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.

ABSTRACT
1. INTRODUCTION
2. OBSERVATION
3. RESULTS
4. DISCUSSION
REFERENCES

• R. OHSAWA(Department of Astronomy, Graduate School of Science, The University of Tokyo)
• T. ONAKA(Department of Astronomy, Graduate School of Science, The University of Tokyo)
• I. SAKON(Department of Astronomy, Graduate School of Science, The University of Tokyo)
• T. I. MORI(Department of Astronomy, Graduate School of Science, The University of Tokyo)
• I. YAMAMURA(Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science)
• M. MATSUURA(Department of Physics & Astronomy, University College London)
• H. KANEDA(Division of Particle and Astrophysical Sciences, G, Nagoya University)
• J. BERNARD-SALAS(Institut d'Astrophysique Spatiale, CNRS/Universite Paris-Sud)
• O. BERNE(Institut de Recherche en Astrophysique et Planetologie, Universite de Toulouse/CNRS)
• C. JOBLIN(Institut de Recherche en Astrophysique et Planetologie, Universite de Toulouse/CNRS)