Browsing by Author "Welch, D. L."

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    NGC 6304: a metal rich cluster with RR Lyrae?
    (2006) De Lee, Nathan; Catelan, Márcio; Layden, Andy; Pritzl, Barton; Smith, Horace; Sweigart, Allen; Welch, D. L.
    We have carried out a new search for variable stars in the metal-rich bulge globular cluster NGC 6304 ([Fe/H] = -0.59) using CCD observations obtained at CTIO. We used two data sets: one was taken on the 0.9m in May and June of 1996, and the second was taken on the 1m Yalo telescope in February and March of 2002. We have identified and obtained BVI light curves for 11 RR Lyrae stars, including 6 RRab and 5 RRc stars within the tidal radius of the cluster, and partial light curves for several long-period variables. Most of the RR Lyrae stars had been previously discovered, although not always recognized to be RR Lyrae type variables. We are able to exclude several RR Lyrae stars as probable field stars. In light of the large number of long-period RRab stars recently discovered within the metal-rich globular clusters NGC 6388 and NGC 6441, it is noteworthy that two of the possible RRab have periods greater than 0.8 days. The nature of these long-period RR Lyrae and the question of their membership will be discussed....
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    The globular cluster M 69: color-magnitude diagram and variable stars
    (2010) Escobar, M. E.; Catelan, Marcio; Zoccali, M.; Smith, H. A.; Pritzl, B. J.; Layden, A.; Gregorsok, J.; Welch, D. L.; Webb, T.
    We present BV photometry and the results of a search for stellar variability in the Galactic globular cluster M 69. The resulting color-magnitude diagram shows significant contamination by field stars. In our variability search we found 62 variable stars, 54 of which were new discoveries....