机译:Studies of NGC 6720 with calibrated HST/WFC3 emission-line filter images. I. structure and evolution
Department of Physics and Astronomy, Vanderbilt University, Box 1807-B, Nashville, TN 37235, United States;
Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, United States;
Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apartado Postal 3-72, Michaoacán, 58090 Morelia, MexicoInstituto de Astronomia, Universidad Nacional Autónoma de México, Apdo, Postal 70-264, 04510 México D.F., Mexico;
instrumentation: miscellaneous; planetary nebulae: individual (Ring Nebula; NGC 6720);