Chemical composition of AY Ceti: A flaring, spotted star with a white dwarf companion

0.15 MB·English

by  G. Tautvaišienė

Astron. Nachr./AN332,No.9/10,1–8(2011)/DOI10.1002/asna.201111597
Chemical composition of AYCeti: A flaring, spotted star with a white
dwarf companion
G.Tautvaisˇiene˙1,⋆,G.Barisevicˇius1,S.Berdyugina2,I.Ilyin3,andY.Chorniy1
1 InstituteofTheoreticalPhysicsandAstronomy,VilniusUniversity,Gosˇtauto12,LT-01108Vilnius,Lithuania
2 KiepenheuerInstitutfu¨rSonnenphysik,Scho¨neckstr6,D-79104Freiburg,Germany
3 Leibniz-Institutfu¨rAstrophysikPotsdam,AnderSternwarte16,D-14482Potsdam,Germany
2
1
0 Received2011Sep20,accepted2011Sep29
2 Publishedonline2011

n
a Keywords binaries:close–stars:abundances–stars:activity–stars:individual(AYCet)
J
ThedetailedchemicalcompositionoftheatmosphereAYCet(HD7672)isdeterminedfromahigh-resolutionspectrum
3
in the optical region. The main atmospheric parameters and the abundances of 22 chemical elements, including key
2
species such as 12C, 13C, N, and O, are determined. A differential line analysis gives Teff = 5080 K, log g = 3.0,
] [Fe/H]=−0.33,[C/Fe]=−0.17,[N/Fe]=0.17,[O/Fe]=0.05,C/N=1.58,and12C/13C=21.Despitethehigh
R chromosphericactivity,theopticalspectrumofAYCetprovidesachemicalcompositiontypicalforfirstascentgiantsafter
S thefirstdredge-up.
.
h (cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
p
-
o
1 Introduction surements,Simonetal.(1985)havedeterminedforAYCet
r
t an orbital period of 56.80 ± 0.03 days, which attributes
s
a The variability of AYCeti (HD7672, 39Cet) was first no- AYCettothesampleofnon-synchronousRSCVnrotators.
[
ticed by Cousins (1962) and later confirmed by Olsen Evenmoreaccurateorbitalelementshavebeendetermined

1 (1974). A spectral class of G5III was assigned to AYCet forAYCetbyFekel&Eitter(1989).
v byCowley&Bidelman(1979),whoalsonotedinitsspec-
From observations with the HEAOII satellite (Walter
9 trumamoderatelystrongCaIIHandKemission,indicating
9 & Bowyer 1981)and fromIUE observations(Simonet al.
thatthisstarmightbeanRSCVnbinary.
6 1985)itwas discoveredthatAYCethasa hotwhite dwarf
4 Fromphotoelectricphotometryobtainedin1971,1972, companion. The UV spectrum of AYCet at 1200–2000A˚
. 1980–81, and 1981–82, Eaton et al. (1983) have deter-
1 shows a hot stellar continuum and a very broad Lyα ab-
mined a mean photometric period of 77.65±0.05 days.
0 sorptionlinewhich canbe matchedto the energydistribu-
2 The full V amplitude of the nearly sinusoidal light curve tionofthewhitedwarfwithTeff =18000Kandlogg =8
1 has been as large as 0.18 mag. For predicting future be-
modelatmosphere.Superimposedonthehotcontinuumare
: haviour of AYCet the authors proposed the ephemeris JD
v high-excitationemissionlinesofthelate-typeprimary(e.g.,
Xi = 244636.0+77.65E days, where the initial epoch is at OI1305A˚ andCIV 1549A˚).Simonetal.determinedthat
time of minimum light. In the same work it was noticed
r that the maximum brightness of AYCet has decreased by the radiusofthe AYCetBwhite dwarfisr2 = 0.012R⊙,
a and the mass m2 =0.55 M⊙, the radius of the primary
0.18mag(fromV =5.35to5.53mag)duringthetenyears
AYCetA is r1 = 6.8 R⊙, and the mass m1 = 2.09 M⊙.
of observations. Strassmeyer et al. (1989)found a slightly
MassandradiusofAYCetwerealsodeterminedinseveral
smaller rotational period of 75.12± 0.03 days from pho-
later studies: r1 = 6.6 R⊙ by Schrijver & Zwaan (1991);
tometry obtained between 1983 and 1986. The amplitude
r1 =8.18R⊙andm1 =1.95M⊙bydaSilvaetal.(2006);
was variable from season to season and changed from ap-
and r1 = 7.9 R⊙ and m1 = 2.0 M⊙ by Massarotti et al.
proximately0.06to0.19magwithinoneyear.Porettietal.
(2008).
(1986) have combined UBV photometry of AYCet from
1980–81,1981–82,and1983–84,andfoundthatthevaria- From observationswith the VLA radio interferometer,
tionsoftheV magnitudecanberepresentedasacombina- Simonetal.(1985)alsoreportedthedetectionoftwovery
tionofthreesinecurveswiththefollowingsemi-amplitudes strongradioflaresonAYCet.Thesecondflarewascharac-
andperiods:0.06magatP1 =77.22d,0.03magatP2 = terizedbyminute-to-minutevariationsintheleft-circularly
79.36d,and0.07magatP3 =1820d. polarized flux. Such highly polarized activity is quite rare
amongtheRSCVnandrelatedsystemsandmostprobably
As well as for λAnd, the orbital period of AYCet is
actsas electron-cyclotronmaser.In orderto studyweather
much smaller than the photometric period. Using 22 mea-
theUVemissionofAYCetisvariable,Simon&Sonneborn
⋆ Correspondingauthor:[email protected] (1987)have obtained IUE observationsof this star on five
(cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
2 G.Tautvaisˇiene˙etal.:ChemicalcompositionofAYCeti
dates between 1983 and 1984. It was found that the spec-
trum ofthe secondaryhasno discerniblechangeseither in −0.2
thelevelofbrightnessofitscontinuumorintheshapeofthe
absorption profile of Lyα. Quite significant changes were H]−0.3
observedinthespectrumoftheprimary.Attheirstrongest, Fe/
[−0.4
the stellar features were up to one hundred times brighter
thanthesamelinesobservedinthequietSun.Therangein
−0.5
linestrengthfromtheminimumtothemaximumbrightness
levelsobservedforAYCetwasroughlyafactorof1.5–2in 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
thechromosphericlinesand5–6inthetransitionregionfea- c l (eV)
tures.Surprisingly,bothUVandpreviouslyobservedradio Fig.1 The [FeI/H] abundance values versus the lower
flares(Simonetal.1985)occurrednearthepeakinvisible excitation potential χl. The mean abundance [FeI/H] =
lightcurve,whenasurfaceoftheprimaryislesscoveredby −0.33isshownasadottedline.
starspots.
Thus,AYCetisharestheattributesofspotted,chromo-
−0.2
spherically active RS CVn binaries: strong CaII H and K
emission,aprominentphotometricwaveinvisuallight,and
intense soft X-ray emission. In addition, AYCet is espe- H]−0.3
e/
ciallyprominentbecauseofitsstrongradioflares.Fromthe [F−0.4
radiopointofview,AYCetmaybeamongthemostactive
stellar sourcesinthe sky(Simonetal.1985).Thepurpose −0.5
ofthisworkwastodeterminethedetailedchemicalcompo-
20 40 60 80 100
sition ofAYCetatmospherefromitshigh-resolutionspec- (cid:176)
EW (mA)
trumintheopticalregion.Inparticular,itwasinterestingto
Fig.2 The [FeI/H] abundance values versus the equiv-
investigatehasstellaractivityalteredabundancesofmixing-
sensitiveelementssuchas12C,13C,andN. alent widths. The mean abundance [FeI/H] = −0.33 is
shownasadottedline.
2 Observations andmethod ofanalysis
The surface gravity logg was found by adjusting the
model’sgravityto yieldthe sameironabundancefromthe
A spectrum of AYCet was observed in August of 1999
FeI and FeII lines. The microturbulent velocity vt value
on the 2.56 m Nordic Optical Telescope using the SOFIN
correspondingtoaminimalline-to-lineFeIabundancescat-
echelle spectrograph with the optical camera, which pro-
teringwaschosenasacorrectvalue.Consequently,[Fe/H]
vided a spectral resolving power of R≈80000, for 26
values do not depend on the equivalent widths of lines
slightly shifted in wavelength spectral orders, each of
(Fig.2).
∼40A˚,inthespectralregionfrom5000to8300A˚.Thede-
tailsofspectralreductionswerepresentedinTautvaisˇiene˙et
2.2 Massdetermination
al. (2010,hereafterPaper I). We selected 147 atomic lines
for the measurementof equivalentwidths and 16 lines for
The mass of AYCet was evaluated from its effective tem-
thecomparisonwithsyntheticspectra.Themeasuredequiv-
perature,luminosityandthe isochronesfromGirardiet al.
alentwidthsoflinesarepresentedinTable1.
(2000).Theluminositylog(L/L⊙) = 1.65wascalculated
Thespectrawereanalysedusingadifferentialmodelat- fromtheHipparcosparallaxπ = 12.41mas(vanLeeuwen
mospheretechniquedescribed in Paper I. Here we present 2007)andV =5.43mag(daSilvaetal.2006),thebolomet-
onlysomedetails. riccorrectioncalculatedaccordingtoAlonsoetal.(1999),
andtheabovementionedreddeningEB−V =0.02.Amass
2.1 Atmosphericparameters of∼2.2M⊙wasfound,whichisclosetothepreviouseval-
uations(Simonetal.1985;daSilvaetal.2006;Massarotti
Initially,theeffectivetemperature,Teff, ofAYCetwas de- etal.2008).
rivedandaveragedfromtheintrinsiccolorindices(B−V)0
and(b−y)0usingthecorrectedcalibrationsbyAlonsoetal. 2.3 Spectrumsyntheses
(1999).ThecolorindicesB−V =0.89andb−y =0.558
weretakenfromMermilliod(1986)andHauck&Mermil- Due to the rotation spectral lines of AYCet are slightly
liod(1998),respectively.AreddeningofEB−V =0.02,es- broadened.Weusedvsini=4.0kms−1becausewiththis
timatedusingtheHakkilaetal.(1997)software,wastaken valuethematchbetweenthesyntheticandobservedspectra
intoaccount.Thetemperaturesdeducedfrombothcolorin- was the best. The same rotation speed was determined by
diceswere 5080K and,noobvioustrendofthe FeI abun- Strassmeieretal.(1988),Berdyugina(1994),andMonteset
danceswiththeexcitationpotentialwasfound(Fig.1). al.(1994).Thisvalueisalsoclosetovsini = 4.5kms−1
(cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(2011) 3
Table1 Measuredequivalentwidthsoflines,EW,intheAYCetspectrum.
Element λ(A˚) EW(mA˚) Element λ(A˚) EW(mA˚) Element λ(A˚) EW(mA˚)
SiI 5517.55 15.2 6266.30 16.8 6646.97 21.4
5645.60 38.2 6274.66 33.0 6786.86 30.5
5665.55 38.7 6285.16 42.6 6793.27 15.1
5793.08 42.8 6292.82 50.6 6839.83 53.7
5948.54 77.9 CrI 5712.78 25.9 6842.69 44.2
6131.85 20.6 5783.87 54.5 6843.65 65.6
7003.57 45.5 5784.97 44.9 6851.64 14.0
CaI 5260.38 44.2 5787.92 56.0 6857.25 27.9
5867.57 32.0 6661.08 14.1 6858.15 54.4
6455.60 73.8 6979.80 48.2 6862.49 31.9
6798.47 10.5 6980.91 12.7 7461.53 48.3
ScII 5526.81 103.7 FeI 5395.22 25.0 FeII 5132.68 35.1
5640.98 65.6 5406.78 44.0 5264.81 50.0
5667.14 52.0 5522.45 51.3 6113.33 13.0
6279.75 51.7 5577.03 11.1 6369.46 22.1
6300.69 11.2 5579.35 13.7 6456.39 67.9
TiI 5648.58 22.1 5607.67 19.1 7711.72 48.1
5662.16 43.9 5608.98 14.0 CoI 5530.78 36.3
5716.45 14.5 5651.48 23.3 5590.71 27.0
5739.48 18.6 5652.33 34.0 5647.23 28.3
5880.27 28.5 5653.86 45.2 6117.00 16.3
5899.30 70.5 5679.03 66.8 6188.98 25.2
5903.31 18.6 5720.90 19.0 6455.00 19.7
5941.76 48.8 5732.30 12.8 6595.86 8.6
5953.17 60.0 5741.86 36.9 6678.82 13.7
5965.83 57.3 5784.67 39.8 NiI 5578.73 77.3
6064.63 30.1 5793.92 40.9 5587.87 77.6
6098.66 10.5 5806.73 62.3 5589.37 27.2
6121.00 11.9 5807.79 15.7 5593.75 41.4
6126.22 54.2 5809.22 63.7 5643.09 13.6
6220.49 20.8 5811.92 15.4 5748.35 50.7
6303.77 25.1 5814.82 30.6 5805.22 38.6
6599.11 31.7 6027.06 74.5 6053.68 19.1
6861.45 17.3 6034.04 10.9 6108.12 88.7
VI 5604.96 14.1 6035.35 7.8 6111.08 34.7
5646.11 16.4 6054.07 11.4 6128.98 44.3
5657.45 22.5 6056.01 73.2 6130.14 19.8
5668.37 20.8 6098.25 20.5 6204.60 23.5
5670.86 49.2 6105.13 14.1 6378.25 33.7
5727.66 31.1 6120.24 20.2 6482.80 59.6
5737.07 35.8 6187.99 58.3 6586.32 64.9
5743.43 26.4 6200.32 98.6 6598.60 22.6
6039.74 35.6 6226.74 34.8 6635.13 20.7
6058.18 11.8 6229.23 56.0 6767.78 111.1
6111.65 36.4 6270.23 72.4 6772.32 54.7
6119.53 51.6 6380.75 60.1 6842.03 32.7
6135.37 32.7 6392.54 33.2 7001.55 25.1
6224.50 27.8 6574.21 62.8 7062.97 25.0
6233.19 25.9 6581.21 46.8 7715.59 55.5
determined by Gray (1989). A slightly lower value of 13C14N features,wasused forthe nitrogenabundanceand
vsini = 2.9kms−1 wasusedbyBattenetal.(1989),and 12C/13Cratiodeterminations.The12C/13Cratiowasdeter-
slightlyhighervalueofvsini=6.0kms−1byFekeletal. minedfromthe(2,0)13C12Nfeatureat8004.7A˚.Allloggf
(1986). values were calibrated to fit to the solar spectrum of Ku-
The method of synthetic spectra was used to deter- rucz(2005)withsolarabundancesfromGrevesse&Sauval
mine the carbon abundance from the C2 line at 5135.5 A˚. (2000).
The interval 7980–8130 A˚, containing strong 12C14N and
www.an-journal.org (cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
4 G.Tautvaisˇiene˙etal.:ChemicalcompositionofAYCeti
1.00
y
sit
n
e0.95
nt
e i
v
ati0.90
el
R
0.85
7987.9 7988.2 7995.5 7995.8 7999.6 7999.9 8000.2 8000.5
(cid:176)
l (A)
Fig.3 Synthetic spectrum fit to 12CN lines. The observed spectrum is shown as a solid line. The dashed lines are
syntheticspectrawith[N/Fe]=0.13,0.23,and0.33dex.
1.00 1.00
y
ty sit
si n
n e
e nt
nt e i0.95
i0.95 v
ve ati
ti el
a R
el
R 0.90 [O I] Sc II
0.90
C 6300.2 6300.5 6300.8
2
(cid:176)
l (A)
5135.5 5135.8
l (A(cid:176) ) Fig.5 Syntheticspectrumfittotheforbidden[OI]lineat
6300A˚.Theobservedspectraareshownassolidline.The
Fig.4 SyntheticspectrumfittotheC2 lineat5135.5A˚. dashedlinesaresyntheticspectrawith[O/Fe]=0.03,0.13,
The observedspectraare shownas solidlines. Thedashed and0.23dex.
linesaresyntheticspectrawith[C/Fe] = −0.03,0.13,and
0.23dex.
tunately, the line-to-line abundance scatter of [Ni/H] from
24linesofNiIwasassmallas0.06dex.
For the evaluation of the ZrI abundance the lines at
Theoxygenabundancewasdeterminedfromtheforbid-
den[OI]lineat6300.31A˚ withtheoscillatorstrengthsfor 5385.13A˚,6127.48A˚,and6134.57A˚ wereused.Theabun-
58Ni and 60Ni from Johansson et al. (2003)and log gf = dance of YII was based on 5402.78 A˚, that of LaII on
−9.917 obtained by fitting to the solar spectrum (Kurucz 6390.48A˚,thatofCeII on5274.22A˚ and6043.38A˚,and
2005) with logA⊙ =8.83 (Grevesse & Sauval 2000). In tthhaetNodfINIdlinIIeoant55227766..88066A˚A˚.,TYhIeIsaytn5t4h0e2ti.c78spA˚e,ctarnudmLfiatIsItaot
Figs. 3, 4, and 5 we show several examples of synthetic
spectrainthevicinityofthe12C14N,C2,and[OI]lines. 6390.48A˚ aredisplayedinFigs.6,7,and8respectively.
Theabundanceofr-processelementpraseodymiumwas
The abundance of NaI was estimated using the line based on the PrII line at 5259.72 A˚ and of europium on
5148.84A˚ which,due to rotationalbroadening,is blended theEuIIlineat6645.10A˚ (Fig.9).Thehyperfinestructure
bytheNiIlineat5148.66A˚.Thesetwolinesaredistinctin of EuII was taken into account when calculating the syn-
theSun,sowewereabletocalibratetheirloggf valuesus- theticspectrum.Thewavelength,excitationenergyandto-
ingthesolar spectrum.However,the sodiumabundancein talloggf =0.12weretakenfromLawleretal.(2001),the
ourstudyisaffectedbytheuncertaintyofthenickelabun- isotopicmeteoriticfractionsof151Eu,47.77%,and153Eu,
dance,originatingfromtheequivalentwidthsmethod.For- 52.23%,andisotopicshiftsweretakenfromBiehl(1976).
(cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(2011) 5
1.00 1.00
y
sit ty
n si
e n
nt e0.96
i0.96 nt
ve e i
ti v
ela ati
R el
Nd II R0.92 La II
0.92
5276.7 5277.0 6390.3 6390.6
(cid:176) (cid:176)
l (A) l (A)
Fig.6 Synthetic spectrum fit to the NdII line at Fig.8 Synthetic spectrum fit to the LaII line at at
5276.806A˚.Theobservedspectrumisshownasasolidline. 6390.48 A˚. The observed spectrum is shown as a solid
Thedashedlinesaresyntheticspectrawith[Nd/Fe]=0.11, line.Thedashedlinesaresyntheticspectrawith[La/Fe]=
0.21,and0.31dex. −0.07,0.03,and0.13dex.
1.00
1.00
y
y t
sit0.95 nsi
n e
e t
t n
in e i0.95
e v
tiv0.90 ati
ela Rel
R Eu II
0.90
0.85 Y II
5402.6 5402.9 6645.0 6645.5
(cid:176) (cid:176)
l (A) l (A)
Fig.7 SyntheticspectrumfittotheYIIlineat5402.78A˚. Fig.9 Synthetic spectrum fit to the EuII line at
Theobservedspectrumisshownasasolidline.Thedashed 6645.10A˚.Theobservedspectrumisshownasasolidline.
linesaresyntheticspectrawith[Y/Fe] = −0.07,0.03and Thedashedlinesaresyntheticspectrawith[Eu/Fe]=0.05,
0.13dex. 0.15,and0.25dex.
2.4 Estimationofuncertainties continuumlevelplacementdependsontheS/Nratio,which
isabout200inourcase.
The sources of uncertainty were described in detail in
Thescatterofthededucedlineabundances,σ,presented
Paper I. The sensitivity of the abundance estimates to
in Table 3, gives an estimate of the uncertainty due to the
changesintheatmosphericparametersfortheassumeder-
rors(±100KforTeff,±0.3dexforlogg,and±0.3kms−1 randomerrors,e.g.,inthecontinuumplacementandtheline
parameters(themeanvalueofσ is0.05dex).Thustheun-
for vt) is illustrated in Table 2. It is seen that possible pa-
certainties in the derived abundances originating from the
rameter errors do not affect the abundances seriously; the
randomerrorsareclosetothisvalue.
element-to-ironratios,whichweusein ourdiscussion,are
evenlesssensitive.The12C/13Cratioisparticularlynotsen- SincetheabundancesofC,N,andOareboundtogether
sitive to changes in the atmospheric parameters. However, by the molecular equilibrium, we have also investigated
it’svaluemightdecreaseby-3orincreaseby+7asaresult howanerrorinoneofthemtypicallyaffectstheabundances
ofraisingorloweringthecontinuumlevel,respectively.The oftheothers.
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6 G.Tautvaisˇiene˙etal.:ChemicalcompositionofAYCeti
Table 2 The sensitivity of stellar atmospherice abun- Table 3 Atmospheric abundances relative to hydrogen,
dancestochangesoftheatmosphericparameters.Thetable [A/H].σ isthestandarddeviationofthemeanvaluedueto
entries show ∆[A/H] for the given changes of the stellar theline-to-linescatter;N isthenumberoflinesusedforthe
parameters. abundancedetermination.
Species ∆Teff ∆logg ∆vt Species N [A/H] σ
+100K +0.3 +0.3kms−1 C(C2) 1 −0.41 −
N(CN) 4 −0.01 0.05
C(C2) 0.02 0.04 0.01
N(CN) 0.10 0.06 0.01 O([OI]) 1 −0.17 −
O([OI]) 0.01 0.14 0.01 NaI 1 −0.16 −
NaI 0.08 −0.01 −0.01 SiI 7 −0.29 0.03
SiI 0.01 0.05 −0.03 CaI 4 −0.22 0.06
CaI 0.07 −0.01 −0.04 ScII 5 −0.22 0.06
ScII −0.01 0.14 −0.07 TiI 18 −0.17 0.04
TiI 0.12 0.00 −0.02 VI 19 −0.15 0.05
VI 0.13 0.00 −0.02 CrI 7 −0.23 0.05
CrI 0.07 0.00 −0.03 FeI 49 −0.33 0.04
FeI 0.07 0.01 −0.05 FeII 6 −0.33 0.06
FeII −0.06 0.16 −0.05 CoI 8 −0.37 0.07
CoI 0.09 0.04 −0.02 NiI 24 −0.42 0.06
NiI 0.06 0.04 −0.06 YII 1 −0.23 −
YII −0.01 0.13 −0.02 ZrI 2 −0.17 0.01
ZrI 0.16 −0.01 0.01 LaII 1 −0.15 −
LaII 0.02 0.14 −0.01 CeII 2 −0.29 0.04
CeII 0.02 0.13 −0.02 PrII 1 −0.25 −
PrII 0.02 0.14 −0.01 NdII 1 −0.03 −
NdII 0.01 0.14 −0.01 EuII 1 −0.18 −
EuII −0.01 0.14 0.01 C/N 5 1.58 0.17
C/N −1.73 −0.49 0.18 12C/13C 1 21 −
12C/13C −2 1 −2
alsopreviouslydeterminedbyBerdyugina(1994),andMg
Theerror∆[O/H] = 0.10causes∆[C/H] = 0.03and and Si were investigated by Ottmann et al. (1998). These
∆[N/H]=0.05;∆[C/H]=0.10causes∆[N/H]=−0.10 resultsareinquitegoodagreementwithours.Theelements
and ∆[O/H] = 0.02. However, ∆[N/H] = 0.10 has no Si,Ti,V,Ni,Y,La,andNdwereinvestigatedbyMcWilliam
effectonboththecarbonandoxygenabundance. (1990).The abundancesof Si, Ti, and Y are close to ours,
buttheabundancesoftheotherelementsareabout0.3dex
lower.Verydifferentresults(notdisplayedinFig.10)were
3 Results and discussion obtainedbySanz-Forcadaetal.(2009).Their[O/Fe]value
isequalto1.25dex,andalsotheotherelement-to-ironratios
From the observed spectrum we determined for AYCet areashighas0.4or0.8dex.Thelogg valueintheirstudy
thefollowingmainatmosphericparameters:Teff =5080K, islowerbyabout0.7dexthaninotherstudies,theeffective
logg =3.0,vt =1.4kms−1,and[Fe/H]=−0.33. temperature is higher by about 200 K, and [Fe/H] = 0.0.
Similar values of effective temperatures for AY Cet ThespectrumofAYCetfortheiranalysiswasobservedin
(lying in the interval from 5000 K to 5100 K) and of Novemberof2002.
logg (from2.8till3.1)havebeendeterminedbyBerdyug- TheevolutionarysequencesintheHertzsprung-Russell-
ina (1994), Biazzo et al. (2007), da Silva et al. (2006), diagram of Girardi et al. (2000) show that AYCet (with
Pallavicini et al. (1992),and Randich et al. (1993).Identi- log(L/L⊙)=1.65and∼2.2M⊙)isafirstascentgiantly-
cal[Fe/H]=−0.33forAY Cethavebeendeterminedalso ingclosetothebottomofthegiantbranchintheareawhere
intherecentstudiesofBiazzoetal.(2007)anddaSilvaet the first dredge-upoccurs. In such stars, the 1st dredge-up
al.(2006).Lowervaluesofthemetallicityweredetermined startswhentheluminositylog(L/L⊙)is≈1.2andendsat
intheearlierstudiesofRandichetal.(–0.5dex,1993)and ≈1.8 (Boothroyd & Sackmann 1999). So, the convective
Berdyugina(–0.58dex,1994).Theabundances[A/H],C/N, envelopeshouldnotreachthedeepestlayersofAYCetyet.
and 12C/13C together with their σ (the line-to-line scatter) In Fig. 11, we compare the C/N and 12C/13C ra-
arelistedinTable3. tios of AYCet with the standard prediction of the 1st
Thevaluesof[El/Fe]obtainedforAYCetaredisplayed dredge-upandwithtwomodelsofextra-mixing.Themodel
inFig.10togetherwithresultsofotheranalysesofthisstar. called ‘cool bottom processing’ (CBP) was proposed by
AbundancesofC,N,O,Li,Zr,Ba,andLainAYCetwere Boothroyd&Sackmann(1999),andthemodelcalled’ther-
(cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(2011) 7
C N O Na Mg Si Ca Sc Ti V Cr Fe Co Ni Y Zr Ba La Ce Pr Nd Eu
0.5
0.4
0.3
0.2
e]
F0.1
El/
[
0.0
−0.1
−0.2
−0.3 This work
Ottmann et al. 1998
−0.4 Berdyugina 1994
McWilliam 1990
−0.5
6 7 8 11 12 14 20 21 22 23 24 26 27 28 39 40 56 57 58 59 60 63
Atomic number Z
Fig.10 ElementabundancesforAYCet,asdeterminedinthiswork(filleddiamonds),byOttmannetal.(1998)(open
diamonds),byBerdyugina(1994)(circles),andbyMcWilliam(1990)(plussigns).
33 Psc
30
2.5
29 Dra
l And
33 Psc
)
o25
rati 2.0
er AY Cet
b
m N
nu20 C/ AY Cet
(
C 1.5
3 29 Dra
1
C/
2 15 l And
1
1st dredge−up 1.0
10 TH
CBP
1.0 1.5 2.0 2.5 3.0 1.0 1.5 2.0 2.5 3.0
Stellar mass (M ) Stellar mass (M )
Sun Sun
Fig.11 Comparisons of 12C/13C and C/N ratios in RS CVn stars with theoretical models. AYCet is marked by the
filled diamond, other RS CVn stars by open diamonds: 33Psc (Barisevicˇius et al. 2011), λAnd (Paper I), and 29Dra
(Barisevicˇiusetal.2010).Thetheoreticalmodelsareexplainedinthetext.
mohalinemixing’(TH)wasproposedbyCharbonnel&La- mass of AYCet, the Li abundance drops to approximately
garde(2010). logA(Li)=1.36(Charbonnel&Lagarde2010).However,
the available determinations of logA(Li) in AYCet show
The position of AYCet in the C/N versus stellar mass
valuesspanningfrom0to0.6dex(Randichetal.1993;Bar-
diagram(Fig.11)showsahigherC/Nratioascomparedto
radoyNavascue´setal.1998;Berdyugina1994;Costaetal.
the 1st dredge-up prediction, as expected from the evolu-
tionary status of AYCet. Concerning the 12C/13C ratio of 2002;Fekel&Balachandran1993).Thedeterminedabun-
dancesoflithiuminAYCetarelowerthanpredictedbythe
AYCet,itisaslowasattheendofthe1stdredge-up.
first dredge-upmodelwhilethe carbonandnitrogenabun-
The abundance of lithium is also very sensitive to
mixing. During the first dredge-up, for a star of the
www.an-journal.org (cid:13)c 2011WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
8 G.Tautvaisˇiene˙etal.:ChemicalcompositionofAYCeti
dancesareinagreementwithit.Thusanyreasonsofthelow Girardi,L.,Bressan,A.,Bertelli,G.,Chiosi,C.:2000,A&AS141,
lithiumabundanceshouldberelatedtoothermechanisms. 371
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Hakkila,J.,Myers,J.M.,Stidham,B.J.,Hartmann,D.H.:1997,AJ
Oneofthestillunansweredquestionsinstellarastrophysics
114,2043
is weatherthecoronalabundancesin coolstarsare similar
Hauck,B.,Mermilliod,M.:1998,A&AS129,431
to the photospheric ones. In the Sun, an enhancement of Johansson,S.,Litzen,U.,Lundberg,H.,Zhang,Z.:2003,ApJ584,
elementswithalowfirstionizationpotential(FIP)isfound 107
inthecoronawithrespecttothephotosphere.Thedifferent Kurucz,R.L.:2005,Mem.Soc.Astron.Ital.Suppl.8,189
compositioninthecoronaandthephotospheremayindicate Lawler,J.E.,Wickliffe,M.E.,DenHartog,E.A.:2001, ApJ563,
1075
thatsomephysicalprocessestakeplacebetweenthecooler
Massarotti,A.,Latham,D.W.,Stefanik,R.P.,Fogel,J.:2008,AJ
photosphericmaterialandthe hottercorona.Sanz-Forcada
135,209
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andcoronalabundancesin12stars.Itisseenthatsomestars
Mermilliod,J.C.:1986,CatalogueofEggen’sUBVdata
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Pallavicini,R.,Randich,S.,Giampapa,M.S.:1992,A&A253,185
Forcadaet al. 2009),we see noFIP effect.Itis interesting
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tonoticethattheabundancesofOandSiareveryclose,the
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of Ni by 0.5 dex, of N by 0.4 dex, and that of Fe is lower Schrijver,C.J.,Zwaan,C.:1991,A&A251,183
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