We present 29 \pm 1 classical Oe stars from RIOTS4 , a spatially complete , spectroscopic survey of Small Magellanic Cloud ( SMC ) field OB stars .
The two earliest are O6e stars , and four are earlier than any Milky Way ( MW ) Oe stars .
We also find ten Ope stars , showing He i infill and/or emission ; five appear to be at least as hot as \sim O7.5e stars .
The hottest , star 77616 , shows He ii disk emission , suggesting that even the hottest O stars can form decretion disks , and offers observational support for theoretical predictions that the hottest , fastest rotators can generate He ^ { + } -ionizing atmospheres .
Our data also demonstrate that Ope stars correspond to Oe stars earlier than O7.5e with strong disk emission .
We find that in the SMC , Oe stars extend to earlier spectral types than in the MW , and our SMC Oe/O frequency , 0.26 \pm 0.04 , is much greater than the MW value , 0.03 \pm 0.01 .
These results are consistent with angular momentum transport by stronger winds suppressing decretion disk formation at higher metallicity .
In addition , our SMC field Oe star frequency is indistinguishable from that for clusters , which is consistent with the similarity between rotation rates in these environments , and contrary to the pattern for MW rotation rates .
Thus , our findings strongly support the viscous decretion disk model and confirm that Oe stars are the high-mass extension of the Be phenomenon .
Additionally , we find that Fe ii emission occurs among Oe stars later than O7.5e with massive disks , and we revise a photometric criterion for identifying Oe stars to J - [ 3.6 ] \geq 0.1 .