[O II] electron density mapping applied to NGC 6826

Extract

The [O II]3726,3729Å doublet is sensitive to electron densities in the range 100 to 10⁴ cm^–3, typical of planetary nebulae, and thus provides an ideal tool for mapping the projected density structure. The first use of the imaging Fabry-Perot TAURUS-II to observe both the [O II] doublet lines, and hence map the electron density, is reported for NGC 6826. If sufficient spectral resolution is achieved both the [O II] lines can be resolved into separate components, opening the way to full 3-D density mapping of PN. Given the low finesse of the etalon and the low expansion velocity in NGC 6826 (10-15 kms^–1), this original hope could not be fulfilled. However, a restricted aim of seeing-limited electron density mapping was accepted.