The positions of the Cepheid variables V Cen and S Norm are marked
in the ,
and
,
diagrams of NGC 5662
(Fig. 15 (click here)) and NGC 6087 (Fig. 16 (click here)) respectively.
For these, we used the UBV data listed by Schaltenbrand & Tammann
(1971). The extremes of variability are also indicated.
Studies by Turner (1982) and more recently by Clariá\
et al. (1991) indicate that the Cepheid variable V Cen located in the
coronal region of NGC 5662 is a cluster member. Similarly, studies by
Feast (1957) and more recently by Turner (1986) and
Mermilliod et al. (1987) confirm that the Cepheid variable S Norm,
located near the optical centre of NGC 6087, is a cluster member. As the present
determination of distances to these clusters is accurate (since it is based on
the CCD photometry of the unevolved part of the cluster MS), it may be worth
while to discuss cluster membership of these variables in the light of
our new data. Our distance determinations for NGC 5662 and NGC 6087
provide the values of and -4.1 for V Cen and S Norm
respectively. These luminosities agree very well with the
corresponding values of -3.4 and -4.1 predicted from the
period-luminosity relation of classical Cepheids given by Madore &
Freedman (1991). The location of these Cepheids in the CM diagrams fits
very well with the stellar evolutionary isochrone appropriate for the average
age of their parent star clusters (see Figs. 15 (click here) and 16 (click here)).
The values of E(B-V) derived by Dean et al. (1978) are 0.29
and 0.18 mag for V Cen and S Norm respectively. These values agree fairly
well with the corresponding values of E(B-V) derived by us for NGC 5662
and NGC 6087 (see Sect. 6). All these various pieces of evidence strongly
suggest that the Cepheid variables V Cen and S Norm are indeed member of the
open star clusters NGC 5662 and NGC 6087 respectively.