S. Casassus , P. J. Storey , M. J. Barlow , and P. F. Roche
HYPERFINE SPLITTING OF [AL VI]3.66UM AND THE AL ISOTOPIC RATIO IN NGC6302 (Poster)

HYPERFINE SPLITTING OF [AL VI]3.66UM AND THE AL ISOTOPIC RATIO IN NGC6302

S. Casassus (1), P. J. Storey (2), M. J. Barlow (2), and P. F. Roche (3)
(1) Departamento de Astronomía, Universidad de Chile
(2) Department of Physics and Astronomy, University College London
(3) Physics Department, Oxford University

The core of planetary nebula NGC 6302 is filled with high-excitation photoionised 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 ionised species. HFS is otherwise blended by thermal or velocity broadening. Spectra containing [AlVI] 3.66$\mu$m $^3$P $_2 \leftarrow ^3$P$_1$, obtained with Phoenix on Gemini-South at resolving powers of up to 75000, resolve the line into five hyperfine components separated by 20 to 60 km ${\rm s}^{-1}$ due to the coupling of the $I=5/2$ nuclear spin of $^{27}$Al with the total electronic angular momentum $J$. $^{26}$Al has a different nuclear spin of $I=5$, and a different HFS, which allows us to place a 3 $\sigma$ upper limit on the $^{26}$Al/$^{27}$Al 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.