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Post Info TOPIC: WZ Sagittae


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WZ Sge
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Title: WZ Sge: an eclipsing cataclysmic variable evolving towards the period minimum
Author: Z.-T. Han, S.-B. Qian, Irina Voloshina, L.-Y. Zhu

We present the photometric results of the eclipsing cataclysmic variable (CV) WZ Sge near the period minimum (P_min). Eight new mid-eclipse times were determined and the orbital ephemeris was updated. Our result shows that the orbital period of WZ Sge is decreasing at a rate of \dot{P}=-2.72(0.23) x 10^- 13 ss^-1. This secular decrease, coupled with previous detection of its donor, suggest that WZ Sge is a pre-bounce system. Further analysis indicates that the observed period decrease rate is about 1.53 times higher than pure gravitational radiation (GR) driving. We constructed the evolutionary track of WZ Sge, which predicts that P_min of WZ Sge is ~77.98(0.90) min. If the orbital period decreases at the current rate, WZ Sge will evolve past its Pmin after ~25.3 Myr. Based on the period evolution equation we find M_2 \simeq 4.04(0.10) x 10^-11 solar masses yr^-1, which is compatible with the current concept of CV evolution at ultrashort orbital periods.

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RE: WZ Sagittae
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Title: XMM-Newton and Swift observations of WZ Sge: spectral and timing analysis
Author: A.A. Nucita\inst (1,2), E. Kuulkers, F. De Paolis, K. Mukai, G. Ingrosso, B.M.T. Maiolo

WZ Sagittae is the prototype object of a subclass of dwarf novae, with rare and long (super)outbursts, in which a white dwarf primary accretes matter from a low mass companion. High-energy observations offer the possibility of a better understanding of the disk-accretion mechanism in WZ Sge-like binaries. We used archival XMM-Newton and Swift data to characterize the X-ray spectral and temporal properties of WZ Sge in quiescence. We performed a detailed timing analysis of the simultaneous X-ray and UV light curves obtained with the EPIC and OM instruments on board XMM-Newton in 2003. We employed several techniques in this study, including a correlation study between the two curves. We also performed an X-ray spectral analysis using the EPIC data, as well as Swift/XRT data obtained in 2011. We find that the X-ray intensity is clearly modulated at a period of about 28.96 s, confirming previously published preliminary results. We find that the X-ray spectral shape of WZ Sge remains practically unchanged between the XMM-Newton and Swift observations. However, after correcting for inter-stellar absorption, the intrinsic luminosity is estimated to be about 2.65X10^ 30 erg/s/cm^2 and 1.57X10^30 erg/s/cm^2 in 2003 and 2011, respectively. During the Swift/XRT observation, the observed flux is a factor of about 2 lower than that observed by XMM-Newton, but is similar to the quiescent levels observed various times before the 2001 outburst.

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WZ Sagittae is an unusual SU UMa star
Period of about 4400 days (?).
Magnitude range: 10.1 v - 19 V

WZ Sagittae.kmz

Position (2000): RA 20h 07m 36.53s, Dec +17 42' 15.3"


The discovery of a large disc of dust around a binary star system could force astronomers to rethink their computer models of the Universe.
Previous observations turned up no sign of the disc at WZ Sagittae.
But data from Nasa's Spitzer infrared telescope confirmed there was much more to this object than previously thought.
The discovery may have implications for the study of everything from supermassive black holes to the formation of planets.
The remarkable find around WZ Sagittae was made by teachers and students from across the US, working with scientists from the Spitzer Science Centre in California and the National Optical Astronomy Observatory in Tucson, Arizona.

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