In this study we analyze the Colour-Magnitude Diagram (CMD) and the Lu
minosity Function (LF) of the SMC cluster NGC 330 on the basis of the
new BV CCD photometry obtained by Vallenari et al. (1994) and the effe
ctive temperatures and bolometric magnitudes of a few supergiant stars
taken from Caloi et al. (1993) and Stothers and Chin (1992a,b). The m
ain goal of this study is to infer the kind of mixing taking place in
stellar interiors. To this aim we make use of three grids of stellar t
racks calculated with different schemes of mixing, namely classical se
miconvection (Bressan et al. 1993), full overshoot (Bressan et al. 199
3; Fagotto et al. 1994), and diffusive overshoot (Deng 1994; Deng et a
l. 1994). All the models are fairly homogeneous as far as the remainin
g input physics is concerned (opacity, nuclear reactions, mass loss ra
tes), and are calculated with the new radiative opacities of Iglesias
et al. (1992). We adopt the colour excess E(B-V) = 0.06 and the true d
istance modulus (m - M)(o) = 18.85. The metallicity of the cluster is
highly uncertain: the observational determinations in fact go from Z =
0.0003 to Z = 0.006. The analysis of the CMD and LF is made by means
of isochrones and synthetic CMDs. These latter allow us to match the C
MD and the LF and to get an estimate of the slope x of the initial mas
s function (IMF) at the same time. With the assumed colour excess and
distance modulus, NGC 330 turns out to possess a metallicity slightly
lower than Z = 0.008 and an age a few 10(7) yr. However, we find that
a significant spread in the age is present. The CMD is compatible with
ages in the range 1 to 2.5 x 10(7) yr for semiconvective models, and
1 to 4.8 x 10(7) yr for full and diffusive overshoot models. Contrary
to what claimed by Caloi et al. (1993) and Stothers and Chin (1992a,b)
, no clear indication arises about the mixing scheme. Indeed, neither
the analysis of the integrated LF nor the location of the blue supergi
ant stars in the theoretical HRD are able to cast light on this point,
even though there is some marginal indication that full and/or diffus
ive overshoot models ought to be preferred. The study of the integrate
d LF suggests that the slope of the IMF is about x = 2.35 for semiconv
ective models, about x = 2.35 for full overshoot models, and x = 2.00
for those with diffusive overshoot.