J/MNRAS/427/1153 Stellar parameters of giants in ω Cen (Simpson+, 2012)
Spectral matching for abundances and clustering analysis of stars on the giant
branches of omega Centauri.
Simpson J.D., Cottrell P.L., Worley C.C.
<Mon. Not. R. Astron. Soc. 427, 1153 (2012)>
=2012MNRAS.427.1153S 2012MNRAS.427.1153S
ADC_Keywords: Clusters, globular ; Stars, giant ; Abundances ; Photometry, UBVRI
Keywords: stars: abundances - stars: AGB and post-AGB -
globular clusters: individual: omega Centauri (NGC 5139)
Abstract:
We have determined stellar parameters and abundances for 221 giant
branch stars in the globular cluster omega Centauri. A combination of
photometry and lower-resolution spectroscopy was used to determine
temperature, gravity, metallicity, [C/Fe], [N/Fe] and [Ba/Fe]. These
abundances agree well with those found by previous researchers and
expand the analysed sample of the cluster. k-means clustering analysis
was used to group the stars into four homogeneous groups based upon
these abundances.
These stars show the expected anticorrelation in [C/Fe] to [N/Fe]. We
investigated the distribution of CN-weak/strong stars on the
colour-magnitude diagram. Asymptotic giant branch stars, which were
selected from their position on the colour-magnitude diagram, were
almost all CN-weak. This is in contrast to the red giant branch where
a large minority were CN-strong. The results were also compared with
cluster formation and evolution models. Overall, this study shows that
statistically significant elemental and evolutionary conclusions can
be obtained from lower resolution spectroscopy.
Description:
Photometry and abundances of the 221 giant branch stars are presented.
For each star, its U, V, j, k magnitudes are given. Each star also had
its [Fe/H], [C/Fe], [N/Fe], [Ba/Fe] derived from spectra of van Loon
et al (2007, Cat. J/MNRAS/382/1353). The U and V photometry is from
Bellini et al. (2009, Cat. J/A+A/493/959) and the j and k photometry
is from 2MASS. All the photometry is in their original system. The
[O/Fe] and [Na/Fe] abundances also presented are from Johnson &
Pilachowski (2010, Cat. J/ApJ/722/1373).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 32 221 Photometry and number of spectra
table4.dat 60 221 Teff, logg and abundances for the stars
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See also:
J/A+A/360/472 : Proper motions in omega Centauri (van Leeuwen+, 2000)
J/MNRAS/382/1353 : Spectral atlas of omega Cen post-MS stars (Van Loon+, 2007)
J/A+A/493/959 : UBV(RI)cHalpha photometry in omega Cen (Bellini+, 2009)
J/ApJ/722/1373 : ω Centauri giants abundances (Johnson+, 2010)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- LEID Star identification number (G1)
7- 11 F5.2 mag Umag ? U band photometry (1)
13- 17 F5.2 mag Vmag ? V band photometry (1)
19- 24 F6.3 mag Jmag J band photometry (2MASS)
26- 30 F5.2 mag Kmag K band photometry (2MASS)
32 I1 --- Nsp Number of 2dF spectra in van Loon et al.
(2007, Cat. J/MNRAS/382/1353) library
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Note (1): From Bellini et al. (2009, Cat. J/A+A/493/959).
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- LEID Star identification number (G1)
7- 10 I4 K Teff Effective temperature
12- 14 F3.1 [cm/s2] logg Surface gravity
16- 19 F4.1 [Sun] [Fe/H] Metallicity
21- 24 F4.1 [Sun] [C/Fe] Abundance [C/Fe]
26- 29 F4.1 [Sun] [N/Fe] Abundance [N/Fe]
31- 35 F5.2 [Sun] [O/Fe] Abundance [O/Fe] (2)
37- 41 F5.2 [Sun] [Na/Fe] Abundance [Na/Fe] (2)
43- 46 F4.1 [Sun] [Ba/Fe] Abundance [Ba/Fe]
48- 52 F5.3 --- S(3839) S(3839) spectral index (3)
54- 58 F5.3 --- CH(4300) CH(4300) spectral index (3)
60 I1 --- Gr [1/4] Group classification from k-means
analysis (4)
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Note (2): from Johnson & Pilachowski (2010, Cat. J/ApJ/722/1373)
Note (3): from van Loon+ (2007, Cat. J/MNRAS/382/1353)
Note (4): the groups are:
1 = metal-poor: [Fe/H]=-1.8 [C/Fe]=-0.4 [N/Fe]=0.3 [O/Fe]=+0.3 [Ba/Fe]=-0.4
2 = intermediate: [Fe/H]=-1.7 [C/Fe]=-0.0 [N/Fe]=0.4 [O/Fe]=+0.4 [Ba/Fe]=+0.4
3 = intermediate: [Fe/H]=-1.7 [C/Fe]=-0.5 [N/Fe]=1.0 [O/Fe]=-0.3 [Ba/Fe]=+0.5
4 = metal-rich: [Fe/H]=-1.3 [C/Fe]=-0.6 [N/Fe]=1.8 [O/Fe]=-0.2 [Ba/Fe]=+0.8
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Global notes:
Note (G1): van Leeuwen et al 2000, Cat. J/A+A/360/472,
<Cl* NGC 5139 LEID NNNNN> in Simbad
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Acknowledgements:
Jeffrey D. Simpson, jeffrey.simpson(at)pg.canterbury.ac.nz
(End) Jeffrey Simpson [UC, New Zealand], Patricia Vannier [CDS] 06-Sep-2012