observaons of southern sky ugsu cataclysmic variables

Observa(ons of Southern Sky UGSU Cataclysmic Variables Dr Ian Kemp* – November 2019 Type 1a supernovae are key ‘standard candles’ used to underpin the cosmological distance scale. Sources of varia(on in these events need to be understood to improve our agreed distance ladder, and a key input may be the configura(on of the precursor systems, the dwarf nova cataclysmic variables. We report observa(ons of 7 UGSU dwarf nova systems in the southern skies over the period 16 Sept to 7 Nov 2019. Observa(ons were made with 500mm PlaneWave op(cal telescopes in Perth (WA), Siding Spring (NSW), and New Mexico (USA). UGSU dwarf novae are characterised by the display of two types of outburst (rapid brightening) – normal outbursts and super-outbursts. We observed super- outbursts in two systems, VW Hyi and WX Hyi, and recorded periodic varia(ons in the light curve of VW Hyi. We observed ‘superhumps’ with a period 112 minutes, slightly greater than the orbital period. This appears to indicate a con(nued slight increase in the superhump period from 109.5 minutes observed in 2004. We also observed shorter period varia(ons of 35 and 15 minutes. These varia(ons have not been noted earlier in the literature although similar behaviour has been seen in at least one other system (Paêrson et al. 2000). The cause of these varia(ons is not known and should be the subject of future study. A dwarf nova system consists of a white dwarf (WD) with a K-M type secondary. The companion fills its Roche lobe and spills material onto the WD forming an accre(on disk (AAVSOa) The accre(on disk is unstable and displays two types of brightening – normal outbursts and super-outbursts. The super-outbursts are caused by gravita(onal instability. During a super-outburst we see ‘superhumps’, caused by the rota(on of a pressure wave in the in the accre(on disk as it collapses onto the WD (Osaki & Kato 2013) We observed a super-outburst in the system VW Hyi. Shown here in combina(on with observa(ons from other members of AAVSO (AAVSOb). Our data are the solid green squares We also observed a super-outburst and two normal outbursts in the system WX Hyi – again our data are the solid green squares. We noted some incorrect data in the AAVSO database – the (ming does not fit the outburst. The super-outburst in VW Hyi was bright enough that we could observe superhumps over several nights – down to 3 minutes per measurement White Dwarf Ellip(cal Accre(on Disk Hot Spot Stream L1 Lagrange Point Secondary Star Time Normal outburst Quiescence Super-outburst Superhumps Magnitude Normal Outbursts Incorrect data Super-outburst Periodici(es were extracted by finding the minima in the light curves (lef hand chart) – there was clearly more than one periodic varia(on (right hand chart). The fundamental superhump averaging 112 minutes was accompanied by two short period features at 35 mins and 15 mins. These are much longer than the WD rota(onal period (2.2 mins), and longer than another documented 2.8 min ‘wiggle’ in the light curve (Woudt & Warner 2002). Conclusions: We observed 7 dwarf nova systems in the southern sky. Two displayed super- outbursts during our observing period. Observa(ons of VW Hyi showed a con(nued slowing in the superhump period, and the presence of a low-period oscilla(on which is currently not explained and should be further inves(gated. WX Hyi is con(nuing its historical paêrn but some of the data in the AAVSO database is incorrect. The other 5 systems were in quiescence and observa(ons were contributed to the AAVSO database for future study. Publica.on Date of observa.on VW Hyi avg. superhump period Long et al. 2009 2004 109.5 Kato et al. 2014 2011 110.4 Present work 2019 112.1 The short period varia(ons are a new phenomenon which needs to be inves(gated in future work. Also the fundamental superhump period seems to be increasing based on data from the last 15 years References AAVSOa: web h^ps://www.aavso.org/vsx/index.php?view=about.vartypes AAVSOb: web h^ps://filtergraph.com/aavso/ Osaki, Y. & Kato, T., PASJ, 2013, 65, 50 Long, K. S., Gänsicke, B. T., Knige, C., Froning, C. S. & Mondard, B., 2009, ApJ, 697, 1512 Kato, T. et al., 2014, PASJ, 66, 90 Paêrson, J., Kemp, J., Jensen, L. et al., 2000, PASP, 112, 1567 Woudt, P. A. & Warner, B., 2002, MNRAS, 333, 411 VW Hyi WX Hyi * Author is currently Hon. Research Associate, ICRAR/UWA, Perth Art is used with permission of the copyright owner; labels added

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Page 1: Observaons of Southern Sky UGSU Cataclysmic Variables

Observa(onsofSouthernSkyUGSUCataclysmicVariablesDrIanKemp*–November2019

Type1asupernovaearekey‘standardcandles’usedtounderpinthecosmologicaldistancescale.Sourcesofvaria(onintheseeventsneedtobeunderstoodtoimproveouragreeddistanceladder,andakeyinputmaybetheconfigura(onoftheprecursorsystems,thedwarfnovacataclysmicvariables.

Wereportobserva(onsof7UGSUdwarfnovasystemsinthesouthernskiesovertheperiod16Septto7Nov2019.Observa(onsweremadewith500mmPlaneWaveop(caltelescopesinPerth(WA),SidingSpring(NSW),andNewMexico(USA).

UGSUdwarfnovaearecharacterisedbythedisplayoftwotypesofoutburst(rapidbrightening)–normaloutburstsandsuper-outbursts.Weobservedsuper-outburstsintwosystems,VWHyiandWXHyi,andrecordedperiodicvaria(onsinthelightcurveofVWHyi.Weobserved‘superhumps’withaperiod112minutes,slightlygreaterthantheorbitalperiod.Thisappearstoindicateacon(nuedslightincreaseinthesuperhumpperiodfrom109.5minutesobservedin2004.

Wealsoobservedshorterperiodvaria(onsof35and15minutes.Thesevaria(onshavenotbeennotedearlierintheliteraturealthoughsimilarbehaviourhasbeenseeninatleastoneothersystem(Pa^ersonetal.2000).Thecauseofthesevaria(onsisnotknownandshouldbethesubjectoffuturestudy.

Adwarfnovasystemconsistsofawhitedwarf(WD)withaK-Mtypesecondary.ThecompanionfillsitsRochelobeandspillsmaterialontotheWDforminganaccre(ondisk(AAVSOa)

Theaccre(ondiskisunstableanddisplaystwotypesofbrightening–normaloutburstsandsuper-outbursts.Thesuper-outburstsarecausedbygravita(onalinstability.Duringasuper-outburstwesee‘superhumps’,causedbytherota(onofapressurewaveintheintheaccre(ondiskasitcollapsesontotheWD(Osaki&Kato2013)

Weobservedasuper-outburstinthesystemVWHyi.Shownhereincombina(onwithobserva(onsfromothermembersofAAVSO(AAVSOb).Ourdataarethesolidgreensquares

Wealsoobservedasuper-outburstandtwonormaloutburstsinthesystemWXHyi–againourdataarethesolidgreensquares.WenotedsomeincorrectdataintheAAVSOdatabase–the(mingdoesnotfittheoutburst.

Thesuper-outburstinVWHyiwasbrightenoughthatwecouldobservesuperhumpsoverseveralnights–downto3minutespermeasurement

WhiteDwarf

Ellip(calAccre(onDisk

HotSpotStream

L1LagrangePoint

SecondaryStar

Time

Normaloutburst

Quiescence

Super-outburstSuperhumps

Magnitude

NormalOutburstsIncorrectdata

Super-outburst

Periodici(eswereextractedbyfindingtheminimainthelightcurves(lefhandchart)–therewasclearlymorethanoneperiodicvaria(on(righthandchart).Thefundamentalsuperhumpaveraging112minuteswasaccompaniedbytwoshortperiodfeaturesat35minsand15mins.ThesearemuchlongerthantheWDrota(onalperiod(2.2mins),andlongerthananotherdocumented2.8min‘wiggle’inthelightcurve(Woudt&Warner2002).

Conclusions:Weobserved7dwarfnovasystemsinthesouthernsky.Twodisplayedsuper-outburstsduringourobservingperiod.Observa(onsofVWHyishowedacon(nuedslowinginthesuperhumpperiod,andthepresenceofalow-periodoscilla(onwhichiscurrentlynotexplainedandshouldbefurtherinves(gated.WXHyiiscon(nuingitshistoricalpa^ernbutsomeofthedataintheAAVSOdatabaseisincorrect.Theother5systemswereinquiescenceandobserva(onswerecontributedtotheAAVSOdatabaseforfuturestudy.

Publica.on Dateofobserva.on

VWHyiavg.superhumpperiod

Longetal.2009 2004 109.5Katoetal.2014 2011 110.4Presentwork 2019 112.1

Theshortperiodvaria(onsareanewphenomenonwhichneedstobeinves(gatedinfuturework.Alsothefundamentalsuperhumpperiodseemstobeincreasingbasedondatafromthelast15years

ReferencesAAVSOa:webh^ps://www.aavso.org/vsx/index.php?view=about.vartypesAAVSOb:webh^ps://filtergraph.com/aavso/Osaki,Y.&Kato,T.,PASJ,2013,65,50Long,K.S.,Gänsicke,B.T.,Knige,C.,Froning,C.S.&Mondard,B.,2009,ApJ,697,1512Kato,T.etal.,2014,PASJ,66,90Pa^erson,J.,Kemp,J.,Jensen,L.etal.,2000,PASP,112,1567Woudt,P.A.&Warner,B.,2002,MNRAS,333,411

VWHyi WXHyi

*AuthoriscurrentlyHon.ResearchAssociate,ICRAR/UWA,Perth

Artisusedwithpermissionofthecopyrightowner;labelsadded

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