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The cataclysmic variable SDSS J214354.59+124457.8 (hereafter SDSS J214354) was observed photometrically on sixty one nights between 2012 July 28 and 2019 May 26. The long term variation of this object shows changes between two phases; a dwarf nova type and a novalike. This implies that the object belongs to the group of Z Cam type stars. The timing analysis of the light curve reveals a periodic signal at 0.13902(5) d, which we identify as the superhump period. However, the fractional superhump excess of 10 per cent longer than the orbital period is exceptionally large. We obtained a mass ratio of ∼0.4, which is above the accepted upper limit of q = 0.33 for the formation of superhumps. We suggest that the object contains a secondary with an evolved core. With an orbital period of 0.126 d, SDSS J214354 is situated at the upper border of the period gap. The long term light curve of SDSS J214354 is similar to those of Z Cam type stars which are characterized by recurring standstills, followed by short intervals with DN type outbursts. Therefore, we conclude that SDSS J214354 is a new member of the Z Cam type stars.

There are several peculiar long-period dwarf-nova like objects, which show rare, low-amplitude outbursts with highly ionized emission lines. 1SWASP J162117$+$441254, BD Pav, and V364 Lib belong to this kind of objects. Some researchers even doubt whether 1SWASP J1621 and V364 Lib have the same nature as normal dwarf novae. We studied the peculiar outbursts in these three objects via our optical photometry and spectroscopy, and performed numerical modeling of their orbital variations to investigate their properties. We found that their outbursts lasted for a long interval (a few tens of days), and that slow rises in brightness were commonly observed during the early stage of their outbursts. Our analyses and numerical modeling suggest that 1SWASP J1621 has a very high inclination, close to 90 deg, plus a faint hot spot. Although BD Pav seems to have a slightly lower inclination ($\sim$75 deg), the other properties are similar to those in 1SWASP J1621. On the other hand, V364 Lib appears to have a massive white dwarf, a hot companion star, and a low inclination ($\sim$35 deg). In addition, these three objects possibly have low transfer rate and/or large disks originating from the long orbital periods. We find that these properties of the three objects can explain their infrequent and low-amplitude outbursts within the context of the disk instability model in normal dwarf novae without strong magnetic field. In addition, we suggest that the highly-ionized emission lines in outburst are observed due to a high inclination and/or a massive white dwarf. More instances of this class of object may be unrecognized, since their unremarkable outbursts can be easily overlooked., Comment: 17 pages, 18 figures, 2 tables with supporting information. Accepted for publication in PASJ

We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of superhump period are found to be composed of three distinct stages: early evolutionary stage with a longer superhump period, middle stage with systematically varying periods, final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods less than 0.08 d show positive period derivatives. Contrary to the earlier claim, we found no clear evidence for variation of period derivatives between superoutburst of the same object. We present an interpretation that the lengthening of the superhump period is a result of outward propagation of the eccentricity wave and is limited by the radius near the tidal truncation. We interpret that late stage superhumps are rejuvenized excitation of 3:1 resonance when the superhumps in the outer disk is effectively quenched. Many of WZ Sge-type dwarf novae showed long-enduring superhumps during the post-superoutburst stage having periods longer than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently, mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives and are excellent candidate for the systems around or after the period minimum of evolution of cataclysmic variables (abridged)., Comment: 239 pages, 225 figures, PASJ accepted

We present near-infrared spectra for five dwarf novae with short orbital periods. We performed fittings of the spectral energy distributions (SEDs) by assuming a power-law distribution for the accretion disk and using template spectra of late-type dwarfs for the secondary star. Two are WZ Sgeor WX Cet-type stars, whose spectra show water absorption features, and one of them shows K I and Na I absorption lines in the J -band. We find that the secondary contributions to the overall SED are larger in WZ Sge stars than in ER UMa stars. The SED fitting suggests M9 and L1 type dwarf companions for our WZ Sge systems, and an M2 dwarf for our ER UMa star. We discuss the direct relationship between the high temperatures of secondary stars and high mass-transfer rates in ER UMa stars. SDSS J013701.06–091234.9 is the only object showing a spectrum dominated by the secondary component. The spectrum strongly suggests that the evolutionary path of SDSS J013701.06–091234.9 is different from that of ordinary CVs, and this object is a candidate of EI Psc-like systems.