J/ApJ/750/L14 Abundances of red giants in NGC 6752 (Carretta+, 2012)
Chemical tagging of three distinct populations of red giants in the
globular cluster NGC 6752.
Carretta E., Bragaglia A., Gratton R.G., Lucatello S., D'Orazi V.
<Astrophys. J., 750, L14 (2012)>
=2012ApJ...750L..14C 2012ApJ...750L..14C
ADC_Keywords: Abundances ; Stars, giant ; Clusters, globular
Keywords: globular clusters: general - globular clusters: individual: NGC 6752 -
stars: abundances - stars: evolution - stars: Population II
Abstract:
We present aluminum, magnesium, and silicon abundances in the
metal-poor globular cluster NGC 6752 for a sample of more than 130 red
giants with homogeneous oxygen and sodium abundances. We find that
[Al/Fe] shows a spread of about 1.4 dex among giants in NGC 6752 and
is anticorrelated with [Mg/Fe] and [O/Fe] and correlated with [Na/Fe]
and [Si/Fe]. These relations are not continuous in nature, but the
distribution of stars is clearly clustered around three distinct Al
values, low, intermediate, and high. These three groups nicely
correspond to the three distinct sequences previously detected using
Stromgren photometry along the red giant branch. These two independent
findings strongly indicate the existence of three distinct stellar
populations in NGC 6752. Comparing the abundances of O and Mg, we find
that the population with intermediate chemical abundances cannot
originate from material with the same composition of the most O- and
Mg-poor population, diluted by material with that of the most O- and
Mg-rich one. This calls for different polluters.
Description:
The abundances of aluminum were derived from GIRAFFE spectra (obtained
with FLAMES, mounted at the ESO VLT-UT2 telescope) with the
high-resolution grating HR21. This setup is centered at 8757Å and
the spectral resolution is R=17300 at the center of spectra. The
observations were made on 2010 July, with an exposure time of 2700s.
The Mg abundances rest on two to three high excitation lines measured
in the spectral ranges of HR11 and HR13, while Si was obtained from
several transitions in the spectral range 5645-6145Å (details and
atomic parameters can be found in Carretta et al. 2009, Cat.
J/A+A/505/139, and Gratton et al. 2003, Cat. J/A+A/404/187,
respectively).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 53 132 [Mg/Fe], [Al/Fe], and [Si/Fe] ratios for red
giants in NGC 6752
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See also:
J/other/Nat/498.198 : Na abundances in NGC6752 (Campbell+, 2013)
J/MNRAS/423/2901 : NGC 6752 multiwavelength survey (Thomson+, 2012)
J/A+A/524/A44 : CN and CH line strengths in 12 globulars (Pancino+, 2010)
J/A+A/517/A81 : 2nd & 3d parameters of HB of GCs (Gratton+, 2010)
J/A+A/505/139 : Abundances of red giants in 17 GCs (Carretta+, 2009)
J/A+A/505/117 : Abundances of red giants in 15 GCs (Carretta+, 2009)
J/A+A/464/927 : Abundances of red giants in NGC 6752 (Carretta+, 2007)
J/AJ/130/1693 : HST-ACS observations of 5 globular clusters (Brown+, 2005)
J/A+A/440/901 : Reddening and metallicity of NGC 6752 (Gratton, 2005)
J/A+A/404/187 : Equivalent widths for metal-poor stars (Gratton+, 2003)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID [1217/48975] Star identification number (1)
7 I1 --- o_[Mg/Fe] [0/3] Number of lines used to determine [Mg/Fe]
9- 13 F5.3 [Sun] [Mg/Fe] [0.07/0.6]? Log of Mg to Fe abundance
15- 19 F5.3 [Sun] e_[Mg/Fe] [0.004/0.3]? Error in [Mg/Fe]
21 I1 --- o_[Al/Fe] [0/2] Number of lines used to determine [Al/Fe]
23- 28 F6.3 [Sun] [Al/Fe] [-0.21/1.6]? Log of Al to Fe abundance
30- 34 F5.3 [Sun] e_[Al/Fe] [0.004/0.3]? Error in [Al/Fe]
36- 37 I2 --- o_[Si/Fe] [0/11] Number of lines used to determine [Si/Fe]
39- 43 F5.3 [Sun] [Si/Fe] [0.3/0.6]? Log of Si to Fe abundance
45- 49 F5.3 [Sun] e_[Si/Fe] [0.004/0.3]? Error in [Si/Fe]
51 I1 --- Al [0/1] Al flag; 1=detection, 0=upper limit
53 A1 --- Pop [EIP-] Population group flag from this paper (2)
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Note (1): ID number as in Caretta et al., 2007, Cat. J/A+A/464/927;
<Cl* NGC 6752 CBG NNNNN> in Simbad.
Note (2): P, I, or E as derived from the cluster analysis. Average values of
parameters for stars in the three populations of red giants in NGC 6752:
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Pop nr Delta(delta_4) [O/Fe] [Mg/Fe] [Al/Fe] [Si/Fe]
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P 15 -0.048±0.006 +0.54±0.04 +0.45±0.02 +0.11±0.04 +0.51±0.01
I 26 -0.002±0.003 +0.25±0.04 +0.42±0.01 +0.74±0.04 +0.48±0.01
E 30 +0.027±0.003 +0.06±0.04 +0.31±0.01 +1.21±0.02 +0.43±0.01
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See section 5 for further details.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 11-Dec-2013