WZ Sge-type dwarf novae are characterized by long recurrence times of outbursts (~10 yr) and short orbital periods (<~ 85 min). A significant part of WZ Sge stars may remain undiscovered because of low outburst activity. Recently, the observed orbital period distribution of cataclysmic variables (CVs) has changed partly because outbursts of new WZ Sge stars have been discovered routinely. Hence, the estimation of the intrinsic population of WZ Sge stars is important for the study of the population and evolution of CVs. In this paper, we present a Bayesian approach to estimate the intrinsic period distribution of dwarf novae from observed samples. In this Bayesian model, we assumed a simple relationship between the recurrence time and the orbital period which is consistent with observations of WZ Sge stars and other dwarf novae. As a result, the minimum orbital period was estimated to be ~70 min. The population of WZ Sge stars exhibited a spike-like feature at the shortest period regime in the orbital period distribution. These features are consistent with the orbital period distribution previously predicted by population synthesis studies. We propose that WZ Sge stars and CVs with a low mass-transfer rate are excellent candidates for the missing population predicted by the evolution theory of CVs.
We have summarized the current understanding and recently obtained findings about WZ Sge-type dwarf novae. We also reviewed the historical development of the understanding of these objects, provided the modern criteria, and reviewed the past research in relation to superhumps, early superhumps and the outburst mechanism. We regard that the presence of early superhumps (reflecting the 2:1 resonance) and long or multiple rebrightenings are the best distinguishing properties of WZ Sge-type dwarf novae. We provided the updated list of nearly 100 WZ Sge-type dwarf novae mainly based on the data obt…
We report on photometric observations of WZ Sge-type dwarf novae, MASTER OT J211258.65+242145.4 and MASTER OT J203749.39+552210.3 which underwent outbursts in 2012. Early superhumps were recorded in both systems. During superoutburst plateau, ordinary superhumps with a period of 0.060291(4) d (MASTER J211258) and of 0.061307(9) d (MASTER J203749) in average were observed. MASTER J211258 and MASTER J203749 exhibited eight and more than four post-superoutburst rebrightenings, respectively. In the final part of the superoutburst, an increase in the superhump periods was seen in both systems. We h…
We report on our photometric observations of the 2016 superoutburst of ASASSN-16eg. This object showed a WZ Sge-type superoutburst with prominent early superhumps with a period of 0.075478(8) d and a post-superoutburst rebrightening. During the superoutburst plateau, it showed ordinary superhumps with a period of 0.077880(3) d and a period derivative of 10.6(1.1) $\times$ 10$^{-5}$ in stage B. The orbital period ($P_{\rm orb}$), which is almost identical with the period of early superhumps, is exceptionally long for a WZ Sge-type dwarf nova. The mass ratio ($q$ = $M_2/M_1$) estimated from the …
We present the analysis of photometric and spectroscopic data on eight candidates for post-nova systems. Five post-novae, V528 Aql, HS Sge, BS Sgr, GR Sgr and V999 Sgr, are successfully recovered. We furthermore identify likely candidates for the fields of V1301 Aql, V1151 Sgr and V3964 Sgr. The spectroscopic properties of the confirmed post-novae are briefly discussed. We find that two of the oldest post-novae in our sample, GR Sgr and V999 Sgr, contain an optically thick accretion disc, and thus can be suspected to have a high mass-transfer rate, contrary to what one would expect from most m…
SU UMa stars are characterized by "superoutbursts" which are brighter at maximum light and which last much longer than the more frequent "ordinary" outbursts of these dwarf novae. Although there are now more than 1180 SU UMa type dwarf novae catalogued, our knowledge on their superoutburst cycle length Cso was hitherto limited to about 6$\%$ of the entire sample of known SU UMa stars. Using public data bases we have determined new Cso values for a total of 206 additional SU UMa stars in the range 17 d $<$ Cso $<$ 4590 d (including some ER UMa and WZ Sge type representants) within total time in…
We report the observation of a new dwarf nova, OT J055717+683226, during its first-ever recorded superoutburst in December 2006. Our observation shows that this object is an SU UMa-type dwarf nova having a very short superhump period of 76.67+/- 0.03 min (0.05324+/-0.00002 d). The next superoutburst was observed in March 2008. The recurrence time of superoutbursts (supercycle) is, hence, estimated to be ~480 d. The supercycle is much shorter than those of WZ Sge-type dwarf novae having supercycles of >~ 10 yr, which are a major population of dwarf novae in the shortest orbital period regime (<…
We report on multicolor photometry of WZ Sge-type dwarf novae, HV Vir and OT J012059.6+325545 during superoutbursts. These systems show early superhumps with the mean periods of 0.057093(45) d for HV Vir and 0.057147(15) d for OT J012059.6+325545, respectively. The observed early superhumps showed a common feature that the brightness minima correspond to the bluest peaks in color variations, which may be a ubiquitous phenomenon among early superhumps of WZ Sge-type dwarf novae. We confirmed that amplitudes of early superhumps depend on wavelength: amplitudes with longer bandpass filters show l…
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 deriva…
LS And was a transient discovered in 1971 in the M31 region and it has been argued whether it could be an intergalactic nova or a dwarf nova. Using the Zwicky Transient Facility (ZTF) data, I found that the object underwent the second known outburst in 2022 April. The behavior was that of a WZ Sge-type dwarf nova with a long fading tail and the light curves of the 1971 and 2022 outbursts matched very well. The light curves suggest that LS And is a typical WZ Sge-type dwarf nova near (but before reaching) the period minimum of cataclysmic variables. The true observed peak of the 1971 outburst w…
ASASSN-14dx showed an extraordinary outburst whose features are the small outburst amplitude (~ 2.3 mag) and long duration (> 4 years). Because we found a long observational gap of 123 d before the outburst detection, we propose that the main outburst plateau was missed and that this outburst is just a "fading tail" often seen after the WZ Sge-type superoutbursts. In order to distinguish between WZ Sge and SU UMa-type dwarf novae (DNe), we investigated Gaia DR2 statistically. We applied a logistic regression model and succeeded in classifying by using absolute Gaia magnitudes $M_{G}$ and Gaia …
We revisit hydrogen shell burning on white dwarfs (WDs) with higher mass accretion rates than the stability limit, \dot M_stable, above which hydrogen burning is stable. Novae occur with mass accretion rates below the limit. For an accretion rate > \dot M_stable, a first hydrogen shell flash occurs followed by steady nuclear burning, so the shell burning will not be quenched as long as the WD continuously accretes matter. On the basis of this picture, some persistent supersoft X-ray sources can be explained by binary models with high accretion rates. In some recent studies, however, the claim …
Stimulated by the recent discovery of the 1 yr recurrence period nova M31N 2008-12a, we examined the shortest recurrence periods of hydrogen shell flashes on mass-accreting white dwarfs (WDs). We discuss the mechanism that yields a finite minimum recurrence period for a given WD mass. Calculating the unstable flashes for various WD masses and mass accretion rates, we identified a shortest recurrence period of about two months for a non-rotating 1.38 M_sun WD with a mass accretion rate of 3.6 x 10^{-7} M_sun yr^{-1}. A 1 yr recurrence period is realized for very massive (> 1.3 M_sun) WDs with v…
In 2015 and 2017, the AM CVn candidate NSV 1440 showed superoutbursts having the characteristic features of WZ Sge-type dwarf novae (DNe). By analogy with hydrogen-rich cataclysmic variables (CVs), we can interpret these outbursts as `double superoutbursts' which are composed of the first superoutburst with early superhumps and the second superoutburst with ordinary superhumps. The object also showed multiple rebrightenings after the main superoutbursts. Early superhumps had been never observed in AM CVn stars and candidates, thus NSV 1440 is the first confirmed WZ Sge-type AM CVn candidate. W…
We present results of observations and analysis of five WZ-type dwarf novae: SDSS J080434.20+510349.2, SDSS J102146.44+234926.3, V1108 Her, ASAS J0025 and WZ Sge in 3 - 7 years after their outbursts. We found: 1) the observational evidences that emerging of the white dwarf nonradial pulsation in SDSS J080434.20+510349.2 [1] is no longer a regular since 3-rd year after 2006 outburst; 2) the true value of orbital period for V1108 Her (0.05672 d) and mass ratio (0.09); 3) The main feature of quiescent light curves of ASAS J0025 is the high-amplitude quasiperiodical light variations probably origi…
We report photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9-mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed the Balmer, He I and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, …
In 2015 March, the notable WZ Sge-type dwarf nova AL Com exhibited an unusual outburst with a recurrence time of ${\sim}$1.5 yr, which is the shortest interval of superoutbursts among WZ Sge-type dwarf novae. Early superhumps in the superoutburst light curve were absent, and a precursor was observed at the onset of the superoutburst for the first time in WZ Sge-type dwarf novae. The present superoutburst can be interpreted as a result of the condition that the disk radius barely reached the 3:1 resonance radius, but did not reach the 2:1 resonance one. Ordinary superhumps immediately grew foll…
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we studied 86 SU UMa-type dwarf novae. We confirmed the general trends such as the relation between period derivatives and orbital periods. There are some systems showing positive period derivatives despite the long orbital periods. We observed the 2011 outburst of the WZ Sge-type dwarf nova BW Scl, and recorded an O-C diagram similar to those of previously known WZ Sge-type dwarf novae. The WZ Sge-type dwarf nova OT J184228.1+483742 showed an unusual pattern of double outbursts composed of an outburst with early superhum…
Continuing the project described by Kato et al. (2009, PASJ, 61, S395, arXiv:0905.1757), we collected times of superhump maxima for 56 SU UMa-type dwarf novae mainly observed during the 2013-2014 season and characterized these objects. We detected negative superhumps in VW Hyi and indicated that the low number of normal outbursts in some supercycle can be interpreted as a result of the disk tilt. This finding, combined with the Kepler observation of V1504 Cyg and V344 Lyr, suggests that the disk tilt is responsible for modulating the outburst pattern in SU UMa-type dwarf novae. We also studied…
We report on multicolour photometry of the short period dwarf nova CSS130418:174033+414756 during the 2013 superoutburst. The system showed an unusually short superhump period with 0.046346(67) d during stage A, which is one of the shortest periods among dwarf novae below the period minimum. We found that the bluest peaks in $g' - I_{\rm c}$ colour variations tend to coincide with the brightness minima of the superhump modulations. We also studied nightly-averaged superhump amplitudes in $g'$, $R_{\rm c}$, and $I_{\rm c}$ bands and found that they have less dependence on wavelength. These prop…
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 127 SU UMa-type dwarf novae observed mainly during the 2016--2017 season and characterized these objects. We provide updated statistics of relation between the orbital period and the variation of superhumps, the relation between period variations and the rebrightening type in WZ Sge-type objects. We obtained the period minimum of 0.05290(2)d and confirmed the presence of the period gap above the orbital period ~0.09d. We note that four objects (NY Her, 1RXS J161659.5+620014, CRTS…
Photometric Analysis of TCP J20171288$+$1156589 -- WZ Sge Type Dwarf Nova with Delayed Ordinary Superhumps Emergence
Institute of Astronomy of the Russian Academy of Sciences（俄罗斯科学院天体物理研究所）；Sternberg Astronomical Institute, Lomonosov Moscow State University（莫斯科国立大学列别捷夫天文研究所）；Astronomical Institute of the Slovak Academy of Sciences（斯洛伐克科学院天文研究所）；Crimean Astrophysical Observatory（克里米亚天体物理观测站）；Vereniging voor Sterrenkunde（比利时天文协会）
Continuing the project described by Kato et al. (2009, PASJ, 61, S395, arXiv/0905.1757), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2017 season and characterized these objects. WZ Sge-type stars identified in this study are PT And, ASASSN-17ei, ASASSN-17el, ASASSN-17es, ASASSN-17fn, ASASSN-17fz, ASASSN-17hw, ASASSN-17kd, ASASSN-17la, PNV J20205397+2508145 and TCP J00332502-3518565. We obtained new mass ratios for 7 objects using growing superhumps (stage A). ASASSN-17gf is an EI Psc-type object below the period minimum. CRTS J080941.3+1715…
Continuing the project described by Kato et al. (2009a, arXiv:0905.1757), we collected times of superhump maxima for SU UMa-type dwarf novae mainly observed during the 2012-2013 season. We found three objects (V444 Peg, CSS J203937 and MASTER J212624) having strongly positive period derivatives despite the long orbital period (Porb). By using the period of growing stage (stage A) superhumps, we obtained mass ratios for six objects. We characterized nine new WZ Sge-type dwarf novae. We made a pilot survey of the decline rate of slowly fading part of SU UMa-type and WZ Sge-type outbursts. The de…
We present one of the largest collections of dwarf novae (DNe) containing 1091 objects that have been discovered in the long-term photometric data from the Optical Gravitational Lensing Experiment (OGLE) survey. They were found in the OGLE fields toward the Galactic bulge and the Magellanic Clouds. We analyze basic photometric properties of all systems and tentatively find a population of DNe from the Galactic bulge. We identify several dozen of WZ Sge-type DN candidates, including two with superhump periods longer than 0.09 d. Other interesting objects include SU UMa-type stars with "early" p…
The impact of nova eruptions on the long-term evolution of Cataclysmic Variables(CVs) is one of the least understood and intensively discussed topics in the field. Acrucial ingredient to improve with this would be to establish a large sample of post-novae with known properties, starting with the most easily accessible one, the orbitalperiod. Here we report new orbital periods for six faint novae: X Cir (3.71 h), ILNor (1.62 h), DY Pup (3.35 h), V363 Sgr (3.03 h), V2572 Sgr (3.75 h) and CQ Vel(2.7 h). We furthermore revise the periods for the old novae OY Ara, RS Car, V365Car, V849 Oph, V728 Sc…
We present our photometric studies of the newly discovered optical transient, OT J012059.6+325545, which underwent a large outburst between 2010 November and 2011 January. The amplitude of the outburst was about 8 mag. We performed simultaneous multi-color photometry by using g', Rc, and i'-band filters from the early stage of the outburst. The time resolved photometry during the early stage revealed periodic variations with double-peaked profiles, which are referred to as early superhumps, with amplitudes of about 0.08 mag. After the rapid fading from the main outburst, we found rebrightening…
As an extension of the project in Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 61 SU UMa-type dwarf novae mainly observed during the 2009-2010 season. The newly obtained data confirmed the basic findings reported in Kato et al. (2009): the presence of stages A-C, as well as the predominance of positive period derivatives during stage B in systems with superhump periods shorter than 0.07 d. There was a systematic difference in period derivatives for systems with superhump periods longer than 0.075 d between this study and Kato et al. (2009). We suggest that th…
We have developed a method for estimating the orbital periods of dwarf novae from the Sloan Digital Sky Survey (SDSS) colors in quiescence using an artificial neural network. For typical objects below the period gap with sufficient photometric accuracy, we were able to estimate the orbital periods with an accuracy to a 1 sigma error of 22 %. The error of estimation is worse for systems with longer orbital periods. We have also developed a neural-network-based method for categorical classification. This method has proven to be efficient in classifying objects into three categories (WZ Sge type,…
We observed the 2006 superoutburst of SDSS J080434.20+510349.2 during its plateau phase, rebrightening phase, and post-superoutburst final decline. We found that this object is a grazing eclipsing system with a period of 0.0590048(2) d. Well-defined eclipses were only observed during the late stage of the superoutburst plateau and the depth decreased during the subsequent stages. We determined the superhump period during the superoutburst plateau to be 0.059539(11) d, giving a fractional superhump excess of 0.90(2)%. During the rebrightening and post-superoutburst phases, persisting superhumps…
We observed the 2018 November outburst of CS Ind and confirmed that it was a genuine superoutburst with a very long [0.12471(1) d in average] superhump period. The superoutburst was preceded by a long precursor, which was recorded first time in SU UMa-type dwarf novae. We interpret that the combination of a sufficient amount of mass in the disk before the ignition of the outburst and the slow development of tidal instability near the borderline of the 3:1 resonance caused a cooling front to start before the full development of tidal instability. This finding provides another support to the rec…
We report our photometric and spectroscopic follow-up observations of the superoutbursts of three dwarf novae (GWAC\,180415A, GWAC\,181017A and GWAC\,181211A) identified independently by the Ground Wide-angle Cameras system, one of the ground-based instruments of the China-France SVOM mission. Based on a combination of our photometry and that taken from the AAVSO, our period analysis of the superhumps enables us to determine the mass ratios to be 0.0967-0.1163, 0.1879-0.1883 and 0.0981-0.1173 for GWAC\,180415A, GWAC\,181017A and GWAC\,181211A, respectively. GWAC\,180415A can be firmly identifi…
I review various phenomena associated with mass-accreting white dwarfs (WDs) in relation to progenitors of type Ia supernovae (SNe Ia). The WD mass can be estimated from light curve analysis in multiwavelength bands based on the optically thick wind theory. In the single degenerate scenario of SNe Ia, two main channels are known, i.e., WD + main sequence (MS) channel and WD + red giant (RG) channel. In each channel, a typical binary undergoes three evolutional stages before explosion, i.e., the wind phase, supersoft X-ray source (SSS) phase, and recurrent nova phase in order of time because th…
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 128 SU UMa-type dwarf novae observed mainly during the 2015-2016 season and characterized these objects. The data have improved the distribution of orbital periods, the relation between the orbital period and the variation of superhumps, the relation between period variations and the rebrightening type in WZ Sge-type objects. Coupled with new measurements of mass ratios using growing stages of superhumps, we now have a clearer and statistically greatly improved evolutionary path …
Continuing the project described by Kato et al. (2009, PASJ 61, S395, arXiv:0905.1757), we collected times of superhump maxima for 51 SU UMa-type dwarf novae mainly observed during the 2010-2011 season. Although most of the new data for systems with short superhump periods basically confirmed the findings by Kato et al. (2009) and Kato et al. (2010, PASJ 62, 1525, arXiv:1009.5444), the long-period system GX Cas showed an exceptionally large positive period derivative. An analysis of public Kepler data of V344 Lyr and V1504 Cyg yielded less striking stage transitions. In V344 Lyr, there was pro…
We report the discovery of forty erupting cataclysmic variable stars in the OGLE-III Galactic disk fields: seventeen objects of U Gem type, four of Z Cam type, and nineteen stars showing outbursts and superoutbursts typical for SU UMa type dwarf novae. In the case of five stars we were able to estimate their supercycle lengths. The obtained lengths are in the range 20-90 d, generally between the typical SU UMa type variables and a few objects classified as the ER UMa type variables. Since there is no significant difference between the two types but a higher mass-transfer rate resulting in more…
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2014-2015 season and characterized these objects. Our project has greatly improved the statistics of the distribution of orbital periods, which is a good approximation of the distribution of cataclysmic variables at the terminal evolutionary stage, and confirmed the presence of a period minimum at a period of 0.053 d and a period spike just above this period. The number density monotonically decreased toward the longer period…
The post-outburst rebrightening phenomenon in dwarf novae and X-ray novae is still one of the most challenging subjects for theories of accretion disks. It has been widely recognized that post-outburst rebrightenings are a key feature of WZ Sge-type dwarf novae, which predominantly have short ($\lesssim$0.06 d) orbital periods. I found four post-outburst rebrightenings in ASASSN-14ho during its 2014 outburst, whose orbital period has recently measured to be exceptionally long [0.24315(10) d]. Using the formal solution of the radial velocity study in the literature, I discuss the possibility th…
Spectra of 76 known dwarf novae from the LAMOST survey were presented. Most of the objects were observed in quiescence, and about 16 systems have typical outburst spectra. 36 of these systems were observed by SDSS, and most of their spectra are similar to the SDSS spectra. 2 objects, V367 Peg and V537 Peg, are the first to observe their spectra. The spectrum of V367 Peg shows a contribution from a M-type donor and its spectral type could be estimated as M3-5 by combining its orbital period. The signature of white dwarf spectrum can be seen clearly in four low-accretion-rate WZ Sge stars. Other…
We report photometric and spectroscopic observations of the eclipsing SU UMa-type dwarf nova ASASSN-18aan. We observed the 2018 superoutburst with 2.3 mag brightening and found the orbital period ($P_{\rm orb}$) to be 0.149454(3) d, or 3.59 hr. This is longward of the period gap, establishing ASASSN-18aan as one of a small number of long-$P_{\rm orb}$ SU UMa-type dwarf novae. The estimated mass ratio, ($q=M_2/M_1 = 0.278(1)$), is almost identical to the upper limit of tidal instability by the 3:1 resonance. From eclipses, we found that the accretion disk at the onset of the superoutburst may r…
A distinguishing trait of the three known Galactic recurrent novae with the shortest orbital periods, T Pyx, IM Nor, and CI Aql, is that their optical decline time-scales are significantly longer than those of the other recurrent systems. On the other hand, some estimates of the mass of the ejecta, the velocity of the ejecta, and the duration of the soft X-rays emission of these systems are of the order of those of the other recurrent systems and the fast classical novae. We put forth a tentative explanation of this phenomenon. We propose that in these systems part of the material transferred …
Changes in the supercycle lengths of some SU UMa-type dwarf novae have been detected by other studies, and indicate that the mass transfer rates noticeably decrease over time. We investigated the supercycle lengths of three SU UMa-type dwarf novae: AR Pic, QW Ser and V521 Peg, to determine if they have detectable changes in their supercycles. We present the results of optical spectroscopic and photometric observations of these sources. Our observations were conducted in 2016 and 2017 at the Boyden Observatory and the Sutherland station of the South African Astronomical Observatory. The quiesce…
Outbursting AM CVn stars exhibit outbursts similar to those observed in different types of dwarf novae. Their light-curves combine the characteristic features of SU UMa, ER UMa, Z Cam, and WZ Sge-type systems but also show a variety of properties never observed in dwarf novae. The compactness of AM CVn orbits and their unusual chemical composition make these systems valuable testbeds for outburst models. We aim for a better understanding of the role of helium in the accretion disc instability mechanism, testing the model for dwarf novae outbursts in the case of AM CVn stars, and aim to explain…
We present high speed photometric observations of 20 faint cataclysmic variables, selected from the Sloan Digital Sky Survey and Catalina catalogues. Measurements are given of 15 new directly measured orbital periods, including four eclipsing dwarf novae (SDSS0904+03, CSS0826-00, CSS1404-10 and CSS1626-12), two new polars (CSS0810+00 and CSS1503-22) and two dwarf novae with superhumps in quiescence (CSS0322+02 and CSS0826-00). Whilst most of the dwarf novae presented here have periods below 2 h, SDSS0805+07 and SSS0617-36 have relatively long orbital periods of 5.489 and 3.440 h, respectively.…
We propose a new method to reconstruct the structure of accretion disks in dwarf novae using multi-band light curves of early superhumps. Our model assumes that early superhumps are caused by the rotation effect of non-axisymmetrically flaring disks. We have developed a Bayesian model for this reconstruction, in which a smoother disk-structure tends to have a higher prior probability. We analyzed simultaneous optical and near-infrared photometric data of early superhumps of the dwarf nova, V455 And using this technique. The reconstructed disk has two flaring parts in the outermost region of th…
We propose a new dynamical method to estimate binary mass ratios by using the period of superhumps in SU UMa-type dwarf novae during the growing stage (the stage A superhumps). This method is based on a working hypothesis in which the period of the superhumps at the growing stage is determined by the dynamical precession rate at the 3:1 resonance radius, a picture suggested in our new interpretation of the superhump period evolution during the superoutburst (Osaki, Kato 2013, arXiv:1305.5877). By comparison with the objects with known mass ratios, we show that our method can provide sufficient…
The star V426 Sge (HBHA~1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a symbiotic star outburst. We aim to confirm the nature of V426 Sge as a classical symbiotic star, determine the photometric ephemeris of the light minima, and suggest the path from its 1968 symbiotic nova outburst to the following 2018 Z And-type outburst. We re-constructed an historical light curve (LC) of V426 Sge from approximately the year 1900, and used original low- and high-resolution spectroscopy complemented …
We observed RZ LMi, which is renowned for the extremely (~19d) short supercycle and is a member of a small, unusual class of cataclysmic variables called ER UMa-type dwarf novae, in 2013 and 2016. In 2016, the supercycles of this object substantially lengthened in comparison to the previous measurements to 35, 32, 60d for three consecutive superoutbursts. We consider that the object virtually experienced a transition to the novalike state (permanent superhumper). This observed behavior extremely well reproduced the prediction of the thermal-tidal instability model. We detected a precursor in t…
Models of nova outbursts suggest that an X-ray flash should occur just after hydrogen ignition. However, this X-ray flash has never been observationally confirmed. We present four theoretical light curves of the X-ray flash for two very massive white dwarfs (WDs) of 1.380 and 1.385 M_sun and for two recurrence periods of 0.5 and 1 years. The duration of the X-ray flash is shorter for a more massive WD and for a longer recurrence period. The shortest duration of 14 hours (0.6 days) among the four cases is obtained for the 1.385 M_sun WD with one year recurrence period. In general, a nova explos…
We present spectroscopic and photometric observations of 17 dwarf-nova superoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei at Okayama Observatory of Kyoto University and through VSNET collaboration. Our spectroscopic observations for six outbursts were performed within 1 d from their optical peak. 11 objects (TCP J00590972+3438357. ASASSN-19ado, TCP J06073081-0101501, ZTF20aavnpug, ASASSN-19ady, MASTER OT J061642.05+435617.9, TCP J20034647+1335125, ASASSN-20kv, ASASSN-20kw, MASTER OT J213908.79+161240.2, and ASASSN-20mf) were previously unknown systems, and our observati…
V476 Cyg (Nova Cyg 1920) is a bright, fast nova reaching a photographic magnitude of 2.0. Using the Zwicky Transient Facility (ZTF) public database, I found that this nova is currently a dwarf nova with a cycle length of ~24 d. Compared to other classical novae currently in dwarf nova-type states, outbursts of V476 Cyg are rapidly rising and short with durations of a few days. Based on the AAVSO observations, this nova was probably already in the dwarf nova-type phase in 2016, 96 years after the nova eruption. I found a possible orbital period of 0.1018002(6) d using the ZTF data, which would …
We present the discovery of a 3h5m orbital-period binary star at the heart of the planetary nebula M 3-1 - the shortest period photometrically-variable central star known and second only to V458 Vul, in general. Combined modelling of light and radial velocity curves reveals both components to be close to Roche-lobe-filling, strongly indicating that the central star will rapidly evolve to become a cataclysmic variable, perhaps experiencing a similar evolution to V458 Vul resulting in a nova eruption before the planetary nebula has fully dissipated. While the short orbital period and near Roche-…
