Detection of Fluorine in Hot Extreme Helium Stars Solves Their Evolution Mystery

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Detection of Fluorine in Hot Extreme Helium Stars Solves Their Evolution Mystery

  • An extreme Helium star (EHe) is a low mass supergiant.
  • It is almost devoid of hydrogen, the most common chemical element of the universe.
  • So far 21 of them have been detected in the galaxy.
  • The origin and evolution of EHe have been shrouded in mystery.


  • Their severe chemical peculiarities challenge the theory of well accepted stellar evolution as the observed chemical composition of these stars does not match with that predicted for low mass evolved stars.
  • A study by Indian Institute of Astrophysics (IIA) detected the presence of singly ionized fluorine for the first time in the atmosphere of hot Extreme Helium stars.
  • It 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.
  • Indian Institute of Astrophysics (IIA) is an autonomous institute of Department of Science and Technology.
  • The research published in astrophysical journal showed fluorine abundances determined from a singly ionized fluorine lines suggest a very high enrichment of fluorine.
  • The suggested enrichment ranges about a factor of 100 to 10000 times higher than normal stars.
  • Accurate determination of the chemical composition is required to find clues to evolution of extreme helium stars.
  • To understand evolutionary sequence of these hydrogen deficit objects, fluorine plays a crucial role.
  • By comparing the observed fluorine abundances with other abundances of key elements, the formation channels responsible for fluorine enrichment can be determined by the scientists.
  • Severe fluorine enrichment with respect to normal stars was observed in the cool EHes along with the cooler classical hydrogen deficient stars.
  • The scientists explored the relationship of hot EHes with the cooler EHes based on their fluorine abundance and spotted it in the former.
  • The detection of enhanced fluorine abundances in the atmospheres of hot EHes solves a decade old mystery about their formation.
  • It firmly places hit EHes in an evolutionary sequence with cool EHes and other hydrogen deficient stars and zeroes in on the evolutionary scenario.

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