Observations obtained with the Spitzer Space Telescope and the WISE satellite have revealed a prominent arc-like structure at 50 ” ( \simeq 0.1 pc ) from the O9.5V/B0.5V system \sigma Ori AB .
We measure a total dust mass of 2.3 \pm 1.5 \times 10 ^ { -5 } M _ { \odot } .
The derived dust-to-gas mass ratio is \simeq 0.29 \pm 0.20 .

We attribute this dust structure to the interaction of radiation pressure from the star with dust carried along by the IC 434 photo-evaporative flow of ionized gas from the dark cloud L1630 .
We have developed a quantitative model for the interaction of a dusty ionized flow with nearby ( massive ) stars where radiation pressure stalls dust , piling it up at an appreciable distance ( \textgreater 0.1 pc ) , and force it to flow around the star .
The model demonstrates that for the conditions in IC 434 , the gas will decouple from the dust and will keep its original flow lines .
Hence , we argue that this dust structure is the first example of a dust wave created by a massive star moving through the interstellar medium .
Our model shows that for higher gas densities , coupling is more efficient and a bow wave will form , containing both dust and gas .

Our model describes the physics of dust waves and bow waves and quantitatively reproduces the optical depth profile at 70 \mu m. Dust waves ( and bow waves ) stratify dust grains according to their radiation pressure opacity , which reflects the size distribution and composition of the grain material .
It is found that in the particular case of \sigma Ori AB , dust is able to survive inside the ionized region .
Comparison of our model results with observations implies that dust-gas coupling through Coulomb interaction is less important than previously thought , challenging our understanding of grain dynamics in hot , ionized regions of space .

We describe the difference between dust ( and bow ) waves and classical bow shocks created by the interaction of a stellar wind with the interstellar medium .
The results show that for late O-type stars with weak stellar winds , the stand-off distance of the resulting bow shock is very close to the star , well within the location of the dust wave .
In general , we conclude that dust waves and bow waves should be common around stars showing the weak-wind phenomenon , i.e. , stars with log ( L / L _ { \odot } ) \textless 5.2 , and that these structures are best observed at mid-IR to FIR wavelengths , depending on the stellar spectral type .
In particular , dust waves and bow waves are most efficiently formed around weak-wind stars moving through a high density medium .
Moreover , they provide a unique opportunity to study the direct interaction between a ( massive ) star and its immediate surroundings .