Metal abundances of RR Lyrae stars in galactic globular clusters

Butler, D.

doi:10.1086/153761

Cited by 94 publications

(69 citation statements)

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“…6. Calibration of the ∆S index with our new analysis and with the data of field RR Lyrae variables from Clementini et al (1995) We obtained ∆S values for 15 of our calibrating clusters from the metallicities of Costar & Smith (1988), inverting the Butler's (1975) relation they used. Our values are not completely identical to those used by Clementini et al (1995); the main differences are that a) we excluded 47 Tuc, since its value for ∆S is based on a single star, possibly not member of the cluster (Tucholke 1992) and b) for NGC 288 we assumed a value of ∆S = 5.9, since the mean value 7.2 cited by Costar & Smith was obtained including spectra taken at phases near maximum light.…”

Section: Comparison With the Metallicity Scale Of Rr Lyrae Starsmentioning

confidence: 99%

Abundances for globular cluster giants. I. Homogeneous metallicities for 24 clusters

Carretta

Gratton

1997

Astron. Astrophys. Suppl. Ser.

628

662

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Abstract. We have obtained high resolution, high signalto-noise ratio CCD echelle spectra of 10 bright red giants in 3 globular clusters (47 Tuc, NGC 6752 and NGC 6397) roughly spanning the whole range of metallicities of the galactic globular cluster system. The analysis of this newly acquired material reveals no significant evidence of starto-star variation of the [Fe/H] ratio in these three clusters. Moreover, a large set of high quality literature data (equivalent widths from high dispersion CCD spectra) was reanalyzed in an homogeneous and self-consistent way to integrate our observations and derive new metal abundances for more than 160 bright red giants in 24 globular clusters (i.e. about 16% of the known population of galactic globulars). This set was then used to define a new metallicity scale for globular clusters which is the result of high quality, direct spectroscopic data, of new and updated model atmospheres from the grid of Kurucz (1992), and of a careful fine abundance analysis; this last, in turn, is based on a common set of both atomic and atmospheric parameters for all the stars examined. Given the very high degree of internal homogeneity, our new scale supersedes the offsets and discrepancies existing in previous attempts to obtain a metallicity scale. The internal uncertainty in [Fe/H] is very small: 0.06 dex (24 clusters) on average, and can be interpreted also as the mean precision of the cluster ranking. Compared to our system, metallicities on the widely used Zinn and West's scale are about 0.10 dex higher for [Fe/H]> −1, 0.23 dex lower for −1 <[Fe/H]< −1.9 and 0.11 dex too high for [Fe/H]< −1.9. The non-linearity of the Zinn and West's scale is significant even at 3σ level. A quadratic transformation is given to correct older values to the new scale in the range of our calibrating clusters (−2.24 ≤[Fe/H] ZW ≤ −0.51). A minor disagreement is found at low metallicities between the metallicity scale based on field and cluster RR Lyrae variables (via a new Send offprint requests to: E. Carretta Table 9 also available in electronic form at the CDS via anonymous ftp 130.79.128.5 or via http://cdsweb.ustrabg.fr/Abstract.html calibration of the ∆S index) and our new cluster metallicities. It could be tentatively ascribed to non-linearity in the [Fe/H]−∆S relationship. The impact of new metallicities on major astrophysical problems is exemplified through a simple exercise on the Oosterhoff effect in the classical pair M 3 and M 15.

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Section: Comparison With the Metallicity Scale Of Rr Lyrae Starsmentioning

confidence: 99%

Abundances for globular cluster giants. I. Homogeneous metallicities for 24 clusters

Carretta

Gratton

1997

Astron. Astrophys. Suppl. Ser.

628

662

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“…In the first three columns of Butler (1975); a careful reading of the references in the last column provides more detail on the sources of the [Fe/H] values.…”

Section: Observational Datamentioning

confidence: 99%

The Absolute Magnitudes of the RR Lyrae Stars

McNamara¹

1997

PASP

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ABSTRACT. We present a new calibration of the relationship between the absolute magnitudes and metal abundances, [Fe/H], of RR Lyrae stars. Temperatures inferred from optical and near-infrared color indices and the new Kurucz models are utilized in conjunction with Baade-Wesselink solutions to derive absolute magnitudes. Temperatures inferred from the optical and near-infrared photometry are -200-300 K higher for the variables than those given from (V-K) color indices and the older Kurucz models. We find M v = 0.287[Fe/H]+ 0.964. This equation gives higher luminosities ( -0.2 mag) for the metal-poor variables than previous B-W calibrations. The RR Lyrae stars in the Large Magellanic Cloud in conjunction with our calibration yield a distance modulus of 18.53. Thus, the Cepheids and RR Lyrae stars give identical distance moduli at ^0.1 mag level. The repercussions of the higher temperatures and higher luminosities of RR Lyrae stars on the distances and ages of globular clusters, distance to the galactic center, the Hubble constant and age of the Universe, and the masses of RR Lyrae stars are discussed.

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“…The first estimates of the cluster's integrated spectral type (Kinman 1959;Kron & Mayall 1960) were G2-G4. Smith (1981), from the spectroscopic metal-abundance parameter ∆S derived for five RR Lyrae stars, found ∆S = 2.8 for NGC 6723, corresponding to [Fe/H] = −0.68 in the metallicity scale of Butler (1975). However, later studies showed a more significant metal deficiency.…”

Section: Introductionmentioning

confidence: 98%

Deep multicolor CCD photometry of the globular cluster NGC 6723

Alcaino

Liller

Alvarado

et al. 1999

Astron. Astrophys. Suppl. Ser.

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Abstract. We have obtained CCD UBV RI photometry of 3620 stars in the globular cluster NGC 6723, one of the few globular clusters with a horizontal branch wellpopulated on both sides of the instability strip. This is the first deep five-color study of NGC 6723. We have determined several important parameters for this cluster. Its color excess is E(B −V ) = 0.11±0.01. The most plausible value of metallicity is [Fe/H] = −1.22 ± 0.15; even lower values are possible. The apparent distance modulus of the cluster is (m − M ) V,6723 = 14.76. From isochrone analysis, we prefer the NGC 6723 age in the range between 15 and 16 Gyr, in the scale of Bergbusch & VandenBerg (1992). We find a close similarity of the shape and slope of the red giant branch in NGC 6723 and M 3 and of the magnitude difference between the main-sequence turnoff and the horizontal branch in NGC 6723, M 3, and M 5.

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Metal abundances of RR Lyrae stars in galactic globular clusters

Cited by 94 publications

References 0 publications

Abundances for globular cluster giants. I. Homogeneous metallicities for 24 clusters

Abundances for globular cluster giants. I. Homogeneous metallicities for 24 clusters

The Absolute Magnitudes of the RR Lyrae Stars

Deep multicolor CCD photometry of the globular cluster NGC 6723

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