The UV spectra of nova-like variables are dominated by emission from the accretion disk, modified by scattering in a wind emanating from the disk. Here we model the spectra of RW Tri and UX UMa, the only two eclipsing nova-likes which have been observed with the Hubble Space Telescope in the far-ultraviolet, in an attempt to constrain the geometry and the ionization structure of their winds. Using our Monte Carlo radiative transfer code we computed spectra for simply-parameterized axisymmetric biconical outflow models and were able to find plausible models for both systems. These reproduce the primary UV resonance lines - N V, Si IV, and C IV - in the observed spectra in and out of eclipse. The distribution of these ions in the wind models is similar in both cases as is the extent of the primary scattering regions in which these lines are formed. The inferred mass loss rates are 6% to 8% of the mass accretion rates for the systems. We discuss the implication of our point models for our understanding of accretion disk winds in cataclysmic variables.
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 observed the 2016 outburst of OT J002656.6+284933 (CSS101212:002657+284933) and found that it has the longest recorded [0.13225(1) d in average] superhumps among SU UMa-type dwarf novae. The object is the third known SU UMa-type dwarf nova above the period gap. The outburst, however, was unlike ordinary long-period SU UMa-type dwarf novae in that it showed two post-outburst rebrightenings. It showed superhump evolution similar to short-period SU UMa-type dwarf novae. We could constrain the mass ratio to less than 0.15 (most likely between 0.10 and 0.15) by using superhump periods in the ear…
We observed ASASSN-19ax during the long outburst in 2021 September-October. The object has been confirmed to be an SU UMa-type dwarf nova with a superhump period of 0.1000-0.1001 d. This object showed two post-superoutburst rebrightenings both in the 2019 and 2021 superoutbursts. These observations have established that ASASSN-19ax belongs to a group of long-period SU UMa-type dwarf novae which show multiple rebrightenings. This phenomenon probably arises from premature quenching of the superoutburst due to the weak 3:1 resonance near the stability border of the resonance, resulting in a consi…
We report unfiltered CCD photometry of the first confirmed superoutburst of the recently discovered dwarf nova, SDSS J083931.35+282824.0 in April 2010. From a quiescence magnitude of ~19.8 it rose to 14.0, an outburst amplitude of at least 5.8 magnitudes. Only the plateau phase of the outburst was observed during which superhumps with peak-to-peak amplitude of up to 0.28 magnitudes were present, confirming this to be an SU UMa type dwarf nova. The mean superhump period was Psh = 0.07836(2) during the first 3 days and this subsequently decreased to 0.07800(3) d. Analysis of the data revealed te…
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…
We report photometry and analysis of a previously unknown SU UMa-type dwarf nova in Bootes detected in outburst by the Catalina Real-time Transient Survey on 2009 May 30 with the discovery identifier CSS090530:144011+494734. This apparently stellar object had previously been catalogued by the Sloan Digital Sky survey as SDSS J144011.01+494733.4. We measured its mean superhump period over the first 3 days following detection as 0.06500(4) d at which point this changed to 0.06438(3) d. We detected a possible orbital period of 0.06322(8) d implying a mean superhump period excess of 0.020(2). Afte…
We report unfiltered photometry during superoutbursts of PU UMa in 2009 and 2012. The amplitude was 4.5 magnitudes above mean quiescence and lasted at least 9 to 10 days. Superhumps were present with a peak-to-peak amplitude of up to ~0.3 mag, thereby confirming it to be a member of the SU UMa family of dwarf novae. The mean superhump period during the later part of the 2012 outburst was Psh = 0.08076(40) d. Analysis of the eclipse times of minimum, supplemented with data from other researchers, revealed an orbital period of Porb = 0.077880551(17) d. The superhump period excess was epsilon = 0…
We investigated the superhump evolution, analysing optical photometric observations of the 2000 February-March, the 2002 October-November, and the 2006 September superoutbursts of SW UMa. The superhumps evolved in the same way after their appearance during the 2000 and the 2002 superoutbursts, and probably during the 2006 one. This indicates that the superhump evolution may be governed by the invariable binary parameters. We detected a periodicity in light curve after the end of the 2000 superoutburst without phase shift, which seems to be the remains of the superhumps. We found QPOs at the en…
MASTER OT J004527.52+503213.8 (hereafter MASTER J004527) is a dwarf nova discovered by the MASTER project in 2013. At 18:20 UTC on 24 October 2020, brightening of this object was reported to vsnet-alert (24843 by Denisenko). This was the second report of a superoutburst after its discovery. Photometric observations were made using the 23.5-cm Schmidt-Cassegrain telescope at Okayama University of Science observatory soon after the alert through 4 November 2020. In this work, we present the photometric data from our observation, and the analysis of the light curves of MASTER J004527 during the 2…
We have discovered a dwarf nova (DN) of type SU UMa in Kepler data which is 7.0 arcsec from the G-type exoplanet survey target KIC 4378554. The DN appears as a background source in the pixel aperture of the foreground G star. We extracted only the pixels where the DN is present and observed the source to undergo five outbursts -- one a superoutburst -- over a timespan of 22 months. The superoutburst was triggered by a normal outburst, a feature that has been seen in all DNe superoutburst observed by Kepler. Superhumps during the super outburst had a period of 1.842+/-0.004 h and we see a trans…
IW And stars are a recently recognized subgroup of dwarf novae which are characterized by (often repetitive) slowly rising standstills terminated by brightening, but the exact mechanism for this variation is not yet identified. We have identified BO Cet, which had been considered as a novalike cataclysmic variable, as a new member of IW And stars based on the behavior in 2019-2020. In addition to this, the object showed dwarf nova-type outbursts in 2020-2021, and superhumps having a period 7.8% longer than the orbital one developed at least during one long outburst. This object has been confir…
We report observations during 2008 October of the first recorded superoutburst of a previously unknown SU UMa-type dwarf nova in Draco located at 19h 14m 43.52s +60d 52m 14.1s (J2000). Simbad lists a 21st magnitude star at this position with identifiers GSC2.3 N152008120 and USNO-B1.0 1508-0249096. The outburst reached magnitude 14.9, its amplitude was approximately 6 magnitudes and its duration at least 11 days. About 11 days after the end of the main outburst there was a short-lived rebrightening by more than 2 magnitudes. Superhumps were observed with a mean period of 0.07117(1) d and ampli…
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…
We studied the background dwarf nova of KIC 11412044 in the Kepler public data and identified it with GALEX J194419.33+491257.0. This object turned out to be a very active SU UMa-type dwarf nova having a mean supercycle of about 150 d and frequent normal outbursts having intervals of 4-10 d. The object showed strong persistent signal of the orbital variation with a period of 0.0528164(4) d (76.06 min) and superhumps with a typical period of 0.0548 d during superoutbursts. Most of the superoutbursts were accompanied by a precursor outburst. All these features are unusual for this very short orb…
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 …
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…
We found that the SU UMa-type dwarf nova NY Ser in the period gap [orbital period 0.097558(6) d] showed standstills twice in 2018. This is the first clear demonstration of a standstill occurring between superoutbursts of an SU UMa-type dwarf nova. There was no sign of superhumps during the standstill, and at least one superoutburst directly started from the standstill. This provides strong evidence that the 3:1 resonance was excited during standstills. This phenomenon indicates that the disk radius can grow during standstills. We also interpret that the condition close to the limit of the tida…
We present photometric study of NY Ser, an in-the-gap SU UMa-type nova, in 2002 and 2013. We determined the duration of the superoutburst and the mean superhump period to be 18 d and 0.10458 d, respectively. We detected in 2013 that NY Ser showed two distinct states separated by the superoutburst. A state of rather infrequent normal outbursts lasted at least 44 d before the superoutburst and a state of frequent outbursts started immediately after the superoutburst and lasted at least for 34 d. Unlike a typical SU UMa star with bimodal distribution of the outbursts duration, NY Ser displayed a …
ER Ursae Majoris is the prototype for a subset of SU UMa-type dwarf novae characterized by short cycle times between outburst, high outburst frequency, and ``negative'' superhumps. It suffers superoutbursts every 43 days, lasting 20 days, normal outbursts every 4 days and has an outburst amplitude of 3 magnitudes. We have carried out a far ultraviolet (FUV) spectral analysis of ER UMa in quiescence, by fitting Far Ultraviolet Spectroscopic Explorer (FUSE) and International Ultraviolet Explorer (IUE) spectra with model accretion disks and high gravity photosphere models. Using the Gaia parallax…
We report photometry of three outbursts of NN Cam in 2007, 2008 and 2009. The 2007 event started with a normal outburst, lasting about 4 days, which was a precursor to a superoutburst lasting at least 13 days. Both the precursor and the superoutburst had an amplitude of 4.9 mag above mean quiescence. Superhumps with a maximum peak-to-peak amplitude of 0.22 mag were detected during the superoutburst with a mean superhump period Psh = 0.07385(56) d. Psh decreased continuously with dPsh /dt = -1.72(23) x 10-3. We used our measurement to confirm that the shorter of two possible values of Porb repo…
We report CCD photometry of the superoutburst of the dwarf nova V1212 Tau obtained during 2011 January and February. The outburst amplitude was at least 6 magnitudes and it lasted at least 12 days. Three distinct superhump regimes were observed. Initially low amplitude superhumps (0.03 to 0.05 magnitude peak-to-peak) with Psh = 0.0782(52) d were present. The superhumps reached a maximum amplitude of 0.31 magnitudes at the beginning of the plateau phase, with Psh = 0.07031(96) d. Subsequently the star began to fade slowly. During the first part of the decline, the period increased with dPsh/dt …
BO Cet is renowned cataclysmic variable having an orbital period above the period gap (0.139835 d) and showing both features of a Z Cam/IW And star and an SU UMa star. Using the Asteroid Terrestrial-impact Last Alert System (ATLAS) forced photometry and the All-Sky Automated Survey for Supernovae (ASAS-SN) Sky Patrol data, I found that BO Cet underwent a superoutburst in 2022 October-November after a series of short, normal outbursts with increasing amplitudes. This sequence of outbursts (supercycle) is what is seen in many SU UMa stars and this observation strengthened the suggestion that the…
We report results of an extensive world-wide observing campaign devoted to a very active dwarf nova star - IX Draconis. We investigated photometric behaviour of the system to derive its basic outburst properties and understand peculiarities of IX Dra as well as other active cataclysmic variables, in particular dwarf novae of the ER Uma-type. In order to measure fundamental parameters of the system, we carried out analyses of the light curve, O-C diagram, and power spectra. During over two months of observations we detected two superoutbursts and several normal outbursts. The V magnitude of the…
Analysis of observations of the SU UMa-type dwarf nova, CP Dra, between February 2001 and April 2009 has revealed 15 outbursts, at least eight of which were superoutbursts. The supercycle length is 230+/-56 d. We report photometry of the 2001 and 2009 superoutbursts which shows that they were remarkably similar to each other in terms of the profile of the outburst light curve and the evolution of the superhumps. The outburst amplitude was 5.5 magnitudes and the Psh during the plateau phase was measured at 0.08335(31) and 0.08343(21) d, respectively. In both cases, Psh decreased during the cour…
We observed the deeply eclipsing SU UMa-type dwarf nova V4140 Sgr and established the very short supercycle of 69.7(3) d. There were several short outbursts between superoutbursts. These values, together with the short orbital period (0.06143 d), were similar to, but not as extreme as, those of ER UMa-type dwarf novae. The object is thus the first, long sought, eclipsing ER UMa-like object. This ER UMa-like nature can naturally explain the high (apparent) quiescent viscosity and unusual temperature profile in quiescence, which were claimed observational features against the thermal-tidal insta…
CCD photometric observations of the dwarf nova V1006 Cyg were carried out in 2015-2017 with 11 telescopes located at 7 observatories. They covered the 2015 superoutburst with rebrightening, five normal outbursts of ~4-day duration and one wide outburst that lasted at least seven days. The interval between normal outbursts was 16 and 22 days, and between superoutbursts is expected to be longer than 124 days. The positive superhumps with the mean period of 0^d.10544(10) and 0^d.10406(17) were detected during the 2015 superoutburst and during the short-term quiescence between rebrightening and th…
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…
We observed the 2014 superoutburst of the SU UMa-type intermediate polar CC Scl. We detected superhumps with a mean period of 0.05998(2) d during the superoutburst plateau and during three nights after the fading. During the post-superoutburst stage after three nights, a stable superhump period of 0.059523(6) d was detected. We found that this object is an eclipsing system with an orbital period of 0.058567233(8) d. By assuming that the disk radius in the post-superoutburst phase is similar to those in other SU UMa-type dwarf novae, we obtained a mass ratio of q=0.072(3) from the dynamical pre…
We summarize the results of a 20-year campaign to study the light curves of BK Lyncis, a nova-like star strangely located below the 2-3 hour orbital period gap in the family of cataclysmic variables. Two apparent "superhumps" dominate the nightly light curves - with periods 4.6% longer, and 3.0% shorter, than P_orb. The first appears to be associated with the star's brighter states (V~14), while the second appears to be present throughout and becomes very dominant in the low state (V~15.7). Starting in the year 2005, the star's light curve became indistinguishable from that of a dwarf nova - i…
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）
We revisit the issue of period variation of the recently claimed red nova precursor candidate KIC 9832227. By using the data gathered during the main mission of the Kepler satellite, those collected by ground-based wide-field surveys and other monitoring programs (such as ASAS-SN), we find that the currently available timing data strongly support a model consisting of the known W UMa binary and a distant low-mass companion with an orbital period of ~13.5 years. The period of the W UMa component exhibits a linear period decrease with a pace of (1.10+/-0.05)x10^{-6} days per year, within the ran…
We present the analysis of hot spot brightness in light curves of the eclipsing dwarf nova IY Ursae Majoris during its normal outburst in March 2013 and in quiescence in April 2012 and in October 2015. Examination of four reconstructed light curves of the hot spot eclipses showed directly that the brightness of the hot spot changed significantly only during the outburst. The brightness of the hot spot, before and after the outburst, was on the same level. Hereby, based on the behaviour of the hot spot, IY UMa during its normal outburst follows the disk-instability model.
We present 8--12\,GHz radio light curves of five dwarf nova (DN) type Cataclysmic Variable stars (CVs) in outburst (RX And, U Gem and Z Cam), or superoutburst (SU UMa and YZ Cnc), increasing the number of radio-detected DN by a factor of two. The observed radio emission was variable on time-scales of minutes to days, and we argue that it is likely to be synchrotron emission. This sample shows no correlation between the radio luminosity and optical luminosity, orbital period, CV class, or outburst type; however higher-cadence observations are necessary to test this, as the measured luminosity i…
CzeV404 is an SU UMa-type dwarf nova in the period gap. Kara et al. (2021) (arXiv:2107.02664) recently published photometric and spectroscopic observations and obtained a mass ratio q=0.16, which is in severe disagreement of q~0.32 estimated from superhump observations (Bakowska et al., 2014). I here present what analysis was wrong or outdated in Bakowska et al. (2014) and provide a new value of q=0.247(5), consistent with the known behavior of superhumps and the evolution of cataclysmic variables. CzeV404 does not look like an unusual dwarf nova as suggested by Kara et al. (2021) and I discus…
WFI J161953.3+031909 was considered to be an eclipsing novalike object in the period gap. Using the Zwicky Transient Facility (ZTF) public database, I found that this object is the first eclipsing Z Cam star in the period gap, and is also most likely an ER UMa star with supercycles of 60-80 d. The longest outburst (most likely a superoutburst) comprised 35-46% of the supercycle in the extreme case. If superhumps are confirmed, this becomes the second object showing both ER UMa and Z Cam states after NY Ser. These objects have anomalously high mass-transfer rates despite that they are in the pe…
The SW Sex stars are a class of cataclysmic variables, originally identified because they shared a number of enigmatic properties - most notably, single-peaked emission lines instead of the double-peaked lines one would expect from their high-inclination accretion discs. We present high time-resolution spectrophotometry of the eclipsing nova-like variables SW Sex and DW UMa, two of the founding members of the SW Sex class. Both systems show single-peaked Balmer and HeII 4686A emission lines that appear to originate from a region in the disc that lies close to, but downstream of, the bright spo…
Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences（保加利亚科学院天文学研究所和国家天文台）；Department of Physics and Astronomy, Shumen University ”Episkop Konstantin Preslavski”（舒门大学“埃皮斯科普·康斯坦丁·普雷斯拉夫斯基”物理与天文学系）
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…
Results of the CCD observations of CzeV404 Her are displayed. During the season of June-August 2014 we detected one outburst and one superoutburst of the star. Clear superhumps with the period of P_sh=0.10472(2) days were observed. The superhump period was decreasing with a high value of P_dot=-2.43(8) x 10^(-4). For 17 eclipses, we calculated an orbital period with the value of P_orb=0.0980203(6) days which indicates that CzeV404 Her belongs to period gap objects and it is the longest orbital period eclipsing SU UMa star. Based on superhump and orbital period determinations, the period excess…
We analysed Kepler data of two similar dwarf novae V344 Lyr and V1504 Cyg in order to study optical fast stochastic variability (flickering) by searching for characteristic break frequencies in their power density spectra. Two different stages of activity were analysed separately, i.e. regular outbursts and quiescence. Both systems show similar behaviour during both activity stages. The quiescent power density spectra show a dominant low break frequency which is also present during outburst with a more or less stable value in V344 Lyr while it is slightly higher in V1504 Cyg. The origin of thi…
The standard disk is often inadequate to model disk-dominated cataclysmic variables (CVs) and generates a spectrum that is bluer than the observed UV spectra [Puebla et al 2007]. X-ray observations of these systems reveal an optically thin boundary layer (BL) expected to appear as an inner hole in the disk. Consequently, we truncate the inner disk. However, instead of removing the inner disk, we impose the no-shear boundary condition at the truncation radius, thereby lowering the disk temperature and generating a spectrum that better fits the UV data. With our modified disk, we analyze the arc…
We have selected three nova-like variables at the long period extreme of nova-like orbital periods: V363 Aur, RZ Gru and AC Cnc, all with IUE archival far ultraviolet spectra. All are UX UMa type nova-like variables and all have $P_{orb} > 7$h. V363 Aur is a bona fide SW Sex star, and AC Cnc is a probable one, while RZ Gru has not proven to be a member of the SW Sex subclass. We have carried out the first synthetic spectral analysis of far ultraviolet spectra of the three systems using state-of-the-art models both of accretion disks and white dwarf photospheres. We find that the FUV spectral e…
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.
We present the results of a multi-component synthetic spectral analysis of the archival far ultraviolet spectra of several key nova-like variables including members of the SW Sex, RW Tri, UX UMa and VY Scl subclasses: KR Aur, RW Tri, V825 Her, V795 Her, BP Lyn, V425 Cas and HL Aqr. Accretion rates as well as the possible flux contribution of the accreting white dwarf are included in our analysis. Except for RW Tri which has a reliable trigonometric parallax, we computed the distances to the nova-like systems using the method of Knigge (2006). Our analysis of seven archival IUE spectra of RW Tr…
During July 2009 we observed the first confirmed superoutburst of the eclipsing dwarf nova SDSS J150240.98+333423.9 using CCD photometry. The outburst amplitude was at least 3.9 magnitudes and it lasted at least 16 days. Superhumps having up to 0.35 peak-to-peak amplitude were present during the outburst, thereby establishing it to be a member of the SU UMa family. The mean superhump period during the first 4 days of the outburst was Psh = 0.06028(19) d, although it increased during the outburst with dPsh/dt = + 2.8(1.0) x 10-4. The orbital period was measured as Porb = 0.05890946(5) d from ti…
