Navegando por Autor "Rodrigues, Claudia Vilega"
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Item 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, MonicaWe 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.Item Modelagem da Variável Cataclísmica Polar 1RXS J174320.1-042953 = V3704 Oph(2022-05-30) Oliveira, Alexandre Soares de; Rodrigues, Claudia Vilega; Oliveira Filho, Irapuan Rodrigues de; Oliveira, Sergio Pilling Guapyassu de; Carciofi, Alex Cavaliéri; Jablonski, Francisco José; Martins, Murilo; São José dos CamposAs variáveis cataclísmicas são sistemas binários, de curto período orbital, formados por uma estrela próxima à sequência principal que transfere matéria para a companheira anã branca. Nas polares, subclasse desses sistemas, a matéria trans- ferida se conecta às linhas do intenso campo magnético da anã branca, formando uma coluna de acreção que conduz a matéria até um choque na sua superfície. Na coluna de acreção e na região do choque é emitida intensa radiação ciclotrônica e em raios-X moles. Nesta tese apresentamos os resultados da modelagem de dados ópticos de fluxo total e fluxo polarizado, juntamente com dados de raios-X, da po- lar 1RXS J174320.1-042953 (= V3704 Oph). A modelagem foi feita com o código CYCLOPS (CYCLOtron emission of PolarS ), que calcula a emissão radiativa de uma região pós-choque tridimensional e não-homogênea, a fim de estimar parâme- tros físicos e geométricos do sistema. Encontramos degenerescência no conjunto de parâmetros quando aplicamos a modelagem a dados de bandas individuais ou ex- clusivamente aos dados de raios-X. Essa degenerescência foi quebrada ao modelar o conjunto completo de dados simultaneamente, resultando em um modelo que apre- senta baixa inclinação, com ?? ˜ 21°, campo magnético no polo da anã branca com valor de 12 ????, considerado baixo para sistemas polares, e alta massa para a anã branca, ?????? ˜ 1,36 ???. Essa massa é incomum entre as anãs brancas em sistemas binários, que caso confirmada tornaria V3704 Oph um objeto de destaque entre as polares.Item 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 deSW 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.Item The contact binary system TYC 7275-1968-1 as seen by optical, UV and X-ray observations(Elsevier) Lima, Isabel de Jesus; Mattiuci, Ana Carolina; Luna, Gerardo Juan Manuel; Oliveira, Alexandre Soares de; Rodrigues, Claudia Vilega; Palivanas, Natália; Nuñez, Natalia EdithWe present an analysis of publicly available X-ray and optical observations of TYC 7275-1968-1, a contact binary, red nova progenitor candidate. The long optical time series of ASAS-3, SuperWASP, CRTS, Gaia, ASASSN, and TESS enabled us to improve its orbital period to 0.3828071 ± 0.0000026 d. We show the presence of an X-ray and UV source associated with TYC 7275-1968-1 from Neil Gehrels Swift Observatory, that was previously assumed to be the counterpart of CD -36 8436 (V1044 Cen), a symbiotic star located 22 arcsec from the red nova candidate. The X-ray data indicate the presence of a region with a temperature of 𝑘𝑇 = 0.8+0.9 −0.1 keV and a luminosity of 1.4+0.1 −0.2 × 1031 erg s−1 in the range 0.3 – 10 keV. The detection of X-rays and modulated UV emission suggests that both components of the binary are chromospherically active.