnetic systems, considering the latest findings about the demography, formation, and evolution of cataclysmic variables.