Using the South African Large Telescope (SALT), astronomers made high-resolution observations of the recently discovered extreme helium star called EC 19529-4430. EC 19529–4430 was found to be the most metal-deficient star in the known population of excess helium stars. The discovery was reported in a research paper published April 5 on the Preprocessing Server. arXiv.

Extreme helium (EHe) stars are supergiants; They are much larger and hotter than the Sun, but less massive. They are almost devoid of hydrogen; This is unusual because hydrogen is the most abundant chemical element in the universe.

EHes are characterized by relatively sharp and strong neutral helium lines; this indicates low surface gravity and an atmosphere dominated by helium. In addition to helium, these stars also contain significant amounts of carbon, nitrogen and oxygen. The first EHe star was discovered in 1942.

EC 19529−4430 is a newly discovered EHe in the Galactic halo located approximately 15,500 light-years away. Its effective temperature is 18,540 K, and its surface appears to consist mainly of helium treated with carbon-nitrogen-oxygen (CNO).

A team of astronomers led by Simon Geoffrey of the Armagh Observatory and Planetarium in Armagh, United Kingdom, decided to continue studying EC 19529-4430 to shed more light on its true nature. For this they used the SALT High Resolution Spectrograph (HRS) and the Robert Stobie Spectrograph (RSS).

SALT observations showed that EC 19529−4430 has an effective temperature of 20700 K and a total metallicity of −1.3 dex. The excess of nitrogen was determined as 1.2 dex, and the excess of carbon and oxygen was determined as 1.5 and 0.7 dex, respectively.

The study confirmed that the surface of EC 19529−4430 consists mainly of CNO-treated helium. The star was also confirmed to belong to a galactic halo and to be in a retrograde orbit, consistent with its low total metallicity. Astronomers added that no pulsations from this star have been detected yet.

Overall, the results show that EC 19529−4430 is the most metal-poor EHe star detected to date. It was also found to be the coldest EHe star, poor in carbon and rich in nitrogen. Trying to explain the origin of EC 19529-4430, the authors of the paper suggest that it is most likely the result of the merger of two helium white dwarfs.

“EC 19529-4430 is likely to have formed from the merger of two helium white dwarfs that formed as a binary system approximately 11 billion years ago and evolved to become the main helium-burning EHe subdwarf,” the researchers wrote. finalize. .