The Sagittarius dSph globular cluster system: variable stars
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Date
2006
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Abstract
We have applied the image subtraction technique to images of four globular clusters which have been suggested to be associated with the Sagittarius dSph galaxy: Arp, NGC634, Palomar2 and Terzan. As a result we have a found a sizeable population of variable stars incluiding RR Lyrae and SX Phoenicis stars in the globular clusters Arp, NGC634 and Terzan. We do not confirm the presence of variable stars that has been previously claimed in Palomar2. In NGC634 we have found 19 RR Lyrae stars (six previously known), and 1 SXstar. Although the real amplitudes of all the variables are not completely determined, the Bailey diagram for the RRab stars, together with the mean of its periods <P_{ab}> = 0.639 d, confirm the Oosterhoff II classification for this cluster. In Arp 2 we have found 9 RRL stars (four previously known) and 3 SXPhe stars. If we only consider the mean period of the RRab stars, <P_{ab}> = 0.593 d, we can classify this cluster as Oosterhoff-intermediate. However, the Bailey diagram does not support this classification, because only one out of eight RRab stars are located in the intermediate region. The RRL specific frequency for this cluster is S_{RR} = 68.8, the highest of all Sagittarius-related globulars, which could be a hint that some of the studied RRL are not Arp members but rather Sagittarius field stars....