We present B and V time-series photometry of Andromeda XXV , the third galaxy in our program on the Andromeda ’ s satellites , that we have imaged with the Large Binocular Cameras of the Large Binocular Telescope .
The field of Andromeda XXV is found to contain 63 variable stars , for which we present light curves and characteristics of the light variation ( period , amplitudes , variability type , mean magnitudes , etc . ) .
The sample includes 58 RR Lyrae variables ( 46 fundamental-mode - RRab , and 12 first-overtone - RRc , pulsators ) , three anomalous Cepheids , one eclipsing binary system and one unclassified variable .
The average period of the RRab stars ( \langle Pab \rangle = 0.60 \sigma = 0.04 days ) and the period-amplitude diagram place Andromeda XXV in the class of the Oosterhoff-Intermediate objects .
From the average luminosity of the RR Lyrae stars we derive for the galaxy a distance modulus of ( m-M ) _ { 0 } = 24.63 \pm 0.17 mag .
The color-magnitude diagram reveals the presence in Andromeda XXV of a single , metal-poor ( [ Fe/H ] = - 1.8 dex ) stellar population as old as \sim 10-12 Gyr traced by a conspicuous red giant branch and the large population of RR Lyrae stars .
We discovered a spherically-shaped high density of stars near the galaxy center .
This structure appears to be at a distance consistent with Andromeda XXV and we suggest it could either be a star cluster or the nucleus of Andromeda XXV .
We provide a summary and compare number and characteristics of the pulsating stars in the M31 satellites analyzed so far for variability .