Do All Low-Mass Stars Undergo Extra Mixing Processes?

Standard stellar evolution models that only consider convection as a physical process to mix material inside of stars predict the production of significant amounts of He-3 in low-mass stars (M < 2 M-circle dot), with peak abundances of He-3/H similar to few x 10(-3) by number. Over the lifetime of the Galaxy, this ought to produce He-3/H abundances that diminish with increasing Galactocentric radius. Observations of He-3(+) in H II regions throughout the Galactic disk, however, reveal very little variation in the He-3 abundance with values of He-3/H similar to the primordial abundance, (He-3/H)(p) similar to 10(-5). This discrepancy, known as the "He-3 problem," can be resolved by invoking in stellar evolution models an extra mixing mechanism due to the thermohaline instability. Here we observe He-3(+) in the planetary nebula (PN) J320 (G190.3-17.7) with the Jansky Very Large Array to confirm a previous He-3(+) detection made with the Very Large Array that supports standard stellar yields. This measurement alone indicates that not all stars undergo extra mixing. Our more sensitive observations do not detect He-3(+) emission from - J320 with an rms noise of 58.8 mu Jy beam(-1) after smoothing the data to a velocity resolution of 11.4 km s(-1). We estimate an abundance limit of He-3/H <= 2.75 x 10(-3) by number using the numerical radiative transfer code NEBULA. This result nullifies the last significant detection of He-3(+) in a PN and allows for the possibility that all stars undergo extra mixing processes.