  The group of lambda Bootis type stars comprises late B- to early F-type,
Population I objects which are basically metal weak, in particular the Fe group
elements, but with the clear exception of C, N, O and S. The present work is a
continuation of the studies by Paunzen et al. (1998, A&A, 335, 533), who
presented first results on the pulsational characteristics of the lambda Bootis
stars. Since then, we have observed 22 additional objects; we found eight new
pulsators and confirmed another one. Furthermore, new spectroscopic data
(Paunzen, 2001, A&A, 373, 633) allowed us to sort out misidentified candidates
and to add true members to the group. From 67 members of this group, only two
are not photometrically investigated yet which makes our analysis highly
representative. We have compared our results on the pulsational behaviour of
the lambda Bootis stars with those of a sample of delta Scuti type objects. We
find that at least 70% of all lambda Bootis type stars inside the classical
instability strip pulsate, and they do so with high overtone modes (Q <
0.020d). Only a few stars, if any, pulsate in the fundamental mode. Compared to
the delta Scuti stars, the cool and hot borders of the instability strip of the
lambda Bootis stars are shifted by about 25mmag, towards smaller (b-y)0. Using
published abundances and the metallicity sensitive indices of the Geneva
7-colour and Stroemgren uvbybeta systems, we have derived [Z] values which
describe the surface abundance of the heavier elements for the group members.
We find that the Period-Luminosity-Colour relation for the group of lambda
Bootis stars is within the errors identical with that of the normal delta Scuti
stars. No clear evidence for a statistically significant metallicity term was
detected.
