J/AJ/118/1245 Elemental abundances in five stars in M54 (Brown+, 1999)
Elemental abundances in five stars in M54, a globular cluster associated
with the Sagittarius galaxy
Brown J.A., Wallerstein G., Gonzalez G.
<Astron. J. 118, 1245 (1999)>
=1999AJ....118.1245B 1999AJ....118.1245B
ADC_Keywords: Abundances ; Clusters, globular
Keywords: globular clusters: individual (M54) - stars: abundances
Abstract:
Chemical abundances in five stars in M54, a globular cluster
associated with the Sagittarius dwarf galaxy, have been determined
using high-resolution echelle spectra. We find the cluster to have
[Fe/H] = -1.55 and possibly halo-normal abundance patterns, although
the [O/Fe] and [α/Fe] ratios lie between solar and the normal
halo values. One star shows the combination of low oxygen and enhanced
Na and Al, symptomatic of deep mixing of ON-cycle and other
proton-capture products; a second star shows a lesser degree of O
depletion unaccompanied by Na and Al excesses. In the cluster Eu is
also enhanced, indicating that about 30% of the Ba in the cluster is
due to the r-process. In general, M54 is similar to globulars of
comparable metallicity in the inner Galactic halo, despite its clear
association with the Sagittarius dwarf spheroidal.
Description:
The observations were taken in two different observing runs with the
CTIO 4 m telescope and Cassegrain echelle spectrograph, with a Loral
3K CCD as a detector, with the 31.6 lines mm-1 grating, air Schmidt
camera, and 226-3 cross disperser grating. The configuration yields a
resolving power λ/δλ = 24,000 and a spectral
coverage of 5500 - 9000 Å.
Objects:
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RA (2000) DE Designation(s)
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18 55 18 -30 28 18 Ibata 1
18 52 02 -30 34 33 Ibata 2
18 54 56 -30 28 48 Ibata 10
18 55 02 -30 28 22 Ibata 11
18 54 56 -30 28 47 Ibata 13
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 83 142 Line data for the Ibata stars
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Ion Ion name
8- 11 F4.2 --- Abd Log Ion's solar number abundance (H=12)
14- 20 F7.2 0.1nm Wave Wavelength of Ion
24- 28 F5.2 eV ExPot Excitation potential
30- 35 F6.2 --- log(gf) Log of the oscillator strength
37- 41 F5.1 10-4nm EqWI1 ? Equivalent width for star Ibata 1 (in mÅ)
43 A1 --- f_EqWI1 [a] Flag on EqWI1 (1)
45- 48 A4 --- n_EqWI1 Special limit on EqWI1 (≤ indicates
less than or equal to)
49- 53 F5.1 10-4nm EqWI2 ? Equivalent width for star Ibata 2 (in mÅ)
55 A1 --- f_EqWI2 [a] Flag on EqWI2 (1)
57 A1 --- l_EqWI2 Limit on EqWI2
58- 62 F5.1 10-4nm EqWI10 ? Equivalent width for star Ibata 10 (in mÅ)
64 A1 --- f_EqWI10 [a] Flag on EqWI10 (1)
67- 71 F5.1 10-4nm EqWI11 ? Equivalent width for star Ibata 11 (in mÅ)
73 A1 --- f_EqWI11 [a] Flag on EqWI11 (1)
75 A1 --- l_EqWI11 Limit on EqWI11
76- 80 F5.1 10-4nm EqWI13 ? Equivalent width for star Ibata 13
(in mÅ)
82 A1 --- f_EqWI13 [ab] Flag on EqWI13 (1)
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Note (1):
a = Line too strong (log(W/λ) > -4.5) to be included in abundance
solution
b = The abundances from the Ba II lines of Ibata 13 are badly mutually
discrepant, and we have no reason to accept one over any of the
others; we accept no fit for Ba for Ibata 13
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History:
From AJ electronic edition.
(End) Greg Schwarz [AAS] 11-Apr-2000