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The structure and dynamics of the protoplanetary mebula M1-92

V.Bujarrabal tex2html_wrap_inline821 , J.Alcolea tex2html_wrap_inline821 , R.Neri tex2html_wrap_inline829
tex2html_wrap_inline821 Observatorio Astronómico Nacional (IGN), Apartado 1143, E-28800 Alcalá de Henares, Spain
tex2html_wrap_inline829 IRAM, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France

Abstract: We present high-resolution ( tex2html_wrap_inline985 ) maps of the tex2html_wrap_inline987 CO J=2-1 in the protoplanetary nebula M1-92, Minkowski's Footprint, obtained with the IRAM interferometer at Plateau de Bure, We confirm the main components found in our previous works: a central disk-like condensation, a bipolar double-shell structure with axial outwards velocity increasing with the distance to the star, and two opposed features at the tips of the nebula where the maximal deprojected velocity is attained, tex2html_wrap_inline991 kms tex2html_wrap_inline799 . The major quality of the present data allows to estimate the very small width of the double-shell walls, tex2html_wrap_inline995 ( tex2html_wrap_inline997 cm), and the diameter of the central disk, 2''-3'' (10 tex2html_wrap_inline1001 cm). The whole structure is probably the remnant of the previous AGB shell, after being shocked by the bipolar post-AGB jets. The mass of the molecular envelope is about 0.9 tex2html_wrap_inline1003 , and its kinetic momentum and energy (released by the wind interaction) are tex2html_wrap_inline1005 grcms tex2html_wrap_inline799 and tex2html_wrap_inline1009 erg, respectively. Since the interaction time must be significantly smaller than the age of the nebula, 900yr, these figures imply very energetic post-AGB jets that cannot be driven by radiation pressure. We also notice that the inner disk-like structure is too large for collimating the very narrow post-AGB jets. We propose that reaccretion of material, ejected during the previous AGB phase, is the most likely mechanism to explain the strongly bipolar and very energetic post-AGB ejections.

To appear in the Astrophysical Journal.