X-ray spectrum (left panel) and pulse profiles in two power levels (proper panel) of HD 49798/RX J0648.0–4418. Credit score: arXiv (2024). DOI: 10.48550/arxiv.2412.18546
In a up to date learn about, an Italian astronomer has investigated the character of a binary gadget referred to as HD 49798/RX J0648.0–4418. Result of the brand new analysis, printed Dec. 24 at the preprint server arXiv, yield necessary insights into the houses of the gadget, proving that it comprises a large and fast-spinning white dwarf.
HD 49798 is a vibrant blue megastar within the southern sky, a subdwarf of O spectral sort (sdO), situated some 1,700 mild years away. It’s the maximum luminous identified sdO, with an absolute magnitude of −0.24 and a bolometric luminosity of four,400 sun luminosities. The efficient temperature of this megastar is estimated to be 47,500 Okay.
HD 49798 has been noticed for many years and its spectrum was once discovered to exhibit distinguished helium and nitrogen traces, whilst the megastar additionally skilled radial pace diversifications. Those findings indicated the presence of a spouse object. On the other hand, its nature remained elusive.
Newer research have detected comfortable X-ray emission with a extremely vital periodicity from the supply designated RX J0648.0–4418, positionally coincident with HD 49798. This periodicity urged the rotation of both a neutron megastar or a white dwarf. Now, a brand new research of the to be had information performed via Sandro Mereghetti of the Institute of House Astrophysics and Cosmic Physics of Milano in Italy, supplies additional proof supporting the white dwarf situation.
“There at the moment are a number of arguments indicating that the spouse of HD 49798 is a large white dwarf, with attention-grabbing implications for the long run evolution of the program,” Mereghetti wrote within the paper.
The learn about discovered that the spouse object is a white dwarf with a mass of one.22 sun plenty and a spin duration of roughly 13.2 seconds, some of the shortest identified amongst white dwarfs. Mereghetti defined that even supposing the mass and spin duration of the spouse also are suitable with the neutron megastar situation, its X-ray luminosity, spin duration evolution and the scale of the X-ray emitting area point out a white dwarf nature.
In line with the paper, the white dwarf emits pulsed X-rays with an excessively comfortable spectrum, powered via accretion from the stellar wind of the subdwarf, which has a radius of about 1.08 sun radii and its mass is round 1.41 sun plenty. The orbital duration of HD 49798/RX J0648.0–4418 was once measured to be roughly 1.55 days.
Mereghetti famous that HD 49798/RX J0648.0–4418 is the one identified accretion-powered X-ray binary by which the mass donor is a sizzling subdwarf. Additionally, the white dwarf’s huge mass and prime spin frequency, in conjunction with the subdwarf’s prime luminosity, reasonably low floor gravity and odd chemical abundances, make HD 49798/RX J0648.0–4418 atypical when in comparison to identical methods.
“Those houses make HD 49798/RX J0648.0–4418 specifically attention-grabbing, no longer simplest within the context of stellar evolution fashions, but in addition for the learn about of sizzling subdwarfs and white dwarfs generally,” the creator of the paper concluded.
Additional information:
Sandro Mereghetti, The huge rapid spinning white dwarf within the HD 49798/RX J0648.0-4418 binary, arXiv (2024). DOI: 10.48550/arxiv.2412.18546
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