K. Justtanont 1, M.J. Barlow 2, X.-W. Liu 2, R.J. Sylvester 2, & A.G.G.M. Tielens 3
1 Stockholm Observatory, 13336 Saltsjöbaden, Sweden Department of Physics and Astronomy
2 University College London, Gower Street, London, WC2E 6BT, UK Kapteyn Institute, P.O.Box 800, 9700 AV Groningen, The Netherlands
The LWS1 full grating scans of the PN, NGC 7027, and post-AGB objects, GL618 and GL2688 reveal a forest of lines which are identified as CO rotational lines. These lines are used as diagnostics for shock and PDR in these objects.
In a PDR model, the gas is heated by UV radiation from the central star while in a shock model, the gas is heated by shock waves. It is then cooled radiatively via atomic fine structure lines and molecular rotational lines. By observing CO emission from stars, their physical parameters can be derived.
For NGC 7027 and GL 618, the hot central star is the source of the ionizing
photons, creating a PDR. From the CO observations, we can estimate
the density of the molecular layer and conclude that the material
is clumpy. GL2688 is a cooler post-AGB star with evidence of
a fast wind. We used a dissociated shock model to derive the
shock velocity and the density. In agreement with earlier work,
we found that the molecular layer is warm (T
500K) and dense
(n
cm-3). This has implications on the last
stage of the evolution off the AGB. Mass loss is most likely to
be in the form of a superwind at the end of the AGB lifetime.
1 Presented on behalf of members of the ISO Post Main Sequence Specialist Astronomy Group : J.-P. Baluteau, M.J. Barlow, J. Cernicharo, M. Cohen, R.J. Cohen, P. Cox, R.J. Emery, E. Gonzales-Alfonso, C. Gry, T. Lim, X.-W. Liu, A. Omont, D. Péquinot, N.-Q. Rieu, B. Swinyard, R.J. Sylvester and Truong-Bach