Hubble Space Telescope Spectroscopy of a Planetary Nebula in an M31 Open Cluster: Hot-Bottom Burning at 3.4 M_⊙

We use imaging and spectroscopy from the Hubble Space Telescope (HST) to examine the properties of a bright planetary nebula (PN) projected within M31's young open cluster B477-D075. We show that the probability of a chance superposition of the PN on the cluster is small, less than or similar to 2%. Moreover, the radial velocity of the PN is the same as that of the cluster within the measurement error of similar to 10 km s(-1). Given the expected similar to 70 km s(-1) velocity dispersion in this region, similar to 8 kpc from M31's nucleus, the velocity data again make it extremely likely that the PN belongs to the cluster. Applying isochrone fitting to archival color-magnitude photometric data from the HST Advanced Camera for Surveys, we determine the cluster age and metallicity to be 290.Myr and Z =0.0071, respectively, implying an initial mass of 3.38(-0.02)(+0.03). for any PN produced by the cluster. From HST's Space Telescope Imaging Spectrograph observations and CLOUDY photoionization modeling, we find that the PN is likely a Type.I planetary, with a nitrogen abundance that is enhanced by similar to 5-6 times over the solar value scaled to the cluster metallicity. If the PN is indeed a cluster member, these data present strong empirical evidence that hot-bottom burning occurs in asymptotic giant branch stars with initial masses as low as 3.4 M-circle dot.