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J/AJ/119/1824     Caby photometry of Ω Centauri        (Rey+, 2000)

CCD photometry of the globular cluster ω Centauri. I. Metallicity of RR Lyrae stars from caby photometry Rey S.-C., Lee Y.-W., Joo J.-M., Walker A., Baird S. <Astron. J. 119, 1824 (2000)> =2000AJ....119.1824R
ADC_Keywords: Abundances, [Fe/H] ; Clusters, globular ; Photometry ; Stars, horizontal branch Keywords: globular clusters: individual (Ω Centauri) - RR Lyrae variable - stars: abundances stars: horizontal-branch Abstract: We present new measurements of the metallicity of 131 RR Lyrae stars in the globular cluster ω Centauri, using the hk index of the Caby photometric system. The hk method has distinct advantages over δS and other techniques in determining the metallicity of RR Lyrae stars and has allowed us to obtain the most complete and homogeneous metallicity data to date for the RR Lyrae stars in this cluster. For RR Lyrae stars in common with the δS observations of Butler, Dickens, & Epps (1978ApJ...225..148B) and Gratton, Tornambe, & Ortolani (1986A&A...169..111G), we have found that our metallicities, [Fe/H]hk, deviate systematically from their δS metallicity, while our [Fe/H]hk for well-observed, field RRab stars are consistent with previous spectroscopic measurements. Description: The Caby photometric system is an expansion of the standard uvby system with the inclusion of a fifth filter, Ca, centered on the K and H lines of Ca II (90 Å FWHM). The hk index is defined as hk = (Ca-b)-(b-y) and is found to be much more sensitive to metal abundance than is the Stromgren m1 index (Anthony-Twarog et al. 1991AJ....101.1902A; Twarog & Anthony-Twarog 1991AJ....101..237T, 1995AJ....109.2828T; Anthony-Twarog & Twarog 1998AJ....116.1922A). All the observations were made using the Cerro Tololo Inter-American Observatory (CTIO) 0.9 m telescope and Tektronix 2048 No. 3 CCD during three nights of an observing run in 1997 March. We covered ω Cen in a 3x3 grid and observed one sequence of this grid per each night. The field size of each grid point was 13.6''x13.6'' with a pixel scale of 0.40''. Our program field, centered on the cluster, covers approximately 40'x40', which roughly corresponds to the area enclosed within the half-tidal radius of ω Cen. Typical exposure times were 1400 s for Ca, 360 s for b, and 180 s for y. Objects: -------------------------------------------------------- RA (2000) DE Designation(s) -------------------------------------------------------- 13 26 45.9 -47 28 37 Omega Cen = NGC 5139 = HD 116790 -------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4.dat 132 131 Caby photometry of ω Cen RR Lyrae stars table5.dat 70 131 Metallicities and photometric parameters for ω Cen RR Lyrae stars
See also: J/AJ/119/1225 : Stroemgren photometry of Omega Centauri (Hughes+, 2000) J/AJ/108/1350 : Omega Cen FUV photometry (Whitney+, 1994) J/MNRAS/250/314 : CCD photometry of omega Cen (Noble+ 1991) J/A+AS/115/297 : BVRI photometry of Central Field of Omega Cen (Lynga+, 1996) J/PASP/106/828 : BVRI photometry of Omega Cen (Walker 1994) Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Number Variable star number 7- 11 F5.3 mag (b-y)1 The dereddened (b-y) color from observation 1 15- 19 F5.3 mag e_(b-y)1 Uncertainty in (b-y)1 23- 27 F5.3 mag hk1 The dereddened hk index from observation 1 31- 35 F5.3 mag e_hk1 Uncertainty in hk1 39- 43 F5.3 mag (b-y)2 ? The dereddened (b-y) color from observation 2 47- 51 F5.3 mag e_(b-y)2 ? Uncertainty in (b-y)2 55- 59 F5.3 mag hk2 ? The dereddened hk index from observation 2 63- 67 F5.3 mag e_hk2 ? Uncertainty in hk2 71- 75 F5.3 mag (b-y)3 ? The dereddened (b-y) color from observation 3 79- 83 F5.3 mag e_(b-y)3 ? Uncertainty in (b-y)3 87- 91 F5.3 mag hk3 ? The dereddened hk index from observation 3 95- 99 F5.3 mag e_hk3 ? Uncertainty in hk3 103-107 F5.3 mag (b-y)4 ? The dereddened (b-y) color from observation 4 111-115 F5.3 mag e_(b-y)4 ? Uncertainty in (b-y)4 119-123 F5.3 mag hk4 ? The dereddened hk index from observation 4 127-131 F5.3 mag e_hk4 ? Uncertainty in hk4
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Number Variable star number 9- 10 A2 --- Type RR Lyrae type 17- 21 F5.2 [Sun] [Fe/H] The final mean weighted iron to hydrogen abundance (relative to solar) derived from the hk index 25- 28 F4.2 [Sun] e_[Fe/H] ? Uncertainty in [Fe/H] 33 I1 --- Obs Number of independent measurements used to obtain [Fe/H] 41- 45 F5.2 [Sun] [Fe/H]S ? The [Fe/H] abundance derived from the δS method (1) 49- 53 F5.2 mag Vmag ? Intensity mean V band magnitude (2) 57- 62 F6.4 d Period ? The RR Lyrae period (2) 65- 68 F4.2 mag Amp ? Amplitude of star in the B band (3)
Note (1): Data from Butler, Dickens, & Epps (1978ApJ...225..148B) and Gratton, Tornambe, & Ortolani (1986A&A...169..111G) Note (2): Data from Butler, Dickens, & Epps (1978ApJ...225..148B) and Kaluzny et al. (1997A&AS..125..343K) Note (3): Data from Sandage (1981ApJ...248..161S)
History: From AJ electronic edition
(End) Greg Schwarz [AAS] 19-Apr-2000
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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