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 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 1978ApJ...225..148B) and Gratton,
Tornambe, & Ortolani (1986A&A...169..111G 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 1991AJ....101.1902A; Twarog & Anthony-Twarog 1991AJ....101..237T 1991AJ....101..237T,
1995AJ....109.2828T 1995AJ....109.2828T; Anthony-Twarog & Twarog 1998AJ....116.1922A 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:
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RA (2000) DE Designation(s)
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13 26 45.9 -47 28 37 Omega Cen = NGC 5139 = HD 116790
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File Summary:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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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
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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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)
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Note (1): Data from Butler, Dickens, & Epps (1978ApJ...225..148B 1978ApJ...225..148B) and
Gratton, Tornambe, & Ortolani (1986A&A...169..111G 1986A&A...169..111G)
Note (2): Data from Butler, Dickens, & Epps (1978ApJ...225..148B 1978ApJ...225..148B) and
Kaluzny et al. (1997A&AS..125..343K 1997A&AS..125..343K)
Note (3): Data from Sandage (1981ApJ...248..161S 1981ApJ...248..161S)
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History:
From AJ electronic edition
(End) Greg Schwarz [AAS] 19-Apr-2000