SIMBAD references

We have observed an ionized halo surrounding the planetary nebula Abell 36. It is barrel-shaped, with dimensions 4°x5°, which is 17 pcx21 pc at a distance of 240 pc. With an average Hα surface brightness of 0.8±0.2 rayleighs, the halo's total Hα flux, 8.3x10^–10 ergs.cm^–2.s^–1, exceeds that of the previously known inner part of the nebula by a factor of 30. The ionized mass of the halo is 48sqrt(ε) M_☉, where ε is the filling factor of the ionized gas. Velocity-resolved Hα spectra indicate that the halo is ambient interstellar matter and not matter ejected from the planetary nebula. The edges of the halo are evident in both 100 µm emission and red optical continuum.