On the assessment of the nature of open star clusters and the
  determination of their basic parameters with limited data
  Our knowledge of stellar evolution and of the structure and chemical
evolution of the Galactic disk largely builds on the study of open star
clusters. Because of their crucial role in these relevant topics, large
homogeneous catalogues of open cluster parameters are highly desirable.
Although efforts have been made to develop automatic tools to analyse large
numbers of clusters, the results obtained so far vary from study to study, and
sometimes are very contradictory when compared to dedicated studies of
individual clusters. In this work we highlight the common causes of these
discrepancies for some open clusters, and show that at present dedicated
studies yield a much better assessment of the nature of star clusters, even in
the absence of ideal data-sets. We make use of deep, wide-field, multi-colour
photometry to discuss the nature of six strategically selected open star
clusters: Trumpler~22, Lynga~6, Hogg~19, Hogg~21, Pismis~10 and Pismis~14. We
have precisely derived their basic parameters by means of a combination of star
counts and photometric diagrams. Trumpler~22 and Lynga~6 are included in our
study because they are widely known, and thus provided a check of our data and
methodology. The remaining four clusters are very poorly known, and their
available parameters have been obtained using automatic tools only. Our results
are in some cases in severe disagreement with those from automatic surveys.
