The diversity of light curve variations of Blazhko stars

2.8 MB·English

by  Ádám Sódor

Astron.Nachr./AN999,No.88,789–792(2006)/DOIpleasesetDOI!
The diversity of light curve variations of Blazhko stars
A´.So´dor1,⋆
KonkolyObservatory,H-1525Budapest,POBox67,Hungary
Thedatesofreceiptandacceptanceshouldbeinsertedlater
1
1 Keywords RRLyraestars–stars:horizontal-branch–surveys–techniques:photometric
0
Theground-basedKonkolyBlazhkoSurveyIandIIaimtocollectaccurate,extended,multicolourlightcurvesofgalactic
2
fieldRRabstarsinordertodeterminetheincidencerateofthemodulationinthesample,tostudythemodulationindetails,

n tostudylong-termchangesinthemodulationpropertiesandtofindchangesinthemeanglobal physicalparametersof
a the stars with Blazhko phase. Here the diversity of light curve variations of Blazhko stars is demonstrated through a
J sub-sampleofthemodulatedRRabstarsfoundbythefirstpartofthissurvey.

6
2 (cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim

]
R 1 Introduction brightshort-period(P <0.5d)variableswithabout750
puls
S nightsofobservations.Asurprisinglyhighnumberofstars
h. ThecyclicvariationsintheshapeofRRLyraelightcurves, (14 out of 30, 47%) has been found to show the Blazhko
p the Blazhko effect, recognized by Blazhko (1907) and effect(Jurcsiketal.,2009).
- Shapley (1916), is one of the most long-lasting riddle of
o InJanuary2009,thesecondpartofthesurvey,KBSII,
stellar pulsation theory. Recent extended studies of these
r was launched extending the sample toward longer periods
t starsrevealedthatthephenomenonmanifestsitselfinmany
s (0.55d> P > 0.6d) using the 1m RCC telescope of
puls
a differentways,whichposesagreatchallengeagainsttheo-
Konkoly Observatory at Piszke´s-teto˝ and also the 60cm
[
riestryingtoexplaintheeffect(Kova´cs,2009). Heyde-Zeisstelescope.Uptonow21RRabstarshavebeen

1 InthispapertheKonkolyBlazhkoSurveyIandIIisin-
observedintheframeoftheongoingKBSIIproject.
v troducedinbriefandthediversityofmodulatedRRablight
9
curvesisdemonstratedthroughasub-sampleoftheBlazhko
9
starsfoundbythesurvey.
0 3 The diversity ofthemodulation
5
.
1 2 The Survey
3.1 Thesample
0
1
Theground-basedKonkolyBlazhkoSurvey(KBS)IandII
1 We demonstrate the diversity of light curve variations of
aim to collect accurate, extended,multicolour light curves
: Blazhkostarsthroughasub-sampleofthemodulatedRRab
v ofnorthernfundamentalmodeRRLyraestarsoftheGalac-
starsfoundbytheKBSI.Fourweaklymodulated(SSCnc,
i
X ticfieldSo´dor(2005)inorderto: DM Cyg, RR Gem, BR Tau) and four strongly modulated
r – determine the incidence rate of the modulation in the (XY And, AQ Lyr, MW Lyr, UZ Vir) stars have been se-
a
sample, lected. Our resultson the analysis of the lightcurvevaria-
– studythemodulationindetails, tions of several of these stars have already been published
– studylong-termchangesinthemodulationproperties, (SSCnc–Jurcsiketal.2006,DMCyg–Jurcsiketal.2009,
– findchangesinthemeanglobalphysicalparametersof RR Gem – Jurcsiketal. 2005, MW Lyr – Jurcsiketal.
thestarswithBlazhkophase. 2008).Alltheselectedvariableswereextensivelyobserved.
The number of data points in V band are between 1400
The PIs of the project are Johanna Jurcsik and Be´la
and 5800 for these objects. The data cover all the pulsa-
Szeidl, co-workers are A´da´m So´dor, Zsombor Hurta and
tion phases in each Blazhko phase for each object. These
others.
Blazhkostars haveonedominantmodulationperiod,how-
The first part of the survey, KBS I, was initiated in
ever, some of them have one or more secondary modula-
January2004usingJohnson-CousinsBV(RI) filtersand
C tionsalso.WehavefoundfurtherBlazhkostarswithmulti-
a Wright CCD camera attached to the automatic 60cm
periodicor irregularmodulationin our survey(RY Com –
Heyde-Zeiss telescope of Konkoly Observatory at Bu-
Jurcsiketal.2009,V759Cyg–Jurcsiketal.2009,CZLac
dapest,Hungary.Thefirstpartisnowfinished,covering30
– So´dor 2009, AQ Lyr – Jurcsiketal. 2009, UZ UMa –
⋆ Correspondingauthor:e-mail:sodor at konkoly dot hu So´doretal. 2006), which adds even more colour to our
presenttopic. We only mentionthe existence of the multi-
(cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
790 A´.So´dor:ThediversityoflightcurvevariationsofBlazhkostars
PP00 == 00..339911 dd BBRR TTaauu PBl1 = 19.3 d
1
--00..55
--00..11
g]
ag]ag] 00 ag]ag] V ma 0.1
V [mV [m V [mV [m 00 ude [
∆∆ 00..55 ∆∆ plit 0.01
m
a
00..11
11 0.001
00 00..55 11 00 00..55 11 0 2.56015 5.12031
PPuullssaattiioonn pphhaassee PPuullssaattiioonn pphhaassee frequency [c/d]
PP00 == 00..442200 dd DDMM CCyygg PBl = 10.6 d
1
--11 --00..11
g]
ma 0.1
V [mag]V [mag]--00..55 V [mag]V [mag] 00 ude [V
∆∆ ∆∆ plit 0.01
00 m
a
00..11
0.001
00 00..55 11 00 00..55 11 0 2.38173 4.76346
PPuullssaattiioonn pphhaassee PPuullssaattiioonn pphhaassee frequency [c/d]
PP00 == 00..339977 dd RRRR GGeemm PBl = 7.2 d
1
--00..11
00..55
g]
ma 0.1
ag]ag] ag]ag] V
V [mV [m 11 V [mV [m 00 ude [
∆∆ ∆∆ plit 0.01
m
11..55 a
00..11
0.001
00 00..55 11 00 00..55 11 0 2.51706 5.03411
PPuullssaattiioonn pphhaassee PPuullssaattiioonn pphhaassee frequency [c/d]
PPP000 === 000...333666777 ddd SSSS CCnncc PBl = 5.3 d
1
--00..11
---000...555 g]
ma 0.1
ag]ag]ag] ag]ag] V
V [mV [mV [m 000 V [mV [m 00 ude [
∆∆∆ ∆∆ plit 0.01
m
a
000...555 00..11
0.001
000 000...555 111 00 00..55 11 0 2.7223 5.44459
PPPuuulllsssaaatttiiiooonnn ppphhhaaassseee PPuullssaattiioonn pphhaassee frequency [c/d]
Fig.1 WeaklymodulatedsampleBlazhkostarsfromKBSI.Theleft-handpanelsdisplaytheV lightcurvesfoldedwith
thepulsationperiod.Themiddlepanelsshowthelightcurvesafterthesubtractionofthemeanpulsationcurves.Intheleft-
handandmiddlepanelsthehighestandlowestpulsationamplitudeBlazhkophasesarehighlighted.Theloops,whichthe
maximumandminimumlightsgoalongduringthemodulation,arealsodrawn.Theright-handpanelsplottheschematic
Fourierspectraofthelightcurvesolutionsinthevicinityofthepulsationfrequency(f )anditsfirstharmonic(2f ).
0 0
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Astron.Nachr./AN(2006) 791
PP00 == 00..339988 dd MMWW LLyyrr PBl = 16.5 d
11 1
--00..44
g]
a
11..55 --00..22 m 0.1
ag]ag] ag]ag] V
∆∆ V [m V [m 22 ∆∆ V [m V [m 00 ..0022 plitude [ 0.01
m
a
00..44
22..55
0.001
00 00..55 11 00 00..55 11 0 2.51462 5.02924
PP00 == 00..339999 dd XXYY AAnndd PBl = 41.4 d
1
--00..55 --00..44
g]
a
--00..22 m 0.1
ag]ag] 00 ag]ag] V
V [mV [m V [mV [m 00 ude [
∆∆ 00..55 ∆∆ 00..22 plit 0.01
m
a
00..44
0.001
00 00..55 11 00 00..55 11 0 2.50799 5.01599
PP00 == 00..335577 dd AAQQ LLyyrr PBl1 = 54.0 d
1
--00..55 --00..44
g]
a
--00..22 m 0.1
V [mag]V [mag] 00 V [mag]V [mag] 00 ude [V
∆∆ ∆∆ 00..22 plit 0.01
00..55 m
a
00..44
0.001
00 00..55 11 00 00..55 11 0 2.80008 5.60015
PP00 == 00..445599 dd UUZZ VViirr PBl = 68.2 d
1
00 --00..44
g]
a
--00..22 m 0.1
V [mag]V [mag] 00..55 V [mag]V [mag] 00 ude [V
∆∆ ∆∆ 00..22 plit 0.01
11 m
a
00..44
0.001
00 00..55 11 00 00..55 11 0 2.17679 4.35358
PPuullssaattiioonn pphhaassee PPuullssaattiioonn pphhaassee frequency [c/d]
Fig.2 Strongly modulated sample Blazhko stars from KBS I. The left-hand panels display the V light curves folded
with thepulsationperiod.Themiddlepanelsshowthelightcurvesafterthesubtractionofthemeanpulsationcurves.In
the left-hand and middle panels the highest and lowest pulsation amplitude Blazhko phases are highlighted. The loops,
whichthemaximumandminimumlightsgoalongduringthemodulation,arealsodrawn.Theright-handpanelsplotthe
schematicFourierspectraofthelightcurvesolutionsinthevicinityofthepulsationfrequency(f )anditsfirstharmonic
0
(2f ).
0
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792 A´.So´dor:ThediversityoflightcurvevariationsofBlazhkostars
periodicmodulationherewithoutgivingdetailsandweare a similarly complex modulation, however, it is less con-
goingtoanalyzetheseobjectslaterinforthcomingpapers. spicuous as the overallstrength of its modulation is much
Theweaklyandstronglymodulatedsampleobjectsare weaker. The residual light curve of MW Lyr, after the re-
shown in Figs. 1 and 2, respectively. The left-hand pan- moval of the best solution, shows also a kind of stochas-
els display the V light curves folded with the pulsation tic behaviour(Jurcsiketal., 2008). There are signs of sec-
period. The middle panels show the light curves after the ondarymodulationperiodsalsoatothersamplestars(MW
subtraction of the mean pulsation curves. In the left-hand Lyr Jurcsiketal. 2008, RR Gem Jurcsiketal. 2005) indi-
and middle panels the highestand lowest pulsation ampli- catingthatmultiperiodicmodulationismuchmoretherule
tudeBlazhkophasesarehighlighted.Theloops,whichthe thantheexceptioninBlazhkostars.
maximumandminimumlightsgo alongduringthe modu-
Acknowledgements. The financial support of the Hungarian
lation,arealsodrawn.Theseloopsarecalculatedfromsyn-
OTKAgrantT-068626isacknowledged.
theticlightcurvestakingintoaccountthedominantmodu-
lationperiodonly.Theright-handpanelsplottheschematic
References
Fourier spectra of the light curve solutions in the vicinity
ofthepulsationfrequency(f )anditsfirstharmonic(2f ).
0 0 Blazhko,S.1907,Astron.Nachr.,173,325
Thepeaksinthesepanelsrepresentthefrequenciesandam- Jurcsik,J.,Hurta,Zs.,So´dor,A´.etal.2009,MNRAS,397,350
plitudesofthecomponentsofthelightcurvesolutions. Jurcsik,J.,So´dor,A´.,Hurta,Zs.etal.2008,MNRAS,391,164
Jurcsik,J.,So´dor,A´.,Szeidl,B.etal.2009,MNRAS,400,1006
Jurcsik,J.,So´dor,A´.,Va´radi,M.etal.2005,A&A,430,1049
3.2 Discussion
Jurcsik,J.,Szeidl,B.,So´dor,A´.etal.2006,AJ,132,61
Kova´cs,G.2009,AIPC,1170,261
Phasemodulation
Shapley,H.1916,ApJ,43,217
Examining the weakly modulated stars we find that only So´dor,A´.2005,AN,328,829
So´dor,A´.2009,CoAst,159,55
slight, if any, phase modulation occurs. BR Tau and
So´dor,A´.,Vida,K.,Jurcsik,J.etal.2006,IBVS,5705
RR Gem has fix points on their rising branches, and their
Szeidl,B.,Jurcsik,J.2009,CoAst,160,17
maximumbrightnessphasesarealsomarginallymodulated
only. The rising branches of DM Cyg and SS Cnc show
weakbutdefinitephasemodulation.
At the same time, all the strongly modulated Blazhko
stars show definite phase modulation. A fix point can be
seenonthelowerpartoftherisingbranchofUZVir,while
the maximumandminimumlightphasesaremodulatedin
allthefourobjects.
Loopsofmaximumandminimumlights
Itisaninterestingobservationthatthedirectionoftheloop
the maximum light goes along during the modulation is
counterclockwiseineachbutonecase,fornon-degenerated
loops.TheonlyexceptionisUZVir.Inaccordancewiththis
observation, the higher frequency modulation peaks (right
side, kf + f ) usually have higher amplitudes than the
0 m
lowerfrequencyones(leftside,kf −f ).Onthemathe-
0 m
matical backgroundsee details at Szeidl&Jurcsik (2009).
The minimum light travels an opposite direction than the
maximumlightdoesineachcases.
Complexmodulation
The modulation of AQ Lyr is rather complex. The dom-
inant modulation period of this star is 54d but the light
variation,whichhavebeenfollowedintwoconsecutiveob-
serving seasons, can be described with sufficient accuracy
only when four or more modulations are taken into ac-
count.Evenso,variationsintheresidualexceedingtheac-
curacy of our measurements remain. BR Tau also shows
(cid:13)c 2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org