J/A+A/464/939 Abundances of red giants in NGC 6218 (Carretta+, 2007)
Na-O Anticorrelation and HB. IV. Detection of He-rich and He-poor stellar
populations in the globular cluster NGC 6218.
Carretta E., Bragaglia A., Gratton R.G., Catanzaro G., Leone F., Sabbi E.,
Cassisi S., Claudi R., D'Antona F., Francois P., James G., Piotto G.
<Astron. Astrophys. 464, 939 (2007)>
=2007A&A...464..939C 2007A&A...464..939C
ADC_Keywords: Clusters, globular ; Stars, population II ; Abundances ;
Radial velocities
Keywords: stars: abundances - stars: atmospheres - stars: Population II -
Galaxy: globular clusters: general -
Galaxy: globular clusters: individual: NGC 6218 (M 12)
Abstract:
We used the multifiber spectrograph FLAMES on the ESO Very Large
Telescope UT2 to derive atmospheric parameters, metallicities and
abundances of O and Na for 79 red giant stars in the Galactic globular
cluster NGC 6218 (M 12). We analyzed stars in the magnitude range from
about 1mag below the bump to the tip of the Red Giant Branch. The
average metallicity we derive is [Fe/H]=-1.31±0.004±0.028dex
(random and systematic errors, respectively), with a very small
star-to-star scatter (rms=0.033dex), from moderately high-resolution
Giraffe spectra. This is the first extensive spectroscopic abundance
analysis in this cluster. Our results indicate that NGC 6218 is very
homogeneous as far as heavy elements are concerned. On the other hand,
light elements involved in the well known proton-capture reactions of
H-burning at high temperature, such as O and Na, show large
variations, anticorrelated with each other, at all luminosities along
the red giant branch. The conclusion is that the Na-O anticorrelation
must be established in early times at the cluster formation. We
interpret the variation of Na found near the RGB-bump as the effect of
two distinct populations having different bump luminosities, as
predicted for different He content. To our knowledge, NGC 6218 is the
first GC where such a signature has been spectroscopically detected,
when combined with consistent and homogeneous data obtained for
NGC 6752 to gain in statistical significance.
Description:
Spectra for 79 RGB stars in NGC 6218 (M 12) were obtained with
FLAMES@VLT using two gratings (HR11, HR13). Abundances of Fe, O, Na
were derived using equivalent widths, model atmospheres and
atmospheric parameters based on photometry.
For each star we give identification, equatorial coordinates, VBJK
magnitudes, heliocentric radial velocity for both gratings, Teff,
logg, [A/H], vt, [Fe/H], [O/Fe], [Na/Fe]. Equivalent widths are
given in tablea.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 91 92 Identification, equatorial coordinates,
BVJK magnitudes, heliocentric radial velocity
table3.dat 56 79 Atmospheric parameters and iron abundance
table5.dat 37 79 O and Na abundances
tablea.dat 37 4819 Equivalent widths for 79 objects
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See also:
J/A+A/455/271 : Abundances of red giants in NGC 6441 (Gratton+, 2006)
J/A+A/464/927 : Abundances of red giants in NGC 6752 (Carreta+, 2007)
J/A+A/464/953 : Abundances of red giants in NGC 6441 (Gratton+, 2007)
J/A+A/464/981 : Abundances of red giants in NGC 6388 (Carreta+, 2007)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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2- 3 I2 --- Seq [1/92] Sequential number
5- 10 I6 --- ID Identification number
(Sabbi et al., 2006, in prep.)
12- 22 F11.7 deg RAdeg Right ascension (J2000.0)
24- 33 F10.7 deg DEdeg Declination (J2000.0)
35- 40 F6.3 mag Bmag Johnson B magnitude
42- 47 F6.3 mag Vmag Johnson V magnitude
49- 54 F6.3 mag Jmag 2MASS J magnitude
56- 61 F6.3 mag Kmag 2MASS K magnitude
63- 68 F6.2 km/s RV11 ? Heliocentric radial velocity for grating HR11
70- 75 F6.2 km/s RV13 ? Heliocentric radial velocity for grating HR13
77- 85 A9 --- HR [HR11,HR13 ] Grating(s) used
87 A1 --- Flag [*] *: stars not used in analysis
89- 91 A3 --- Mem [NM? ] Non member (NM) or doubtful member (NM?)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID Identification number
(Sabbi et al., 2006, in prep.)
8- 11 I4 K Teff Effective temperature
13- 16 F4.2 [cm/s2] logg Gravity
18- 22 F5.2 [Sun] [A/H] Metallicity
24- 27 F4.2 km/s Vt Microturbulent velocity
29- 30 I2 -- o_FeI Number of lines of Fe I
32- 36 F5.2 [Sun] [Fe/H]I Average star [Fe/H]I
38- 42 F5.3 [Sun] e_[Fe/H]I rms uncertainty on [Fe/H]I
44 I1 -- o_FeII ? Number of lines of Fe II
46- 50 F5.2 [Sun] [Fe/H]II ? Average star [Fe/H]II
52- 56 F5.3 [Sun] e_[Fe/H]II ? rms uncertainty on [Fe/H]II
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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- 6 I6 --- ID Identification number
(Sabbi et al., 2006, in prep.)
8 I1 --- o_O ? Number of lines of O
10- 14 F5.2 [Sun] [O/Fe] ? Average [O/Fe]
16- 19 F4.2 [Sun] e_[O/Fe] ? rms uncertainty on [O/Fe]
22 I1 --- o_Na ? Number of lines of Na
24- 28 F5.2 [Sun] [Na/Fe] ? Average [Na/Fe]
30- 33 F4.2 [Sun] e_[Na/Fe] ? rms uncertainty on [Na/Fe]
35 I1 --- gr [1/3]? Grating used (1)
37 I1 -- l_O [0/1]? Flag for measure/limit for O (2)
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Note (1): Flags for grating as follows:
1 = HR13 only
2 = both HR11 & HR13
3 = only HR11
Note (2): Flags for measure/limit for O as follows:
0 = O upper limit
1 = O measured
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Byte-by-byte Description of file: tablea.dat
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Bytes Format Units Label Explanations
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1- 6 I6 ---- ID Identification number
(Sabbi et al., 2006, in prep.)
8- 11 F4.1 --- --- Atomic number and ionization stage (1)
13- 19 F7.2 0.1nm lambda Wavelength
21- 24 F4.2 eV EP Excitation potential
26- 31 F6.2 [cm/s2] loggf Surface gravity
33- 37 F5.1 0.1pm EW Equivalent width
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Note (1): NN.1 for neutral, NN.2 for singly ionized
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Acknowledgements:
Eugenio Carretta, eugenio.carretta(at)oabo.inaf.it
References:
Carreta et al., Paper I, NGC 2808 2006A&A...450..523C 2006A&A...450..523C
Carreta et al., Paper II, NGC 6752 2007A&A...464..927C 2007A&A...464..927C, Cat. J/A+A/464/927
Gratton et al., Paper III, NGC 6441 2006A&A...455..271G 2006A&A...455..271G, Cat. J/A+A/455/271
Gratton et al., Paper V, NGC 6441 2007A&A...464..953G 2007A&A...464..953G, Cat. J/A+A/464/953
Carreta et al., Paper VI, NGC 6388 2007A&A...464..967C 2007A&A...464..967C, Cat. J/A+A/464/967
(End) Patricia Vannier [CDS] 22-Feb-2007