The narrow-band Δa photometric system measures the flux depression at λ5200 Å by comparing the flux at the band centre to adjacent regions. It has been shown that virtually all peculiar stars with magnetic fields (mCPs) have significant positive Δa values (of up to +100 mmag), whereas Be/Ae/B[e] and metal weak stars (including lambda Bootis types) exhibit significant negative values of Δa. By using this photometric system we are therefore able to detect chemically peculiar (CP), emission types and metal-weak stars in an efficient way. The poster presented the first results of our survey of the Small Magellanic Cloud. In the selected field we found only 0.5 % of bona fide CP stars against 15 % in our Galaxy.
