Browsing by Author "Corwin, T. M."

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    Newly Discovered Variable Stars in the Golbular Cluster NGC 6864 (M75)
    (2005) Corwin, T. M.; Scott, N. J.; Catelan, Márcio; Smith, H. A.
    Using Alard's (2000) image-subtraction method, we recently discovered a number of new variables in this cluster, pointing to an unusual Oosterhoff-intermediate classification (Corwin et al. 2003). The present study also uses image subtraction with the data reported on in our previous analysis. This time, however, the image subtraction threshold was substantially reduced. This produced thousands of false identifications, but, in addition to the previoulsy known variables, we found four new variables, all very close to the cluster core. Here we present periods and light curves for the four new variables....
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    The Trimodal Horizontal Branch of M75 (NGC 6864)
    (2002) Catelan, Marcio; Borissova, J.; Ferraro, F. R.; Corwin, T. M.; Smith, H. A.
    Deep UBVI photometry for a large field covering the distant globular cluster M75 (NGC 6864) is presented. We confirm a previous suggestion (Catelan et al. 1998) that M75 possesses a bimodal horizontal branch (HB) bearing striking resemblance to the well-know case of NGC 1851. In addition, we detect a third, smaller grouping of stars may correspond to the upper part of a very extended, though thinly populated, blue tail. Thus M75 appears to have a trimodal HB. The presence of the "Grundahl jump" is verified using the broadband U filter.
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    Variable stars in the globular cluster M15
    (2006) Corwin, T. M.; Borissova, J.; Catelan, Marcio; Smith, H. A.; Kurtev, R.
    We present new BV CCD photometry for variables in the globular cluster M15. The photometry used was obtained with the image subtraction package ISIS. The data were acquired on an observing run in 2001 and range over 11 observing nights. For 32 previously known variables, we obtained period for the first time. Improved periods were obtained for 28 previously known variables, and 13 new variables were found. For some of the variables intensity- and magnitude-averaged B and V magnitudes, magnitude-averaged colors, and pulsation amplitudes were obtained using DAOPHOT to calibrate the ISIS light curves.