Our understanding of the universe is never static. As new discoveries challenge long-held theories, we find ourselves constantly revising our picture of the cosmos. Few fields capture this dynamic process as vividly as astrochemistry, where chemistry and physics intersect to unravel the mysteries of stars and planets. My journey into this field began with a deep fascination for these two disciplines; as a student at Emory University, I found astrochemistry to be the perfect area to bridge these interests. Over time, this curiosity led me to Dr. Alissa Bans, an astrophysics lecturer at Emory University (as well as Director of Undergraduate Studies and Director of the Emory Observatory). It was under her mentorship that I came across the lithium enrichment phenomenon in K-G type red giant stars—a puzzle that, if solved, could reshape our models of stellar evolution.

Red giant stars, the remnants and future evolutions of main-sequence stars like our Sun, are expected to have depleted lithium levels due to the intense nuclear processes that occur as they evolve. Main sequence stars evolve to red giants as the hydrogen in their cores fuse to completion, initiating helium fusion. Conventional models predict trace amounts of lithium in older stars, as this evolutionary transition phase is associated with internal convection bringing lithium to the centre of the star to be destroyed in hot temperatures. However, in my investigations I found something unexpected.

It happened by accident. Dr. Bans was analysing a set of stars identified through the Disk Detective citizen project, an initiative that uses ALLWISE data from the Wide-Field Infrared Survey Explorer (WISE) mission to mark stellar objects for their excessive emission of light in the infrared regime. This infrared excess is typical of young stellar objects, Dr. Bans’ area of research and expertise, as it is indicative of the presence of circumstellar material. However, she realised that many old red giants were accidentally included in the set too, 144 to be exact, due to their unusually high infrared excess. Upon initial analysis, Dr. Bans and I noticed that many seemed to exhibit high lithium abundance. This anomaly not only challenges current models of stellar evolution but also opens up new avenues of inquiry into the processes governing these stars.

I dove headfirst into this intriguing problem, using spectroscopic data and creating a comprehensive Python algorithm to quantify lithium abundances in these stars. I searched for correlations that could explain their unusual characteristics. Infrared excess, rotational velocity, metallicity—each of these parameters became pieces of the puzzle as I sought to understand why these stars defied the standard models.

Working with optical spectra obtained from the FAST and REOSC spectrographs, I quantified the lithium absorption line at 6707.8 Angstroms. Through careful analysis, I identified which of these infrared excess red giants contained unusually high lithium levels. The observation of lithium enrichment and infrared excess characteristics in this specified set suggests that these stars may have undergone some kind of mass ejection event, possibly linked to the ingestion of a planet or brown dwarf, or a process akin to mass transfer in binary systems. My exploration was built on earlier research but took it a step further by identifying new links between these characteristics, helping to narrow down the possible explanations for this enrichment.

My findings were particularly striking when comparing the lithium abundance in these stars with their infrared excess. I was surprised to discover that 15% of those 144 K-G giants exhibited levels of lithium abundance far beyond what current theories allow—a huge percentage, given that typically only 1–2% of all existing K-G giants have been identified as presenting with peculiarly high lithium abundance (Holanda et al., 2020). This is a substantial increase over the expected percentage and suggests a strong correlation between the infrared excess and lithium enrichment—an idea that could point to previously unidentified processes at work. Plus, this relationship between lithium abundance and infrared excess in K-G giants has been observed before (Rebull et al. 2015) emphasising the significance of the correlation.

What makes this connection so captivating is that infrared excess can be an indicator of circumstellar material, such as a dust disk or mass ejection event (usually associated with young stellar objects like those of Dr. Bans’ research). Thus, in some of these lithium-enriched K-G giant stars, the lithium enrichment could be tied to mass loss through stellar winds or external accretion such as the engulfment of a nearby planet or brown dwarf. Alternatively, it might represent internal processes that are yet to be fully understood, such as thermal pulses or other short-lived phenomena during the late stages of stellar evolution.

Further analysis of the stars’ rotational velocities also added another dimension to this puzzle. Higher-than-expected rotational velocities in these stars could be evidence of angular momentum transfer, possibly from a nearby object that was engulfed. On the other hand, it could point to internal processes like rapid rotation triggering lithium production. By correlating rotational velocity with lithium levels, I identified potential links between these characteristics, suggesting that multiple mechanisms—both internal and external—could be driving the lithium enrichment. The results of my analysis revealed that all the lithium-enriched, infrared excess stars had projected rotational velocity in the same range, indicating all these objects fall in a similar location on the stellar evolutionary track. Because of this, these findings allude to lithium abundances being associated with a specific internal process that occurs at this stage in stellar evolution. Insignificant metal abundances found in my objects made the hypothesis of lithium enrichment due to engulfment of a nearby planet or brown dwarf null, further supporting the idea of a specific stellar evolutionary stage internal process creating excess lithium in my K-G giants.

But why was this discovery, this investigation, so important? Lithium is not just another element in the periodic table—it plays a crucial role in our understanding of stellar nucleosynthesis, the process by which stars produce heavier elements from lighter ones. If stars are producing more lithium than we thought, or if external processes are enriching their lithium, it forces us to rethink how these stars evolve and what mechanisms might be at play. My findings heavily suggest that mass ejection or other internal processes might be responsible for the lithium abundance phenomena—ideas that push the boundaries of current stellar evolution models.

The lithium enrichment phenomenon isn’t just an anomaly to be explained; it represents a crack in the foundation of established theories, a sign that we may need to adjust our understanding of how stars evolve. Science, after all, is built on the willingness to revisit old ideas in light of new data. As I delved deeper into the literature, I found that this has always been the case. From early work in the 1970s by Dr. Cameron and Dr. Fowler of NASA’s Goddard Space Institute on internal thermonuclear production of lithium, to more recent investigations by Dr. Rebull of CalTech into lithium anomalies in red giants, the scientific community has consistently returned to this puzzle, each time with new tools and insights.

Science is often a story of gradual progress, but sometimes, a single anomaly can trigger a deeper shift in our understanding. The presence of lithium-rich red giants, once thought to be a rare curiosity, may hold the key to unlocking new mechanisms of stellar evolution. By connecting my results with previous work and re-examining older models, I have sought to contribute to this evolving picture, pushing beyond the standard explanations to propose new ideas about how stars like these giants might develop. My research is one step in an ongoing journey, but it speaks to the broader nature of scientific discovery: the constant reevaluation, the testing of new hypotheses, and the search for deeper truths.

As our understanding of the universe evolves, so too does the technology we use to explore it. Much of my research relied on data from the Wide-field Infrared Survey Explorer (WISE) mission, as well as contributions from citizen scientists participating in the Disk Detective project. This kind of collaborative, data-driven research is emblematic of the technological advancements that are propelling the field of astrophysics forward. It is through these tools—space-based observatories, advanced spectrographs, and data analytics—that we can continue to challenge old models and push toward new frontiers.

The lithium enrichment phenomenon is more than just an interesting anomaly; it is a signpost pointing toward a future where our understanding of stellar evolution is richer and more complex than we ever imagined. The universe is vast and full of mysteries, and as we uncover more about it, we must be ready to revise, adapt, and innovate. This research represents one such revision—a small but significant adjustment to the way we think about stars. It is, in its own way, a “Liftoff” into new realms of knowledge.