First Kepler results on compact pulsators VI. Targets in the final half of the survey phase

0.66 MB·English

by  R. H. Østensen

Mon.Not.R.Astron.Soc.000,1–11(2010) Printed24January2011 (MNLATEXstylefilev2.2)
First Kepler results on compact pulsators
VI. Targets in the final half of the survey phase
R. H. Østensen,1⋆ R. Silvotti,2 S. Charpinet,3 R. Oreiro,1,4 S. Bloemen,1 A. S. Baran,5,7
M. D. Reed,6 S. D. Kawaler,7 J. H. Telting,8 E. M. Green,9 S. J. O’Toole,10 C. Aerts,1,11
1
1 12 12 12 13 14 6
B. T. Ga¨nsicke, T. R. Marsh, E. Breedt, U. Heber, D. Koester, A. C. Quint,
0
2 D. W. Kurtz,15 C. Rodr´ıguez-Lo´pez,16,17 M. Vucˇkovic´,1,18 T. A. Ottosen,8,19

n S. Frimann,8,19 A. Somero,8,20 P. A. Wilson,8,21 A. O. Thygesen,8 J. E. Lindberg,8,22
a
19 19 23 23
J H. Kjeldsen, J. Christensen-Dalsgaard, C. Allen, S. McCauliff

1 23
and C. K. Middour
2
1InstituutvoorSterrenkunde,K.U.Leuven,Celestijnenlaan200D,3001Leuven,Belgium

] 2INAF-OsservatorioAstronomicodiTorino,Stradadell’Osservatorio20,10025PinoTorinese,Italy
R 3Laboratoired’AstrophysiquedeToulouse-Tarbes,Univ.deToulouse,14Av.EdouardBelin,Toulouse31400,France
S 4InstitutodeAstrof´ısicadeAndaluc´ıa,GlorietadelaAstronom´ıas/n,18008Granada,Spain
. 5Mt.SuhoraObservatory,CracowPedagogicalUniversity,Podchorazych2,30-084Krakow,Poland
h 6DepartmentofPhysics,Astronomy,andMaterialsScience,MissouriStateUniversity,Springfield,MO65804,USA
p 7DepartmentofPhysicsandAstronomy,IowaStateUniversity,Ames,IA50011,USA
- 8NordicOpticalTelescope,38700SantaCruzdeLaPalma,Spain
o
9StewardObservatory,UniversityofArizona,933N.CherryAve.,Tucson,AZ85721,USA
r
t 10AustralianAstronomicalObservatory,POBox296,EppingNSW1710,Australia
s 11DepartmentofAstrophysics,IMAPP,RadboudUniversityNijmegen,6500GLNijmegen,TheNetherlands
a
[ 12DepartmentofPhysics,UniversityofWarwick,CoventryCV47AL,UK
13Dr.KarlRemeis-Observatory&ECAP,AstronomicalInst.,FAUErlangen-Nuremberg,Sternwartstr.7,96049Bamberg,Germany

1 14Institutfu¨rTheoretischePhysikundAstrophysik,Universita¨tKiel,24098Kiel,Germany
v 15JeremiahHorrocksInstituteofAstrophysics,UniversityofCentralLancashire,PrestonPR12HE,UK
0 16DepartamentodeF´ısicaAplicada,Univ.deVigo,CampusLagoas-Marcosendes/n,36310Vigo,Spain
5 17UniversityofDelaware,DepartmentofPhysicsandAstronomy,217SharpLab,Newark,DE19716,USA
1 18EuropeanSouthernObservatory,AlonsodeCo´rdova3107,Vitacura,Casilla19001,Santiago,Chile
4 19DepartmentofPhysicsandAstronomy,AarhusUniversity,8000AarhusC,Denmark
. 20TuorlaObservatory,DepartmentofPhysicsandAstronomy,UniversityofTurku,Va¨isa¨la¨ntie20,FI-21500,Piikkio¨,Finland
1
21AstrophysicsGroup,SchoolofPhysics,UniversityofExeter,StockerRoad,ExeterEX44QL,UK
0
22CentreforStarandPlanetFormation,Nat.Hist.MuseumofDenmark,Univ.ofCopenhagen,Ø.Voldgade5-7,CopenhagenDK-1350,Denmark
1
23OrbitalSciencesCorporation/NASAAmesResearchCenter,MoffettField,CA94035,USA
1
:
v
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Released2010XxxxxXX
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ABSTRACT
We present results from the final six months of a survey to search for pulsations in white
dwarfs and hot subdwarf stars with the Kepler spacecraft. Spectroscopic observations are
usedtoseparatetheobjectsintoaccurateclasses,andweexplorethephysicalparametersof
thesubdwarfB(sdB)starsandwhitedwarfsinthesample.FromtheKeplerphotometryand
our spectroscopic data, we find that the sample contains 5 new pulsators of the V1093Her
type,oneAMCVntypecataclysmicvariable,andanumberofotherbinarysystems.
This completes the survey for compact pulsators with Kepler. No V361Hya type of
short-periodpulsating sdB stars were found in this half, leaving us with a total of one sin-
gle multiperiodic V361Hya and 13 V1093Her pulsators for the full survey. Except for the
sdBpulsators,nootherclearlypulsatinghotsubdwarfsorwhitedwarfswerefound,although
a few low-amplitudecandidatesstill remain. The most interesting targets discoveredin this
surveywillbeobservedthroughouttheremainderoftheKeplerMission,providingthemost
long-termphotometricdatasetsevermadeonsuchcompact,evolvedstars.Asteroseismicin-
vestigations of these datasets will be invaluable in revealing the interior structure of these
stars,andwillboostourunderstandingoftheirevolutionaryhistory.
Key words: surveys – stars: oscillations – binaries: close – subdwarfs – white dwarfs –
Kepler.
(cid:13)c 2010RAS
2 R. H. Østensenet al.
1 INTRODUCTION
Table2.Logofspectroscopicobservations.
TheKeplerspacecraftwaslaunchedinMarch2009, withthepri-
mary aim to find Earth-sized planets within the habitable zone Run Dates Telescope P.I.,Observer
around solar-like stars using the transit method (Boruckietal.
N1 2008September20–21 NOT JHT,AS
2010).Inordertohaveahighprobabilityoffindingsuchplanets, N2 2008September22–26 NOT RO
the spacecraft continuously monitors the brightness of ∼100000 W1 2009April11–12 WHT CA,RHØ
stars with close to micromagnitude precision. As a byproduct of W2 2009July14–16 WHT CA,TAO
theplanethunt,highqualityphotometricdataofvariablestarsare N3 2009September7 NOT JHT,JL
obtained,anincrediblyvaluableinputforthestudyofbinarystars N4 2010June9 NOT JHT,AT
(Prsaetal.2010)andasteroseismology(Gillilandetal.2010a). W3 2010July2–6 WHT CA,RHØ
N5 2010September27 NOT JHT,SF,PW
Thefirstfour quartersof theKepler Missionwerededicated
toasurveyphase,andasubstantialnumberoftargetslotsforshort
cadenceobservationsweremadeavailabletotheKeplerAsteroseis-
micScienceConsortium(KASC);512slotsintheinitialrollposi- ForanintroductiontothepulsatingsubdwarfBstars,werefer
tion(Q1) and 140 inthefollowing quarters. Theseriesof papers
thereadertotheearlierpapersinthisseries.Inthepresentarticle
of which thisisthe sixth, deals withthe search for compact pul-
wewillprovidephotometricvariabilitylimitsonallthestarsfrom
sators 1, and the results from the first half of the survey are de-
thesecondhalfofthesampleandphysicalparametersforthehot
scribedinPaper I(Østensenetal.2010c).Paper II(Kawaleretal. subdwarfstars,aswedidinPaperI.Moreover,wewillalsoprovide
2010a) describes KIC10139564, a short-period subdwarf B pul-
physicaldatafromourspectroscopyonthewhitedwarfstars.
sator(V361Hyastar).Fivelong-periodsdBpulsators(V1093Her
We will also present analysis of the Kepler photometry for
stars) are described in Paper III (Reedetal. 2010), and one of a number of objects that display long-period variability features,
them, KPD1943+4058, is given a detailed asteroseismic analy-
andformanyoftheseweconcludethattheyaremostlikelytobe
sis in Paper IV (VanGrooteletal. 2010). An asteroseismic anal- binarysystemscomposedofahotsubdwarfandawhitedwarfor
ysisonanotherofthestarsinPaperIII,KIC2697388,isgivenby mainsequencestar.
Charpinetetal.(2011).TwomoreV1093Herpulsatorsthatappear
tobeinshort-periodbinarysystemswithM-dwarfcompanionsare
describedinPaperV(Kawaleretal.2010b).
The first half of the survey also revealed that the eclips-
ing sdB+dM binary, 2M1938+4603 (KIC9472174), is alow am- 2 SURVEYSAMPLE
plitude pulsator with an exceptionally rich frequency spectrum
Themethodsusedtoselectthesamplestarsweredescribedindetail
(Østensenetal.2010a),andthesdB+WDbinary,KPD1946+4340
(KIC7975824), was found to show eclipses, ellipsoidal modula- inPaperI.Inbrief,threegroupssubmittedtargetsbasedonsixdif-
ferentselectionmethods,whichwedesignatea–finTable1.Only
tionandDopplerbeamingeffects(Bloemenetal.2010).Thecur-
twostarsinthecurrenthalfofthesamplewerealreadyclassifiedas
rent paper describes the content of the compact pulsator sample
compactstarsfromearliersurveys(samplea),FBS1907+425and
observedinthesecondhalfofthesurveyphase.
FBS1903+432(Abrahamianetal.1990).Thefirstoneofthesealso
The Kepler field of view covers 105 square degrees, and is
beingobservedinabroadbandpass(4200–9000A˚)using42CCDs appearsinthe2MASScolor-selectedsample(b),butwasdropped
asacandidateafterfollow-upspectroscopy demonstratedthatthe
mountedinpairson21modules.AlthoughtheKeplerphotometer
starwasanormalB-star.Itdid,however,reenterthesurveysample
samplesthefieldevery6.54s,telemetryrestrictionsdonotpermit
throughtheKICcolorselectedsample(f).Eightstarsappearinthe
theimagingdatatobedownloaded.Instead,pixelmasksoftargets
deemed tobe of interest must be uploaded to the spacecraft, and SEGUEextension(Yannyetal.2009)oftheSloanDigitalSkySur-
vey (SDSS,Stoughtonetal. 2002) (c), and all these are compact
thesepixelsareaveragedintosamplesofeitherapproximatelyone
objects.Seventeen ofthestarswereselectedbasedonUV-excess
minute(shortcadence;SC)orhalfanhour(longcadence;LC).
fromGalexsatellitedata(Martinetal.2005)(d),andthesearealso
The primary goal of the asteroseismology survey phase is
allhotsubdwarfsorwhitedwarfs.Sevenstarswerechosenbased
thereforetoidentifythemostinterestingpulsatorsinthesample,so
ontheirpositioninthereducedpropermotion(RPM)diagram(e),
that these objects can thenbe followed throughout theremaining
butonly fiveof theseturned out tobecompact objects. Asmany
yearsof themission. Theprimarygoals for thecompact pulsator
as 22 stars were selected based only on KIC gri colors (f), and
survey were set out in Paper I, and for the subdwarf B pulsators
ofthese,14werenotincludedinanyoftheothersamples.Ofthe
asubstantiallistoftargetsforfurtherstudywereidentified.How-
latter,9werecompact starsand fivenormal B– Fstars. Intotal,
ever, no clearly pulsating white dwarf was found in the first part
fourB-andfourF-starscontaminateoursampleof47targets,and
ofthesample,anditwashoped thatthesecond partwould bring
willnotbediscussedfurtherhere.Theremainingcompactpulsator
more luck. This did not happen, so weare still without any con-
candidates havebeen spectroscopically classifiedasWDsor WD
firmedwhitedwarfpulsatorstofollowforthespecifictargetpartof
composites(6objects),andhotsubdwarfsorsubdwarfcomposites
theKeplerMission.Analysisofthefiveunambiguous V1093Her
(33objects),asdescribedinthefollowingsection.
pulsatorsfoundinthissecondhalfofthesurveyarepresentedby
Onetargetinthefinalsample,KIC10784623,wasscheduled
Baranetal.(2011,Paper VII).Astudyoftheperiodspacingsob-
forobservationsbutwasnotobserved,asithappenstobelocated
served inmany of the V1093Her starsfrom the survey has been
on module 3 which suffered a technical fault early in the fourth
givenbyReedetal.(2011,PaperVIII).
quarter(seeSection4),andisnolongerinuse.Sincethespacecraft
isrotatedeveryquarterinordertokeepitssunshadefacinginthe
1 Theterm‘compactpulsators’isusedtoencompassallthevariousgroups rightdirection,itcouldbepossibletoobserveitatsometimelater
ofpulsatingwhitedwarfsandhotsubdwarfstars. inthemission.
(cid:13)c 2010RAS,MNRAS000,1–11
FirstKeplerresultson compactpulsatorsVI 3
Table1.CompactpulsatorcandidatesobservedwithKeplerinQ3andQ4.
KIC Name Run RA(J2000) Dec(J2000) Kp Fcont Sample Class
2020175 J19308+3728 Q3.1 19:30:48.5 +37:28:19 15.49 0.722 ce† sdB
2303576 J19263+3738 Q3.3 19:26:18.9 +37:38:15 17.45 0.928 c He-sdO
2304943 J19275+3738 Q3.3 19:27:33.8 +37:38:55 16.18 0.692 c sdB
2850093 J19237+3801 Q3.2 19:23:47.2 +38:01:44 14.73 0.298 f F
3343613 J19272+3827 Q3.2 19:27:15.0 +38:27:19 15.74 0.469 df He-sdOB
3353239 J19367+3825 Q4.1 19:36:46.3 +38:25:27 15.15 0.099 f sdB
3527028 J19024+3840 Q4.2 19:02:25.7 +38:40:20 17.09 0.465 c sdB
3938195 J19048+3903 Q4.1 19:04:49.5 +39:03:16 15.30 0.908 f F
4547333 J19082+3940 Q3.3 19:08:17.1 +39:40:36 16.32 0.253 c‡ AMCVn
5340370 J18535+4035 Q4.2 18:53:31.1 +40:35:19 17.08 0.128 c sdB
5557961 J19514+4043 Q4.3 19:51:26.2 +40:43:36 15.82 0.647 f F
5769827 J18547+4105 Q4.1 18:54:45.0 +41:05:15 16.62 0.952 c DA0
5938349 J18521+4115 Q3.2 18:52:10.1 +41:15:15 16.05 0.079 c sdB
6371916 J19370+4145 Q3.3 19:37:01.1 +41:45:39 14.97 0.361 e B
6522967 J19279+4159 Q3.2 19:27:58.7 +41:59:03 16.91 0.622 d sdB
6614501 J19368+4201 Q3.3 19:36:50.0 +42:01:44 16.09 0.600 f sdB
6878288 J19436+4220 Q3.1 19:43:37.0 +42:20:58 16.67 0.686 f He-sdOB
7104168 FBS1907+425 Q3.1 19:08:45.7 +42:38:32 15.48 0.189 af sdB
7129927 J19409+4240 Q3.1 19:40:59.4 +42:40:31 16.59 0.585 e† DA+DA
7335517 J18431+4259 Q3.2 18:43:06.7 +42:59:18 15.75 0.295 df sdO+dM
7668647 FBS1903+432 Q3.1 19:05:06.2 +43:18:31 15.40 0.226 af sdBV
7799884 J18456+4335 Q4.1 18:45:37.2 +43:35:25 16.87 0.109 d sdB
8054179 J19569+4350 Q3.1 19:56:55.6 +43:50:17 14.43 0.093 f He-sdOB
8302197 J19310+4413 Q3.3 19:31:03.4 +44:13:26 16.43 0.256 f sdBV
8874184 J19084+4508 Q4.1 19:08:24.7 +45:08:32 16.52 0.091 d sdB
9095594 J19369+4526 Q3.2 19:36:59.4 +45:26:27 17.69 0.434 d sdB
9211123 J19144+4539 Q3.3 19:14:27.7 +45:39:10 16.10 0.447 d sdB
9637292 J19030+4619 Q3.1 19:03:02.0 +46:19:55 16.68 0.513 f B
10001893 J19095+4659 Q3.2 19:09:33.5 +46:59:04 15.85 0.710 df sdBV
10149211 J19393+4708 Q4.2 19:39:18.3 +47:08:55 15.52 0.240 f sdB
10198116 J19099+4717 Q4.1 19:09:59.4 +47:17:10 16.41 0.238 de DA
10207025 J19260+4716 Q3.3 19:26:05.9 +47:16:31 15.04 0.068 f He-sdO
10449976 J18472+4741 Q3.2 18:47:14.1 +47:41:47 14.86 0.006 df He-sdOB
10462707 J19144+4737 Q4.1 19:14:29.1 +47:37:41 16.89 0.072 d sdB
10553698 J19531+4743 Q4.1 19:53:08.4 +47:43:00 15.13 0.385 f sdB
10579536 J18465+4751 Q3.1 18:46:33.9 +47:51:08 17.10 0.800 e† B
10784623 J19045+4810 Q4.2 19:04:34.9 +48:10:22 16.95 0.065 d sdB
10789011 J19136+4808 Q3.2 19:13:36.3 +48:08:24 15.50 0.031 df sdOB
10961070 J18534+4827 Q4.2 18:53:29.5 +48:27:52 16.99 0.970 d sdOB
10966623 2M1908+4829 Q3.2 19:08:12.8 +48:29:35 14.87 0.030 bf B
11337598 J18577+4909 Q3.3 18:57:47.3 +49:09:38 16.11 0.225 d DA
11350152 J19268+4908 Q3.1 19:26:51.5 +49:08:49 15.49 0.023 d sdB+F/G
11400959 J19232+4917 Q4.1 19:23:17.2 +49:17:31 16.89 0.577 d sdB
11558725 J19265+4930 Q3.3 19:26:34.1 +49:30:30 14.95 0.028 f sdBV
11604781 J19141+4936 Q3.1 19:14:09.0 +49:36:41 16.72 0.006 e† DA
12021724 J19442+5029 Q4.2 19:44:12.7 +50:29:39 15.59 0.558 e† sdB
12069500 J19419+5031 Q4.1 19:41:58.6 +50:31:09 13.63 0.654 f F
Notes.—Thedecimalpointtotherunnumbersindicatestherelevantmonthofthemissionquarter.
KpisthemagnitudeintheKeplerbandpass.FcontisthecontaminationfactorfromtheKIC(zeroisnocontamination).
Thesamplesare:a:Literature,b:2MASS,c:SDSS,d:GALEX,e:Reducedpropermotion(RPM),f:KICcolor.
A†markstargetswithTNGphotometry.‡:DescribedinFontaineetal.(2010).
3 SPECTROSCOPY notbeenusedforthiswork.Alldatawerereducedwiththestan-
dardIRAFproceduresforlong-slitspectra.
AllthetargetsinTable1wereobservedwithlowresolutionspec-
trographsatvarioustelescopes,aslistedinTable2.Theobserva-
3.1 Thewhitedwarfs
tionsattheNordicOpticalTelescope(NOT)weredonewiththeAL-
FOSCspectrograph,withgrism#6in2008,andgrism#14inafter Thereareonlyfivewhitedwarfscontainedinthesecondhalfofthe
that.BothgiveR≈600forthe∼ 1′′ slitweused,andλ=3300– surveysample,andallshowBalmerlinedominatedspectratypical
6200A˚. On the William Herschel Telescope (WHT) we used the ofDAwhitedwarfs.OneobjectwasinitiallyclassifiedasaDBstar
ISISspectrographwithgratingR300Bonthebluearm(R≈1600, inoursurvey,andcausedquitesomeexcitementwhentheKepler
λ=3100–5300A˚).Redarmspectrawerealsoobtained, buthave light curve was released displaying clear variability with periods
(cid:13)c 2010RAS,MNRAS000,1–11
4 R. H. Østensenet al.
Table3.Spectroscopicpropertiesofthewhitedwarfs,includingthe8from
PaperI(markedwith†).
Survey Teff logg
KIC name (kK) (dex) Class Run
3427482† J19053+3831 Poorfit DA W2
4829241† J19194+3958 19.4(5) 7.8(3) DA2 W1
5769827 J18547+4105 66(2) 8.2(3) DA0 W1
6669882† J18557+4207 30.5(5) 7.4(3) DA1 W2
7129927 J19409+4240 CompositeDA2+DA3 N3,N5
8682822† J19173+4452 23.1(5) 8.5(3) DA2 W1
9139775† J18577+4532 24.6(5) 8.6(3) DA2 W2
Figure1. Spectrumandline-profilefittoKIC11337598,assumingaro-
10198116 J19099+4717 14.2(5) 7.9(3) DA3 W1
tational broadening of1500km/s.Thespectrum,inparticular thehigher-
10420021† J19492+4734 16.2(5) 7.8(3) DA3 W3
resolutionred-arm part,israthernoisy,buttheextraordinary broadcores
11337598 J18577+4909 22.8(5) 8.6(3) DA2 N1,W3
areclearlyevident.Theticksmark5A˚ ontheX-axis,and2percentofthe
11514682† J19412+4925 32.2(5) 7.5(3) DA1 W1
continuumlevelontheY-axis.Theuncertaintiesstatedonthefigurearethe
11604781 J19141+4936 9.1(5) 8.3(3) DA5 W2
formalfittingerrors.TherealerrorsaremuchlargersincetheRVandvsini
11822535† WDJ1943+500 36.0(5) 7.9(3) DA1 N2
arenotfittedsimultaneously.
6862653† J19267+4219 Poorfit DB W2
periodof about 40sfor atypical WD,which isabout half of the
breakup velocity (higher if seen at low inclination angle). While
thespinperiod ishigher thantheKepler SCsampling frequency,
ifamodulationwiththisperiodwerepresentinthelightcurve,it
mightstillshowupintheFouriertransform,asthehighsensitiv-
ityofKeplerphotometrywouldhavepermittedustoseesuchhigh
frequenciesasreflectionsacrosstheNyquist frequency. Although
thefitshowninFig.1looksreasonableconsideringthenoise,we
cannotcompletelyruleoutaweakmagneticfieldasapossibleal-
ternative, or contributing effect tothe Balmer line broadening. A
muchhigherS/Nspectrumwouldberequiredtoclearlydistinguish
thesepossibilities.TheKeplerlightcurveshowsnohigh-frequency
signal,butdoesshow alow-amplitudelong-periodpeak(seesec-
tion4.3).
Figure2. Spectrumandline-profilefittotwoobservationsofKIC7129927, In three cases the spectra do not provide acceptable fits.
takenayearapart.Bothspectrashowthatthetargethasunusuallynarrow
When fitting KIC7129927, the solution converges to about
BalmerlinecoressuperimposedonanormalbroadDAprofile.Theuncer-
T =23000K and logg=7.3, but the cores are clearly not well
tainties stated on the figure are the formal fitting errors, butas the fit is eff
fitted(Fig.2).A new spectrumwasrecentlyobtained, anditwas
obviouslyfarfromadequateandtheobjectmostlikelycomposite,thebest
confirmed thatthe strangefeatures inthecoresof theDA2 spec-
fitsolution canbequitefarfromthethetrueparameters ofthebrightest
systemcomponent. trumwerereal.Weconclude that thesefeaturescanbeexplained
byacompositeDA+DAbinary,withthefaintercomponenthaving
somewhatnarrowerBalmerlinesthanthehottercomponent.There
resembling aV777Her pulsator. However, after several effortsto may be a small shift between the cores of the broad and narrow
fit the broad helium lines with DB model atmospheres failed, it components,butthisishardtoquantifyfromthelowS/Nspectra
was realised that the object is actually an AMCVn type of cata- currentlyavailable.ThelowS/Nalsopreventsareliabledecompo-
clysmicvariable,inwhichheliumisaccretedontoawhitedwarf. sition,sodeeperspectroscopyofthisobjectisencouraged.
Thisobject,KIC4547333,cannotbeanalysedwiththemodelspec- Thetwocasesmarkedwith‘Poorfit’inTable3areoffainttar-
trausedforthispaper.Asuitablegridofmodelspectradeveloped getsobtainedinbrightskyconditions,andthebackgroundsubtrac-
especially for the analysis of this interesting system is described tionappearstobeinadequate.Theintentionwhenthespectrawere
inFontaineetal.(2010).SincealldetailsofKIC4547333arepro- madewasonlytoprovideaspectroscopicclassforallthetargetsin
videdinthatpaper,wewillnotdiscussitfurtherhere. thesample,andinthesecasesthequalityturnedouttobetoopoor
InTable3welistthefiveWDsofthecurrentsampletogether toobtainreliablephysicalparameters.However,thereisnodoubt
withthesevenDAsandtheDBfromPaper I.Wehaveattempted abouttheclassification.ThestarlistedasaDAwhitedwarfshows
tofitmodelgridspectratotheseWDs,usingthesameprocedureas thebroadanddeepBalmerlinestypicalforDAsnottoofarfrom
forthesdBsandthegridsdescribedinKoester(2010). theZZCetiinstabilitystrip.TheDBismostlikelyaround16000K,
One of the five DAs, KIC11337598, appears to be an un- muchtoocooltobeaV777Herpulsator.AtKp=18.2itisalsothe
usually rapid rotator (Fig. 1). A rotational velocity of vsini= fainteststarinoursample.Asnoneofthesestarsshowanysignof
1500kms−1hadtobeimposedonthemodelinordertogetarea- variabilityabovethe4-sigmalimit,wehavenotattemptedtoobtain
sonablefit.Thisverysubstantialvelocitycorrespondstoarotation higherqualityspectra.
(cid:13)c 2010RAS,MNRAS000,1–11
FirstKeplerresultson compactpulsatorsVI 5
Table4.PropertiesofthesdBstarswithnosignificantpulsations.
100–500µHz 500–2000µHz 2000–8488µHz Spectroscopicdata
σ A+ f+ σ A+ f+ σ A+ f+ Teff logg logy
KIC Name ppm σ µHz ppm σ µHz ppm σ µHz (kK) (dex) (dex) Run
2020175 J19308+3728 30 3.4 482 29 3.5 1345 29 3.7 4432 33.0(9) 5.90(5) –1.5(1) N1
2304943 J19275+3738 53 4.8 365 50 3.2 655 51 3.8 2290 31.2(5) 5.82(7) –1.7(1) N2
3353239 J19367+3825 20 3.0 497 20 3.3 835 19 3.4 4658 32.4(2) 5.75(5) –2.7(2) W1
3527028 J19024+3840 96 2.9 376 93 3.5 1899 94 3.7 3116 30.1(3) 5.58(5) –2.7(4) W2
5340370 J18535+4035 96 3.0 107 94 3.3 1832 94 3.5 4244 30.2(2) 5.61(4) –2.4(1) W2
5938349 J18521+4115 54 2.9 457 54 3.8 1422 54 4.4 6517 31.9(5) 5.83(6) –2.6(2) W1
6522967 J19279+4159 65 3.5 217 63 3.4 1228 63 4.4 8082 34.3(6) 5.27(9) –2.7(4) W1
6614501 J19368+4201 28 5.3 365 27 3.4 1179 27 4.1 4381 23.1(4) 5.50(5) –3.0(1) W1
7104168 FBS1907+425 18 3.1 448 18 3.6 732 18 3.8 3557 36.5(5) 5.67(10) –0.7(1) N1
7799884 J18456+4335 57 3.1 368 56 4.0 564 56 3.6 7327 31.8(4) 5.68(6) –2.0(1) N1
8874184 J19084+4508 50 3.1 316 46 4.1 1813 46 3.8 8361 32.4(9) 5.84(6) –1.8(1) N2
9095594 J19369+4526 74 3.3 297 71 3.4 1254 71 3.7 8010 29.3(4) 5.19(6) –3.0(1) W1
9211123 J19144+4539 28 3.0 283 27 3.4 1658 26 3.8 2033 34.7(4) 5.11(6) –2.9(1) N2
10149211 J19393+4708 22 6.9 370 22 3.4 1434 21 3.6 6124 27.6(4) 5.42(5) –2.7(1) W1
10462707 J19144+4737 57 3.6 368 57 3.9 561 57 4.1 8206 28.6(4) 5.25(6) –3.0(1) W1
10784623 J19045+4810 Notobservedyet 29.4(5) 5.44(8) –2.9(1) N2
10789011 J19136+4808 23 3.9 364 22 3.2 1513 22 3.9 6243 34.1(2) 5.69(5) –1.4(1) N2
10961070 J18534+4827 108 3.1 421 107 3.7 587 109 4.1 4623 37.4(3) 6.05(5) –1.0(1) W2
11350152 J19268+4908 24 3.6 253 20 4.2 630 19 3.6 5958 35.6(3) 5.57(5) –1.7(1) N2
11400959 J19232+4917 51 3.4 477 49 3.4 688 49 3.9 5568 39.5(4) 6.12(4) –2.9(1) W2
12021724 J19442+5029 30 3.3 436 29 3.5 531 29 3.7 7527 26.2(3) 5.40(4) –2.3(1) W1
Notes.—σisthemeanoftheamplitudespectrumintheregionstated.A+andf+givetheamplitudeandfrequencyofthehighestpeak.
3.2 Thehotsubdwarfstars just at the LC frequency, fLC=566.391µHz, but at all har-
monics of this frequency up to the Nyquist frequency, which
Themajorityofthestarsconstitutingthecurrenthalfofoursurvey
samplearenormalsdBorsdOBstars(26objects),outofwhichone is fNyq=15fLC=0.5fSC=8496.356µHz. In most short-cadence
light curves, this artefact comb has its strongest peak at
isclearlycompositewithanF/Gtypecompanion. Oftheremain-
ingsubdwarfs,oneisaheliumpoorsdOstar,andsixareHe-rich 9fLC=5098µHz. For details on the Kepler data processing
pipeline,seeJenkinsetal.(2010).
sdOorsdOBstars.Notethatwedistinguishbetweenthecommon
TheKeplerspacecraftperformsarolleveryquarter,inorder
He-sdOB stars that show HeI and HeII lines with almost equal
tokeepitssolarpanelsandsunshieldfacingthesun.Themission
depth, and the hotter and rarer He-sdO stars that show predomi-
thereforenaturallybreaksdownintoquarterlycycles,andthetwo
nantlyHeIIlines.Theformerareseeninvarioussurveystoform
quartersofdataanalysedherearereferredtoasQ3andQ4.Each
anarrowbandataround40000K(e.g.Stroeeretal.2007),while
quarteristhensplitintomonthlythirds,andthecollectedphotomet-
the latter do not cluster in the T /logg-plane (Østensen 2009).
eff ricdataaredownloadedaftereachsuchrun.Whenthishappens,the
As in Paper I, we have fitted the spectra of the sdB and sdOB
spacecraftmustchangeitsattitudetopointitsmainantennaatthe
stars to model grids, in order to determine effective temperature
Earth. During these events, observations cease and the change in
(T ),surfacegravity(logg),andphotosphericheliumabundance
eff pointingcausesathermaltransientinthespacecraftanditsinstru-
(logy=logNHe/NH).Thefittingprocedureusedwasthesameas ment.Afterwards,thespacecrafttakessomedaystoreachanequi-
thatofEdelmannetal.(2003),usingthemetal-lineblanketedLTE
libriumstate,andlightcurvesofmanytargetsshowdeviations,as
modelsofsolarcompositiondescribedinHeberetal.(2000).The
shifts in the focal plane slightly changes the contamination from
usualcautionaboutsystematiceffects,whencomparingparameters
nearbyobjects.Similarthermaltransientsareseenafterunforeseen
derivedfromfittingupongridscreatedusingdifferentmethodolo-
events cause the spacecraft to enter safe mode and switch off its
gies,obviouslyapplies.Forthenon-pulsatorswelistthephysical
detector electronics, which then takes some time to warm up af-
parametersinTable4togetherwiththevariabilitylimitsfromthe
terresumptionofnormaloperations.Pointingtweaksalsoproduce
frequency analysis discussed in the next section. The parameters
discontinuities in faint objects due to changes in the contamina-
ofthepulsatorsaregiveninTable6,togetherwiththeirvariability
tionfromnearbyobjects,butduringQ3andQ4nopointingtweaks
data.FortheHe-richsubdwarfsandthehotsdOwedonotprovide
wererequired,leavingfewercorrectionsnecessarythanintheear-
physicalparameters,astheyarebeyondtherangeofourLTEgrid.
lierquarters.Alldatasetscouldbecorrectedbyoneortwocontin-
uouscurves,consistingofaleadingexponentialdecayfollowedby
apolynomialofnomorethanthirdorder.
4 KeplerPHOTOMETRY Onlyfoureventsaresignificantenoughtorequirecorrections
totheQ3andQ4lightcurves.Thereisa1-dgapinQ3.1data,be-
The Kepler photometer operates with an intrinsic exposure cy-
tweenMJD55113.55and55114.34,causedbyalossoffinepoint-
cle consisting of 6.02-s integrations followed by 0.52-s read- ingcontrol.2KeplerenteredsafemodeattheveryendofQ3.2,so
outs. The SC photometry is a sum of 9 such integrations,
and LC photometry are a sum of 270 (Gillilandetal. 2010b).
The LC cycle produces artefacts in the SC light curve, not 2 ThetimesusedherearemodifiedJuliandates(MJD=JD–2500000.5).
(cid:13)c 2010RAS,MNRAS000,1–11
6 R. H. Østensenet al.
Table5.Propertiesofthenon-sdBstarswithnosignificantpulsations.
100–500µHz 500–2000µHz 2000–8488µHz
σ A+ f+ σ A+ f+ σ A+ f+ Spectroscopic
KIC Surveyname (ppm) (σ) (µHz) (ppm) (σ) (µHz) (ppm) (σ) (µHz) classification
2303576 J19263+3738 102 2.9 345 101 3.3 788 100 3.9 2160 He-sdO
3343613 J19272+3827 43 3.9 364 40 3.4 1441 39 3.7 7517 He-sdOB
5769827 J18547+4105 59 3.1 236 56 3.5 577 55 3.6 6507 DA0
6878288 J19436+4220 42 3.6 148 42 3.4 1664 42 3.9 4311 He-sdOB
7129927 J19409+4240 39 3.2 418 38 3.4 960 38 3.9 5495 DA+DA
7335517 J18431+4259 31 3.6 187 33 3.7 801 32 3.9 5533 sdO
8054179 J19569+4350 14 3.4 236 12 3.3 1499 12 3.8 2108 He-sdOB
10198116 J19099+4717 32 5.5 369 31 4.0 1485 31 3.8 5541 DA3
10207025 J19260+4716 40 3.4 107 35 3.3 591 35 4.0 7486 He-sdO
10449976 J18472+4741 15 3.1 459 16 3.3 1200 16 4.1 4569 He-sdOB
11337598 J18577+4909 67 2.9 288 64 3.6 817 64 3.7 7858 DA1(rot)
11604781 J19141+4936 59 3.1 350 59 3.7 1405 59 3.9 5677 DA5
Notes.—σisthemeanoftheamplitudespectrumintheregionstated.A+andf+givetheamplitudeandfrequencyofthehighestpeak.
the event did not affect those light curves significantly, but Q3.3 significantpeaksbetween364and372µHz,whichweconsiderto
lightcurvesareslightlyshorterthanintended,afterthetwodaysof be spurious. Excluding this frequency range would drop A+ for
downtime, and the firstfew days of these suffer froma more se- thelow-frequencyrangetobelow3.3σforallthreestars.Twostars
verethermalexcursionthanusual.InQ4.1,onMJD55205,CCD- showpeaksat4.4σinthehigh-frequencydomain,butthesepeaks
module 3 failed. The loss of the module produced temperature aretoolowtobesignificantifthelightcurveissplitintohalves,
drops within the photometer and telescope structure (VanCleve andwethereforeconsidertheevidenceofpulsationsinthesestars
2010),andtheseaffectthelightcurvesinaminorway,similarto tobetooweaktoclaimdetection.Noneofthestarsshowanyother
apointingtweak.Themostsignificanteventhappenedinthemid- peakshigherthan4σinthehighfrequencyregion,eitherinthefull
dleofQ4.2,whenthespacecraftenteredsafemodefor4fulldays lightcurve,orintheindividualhalves.
betweenMJD55229.35and55233.31,thelongestdowntimeofthe Asmentionedabove,theLCartefactsintroducedatnfLC up
firstmissionyear. to the Nyquist frequency makes us effectively blind to pulsators
withperiodsatthesefrequencies.However,duetothe30dlength
oftheruns,theresolutionissufficientlyhighthattheseblindspots
4.1 Pulsationlimits are quite insignificant. A second cause of concern isthe Nyquist
limititself,whichat120srepresentsaperiodtypicallyseeninsdB
InTable4andTable5welistthelimitsfromourFourieranalysis stars.Ofthe49sdBVstarslistedinØstensenetal.(2010b),13have
oftheKeplerlightcurveswherenoclearpulsationswerefound,for periodsatorshorterthan120s.Theshortestperiodreportedtodate
thenon-sdBandsdBstarsrespectively.AsinPaper Iweprovide, is78sinEC01541–1409(Kilkennyetal.2009).ThesdOpulsator,
forthreedifferentfrequencyranges,thearithmeticmean(whichwe J16007+0748 (Woudtetal. 2006), is a particular case of concern
considertobethestandarddeviation,σ)oftheamplitudespectrum since all the 13 periods detected in this star lie between 57 and
in each frequency range, and the amplitude (A+) and frequency 119s(Rodr´ıguez-Lo´pezetal.2010).However,periodsshorterthan
(f+)ofthehighestpeak.A+isgivenastheratioofthepeakampli- theNyquistlimitarestilldetectable,withasmearingpenaltyfactor
tudeandtheσlevel.Frequenciesassociatedwithbinaryandother givenbysin(x)/x,wherex=πf∆texp(Kawaleretal.1994).The
typesoflong-periodvariabilityarediscussedinSection4.3. smearingdrivesallamplitudestozeroasthesamplingfrequencyis
AsnotedinPaperI,peakswithamplitudesashighas4.1σare approached, butformostfrequenciesbetweenfNyq andthesam-
seeninmanyofthelightcurves,andwedonotconsidertheseto plingfrequencytherecoveredamplitudes arestillsignificant. For
besignificant.Frequenciesassociatedwithbinaryandothertypes Kepler, weshould recover 30percent of theamplitude for pulsa-
oflong-periodvariabilityarediscussedinSection4.3. tionperiodsof80s.Thecorrespondingfrequencieswillappearin
For the binaries with harmonics that have significant ampli- theFTreflectedaroundfNyq,aswasseenforthefirstharmonicof
tudes above 100µHz, we fitted the main period (and harmonic) themainpulsationmodeinKIC10139564(PaperII).
with sines as part of the detrending process. The residual light
curves were then sigma-clipped at 4-σ to remove outliers before
beginningtheFourieranalysis.Onlyfortherelativelyhighampli-
4.2 Thenewpulsators
tudebinary,KIC7335517,didthisprocedureleaveanysignificant
residuals. For thiscase, theA+ listedinTable5 ignores thefirst FiveclearV1093Herpulsatorsweredetectedinthesecondhalfof
threeharmonicsofforb=84.33µHz. thesurveyphase(Table6).Thenoiselevel(σ)wasmeasuredinthe
Forthenon-sdB stars,theonlymarginallysignificant period region 1000–2500µHz. In addition to the number of significant
(5.5σ) is seen in KIC10198116, at 369µHz. However, structure pulsationmodesdetectedintheKeplerphotometry(N ),andthe
f
between 360 and 370µHz is seen in many other stars of a wide minimumandmaximumpulsationfrequencies,wealsoprovidethe
range of spectral types and observed invarious quarters, and has power-weightedmeanfrequency,f .Thespectroscopicparame-
med
nowbeenflaggedasmostlikelyinstrumentalinorigin. tersasdeterminedfromourfitsarealsolisted,andallstarsareseen
ThelimitsforthesdBstarsthatwerenotfoundtoshowclear toclusteratthehotendoftheg-moderegionbetween26000and
pulsationsaregiveninTable4.Hereweseethreestarsthatshow 28000K.
(cid:13)c 2010RAS,MNRAS000,1–11
FirstKeplerresultson compactpulsatorsVI 7
Figure3.TheTeff/loggplaneforthesdBstarsinoursample.Redsymbolsindicatethepulsators,bluesymbolsthenon-pulsators,withthetransientpulsator
ofPaperImarkedwithagreenbulletandtheasyetunobservedsdBwithabrownsymbol.TheapparentlysinglesdBsaremarkedwithbullets,thesdB+dM
reflectionbinaries withtriangles, andthesdB+WDswithstars.Thecurvesindicate theapproximate location ofthezero-ageandterminal-age EHBfora
canonicalsdBmodel.
Table6.PropertiesofthesdBVstars.
Keplerdata Spectroscopicdata
σ Nf fmed fmin fmax Teff logg logy
KIC Name (ppm) (µHz) (µHz) (µHz) (kK) (dex) (dex) Run
7668647 FBS1903+432 22 15 173.3 115.9 345.8 27.7(3) 5.45(4) –2.5(1) N1
8302197 J19310+4413 41 6 183.3 126.3 305.8 26.4(3) 5.32(4) –2.7(1) W2
10001893 J19095+4659 23 24 262.9 77.5 391.4 26.7(3) 5.30(4) –2.9(1) N2
10553698 J19531+4743 19 30 228.1 104.3 492.9 27.6(4) 5.33(5) –2.9(2) W1
11558725 J19265+4930 17 36 260.5 78.2 390.9 27.4(2) 5.37(3) –2.8(1) W1
Of the 5 V1093Her pulsators described in Paper III,3were ple,wehereclearlyhavenon-pulsatorsatTeff lowerthanthetran-
found to show low-amplitude short-period pulsations in the fre- sitionregionbetweenthep-andg-modepulsators(at∼28000K).
quencyrangetypicalforV361Hyastars.Recently,Charpinetetal.
(2011) have concluded that thesingle short period peak found in
KIC2697388isconsistentwithapredictedp-modeintheirmodel
KIC6614501 atT =23100K isunusual as itlieswell be-
that fits the observed g-mode spectrum, thereby making the case eff
lowtheextremehorizontal branch(EHB)inFig.3.Italsoshows
thattheseobjectsrepresentanewkindofhybridsdBV.
alightcurvesignaturethatweinterpretasbinary,asdiscussedin
Inthecurrentsample,KIC7668647showstwopeaksat4738 Section4.3,below.ThiscouldindicatethatthissdBisanotherex-
and4739µHz,ataround5σ.Thepeaksaremostsignificantinthe ampleoftherarepost-RGBwhitedwarfprogenitorsthatareevolv-
firsthalfoftherun,anddropbelowthe4-σlimitinthesecondhalf ingdirectlyfromanRGBevolutioninterruptedbyacommonen-
of the run. KIC8302197 shows no significant peaks (higher than velopeejectionandtowardsthewhitedwarfcoolingcurve,suchas
4.1σ)intheshort-period pulsationrange. KIC10001893 showsa HD188112 (Heberetal. 2003). Unlike the EHB stars, for which
single 5.7-σ peak at 2925.8µHz. KIC10553698 shows a pair of thecoremanagedtoreachsufficientmassforheliumignitionbe-
4.5-σ peaks at 3073µHz, and also some structure at 4070µHz. foretheenvelopewasejected,thesestarsaremuchlessmassiveand
KIC11558725alsoshowspeaksat3073µHz,thehighestat8.7σ. willbecomelowmassHe-coreWDs.Thecurrenttemperatureand
It is suspicious that two stars show the same frequency, but the gravityofKIC6614501 isconsistentwiththeevolutionary tracks
formerwasobservedinQ4.1andthelatterinQ3.3.Thus,itisnot ofDriebeetal.(1999)foramassoftheprimaryof∼0.24M .Its
⊙
obviousthattheseareartefacts,andnoneofthefrequenciesfound FTdoesshowsomeweakpeaksaround365µHz,butasmentioned
inthese starshave been associated withartefacts before. Thus, it earlier,thesearemostlikelyartefacts.
appearsthatfourofthefivelong-periodpulsatorsmightbehybrid
pulsators,buttheamplitudesarelowsothehybridnatureneedsto
beconfirmed.SeePaperVIIformoredetails.
KIC12021724 is located at 26200K and has absolutely
Fig.3isidenticaltoFig.3inPaper I,butwiththenew pul- no significant peaks in the FT above 35µHz. However, like
satorsandnon-pulsatorsadded.Unlikeinthefirsthalfofthesam- KIC6614501,itshowsalikelybinaryperiod.
(cid:13)c 2010RAS,MNRAS000,1–11
8 R. H. Østensenet al.
Table7.Binariesandotherlong-periodvariables. KIC 11350152
KIC P(de)riod A(%m)p. Class vMaariianbility I/I] 1.01
Dx [
23350237507268 02..1190250460 00..85 HsdeB-s+d?O+? buinnk/ncoowntn ve flu 1.00
5340370 0.20–0.72 ... sdB+? unknown ati
el
6614501 0.15746 0.12 sdB+WD? binary R 0.99
6878288 3.04065 1.0 He-sdOB+? unknown
8874184 2.63670 0.8 sdB+? var.comp
7335517 0.13725 6.0 sdO+dM reflection
0 5 10 15 20 25 30
8054179 ... 0.02 He-sdOB aperiodic
10149211 0.60513 0.5 sdB+? var.comp Time [RHJD + 55092]
10462707 0.78880 0.08 sdB+WD? binary
Figure5.Thelight curve ofKIC11350152 is dominated byaperiod of
11337598 0.09326 0.04 DA1(rot) spinperiod?
3.16d,buttheshapeofthelightcurveischangingfromcycletocycle.The
11350152 3.3 1.5 sdB+F/G var.comp
lightcurvewasbinnedsothateachpointrepresents 20SCexposures,in
11604781 4.87988 0.5 DA5 unknown
ordertoreducethenoise.
12021724 0.67490 0.07 sdB+WD? binary
such a cool DA, the companion would have to be substellar not
4.3 Binariesandotherlong-periodvariables
tocontributetotheopticalspectrum.Therearenofeaturesinour
InTable7welistthe14binariesandother long-period variables classificationspectrumthatcanoffercluestotheoriginofthepho-
thatwehavedetectedinthecurrenthalfof thesample.Theperi- tometricvariability,suchastraceofacompanionormagneticfield,
odsrangefrom3.3hourstoalmostfivedays,andthepeak-to-peak sowehaveatpresentnotheorythatcouldexplainthe4.88dsignal.
amplitudesrangefromafewpercenttoafewhundredppm. KIC10149211and8874184showvariationswithamainpe-
The sdO star KIC7335517 is the clearest binary candidate, riodandastrongfirstharmonic,andsmallbutsignificantchanges
withthemaximaslightlysharperthantheminima(Fig.4,upperleft in the shape of the modulation between the first and the second
panel),asistypicalforthetemperatureeffectsthatareseenwhena halves.Suchvariationsareunlikelytooriginatefromthehotsub-
hotsubdwarfirradiatesonehemisphereofacoolcompanion.The dwarfstaritself,andwithFcont between9and24%theyaremost
foldedlightcurveissimilartothatofKBS13,observedinQ1,and likelyfromacontaminatingobject.Apossibleinterpretationisthat
thesemi-amplitudeisaboutthesame.Wejudgethetemperatureof the contaminating star is heavily spotted, and has more spots on
the primary to be above 40000K, so the reflection effect should onehemispherethanontheother(seee.g.Siwaketal.2010).
be much higher than what is seen, if the system is seen at high TheFTofKIC11350152isdominatedbyastrong3.16-dpe-
inclination.Thus,thesystemismostlikelyseenatlowinclination, riod,anditsfirstharmonic.Therearenoothersignificantpeaksin
asforKBS13,orelsethecompanionissubstellar. the FT. As shown in Fig. 5, there are substantial variations from
Theremaining9objectsshowninFig.4alldisplayverylow cycletocycle. Alsohere themost likely interpretationisthat the
level photometric modulations that may be due to orbital effects, main period seen is the rotation period of a spotted companion,
but we do not consider any of these as being likely to have M- butapulsatingcompanioncannotberuledout.Ourbluespectrum
dwarf companions. A more likely companion would be a white showsclearsignaturesofanF–Gcompanion,withKandHlines
dwarf,inwhichcasethelightcurveshoulddisplayacombination toobroadtobeinterstellar,andaclearg-band.The2MASSIRpho-
ofellipsoidaldeformationandDopplerbeaming,suchasseenfor tometryindicatesarisingIRflux,andtheobjectappearssinglein
KPD1946+4340(Bloemenetal.2010).Inparticular,KIC6614501 images,sothethecoolstarislikelytobetheaccretorresponsible
hasthedouble-peakedstructure,withalternatingmaximaandmin- forstrippingtheenvelopeoffthesdBprogenitorwhenitwasonthe
imaofroughlyequaldepth,thatcharacterisessuchbeamingbina- redgiantbranch.Also,Fcont isinsignificantsothevariationscan
ries.Splittingthelightcurveinhalvesrevealsaconsistent shape, notbeascribedtoanynearbyobjects.
asexpectedforanorbitaleffect.KIC10462707andKIC12021724 KIC5340370 shows unusual behaviour below 100µHz.The
arealsolikelytobesdB+WDbinaries,andaWDcompanionisa periodsappear tochange completelybetween thefirsthalf of the
possibleinterpretationfortheHe-sdOKIC2303576aswell. run and the second, so we have computed a wavelet transform
KIC6878288, 11604781 and 3527028, all show monoperi- (WFT)ratherthantheregularFouriertransform,usingtheWWZ
odic light curve variations that range between two and five days, algorithm of Foster (1996). The WFT is shown in Fig. 6, and in
and does not change between the first and second halves of the thefirsthalftwoclearpeaksarefoundat0.55and0.73d(16and
run.TheHe-sdOBKIC6878288andtheregularsdBKIC3527028 20µHz).Inthesecondhalf,thesepeaksarebarelydetectable,but
are unlikely to show such long periods intrinsically. But both have been replaced by broad features in the region between be-
havecontaminationfactors, Fcont,indicatingthataround halfthe tween0.2and0.4d(∼30and60µHz).
light comes from other sources near the intended target. This KIC8054179showsalightcurvewithconsiderablepowerin
makes it rather futile to speculate about whether the modula- theFTatfrequenciesbelow100µHz,butnoclearpeaks.Theam-
tion comes from the the subdwarfs, close companions, or nearby plitudeofthevariabilityisonlyatthe200ppmlevel,andcaneasily
objects. KIC11604781 is the only regular white dwarf star in becausedbyacontaminatingstar.However,itisinterestingtonote
thecurrent samplethatshowsanylong-period modulations. With thatinthefirsthalfofthesurvey,wealsosawaperiodicvariabil-
Fcont=0.006, any reasonable effect from a contaminating object ityinanotherHe-sdOBstar,KIC9408967,butthenatasomewhat
iseffectivelyruledout.Thespectrumisalsovoidofanyfeatures higheramplitudethanhere.
indicating a cool companion, even in the region around Hα. For TheWD which wesuspected to bean extremely rapidrota-
(cid:13)c 2010RAS,MNRAS000,1–11
FirstKeplerresultson compactpulsatorsVI 9
1.020 1.002
1.000 1.000
0.998
0.980 KIC 7335517 P=0.13725 d KIC 11604781 P=4.87988 d
1.004
1.005
1.002
1.000 1.000
0.998
0.995 KIC 6878288 P=3.04065 d KIC 3527028 P=2.10540 d
I/I] 0.996
Dx [ 1.005 1.001
u
ve fl
d relati 1.000 1.000
ne
n
hase bi 0.995 KIC 2303576 P=0.19206 d 0.999 KIC 6614501 P=0.15746 d
P
1.004
1.001
1.002
1.000 1.000
0.998
0.999
0.996 KIC 8874184 P=2.63670 d KIC 10462707 P=0.78880 d
1.001
1.002
1.000 1.000
0.998
KIC 10149211 P=0.60513 d KIC 12021724 P=0.67490 d
0.999
0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00
Phase Phase
Figure4.Dataoftenbinarycandidatesfoldedonthemainperiod.ThelightcurveswerefoldedontheperiodsgiveninTable7andrepeatedoneachpanel.
Forthefirsttwoweused250bins,andthedataareplottedaspoints.Fortherestweusedeither100binsor30bins,duetothelowersignal,andtheerrorbars
shownarethermsvaluesforthepointsineachbin.Wealsosubdividedthe8lastobservationrunsintotwohalves,andfoldedtheseseparately.Theresulting
curvesareshownascontinuousgreenandbluelines.Twocyclesareshownforclarity.
torinsection3.1,KIC11337598,showsnosignificantpeaksinthe
FT, except a single low amplitude peak at 124µHz, (=0.093d).
Withanamplitudeofonly360ppmthisisfartoolowtobeabi-
narysignalforsuchashortperiodorbit,unlessthesystemisseen
improbably close to pole on. If the 0.093d period is instead the
spin period of the WD, then the spectroscopic broadening can-
not be caused by rotation. A possible explanation could involve
a relatively weak magnetic field causing Zeeman splitting of the
Balmer lines, being sufficiently strong to produce the observed
broadening without producing resolved splitting at our low S/N.
The 0.093d photometric period could then be the spin period of
the WD, made visible by weak spots on the surface of the WD,
as observed in WD1953–011 (Brinkworthetal. 2005). A similar
periodof0.0803dwasobservedinGD356,althoughattentimes
theamplitude,andinterpretedinasimilarwaybyBrinkworthetal.
Figure6. ThewavelettransformofKIC5340370showsclearperiodicities (2004).WithFcont=0.225thesignalcanalsobefromacontami-
natingobject,sonofirmconclusionscanbemade.Butbetterspec-
atabout0.55and0.72dinthefirstpartofthelightcurve.Theseapparently
troscopycouldeasilybeinvokedtodetectanyZeemansplittingof
disappearcompletelyandarereplacedbrieflybypeaksat0.2and0.23d,
whicharequicklyreplacedbyastrongandbroadstructurebetween0.31 theBalmerlines,orconfirmouroriginalhypothesisofrapidrota-
and0.39d.Thegapcorrespondstothe4dsafingeventinQ4.2. tion.Ineithercase,KIC11337598isanintriguingWD.
(cid:13)c 2010RAS,MNRAS000,1–11
10 R. H.Østensen etal.
5 DISCUSSIONANDCONCLUSIONS twoappeartobesdB+WDshort-periodbinaries,judgingfromthe
long-periodvariationsintheirlightcurves.Thesearealsotheonly
WehavecompletedasurveyforcompactpulsatorswithKepler,and
twoshort-periodsdB+WDbinarieswehavebeenabletoidentify
asfarasthesubdwarfBstarsareconcernedthesurveyhasbeena
in the current sample. We do not see any reason why pulsations
greatsuccess.Unfortunately,nopulsatingwhitedwarfswerefound
should be systematically suppressed in sdB+WD binaries. After
inthesurveysample.Thisisnotentirelysurprisingasthenumber
all, the well-studied V361Hya star KLUMa is known to be in a
ofDAwhitedwarfssurveyedisonly13,andofthoseonlyacouple
P=0.376d binary with a WD companion (O’Tooleetal. 2004),
areanywhereclosetotheZZCetiinstabilitystrip.Onestarthatsits
and V2214Cygin aP=0.095d binary (Geieretal. 2007). How-
slightlyabovetheinstabilityregionisKIC10420021, observedin
ever,aspointedoutbyØstensen(2009),KLUMaistheonlywell-
Q2.2.AswenotedinPaperI,itdoeshavea4.5-σpeakintheFTat studied sdBV of those known to be located in the boundary re-
196.4µHz.ItwasreobservedforthreemonthsinQ5,butaquick
gionbetweentheV361HyaandtheV1093Herpulsatorsforwhich
analysisofthisrecentlyreleasedlightcurverevealsnotraceofany
hybrid pulsations has not been detected. One may speculate that
significantsignalsatperiodsshorterthanafewdays.
g-modes can be suppressed somehow in sdB+WD binaries, but
The spectroscopic survey used to describe the targets in Pa- this is not the case. Of the 9 V1093Her stars described in the
perIandinthispaperwasconductedmostlyafterthedeadlinefor literature, 3 have been published as sdB+WD binaries; HZCnc
submittingtargetsfortheKeplersurveyphasehadpassed.Ifsuch (P=27.81d, Morales-Ruedaetal.2003),V2579Oph(P=0.83d,
a survey had been made earlier, it would have been evident that Foretal.2006)andPG0101+039 (P=0.57d, Geieretal.2008).
theWDsamplewastoosmalltohaveasignificantchanceofcon- However,inthecaseofKIC6614501,itspositionbelowthecanon-
tainingWDpulsators.ButifmorestarsfainterthanKp=17.5had ical EHB is unexpected for an sdB that has evolved through
been retained in the sample, the chance of finding WD pulsators common-envelope ejection.Theabsenceof pulsationsinthisstar
wouldhavebeenmuchhigher,sinceatsuchfaintmagnitudeshot can therefore be explained if it isa low-mass post-RGB star that
subdwarfs will have to be located beyond the Galactic disk, and hasnotignitedheliuminitscoreratherthanaregularEHBstar,as
no longer dominate UV-selected samples. As we have seen from suchstarswouldevolvetoorapidlytobuildupaZ-bumpthatcan
thefewstarsinoursamplethathavemagnitudesclosetoKp=18, drivepulsations.
theKeplerphotometryisstillexcellentwith4-sigmadetectionlim-
itsaroundthemillimagnitudelevel,evenaftertakingintoaccount
substantialcontaminationfactors. Thetotalfractionofpulsatorsbelow28000Kendeduptobe
That the survey did not reveal any sdO pulsators was not a 12outof16,or75percent,thesamenumberastheroughestimate
surprise,sinceonlyonesuchobjecthavebeenrevealedtodate,im- givenbyGreenetal.(2003).Wearestillpuzzledbythelargefrac-
plyingthattheseobjectsareexceedinglyrare.Ofthetwoobjectsin tion of sdB stars that show no trace of pulsations in spite of the
thesurveyclassifiedassdO+F/Gbinaries,similartotheprototype unprecedented duration and low noise level provided by Kepler.
J16007+0748 (Woudtetal.2006),one(KIC9822180) didshowa Wehadexpectedthatthefractionofpulsatorswouldincreasewith
marginalpeakandwillbereobservedforthreemonthsinQ6.Inthe increasingprecision,butevidentlythishasnothappened.
currenthalfofthesampleonlyonesdOstarisnotheliumrich,and
thatobject,KIC7335517,istheclearestphotometricbinaryinthe
sample.ThisobjectismostlikelymuchcoolerthanJ16007+0748, Thanks to the exceptional precision of the Kepler measure-
andmoresimilartotheeclipsingsdO+dMbinaryAADor,butseen ments,wecannowconcludethattherecertainlyaresdBstars,both
atalowinclinationangle. on the hot and cold end of the EHB, that show no trace of pul-
DuringthefirstyearoftheKeplerMission,wehavesurveyed sations.Possibleexplanationsforthenon-pulsatorswouldhaveto
32 sdB pulsator candidates hotter than 28000K, and found only answerwhythepulsationdrivingmechanismissuppressedinsome
one clear and unambiguous V361Hya pulsator (Paper II). One EHBstarsandnotothers.Theymayrepresentalow-metalicitypop-
other sdB star shows a single significant short-period frequency ulationthateitherstartedoutbeinglowiniron-groupelements,or
that dropssystematically inamplitude until itisbelow thedetec- evolved to have low metalicity envelopes, as may be the case in
tionlimit(PaperI).Athirdpulsator,2M1938+4603,wasfoundin mergermodels.Timedependentchangesintheironprofilesasdis-
aneclipsingbinary,andshowsanexceptionallyrichpulsationspec- cussedbyFontaineetal.(2006a,b)canalsoexplainnon-pulsators;
trum,thatincludesshort,longandintermediateperiods.However, TheymaybetheyoungestamongtheEHBpopulation,forwhich
ithasnostrong(above500ppm)pulsationmodes,whichmakesit anironopacitybumpinthedrivingregionhasyettoaccumulate,
quite an exceptional hybrid pulsator. All these starswere discov- ortheycanbetheoldestEHBstarsforwhichlow-levelwindshave
ered in the first half of the survey sample, and the current sam- depletedtheironreservoir.
pleof17starsabove28000KcontainsnofurtherV361Hyapul-
sators.Thismeansthatthenumberofshort-periodpulsatorsfound
intheKeplersampleisactuallylessthanthe10percentfractionthat Another significant result of our survey is that many of the
hasbeenfoundinground-basedsurveys(Østensenetal.2010b),at V1093Her pulsators show signs of hybrid behaviour, with single
leastwhenconsideringthat2M1938+4603wouldhavebeenalmost low-amplitudemodesinthehighfrequencyregion.TheV361Hya
impossibletorecogniseasapulsatorfromtheground. pulsatorwefoundalsodisplaysasinglemodeinthelong-periodre-
FortheV1093Herpulsators,inthefirsthalfofthesurveywe gion.ThisindicatesthathybridbehaviourisnotunusualforsdBV
found only one star below 28000K that was not pulsating, and starsregardlessoftheirpositionontheEHB,andnotconfinedto
that one was less than one σ below this temperature limit. That theDWLynstarsthatsitsontheboundarybetweentheshort-and
ledustothepreliminaryconclusionthatallsdBsbelow28000K long-periodpulsatorsintheT /loggplane.WithKeplertargeting
eff
may be pulsators. However, in the current sample we find that thesepulsatorsatregularintervalsthroughoutitsmission,wewill
only 5 out of 8 stars below 28000K are pulsators. Only one of soonknowiftheselowlevelhybridmodesaretransientorpersis-
thesearewithin1-σ of thetemperature boundary. Theremaining tentfeaturesofthepulsationspectraofthesestars.
(cid:13)c 2010RAS,MNRAS000,1–11