Astronomers discover the most metal-poor extreme helium star

Utilizing the Southern African Massive Telescope (SALT), astronomers have carried out high-resolution observations of a not too long ago detected excessive helium star designated EC 19529–4430. It turned out that EC 19529–4430 is essentially the most metallic poor among the many inhabitants of identified excessive helium stars. The discovering was reported in a research paper revealed April 5 on the pre-print server arXiv.

Excessive helium (EHe) stars are supergiants a lot bigger and warmer than the sun, however much less large. They’re virtually devoid of hydrogen, which is uncommon, as hydrogen is essentially the most plentiful chemical ingredient within the universe.

EHes are characterised by comparatively sharp and powerful traces of impartial helium, which signifies low floor gravities and atmospheres dominated by helium. In addition to helium, these stars even have vital quantities of carbon, nitrogen and oxygen. The First EHe star was detected in 1942.

EC 19529−4430 is a not too long ago found EHe within the Galactic halo, situated at a distance of about 15,500 light years. It has an effective temperature of 18,540 Ok and its floor seems to be composed primarily of carbon-nitrogen-oxygen (CNO)-processed helium.

A group of astronomers led by Simon Jeffery of the Armagh Observatory and Planetarium in Armagh, UK, has determined to additional examine EC 19529−4430 in an effort to shed extra gentle on its true nature. For this objective, they employed SALT’s Excessive Decision Spectrograph (HRS) and Robert Stobie Spectrograph (RSS).

SALT observations discovered that EC 19529−4430 has an efficient temperature of 20,700 Ok and an total metallicity at a stage of -1.3 dex. The nitrogen was discovered to be 1.2 dex overabundant, whereas carbon and oxygen had been measured to be 1.5 and 0.7 dex underabundant, respectively.

The research confirmed that the floor of EC 19529−4430 consists principally of CNO-processed helium. It additionally confirmed that the star belongs to the Galactic halo, which is in step with its low total metallicity, and is on a retrograde orbit. The astronomers added that no pulsations from this star have been recognized up to now.

All in all, the outcomes point out that EC 19529−4430 is essentially the most metal-poor EHe star detected to this point. Furthermore, it seems that additionally it is the best identified carbon-poor and nitrogen-rich EHe star.

Attempting to elucidate the origin of EC 19529−4430, the authors of the paper suppose that it’s almost definitely a results of a merger of two helium white dwarfs.

“It’s almost definitely that EC 19529−4430 shaped from the merging of two helium white dwarfs, which themselves shaped as a binary system some 11 billion years in the past, and that it’s going to evolve to turn out to be a core helium-burning EHe subdwarf,” the researchers conclude.

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