In a latest examine, an Italian astronomer has investigated the character of a binary system generally known as HD 49798/RX J0648.0–4418. Results of the brand new analysis, printed Dec. 24 on the preprint server arXiv, yield essential insights into the properties of the system, proving that it comprises a large and fast-spinning white dwarf.
HD 49798 is a vivid blue star within the southern sky, a subdwarf of O spectral kind (sdO), situated some 1,700 gentle years away. It is probably the most luminous recognized sdO, with an absolute magnitude of −0.24 and a bolometric luminosity of 4,400 photo voltaic luminosities. The efficient temperature of this star is estimated to be 47,500 Okay.
HD 49798 has been noticed for many years and its spectrum was discovered to showcase outstanding helium and nitrogen traces, whereas the star additionally skilled radial velocity variations. These findings indicated the presence of a companion object. However, its nature remained elusive.
More latest research have detected gentle X-ray emission with a extremely vital periodicity from the supply designated RX J0648.0–4418, positionally coincident with HD 49798. This periodicity steered the rotation of both a neutron star or a white dwarf. Now, a brand new evaluation of the obtainable knowledge performed by Sandro Mereghetti of the Institute of Space Astrophysics and Cosmic Physics of Milano in Italy, gives additional proof supporting the white dwarf situation.
“There are actually a number of arguments indicating that the companion of HD 49798 is a large white dwarf, with attention-grabbing implications for the long run evolution of this method,” Mereghetti wrote within the paper.
The examine discovered that the companion object is a white dwarf with a mass of 1.22 photo voltaic plenty and a spin interval of roughly 13.2 seconds, one of many shortest recognized amongst white dwarfs. Mereghetti defined that though the mass and spin interval of the companion are additionally appropriate with the neutron star situation, its X-ray luminosity, spin interval evolution and the scale of the X-ray emitting area point out a white dwarf nature.
According to the paper, the white dwarf emits pulsed X-rays with a really gentle spectrum, powered by accretion from the stellar wind of the subdwarf, which has a radius of about 1.08 photo voltaic radii and its mass is round 1.41 photo voltaic plenty. The orbital interval of HD 49798/RX J0648.0–4418 was measured to be roughly 1.55 days.
Mereghetti famous that HD 49798/RX J0648.0–4418 is the one recognized accretion-powered X-ray binary through which the mass donor is a sizzling subdwarf. Moreover, the white dwarf’s massive mass and excessive spin frequency, along with the subdwarf’s excessive luminosity, comparatively low floor gravity and peculiar chemical abundances, make HD 49798/RX J0648.0–4418 uncommon when in comparison with comparable programs.
“These properties make HD 49798/RX J0648.0–4418 notably attention-grabbing, not solely within the context of stellar evolution fashions, but in addition for the examine of sizzling subdwarfs and white dwarfs basically,” the creator of the paper concluded.
More data:
Sandro Mereghetti, The huge quick spinning white dwarf within the HD 49798/RX J0648.0-4418 binary, arXiv (2024). DOI: 10.48550/arxiv.2412.18546
Journal data:
arXiv
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Unusual binary system hosts a large fast-spinning white dwarf (2025, January 2)
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