PoS(GOLDEN 2017)063 https://pos.sissa.it/ renowned for its iods, we estimated an orbital l periods. The exceptionally t. rate, respectively. We consider and 2016, and possible negative 16. The supercycles observed in r to RZ LMi, and even above that of 0.10, which is larger than mass and 48 d, which require very high d. Especially in 2016, we observed va-like state. We detected growing ined by a stripped secondary with an IV Taiwan [email protected] , e Commons al License (CC BY-NC-ND 4.0). and VSNET collaboration team b , Taichi Kato a [email protected] of some ordinary SU UMa-type dwarf novae with similar orbita with a period ofperiod 0.05710(1) of d. 0.05792 d. By The usingratios orbital the in period WZ two suggests Sge-type a per dwarf mass novae ratio with orbital periods simila high mass-transfer rate in this objectevolved may core possibly in a be system ecpla evolving toward an AM CVn-type objec (stage A) superhumps with a mean period of 0.0602(1) d in 2013 that the object virtually experienced a transition to the no both were longer than previously reportedtwo values exceptionally of long 19 superoutbursts withmass drations transfer of rate, 28 97 d % and 99 % of the critical mass transfer extremely short ( 19 d) and regular supercycle, in 2013 and 20 We report on the photometric observation of RZ LMi, which is a Copyright owned by the author(s) under the terms of the Creativ c University of Kyoto, Japan E-mail: ° The Golden Age of Cataclysmic Variables11-16 and September, Related 2017 Objects Palermo, Italy Ryoko Ishioka The bridge between ER Ursae Majoris-typeand dwarf nova-like nova system Institute of Astronomy and Astrophysics, Academia Sinica, Attribution-NonCommercial-NoDerivatives 4.0 Internation b a PoS(GOLDEN 2017)063 upercycle t the tidal third body campaigns are hort supercycle that the system , and that there s of 2013 March pe stars (cf. [8]). 16, and detected q etations predict the . We also used the as possible negative mong DNe, there are ance ([12]; [13]), we ized by repetitive out- ered as an ultraviolet- e DNe by the detection called superhumps, are of all observations were e same way as described t, see [7]]. Currently, six xtremely short supercycle ). To determine the mass -type DNe. see e.g. [2]). very attempt, and without utbursts, lasting for a few ns between 2014 March 8 eroutburst is much weaker f stage-A superhumps rep- dwarf nova ER UMa with a from periods of positive and orb P and a period of stage A superhumps. -like system orb P 1 . We also estimated q and ) are a few percent longer than the corresponding post R SH P and the large disk radius after the superoutburst in RZ LMi. Existence of a q , the evolutionary status of RZ LMi remained unclear. q ). RZ LMi is one of the most enigmatic SU UMa-type DNe with an ultrashort (19 d) s Dwarf novae (DNe) are a class of cataclysmic variabls (CVs) character Though some explanations were proposed, the mechanism of the extremely s Our time-resolved photometric campaigns were carried out during the period In this paper, we briefly reported our photometric campaigns which caught and orb orb P ( bursts caused by a thermal-viscousSU instability UMa of stars, the which accretion areweeks disk characterized in by ([1]). addition long to A short outbursts, normal called outbursts.observed supero Short during periodic superoutbursts modulations, (for so detailsThe of periods CVs, of DNe, superhumps and ( SU UMa The bridge between ER Ursae Majoris-type dwarf nova and nova 1. Introduction and unusually regular outburstexcess pattern. [3], This and was object confirmedof was as superhumps a originally ([4]; member discov of [5]) the after SUshort the UMa-typ supercycle discovery of of another 43 SU dSU UMa-type ([6]) UMa-type [for stars including more RZ details LMi of and ER a UMa history are of usually this called ER objec UMa-ty negative superhumps, and calculated the mass ratio using Note that this paper is apublished. summary of [7] in which more details of the results of2. our Observations and Analysis became critically close tostage-A the superhumps stability border, during a twosuperhumps permanent superoutbursts and superhumper, in post in superoutburst 2013 20 superhumps.resenting and the 2016 Using growing the as phase periods well obtained of o the superhumps relation at between the radius of the 3 :1 reson is also suggested as theratio, origin we of need to the detect very theP regular orbital outburst period, pattern however, RZ ([11] LMi has defied e and regular outburst pattern remained mystery. [9]of demonstrated RZ that LMi an can e be reproduced ifin the RZ strength of LMi tidal than torques during intorque a ER sup is UMa too due small to to an extremely maintain small the mass superoutburst ratio. in [10] systems suggested with tha very small 5 – April 29 anddata from 2016 the February AAVSO International 25 Database, –and some May June snapshot 22, observatio 10 and with historical photographic 33corrected data telescopes to reported barycentric on by Julian 29 [14]. Days sites The (BJD).in times [15] The and data [16]. were analyzed in th occurs a decoupling between tidalvery and small thermal instabilities. These two interpr PoS(GOLDEN 2017)063 egular superout- 2016 (lower panel) uent outbursts with a ]). The extremely long r than the reported stable cycle (20 d) of this object . The 2nd (SC2) and 3rd permanent outburst” state , respectively. The 4th su- g the two supercycles were g support to the explanation ) campaigns. (E-figure1 in [7]) nsfer rate becomes extremely -like system 2 Overall light curves of RZ LMi of 2013 (upper) and 2016 (lower The existence of a stable clock such as a third body as the mechanism of the r Figure 1 shows the general light curves of the 2013 (upper panel) and One prediction of TTI model is that high mass transfer rate produces freq Figure 1: bursts ([17];[11]) is excluded by the variable supercycles. observations, including six supercycles andpercycle three (SC4) complete in supercycles 2013 was 26 d,in which 2013. was longer The than duration the typical(SC3) of super supercycles the in 2016 superoutburst were for 32 this dsupercycle and supercycle (19 60 was d, d) which 17 of were d this 2-3 times26 object. longe d The and durations 48 of d, respectively. superoutbursts durin The bridge between ER Ursae Majoris-type dwarf nova and nova 3. Results and Discussion 3.1 Outburst pattern in 2013 and 2016 3.2 Supercycle, Superoutbust Duration and Mass Transfer Rate short supercycle [18]. However, it also predictshigh, that supercycle when lengthen the again, mass tra then thewhen system eventually the reaches mass the ” transfer ratesupercycles in reaches 2016 the reproduced this critical prediction valueof exactly, providing (see the stron figure unusual short 2 supercycles in in [18 ER UMa-type objects. PoS(GOLDEN 2017)063 , a 42 f the (3.2) (3.1) . 0 = 0 R for the 2013 , we obtained a ce these values are ch superoutburst in nd almost became a are the same between rom an ER UMa-type ([19]; [20]). 0 of 0.0601(1) d with the e radius of the 3 :1 reso- of 6 d [4] is reproduced R , object which experienced d as the period of stage A 2 required to produce a hot, / erhump phase are presented 1 ˙ rst (2013-SC4).(Fig.6 in [7]) M and − )] vis t supermax t crit ˙ M / , ˙ -like system 0 . M 3 ( ) − is the critical crit 1 , d )][ crit R e / M / 0 3 1 R ( − ) is formulated as below [9]: during each superoutburst. We take the parameters in − 1 ( 1 ˙ / M is the fraction of the disk mass accreted during a super- ∼ M f M [ supermax M f t f representing the disk radius at the end of a superoutburst and vis t crit ∼ , d R and supermax t 0 R 5. The duration of each superoutburst in 2016 requires 97% and 99% o . 0 = 2 d and an assumption of a large disk radius at the end of a superoutburst Growing superhumps at the start of the 2013 April superoutbu . crit is the viscous depletion timescale and 11 ˙ M / vis = t ˙ M vis The duration of a superoutburst ( We detected growing (stage A) superhumps at the very early phase of ea t Figure 2: where stable disk, respectively. The factor outburst expressed by nance at the start of a superoutburst), respectively. If we assume at the start of a superoutburst (assuming that the disk critically reaches th different superoutbursts, we can estimate The bridge between ER Ursae Majoris-type dwarf nova and nova 2013 (SC4) and 2016 (SC3). Thosein light curves Figures during 2 the stage and Aperiod sup 3. of 0.0602(3) Using d theApril with data superoutburst. the between phase For BJD dispersion thesame minimization 2456381.41 method 2016 (PDM:[21]) and by superoutburst, using method 2456381.88 we the dataconsistent obtained between with a BJD each 2457483.01 period other, and we 2457484.40.superhumps. adopted Sin an averaged value of 0.0602(1) [9], with critical mass transfer rate. RZ LMipermanent was superhumper. critically This close object to showed the an stabilityobject almost border, to a complete a transition permanent f superhuper (Nova-likethe object). transitions BK between Lyn ER is UMa-type another object and a permanent superhumper 3.3 Growing (stage-A) superhumps where a is the binary separation. Then, the historical shortest PoS(GOLDEN 2017)063 q t- orb P with (3.4) (3.5) (3.6) (3.3) q period of , where SH P , we can directly superhumps and , see [22]. This / r shown in figure 4. orb orb the 2013 March su- q P P ectly determin d of 0.0594(2) d. This .05969(2) d, assuming and and the dimensionless − and urst. q q 1 adius of the 3 :1 resonance ≡ t superhumps to constrain further normal outburst. We post ε rst (2016-SC3). (Fig.3 in [7]) r perhumps with a run covering , , , , ) 3 ) ) -like system / r 1 3:1 ( r − post ( R ) r / R ( q ) ) R q q + ) ( ( q 1 Q ( Q ( ) 4 Q 3 = / 2 )= − orb )= ( 3 ω / = post stageA ( dyn ( ∗ 3:1 ∗ ω ε r ε q and post r are the fractional excess and disk radius immediately after the ou post r from the observed ieta of stage A superhumps under the assumption that the is the angular orbital frequency. For the dependencies on Growing superhumps at the start of the 2016 April superoutbu is equal to the fractional superhump excess in frequency: is the radius of the 3:1 resonance; q and orb are the orbital period and superhump period, respectively. If we know , measured in units of the binary separation a by 3:1 ) orb r ω r ω SH By solving equations (4) and (5) simultaneously using the periods of stage A The orbital period of RZ LMi, however, is not known, thus we cannot dir The dynamical precession rate in the disk can be expressed using On March 20, 2013, We observed the object in quiescence closely after / P post Figure 3: ( dyn ∗ the above method. Instead, we canand use the the disk radius period as of introduced post in superoutburs [23]: where determine ε burst, respectively. stage A superhumps reflects the purely dynamical[13]. precession rate at the r ω and The bridge between ER Ursae Majoris-type dwarf nova and nova where radius, post-superoutburst superhumps, we can obtain the relation between peroutburst, during which the object displayedcontinuous post-superoutburst six su cycles. A PDM analysisvariation of was this continuous also run present yielded on a March perio combined 24, the 2013, quiescent in data quiescence on after March one that 20 the and superhump 24 phase and and obtained period a did period not of change 0 during3.5 a normal Relation outb between 3.4 Post-superoutburst superhumps PoS(GOLDEN 2017)063 1 − for 1) of post − r orb P for positive / + ε SH istent signal of fer rates, which P ≡ ers (see subsection the phase in which and a large ε tion operator (Lasso) q , where g superoutburst (2016- | DM analysis of the data − ε | g signals in non-uniformly he superhump period in this 2 d in the analysis of the Kepler d in permanent superhumpers. ∼ + ε 42 for this particular object, which . 0 -like system = in figure 5. orb post r P 5 ), there is a weaker signal around 17.50–17.55 cd 1 − derived from the periods of stage A superhumps and post- post r and q in SU UMa-type DNe are estimated to be 0.30-0.38 using the same method for negative superhumps. If this is alsk the case for RZ LMi, we obtain the − post ε − r Relation between to be as large as 0.10(2). Though [9] and [10] predict a very small q Figure 5 shows the result for RZ LMi in 2016. In addition to the strong pers We analysed the light curves using the least absolute shrinkage and selec There is an empirical relation between the absolute superhumps excesses ( method ([24]; [25]). Two-dimensional Lasso power spectradata introduce as [26] and [12]sampled have ground-based been data proven (see to e.g., [28]). be very effective in detectin orbital period of 0.05792 d. This period is labeled as superoutburst superhumps. (Fig. 10 in [7]) 3.6 Negative superhumps superhumps and Figure 4: The bridge between ER Ursae Majoris-type dwarf nova and nova The values of superhumps around 16.8 cycles per day (cd between BJD2457510 and 2457530, thatSC2). is We a consider later that phase the ofbetween signal BJD the is 2457510 a long-lastin and 2457530 possible yielded negative a superhumps. periodinterval of was A 0.05710(1) 0.059555(4) d. P d. T Negative superhumpsIt are may often be observe possible thatthe negative condition of superhumps the in object RZ was3.1). almost LMi the were same excited as that during in permanent superhump 3.7 Orbital period and mass ratio negative and positive superhumps in NL objects. The relation is [13]. The smaller valuesis are unlikely those to for be WZ the Sge-type case DNe for with RZ LMi. small mass [9] trans assumed RZ LMi, our result indicates the predictions are not true at the same time. requires PoS(GOLDEN 2017)063 = q rties the period 2(1) d gives 3:1 resonance, is object may be tremely high is consistent with q e disk cannot be explained by ve. Upper: Light curve. Lower: . If this is correct, the disk radius of this object cannot be as small as q post r -like system umps. (Fig. 11 in [7]) uperhumps. A weaker signal around 17.0–17.5 c/d [see table 1 in [13]]. The ) 5 6 ( 105 . 0 is the very short duration (less than 1 d) of stage A su- [29], which has been confirmed in WZ Sge-type DNe [30]. q = 2 q q we suggested is similar to or even larger than those of ordinary / q derived from the periods of stage A superhumps and negative (Figure 6). post of 0.0528164(4) d and very frequent outbursts [27]. These prope orb r P orb P . and q q , which is equivalent to derived in subsection 3.6 is correct, RZ LMi cannot be an object close to ) 2 q Two-dimensional Lasso period analysis of the 2016 light cur ( for a very short ) 2 038 ( . There is at least one other object, GALEX J194419.33+491257.0, with ex If the A supporting evidence for a large If this is indeed the orbital period, the period of stage A superhumps of 0.60 0 141 = . 0 are somehow similar to those of RZ LMi and [27] suggested the possibility that th SU UMa stars with similar minimum or a period bouncer. The those in WZ Sge-type DNe. 3.8 Evolutionary status The rapid growth of superhumps in RZ LMi indicates that the and expected to be proportional to 1 perhumps in RZ LMi. The duration is considered to reflect the growth time of the at the end of a superoutburstan is exceptionally small large, as required by [9], but the larg superhumps in subsection 4.2 (figure 4) assuming the large the relation between Figure 5: The bridge between ER Ursae Majoris-type dwarf nova and nova Lassoperiod analysis.the strong signal around 16.8 c/d is s ε between BJD 2457510 and 2457530 is possible negative superh PoS(GOLDEN 2017)063 by a ˙ M 34 e secular increases -type state ˙ within time M ˙ . M terpretaion, [31] orb phase of posterup- P ario given by [19]. Acta Astron , ombined with the po- Z LMi may be a result increase if DNe via ER UMa-type t stable or secularly in- cluding RZ LMi. type CV. This condition for its ics. The Mdot variations period. (Fig. 12 in [7]) ˙ M nt superhumper) state to the of RZ LMi strongly increased warf novae -like system . It is likely that RZ LMi changed ˙ M 7 Location of RZ LMi on the diagram of mass ratio versus orbital Accretion in cataclysmic binaries. IV – Accretion disks in d (see subsection 3.1), which is apparently the case for RZ LMi. We studied th 2 in the last two decades. The changing supercycle suggests fluctuating crit ∼ ˙ M (1995) 161. In RZ LMi, the mass transfer rate is not secularly decreasing as in the scen They, however, disregarded the possibility that the supercycle can also There is an idea that ER UMa stars are transitional objects during the cooling Figure 6: [1] J. Smak, BK Lyn also returned to[20]. ints The original hypothetical NL cooling state sequence in fromDNe NL late after objects 2013 nova to from eruptions SU is its UMa-type not temporallook very more ER consistent irregular UMa with with time-scales observational of statics of several a years. rare The evolutionary high condition activity with of a R relatively massive secondary. 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RZ LMi - the most active SU UMa and a Bellwether for cataclysmic variable evolution 47 of Superhumps in SU UMa-Type Dwarf Novae. IV. The Fourth Year 443–449. of an extreme ER UMa star, RZ Leonis Minoris Orionis: Three cataclysmic variables with similar and unus [9] Y. Osaki, [8] T. Kato, D. Nogami, H. Baba, S. Masuda, K. Matsumoto and C. [7] T. Kato, R. Ishioka, K. Isogai, M. Kimura, A. Imada, I. Mil [6] T. Kato and C. Kunjaya, [5] D. Nogami, T. Kato, S. Masuda, R. Hirata, K. Matsumoto, K. [3] V. A. Lipovetskii and J. A. Stepanyan [4] J. W. Robertson, R. K. Honeycutt and G. W. Turner, [2] B. Warner, [16] T. Kato, P. A. Dubovsky and I. Kudzej, [17] J. W. Robertson, R. K. Honeycutt, G. W. Turner, [10] C. Hellier, [18] Y. Osaki, [13] T. Kato and Y. Osaki, [15] T. Kato, A. Imada, M. Uemura, D. Nogami, H. Maehara, R. Is [14] O. D. Pikalova and S. Y. Shugarov, [19] J. Patterson, H. Uthas, J. Kemp, E. de Miguel, T. Krajci, [11] A. Olech, M. Wisniewski, K. Zloczewski, L. M. Cook, K. 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Analysis of Kepler light curve of the novalike cataclysmic v Period analysis using the Least Absolute Shrinkage and Sele Hydrodynamic simulations of accretion disks in cataclysmi Sss j122221.7-311523: Double superoutburst in the best can 65 GALEX J194419.33+491257.0: An unusually active SU UMa-typ Was always the time segment between the superoutbursts filled by dense As for RZ LMi, the ourbust parttern is basically very regular. One super (2013) 76. Period determination using phase dispersion minimization (2012) 122. PASJ 65 , 64 Regression shrinkage and selection via the lasso A model for tidally driven eccentric instabilities in fluid d PASJ PASJ , WZ Sge-type dwarf novae , positive superhumps in ER Ursae Majoris with a very short orbital period in the Kepler data (2012) 1338. 953–960. period bouncer 8751494 (Lasso) superhump phenomenon in su uma stars outbursts followed by two normalbecomes longer, outbursts it with seems supercycle to oftreme be case about due was to what 20 is a d. observed longerthe in superoutburst, 2016. system so is For quiet some the ( other system objetcts, with it less is normal sugg outbursts) when there exist negative s [29] S. H. Lubow, [30] T. Kato, [31] M. Otulakowska-Hypka, A. Olech, [28] T. Ohshima, T. Kato, E. Pavlenko, H. Akazawa, K. Imamura DISCUSSION VOJTECH SIMON: series of normal outbursts or were any segments longer than the short on quiessent state (with only a few normal outbursts)? RYOKO ISHIOKA: [22] M. Hirose and Y. Osaki, [23] T. Kato and B. Monard, [24] R. Tibshirani, The bridge between ER Ursae Majoris-type dwarf nova and nova [21] R. F. Stellingwerf, [27] T. Kato and Y. Osaki, [26] T. Kato and H. Maehara, [25] T. Kato and M. Uemura,