Studies of RR Lyrae variable stars in the unusual globular cluster Omega Centauri. I - Spectroscopic observations

Butler, D.; Dickens, R. J.; Epps, E. A.

doi:10.1086/156476

Cited by 95 publications

(75 citation statements)

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“…from Butler et al (1978). We see that although there seems to be a trend of increasing amplitude, decreasing period with increasing metallicity, there are some longer period RRc stars found in the more intermediate metallicity range.…”

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confidence: 66%

“…Butler, Dickens, & Epps (1978), Caputo (1981), and Clement & Rowe (2000) have noted, however, that u Centauri might contain a few RRLs similar to those in an Oosterho † type I cluster. In addition, as noted in Pritzl et al (2000), u Centauri contains a number of very long period RRab stars, similar in period and amplitude to the longer period RRab stars in NGC 6441.…”

Section: 4mentioning

confidence: 99%

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Variable Stars in the Unusual, Metal-rich, Globular Cluster NGC 6441

Pritzl

Smith

Catelan

et al. 2001

The Astronomical Journal

130

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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 D104, with 48 new variables being found in this survey. A signiÐcant number of the variables are RR Lyrae stars (D46), most of which are probable cluster members. As was noted by Layden et al. in 1999, the periods of the fundamental-mode RR Lyrae stars are unusually long compared with Ðeld stars of similar metallicity. The existence of these long-period RRab stars is consistent with Sweigart & CatelanÏs prediction that the horizontal branch of NGC 6441 is unusually bright. This result implies that the metallicity-luminosity relationship for RR Lyrae stars is not universal. We discuss the difficulty in determining the Oosterho † classiÐcation of NGC 6441 because of the unusual nature of its RR Lyrae stars. A number of ab-type RR Lyrae stars are found to be both brighter and redder than the other probable RRab found along the horizontal branch, which may be a result of blending with stars of redder color. A smaller than usual gap is found between the shortest period fundamental-mode and the longest period Ðrst-overtoneÈmode RR Lyrae stars. We determine the reddening of the cluster to be E(B[V ) \ 0.51^0.02 mag, with substantial di †erential reddening across the face of the cluster. The mean V magnitude of the RR Lyrae is found to be 17.51^0.02 mag, resulting in a distance of 10.4È11.9 kpc, for a range of assumed values of for RR Lyrae stars. The possibility that stars in NGC 6441 SM V T may span a range in [Fe/H] is also discussed.

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confidence: 66%

Section: 4mentioning

confidence: 99%

Variable Stars in the Unusual, Metal-rich, Globular Cluster NGC 6441

Pritzl

Smith

Catelan

et al. 2001

The Astronomical Journal

130

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“…Moreover, with an abundance ranging from solar to [Fe/H] \ [2.0 (Butler, Dickens, & Epps 1978 ;Persson et al 1980 ;Suntze † & Kraft 1996), this one cluster allows the opportunity to explore the abundance sensitivity of the M[DDO51 index, as well as to calibrate the giant star color-magnitude relation as a function of metallicity for old stellar populations, without introduction of relative systematic errors produced by di †erential distance errors. To explore the giant distribution in the (M M[DDO51) and the M) planes, we have…”

Section: U Centaurimentioning

confidence: 99%

Exploring Halo Substructure with Giant Stars. I. Survey Description and Calibration of the Photometric Search Technique

Majewski

Ostheimer

Kunkel

et al. 2000

The Astronomical Journal

143

192

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We have begun a survey of the structure of the Milky Way halo, as well as the halos of other Local Group galaxies, as traced by their constituent giant stars. These giant stars are identiÐed via large-area, CCD photometric campaigns. Here we present the basis for our photometric search method, which relies on the gravity sensitivity of the Mg I triplet]MgH features near 5150 in FÈK stars, and which A is sensed by the Ñux in the intermediate-band DDO51 Ðlter. Our technique is a simpliÐed variant of the combined Washington/DDO51 four-Ðlter technique described by Geisler, which we modify for the speciÐc purpose of efficiently identifying distant giant stars for follow-up spectroscopic study : We show here that for most stars the Washington color is correlated monotonically with the Washington By combining the data on stars from di †erent clusters, and by taking advantage of the wide abundance spread within u Centauri, we verify the primary dependence of the M[DDO51 color on luminosity and demonstrate the secondary sensitivity to metallicity among giant stars. Our empirical results are found to be generally consistent with those from analysis of synthetic spectra by Paltoglou & Bell.Finally, we provide conversion formulae from the (M, system to the (V , V [I) system, corre-M[T 2 ) sponding reddening laws, as well as empirical red giant branch curves from u Centauri stars for use in deriving photometric parallaxes for giant stars of various metallicities (but equivalent ages) to those of u Centauri giants.

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“…The cluster co Cen, which is inhomogeneous in both Ca and Fe (Freeman and Rodgers 1975;Butler et al 1978;Cohen 1981;Gratton 1982;Francois et al 1988;Brown and Wallerstein 1993;Norris and Da Costa 1995b;Smith et al 1995), appears to be an exception to this generality. Observations suggest that it has sustained enrichment in heavy elements that were produced in supernova explosions or their high-mass progenitor stars.…”

Section: Discussionmentioning

confidence: 96%

On the Possibility of Nova Enrichment of Globular Clusters

Smith¹,

Kraft²

1996

PASP

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ABSTRACT. Primordial chemical enrichment of globular clusters by Ne novae could provide a means for producing significant enhancements in 13 C, 25 Mg, and 27 A1 abundances among cluster stars, if such novae eject on the order of 10" 4 M 0 of processed material. Enrichment by Ne novae may lead to cluster giants which have relatively large surface [Al/Fe] abundance ratios, either through direct enhancement of the 27 A1 surface abundances of the main-sequence progenitors of these stars, or through primordial enhancements in 25 Mg, which can be converted to 27 A1 by proton-addition nucleosynthesis in the O^N burning shell of red giants.

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Studies of RR Lyrae variable stars in the unusual globular cluster Omega Centauri. I - Spectroscopic observations

Cited by 95 publications

References 0 publications

Variable Stars in the Unusual, Metal-rich, Globular Cluster NGC 6441

Variable Stars in the Unusual, Metal-rich, Globular Cluster NGC 6441

Exploring Halo Substructure with Giant Stars. I. Survey Description and Calibration of the Photometric Search Technique

On the Possibility of Nova Enrichment of Globular Clusters

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