Márcio Catelan

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The red-giant branch (RGB) in globular clusters is extended to larger brightness if the degenerate helium core loses too much energy in "dark channels." Based on a large set of archival observations, we provide high-precision photometry for the Galactic globular cluster M5 (NGC 5904), allowing for a detailed comparison between the observed tip of the RGB(More)
It has recently been suggested that the presence of multiple populations showing various amounts of helium enhancement is the rule, rather than the exception, among globular star clusters. An important prediction of this helium enhancement scenario is that the helium-enhanced blue horizontal branch (HB) stars should be brighter than the red HB stars which(More)
We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6441 using time-series BV photometry. The total number of variables found near NGC 6441 has been increased to ∼ 104, with 48 new variables being found in this survey. A significant number of the variables are RR Lyrae stars (∼ 46), most of which are probable cluster(More)
We review and discuss horizontal branch (HB) stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters in the HB(More)
The outer-halo globular cluster NGC 6229 has a peculiar horizontal-branch (HB) morphology, with clear indications of a bimodal HB and a “gap” on the blue HB. In this paper, we present extensive synthetic HB simulations to determine whether peculiar distributions in the underlying physical parameters are needed to explain the observed HB morphology. We find(More)
A “jump” in the blue horizontal-branch (HB) distribution in the V , u − y color-magnitude diagram has recently been detected in the globular cluster (GC) M13 (NGC 6205) by Grundahl, VandenBerg, & Andersen (1998). Such an effect is morphologically best characterized as a discontinuity in the u, u− y locus, with stars in the range 11,500 K . Teff . 20,000 K(More)
Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main-sequence today. Almost all of the stars born with more mass than 0.8 M⊙ have evolved to form the white dwarf cooling sequence of these systems, and the(More)
NGC 6388 and NGC 6441 are anomalies among Galactic globular clusters in that they cannot be readily placed into either Oosterhoff group I or Oosterhoff group II despite their significant numbers of RR Lyrae variables. The mean pulsation periods, 〈Pab〉, of their RRab variables, at 0.71 d and 0.76 d, respectively, are even larger than for Oosterhoff II(More)