Extreme helium star

• A study by the Indian Institute of Astrophysics (IIA) which detected the presence of singly ionised fluorine for the first time in the atmospheres of hot Extreme Helium Stars makes a strong case that the main formation of these objects involves a merger of a carbon-oxygen (CO) and a Helium (He) white dwarf.

About:

• An extreme helium star or EHe is a low-mass supergiant that is almost devoid of hydrogen, the most common chemical element of the universe.

• There are 21 of them detected so far in our galaxy.

• The origin and evolution of these Hydrogen deficient objects have been shrouded in mystery.

• Since there are no known conditions where stars devoid of hydrogen can be formed from molecular clouds, it is theorized that they are the product of the mergers of helium-core and carbon-oxygen core white dwarfs.

Hydrogen-Deficient Stars:

• Extreme helium stars form a sub-group within the broader category of hydrogen-deficient stars.

• The latter includes cool carbon stars like R Coronae Borealis variables, helium-rich spectral class O or B stars, population I Wolf–Rayet stars, AM CVn stars, white dwarfs of spectral type WC, and transition stars like PG 1159.