@article{steffen2013mnras,
  title = {A wind-shell interaction model for multipolar planetary nebulae},
  author = {Steffen, Wolfgang and Koning, Nicholas and Esquivel, A and Garcia-Segura, G. and Garcia-Diaz, Ma. T. and Lopez, J.A. and Magnor, Marcus},
  journal = {Monthly Notices of the Royal Astronomical Society},
  volume = {436},
  number = {1},
  pages = {470--478},
  month = {Sep},
  year = {2013}
}