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Angular Expansion of Nova Shells

Nova shells can provide us with important information on their distance, their interactions with the circumstellar and interstellar media, and the evolution in morphology of the ejecta. We have obtained narrow-band images of a sample of five nova shells, namely DQHer, FHSer, TAur, V476Cyg, and V533Her, with ages in the range from 50 to 130 years. These images have been compared with suitable available archival images to derive their angular expansion rates. We find that all the nova shells in our sample are still in the free expansion phase, which can be expected, as the mass of the ejecta is 7-45 times larger than the mass of the swept-up circumstellar medium. The nova shells will keep expanding freely for time periods up to a few hundred years, reducing their time dispersal into the interstellar medium.