COSAM News Articles 2019 December Auburn Graduate Discovers a New Atomic Process First Proposed by Auburn Researcher in 2010: Potential to Drastically Change Models of Astrophysical Plasmas

Auburn Graduate Discovers a New Atomic Process First Proposed by Auburn Researcher in 2010: Potential to Drastically Change Models of Astrophysical Plasmas

Published: 12/17/2019

By: Maria Gebhardt

Dr. Ahmad Bassam Ahmed Nemer has found evidence of a new atomic process, First Evidence of Enhanced Recombination in Astrophysical Environments and the Implications for Plasma Diagnostics, which has just been published in Astrophysical Journal Letters.

The new recombination process was originally a purely theoretical prediction proposed in 2010 by an Auburn University faculty member Dr. Francis Robicheaux (now at Purdue University). Dr. Nemer’s research provides spectroscopic evidence of Rydberg Enhanced Recombination (RER) in Planetary Nebulae (PNe) and symbiotic stars.

The discovery has the potential to impact a wide array of applications including:

  • Interstellar and Intergalactic media,
  • Environments surrounding supermassive black holes at the center of every galaxy known as AGN, and
  • Measurements for elemental abundances of low temperature astrophysical plasmas with longstanding discrepancies based on methods also known as the Abundance Discrepancy problem.


“The first half of this project investigated the context for which this process would be relevant and based on that we would determine the best astrophysical environment to detect RER,” explained Dr. Nemer.

The research found the best candidate would include low temperature plasmas, and carbon ions would produce the greatest effects while being easily measured from ground telescopes.

“An extremely detailed model for the carbon ions was built to understand the emissions spectrum from these ions,” he added. “The predictions of this comprehensive atomic model that describes a low temperature astrophysical environment.”

The prediction indicated that a spectrum would exhibit emission lines from RER. These results were compared to multi-phase simulation results with observations of PNe.

“Our research team found an absolutely spectacular match between our model predictions and the observed spectra which marks the very first evidence of a completely new process,” Dr. Nemer said.

The applications of this discovery has direct impacts. First of all, this new research provides insight on fractional abundance of ions based on prediction models.

“RER is proven in our project to have a significant effect on the recombination rates that affect the ionization balance between charge states,” Dr. Nemer said. “Therefore, the accurate understanding of the relevant processes controls the accuracy of our fractional abundance prediction, and hence our ultimate assumptions about elemental abundances.”

Additionally, this research helps to understand chemical composition and formation of PNe.

“Planetary Nebulae are one of the late stages of stellar evolution cycle, and understanding the chemical composition provides information on their formation process, the characteristics of its progenitor, and can be used as a probe for stellar evolution and galaxy metallicity,” Dr. Nemer shared. “For example, the ratio of carbon to oxygen in the plasma is typically used as an indication of mixing processes in stars such as convection, and the research showed that the ratio changed by 15 percent in PNe due to RER.”

The applications of the research have the potential to change existing information and models.

“This project resulted in an array of important data including that RER and the emission lines it produces might provide a new tool to measure elemental abundances, which in turn has the potential to resolve this discrepancy,” Dr. Nemer explained.

Nemer graduated with his doctoral degree in physics from Auburn University and is now a postdoc in the Department of Astrophysical Sciences at Princeton University. His research area focused on theoretical atomic physics at Auburn, and his dissertation “Discovery of enhanced recombination in astrophysical environments and the implications for plasma diagnostics” focused on the study of PNe.

Collaborators on this project include:

  • Dr. Stuart Loch: Auburn University (Nemer’s advisor)
  • Dr. Mitch Pindzola: Auburn University
  • Dr. Nick Sterling: University of West Georgia, Carrollton, GA, USA
  • Dr. John Raymond : Center for Astrophysics Harvard & Smithsonian, Cambridge, MA, USA
  • Dr Andrea Dupree: Center for Astrophysics Harvard & Smithsonian, Cambridge, MA, USA
  • Dr. Jorge Garcia-Rojas
o            Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
o            Universidad de La Laguna, La Laguna, Tenerife, Spain
  • Dr Qianxia Wang: Rice University, Houston, TX, USA
  • Dr. Connor Ballance: Queen's University of Belfast, Belfast, UK


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