A&A Supplement series, Vol. 123, May II 1997, 83-92
Received August 5; accepted September 9, 1996
C. Jordi - E. Masana - F. Figueras - J. Torra
Send offprint request: C. Jordi;e-mail: carme@facjn0.am.ub.es
Departament d'Astronomia i Meteorologia, Universitat de Barcelona,
Avda. Diagonal 647, E-08028 Barcelona, Spain
In recent years, several authors have revised the calibrations used
to compute physical parameters
(
, 
, log g, [Fe/H])
from intrinsic colours in the 
photometric system.
For reddened stars, these intrinsic colours can be computed through the
standard relations among colour indices for each of the regions
defined by Strömgren (1966) on the HR diagram.
We present a discussion of the coherence of these calibrations for main-sequence stars. Stars from open clusters are used to carry out this analysis. Assuming that individual reddening values and distances should be similar for all the members of a given open cluster, systematic differences among the calibrations used in each of the photometric regions might arise when comparing mean reddening values and distances for the members of each region.
To classify the stars into Strömgren's regions we extended the algorithm presented by Figueras et al. (1991) to a wider range of spectral types and luminosity classes.
The observational ZAMS are compared with the
theoretical ZAMS from stellar evolutionary models, in the
range 
K. The discrepancies are also discussed.
keywords: stars: fundamental parameters -- open clusters and associations: general -- stars: distances -- HR diagram -- stars: general -- techniques: photometric