×

UPSC Courses

DNA banner

DAILY NEWS ANALYSIS

  • 22 June, 2020

  • 8 Min Read

Extreme Helium Stars (EHe)

Detection of ?uorine in hot Extreme Helium Stars solves their evolution mystery

  • 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.

Mystery of EHe resolved

  • The origin and evolution of these Hydrogen deficient objects 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 do not match with that predicted for low mass evolved stars.
  • A study by the Indian Institute of Astrophysics (IIA) an autonomous institute of Department of Science and Technology which detected the presence of singly ionised ?uorine 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.

Evolution of EHe

  • The ?uorine abundances determined from singly ionized fluorine (F II) lines suggest a very high enrichment of ?uorine, about a factor of 100 to 10000 times higher than normal stars.
  • Clues to evolution of extreme helium stars require accurate determinations of their chemical composition, and the peculiarities, if any, become very important.
  • Fluorine plays a very crucial role in this regard to determine the actual evolutionary sequence of these hydrogen de?cient objects.
  • Severe ?uorine enrichment w.r.t normal stars (of the order of 800 − 8000) was observed in the cool EHes along-with the cooler classical hydrogen de?cient stars, the RCB variables (R Coronae Borealis Stars) hinting at close evolutionary connection between them.
  • The scientists explored the relationship of hot EHes (EHes having e?ective temperature ≥ 14000K), with the cooler EHes, based on their ?uorine abundance and spotted it in the former, thus establishing an evolutionary connection across a wide range of e?ective temperature.
  • High-resolution echelle spectra of 10 hot EHes were obtained from Hanle Echelle Spectrograph (HESP) mounted on the 2-m Himalayan Chandra Telescope at the Indian Astronomical Observatory (IAO) in Hanle, Ladakh, (remotely operated by IIA) including data from McDonald Observatory, USA, and ESO archives.
  • The varied range of observed ?uorine abundance across stars having similar atmospheric parameters points out the difference in the individual star’s evolution and the ensuing nucleosynthesis.
  • Particularly, the enrichment of ?uorine in the atmospheres of carbon-rich EHes and absence of the same in carbon-poor EHes suggest that ?uorine is profusely produced during the merger of a He-CO WD resulting in a carbon-rich EHe, whereas He-He WD merger that results in carbon-poor EHes does not account for ?uorine overabundance.
  • The detection of enhanced ?uorine abundances in the atmospheres of hot EHes solves a decade-old mystery about their formation.
  • It ?rmly places hot EHes in an evolutionary sequence with cool EHes and other hydrogen-deficient stars and zeros in on the evolutionary scenario, which involves the merger of two double degenerate white dwarfs (WDs).

Source: PIB


Sun, Solar Missions & Solar Phenomenon

Sun, Solar Missions & Solar Phenomenon Context: This topic is important for UPSE Prelims and Mains GS Paper3. Aurora An aurora also known as the polar lights or aurora polaris, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic&nb

Changes in the Prompt Corrective Action norms for bank

Changes in the Prompt Corrective Action norms for banks Context: This topic is important for UPSE GS Paper 3. What will commercial banks under scrutiny need to do to get out of the restrictions imposed by the central bank? The story so far: The RBI issued a notification on November 2 revising norms for commercial banks to be placed under t

Study on Countries’ commitment on Climate Change

Study on Countries’ commitment on Climate Change Context: This topic is important for UPSE GS Paper 3. The findings, while optimistic, come amidst the deliberations underway at Glasgow. How effective are climate change pledges made by countries in containing global warming?  A study published Friday in the journal Science fin

National Investment and Manufacturing Zones (NIMZ)

About National Investment and Manufacturing Zones (NIMZ) The Government of India (GoI) has announced a National Manufacturing Policy, 2011, with the objective of enhancing the share of manufacturing in GDP to 25% within a decade and creating 100 million jobs. NIMZs are one of the important instruments to achieve it. As per the Policy, &ldqu

International Financial Services Centre (IFSC)

What is an International Financial Services Centre (IFSC)? An IFSC caters to customers outside the jurisdiction of the domestic economy.  Such centres deal with flows of finance, financial products and services across borders.  London, New York and Singapore can be counted as global financial centres. 

Students Achievement

Search By Date

Newsletter Subscription
SMS Alerts