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Dalnodar, Silvia. The ionization state of the halo planetary nebula NGC 2438. Planetary Nebulae: An Eye to the Future, Proceedings of the International Astronomical Union, IAU Symposium 283: 338–339. August 2012. Bibcode:2012IAUS..283..338D. arXiv:1109.5609. doi:10.1017/S1743921312011313.
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Dalnodar, Silvia. The ionization state of the halo planetary nebula NGC 2438. Planetary Nebulae: An Eye to the Future, Proceedings of the International Astronomical Union, IAU Symposium 283: 338–339. August 2012. Bibcode:2012IAUS..283..338D. arXiv:1109.5609. doi:10.1017/S1743921312011313.