First Overtone CO Bands in the Giant Component of RS Ophiuchi: the 12C/13C Ratio in 2008

0.31 MB·English

by  Ya. V. Pavlenko

Mon.Not.R.Astron.Soc.000,1–??(2002) Printed11January2010 (MNLATEXstylefilev2.2)
First Overtone CO Bands in the Giant Component of
RS Ophiuchi: the 12C/13C Ratio in 2008
0 Ya. V. Pavlenko1⋆, Charles E. Woodward2, M.T.Rushton3, B. Kaminsky1, A.Evans4
1
0 1Main Astronomical Observatory, Academy of Sciencesof the Ukraine, Golosiiv Woods, Kyiv-127, 03680 Ukraine
2 2Department of Astronomy, School of Physics and Astronomy, 116 Church Street, S. E., Universityof Minnesota, Minneapolis, MN 55455
3Jeremiah Horrocks Institute for Astrophysics and Supercomputing, Universityof Central Lancashire, Preston, Lancashire PR1 2HE
n 4Astrophysics Group, Keele University,Keele, Staffordshire, ST5 5BG, UK
a
J

1
1

] ABSTRACT
R We present an analysis of a high resolution (R ≃ 40000) infrared spectrum of the
S RS Oph secondary around the first overtone CO bands, obtained in 2008 May on
. the Gemini South 8m. The 12CO and13CObands arewell-resolved,andwe compute
h
syntheticspectratodeterminethe12C/13Cratio.Wefind12C/13C≃16±3,consistent
p
- with the interpretation of the secondary as red giant which has evolved beyond the
o first drege-up phase of evolution.
r
t Key words: binaries:symbiotic—novae,cataclysmicvariables—stars:abundances
s
a — stars: individual (RS Oph)
[

1
v
8
1 INTRODUCTION Pavlenko et al. (2008) showed that the secondary in
6 RS Oph is a RG with T = 4100±100 K and solar metal-
6 RSOphiuchiisarecurrentnova(RN),aninteractingbinary eff
licity,butwith a deficitof carbon andan overabundanceof
1 systeminwhichmultiplenovaoutburstshavebeenobserved;
nitrogen with respect to solar. Rushton et al. (2009) have
1. it has undergone eight known or suspected outbursts since modeled the spectral energy distribution of RS Oph in the
0 1898 (Anupama 2008), the most recent occurring on 2006
near-IR(1–5µm)andfoundthatT isessentially constant
0 February 12.83; we takethis date as t=0. eff
overtheperiod2006August–2008July.Nitrogenoverabun-
1 RSOphconsistsofawhitedwarf(WD)primarycloseto
dance, and carbon underabundance, is typical of “normal”
: theChandrasekharlimit,accretingmaterialfromaredgiant
v red giants due to the conversion of C to N in the CN-cycle
(RG)secondary withasubstantialwind (Fekelet al.2000).
i of hydrogen burning and the subsequent dredge-up of the
X The RN eruption is explained in terms of a thermonuclear
products on the RGB (e.g., Smith & Lambert 1985, 1986;
r runaway(e.g.,Starrfield2008;Anupama2008)followingthe
a Smiljanic et al. 2009). Furthermore, the material accreting
accretion of sufficient mass by the WD to trigger ignition.
onto the WD from the M giant secondary in the RS Oph
If the mass accreted by the WD is greater than the mass
systemlikelyisN-enhanced(seeFig.14ofNess et al.2009).
ejected then the mass of the WD must increase, so the ra-
Interestingly,theCandNabundancesforRSOphfoundby
tioofmassaccreted tomassejectedwill determinewhether
Pavlenkoet al.(2008)aresimilartothoseintheRG-WDbi-
or not RS Oph is a potential Type Ia supernova progeni-
nary(star#69)intheopenclusterIC4756(Smiljanic et al.
tor(Sokoloski et al.2006;Panagia et al.2006).Drakeet al.
2009).
(2009), modeling the X-ray absorption spectra observed 0
with Chandraafter the2006 February outburst,argue that The12C/13Cisotopicratioisofkeyimportanceforun- 0 1
the mass ejected from the WD in the RS Oph system is derstanding the evolutionary status of RGs. At the beygin -2
∼the5R×G10in−6thMe⊙R.SHOopwhevseyrs,teWmorltoesresse∼t 1a0l.−(820M0⊙7)yarr−g1u,ewthhialet nveinlogpoefbtrhiengRsGnubcrlaenacrh-p(rRocGeBss)e,dthmeadteteerpaefrnoinnmgtcuhoenvcaeocrtreivuepetno-
iWgnetsDetrin-aogcucttrhbeatuetrss≈tat2in×rat1etr0evs−ao8lf.M1I0n⊙−teo1rf0cm<∼omatMp˙earaircacisl<∼oisn1a0oc−fcr9meMtaes⊙ds-dyluor−srsi1n,rgsauttheges- itcnhagrebsoounnrfsiatsceoeltloaoprfitcmhreaasststiofaarndt.deA:cmrs eaeats1raeelssluiu1cltpty otof(CJtahhefaarficbrtosotnrnd∼erle2d10g9,e9d-4ue)pp,,eantnhdde-
a
fromtheRG,totheamountofmaterialejectedbytheWD, standardDmodrels of stellar evolution predict no change in
can determine whether symbotic systems are candidate SN 12C/13C thereafter. However, observations of evolved RGs
progenitors (Panagia et al. 2006); however mass-loss rates withprogenitormass <∼2M⊙ indicatethatthe12C/13Cra-
are of course difficult to pin down observationally. tio continues to decrease after the completion of the first
dredge-upevent(Smith et al.2002;Tautvaiˇsiene˙ et al.2005;
Smiljanic et al. 2009, and references therein). Most prob-
⋆ E-mail:[email protected] ably further mixing, or some non-standard mixing mecha-
2 Ya. V. Pavlenko et al.
nisms,workinlowmassstarsastheyareascendingtheRGB Thesevaluesofthevirtualcontinuumwespecifyaspseudo-
(Charbonnel1994,1995).Anti-correlationofthecarbonand continuum. The results of the fits depends on the pseudo-
nitrogen abundances, as is seen in RS Oph (Pavlenko et al. continuumlevel, as discussed in section 4.
2008), is well known for a variety of RGs with a range of
metallicities (Smith et al. 2005, and references therein).
The 12C/13C ratio is also of fundamental importance
in understanding the nature of the secondary of RNe, as it 3 ANALYSIS PROCEDURE
isareflectionoftherelativeimportanceof12C,13Cprocess-
3.1 Spectral synthesis
inganddredge-up.Followingthe1985eruption,Evans et al.
(1988) estimated a 12C/13C ratio of ∼ 10 for the RG in We have used the technique of synthetic spectra to carry
RS Ophon the basis of a low resolution infrared (IR)spec- out our analysis of the IR spectrum of RS Oph; details
trum, while Scott et al. (1994) found that the strength of maybefoundinPavlenko et al.(2004,2008).Wecomputed
the first overtone CO bands declined by a factor ∼10 over the spectra within the classical framework, assuming LTE,
the first 7 years after the eruption (see also Harrison et al. plane-parallel media, and no sinks or sources of energy in
1993). the atmosphere; transfer of energy is provided by the radi-
In this paper, we discuss Phoenix echelle observations ation field and by convection. Strictly speaking, these as-
of the first overtone vibration-rotation features of CO, ob- sumptions are not completely valid in the atmosphere of
tainedinMay 2008, some831daysafterthe2006 outburst, theRGin RSOph;however,thisapproach allows ustode-
to determine the 12C/13C ratio in the atmosphere of the scribe the IR spectral energy distribution of RS Oph over
RS Ophsecondary. a wide range of wavelengths, and we consider that none of
our assumptions is of crucial importance in the spectrum
formation processes.
In the most general case, any determination of
2 OBSERVATIONS AND REDUCTION
abundance depends on many adopted parameters:
High-resolutionHKM-bandspectralobservationsofRSOph Teff, logg and Vt, and the abundance of other ele-
were carried out on the Gemini-South 8 m telescope using ments. In this paper we solve a restricted task us-
thePhoenixspectrograph(Hinkleet al.2003)duringqueue ing fits to the two observed narrow spectral regions
observingrunsonthenightsof23and24May2008UT(days in the inrared. Therefore, to reduce the number of fit-
830.7, 831.7 from the2006 eruption),aspart ofourGemini ted parameters in the minimization procedure, we adopt
programGS-2008A-Q47.Definingzeroorbitalphaseasmax- for the secondary atmosphere Teff= 4200 K and logg =
imum RG radial velocity, the observations discussed here 0.0, obtained from fitting near-IR low resolution spectra
were obtained at binary phase 0.78, when approximately (Pavlenkoet al. 2008). We then fix the abundances of car-
88% (assuming the adopted inclination ∼ 40◦; Fekel et al. bon and nitrogen at logN(C)=−4.2 and logN(N)=−3.2
2000; Ribeiro et al. 2009) of the visible photosphere of the on the scale ΣNi = 1, as also determined from fitting
RGwas illuminated by theWD. thelowresolutionspectra byPavlenko et al.(2008);
ObservationsofRSOph(aswellasthetelluricstandard otherabundances are taken to besolar.
HR6378=ηOph[A2 V,V=2.43]atacomparableairmass) Weassumethattheobservedspectraarebroadenedby
were obtained by nodding the target at multiple positions macroturbulencein theRGatmosphere, andbyinstrumen-
alongthelongaxisofthe14′′×0.34′′ slit (e.g., Smith et al. tal broadening; both are implemented in the modelling by
2002).Observationsofthetelluricstandardwereconducted smoothingthecomputedspectrawithagaussianofFWHM
immediately before and after observations of RS Oph,with ∼1.9˚A, which is a reasonable approach for fitting stellar
flatsanddarksbeingobtainedattheconclusion ofeachob- spectra. In fact, the appropriate values of FWHM were de-
servational sequence comprising a given grating and order- terminedbyourminimisation procedurefittingtoobserved
sorting filter combination. With our instrument configura- spectrum (see Pavlenko et al. 2004).
tion,thePhoenixspectrographproducessingle-orderechelle To determine the isotopic ratio 12C/13C we follow
spectra with a resolution of R = λ/∆λ ≈ 40000 (corre- conventional procedures. Namely, we define x as the frac-
sponding to a resolution element of ∼ 4 pixels). Individual tion of 12CO molecules, i.e. x = N(12CO)/(N(12CO) +
spectrawerereducedandcombinedusingstandardIRdata N(13CO), where N(M) is the number density of the
0
reduction techniques, as well as those unique to Phoenix moleculeM.Then,thefraction of13COmolecules isclearly 1
0
(Hinkleet al.2003,2007).Table1summarizes theobserva- N(13CO)/(N(12CO)+N(13CO))=1−x.In thisapproach2
y
tional datadiscussed herein. we operate with two parameters, i.e. the abundancerof car-
a
The echelle spectra discussed here covered the 2.32− bon,logN(C)(as specified above)andntheuisotopic ratio
2.33 µm and 2.36−2.38 µm spectral regions; we refer to 12C/13C=N(12CO)/N(13CO)=x/J(1−a x).Thenallsyn-
theseasspectra“B”and“R”respectively.Bothspectraare thetic spectra are compu1ted1 f or the 12CO and 13CO
affected by curvature of the echelle orders. We reduce the molecular densitifest,:d etermined by taking into ac-
intensitiesofspectralfeaturesinmostregionsusingthethe- count the inpr uat isotopic ratio 12C/13C.
D
oreticalspectrumcontinuumasreferencepoints.Theeffects The “B” spectrum contains no 13CO lines, only 12CO
aremorepronouncedinthe“B”spectralregion (seeFig.1) (Fig. 1). Again, we note that, in the most general
and we work with the spectra in terms of residual fluxes. case, the intensities of these lines depend on both
We cannot determine the real continuum due to noise at log N(C) and Vt.Weusedthisspectrumtodeterminethe
the minimum fluxes. Therefore, we carried out fits to the microturbulent velocity Vt for the adopted value of log
observed spectrum using different levels of the continuum. N(C) in the atmosphere of the RG. The “R” spectrum
First Overtone CO Bands in the Giant Component of RS Ophiuchi: the 12C/13C Ratio in 2008 3
ing, because they form in low density regions of the RG
Table 1.GEMINIPHOENIXOBSERVATIONALSUMMARY
atmosphere;
– thermal velocities of the CO molecule are lower than
Date Filter λrange Exposure Airmass thoseofCandOatoms duetoitshighermass. FortheCO
(2008UT) (µm) (s) molecular lines, broadening by microturbulence dominates,
especially in thelow temperature regime; we determine the
23May K4308 2.32−2.33 1650 1.18 microturbulence velocity in Section 4.
24May K4220 2.36−2.38 1870 1.12 – the wings of molecular lines are blended in the spectra
of theRG.
The contributions of the various molecular and atomic
species to thetotal opacity in the2.28–2.39µm spectral re-
2.5
gionareshowninFig.1,fromwhichweseethatabsorption
a)
byCO dominates.
2 Fulldetailsofourprocedureoffittingtheoreticalfluxes
to observed SEDsmay befound in Pavlenko et al. (2004).
b)
1.5
C
+ c)
ux 3.2 The effect of circumstellar dust
Fl 1
d)
Dust is present in the RS Oph system (Evanset al. 2007;
f) van Loon 2008; Woodward et al. 2008), emitting primarily
0.5
at λ>∼10µm. However Rushton et al. (2009) have shown
e) that there is also evidence for dust emission at shorter
0 (>∼5µm) wavelengths, and that emission by the dust en-
2.28 2.3 2.32 2.34 2.36 2.38 velope may be variable.
Wavelength (micron) The properties of the dust shell around RS Oph have
Figure1.Theoreticalspectraofdifferentspeciesinourspectral been discussed by Evans et al. (2007), van Loon (2008)
region,convolvedbyaGaussianwithahalf-widthof×10−8µm. and Woodward et al. (2008). Pavlenko et al. (2008) and
Syntheticspectrawerecomputedforamodelatmospherehaving Rushtonet al.(2009)haveshownthatthe2µmspectralre-
Teff =4000,logg =0,[Fe/H]=0.0 for (a) 12CO (b) 13CO and gion of RS Oph is not affected by emission from the hot
(c)theVALDlinelists.Observedspectra(d,e,f)inbothspectral (∼500−600 K) dust known to currently envelop RS Oph,
regions are also shown. The “B” spectrum is shown “as is” (d), which is likely a permanent feature of the system. As this
and after echelle order curvature reduction (e). The flux scale
dustemission becomes prominent longward of 3µm,we are
is arbitrary, and all spectra areshifted vertically to simplifythe
justified in carrying out ouranalysis for thedust-freecase.
plot.
contains both 12CO and 13CO lines; we used this spectrum 4 RESULTS
to determinethe carbon isotopic ratio 12C/13C. In principle the 12C/13C isotopic ratio can be determined
A set of continuum opacity sources from AT- from any pair of the unblended lines of 12CO and 13CO.
LAS9 (Kurucz 1993) with some additional amendments However, in our spectra these lines are blended and we are
(Pavlenkoet al. 2004) was used in our modeling, as well as unableto distinguish the 12CO lines from theweaker 13CO
theVALDatomiclinelist(Kupkaet al.1999),andlinelists lines at our spectral resolution. Absorption of both species
of12COand13COfromGoorvitch(1994).Thequalityofthe form commonblendsintheobservedandmodelled spectra.
Goorvitch data is demonstrated by the fact that Pavlenko Only the band heads of the CO system can be clearly in-
(2008)recentlyfittedtheoreticalspectratoahighsignal-to- dentified in the spectrum, formed by saturated lines which
noise 2.3µm spectrum of Arcturus, giving excellent fits to haveratherweakdependenceontheCOabundances.More-
theCObands.Watervaporlineswerenotincludedbecause over, they form in the outermost layers of RG atmosphere
0
numerical experiments with the Barber et al. (2006) H2O which cannot be modelled in the framework of classical ap- 1
0
line list showed that their contribution to the total opacity proach.Non-saturatedlines,especiallythoseofintermediate2
in the wavelength range under consideration is negligible. strength, are a better choice for the abundance deterrmyin a-
a
WeadopttheVoigtprofileH(a,v)fortheshapeofeachline; tion;howevertheyaresensitivetothemicrnotuurbulentveloc-
here a = (γ2+γ4+γ6)/(4×π×∆νD),v = ∆ν/∆νD (see ity. J a
Gray 2005, for details). Damping constants γ2, γ4, and γ6 Wedeterminedthemicr1otu1rbu lentvelocityfromthefits
arerespectivelyduetothenatural,vanderWaalsandStark tothe“B”spectrumf (t2.:32 −2.33µm),whichisformedcom-
broadening of atomic and molecular lines, computed us- pletely by absor rpation of 12CO lines. The spectrum shows a
D
ingdatafromvariousdatabases(Kurucz1993;Kupkaet al. strong dependence on Vt (Fig. 2). The minimization proce-
1999), or the approximation of Unso¨ld (1955). Natural and dure for the parameter S (see below) gives a definite value
vanderWaals broadeningdominate in thecase of RSOph, forthemicroturbulentvelocityofVt=3.0±0.5kms−1(close
due to the low pressure and electron density in the RG at- to the value assumed in Pavlenkoet al. 2008). In what fol-
mosphere. We notethat lows, wecomputespectrawith Vt =3kms−1 tofitthe“R”
– molecular lines are less sensitive to pressure broaden- spectrum and determinethe12C/13C ratio in RSOph.
4 Ya. V. Pavlenko et al.
10 1
9.5
0.9
9
0.8
8.5
s
e
x 0.7
8 4000/0.0 u
Fl
d
S 7.5 e 0.6
s
ali
7 m
or 0.5
6.5 N
0.4
6 4200/0.0 RS Oph
0.3 4200/0.0, Vt = 2 km/s
5.5 4200/0.0, V = 3 km/s
t
4200/0.0, V = 4 km/s
t
5 0.2
1 2 3 4 5 6 2.32 2.322 2.324 2.326 2.328 2.33
Microturbulent Velocity (km/s) Wavelength (micron)
Figure 2.Left:dependence of S onthe adopted Vt.Right:fits ofspectra computed withdifferentVt totheobserved “B”spectrum of
RSOph.ModelatmospherehasTeff =4200K,logg=0.0(Rushtonetal.2009)
1.2
13
CO
1.1
12
CO
1
0.9
0.8
s
e
x
u
0.7
l
F
0.6
0.5
RS Oph
0.4 12C/13C=13
12 13
C/ C=16
13
12 13 CO band head
0.3 C/ C=19 0
1
0
2
2.366 2.368 2.37 2.372 2.374 2.37y6
r
a
u
Wavelength (micron) n
a
J
1
F0.i9g0u,r0e.932,.S0.p9e4ctarrael sfihtsowconm; tphuetecdolwouitrhkdeiyffeisreanstp12eCr/th1e3C12tCo/t1h3eCobrasetirov.edSp“eRct”raspoefct1r2uCmOoafnfdRSt13O:CpO hm.1PolseecuudleosnttiankueunmfrpoomsittihoensFaigt.1rνar=e
a
shownonthetop.,onesareshiftedony-axiestosimplifytheplot. D r
First Overtone CO Bands in the Giant Component of RS Ophiuchi: the 12C/13C Ratio in 2008 5
puted for our assumed T , logg and abundances to the
5 eff
observed “R” spectrum.
Interpretation of the “R” spectrum is not as straight-
4.5 forward asthat ofthe“B”spectrum,inthat thenoiselevel
0.92/16 increasestolongerwavelengths.Indeedthenoiselevelinthe
“R”spectralregionisgenerallyhigherthanthatinthe“B”,
4
0.84/49 likely due to a decrease in atmospheric transmission long-
S ward of about 2.4µm. Also, absorption features are seen
in the “R” spectrum which cannot be identified with CO;
3.5 0.86/32
0.90/19 most likely, these are a consequence of the data reduction
procedure, where time-variable telluric features are not ad-
3 equately removed from the spectra. Indeed comparison of
0.88/24 thecomputedand“R”spectrarevealsthepresenceofsome
unidentified features in the observed spectrum, although
2.5 some of these may be artifacts produced by the removal of
10 20 30 40 50 60 70 80
thetelluricspectrum.Thisisnottrueforthe“B”spectrum.
12C/13C
The13COlines,whichareourmaininterest,areclearlyseen
Figure4. DependenceofSontheadopted12C/13C.Themodel inthe“R”spectralregion; noneoftheunidentifiedfeatures
atmospherehasTeff =4200K,logg=0.0(Pavlenkoetal.2008), in the “R” spectrum region are identified with 12CO, 13CO
Vt =3kms−1.Curvesontheplotarelabelledbyapairofnum- lines and so theirpresence does not affect our conclusions.
bers d/xxx, wheredand xxx arethe adopted level of continuum
andthe12C/13CratiofoundattheminS.
5 DISCUSSION
To determine the 12C/13C ratio, we fitted computed
We have determined the 12C/13C isotopic ratio in the at-
spectra to theobserved “R” spectrum. Wenotethat:
mosphere of theRS Ophsecondary for orbital phase 0.78 –
(i) in the computed spectrum we see flux maxima which
whenapproximately88%ofthevisibleRGsurfacewasirra-
canbetreatedascontinuum.Atthesewavelengthsthecon-
diated by ultraviolet radiation emitted by the WD – to be
tribution of absorption in theline wings is negligible.
16±3. This is consistent with that expected after the first
(ii) the “R” spectrum is affected by noise, as already
dredge-up (Charbonnel 1994), and suggests that the RG in
noted. We attribute these features to noise because their
RS Oph has undergone first dredge-up and has evolved be-
widths donot match thespectral resolution;
yondthis evolutionary stage.
(iii) tostudytheeffectthecontinuumlevelhasonourre-
In spectra shown by Rushton et al. (2009), numerous
sultswevariedthelevelof continuumin theobservedspec-
trum;for each individuallevelwe found valuesof 12C/13C. emissionlinesarevisibleinthespectralregionsaround1.0−
1.8µm.Theseforminmaterialejectedinthe2006eruption,
The continuum level in the observed spectrum was orintheshockedorionizedRGwind,ineachcasewellaway
adopted at the following points: d = rν/rmax = fromthephotosphereofthesecondary.Moreover,inoptical
0.88,0.90,0.92,0.94,0.96,0.98,1.00, the value d = 1.00 cor- spectra we see pronounced effects of irradiation.
respondingtotheleveloftheformalmaximumfluxFmax in By the time of our observations in 2008, RS Oph had
theobservedspectrum,hererν =Fν/Fc istheresidualflux. essentially returned to quiescence, and we donot expect ir-
Adopted levels of continuum Fc in the observed spectrum radiation to have a strong impact on the spectrum in the
are clearly seen in Fig. 3. 2µm region. Furthermore, the molecular bands we observe
In the Fig. 3 we show the dependence of the synthetic in the IR are formed deep in the atmosphere of the RG.
spectra on the 12C/13C ratio for Vt=3kms−1, while in However,asevidencedbythestrongemissionlinespectrum
Fig. 4 we show the dependence of the best-fit parameter (Rushtonet al. 2009), a hot circumstellar envelope exists
S = P(1−rνsynt/rνobs)2 on the 12C/13C ratio for different and may affect the spectral details, even in the IR. As we
levels of continuumd in the observed spectrum. seeinFig.2,thefitstothesaturated12COυ=3→1band
Using our fitting procedure, we found a clear depen- at λ 2.32µm are imperfect, in that the observed molecu-
0
dence of the minimum S value and of the 12C/13C ra- larlinesareshallowerthanthetheoreticalbands,whichare 1
0
tio on the level of pseudo-continuum. The formal best-fit more saturated. This poorer fit could, in part, be due to2
(12C/13C=24±3) is obtained with d=0.88. However, vi- theuncertaintyinthecontinuumlevelinthe“R”sprectyru m
a
sualcomparisonwiththeobservedspectrumshowsthatthe (Fig. 3). On the other hand, weakening onf thue CO can be
a
level of the theoretical pseudo-continuum is too low in this interpreted as a consequence of highJer temperatures in the
case. As we see from Fig. 3, the best-fits with 12C/13C= regionswhereitisformed,so1 th1at thestructureoftheouter
13−19 well reproduce the profiles of the CO lines, depen- layersoftheatmospfhetre: o ftheRGmaydifferfromtheclas-
a
dent on the chosen pseudo-continuum and noting that the sical model atmr osphere assumed here.
D
valuesofS arehighduetothepresenceofunidentifiedspec- We note that Rushton et al. (2009) report weaker CO
tralfeatures.Mostlikely,thesefeaturesformbeyondtheat- first overtone absorption in their 2007 observations than in
mosphere of theRG(see below). Therefore, using goodness their 2006 and 2008 observations. Similar changes were ob-
of fit as judged “by eye” to complement our minimization served following the 1985 outburst by Scott et al. (1994),
procedure, we choose the value 12C/13C=16±3 from the who attributed this behaviour to contamination of the RG
best-fits of synthetic spectra and pseudo-continuum, com- by the 1985 ejecta. Rushtonet al. conclude that the RG is
6 Ya. V. Pavlenko et al.
intrinscially variable. In addition we may expect strong ef- We thank an anonymous Referee for helpful comments on
fectsduetoinhomogeneities,astellarwind,andNLTE,but an earlier version of this paper.
a consideration of these factors is beyond the scope of this
paper. These phenomenaaffect thespectra of single canon-
ical giants like Arcturus(see discussion in Tsuji 2009).
REFERENCES
With the mass function from Fekelet al. (2000), incli-
nationfromFekelet al.(2000)andRibeiro et al.(2009),we Anupama, G. C. 2008, in ASP Conference Series 401, RS
determine a mass ∼2.25M⊙ for the RG if the WD is close Ophiuchi(2006)andtherecurrentnovaphenomenon,eds.
to the Chandrasekhar limit. While the 12C/13C ratio after A.Evans,M.F.Bode,T.J.O’Brien,M.J.Darnley,(San
first dredge up is insensitive to themass of theRG progen- Franscico: ASP),31
itor (and of course the situation in RS Oph is complicated Barber R.J., TennysonJ., HarrisG.J., Tolchenov R.2006,
by its binarity and RN eruptions), the 12C/13C ratio we MNRAS,368, 107
findisconsistentwiththisvaluebecause,onthebasisofthe Brandi, E., Quiroga, C., Miko lajewska, J., Ferrer, O. E.,
12C/13C ratio, we can probably exclude a progenitor mass Garcıa, L. G. 2009, A&A,497, 815
for the RG below ∼ 1M⊙ (cf. Fig. 2 of Charbonnel 1994). Charbonnel. C. 1994, A&A,282, 811
WecanalsoofcourseconcludethattheWDprogenitorhad Charbonnel. C. 1995, ApJ,453, L41
mass > 2.25M⊙ so that some 0.8M⊙ of material has been Drake, J. J., et al. 2009, ApJ,691, 418
deposited in theenvironmentof RS Ophin addition toany Evans,A.,Callus,C.M.,Albinson,J.S.,Whitelock,P.A.,
material contributed by theRGwind. Glass, I. S., Carter, B., Roberts, G. 1988, MNRAS, 234,
755
Evans, A., et al. 2007, ApJ,671, L175
Fekel, F. C., Joyce, R. R., Hinkle, K. H., Skrutskie, M. F.
6 CONCLUSIONS
2000, AJ, 119, 1375
We have carried out an analysis of a high resolution spec- Goorvitch, D.1994, ApJs, 95, 535
trum of the RG component of the RN RS Oph. We find Gray,D.F.,2005,TheObservation andAnalysisof Stellar
12C/13C= 16 ± 3, which sheds new light on the history Photospheres, Third edition, Cambridge University Press
and evolution of the RS Oph system. The secondary star Harrison, T. E., Johnson, J. J., Spyromilio, J. 1993, AJ,
inRSOphisaRGwithadeficiencyofcarbonandanover- 105, 320
abundance of nitrogen, as predicted by theories of the first Hinkle, K.H., et al. 2003, Proc. SPIE, 4834, 353
approach to the RGB after first dredge up. The 12C/13C Hinkle, K.H., et al. 2007, ApJ, 664, 501
ratio we have found is consistent with the typical values Kupka, F., Piskunov, N., Ryabchikova, T. A., Stempels,
(Smiljanic et al. 2009) observed in the atmospheres of RG H.C., Weiss, W. W. 1999, A&As, 138, 119
starsin open clustersafterfirst dredgeup,andfurthersug- Kurucz,R.L.1993,CDROM9,18(Harvard-Smithsonian
gests that the RG in RS Oph has undergone some further Observatory)
mixing,which would havedepressed the12C/13Cratiostill Ness, J.-U., et al. 2009, ApJ, 137, 3414
further. Panagia,N.,VanDyk,S.D.,Weiler,K.W.,Sramek,R.A.,
Furthermore,inviewofthestrongvariabilityoftheCO Stockdale, C. J., Murata, K. P. 2006, ApJ, 646, 369
bands following the 1985 (Harrison et al. 1993; Scott et al. Pavlenko, Ya.V. 1997, Astron. Reps, 41, 537
1994)and2006(Rushtonet al.2009)eruptions,itisimpor- Pavlenko, Ya.V. 2008, Astronomy Reports, 52, 749
tant to monitor the IR spectrum of the RG in RS Oph to Pavlenko, Ya.V., Jones, H. R.A. 2002, A&A,396, 967
understand thereason for thechanges observed. Pavlenko, Ya. V., Geballe, T. R, Evans, A., Smalley, B.,
Wewillprovideadetailedanalysisofabundancesinthe Eyres,S.P.S.,Tyne,V.H.,Yakovina,L.A.2004, A&A,
RGin RS Ophin forthcoming papers. 417, L39
Pavlenko, Ya. V., Evans, A., Kerr, T., Yakovina, L. A.,
Woodward, C. E., Lynch, D., Rudy, R., Pearson, R. L.,
Russell, R.W. 2008, A&A,485, 541
7 ACKNOWLEDGMENTS
Ribeiro, V.A. R.M., et al. 2009, ApJ,703, 1955
This manuscript is based on observations obtained at the Rushton,M., et al. 2009, MNRAS,in press.
0
GeminiObservatory,whichisoperatedbytheAssociationof SokoloskiJ.L.,LunaG.J.M.,MaiK.,KenyonS.J.2006, 1
0
UniversitiesforResearchinAstronomy,Inc.,underacooper- Nature,442, 276 2
y
ativeagreementwiththeNSFonbehalfoftheGeminipart- Scott, A. D., Rawlings, J. M. C., Krautter, J., Evrans, A.
a
nership: the National Science Foundation (United States), 1994, MNRAS,268, 749 n u
a
theScienceandTechnologyFacilitiesCouncil(UnitedKing- Smiljanic, R., Gauderon, R., NoJrth, P., Barbuy, B.,
1
dom),theNationalResearchCouncil(Canada),CONICYT Charbonnel, C., Mowlav1i, N. 2009, A&A, in press
(Chile), the Australian Research Council (Australia), Min- (arXiv:0810.1701vf2t) :
a
ist´erio da Ci´encia e Tecnologia (Brazil) and Ministerio de Smith, G. H,r Briley, M. M., Harbeck, D. 2005, AJ, 129,
D
Ciencia, Tecnolog´ıa e Innovaci´on Productiva (Argentina). 1589
This work was supported by an International Joint Smith, V.V., Lambert, D. L.1986, ApJ, 311, 843
Project Grant from the UK Royal Society. YP’s and BK’s Smith, V.V., Lambert, D. L.1985, ApJ, 294, 326
studies are partially supported by a program Cosmomicro- Smith,V.V.,Hinkle,K.H.,Cunha,K.2002,AJ,124,3241
physicsofNASUUkraine.Thisresearchhasmadeuseofthe Starrfield,S.2008,inASPConferenceSeries401,RSOphi-
SIMBAD database, operated at CDS, Strasbourg, France. uchi (2006) and the recurrent nova phenomenon, eds. A.
First Overtone CO Bands in the Giant Component of RS Ophiuchi: the 12C/13C Ratio in 2008 7
Evans, M. F. Bode, T. J. O’Brien, M. J. Darnley, (San
Franscico: ASP),4
Tautvaiˇsiene˙,G.,Edvardsson,B.,Puzeras,E.,Ilyin,I.2005
A&A,431, 933
Tsuji, T. 2009, astro-ph/0907.0065.
Unso¨ld, A. 1955, Physik der Sternatmospheren, 2nd ed.
(Springer:Berlin)
van Loon, J. Th. 2008, in ASP Conference Series 401, RS
Ophiuchi(2006)andtherecurrentnovaphenomenon,eds.
A.Evans,M.F.Bode,T.J.O’Brien,M.J.Darnley,(San
Franscico: ASP),90
Wallerstein, G., Harrison, T., Munari, U., Vanture, A.
2008, PASP,120, 492
Woodward, C. E., et al. 2008, in ASP Conference Series
401, RS Ophiuchi (2006) and the recurrent nova phe-
nomenon,eds.A.Evans,M.F.Bode,T.J.O’Brien,M.J.
Darnley,(San Franscico: ASP), 260
Worters, H. L., Eyres, S. P. S., Bromage, G. E., Osborne,
J. P. 2007, MNRAS,379, 1557
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