Lithium rich red giants


Researchers at the Indian Institute of Astrophysics (IIA), an autonomous institute under the Department of Science &Technology, Govt. of India, have discovered hundreds of Li-rich giant stars indicating that Li is being produced in the stars and accounts for its abundance in the interstellar medium. They have also associated such Li enhancement with central He-burning stars, also known as red clump giants, thereby opening up new vistas in the evolution of the red giant stars.

About Lithium 

  • Lithium (Li), is one of the three primordial elements, apart from Hydrogen and Helium (He), produced in the big bang nucleosynthesis (BBN) whose models predict primordial Li abundance (A(Li) ~2.7~dex). However, the present measurement of Li in the interstellar medium and very young stars is about 4 times more than the primordial value.
  • Thus, identifying sources of Li enrichment in our Galaxy has been a great interest to researchers to validate Big Bang Nucleosynthesis as well as a stellar mixing process.
  • Apart from reactions, in which high energy cosmic ray particles bombard with heavier nuclei such as carbon and oxygen-producing lighter particles such as Li, stars are also proposed as likely Li source in the Galaxy. In general, stars are considered as Li sinks.
  • This means that the original Li, with which stars are born, only gets depleted over stars’ life-time as Li burns at relatively very low temperatures of about 2.5X106 K – a range which is easily encountered in stars.