Browsing by Author "Pritzl, Barton J."

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    Deep HST photometry of NGC 6388
    (2006) Catelan, M.; Stetson, Peter B.; Pritzl, Barton J.; Smith, Horace A.; Kinemuchi, Karen; Layden, Andrew C.; Sweigart, Allen V.; Rich, R. M.
    Using the Hubble Space Telescope, we have obtained the first color-magnitude diagram (CMD) to reach the main-sequence turnoff of the Galactic globular cluster NGC 6388. From a comparison between the cluster CMD and that of 47 Tucanae, we find that the bulk of the stars in these two clusters have nearly the same age and chemical composition. On the other hand, our results indicate that the blue horizontal branch and RR Lyrae components in NGC 6388 are intrinsically overluminous, which must be due to one or more, still undetermined, noncanonical second parameter(s) affecting a relatively minor fraction of the stars in NGC 6388.
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    Erratum: "Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388" [Astron. J. 124, 949 (2002)]
    (2003) Pritzl, Barton J.; Smith, Horace A.; Catelan, Márcio; Sweigart, Allen V.
    In Tables 4 and 5, we inadvertently listed Modified Heliocentric Julian Dates instead of ordinary Heliocentric Julian Dates as indicated in the table headings. To make the listed dates match the table headings, 0.5 should be added to the listed dates. Corrected tables with ordinary Heliocentric Julian Dates are given below. We thank Christine Clement, who noticed this error and brought it to our attention....
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    Variable Stars in Metal-Rich Globular Clusters: NGC 6304 and NGC 6569
    (2002) Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.
    It has recently become evident that the RR Lyrae in metal-rich globular clusters ([Fe/H]> -1.0) have properties different from those of metal-rich RR Lyrae found in the field. In particular, they have longer periods than field RR Lyrae of similar metallicities, implying that the cluster RR Lyrae are more luminous than their field counterparts. Because RR Lyrae stars are major Population II standard candles, this finding has consequences for the ages of globular clusters and the galactic and extragalactic distance scales. We propose observations with the YALO telescope to obtain B,V CCD photometry of the RR Lyrae in the metal-rich globular clusters NGC 6304 and NGC 6569. These data will be used to obtain accurate periods and light curves for the RR Lyrae and will be compared to those in other systems to determine their relative luminosities. Direct comparisons will also be made to the other metal-rich globular clusters known to contain RR Lyrae.
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    Variable stars in the fornax dsph galaxy. I. The globular cluster fornax
    (2007) Greco, Claudia; Clementini, Gisella; Catelan, Marcio; Held, Enrico V.; Poretti, Ennio; Gullieuszik, Marco; Maio, Marcella; Rest, Armin; De Lee, Nathan; Smith, Horace A.; Pritzl, Barton J.
    Variable stars have been identified for the first time in Fornax 4, the globular cluster located near the center of the Fornax dwarf spheroidal galaxy. By applying the image-subtraction technique to B and V time series photometry obtained with the MagIC camera of the 6.5m Magellan Clay telescope and with the wide field imager of the 4 m Blanco CTIO telescope, we detected 27 RR Lyrae stars (22 fundamental-mode, 3 first-overtone, and 2 double-mode pulsators) in a 2.4' x 2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, < Pab > = 0: 594 days and P(ab,min) = 0.5191 days, respectively, as well as the revised position of the cluster in the horizontal branch type-metallicity plane, all consistently point to an Oosterhoff-intermediate status for the cluster, unlike what is seen for the vast majority of Galactic globular clusters, but in agreement with previous indications for the other globular clusters in Fornax. The average apparent magnitude of the RR Lyrae stars located within 3000 from the cluster center is < V(RR)> = 21.43 +/- 0.03 mag (sigma = 0.10 mag, average of 12 stars), leading to a true distance modulus of mu(0) = 20.64 +/- 0.09 mag or mu(0) = 20.53 +/- 0.09 mag, depending on whether a low ([Fe/H] = -2.0) or a moderately high ([Fe/H] = -1: 5) metallicity is adopted.