magnitude at minimum luminosity
[]For observations with Hipparcos, and for the preparatory
numerical simulations of the mission, 
magnitudes at maximum and minimum luminosities were computed from the
available luminosity curves (Mennessier & Figueras 1989). However, it
was considered more useful to the future user to give here the
magnitudes at maximum and minimum luminosities, rather than
the magnitudes. These magnitudes are those
of the GCVS except for some stars for which more precise observations
were available, and for the Mira stars. Indeed the GCVS gives the
maximum and minimum magnitudes observed for each star. Due to the
significant variability of Miras from one cycle to another one, it was
considered more appropriate to give here the mean magnitudes of the
luminosity extrema. A comparison of GCVS magnitudes with the mean
magnitudes of the luminosity extrema, obtained from 30 years of
observation for about 200 Miras by Campbell (1955), gives the following
statistical relations (where 
is the period, and
and 
are the magnitudes at maximum
and minimum luminosities given in the GCVS respectively):
