End to End Modeling of a Planetary Nebula

As part of a project dealing with accurate determination of chemical abundances in Planetary Nebulae (PNe) using state-of-art modeling techniques and complete multiwavelength observational data sets, several papers have been published over the years.

In the latest in this series (A&A, vol.462, p179, 2007), while dealing with the case of the PN Hubble 5, a new genre of modeling methodology called an "end-to-end modeling" has been introduced FOR THE FIRST TIME which deals with not only the usual ionized zone but also a neutral zone and a photodissociation region (PDR) all packed together in a single structure. Molecules and dust grains have also been introduced in a self-consistent way. Background radiation sources (like Cosmic ray background and Galactic general background) have also been considered in the calculations for the first time

HST image of Hubble 5 (credit:
B.Balick, V.Icke, G.Mellema, & NASA)

During the trial phase of modeling, it was noticed that forming H2 molecules and getting them to emit the required amount of flux in the observed lines were quite tough. Only by adding a neutral zone containing lots of dust grains, and increasing the gas density [N(H)] at the outer edge, we could achieve the required emission in H2 lines. It was found that the Silicate grains and H2 molecules can exhibit a `synergy' which leads to strong emission in H2 molecular lines. Extending this idea in an intuitive way, the authors speculate that the total dust mass in the Galaxy could have been underestimated since H2 molecular emission is observed to be very strong in many different locales and the above-mentioned `synergy' could be the mechanism. (R. Surendiranath and S. R. Pottasch)