The mass and temperature distribution in the protoplanetary nebula M1-92: interferometric observations

V. Bujarrabal , J. Alcolea , R. Neri , M. Grewing
Observatorio Astronómico Nacional (I.G.N), Apartado 1143, E-28800 Alcalá de Henares, Spain
Institut de Radio Astronomie Millimétrique (IRAM), 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France
Abstract: We present high-resolution J=1-0 maps of the protoplanetary nebula M1-92, Minkowski's Footprint, obtained with the IRAM interferometer at Plateau de Bure. Previous J=1-0 maps and single-dish observations of the J=1-0, J=2-1 and J=3-2 transitions in both isotopic substitutions are also discussed. The cartography confirms the axial symmetry and complex structure already found from data. The gas velocity presents a dominant axial component that increases in absolute value from the center, up to a (de-projected) velocity of 70 kms . Most of the observed emission is at velocities clearly above the expected AGB expansion kinematics. This fact, together with a remarkable continuity found along the axis in the structure and velocity of the nebula, is interpreted as showing that the present CO nebula has been shaped by momentum transport from the fast post-AGB flow to the rest of the (AGB) envelope, probably by means of a bow-like shock.

The comparison of the different transitions is used to deduce the physical conditions in the molecular gas. Most of the observed (post-shock) material is found to have a low temperature of about 15K, indicating that the cooling processes are efficient after the passage of the shock. Typical densities of cm are deduced, corresponding to a total gas mass of about 1 M . This high value shows that most of the nebular material is molecular and probed by the CO observations. Therefore, our maps effectively represent the disruption of the AGB envelope by the passage of a shock, allowing a description of the physical conditions in the nebula during this evolutionary phase.