Browsing by Author "Stetson, Peter B."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    New Variable Stars in CMa Globular Cluster Candidates
    (2011) Amigo, Pía; Catelan, Márcio; Stetson, Peter B.; Smith, Horace A.; Cacciari, Carla; Zoccali, Manuela
    We present the preliminary results of an image-subtraction analysis of the Galactic globular cluster M79 (NGC 1904), as well as a new investigation of the variable star population in NGC 1851. Both M79 and NGC 1851 have been previously associated with the Canis Major overdensity, which has been suggested to have an extragalactic origin. We found 6 new RR Lyrae in M79, and also recovered 3 previously known RR Lyrae. The average period of the 5 ab-type RR Lyrae is 0.68 d, corresponding to an Oosterhoff II classification -- which is unusual, though not unprecedented, for systems of extragalactic origin. We also report on the discovery of at least 4 previously unknown variables in NGC 1851....
  • Thumbnail Image
    Item
    RR Lyrae Variables in NGC 2808
    (2011) Kunder, Andrea; Stetson, Peter B.; Catelan, Marcio; Amigo, Pía; de Propris, Roberto
    NGC 2808 is a unique globular cluster with not only a bimodal-horizontal branch (HB) but also with gaps on the blue horizontal branch. Adequate interpretation of the nature of the detected peculiarities in "bimodal" and "gap" clusters is of paramount importance for understanding the nature of the second parameter phenomenon and scenarios for the formation of the Galaxy. Although RR Lyrae variables are HB stars that can provide powerful constraints to models on the origin of bimodal HBs, unfortunately, until recently, only one RR Lyrae variable was known in this cluster. Here we present the first calibrated time-series CCD photometry for newly discovered fundamental mode RR Lyrae variables in NGC 2808, with observations over a range of twenty years. Investigations of RR Lyrae variable stars in this peculiar, bimodal-horizontal branch globular cluster are carried out to account for its formation, and the effects of helium enrichment and differential reddening. The Oosterhoff classification of NGC 2808, which has recently been associated with a previously unknown dwarf galaxy in Canis Major, is also discussed....
  • Thumbnail Image
    Item
    The GeMS/GSAOI galactic globular cluster survey (G4CS). I. A pilot study of the stellar populations in NGC 2298 and NGC 3201
    (2018) Monty, Stephanie; Puzia, Thomas H.; Miller, Bryan W.; Carrasco, Eleazar R.; Simunovic, Mirko; Schirmer, Mischa; Stetson, Peter B.; Cassisi, Santi; Venn, Kim A.; Dotter, Aaron