L. Guzman-Ramirez, J. R. Rizzo, A. A. Zijlstra, C. García-Miró, C. Morisset, M. D. Gray. 2016. First Detection of 3He+ in the Planetary Nebula IC418. Monhtly Notices of the Royal Astronomical Society 460, 1, DOI: 10.1093/mnrasl/slw070
The He-3 isotope is important to many fields of astrophysics, including stellar evolution, chemical evolution, and cosmology. The isotope is produced in low-mass stars which evolve through the planetary nebula (PN) phase. He-3 abundances in PNe can help test models of the chemical evolution of the Galaxy. We present the detection of the He-3(+) emission line using the single dish Deep Space Station 63, towards the PN IC 418. We derived a He-3/H abundance in the range 1.74 +/- 0.8 x 10(-3) to 5.8 +/- 1.7 x 10(-3), depending on whether part of the line arises in an outer ionized halo. The lower value for He-3/H ratio approaches values predicted by stellar models which include thermohaline mixing, but requires that large amounts of He-3 are produced inside low-mass stars which enrich the interstellar medium (ISM). However, this overpredicts the He-3 abundance in H ii regions, the ISM, and protosolar grains, which is known to be of the order of 10(-5). This discrepancy questions our understanding of the evolution of the He-3, from circumstellar environments to the ISM.