We have surveyed four of the globular clusters in the Fornax dwarf galaxy ( clusters 1 , 2 , 3 , and 5 ) for RR Lyrae stars , using archival F555W and F814W Hubble Space Telescope observations .
We identify 197 new RR Lyrae stars in these four clusters , and 13 additional candidate horizontal branch variable stars .
Although somewhat restricted by our short observational baseline , we derive periods and light-curves for all of the stars in the sample , and calculate photometric parameters such as mean magnitudes and colours .
This is the first time that RR Lyrae stars in the Fornax globular clusters have been quantitatively identified and measured .
We find that the Fornax clusters have exceptionally large specific frequencies of RR Lyrae stars , in comparison with the galactic globular clusters .
It is likely that Fornax 1 has the largest specific frequency measured in any globular cluster .
In addition , the Fornax clusters are unusual in that their RR Lyrae populations possess mean characteristics intermediate between the two Oosterhoff groups defined by the galactic globular clusters .
In this respect the RR Lyrae populations in the Fornax clusters most closely resemble the field populations in several dwarf galaxies .
Fornax 5 has an unusually large fraction of RRc stars , and also possesses several strong RRe ( second overtone pulsator ) candidates .

With a large sample of horizontal branch variable stars available to us , we revise previous measurements of the horizontal branch morphology in each cluster .
The Fornax clusters most closely resemble the “ young ” galactic halo population defined by Zinn in that their horizontal branch morphologies are systematically redder than many galactic clusters of similar metallicity .
We also confirm the existence of the second parameter effect among the Fornax clusters , most markedly between clusters 1 and 3 .
The edges of the instability strip are well defined in several of the Fornax clusters , and we are able to make measurements of the intrinsic V - I colours of these edges .
Finally , we determine foreground reddening and distance estimates for each cluster .
We find a mean distance modulus to the Fornax dwarf of ( m - M ) _ { 0 } = 20.66 \pm 0.03 ( random ) \pm 0.15 ( systematic ) .
Our measurements are consistent with a line of sight depth of \sim 8 - 10 kpc for this galaxy , which is in accordance with its dimensions as measured in the plane of the sky .
This approximately spherical shape for Fornax is incompatible with tidal model explanations for the observed high internal stellar velocity dispersions in many dwarf spheroidal galaxies .
Dark matter dominance is suggested .