Variable stars in the Fornax dSph Galaxy. I. The Globular Cluster Fornax 4
C. Greco (1,2,3), G. Clementini (1), M. Catelan (4), E. V. Held (5),, E. Poretti (6), M. Gullieuszik (7), M. Maio (1), A. Rest (8), N. De Lee (9),, H. A. Smith (9), B. J. Pritzl (10) ((1) INAF - Osservatorio Astronomico di, Bologna, (2) Dipartimento di Astronomia

TL;DR
This study reports the first identification of variable stars in the Fornax 4 globular cluster, revealing its Oosterhoff-intermediate status and providing distance estimates based on RR Lyrae stars.
Contribution
The paper presents the first detection and analysis of variable stars in Fornax 4, using advanced image subtraction techniques to determine its Oosterhoff classification and distance.
Findings
27 RR Lyrae stars identified in Fornax 4
Fornax 4 classified as Oosterhoff-intermediate
Distance modulus estimated at ~20.6 mag
Abstract
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'x2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, <Pab>= 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…
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