B Eswar Reddy

IIA, Bengaluru

B Eswar Reddy is a Senior Professor and Dean of the Faculty of Sciences at the Indian Institute of Astrophysics, Bengaluru. He received his PhD in 1997 from IIA, and after six years of post-doctoral stints in the USA (the University of Texas Austin and Valparaiso University), he moved back to IIA, Bengaluru, as faculty. His research interests mainly revolve around the chemical tagging of stars to understand star evolution, nucleosynthesis aspects and the evolution of the galaxies. His work on the Milky Way Galaxy is well known for its chemical decomposition of the Galactic Disk into thin and thick disks and for discovering the He-flash as the source of high Li abundance among giants. He is also spearheading India's participation in the Thirty Meter Telescope International Observatory or TIO as the Programme Director of the India TMT centre. Elected as Fellow in 2023.

B Eswar Reddy

SESSION 3B - Lectures by Fellows/Associates

Praveen Chaddah, Gurugram

Evolution of the element lithium in the universe - A case of anomalously high lithium in red giant stars

Lithium (Li) is a light element with atomic number Z=3, known to have a primordial origin along with two other elements - H and He. The present Big Bang nucleosynthesis models with measured cosmological parameters predict Li abundance of A(Li) = log N (Li)/N(H) + 12 = 2.7 - dex . The predicted primordial value is a factor of 4 less than the Li abundance measured in the interstellar medium and very young stars (A(Li) = 3.3-dex), implying Li emichment over the cosmic time scale. Studies have identified a few sources: cosmic ray spallation, stellar explosions, nucleosynthesis, and star mass loss. Our focus is on Li in stars. Stars are known to be sinks of Li rather than producers, validated by both theory and general observations. The finding of a surprisingly large amount of Li in a few red giants has challenged the general understanding of Li evolution in stars. Sometimes, the value exceeds an order of magnitude more than the current ISM value and three to four orders more than the model predictions. The high amount of Li in red giants has been a puzzle for over four decades since its discovery in the early 1980s. Our recent efforts will be described in the talk while providing multiple pieces of evidence that lithium enhancement takes place during the helium flash, and Li-rich giants are common among He-core burning stars.

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