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 i X Released2010XxxxxXX r a 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