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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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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?)
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
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
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
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)
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
Byte-by-byte Description of file: tablea.dat
Bytes Format Units Label Explanations
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
Note (1): NN.1 for neutral, NN.2 for singly ionized
Acknowledgements: Eugenio Carretta, eugenio.carretta(at) References: Carreta et al., Paper I, NGC 2808 2006A&A...450..523C Carreta et al., Paper II, NGC 6752 2007A&A...464..927C, Cat. J/A+A/464/927 Gratton et al., Paper III, NGC 6441 2006A&A...455..271G, Cat. J/A+A/455/271 Gratton et al., Paper V, NGC 6441 2007A&A...464..953G, Cat. J/A+A/464/953 Carreta et al., Paper VI, NGC 6388 2007A&A...464..967C, Cat. J/A+A/464/967
(End) Patricia Vannier [CDS] 22-Feb-2007
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