  The study of chemically peculiar (CP) stars in open clusters provides
valuable information about their evolutionary status. Their detection can be
performed using the $\Delta a$ photometric system, which maps a characteristic
flux depression at $\lambda \sim 5200$ \AA. This paper aims at studying the
occurrence of CP stars in the earliest stages of evolution of a stellar
population by applying this technique to Hogg 16, a very young Galactic open
cluster (about 25 Myr). We identified several peculiar candidates: two B-type
stars with a negative $\Delta a$ index (CD-60 4701, CPD-60 4706) are likely
emission-line (Be) stars, even though spectral measurements are necessary for a
proper classification of the second one; a third object (CD-60 4703),
identified as a Be candidate in literature, appears to be a background B-type
supergiant with no significant $\Delta a$ index, which does not rule out the
possibility that it is indeed peculiar as the normality line of $\Delta a$ for
supergiants has not been studied in detail yet. A fourth object (CD-60 4699)
appears to be a magnetic CP star of 8 M$_\odot$, but obtained spectral data
seem to rule out this hypothesis. Three more magnetic CP star candidates are
found in the domain of early F-type stars. One is a probable nonmember and
close to the border of significance, but the other two are probably pre-main
sequence cluster objects. This is very promising, as it can lead to very strong
constraints to the diffusion theory. Finally, we derived the fundamental
parameters of Hogg 16 and provide for the first time an estimate of its metal
content.
