Photoionization Modelling of H II Region for Oxygen Ions

Abstract

We present phoionization model calculations of ionization fraction of hydrogen, helium and oxy-gen at low density of photoionized nebulae using the photoionization code CLOUDY. The ionization parameter is between -2.0 ≤ log(U) ≤ 1.0, and we study them by changing the abundances of oxy-gen from -2.5 ≤ log(O/H) ≤ -5.0. This was tested first by Campbell (1988) [1]. But, this was differ-ent in highest abundances of oxygen, filling factor and carbon abundances. We change the abun-dances of carbon by 0.5 dex of solar value, to avoid formation CO in the process. We include the charge transfer interaction between oxygen ions and hydrogen atom. Based on this process, we have calculated the ionization profiles of O 0 , O + , O 2+ O 3+ and O 4+ in the presence and absence of charge exchange between hydrogen and oxygen. In this work, we assumed the effective rate of co-efficient for the charge transfer is the order of ≈10 -9 cm -3 -s -1 .