Poster abstract details

We investigate the infrared emission bands from Polycyclic Aromatic Hydrocarbons (PAHs) in galactic planetary nebulae (PNe). Several studies have pointed out that the PAH band profiles vary with the object types, especially from interstellar to circumstellar environments. PAHs in PNe are assumed to be in transition from circumstellar PAHs to interstellar PAHs. Thus, investigation of PAHs in PNe are interesting for understanding of physical and chemical processes on PAHs. We obtain 84 near-infrared spectra of galactic PNe with the AKARI/IRC. For 31 of them, we retrieve mid-infrared spectra with the Spitzer/IRS from the Spitzer Heritage Archive. Evolved PNe are selected taking account of the temperature of their central stars, and the evolutionary phase is estimated by the emission line ratio [SIV]${}_{10.51}$/[NeII]${}_{12.81}$. As a result, we find that the strength of the PAH bands around 3$\,\mu$m relative to other mid-infrared PAH bands are significantly enhanced along with the PN evolution. In addition, we find that the band ratio of 3.4 to 3.3$\,\mu$m is also enhanced with evolution. Since these 3$\,\mu$m bands are believed to be attributed to C-H bonds in relatively small PAHs. For a consistent explanation, we propose that the increases indicate an unusual PAH processing, such as hydrogenation, on PAHs in evolved PNe.