Marildo G. Pereira

The Orbital Period of the Accreting Pulsar GX 1+4

We report strong evidence for a approximately 304 day periodicity in the spin history of the accretion-powered pulsar GX 1+4 that is most probably associated with the orbital period of the system. We have used data from the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory to show a clear periodic modulation of the pulsar frequency from 1991 to date, in excellent agreement with the ephemeris proposed by Cutler, Dennis, & Dolan in 1986. Our results indicate that the orbital period of GX 1+4 is 303.8+/-1.1 days, making it the widest known low-mass X-ray binary system by more than 1 order of magnitude and putting this long-standing question to rest. A likely scenario for this system is an elliptical orbit in which the neutron star decreases its spin-down rate (or even exhibits a momentary spin-up behavior) at periastron passages due to the higher torque exerted by the accretion disk onto the magnetosphere of the neutron star. These results are not inconsistent with either the X-ray pulsed flux light curve measured by BATSE during the same epoch or the X-ray flux history from the All-Sky Monitor on board the Rossi X-Ray Timing Explorer.

Multi-band characterization of the hot Jupiters: WASP-5b, WASP-44b and WASP-46b

We have carried out a campaign to characterize the hot Jupiters WASP-5b, WASP-44b and WASP-46b using multiband photometry collected at the Observatorio do Pico Dos Dias in Brazil. We have determined the planetary physical properties and new transit ephemerides for these systems. The new orbital parameters and physical properties of WASP-5b and WASP-44b are consistent with previous estimates. In the case of WASP-46b, there is some quota of disagreement between previous results. We provide a new determination of the radius of this planet and help clarify the previous differences. We also studied the transit time variations including our new measurements. No clear variation from a linear trend was found for the systems WASP-5b and WASP-44b. In the case of WASP-46b, we found evidence of deviations indicating the presence of a companion but statistical analysis of the existing times points to a signal due to the sampling rather than a new planet. Finally, we studied the fractional radius variation as a function of wavelength for these systems. The broad-band spectrums of WASP-5b and WASP-44b are mostly flat. In the case of WASP-46b we found a trend, but further measurements are necessary to confirm this finding.

HS 2231+2441: an HW Vir system composed of a low-mass white dwarf and a brown dwarf

HW Vir systems are rare evolved eclipsing binaries composed by a hot compact star and a low-mass main-sequence star in a close orbit. These systems provide a direct way to measure the fundamental properties, e.g. masses and radii, of their components, hence they are crucial to study the formation of sdB stars and low-mass white dwarfs, the common-envelope phase, and the pre-phase of cataclysmic variables. Here we present a detailed study of HS 2231+2441, an HW Vir type system, by analysing BVR

Evidence for a 304-day orbital period for GX 1+4

_C

Discovery of Optical Pulsations in V2116 Ophiuchi ≡ GX 1+4

I

Analysis of the variability in the sdB star KIC 10670103: DFA approach

_C

Erratum: "The Orbital Period of the Accreting Pulsar GX 1+4" (ApJ, 526, L105 [1999])

photometry and phase-resolved optical spectroscopy. The spectra of this system, which are dominated by the primary component features, were fitted using NLTE models providing effective temperature Teff = 28500

Discovery of Optical Pulsations in V2116 Ophiuchi equivalent to GX 1+4

\pm

Sobre o mestrado profissional em astronomia da UEFS

500 K, surface gravity log g = 5.40

Usina de cincias: um espao pedaggico para aprendizagens mltiplas

\pm