The mass and temperature distribution in the protoplanetary nebula M 1-92: CO interferometric observations
V. Bujarrabal 1,
J. Alcolea 1,
R. Neri 2 and
M. Grewing 2
Received 19 April 1996 / Accepted 23 July 1996
We present high-resolution 13 CO J =1-0 maps of the protoplanetary nebula M 1-92, Minkowski's Footprint, obtained with the IRAM interferometer at Plateau de Bure. Previous 12 CO 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 12 CO data. The gas velocity presents a dominant axial component that increases in absolute value from the center, up to a (deprojected) velocity of 70 km s-1. 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 15 K, indicating that the cooling processes are efficient after the passage of the shock. Typical densities of 3 104 - 2 105 cm-3 are deduced, corresponding to a total gas mass of about 1 . 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 present in the nebula during this evolutionary phase.
Key words: circumstellar matter stars: AGB and post-AGB planetary nebulae: individual: M 1-92 radio lines: stars
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998