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HD 49798
Binary star system in the constellation Puppis From Wikipedia, the free encyclopedia
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HD 49798 is a binary star in the constellation Puppis about 521 ± 14 parsecs (1,699 ± 46 ly) from Earth. It has an apparent magnitude of 8.3, making it one of the brightest known O class subdwarf stars.[10]
HD 49798 was discovered in 1964 to be a rare hydrogen-deficient O class subdwarf, and was the brightest known at the time.[11] This was identified as a binary star, but the companion could not be detected visually or spectroscopically.[12]
The X-ray source RX J0648.0-4418 was discovered close to HD 49798's location in the sky. Only the space telescope XMM-Newton was able to identify the source. It is a white dwarf with about 1.3 solar masses, in orbit about HD 49798 and rotating once every 13 seconds;[13] this rotation is speeding up by 72.0±0.6 ns per year.[6] This is detected from the 13-second X-ray pulse, which results from the stellar wind accreting onto the compact object.[10] It has been proposed that the white dwarf is surrounded by a debris disk. In this model, the material of the disk would be funneled onto the poles of the dwarf via the magnetic field, which would explain the observed X-ray pulses.[10] This system is considered a likely candidate to explode as a type Ia supernova within a few tens of thousands of years.[14][15]
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