Green Bank Telescope observations of ³He⁺: planetary nebulae
Files
First author draft
Date
2021-03
Authors
Bania, Thomas M.
Balser, Dana S.
Version
First author draft
OA Version
Citation
T.M. Bania, D.S. Balser. 2021. "Green Bank Telescope Observations of $^3$He$^+$: Planetary Nebulae" The Astrophysical Journal: an international review of astronomy and astronomical physics, Volume 910, Issue 1, pp.73-73. https://doi.org/10.3847/1538-4357/abd543
Abstract
We use the Green Bank Telescope to search for ³He⁺ 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 ²H, ³He,
⁴He, and ⁷Li were produced in significant amounts and these abundances
have since been modified primarily by stars. Observations of ³He⁺ in H II
regions located throughout the Milky Way disk reveal very little variation in
the ³He/H abundance ratio -- the "³He Plateau" -- indicating that the net
effect of ³He production in stars is negligible. This is in contrast to much
higher ³He/H abundance ratios reported for some planetary nebulae. This
discrepancy is known as the "³He Problem". We use radio recombination lines
observed simultaneously with the ³He⁺ transition to make a robust
assessment of the spectral sensitivity that these observations achieve. We
detect spectral lines at ∼ 1 -- 2 mK intensities, but at these levels
instrumental effects compromise our ability to measure accurate spectral line
parameters. We do not confirm reports of previous detections of ³He⁺ in NGC
3242 nor do we detect ³He⁺ emission from any of our sources. This result
calls into question all reported detections of ³He⁺ emission from any
planetary nebula. The ³He/H abundance upper limit we derive here for NGC
3242 is inconsistent with standard stellar production of ³He and thus
requires that some type of extra mixing process operates in low-mass stars.