In general , H ii regions do not show clear signs of self-enrichment in products from massive stars ( M \geq 8 M _ { \odot } ) .
In order to explore why , I modeled the contamination with Wolf-Rayet ( WR ) star ejecta of metal-poor ( Z = 0.001 ) H ii regions , ionised either by a 10 ^ { 6 } -M _ { \odot } cluster of coeval stars ( cluster 1 ) , or a cluster resulting from continuous star formation at a rate of 1 M _ { \odot } yr ^ { -1 } ( cluster 2 ) .
The clusters have Z = 0.001 and a Salpeter initial mass function ( IMF ) from 0.1 to 120 M _ { \odot } .
Independent one dimensional constant density simulations of the emission-line spectra of unenriched H ii regions were computed at the discrete ages 1 , 2 , 3 , 4 , and 5 Myr , with the photoionisation code CLOUDY ( ) , using as input , radiative and mechanical stellar feedbacks predicted by the evolutionary synthesis code STARBURST99 ( ) .
Each H ii region was placed at the outer radius of the adiabatically expanding superbubble of ( ) .
For models with thermal and ionisation balance time-scales of less than 1 Myr , and with oxygen emission-line ratios in agreement with observations , the volume of the superbubble and the H ii region were uniformly and instantaneously polluted with stellar ejecta predicted by STARBURST99 .
I obtained a maximum oxygen abundance enhancement of 0.025 dex , with cluster 1 , at 4 Myr .
It would be unobservable .