Variable stars have been identified for the first time in Fornax 4 , the globular cluster located near the center of the Fornax dwarf spheroidal galaxy .
By applying the image subtraction technique to B,V time series photometry obtained with the MagIC camera of the 6.5-m Magellan/Clay telescope and with the wide field imager of the 4-m Blanco/CTIO telescope , we detected 27 RR Lyrae stars ( 22 fundamental mode , 3 first overtone , and 2 double-mode pulsators ) in a 2.4 ^ { \prime } \times 2.4 ^ { \prime } area centered on Fornax 4 .
The average and minimum periods of the ab- type RR Lyrae stars , \langle P _ { ab } \rangle = 0.594 d and P _ { ab,min } = 0.5191 d , respectively , as well as the revised position of the cluster in the horizontal branch type–metallicity plane , all consistently point to an Oosterhoff-intermediate status for the cluster , unlike what is seen for the vast majority of Galactic globular clusters , but in agreement with previous indications for the other globular clusters in Fornax .

The average apparent magnitude of the RR Lyrae stars located within 30 \arcsec from the cluster center is \langle V ( RR ) \rangle = 21.43 \pm 0.03 mag ( \sigma = 0.10 mag , average on 12 stars ) , leading to a true distance modulus of \mu _ { 0 } = 20.64 \pm 0.09 mag or \mu _ { 0 } = 20.53 \pm 0.09 mag , depending on whether a low ( { [ Fe / H ] } = -2.0 ) or a moderately high ( { [ Fe / H ] } = -1.5 ) metallicity is adopted .