Green Bank Telescope Observations of ${\bf ^3He^{\bf +}}$: Planetary Nebulae
T. M. Bania, Dana S. Balser

TL;DR
This study uses the Green Bank Telescope to search for $^3He^+$ in planetary nebulae, finding no confirmed detections and challenging previous reports, which impacts understanding of stellar $^3He$ production.
Contribution
First sensitive search for $^3He^+$ in multiple planetary nebulae with non-detections, questioning prior detections and implications for stellar nucleosynthesis models.
Findings
No confirmed $^3He^+$ detections in the sample.
Instrumental effects limit spectral line measurement accuracy.
Results challenge standard stellar $^3He$ production theories.
Abstract
We use the Green Bank Telescope to search for emission from a sample of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009. During the era of primordial nucleosynthesis the light elements , , , and were produced in significant amounts and these abundances have since been modified primarily by stars. Observations of in H II regions located throughout the Milky Way disk reveal very little variation in the abundance ratio -- the " Plateau" -- indicating that the net effect of production in stars is negligible. This is in contrast to much higher abundance ratios reported for some planetary nebulae. This discrepancy is known as the " Problem". We use radio recombination lines observed simultaneously with the transition to make a robust assessment of the spectral sensitivity that…
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