NBC News Scripts
WBAP-TV (Television station : Fort Worth, Tex.)
1954-12-31
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15 records were found.
The highly luminous (>1037 erg s−1) supersoft X-ray sources (SSSs) are believed to be Eddington-limited accreting white dwarfs undergoing surface hydrogen burning. The current paradigm for SSSs involves thermally unstable mass transfer from a 1–2 M⊙ companion. However, this model has never been directly confirmed and yet is crucial for the evolution of cataclysmic variables (CVs) in general, and for the establishment of SSSs as progenitors of Type Ia supernovae in particular. The key SSS is RX J0513.9 — 6951 which has recurrent X-ray outbursts every 100–200 d (lasting for ~40 d) during which the optical brightness declines by 1 mag. We present the first XMM observations of RX J0513.9 — 6951 through one of its optical low states. Our results show that as the optical low state progresses, the temperature and X-ray luminosity decrease, be...
We performed extensive, multi-wavelength observations of the prototypical symbiotic star Z Andromedae between 2000 and 2003, during a large eruption. The rise to optical maximum occurred in three distinct stages. During the first stage, the rise was very similar to an earlier, small outburst which we determined was due to a disk instability. In the second stage, an optically thick shell of material was ejected, and in the third stage, the shell cleared to reveal a white dwarf whose luminosity was roughly 10(4)L(circle dot). We suggest that the outburst was powered by an increase in the rate of nuclear burning on the white-dwarf surface, triggered by a sudden burst of accretion. This outburst thus combined elements of both dwarf novae and classical novae.
We describe the first results from a program of multi-wavelength monitoring of symbiotic binary stars in outburst. The prototypical symbiotic star Z Andromedae was observed extensively at radio, optical, far-UV, and X-ray wavelengths during its current (ongoing) outburst. These observations provide evidence for an initial obscuration or the source of ionizing radiation by an optically thick shell of material, outflow with velocities of 100s of km/s, plus collisional excitation and shock heating of the red-giant wind. In addition, the optical light curve reveals variability on time scales as short as days on both the rise to and decline from optical maximum.
We describe observational evidence for a new kind of interacting binary star outburst that involves both an accretion instability and an increase in thermonuclear shell burning on the surface of an accreting white dwarf. We refer to this new type of eruption as a combination nova. In late 2000, the prototypical symbiotic star Z Andromedae brightened by roughly 2mag in the optical. We observed the outburst in the radio with the VLA and MERLIN, in the optical both photometrically and spectroscopically, in the far-ultraviolet with FUSE, and in the X-rays with both Chandra and XMM-Newton. The 2 year long event had three distinct stages. During the first stage, the optical rise closely resembled an earlier, small outburst that was caused by an accretion disk instability. In the second stage, the hot component ejected an optically thick shel...
