Abstract
We present a detailed photoionization model of the Ultra Compact H II (UCH II) region G29.96-0.02 based on the combined ISO SWS and LWS spectrum. Most of the observed line intensities are reproduced when G29.96-0.02 is described by a nebula with two different density regimes. We find that the ionizing star is cooler than the spectral type determined from near-IR measurements and that its age is ~ 3×10^6 yr, i.e., older than the expected lifetime of UCH II regions. Accurate abundances for the main elements are derived.
