Chemical composition of evolved stars in the open cluster IC 4651

0.58 MB·English

by  Šarūnas Mikolaitis

Mon.Not.R.Astron.Soc.000,1–??(2010) Printed6January2011 (MNLATEXstylefilev2.2)
Chemical composition of evolved stars in the open cluster
⋆
IC 4651
1 Sˇaru¯nas Mikolaitis,1† Graˇzina Tautvaiˇsiene˙,1 Raffaele Gratton,2 Angela Bragaglia3
1
and Eugenio Carretta3
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2 1Institute of Theoretical Physics and Astronomy, Vilnius University,Goˇstauto 12, Vilnius 01108, Lithuania
2INAF - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
n
3INAF - Osservatorio Astronomico di Bologna, ViaRanzani 1, I-40127 Bologna, Italy
a
J

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Accepted 2010.....;Received2010.....;inoriginalform2010......

]
R
S ABSTRACT
. Wepresentananalysisofhigh-resolutionspectraofthreecore-helium-burning‘clump’
h
starsand two firstascentgiants in the opencluster IC 4651.Atmospheric parameters
p
- (Teff, log g, vt, and [Fe/H]) were determined in our previous study by Carretta et al.
o (2004). In this study we present abundances of C, N, O and up to 24 other chemical
r elements. Abundances of carbon were derived using the C2 Swan (0,1) band head at
t
s 5635.5˚A.Thewavelengthinterval7980–8130˚A,withstrongCNfeatures,wasanalysed
a in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen
[
abundances were determined from the [Oi] line at 6300 ˚A. Compared with the Sun

1 andotherdwarfstarsoftheGalacticdisk,meanabundancesintheinvestigatedclump
v stars suggest that carbon is depleted by about 0.3 dex, nitrogen is overabundant by
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about 0.2 dex and oxygen is close to solar. This has the effect of lowering the mean
3 C/N ratio to 1.36 ± 0.11. The mean 12C/13C ratios are lowered to 16 ± 2. Other
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investigated chemical elements have abundance ratios close to the solar ones.
0
1. Keywords: stars:abundances–stars:atmospheres–stars:horizontalbranch–open
0 clusters and associations: individual: IC 4651.
1
1
:
v
i 1 INTRODUCTION cluster.Theorbitaleccentricityise=0.19andthemeanra-
X
diusofgalactocentricorbitis8.6kpc,itsmaximumdistance
This work is continuing our efforts in studying evolution-
ar ary abundance alterations in evolved stars of open clusters −fro4m9◦5th6.e0G′;all=act3i4c0p.0la8n8◦e,ibs1=90−p0c7.(9α0270◦0)0.=17h24.8m,δ2000 =
(Tautvaiˇsiene˙ et al. 2000, 2005; Mikolaitis et al. 2010). Our
main aim is to determine detailed elemental abundances of
Resultsofextensivephotometricstudieswerepublished
carbon, nitrogen and oxygen, and carbon isotope 12C/13C
first by Eggen (1971) and Lindoff (1972) and later on by
ratiosinstarsofopenclustersinordertobetterunderstand
Anthony-Twarog& Twarog (1987, 2000), Anthony-Tworag
reasonsofabundancealterationscausedbystellarevolution.
et al. (1988). However, the most recent photometric study
Informationonabundancesofheavierchemicalelementswill
wasperformedbyMeibom(2000)andMeibometal.(2002).
be used for deriving the time evolution of abundances in
They combined photometric observations and radial veloc-
theGalacticdiskundertheBolognaOpenClusterChemical
ity measurements for the 44 single member stars down to
Evolution(BOCCE)study(Bragaglia&Tosi2006,Carretta V =14.5 mag and determined E(B−V)=0.10 mag, the
et al.2007, andreferences therein).Inthiswork,ourtarget distance d = 1.01±0.05 kpc, and the mean radial velocity
of investigations is the open cluster IC 4651. equal to −30.76±0.20 kms−1. It was found that 37% of
The open cluster IC4651 is an intermediate-age
giant members are spectroscopic binaries with periods up
(1.7 Gyr) open cluster located 140 pc below the Galactic
to 5000 days, and 52% of the main-sequence and turn-off
plane and 7.1 kpc form the Galactic centre (Meibom et al.
membersarebinarieswithperiodslessthan1000days.The
2002; Pasquini et al. 2004). Meibom et al. (2002) provided estimatedtotalmassofIC4651is≈630M⊙ (Meibometal.
calculationsofthespacemotionandtheGalacticorbitofthe
2002). The turn-off mass of the IC4651 stars M =1.69M⊙
was obtained by Carretta et al. (2004) reading the turn-off
⋆ Based on observations collected at ESO telescopes under pro- valuesontheGirardietal.(2000)isochronesforsolarmetal-
grammes65.N-0286andinpart169.D-0473 licity at the age of the cluster of 1.7 Gyr as determined by
† E-mail:[email protected] Meibom et al. (2002).
2 Sˇaru¯nas Mikolaitis et al.
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V
12
13
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0.4 0.6 0.8 1.0
b - y Figure 2. Fieldof 8 x 8 arcmin2 centered on IC4651, with the
programmestarsindicatedbytheirnumbersaccordingtoLindoff
Figure 1. The colour-magnitude diagram of the open cluster
(1972).
IC4651. The stars investigated in this work are indicated by
the filled squares. The stars of two other high-resolution spec-
tral abundance studies are shown in this plot as well: the work
of Pace et al. (2008) is marked by triangles and of Pasquini et 2 OBSERVATIONS AND METHOD OF
al. (2004) – by diamonds. The diagram is based on Str¨omgren ANALYSIS
photometrybyAnthony-Twarog&Twarog(2000).
The spectra of five cluster stars (IC4651 27, 56, 72, 76 and
146) were obtained with the spectrograph FEROS (Fiber-
fed ExtendedRangeOpticalSpectrograph) mountedat the
1.5 m telescope in La Silla (Chile). The resolving power is
R = 48000 and the wavelength range is λλ 3700–8600˚A.
There were several photometric studies that evaluated Three stars (27, 76, 146) belong to the red clump of the
the metallicity of IC4651. Based on uvby −Hβ photome- cluster, the IC 4651 72 star is a first-ascent giant, and the
try, [Fe/H] = 0.23±0.02 was found by Anthony-Twarog star 56 is an RGB-tip giant (see Fig. 1). The finding chart
& Twarog (1987), [Fe/H] = 0.18±0.05 by Nissen (1988), of the investigated stars is shown in Fig. 2. The log of ob-
and [Fe/H]=0.077±0.012 by Anthony-Twarog & Twarog servations and S/N are presented in the paper by Carretta
(2000). at al. (2004).
Highresolution spectroscopicdatastartedtoappearin InthesamepaperbyCarrettaetal.(2004),allthemain
thebeginningofthemillennium.Bragaglia etal.(2001) de- atmospheric parameters for the observed stars were deter-
terminedthemeanmetallicityoffiveevolvedstars[Fe/H]= mined. For the convenience we present them in this paper
0.16 ± 0.01. Pasquini et al. (2004) provided the cluster as well (Table 1). The effective temperatures were derived
metallicity [Fe/H] = 0.10 ± 0.03 from the analysis of 22 byminimizingtheslopeoftheabundancesfromneutralFei
faint main sequence stars of the cluster. Abundances of lineswithrespecttotheexcitationpotential.Usingtheline-
the iron peak, α-elements and lithium were investigated in depth ratios (LDR) technique, Biazzo et al. (2007) have
theirstudyaswell.Carrettaetal.(2004) foundtheaverage determined higher effective temperatures for other clump
[Fe/H]=0.11±0.01for5evolvedstarsofthecluster,which starsin NGC4651 andhaveraised doubtsthatthetemper-
we analyse further in this our work. Pace at al. (2008) pro- ature determinations by Carretta et al. were likely too low.
vided the abundance measurements of Fe, Ca, Na, Ni, Ti, Wehavecheckeddependencesoftheotherchemicalelement
Al, Cr, Si for 20 solar-type stars belonging to IC4651 and lineswithrespecttotheexcitationpotentialanddidnotfind
found[Fe/H]=0.12±0.05. Andfinally,Santosetal.(2009) slopes.Thus,wedonotdoubtinthecorrectnessofeffective
derivedthemeanmetallicity[Fe/H]=0.15±0.02forIC4651 temperature determinations for IC4651 giants by Carretta
from fivedwarf stars. et al.
In our work for the open cluster IC4651, the detailed The gravities (log g) were derived by Carretta et al.
abundanceanalysis of almost 30 chemical elements is done. from theiron ionization equilibrium.Inourstudywefound
Abundances of such key chemical elements as 12C, 13C, N, a very good agreement between neutral and singly ionised
O as well as representatives of s- and r-processes are deter- species of Cr and Ti, which strongly support the reliabil-
mined. ityof theatmospheric parameters, in particular thegravity
The colour-magnitude diagramme of IC4651 with the valuesderivedfromtheionizationequilibriumofFe.Themi-
stars analysed in threemost comprehensive chemical abun- croturbulentvelocitiesweredeterminedassumingarelation
dancestudies(Pasquinietal.2004;Paceetal.2008andthis betweenloggandvt.TheATLASmodelswithovershooting
work) indicated is presented in Fig. 1. were used for the analysis. The Fei lines were restricted to
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______IIIIIII__II___IIII____I____III_I____I__II________I__II____II_________I___________I__________I_______I__II_______________________________________________________________________I_____________I____II_IIII__I_________I_I_II__I__________________________________________________________________________________________________________________________________IIIIIII__IIII__I____________________I___II____I____I_______________________I____I__________I_______I____I_I__I_______III_I___I___I___II_______________________I_I_______I___________I__________________I___I________________II_______I____I__II__I_II______I_______I___________________________II_I_____I__________________I_I________________I__I__I_I___I_I_________I_________I____I_________________I______I__________I__I___________________________I_I________________________I_________________________________I_______________________II___________________________________________I________________I__________I_I___I______I_____________II___I________________I_________I_II_I____I_1IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII_I____IIIIIIIIIIII_I___I_II__I_I__________I_________I_I_II_II___II____I__II_I__I__________I__II________________I____I___II__IIIIIIIIIIIIIIIIIIIIIII___IIIIIII__I__II_I__III_III_I_II________________IIIIIIIIIIIIII_____________IIIII__II__I_I_I_I___II_I_I_II_II______________I______I_________II__II__I_II_I_______________I__________IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII2IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII_________________________________________IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
6429.89-Co_I
6430.85-Fe_I
6432.68-FeII
6436.40-Fe_I
6440.93-Mn_I
6442.94-FeII
6445.75-Zr_I
6446.40-FeII
6450.18-Co_I
6452.31-V__I
6454.99-Co_I
6455.60-Ca_I
6456.38-FeII
6464.67-Ca_I
6475.63-Fe_I
6477.85-Co_I
6481.87-Fe_I
6482.19-FeII
6482.80-Ni_I
6491.23-FeII
6494.50-Fe_I
6494.99-Fe_I
6495.74-Fe_I
6496.46-Fe_I
6496.91-BaII
6498.94-Fe_I
6508.83-Ca_I
6509.60-Fe_I
6516.08-FeII
6518.37-Fe_I
6529.18-Cr_I
6531.42-V__I
6532.88-Ni_I
6533.93-Fe_I
6537.92-Cr_I
6572.79-Ca_I
6574.25-Fe_I
6580.23-Ni_I
6581.21-Fe_I
6583.69-Si_I
6586.32-Ni_I
6587.62-C__I
6591.30-Fe_I
6592.51-Ni_I
6593.87-Fe_I
6595.86-Co_I
6598.60-Ni_I
6599.10-Ti_I
6604.59-ScII
6606.94-TiII
6608.02-Fe_I
6609.11-Fe_I
6612.19-Cr_I
66661133..7842--YFe__III
66662245..8042--VFe___II
wereperformedbyspectralsynthesismethod.Thezirco-thanum,cerium,neodymiumandeuropiumabundancesThedeterminationofzirconium,yttrium,barium,lan-Allinesat6696.03A,6698.67A,7835.30Aand7836.13A.˚˚˚˚iA;andaluminumfromtheA,6319.24A,6318.715711.09˚˚˚6160.75A;magnesiumfromtheMglinesat4730.04A,˚˚ialentwidthsoftheNalinesat5688.22A,6154.23Aand˚˚i(1999).Abundancesofsodiumweredeterminedfromequiv-NLTEtakenintoaccountasdescribedbyGrattonetal.TheabundancesofNaandMgweredeterminedwithstarsthe[O]linewasnotcontaminatedbytelluriclines.itakenfromJohanssonetal.(2003).InthespectraofIC4651isotopiclinecomponents,whichblendtheoxygenline,wereden[O]lineat6300A.ThegfvaluesforNiandNi˚i5860derivedtheoxygenabundancefromsynthesisoftheforbid-forthenitrogenabundanceandC/Cratioanalysis.We1213containsstrongCNandCNfeatures,soitwasused121413140–1bandheadat5630.5A.Theinterval7980–8130A˚˚5636AintervaltocomparewithobservationsofCSwan2˚FortheCdeterminationwecalculatedthe5632–2 somedetails.Mikolaitisetal.(2010,PaperI).HerewewillremindonlyInthisworkweusedthesamemethodofanalysisasinal.Fig.3.Formoredetailsanderrorestimates,seeCarrettaetingblue-ward.Twoexamplesofspectraarepresentedinlemsoflinecrowdinganddifficultiesinthecontinuumtrac-thespectralrange5500–7000Ainordertominimizeprob-˚ Starnumbers,VandBVfromLindoff(1972)−∗ 14610.941.1447302.140.101.217610.941.1746202.260.111.217210.411.3345002.230.131.21568.951.6839500.290.341.46−2710.861.2346102.520.101.17 (mag)(mag)(K)(kms)1−efftStarVBVTlogg[A/H]v−∗ IC4651.AdoptedatmosphericparametersforobservedstarsinTable1. IC4651.Anoffsetof0.5inrelativefluxisappliedforclarity.SmallsamplesofstellarspectraofprogrammestarsinFigure3. (¯) 663066326634663666386640664266446646 FFCCFFFNCFFEFNeeeeeeeeuroiri I I IIIIIIIIIIIIII 0.5 1.0IC 4651 27 1.5 IC 4651 56 Ch
e
m
i
c
linesynthesis.AhyperfinestructurefortheEulinewasalsousedfortheiiabundancesweredeterminedusingtheEulineat6645A.˚iilineswerechosen:5092A,5249Aand5319A.Theeuropium˚˚˚crowdingintheregionofneodymiumlines,onlythreeNdiieterspresentedbyDenHartog&Lawler(2003).Duetolineneodymiumabundancewasdeterminedusingatomicparam-ceriumfromtheCelinesat5274Aand6043A.The˚˚iiweredeterminedfromLalinesat6320Aand6390A,˚˚iiMashonkina&Gehren(2000).ThelanthanumabundancesfromMcWilliam(1998)andforthelineat6496Afrom˚AAand6141isotopiccompositionfortheBalinesat5853˚˚iiand6127A.Weadoptedthebariumhyperfinestructureand˚niumabundanceswerederivedusingtheZrlinesat4687A˚i C/C–2–211213Eu0.030.13–0.07iiNd0.010.13–0.04iiCe0.020.12–0.03iiLa0.030.08–0.10iiBa–0.030.14–0.02iiZr0.000.12–0.07iY0.16–0.02–0.14iiZn–0.050.07–0.07iCu0.020.03–0.06iNi0.000.07–0.05iCo0.020.05–0.07iMn0.08–0.04–0.06iCr–0.090.14–0.03iiCr0.100.00–0.06iV0.160.01–0.09iTi–0.030.13–0.06iiTi0.16–0.02–0.08iSc–0.020.13–0.05iiCa0.11–0.04–0.06iSi–0.060.07–0.02iAl0.080.00–0.03iMg0.030.00–0.03iF666666666666Na0.09–0.05–0.04e666666i I113779......034472824217O([O])–0.05–0.050.00------CNFFFCieeerir______IIIIIIN(CN)0.050.000.052C(C)–0.050.050.00 +03kms.+100K+03.Species1−eff∆∆logTg∆vt tohydrogen,[A/H][A/Fe],areoftenconsiderablysmallerthanabundancesrelativeNotethattheeffectson“relative”abundances,forexampleonthelogarithmicabundancesrelativetohydrogen,∆[A/H].changesforthestarIC465172.ThetableentriesshowtheeffectsEffectsonderivedabundancesresultingfrommodelTable2. 3alcompositionofevolvedstarsinIC4651
6677.99-Fe_I
6678.82-Co_I
6680.14-Cr_I
6687.49-Y__I
6696.02-Al_I
6696.31-Fe_I
6698.66-Al_I
6699.13-Fe_I
6703.56-Fe_I
6704.48-Fe_I
6707.78-Li_I
6709.89-Ca_I
6710.31-Fe_I
66771133..0149--FFee__II
6713.74-Fe_I
6716.23-Fe_I
6716.67-Ti_I
6721.84-Si_I
6725.35-Fe_I
6726.67-Fe_I
6732.06-Fe_I
6733.15-Fe_I
6736.52-Fe_I
6737.98-Fe_I
6739.52-Fe_I
6741.63-Si_I
6743.12-Ti_I
6745.10-Fe_I
6745.55-Ti_I
6745.96-Fe_I
6746.95-Fe_I
6750.15-Fe_I
6751.44-Cr_I
6752.71-Fe_I
6753.46-Fe_I
6762.36-Zr_I
6764.09-Fe_I
6767.78-Ni_I
6772.31-Ni_I
6783.26-Fe_I
6786.42-Fe_I
6786.86-Fe_I
6793.26-Fe_I
6794.61-Fe_I
6796.12-Fe_I
6798.47-Ca_I
6801.86-Fe_I
6804.27-Fe_I
6806.84-Fe_I
6810.26-Fe_I
6814.94-Co_I
6820.36-Fe_I
6824.84-Fe_I
6828.59-Fe_I
6833.23-Fe_I
6837.01-Fe_I
6839.83-Fe_I
6841.34-Fe_I
6842.03-Ni_I
6842.69-Fe_I
6843.65-Fe_I
666666666666666666666666666666666666666677777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777788888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888888999999999999999999888888888888888888999999999999999999999900000000000000000000000000000000001111111111111111111111111112222222222222222222222222223333333333333333333444444444444444444444444444444444444444455555555555555555555556666777777777777777777888888888888888888889999999999999999900000000000000011222222222222222333333333333333334444444444444444444555555555555555566666666666666666666777777777777778888889999999999000122335668888999455555566666678889112233455677777777889900001111222223333455666667777888890001111111222333455677888990111111222222223345566888880001123555556688999000001111122334444444556666777788888999900012223444555666788881588111122344445777899000122233344455667791111233444555779900223444566799912001333444566799011233345566788890122223333445677889111225677888999900011112233357888999001111455667770247891112234467139469697083599236814557801112450238465636515001366889086901370477224440448447288990279344502790123468247028218669189048246679012456895531608455681162678115792615356001151578812070235779451368136911148115816751251017125348423687708015937756881145079027301625614955397962278527159459056629475667658523629796029288449539507758903845722761224564459340713012045576719234257866701361923645238289021278227360234818322363517988359050221399401411....................................................................................................................................................................................................................................................................................................................................................................................................................................568172112494396502562004220349559387956865593936390680392609904050813369438469411590295999544989151182471656723402693807195829571550769158792392655181671933652509207393035352753647937060520280711458046099017039624375026655281913559249677723135913760733843831081961354853896776082169813783631518726859623013451526857784391854965938176690201087781237190803068926149943936374346687401946896922890025571311981184388045668352642615404539193159687929143263102959325914765806856472702325721837114927798680476579086290267679975292439748609750963281295478336575747129348734030852885592668351325913092928457973300757361633714339980160419208061728501619790669689861485500274649805677738454955395074175442892174533762540323131185918158554004234637790514719667787448488581259700738266307800381614937893316294925629718702165366034568289750198500317999807------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------SFFFFFFFNTFFFFFCCFNFCCFFFFNFFFNSFCFCCFTFFNSFFFSSFFFFNNNSFFCFNFFTFSFEFFACCFZFFNCFCFCFNFFFFTFFFNFFFTFFFSFTTFEFNFFFNSFPSSSTFFFFFSNFEFFFFNVFFCTFAFNNNSFCFNFSFSCFFFNFCFNFFFFFFSFFTNFFFFNFFFNSFFFFFFFNNNFFFFFNNFCFNFFFFFMSSFFNFFNFFFFNFOOOFNSRFFFFSNFAAFFSNFNFMFMSFNSSSFFFTFFFSSTCFSTFSSSFCATFCCFFFFMNSFFNFCCFFFFFMMSFCSFNTFTFTTTFTFTFFFTFTTFSSTTFMFFSSFFZFSFFSFCFFSSFSNFFFFFFNFCNFTTNFTFFFNNMMNSSFFSNAAFAAFSSCACMSFCSNFFCCFOCFNCCSSCCSFCNeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeereeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeereeeeeeeeeeeeeeeeeeeeeeeeeeeeeiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiruiuibiiiiu_iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiirrirriirrriiiioilo_i___iiiiiirliiirioio__iiiiiiioiiiiibilliiiooluo__aa_iai_ai_i__illllalrrirar_r_aaaa____gggggggggg_____I______________________________________________________________________________I_____________________________________________________________________________________________________________________________________II_______I____________________I______I_________I_____________I_____________I________________________________________________________________________I_________II_______I___III_II_II______________IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII_II_______IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
4
Table 3.Abundancesrelativetohydrogen[El/H].Thequotederrors,σ,arethestandarddeviationsinthemeanvalueduetotheline-to-linescatterwithinthespecies.Thenumberof
linesusedisindicatedbyn.Thelasttwocolumnsgivethemean[El/Fe]andstandarddeviationsfortheclusterstars27,72,76and146.
Sˇ
a
27 56 72 76 146 Mean r¯u
n
Species [El/H] σ n [El/H] σ n [El/H] σ n [El/H] σ n [El/H] σ n [El/Fe] σ a
s
M
C(C2) –0.15 1 –0.64 1 –0.12 2 –0.17 1 –0.15 1 –0.26 0.02 i
k
N(CN) 0.36 0.07 24 –0.09 0.11 18 0.35 0.07 24 0.30 0.06 24 0.27 0.09 23 0.21 0.04 o
O([OI]) 0.05 1 –0.27 1 0.09 1 0.16 1 0.18 1 0.01 0.06 la
Nai 0.09 0.05 3 –0.25 0.02 3 0.10 0.04 3 0.10 0.05 3 0.07 0.04 3 –0.02 0.01 it
i
Mgi 0.05 0.07 4 –0.40 0.08 4 0.05 0.09 4 0.09 0.05 4 0.08 0.09 4 –0.04 0.03 s
Ali 0.11 0.05 4 –0.22 0.07 4 0.13 0.02 4 0.17 0.04 4 0.09 0.03 4 0.02 0.03 et
Sii 0.25 0.08 9 –0.35 0.09 6 0.25 0.10 8 0.20 0.07 9 0.21 0.09 9 0.12 0.03 a
Cai 0.17 0.05 9 –0.28 0.08 6 0.13 0.09 10 0.17 0.09 8 0.17 0.10 8 0.05 0.04 l.
Scii 0.17 0.02 9 –0.50 0.05 9 0.14 0.06 8 0.15 0.06 9 0.18 0.05 9 0.05 0.03
Tii 0.25 0.08 24 –0.20 0.07 9 0.23 0.09 24 0.18 0.08 26 0.21 0.10 28 0.11 0.03
Tiii 0.21 0.09 6 –0.30 0.09 8 0.19 0.07 7 0.23 0.09 11 0.14 0.09 11 0.08 0.04
Vi 0.20 0.07 9 –0.58 0.02 9 0.17 0.09 5 0.25 0.05 9 0.27 0.04 9 0.11 0.05
Cri 0.10 0.05 19 –0.51 0.06 11 0.08 0.09 25 0.10 0.09 24 0.10 0.09 24 –0.01 0.02
Crii 0.05 0.04 6 –0.50 0.05 6 0.00 0.09 9 0.08 0.09 6 0.07 0.04 6 –0.06 0.05
Mni 0.20 0.04 6 –0.47 0.01 6 0.21 0.05 5 0.15 0.01 6 0.18 0.06 6 0.07 0.03
Coi 0.25 0.07 8 –0.18 0.09 5 0.20 0.07 9 0.24 0.08 8 0.27 0.08 8 0.13 0.04
Nii 0.17 0.08 34 –0.25 0.10 30 0.20 0.09 34 0.17 0.07 36 0.17 0.08 36 0.07 0.01
Cui 0.05 0.06 3 –0.33 0.07 3 0.08 0.02 3 0.16 0.01 3 0.10 0.02 3 –0.01 0.05
Zni 0.00 0.06 2 –0.28 0.02 2 0.10 0.09 2 0.07 0.07 2 0.07 0.08 2 –0.05 0.03
Yii 0.07 0.05 6 –0.25 0.03 6 0.10 0.04 6 0.04 0.01 6 0.14 0.04 6 –0.02 0.05
Zri 0.03 0.08 2 –0.34 0.01 2 0.00 0.05 2 0.04 0.02 2 0.00 0.05 2 –0.09 0.03
Baii 0.03 0.03 3 –0.29 0.04 2 0.08 0.07 3 0.05 0.05 3 0.05 0.05 3 –0.06 0.01
Laii 0.18 0.02 2 –0.33 0.02 2 0.10 0.05 2 0.15 0.03 2 0.15 0.05 2 0.03 0.05
Ceii 0.22 0.08 2 –0.30 0.02 2 0.20 0.07 2 0.24 0.01 2 0.20 0.07 2 0.11 0.03
Ndii 0.27 0.08 3 –0.18 0.04 2 0.28 0.06 3 0.15 0.05 3 0.18 0.03 3 0.11 0.06
Euii 0.14 1 –0.25 1 0.10 1 0.13 1 0.10 1 0.01 0.03
C/N 1.23 1.12 1.34 1.35 1.5 1.36 0.11
12C/13C 17 14 15 14 18 16 2
Chemical composition of evolved stars in IC 4651 5
2.1 Estimation of uncertainties
1.0
The sources of uncertainty were described in detail in our
Paper I. 0.9
Thesensitivityoftheabundanceestimatestochangesin
theatmosphericparametersbytheassumederrors(±100K 0sity.8
for Teff, ±0.3 dex for log g and ±0.3 km s−1 for vt) is illus- en
tbrlaetpedarfaomrethteersetrarroIrCsd4o65n1o7t2aff(Tecatbltehe2)a.bIutnisdsaenecnesthseartiopuosslsyi-; 0ve Int.7 ScII
the element-to-iron ratios, which we use in our discussion, ati
0el.6
areevenlesssensitive.Thesensitivityofironabundancesto R
stellar atmospheric parameters were described in Carretta
0.5
et al. (2004). [OI]
Thescatterofthededucedlineabundancesσ,presented
in Table 3, gives an estimate of the uncertainty due to the 0.4
randomerrors,e.g.incontinuumplacementandthelinepa-
6300.0 6300.2 6300.4 6300.6 6300.8
rameters (themean valueofσ is0.06). Thustheuncertain- (¯)
tiesinthederivedabundancesthataretheresultofrandom
errors amount to approximately thisvalue. Figure4.Fittotheforbidden[Oi]lineat6300˚AinIC465156.
SinceabundancesofC,NandOareboundtogetherby The observed spectrum is shown as a solid linewith black dots.
Synthetic spectra with[O/Fe]=0.3, 0.08, and0.13 areshownas
themolecularequilibriuminthestellaratmosphere,wehave
solidgraylines.
alsoinvestigatedhowanerrorinoneofthemtypicallyaffects
the abundance determination of another. ∆[O/H] = 0.10
causes∆[C/H]=0.05and∆[N/H]=−0.10,∆[C/H]=0.10
causes∆[N/H]=−0.15and∆[O/H]=0.02,∆[N/H]=0.10 Table4.Themean[El/Fe]forgiant(G)andmain-sequence(MS)
hasnoeffectoneitherthecarbonortheoxygenabundances. stars of IC4651 investigated in this work, Pasquini et al. (2004)
andPaceetal.(2008).
Thiswork Pasquini Pace
3 RESULTS AND DISCUSSION
Species [El/Fe] [El/Fe] [El/Fe] [El/Fe]
The abundances relative to hydrogen [El/H]1 and σ (the G G MS MS
line-to-linescatter) derivedforupto27neutralandionized
Nai 0.00 0.19 –0.09 –0.03
species (including 13C) for the programme stars are listed Mgi –0.05 0.09 0.13
inTable3.Theaverageclusterabundances[El/Fe]anddis- Ali 0.03 0.07 –0.07 –0.10
persionsaboutthemeanvaluesforIC4651arepresentedin Sii 0.09 0.08 0.07 –0.02
Table 3 as well. They are calculated from the results deter- Cai 0.05 0.00 0.04 0.04
mined for the stars 27, 72, 76 and 146. Due to the differ- Scii 0.01 0.11 –0.11
ent [Fe/H], which is by 0.4 dex lower than of other cluster Tii 0.11 0.12 0.08 –0.02
stars, the star 56 was not used in the average calculations Tiii 0.07 0.18 0.00
eventhoughitsvaluesdonotchangetheaverageabundances Cri –0.05 –0.02 0.11
Nii 0.07 0.10 0.01 –0.02
much.Forthemajorityofthechemicalelementsthechanges
are just ±0.01−0.02 dex, only for Sii and Scii the differ-
ence is 0.04 dex, and for Vi – 0.07 dex. From its element
to iron ratios, C/N and 12C/13C ratios, this star within er-
Pasquinietal.(2004)investigatedspectraofbothgiants
rors of uncertainties is indistinguishable from other evolved
and main-sequence stars in IC4651. The authors expressed
starsofthiscluster.However,wethinkthatwithmoreade-
their strong believe that [Na/Fe] ratio is comprehensively
quatemodelatmospheresthisstarcanbeinvestigatedmore
higher in the giants in comparison to the main-sequence
accurately. In Fig. 4 we show an example of spectrum syn-
theses for the [Oi] line in IC465156. In Fig. 3 a sample of stars and that this is due to internal nucleosynthesis and
mixing. However, neither Pace et al. (2008), neither our
its spectrum is shown as well.
studymayconfirmthisstatement.InTable3,wepresentthe
In IC4651, the majority of investigated chemical ele-
mean [El/Fe] for giant and main-sequence stars of IC4651
ments have abundance ratios close to the solar ones. The
mean cluster [α/Fe] ≡ 1([Mg/Fe] + [Si/Fe] + [Ca/Fe] + investigated inourwork,Pasquiniet al.(2004) andPaceet
[Ti/Fe]) = 0.06 ± 0.07 (4s.d.), which is close to the solar al. (2008). In ourwork,theabundancesof Naand Mg were
determined with NLTE taken into account, and we do not
value.
Abundances of Nai, Ali, Sii, Cai, Tii and Nii were findan overabundanceof these chemical elements.
InFig.4ofPaperI,wepresentedtheradialdistribution
determined for the main-sequence stars of IC4651 by Pace
ofsomeelementalabundancesforBOCCEclustersanalysed
etal.(2008).Themean[El/Fe]ratiosinthesestarsarevery
so far, and for others in recent studies. IC4651 agrees well
close to solar as well.
withresultsofotheropenclustersatthesameRgcof7.1kpc.
In the following sections we will discuss in more detail
1 In this paper we use the customary spectroscopic notation the results of carbon and nitrogen abundance determina-
[X/Y]≡log10(NX/NY)star−log10(NX/NY)⊙ tions.
6 Sˇaru¯nas Mikolaitis et al.
ThemeannitrogentoironabundanceratioinIC4651is
1.0
[N/Fe]=0.21±0.04. Thisshowsthatnitrogen isoverabun-
dant in these evolved stars of IC4651, since [N/Fe] values
0.9
in the Galactic main-sequence stars are about solar at the
y C2 solar metallicity (c.f. Shi et al. 2002). Unfortunately, nei-
sit0.8 thercarbon, neither nitrogen abundances were investigated
n
e
nt in the main sequence stars of IC4651 by Pace et al. (2008)
e I0.7 and Pasquini et al. (2004).
ativ ThemeanC/NratiosinIC4651isequalto1.36±0.11.
el0.6 Thesmallest valueof C/N=1.12 was obtained for thestar
R
FeI IC465156.
0.5 The12C/13Cratiosweredeterminedforallprogramme
FeI starsfrom the(2,0) 13C14Nfeatureat8004.728 ˚A.InFig.6
0.4 weshowasmallregionofIC465172spectrumtogetherwith
spectralsynthesesobtainedwiththreedifferentvaluesofthe
5634.0 5634.5 5635.0 5635.5 5636.0 carbonisotopicratio.Wefindthatthemean12C/13Cratios
(¯) are about 16±2 in theevolved stars investigated.
The solar carbon and nitrogen abundances used in our
Figure 5.Small region of IC4651 27 spectrum (solid black line
with black dots) at C2 Swan (0,1) band head 5635.5 ˚A, plotted work are logAC = 8.52 and logAN = 7.92 (Grevesse &
together with synthetic spectra with [C/Fe] values lowered by Sauval 2000), so the solar C/N = 3.98. The 12C/13C ra-
−0.2dex(lowergrayline),−0.25dex(middlegrayline)and−0.3 tio in the solar photosphere is equal to 89 (Coplen et al.
(uppergrayline). 2002).
3.2 Comparison of 12C/13C and C/N ratios with
1.00
theoretical models
The carbon and nitrogen abundances, C/N and especially
0.95 the carbon isotope ratios 12C/13C are key tools for stel-
y lar evolution studies. Investigations of abundances of these
nsit 13 14 chemical elements in atmospheres of clump stars of open
nte0.90 C N clustersmayprovideacomprehensiveinformationonchem-
e I icalcompositionchanges.Theclumpstarshaveaccumulated
v
ati0.85 all chemical composition changes that have happened dur-
el ing their evolution along the giant branch and during the
R
helium flash.
In Fig. 7 and 8, we compare the mean carbon isotope
0.80
and C/N ratios of clump stars in different open clusters as
12 14 12 14 12 14 a function of turn-off mass with the theoretical models of
C N C N C N
0.75 the1st dredge-up,thermohalinemixing(TH),thermohaline
8003.0 8003.5 8004.0 8004.5 8005.0 mixing together with rotation-induced mixing for stars at
(¯) the zero age main sequence (ZAMS) having rotational ve-
Figure 6.Small region of IC4651 72 spectrum (solid black line locities of110kms−1,250kms−1 and 300kms−1 computed
withblackdots)with13C14Nfeature.Greylinesshowsynthetic by Charbonnel & Lagarde (2010); and Cool Bottom Pro-
spectra with12C/13Cratios equal to 13(lower line),15(middle
cessing model (CBP) by Boothroyd & Sackman (1999).
line)and17(upper line).
The most resent modelling of extra-mixing processes
wasdonebyCharbonnel&Lagarde(2010).Theyarebased
on ideas of Eggleton et al. (2006) and Charbonnel & Zahn
3.1 Carbon and nitrogen abundances
(2007).Eggletonetal.(2006)foundameanmolecularweight
The average value of carbon to iron ratio in IC4651 is (µ)inversionintheir1M⊙stellarevolutionmodel,occurring
[C/Fe] = −0.27±0.02. In Fig. 5, a fit to the IC4651 27 aftertheso-calledluminositybumpontheredgiantbranch,
spectrum at C2 5635.5 ˚A is shown. whentheH-burningshellsourceentersthechemicallyhomo-
We compared the carbon abundance in IC 4651 with geneouspartoftheenvelope.Theµ-inversionisproducedby
carbonabundancesdeterminedfordwarfstarsintheGalac- thereaction3He(3He,2p)4He,aspredictedbyUlrich(1972).
ticdisk.Shietal.(2002)performedanabundanceanalysisof It does not occur earlier, because the magnitude of the µ-
carbonforasampleof90FandGtypemain-sequencedisk inversion is small and negligible compared to a stabilizing
stars using Ci and [Ci] lines and found [C/Fe] to be about µ-stratification. Following Eggleton et al. (2006), Charbon-
solar at the solar metallicity. Roughly solar carbon abun- nel & Zahn (2007) have computed stellar models including
danceswerefoundbyGustafssonetal.(1999)whoanalysed theprescription byUlrich(1972) andextendedthemtothe
asampleof80lateFandearlyGtypedwarfsusingthefor- case of a non-perfect gas for the turbulent diffusivity pro-
bidden [Ci] line. The ratios of [C/Fe] in our stars lie about duced by that instability in a stellar radiative zone. They
0.3 dex below the values obtained for dwarf stars of the found that a doublediffusiveinstability referred to as ther-
Galactic disk. mohaline convection, which has been discussed long ago in
Chemical composition of evolved stars in IC 4651 7
Table 5.12C/13CandC/Nratiosalongwithturn-offmass,age,galactocentric distanceandatmosphericparametersforclumpstars
Cluster Star MTO(M⊙) Age(Gyr) Rgc(kpc) Teff(K) logg [A/H] 12C/13C C/N Ref.∗
NGC752 1 1.60 2.0 8.75 5000 2.85 0.1 16 – 1
75 4900 2.85 0.1 13 – 1
77 4900 2.85 0.2 16 – 1
213 5000 2.90 0.1 14 – 1
295 5000 2.90 0.2 15 – 1
NGC2360 50 2.02 1.15 6.32 5015 2.90 –0.03 – 1.04 5
62 5105 3.15 0.12 – 1.38 5
86 4960 2.65 –0.06 – 0.93 5
12 4800 2.70 0.2 14.5 – 1
NGC2447 28 1.90 0.45 6.51 5060 2.70 –0.01 – 0.69 5
34 5120 2.90 –0.01 – 0.87 5
NGC2682 F84 1.20 5.0 9.05 4750 2.4 –0.02 20 1.15 3
F141 4730 2.4 –0.01 16 1.32 3
F151 4760 2.4 –0.03 17 1.32 3
F164 4700 2.5 0.00 18 1.62 3
F224 4710 2.4 –0.11 8 1.58 3
F226 4730 2.4 –0.02 15 1.62 3
F84 4800 2.70 0.0 11.5 – 1
F141 4800 2.70 0.0 10.5 – 1
F164 4800 2.70 0.0 10.5 – 1
NGC2714 5 2.91 0.40 8.34 5070 2.70 0.12 – 0.83 5
NGC3532 19 3.03 0.35 7.87 4995 2.65 0.11 12 1.02 5
122 5045 2.60 –0.02 – 0.93 5
596 5020 2.50 0.04 – 0.95 5
HD95879 5000 2.25 0.08 10 1.10 2
HD96174 5000 2.17 0.00 15 0.59 2
HD96175 5100 2.25 0.12 15 0.44 2
HD96445 5000 2.36 0.13 10 1.51 2
NGC5822 201 2.19 0.9 8.10 5035 2.85 0.05 13 0.87 5
316 5110 3.05 0.16 – 1.00 5
NGC 6134 39 2.34 0.7 7.6 4980 2.52 0.24 9 1.48 6
69 4950 2.83 0.11 12 1.38 6
75 5000 3.10 0.22 7 1.41 6
114 4940 2.74 0.11 6 1.05 6
129 5000 2.98 0.05 8 0.98 6
157 5050 2.92 0.16 12 1.10 6
30 4980 2.95 0.21 12 0.93 5
NGC6281 3 3.18 0.3 8.47 4915 2.30 0.01 12 0.64 5
4 5015 2.50 0.09 12 0.95 5
NGC6633 100 2.79 0.45 8.42 5015 2.85 0.11 21 0.91 5
NGC7789 K605 1.60 1.4 9.43 4860 2.4 –0.02 10 1.05 4
K665 4970 2.4 0.00 9 1.45 4
K732 4900 2.3 0.02 7 1.51 4
IC2714 5 2.85 0.40 8.34 5070 2.70 0.12 – 0.83 5
IC4651 27 1.69 1.7 7.1 4610 2.52 0.10 17 1.23 7
76 4620 2.26 0.11 14 1.35 7
146 4730 2.14 0.10 18 1.50 7
IC4756 12 2.37 0.7 7.23 5030 2.75 –0.01 11 0.91 5
14 4720 2.47 0.03 17 1.02 5
38 5075 3.00 0.05 10 1.20 5
69 5130 3.00 0.08 5 1.15 5
144 5200 3.20 0.0 18 – 1
176 5200 3.00 0.0 12 – 1
228 5000 2.90 0.0 21 – 1
296 5000 2.90 0.0 18 – 1
∗ 1–Gilroy(1989); 2–Luck(1994); 3–Tautvaiˇsiene˙ etal.(2000); 4–Tautvaiˇsiene˙ etal.(2005); 5–Smiljanicetal.(2009);
6–Mikolaitisetal.(2010); 7–Thiswork.
8 Sˇaru¯nas Mikolaitis et al.
theliterature (Stern 1960), is important in evolution of red
giants. This mixing connects the convective envelope with
30 1st dredge-up
theexternalwingofhydrogenburningshellandinducessur-
TH
face abundancemodifications in red giant stars. TH+V(110)
Charbonnel &Lagarde (2010) also computedthemod- TH+V(250)
els of rotation-induced mixing for stars at the zero age TH+V(300)
main sequence having rotational velocities of 110kms−1, CBP
250kms−1 and 300kms−1. Typical initial ZAMS rotation 20
C
velocities were chosen depending on the stellar mass based 13 C/
on observed rotation distributions in young open clusters 12
(Gaig´e 1993). The convective envelpoe was supposed to ro-
tate as a solid body through the evolution. The transport
coefficients for chemicals associated to thermohaline and
10
rotation-induced mixings were simply added in the diffu-
sionequationandthepossibleinteractionsbetweenthetwo
mechanismswerenotconsidered.Therotation-inducedmix-
ingmodifiestheinternalchemicalstructureofmainsequence 1.0 1.5 2.0 2.5 3.0 3.5 4.0
stars, although its signatures are revealed only later in the M/MSun
stellar evolution.
Figure 7. The average carbon isotope ratios in clump stars of
The models by Boothroyd & Sackmann (1999) include
openclustersasafunctionofstellarturn-offmass.Theresultof
the deep circulation mixing below the base of the standard this work is marked by the filled square; from Mikolaitis et al.
convective envelope, and the consequent ”cool bottom pro- (2010)andTautvaiˇsiene˙ etal.(2000, 2005)–opensquares;from
cessing” (CBP) of CNO isotopes. Smiljanic et al. (2009) – open triangles; from Luck (1994) – re-
The theoretical models were compared to the observa- versedopentriangle;fromGilroy(1989)–opencircles.Themod-
tional data of 12C/13C and C/N listed in Table 5, which elsofthe1st dredge-up,thermohalinemixing(TH)androtation-
wecollectedforclumpstarsofopenclustersinvestigatedby inducedmixing(V)aretakenfromCharbonnel&Lagarde(2010).
TheCBPmodelofextra-mixingistakenfromBoothroyd&Sack-
Mikolaitisetal.(2010),Smiljanicetal.(2009),Tautvaiˇsiene˙
mann(1999).
et al. (2000, 2005), Luck (1994) and Gilroy (1989). From
Gilroy (1989) we selected 4 clusters with well defined red
clumpstars.Luck(1994)derivedcarbonisotoperatiosfor8
open clusters, howeveronly one clusterwas included toour
comparison since for other clusters it was very difficult to
identify stars of red clump. The turn-off masses, ages and 2.5
1st dredge-up
galactocentric distances were choosen from the most recent TH
studies and used for displaying of other 12C/13C and C/N TH+V(110)
investigations for the same cluster, if available. 2.0 TH+V(250)
InFig.7and8wecanseethatforclusterswithstarsof TH+V(300)
smallerturn-offmassesthe12C/13CandC/Nvaluesareina CBP
1.5
good agreement with both models of extra-mixing used for
thecomparison.However,12C/13Cvaluesintheclumpstars C/N
with turn-off masses of 2–3 M⊙ in most of the investigated
1.0
clusters are lower than predicted by the available models
and need modelling of larger extra-mixing.
0.5
3.3 Final remarks
Carbon and nitrogen are important products of nucleosyn- 1 2 3 4
thesisprocessesinstellarinteriors,andtheevidenceoftheir M/MSun
abundance variation during stellar evolution is a signature
of physical mixing processes between the atmosphere and Figure8.Theaveragecarbontonitrogenratiosinclumpstarsof
openclustersasafunctionofstellarturn-offmass.Themeaning
deeper layers of a star. Such abundance alterations may be
ofsymbolsareasinFig.7.
welltracedinopenclusters.Theyprovideauniquepossibil-
ityforinvestigation ofanumberofstars ofnearly thesame
age, distance and origin, as open cluster stars are claimed
tobeformed in thesame protocloud of gas anddust.Open
clusters have a high reliability of mass, distance, evolution- 1998,Grattonetal.2000,Chanam´eetal.2005, Cantiello&
ary phase and abundancedeterminations. Langer 2010; Charbonnel & Lagarde 2010 for more discus-
Extra-mixingprocessesmaybecomeefficientonthered sion).
giantbranchwhenstarsreachtheso-calledRGBbump,and The comparison of the observational data with theo-
maymodify thesurface abundances.Itisknown thatalter- retical models of stellar evolution shows that processes of
ationsof12C/13Cand12C/14Nratiosdependonstellarevo- extra-mixing in stars of open clusters with turn-off masses
lutionarystage,massandmetallicity (seeCharbonneletal. of 2–3 M⊙ are larger than predicted.
Chemical composition of evolved stars in IC 4651 9
ACKNOWLEDGMENTS Mikolaitis Sˇ., Tautvaiˇsiene˙ G., Gratton R., Bragaglia A.,
Carretta E., 2010, MNRAS,407, 1866
This research has made use of Simbad, VALD and NASA
Nissen P. E., 1988, A&A,199, 146
ADSdatabases.BertrandPlez(UniversityofMontpellierII)
Pasquini L., Randich S., Zoccali M., Hill V., Charbonnel
andGuillermoGonzalez(WashingtonStateUniversity)were
C., Nordstr¨om B., 2004, A&A,424, 951
particularly generous in providing us with atomic data for
Pace G., Pasquini L., Franc¸ois P., 2008, A&A,489, 403
CNandC2molecules,respectively.Sˇ.M.andG.T.weresup- SantosN.C.,LovisC.,PaceG.,MelendezJ.,NaefD.,2009,
portedbytheMinistryof EducationandScienceofLithua-
A&A,493, 309
nia via LitGrid programme and by the European Commis-
ShiJ. R., Zhao G., Chen Y.Q., 2002, A&A,381, 982
sion via FP7 Baltic Grid II project.
Smiljanic R., Gauderon R., North P., Barbuy, B., Char-
bonnelC., Mowlavi N., 2009, A&A,502, 267
Stern,M. E. 1960, Tellus, 12, 172
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