We present simultaneous $g'$, $R_{\rm c}$, and $I_{\rm c}$ photometry of the notable dwarf nova ER UMa during the 2011 season. Our photometry revealed that the brightness maxima of negative superhumps coincide with the bluest peaks in $g' - I_{\rm c}$ colour variations. We also found that the amplitudes of negative superhumps are the largest in the $g'$ band. These observed properties are significantly different from those observed in early and positive superhumps. Our findings are consistent with a tilted disk model as the light source of negative superhumps.
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…
Osaki and Kato (2012) interpreted variations of the negative superhump periods, discovered by them in dwarf nova V1504 Cyg, as evidence in favor of the thermal-tidal instability model for superoutbursts. It is shown that their interpretation was incorrect. The observational evidence is recalled showing that superoutbursts are due to the enhanced mass transfer rate.
Negative superhumps are believed to arise in cataclysmic variable systems when the accretion disk is tilted with respect to the orbital plane. Slow retrograde precession of the line-of-nodes results in a signal---the negative superhump---with a period slightly less than the orbital period. Previous studies have shown that tilted disks exhibit negative superhumps, but a consensus on how a disk initially tilts has not been reached. Analytical work by Lai suggests that a magnetic field on the primary can lead to a tilt instability in a disk when the dipole moment is offset in angle from the spin …
Negative superhumps in cataclysmic variable systems result when the accretion disc is tilted with respect to the orbital plane. The line of nodes of the tilted disc precesses slowly in the retrograde direction, resulting in a photometric signal with a period slightly less than the orbital period. We use the method of smoothed particle hydrodynamics to simulate a series of models of differing mass ratio and effective viscosity to determine the retrograde precession period and superhump period deficit $\varepsilon_-$ as a function of system mass ratio $q$. We tabulate our results and present fit…
We presents result of CDD photometry for SU UMa dwarf nova NY Her during 6 nights in June 2017 when object was in quiescence. Light curves clearly show strong amplitude variations in a range of 0m.7-1m.1. Time series analysis revealed a period 0.07141(5) d, that we identified as the period of possible negative superhumps of NY Her.
Negative superhumps are detected in the light curves of RW Tri collected in September 1994 (Smak 1995) and November/December 1957 (Walker 1963). New system parameters, obtained using $K_2$ and $V_{2,rot}\sin i$ (from Poole et al. 2003) and $q$ (estimated from $P_{nSH}$), are $M_1=0.60\pm 0.20M\odot$, $M_2=0.48\pm 0.15M\odot$, $A=1.13\pm 0.09\times 10^{11}$cm and $i=72.5\pm 2.5$.
We analyzed the Kepler long cadence data of KIC 7524178 (=KIS J192254.92+430905.4), and found that it is an SU UMa-type dwarf nova with frequent normal outbursts. The signal of the negative superhump was always the dominant one even during the superoutburst, in contrast to our common knowledge about superhumps in dwarf novae. The signal of the positive superhump was only transiently seen during the superoutburst, and it quickly decayed after the superoutburst. The frequency variation of the negative superhump was similar to the two previously studied dwarf novae in the Kepler field, V1504 Cyg …
The multi-site photometric observations of MN Dra were made over 77 nights in August-November, 2009. The total exposure was 433 hours. During this time the binary underwent two superoutbursts and five normal outbursts. During the course of first superoutburst period of positive superhumps decreased with extremely large $\dot P = -1.5 \times 1.0^{-4}$ for SU UMa-like dwarf novae, confirming known behavior of MN Dra [1]. Between the superoutbursts MN Dra displayed negative superhumps. Their period changed cyclically around 0.096-day value.
I analyzed All-Sky Automated Survey for Supernovae (ASAS-SN) Sky Patrol data of ES Dra and classified it to be a Z Cam star with VY Scl-type fading episodes. An analysis of Transiting Exoplanet Survey Satellite (TESS) observations showed that this object shows shallow eclipses and that the orbital period is 0.17749895(17) d. Negative superhumps with a period of 0.167830(2) d and the beat phenomenon between the period of negative superhumps and the orbital period were detected in the TESS data between 2020 January and March. The orbital profile systematically varied depending on the beat phase …
We report on a discovery of "negative" superhumps during the 2011 January superoutburst of ER UMa. During the superoutburst which started on 2011 January 16, we detected negative superhumps having a period of 0.062242(9) d, shorter than the orbital period by 2.2%. No evidence of positive superhumps was detected during this observation. This finding indicates that the disk exhibited retrograde precession during this superoutburst, contrary to all other known cases of superoutbursts. The duration of this superoutburst was shorter than those of ordinary superoutbursts and the intervals of normal …
Negative superhumps in cataclysmic variables driven by retrograde apsidal disk precession
University of Nevada, Las Vegas（内华达大学拉斯维加斯分校）；Nevada Center for Astrophysics, University of Nevada, Las Vegas（内华达天体物理中心，内华达大学拉斯维加斯分校）；Space Telescope Science Institute（太空望远镜科学研究所）
We report the results of 67h of CCD photometry of the recently discovered dwarf nova SDSS J210014.12+004446.0. The data were obtained on 24 nights spanning a month. During this time we observed four ordinary outbursts lasting about 2-3 days and reaching an amplitude of ~1.7 mag. On all nights our light curve revealed persistent modulation with the stable period of 0.081088(3) days. These humps were already observed on one night by Tramposch et al. (2005), who additionally observed superhumps during a superoutburst. Remarkably, from scant evidence at their disposal they were able to discern the…
Using smoothed particle hydrodynamics, we numerically simulate steady state accretion discs for Cataclysmic Variable Dwarf Novae systems that have a secondary-to-primary mass ratio (0.35 \le q \le 0.55). After these accretion discs have come to quasi-equilibrium, we rotate each disc out of the orbital plane by (δ= (1, 2, 3, 4, 5,) or (20)^{o}) to induce negative superhumps. For accretion discs tilted $5^{o}$, we generate light curves and associated Fourier transforms for an atlas on negative superhumps and retrograde precession. Our simulation results suggest that accretion discs need to be ti…
The origin of tilted disks in cataclysmic variables is explained in terms of a model involving the stream-disk interactions. Tilted, precessing disk causes periodically variable asymmetry in the irradiation of the two hemispheres of the secondary component, resulting in variable vertical component of the velocity of the stream. The following stream-disk interactions provide additional vertical acceleration to disk elements needed to produce and maintain disk tilt. Predictions based on this model compare favorably with observations.
A radial velocity study is presented of the cataclysmic variable V378 Pegasi (PG 2337+300). It is found to have an orbital period of 0.13858 +/- 0.00004 d (3.32592 +/- 0.00096 hours). Its spectrum and long-term light curve suggest that V378 Peg is a nova-like variable, with no outbursts. We use the approximate distance and position in the Galaxy of V378 Peg to estimate E(B-V) = 0.095, and use near-infrared magnitudes to calculate a distance of 680 +/- 90 pc and M_V = 4.68 +/- 0.70, consistent with V378 Peg being a nova-like. Time-resolved photometry taken between 2001 and 2009 reveals a period…
We report on the analysis of the Kepler short-cadence (SC) light curve of V344 Lyr obtained during 2009 June 20 through 2010 Mar 19 (Q2--Q4). The system is an SU UMa star showing dwarf nova outbursts and superoutbursts, and promises to be a touchstone for CV studies for the foreseeable future. The system displays both positive and negative superhumps with periods of 2.20 and 2.06-hr, respectively, and we identify an orbital period of 2.11-hr. The positive superhumps have a maximum amplitude of ~0.25-mag, the negative superhumps a maximum amplitude of ~0.8 mag, and the orbital period at quiesce…
We report the results of photometry of the WZ Sge-type dwarf nova V455 And. Observations were obtained over 19 nights in 2013 and 2014. The total duration of the observations was 96 h. We clearly detected three coherent oscillations with periods of 80.376+/-0.003 min, 40.5431+/-0.0004 min and 67.619685+/-0.000040 s. The 67.619685-s period can be the spin period of the white dwarf. The 40.5431-minute period is the first harmonic of the orbital period. The 80.376-minute oscillation can be a negative superhump because its period is 0.9% less than the orbital period. This oscillation was evident b…
We present a detailed photometric study of the bright cataclysmic variable BG Tri using ground-based observations mainly from Rozhen Observatory, ASAS-SN, TESS, and WASP sky surveys. We report the discovery of a negative superhump with P$_{-sh}$ = 0.1515(2) days and a co-existing superorbital variation with P=3.94(53) days in data from 2019 and 2020. A positive superhump with P$_{+sh}$ = 0.1727(14) days is also discovered in data from 2006. The obtained negative superhump deficit $\varepsilon_{-}$=0.044(1) and the positive superhump excess $\varepsilon_+$=0.090(9) give us an independent photom…
We have studied the SC (short cadence) Kepler light curve of an SU UMa star, V1504 Cyg, which extends for a period of about 630 d. All superoutbursts in V1504 Cyg have turned out to be of the precursor-main type and the superhump first appears near the maximum of the precursor. The superhumps grow smoothly from the precursor to the main superoutburst showing that the superoutburst is initiated by the tidal instability (as evidenced by growing superhump) as envisioned in the thermal-tidal instability (TTI) model proposed by Osaki (1989). We have performed power spectral analysis of the light cu…
We have studied the short-cadence Kepler public light curves of SU UMa stars, V344 Lyr and V1504 Cyg extending over a period of more than two years by using power spectral analysis. We determined the orbital period of V344 Lyr to be Porb=0.087903(1) d. We also reanalyzed the frequency variation of the negative superhump in a complete supercycle of V1504 Cyg with additional data of the O-C diagram, confirming that its characteristic variation is in accordance with the thermal-tidal instability model. We present a new two-dimensional period analysis based on a new method of a least absolute shri…
We carried out the photometric observations of the SU UMa-type dwarf nova ER UMa during 2011 and 2012, which showed the existence of persistent negative superhumps even during the superoutburst. We performed two-dimensional period analysis of its light curves by using a method called "least absolute shrinkage and selection operator" (Lasso) and "phase dispersion minimization" (PDM) analysis, and we found that the period of negative superhumps systematically changed between a superoutburst and the next superoutburst. The trend of the period change can beinterpreted as reflecting the change of t…
We report K2 observations of the eclipsing cataclysmic variable V729 Sgr which covered nearly 80 days in duration. We find five short outbursts and two long outbursts, one of which shows a clear plateau phase in the rise to maximum brightness. The mean time between successive short outbursts is ~10 d while the time between the two long outbursts is ~38 d. The frequency of these outbursts are unprecedented for a CV above the orbital period gap. We find evidence that the mid-point of the eclipse occurs systematically earlier in outburst than in quiescence. During five of the six quiescent epochs…
Variability on all time scales between seconds and decades is typical for cataclysmic variables (CVs). One of the brightest and best studied CVs is TT Ari, a nova-like variable which belongs to the VY Scl subclass, characterized by occasional low states in their light curves. It is also known as a permanent superhumper at high state, revealing "positive" (P_S > P_0) as well as "negative" (P_S < P_0) superhumps, where P_S is the period of the superhump and P_0 the orbital period. TT Ari was observed by the Canadian space telescope MOST for about 230 hours nearly continuously in 2007, with a tim…
KIC 9406652 is a cataclysmic variable (CV), sub-classified as `IW And-type star', showing a repetition of standstills with oscillatory variations terminated by brightening. This system showed negative superhumps, semi-periodic variations having periods slightly shorter than the orbital period, and super-orbital signals, both of which are believed to originate from a precessing, tilted accretion disk. We have re-examined its Kepler light curve extending over 1500 d. In accordance with a cycle of the IW And-type light variation, the frequency of negative superhumps showed a reproducible variatio…
The timing capabilities and sensitivity of Kepler, NASA's observatory to find Earth-sized planets within the habitable zone of stars, are well matched to the timescales and amplitudes of accretion disk variability in cataclysmic variables. This instrumental combination provides an unprecedented opportunity to test and refine stellar accretion paradigms with high-precision, uniform data, containing none of the diurnal or season gaps that limit ground-based observations. We present a 3-month, 1 minute cadence Kepler light curve of V344 Lyr, a faint, little-studied dwarf nova within the Kepler fi…
We investigated whether the predictions and results of Stanishev et al (2002) concerning a possible relationship between eclipse depths in PX And and its retrograde disc precession phase, could be confirmed in long term observations made by SuperWASP. In addition, two further CVs (DQ Her and V795 Her) in the same SuperWASP data set were investigated to see whether evidence of superhump periods and disc precession periods were present and what other, if any, long term periods could be detected. The results of our period and eclipse analysis on PX And confirm that the negative superhump period i…
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…
Light curves of AM CVn are analyzed by decomposing them into their Fourier components. The amplitudes of the fundamental mode and overtones of the three components: the superhumps, the negative superhumps and the orbital variations, are found to be variable. This implies that variations in the shape of the observed light curve of AM CVn are not only due to the interference between those components, but also due to the variability of their parameters.
We analyzed a Kepler light curve of KIC 8751494, a recently recognized novalike cataclysmic variable in the Kepler field. We detected a stable periodicity of 0.114379(1) d, which we identified as being the binary's orbital period. The stronger photometric period around 0.12245 d, which had been detected from the ground-based observation, was found to be variable, and we identified this period as being the positive superhump period. This superhump period showed short-term (10-20 d) and strong variations in period most unexpectedly when the object entered a slightly faint state. The fractional s…
$TESS$ photometric data of LS~Cam from sectors 19, 20 and 26 are analysed. The obtained power spectra from sectors 19 and 20 show multiple periodicities - orbital variations ($P_{orb} = 0.14237$ days), slightly fluctuating superorbital variation ($ P_{so} \approx 4.03$ days) and permanent negative superhump ($P_{-sh} = 0.1375$ days). In sector 26 an additional positive superhump ($P_{+sh} = 0.155$ days) is present. Using relations from literature, the mass ratio and the masses of the two components are estimated to be $q =0.24$, $M_1 = 1.26M_\odot$, and $M_2 = 0.30 M_\odot$ respectively.
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…
We present time-resolved CCD photometry of a dwarf nova NSV 4838 (UMa 8, SDSS J102320.27+440509.8) during the 2005 June and 2007 February outburst. Both light curves showed superhumps with a mean period of 0.0699(1) days for the 2005 outburst and 0.069824(83) days for the 2007 outburst, respectively. Using its known orbital period of 0.0678 days, we estimated the mass ratio of the system to be $q$=0.13 based on an empirical relation. Although the majority of SU UMa-type dwarf novae having similar superhump periods show negative period derivatives, we found that the superhump period increased a…
A probable inside-out dwarf nova outburst from the period bouncer candidate ASASSN-25dc
South African Astronomical Observatory（南非天文台）；University of Cape Town（开普敦大学）；Okayama Observatory, Kyoto University（京都大学冈山天文台）；Kyoto University（京都大学）；Kanazawa University（金泽大学）；The University of Tokyo（东京大学）；University of the Free State（自由州大学）
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…
Context: We present results of an extensive world-wide observing campaign of MN Draconis. Aims: MN Draconis is a poorly known active dwarf nova in the period gap and is one of the only two known cases of period gap SU UMa objects showing the negative superhumps. Photometric behaviour of MN Draconis poses a challenge for existing models of the superhump and superoutburst mechanisms. Therefore, thorough investigation of peculiar systems, such as MN Draconis, is crucial for our understanding of evolution of the close binary stars. Methods: To measure fundamental parameters of the system, we colle…
Eclipse Properties and Superhump Evolution in the SU UMa-Type Dwarf Nova Z Cha
Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Department of Astronomy, School of Physics and Astronomy, Yunnan University（云南大学物理与天文学院天文学系）
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…
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…
A CCD photometry of the dwarf nova MASTER OT J172758.09 +380021.5 was carried out in 2019 during 134 nights. Observations covered three superoutbursts, five normal outbursts and quiescence between them. The available ASASSN and ZTF data for 2014-2020 were also examined. Spectral observations were done in 2020 when the object was in quiescence. Spectra and photometry revealed that the star is an H-rich active ER UMa-type dwarf nova with a highly variable supercycle of ~50-100 d that implies a high and variable mass-transfer rate. This object demonstrated peculiar behaviour: short-lasted superou…
