|
We present a new photometric study of the globular cluster
NGC288 in Stromgren u, v, b, y, and H β system. We compare
our dataset with Bergbusch's (1993) to get the (b-y)-(B-V)
relation. The transformation relations are different from
those of Bond's (1980) and Anthony-Twarog & Twarog's (1994).
One of scientific goals of this study was to use Stromgren m1
index to investigate the metal content variation within
NGC288. This cluster is known to have an intermediate
metallicity but its color-magnitude diagram has a pure blue
horizontal branch, which is a signature of metal poor
stellar population. However, the large uncertainty in the m1
index calibration made it difficult for us to evaluate the
metallicity of cluster stars. Demarque and Yi's
isochrones (1996, private communication) were applied to
Bergbusch's dataset, and we obtained distance modulus of (m-
M)=14.9 ± 0.2, color excess of $E(B-V)=0.03$, and age
of 15 ± 3 Gyr. Vandenberg's (1985) isochrones for
Stromgren system were also applied to Bergbusch's and our
data. We find that the isochrone fits to different
photometric systems give rather inconsistant solutions.
The source of this discrepancy may become clear when the
Demarque and Yi's isochrones for Johnson system are converted
to those of Stromgren system. We note that Kurucz model
atmospheres provide a useful ground for this conversion work
as well as theoretical study of Stromgren characteristics
of globular cluster stars.
|