INVESTIGATION OF PAHs IN GALACTIC PLANETARY NEBULAE WITH THE AKARI/IRC AND THE SPITZER/IRS

Abstract

Polycyclic aromatic hydrocarbons (PAHs) in Galactic planetary nebulae (PNe) are investigated by means of the unidentified infrared (UIR) bands. Continuous near-to mid-infrared spectra of PNe are obtained with the AKARI /IRC and the Spitzer /IRS. All 19 PNe in the present study show prominent dust emissions and we investigate the variation in the intensity ratios among the UIR bands. The ionization fraction and the size distribution of PAHs in PNe are derived using the UIR band ratios. We find that the ionization fraction of PAHs in PNe is around 0.0-0.6 and that small PAHs are scarce. The present result indicates a systematic trend of the 3.4 µm aliphatic feature to become weak as the PAH ionization fraction increases.

Akari Observations of the Interstellar Medium

“…Furthermore, NIR spectroscopy maintains its high sensitivity even in the warm mission phase (Onaka et al, 2010b) although the spectral resolution is rather low (∼ 100 with the grism). It provides significant information on the various ice species (Shimonishi et al, 2010;Aikawa et al, 2012) and on the UIR band emission at 3.3-3.5 µm in a variety of objects (Boulanger et al, 2011;Kaneda et al, 2012;Ohsawa et al, 2012). In particular, the UIR bands in this spectral range contain unique information on the aromatic and aliphatic bonds in the band carriers (Kwok & Zhang, 2011;Jones, 2012).…”