26 Sep 2022
A team of international astronomers, led by researchers at the Instituto de Astrofísica de Canarias, has discovered a surprising high lithium abundance in the atmosphere of the companion star of the millisecond binary pulsar PSR J1023+0038.
A millisecond binary pulsar is a type of binary system consisting of a low-mass companion star and a neutron star or pulsar with a rotation period of a few milliseconds.
Using high resolution spectroscopy taken with the Very Large Telescope (VLT) at the European Southern Observatory (ESO) in Paranal (Chile) and archival spectra from the William Herschel Telescope (WHT), the team has performed a detailed chemical analysis of the spectrum of the solar-type companion star of the millisecond binary pulsar PSR J1023+0038.
Astronomers found that the companion star is metal-rich star with very different abundances of chemical elements from the elemental abundances observed in companion stars in X-ray binaries and in stars in the solar neighbourhood. "We have surprisingly detected a higher amount of lithium than observed in stars with the same effective temperature, Population I stars and X-ray binaries," explains Tariq Shahbaz, IAC researcher and first author of the study.
According to the study, the pulsed gamma-ray emission that occurs in most millisecond binary pulsars involves a copious production of particles, some of which end up as part of the magnetised wind that emerges from the pulsar at high speed. "The impact of gamma rays and relativistic particle flow with the atmosphere of the companion star fragments the carbon, nitrogen and oxygen nuclei present and generates new lithium, which leads to an enhanced abundance of this chemical element," says Jonay González Hernández, researcher at the IAC and co-author of the study.
[Image]
The pulsar-state spectrum (black) and disc-state spectrum (blue) of the binary millisecond pulsar PSR J1023+0038 in the spectral region 6690–6730 Å, showing the Al I 6696 Å and Li I 6708 Å doublets. Note the contamination of the disc-state spectrum from the broad He II 6678 Å emission line arising from the accretion disc