NGC 7027: Probing the kinematics and excitation conditions of the warm molecular gas

Abstract

Tracking the mass-loss history of planetary nebulae (PNe) by means of molecular emission lines (mainly mm and sub-mm ranges) is fundamental to gain insight into the mechanism of nebular shaping. This is particularly important in cases such as NGC 7027, where most of the nebula is constituted by molecular gas (85% of a total of 1.4 M_⊙, see Fong et al. 2001).

To this aim, Herschel/HIFI provides an invaluable tool to probe warm molecular gas (~50-1000 K). It produces 1-D, high resolution spectra of the whole nebula (convolved with the telescope beam) in high-excitation molecular transitions (e.g. CO J=6–5, 10–9 and 16–15). Although the morphological information is therefore lost, the kinematics and the excitation conditions can be studied with unprecedented detail (see (see Bujarrabal et al. 2011).).

We have developed a code, shapemol, which, used along the existing SHAPE software (Steffen et al. 2010), implements spatiokinematical modeling with accurate non-LTE calculations of line excitation and radiative transfer in molecular species. The high quality of the data, together with this code, have allowed us to study, for the first time, the kinematics and excitation conditions of the warm gas of a PN with such a high-excitation.