{
  "id": "2012.11707",
  "version": "v1",
  "published": "2020-12-21T22:08:32.000Z",
  "updated": "2020-12-21T22:08:32.000Z",
  "title": "Green Bank Telescope Observations of ${\\bf ^3He^{\\bf +}}$: Planetary Nebulae",
  "authors": [
    "T. M. Bania",
    "Dana S. Balser"
  ],
  "comment": "Accepted for publication in The Astrophysical Journal",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "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 $\\sim$ 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-12-21T22:08:32.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "green bank telescope observations",
      "planetary nebula",
      "measure accurate spectral line parameters",
      "milky way disk reveal"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}