Observations and light curve solutions of the W UMa binaries V796 Cep, V797 Cep, CSS J015341.9+381641 and NSVS 3853195

0.54 MB·

by  D. P. Kjurkchieva

ResearchinAstronomyandAstrophysicsmanuscriptno.
(LATEX: 0253.tex; printedonJanuary18,2017; 1:16)
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1 Observations and light curve solutions of the W UMa binaries
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V796 Cep, V797 Cep, CSS J015341.9+381641 and NSVS 3853195
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a
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7 D.P.Kjurkchieva1,V.A.Popov1,2,S.I.Ibryamov1,D.L.Vasileva1,N.I.Petrov3
1

]
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1 DepartmentofPhysics,ShumenUniversity,115UniversitetskaStr.,9712Shumen,Bulgaria;
S
. [email protected]
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p 2 IRIDAObservatory,RozhenNAO,Bulgaria
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o 3 InstituteofAstronomyandNAO,BulgarianAcademyofSciences,72TsarigradskoShoseBlvd.,1784
r
t
s Sofia,Bulgaria
a
[
Received;ccepted
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7 AbstractPhotometricobservationsin Sloan g’andi’ bandsoffourW UMabinaries,V796
4
0 Cep,V797Cep,CSSJ015341.9+381641andNSVS3853195,arepresented.Ourobservations
.
1 showed that CSS J015404.1+382805and NSVS 3853195are the same star. We determined
0
7 theinitialepochsT0ofalltargetsandimprovedtheperiodofNSVS3853195.Thelightcurve
1
: solutionsofourdatarevealedthatthecomponentsofeachtargetarealmostthesameinmass,
v
i temperature,radiusandluminosity.ThestellarcomponentsareofGandKspectraltypesand
X
r undergopartialeclipses.Allsystemshavebarely-overcontactconfigurationsandbelongtoH
a
subtypeWUMabinaries.Weestablishedthattherelationbetweentheluminosityratiol2/l1
andmassratioqofourtargetsisapproximatelyl2/l1 =q1.5.
Key words: stars: binaries: eclipsing; stars – fundamental parameters; stars – individual
(V796Cep,V797Cep,CSSJ015341.9+381641,NSVS3853195)
2 Kjurkchievaetal.
1 INTRODUCTION
The creation of stellar evolutional scheme requires a knowledge of the fundamental parameters of stars
in different stages of their evolution. Eclipsing binary systems, especially W UMa binaries, are the most
importantsourcesofsuchinformation.Itissupposedthattheyareresultfromtheevolutionofwidebinaries
by angular momentum loss and mass-ratio reversals (Stepien 2006, Qian 2003). Around 25 % of main-
sequencestarbinarieshaveseparationssmallenoughsowhentheirprimariesascendthegiantbranch,mass
transfervia Roche-lobeoverflowputsthe beginingofa commonenvelopephase(Willems & Kolb 2004).
Atthisstagethetwostarsorbitwithinasingleenvelopeofmaterial,quicklylosingangularmomentumand
spiralingtowardseachother(Webbink1984;Ivanovaetal.2013).Thecommon-envelopephaseisprobably
ashort-livedstagethatendsbyenvelopeejectionandatighterbinaryorbyamerger.Butunderstandingof
commonenvelopestageremainsoneofthemostimportantunsolvedproblemsinstellarevolution(Ivanova
etal.2013).
The components in a W UMa system have nearly equal surface temperatures in spite of their often
greatlydifferentmasses(Binnendijk1965).ThemodelofLucy(1968b),Lucy(1968a)explainedthiseffect
by a common convective photosphere which embedded two main sequence stars. As a result one should
expect the observable luminosities to have another dependence on the mass ratio than would be the case
of two main sequence stars in detached configuration.The conditionfor equalsurface temperaturesleads
tospecificperiod-luminosity-color(PLC)relationsofWUMastars(Rucinski1994,Rucinski&Duerbeck
1997)allowingcurrentlytopredicttheirabsolutemagnitudesM toabout0.25mag(Rucinski2004).The
V
PLCrelationscombinedwiththeeasedetectionmakethesebinariesusefultracersofdistance(Klagyivik&
Csizmadia2004;Getteletal.2006;Ekeretal.2009).Moreover,theWUMastarsareimportanttargetsfor
themodernastrophysicsbecausetheygiveinformationfortheprocessesoftidalinteractions,masslossand
masstransfer,angularmomentumloss,mergingorfusionofthestars(Martinetal.2011).
In this paper we present photometric observations and light curve solutions of four W UMa bi-
naries: V796 Cep (GSC 04502-00138, TYC 4502-138-1), V797 Cep (GSC 04502-01040, 2MASS
J01424764+8007522),CSSJ015341.9+381641,NSVS3853195(CSSJ015404.1+382805).Table1presents
thecoordinatesofourtargetsandavailableinformationfortheirlightvariability.
LightcurvesolutionsoffourWUMabinaries 3
Table1 ParametersofourtargetsfromtheVSXdatabase
Target RA Dec Period V Amplitude Type
[d] [mag] [mag]
V796Cep 014136.39 +800419.1 0.3929661 12.20 0.65 EW
V797Cep 014247.64 +800752.3 0.270416 14.60 0.40 EW
CSSJ015341.9+381641 015341.95 +381641.1 0.347518 13.47 0.40 EW
NSVS3853195 015404.05 +382805.2 0.29253 13.52 0.39 EW
Table2 Journalofourphotometricobservations
Target Date Exposureg′ Exposurei′ Numberg′ Numberi′
V796Cep,V797Cep 2015Oct25 90 120 125 125
2015Oct26 90 120 84 82
2015Oct27 90 120 60 59
2015Oct28 90 120 146 146
CSSJ015341.9+381641,NSVS3853195 2015Nov07 60 90 85 84
2015Nov08 60 90 67 75
2015Nov11 60 90 84 84
2015Nov12 60 90 43 42
2015Nov13 60 90 84 85
2 OBSERVATIONS
OurCCDphotometricobservationsofthetargetsinSloang’,i’bandswerecarriedoutatRozhenNational
AstronomicalObservatorywiththe30-cmRitchey-Chre´tienAstrograph(locatedintotheIRIDASouthdome)
using CCD camera ATIK 4000M (2048 × 2048 pixels, 7.4 µm/pixel, field of view 35 × 35 arcmin).
Informationfor ourobservationsis presentedin Table 2. In fact, the pairsV796Cep, V797Cep andCSS
J015341.9+381641,NSVS3853195fallontwoobservedfields(seecoordinatesinTable1).
Thedatawereobtainedduringphotometricnightswithseeingwithin1.1–1.9arcsecandhumiditybelow
70%.Twilightflatfieldswereobtainedforeachfilter,darkandbiasframeswerealsotakenthroughoutthe
run.Theframeswerecombinedrespectivelyintoasinglemasterbias,darkandflatframes.Thestandardpro-
cedurewasusedforreductionofthephotometricdata(de-biasing,darkframesubtractionandflat-fielding)
bysoftwareAIP4WIN2.0(Berry&Burnell2006).
4 Kjurkchievaetal.
Table3 Listofthestandardstars
Label StarID RA Dec g’ i’
Target1 V0796Cep 014136.39 +800419.10 12.320 11.789
Target2 V0797Cep 014247.64 +800752.30 14.966 14.025
Chk UCAC4851-002007 014116.52 +800421.76 13.755(0.010) 13.018(0.010)
C1 UCAC4851-002085 014507.01 +801045.03 13.238(0.011) 12.534(0.011)
C2 UCAC4851-002011 014128.03 +801118.42 13.870(0.010) 13.351(0.012)
C3 UCAC4851-002002 014056.97 +800414.51 13.448(0.009) 12.844(0.010)
C4 UCAC4851-002062 014356.73 +800208.49 14.205(0.011) 13.452(0.013)
C5 UCAC4850-002063 014151.38 +795658.55 13.257(0.007) 12.651(0.009)
C6 UCAC4851-002028 014225.41 +800100.68 13.898(0.009) 13.058(0.009)
Target3 CSSJ015341.9+381641 015341.95 +381641.10 13.897 13.117
Target4 NSVS3853195 015404.05 +382805.26 14.054 13.178
Chk UCAC4643-007188 015430.68 +382900.15 13.104(0.014) 11.754(0.009)
C1 UCAC4644-007104 015412.54 +383649.06 13.975(0.016) 13.902(0.018)
C2 UCAC4643-007165 015404.61 +383554.88 14.112(0.011) 13.419(0.015)
C3 UCAC4643-007180 015423.95 +383542.60 14.061(0.014) 13.369(0.015)
C4 UCAC4643-007204 015450.23 +383352.57 13.971(0.019) 13.147(0.015)
C5 UCAC4643-007182 015426.03 +382938.62 13.720(0.009) 13.012(0.011)
C6 UCAC4643-007126 015326.47 +383002.18 13.702(0.016) 12.978(0.013)
C7 UCAC4642-006881 015412.52 +382356.10 13.937(0.012) 12.907(0.011)
C8 UCAC4642-006842 015330.38 +382034.86 13.929(0.024) 13.071(0.018)
C9 UCAC4642-006908 015436.06 +382004.67 14.068(0.013) 11.491(0.014)
C10 UCAC4642-006921 015446.30 +381935.13 13.161(0.021) 11.764(0.014)
C11 UCAC4643-007147 015351.89 +382810.11 12.849(0.018) 12.191(0.014)
We usedaperturephotometrywithradiusof1.5FWHM ofthe starimage,alongwithskybackground
measurementswith annuli enclosing a comparable area. The light variability of the targets was estimated
withrespectto nearbycomparison(constant)starsinthe observedfieldofeachtarget,socalledensemble
photometry.Acheckstarservedtodeterminetheobservationalaccuracyandtocheckconstancyofthecom-
parisonstars.TheCCDensemblephotometrycalculatesthedifferencebetweentheinstrumentalmagnitude
ofthetargetandacomparisonmagnitudeobtainedfromthemeanoftheintensitiesofthecomparisonstars.
The use of numerouscomparison stars scattered over the CCD field increases considerably the statistical
accuracyofthecomparisonmagnitude(Gilliland&Brown1988,Honeycutt1992).
LightcurvesolutionsoffourWUMabinaries 5
0.99 c2
0.98 1.6
0.97 1.4
1.2
q 0.96
1.0
0.95
0.94
0.93
69.0 69.5 70.0 70.5 71.0 71.5
i
Fig.1 Illustrationoftheq-searchanalysisforV796Cep:thedifferentisolinescircumscribethe
areaswhosenormalizedχ2 aresmallerthanthemarkedvalues;theemptycirclecorrespondsto
thefinalvalueofthemassratioandorbitalinclinationgiveninTable5.
WeperformedtheensembleaperturephotometrywiththesoftwareVPHOT.Table3presentsthecoor-
dinatesofthecomparisonandcheckstarsofourtargetsfromthecatalogueUCAC4(Zachariasetal.2013)
and their magnitudesfrom the catalogue APASS DR9 (Henden 2016). The values in brackets correspond
to the standarddeviationsof the standardstars duringthe observationalnights. The choiceof comparison
andcheckstarsinthesamefieldofviewofthetargetsmeanspracticallyequalextinctionsforallstars.The
transformationoftheobtainedinstrumentalmagnitudestostandardoneswasmademanually.Forthisaim
weusedthemeancoloroftheensemblecomparison-star(g′−i′) andtransformationcoefficientsofour
comp
equipment(calculated earlier using standardstar field M67). The calculated correctionsof the instrumen-
talmagnitudesforourtargetswerefrom−0.0008magto0.0003maging′ filter(withintheobservational
precision)andfrom−0.0258magto0.0085magini′filter.
We determined the times of the individualminima (Table 4) by the method of Kwee & van Woerden
(1956).
3 LIGHTCURVESOLUTIONS
ThelightcurvesofourtargetsweresolvedbythecodePHOEBE (Prsa&Zwitter2005).Itisbasedonthe
Wilson–Devinney(WD)code(Wilson& Devinney1971,Wilson1979)butalso providesa graphicaluser
6 Kjurkchievaetal.
13.6
V796Cep V797Cep
11.6
14.0 i'
12.0 i' 14.4
es es14.8
d12.4 d
u u
nit g' nit g'
g g
Ma Ma15.2
12.8
15.6
13.2
16.0
13.6 16.4
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Phase Phase
12.8
12.8
CSSJ015341.9+381641 NSVS3853195
13.2
13.2 i' i'
13.6
13.6
s s
e e14.0
d d
nitu14.0 g' nitu g'
g g
Ma Ma14.4
14.4
14.8
14.8
15.2
15.2
15.6
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Phase Phase
Fig.2 Thefoldedlightcurvesofthetargetswiththeirfitsandthecorrespondingresiduals(shifted
verticallybydifferentamounttosavespace).
interface and modeling in Sloan filters of our observations.We used the traditionalconventionthe Min. I
(phase0.0)tobethedeeperlightminimumandthestarthatiseclipsedatMin.Itobeaprimarycomponent.
MeantemperaturesT ofthebinariesweredeterminedinadvance(seeTable6further)onthebasisof
m
theirinfraredcolorindices(J-K)fromthe2MASScatalogandthecalibrationcolor-temperatureofTokunaga
(2000). The preliminary runs revealed that all targets are overcontact systems. Hence, we applied mode
LightcurvesolutionsoffourWUMabinaries 7
Fig.3 3Dconfigurationsofthetargets
Table4 Timesofminimaofourtargets
Target Min.I Min.II IRIDAcycle
V0796Cep 2457321.43582(9) - 0.0
- 22457322.41776(13) 2.5
2457323.40045(19) - 5.0
- 2457324.38263(8) 7.5
2457324.57929(1) - 8.0
V0797Cep 2457321.31715(74) - 0.0
- 2457321.45201(25) 0.5
2457321.58629(22) - 1.0
- 2457322.26135(33) 3.5
2457322.39815(24) - 4.0
- 2457323.34511(22) 7.5
2457324.29034(18) - 11.0
- 2457324.42626(3) 11.5
CSSJ015341.9+381641 - 2457333.44320(11) -0.5
2457333.61496(31) - 0.0
- 2457334.48599(14) 2.5
2457338.47982(18) - 14.0
- 2457340.39396(31) 19.5
2457340.56578(15) - 20.0
NSVS3853195 - 2457333.44266(9) -0.5
2457333.59001(21) - 0.0
2457334.46774(15) - 3.0
- 2457338.41610(11) 16.5
2457338.56296(13) - 17.0
2457339.44062(12) - 20.0
- 2457340.46366(14) 23.5
8 Kjurkchievaetal.
”Overcontact binary not in thermal contact” of the code. Firstly we fixed T1 = Tm and varied the initial
epoch T0 and period P to search for fitting the phases of light minima and maxima. After that we fixed
their values and varied simultaneously secondary temperature T2, orbital inclination i, mass ratio q and
potentialΩtosearchforreproducingofthewholelightcurves.Thedataini’andg’bandsweremodelled
simultaneously.
We adopted coefficients of gravity brightening g1 = g2 = 0.32 and reflection effect A1 = A2 = 0.5
appropriateforlate-typestarswhilethelinearlimb-darkeningcoefficientsforeachcomponentandeachcolor
were updatedaccordingto the tablesofvanHamme(1993).Solarmetallicity wasassumedforthe targets
becausetheyconsistoflatestarsfromthesolarvicinity.Inordertoreproducethelightcurvedistortionswe
usedcoolspotswhoseparameters(longitudeλ,angularsizeαandtemperaturefactorκ)wereadjusted.
After reaching the best solution we varied together all parameters (T2, i, q, Ω, T0 and P) around the
valuesfromthelastrunandobtainedthefinalmodel.InordertodeterminestellartemperaturesT1 andT2
aroundthemeanvalueT weusedtheformulae(Kjurkchievaetal.2016b):
m
∆T
T1 =Tm+ , (1)
c+1
T2 =T1−∆T, (2)
wherec=l2/l1(luminosityratio)and∆T =Tm−T2PH weretakenfromthelastPHOEBEfitting.
AlthoughPHOEBE (asWD)workswithpotentials,itgivesapossibilitytocalculateallvalues(polar,
point, side, and back) of relative radius r = R /a of each component (R is linear radius and a is or-
i i i
bitalseparation).Intheabsenceofradialvelocitycurvesweputasdefaulta=1becausefromphotometry
onlywe cannotdeterminebinaryseparation.Moreover,PHOEBE yieldsasoutputparametersbolometric
magnitudesMi ofthetwo componentsinconditionalunits(whenradialvelocitydataarenotavailable).
bol
Buttheir differenceM2 −M1 determinesthetrue luminosityratio c = L2/L1 = l2/l1.Filloutfactor
bol bol
f =[Ω−Ω(L1)]/[Ω(L2)−Ω(L1)]canbealsocalculatedfromtheoutputparametersofPHOEBEsolution.
In order to take into account the effect of expected correlation between the mass ratio and orbital in-
clinationwecarriedoutq-searchanalysisasdescribedinKjurkchievaetal.(2016b).Forthisaimwefixed
thecomponenttemperaturesandradiiaswellasthespotparametersandcalculatedthenormalizedχ2fora
two-dimensionalgridalongiandq.Figure1illustratestheresultfromthisq-searchprocedureforthetarget
V796Cep.
Table 5 contains final values of the fitted stellar parameters and their PHOEBE uncertainties: initial
epochT0; periodP;mass ratioq;inclinationi;potentialΩ; secondarytemperatureT2PH. Table6 exhibits
LightcurvesolutionsoffourWUMabinaries 9
Table5 Valuesofthefittedparameters
Star T0 P q i Ω T2PH
V796Cep 2457321.43582(9) 0.392966 0.948(2) 70.7(1) 3.612(7) 6400(19)
V797Cep 2457321.31715(74) 0.270416 0.886(2) 64.7(1) 3.525(2) 4625(42)
CSSJ015341.9+381641 2457333.61496(31) 0.347518 0.892(2) 70.0(2) 3.490(1) 5607(28)
NSVS3853195 2457333.59001(21) 0.292524(4) 0.899(2) 69.8(1) 3.539(3) 5592(30)
Table6 Calculatedparameters
Target Tm T1 T2 r1 r2 f l2/l1
V796Cep 6407 6410(19) 6403(19) 0.421(1) 0.412(1) 0.101 0.951
V797Cep 4770 4833(44) 4688(42) 0.424(1) 0.403(1) 0.075 0.771
CSSJ015341.9+381641 5715 5765(29) 5657(28) 0.434(1) 0.414(1) 0.166 0.867
NSVS3853195 5688 5733(31) 5637(30) 0.425(1) 0.406(1) 0.089 0.865
Table7 Parametersofthecoolspotsofthetargets
Star β λ α k
V796Cep 90(5) 35(1) 5.0(1) 0.90(1)
CSSJ015341.9+381641 90(5) 90(1) 20.0(1) 0.80(1)
NSVS3853195 80(5) 120(1) 25.0(2) 0.95(1)
thecalculatedparameters:stellartemperaturesT1,2;stellarradiir1,2 (backvalues);filloutfactorf;ratioof
relative stellar luminosities l2/l1. Their errorsare determinedfrom the uncertaintiesof outputparameters
used for their calculation. Table 7 gives information for the spot parameters. The synthetic light curves
correspondingtooursolutionsareshowninFig.2ascontinuouslines.
The mean (g’, i’) residuals for the final fittings are: (0.005, 0.007) for V796 Cep; (0.021, 0.022) for
V797Cep;(0.009,0.012)forCSSJ015341.9+381641;(0.009,0.013)forNSVS3853195.Themean(g’,i’)
residualsofthestandardstars(Table3)forthefirstandsecondpairsoftargetsarecorrespondingly(0.010,
0.011)and(0.017,0.015).Hence,ourfittingsareexcellentforthethreetargetsandverygoodforthefaint
star V797 Cep (Fig. 2). The small imperfectnessof our modelingmay due to inadequatetreatmentof the
overcontactbinaries(Prsaetal.2016)andtolongexposures(Kipping2010).
10 Kjurkchievaetal.
0.35
0.30
0.25
0.20
f0.15
0.10
0.05
0.00
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
q
Fig.4 Distributionfilloutfactor–massratioofWUMastars:redtrianglesareforshallowcontact
highmassratiotargets;blackcirclesarefortargetswith decreasingperiodsfromthesampleof
Yang(2013)
4 CONCLUSIONS
Themainresultsfromthelightcurvesolutionsofourdataareasfollows.
(1)WedeterminedtheinitialepochsT0ofthefourtargets(Table5).
(2) We improved the period of NSVS 3853195 (Table 5) on the base of all photometric data: CRTS,
NSVS,SWASPandIRIDA.Thepreviousperiodvaluesoftheotherthreetargetsfittedwellourdata.
(3)OurobservationsrevealedthatCSSJ015404.1+382805andNSVS3853195arethesamestar(while
VSXidentifiedtwostars).
(4) The components of each target are almost the same in mass, temperature, radius and luminosity
(Tables5-6).
(5)ThestellarcomponentsofalltargetsareofGandKspectraltypesandtheyundergopartialeclipses.
(6)Alltargetshaveovercontactconfigurationswithsmallfilloutfactor(Fig.3,Table6).Thismeansthat
theyprobablyarenewlyformedcontactbinaries(Qianetal.2014).
(7)ThreebinariesrevealedO’Connelleffectthatwasreproducedbycoolspots(Table7)ontheirprimary
components.Theyareappearancesofthemagneticactivityofthesetargets.
(8)Allourtargetshavemassratioq ≥0.88(Table5),i.e.theybelongtotheHsubtypeWUMasystems
(withq ≥0.72).Csizmadia&Klagyivik(2004)revealedthatthedifferentsubtypesofWUMa’sarelocated
intodifferentregionsonthemassratio–luminosityratiodiagram(theirfig.1)butabovethelinel2/l1 =q4.6