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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.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 Revised ephemeris and orbital period derivative of the supersoft X-ray source CAL 87 based on 34 yr of observations(Royal Astronomical Society) Stecchini, Paulo Eduardo Freire; Jablonski, Francisco José; Diaz, Marcos P.; D’Amico, Flávio; Oliveira, Alexandre Soares de; Palivanas, Natália; Saito, Roberto KalbuschIn this study, we present an analysis of over 34 yr of observational data from CAL 87, an eclipsing supersoft X-ray source. The primary aim of our study, which combines previously analysed measurements as well as unexplored publicly available data sets, is to examine the orbital period evolution of CAL 87. After meticulously and consistently determining the eclipse timings, we constructed an O − C (observed minus calculated) diagram using a total of 38 data points. Our results provide confirmation of a positive derivative in the system’s orbital period, with a determined value of s s−1. We observe a noticeable jitter in the eclipse timings and additionally identify a systematic delay in the X-ray eclipses compared to those observed in longer wavelengths. We discuss the interplay of the pertinent factors that could contribute to a positive period derivative and the inherent variability in the eclipses.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.