2005MNRAS.359.1386C

The core of planetary nebula NGC 6302 is filled with high-excitation photoionized gas at low expansion velocities. It represents a unique astrophysical situation in which to search for hyperfine structure (HFS) in coronal emission lines from highly ionized species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing [Alvi] 3.66 µm ³P₂⟵³P₁, obtained with Phoenix on Gemini South at resolving powers of up to 75000, resolve the line into five hyperfine components separated by 20-60 km/s as a result of the coupling of the I= 5/2 nuclear spin of ²⁷Al with the total electronic angular momentum J. The isotope ²⁶Al has a different nuclear spin of I= 5, and a different HFS, which allows us to place a 3σ upper limit on the ²⁶Al/²⁷Al abundance ratio of 1/33. We measure the HFS magnetic dipole coupling constants for [Alvi], and provide the first estimates of the electric quadrupole HFS coupling constants obtained through astronomical observations of an atomic transition.