We report the discovery of a one magnitude increase in the optical brightness of the 59.63 minute orbital period AM CVn binary SDSS J113732.32+405458.3. Public $g$, $r$, and $i$ band data from the Zwicky Transient Facility (ZTF) exhibit a decline over a 300 day period, while a few data points from commissioning show that the peak was likely seen. Such an outburst is likely due to a change in the state of the accretion disk, making this the longest period AM CVn binary to reveal an unstable accretion disk. The object is now back to its previously observed (by SDSS and PS-1) quiescent brightness that is likely set by the accreting white dwarf. Prior observations of this object also imply that the recurrence times for such outbursts are likely more than 12 years.
We report on multi-wavelength observations during quiescence and of the first detected outburst of the ~60 min orbital period AM CVn SDSS J113732+405458. Using X-ray and UV observations we determined an upper limit duration of the event of about one year. The amplitude of the outburst was remarkably small, of around one magnitude in r and 0.5 magnitudes in g. We have also investigated the color variations of SDSS J113732+405458 and other long period AM CVns in outbursts and identified a track on the color-magnitude diagram that is not compatible with the predictions of the disk instability mod…
Using \emph{TESS} we are doing a systematic study of outbursting AM~CVn systems to place some limits on the current outbursts models. We present the \emph{TESS} light curve (LC) for 9 AM~CVns showing both superoutbursts (SOs) and normal outbursts (NOs). The continuous coverage of the outbursts with \emph{TESS} allows us to place stringent limits on the duration and structures of the SOs and the NOs. We present evidence that in at least some of the systems enhanced mass transfer (EMT) has to be taken into account to explain the observed LC of the SOs and rebrighthening phase after the SOs. For …
We briefly summarize the observational properties of ultra-compact binaries called AM CVn stars. We analize their outbursts originating from the thermal-viscous instability in helium accretion disc. We present our preliminary results in applying the model of Dwarf Novae outbursts to helium discs. We can calculate models of outbursts of reasonable amplitude of 2 mag with a constant alfa parameter throughout the calculation. Setting the mass transfer rate close to its upper critical value produces model lightcurves that resemble short superoutbursts.
ASASSN-21au is an ultracompact accreting white dwarf binary (AM CVn) with a period of approx. 58 min. Using multiwavelength observations of the system, we discovered a dichotomy in the behavior of outbursts in AM CVns. The binary showed an initial brightness increase which lasted for at least 82 days, followed by an additional increase which lasted 2 weeks. Afterwards ASASSN-21au went into superoutburst with a total duration of 19 days, showing an amplitude with respect to quiescence of approx. 7.5 mags in g, with a precursor and an echo outburst. A correlation between X-rays, UV and optical w…
We report unfiltered photometry of the first confirmed outburst of the AM CVn system SDSS J012940.05+384210.4 during 2009 December. At its brightest the star was magnitude 14.5, 5.4 magnitudes above mean quiescence. Although the first part of the outburst was not observed, six remarkable rebrightening events were observed during the course of the outburst. Forty-one days after the outburst was detected, the star was still 1.7 magnitudes above quiescence. Superhumps were observed during the outburst with a peak-to-peak amplitude of 0.06 mag and Psh = 37.9(2) min. We also used archival data to s…
The AM CVn systems are a class of He-rich, post-period minimum, semi-detached, ultra-compact binaries. Their long-term light curves have been poorly understood due to the few systems known and the long (hundreds of days) recurrence times between outbursts. We present combined photometric light curves from the LINEAR, CRTS, and PTF synoptic surveys to study the photometric variability of these systems over an almost 10 yr period. These light curves provide a much clearer picture of the outburst phenomena that these systems undergo. We characterize the photometric behavior of most known outburst…
We present extensive photometric and spectroscopic observations of PTF1 J071912.13+485834.0, an outbursting AM CVn system discovered by the Palomar Transient Factory (PTF). AM CVn systems are stellar binaries with some of the smallest separations known and orbital periods ranging from 5 to 65 minutes. They are believed to be composed of a white dwarf accretor and a (semi)-degenerate He-rich donor and are considered to be the helium equivalents of Cataclysmic Variables. We have spectroscopically and photometrically identified an orbital period of 26.77 \pm 0.02 minutes for PTF1 J071912.13+48583…
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 results of our analysis of up to 15 years of photometric data from eight AM CVn systems with orbital periods between 22.5 and 26.8 min. Our data has been collected from the GOTO, ZTF, Pan-STARRS, ASAS-SN and Catalina all-sky surveys and amateur observations collated by the AAVSO. We find evidence that these interacting ultra-compact binaries show a similar diversity of long term optical properties as the hydrogen accreting dwarf novae. We found that AM CVn systems in the previously identified accretion disc instability region are not a homogenous group. Various members of the analys…
The AM Canum Venaticorum (AM CVn) binaries are a rare group of hydrogen-deficient, ultra-short period, mass-transferring white dwarf binaries, and are possible progenitors of type Ia supernovae. We present time-resolved spectroscopy of the recently-discovered AM CVn binary SDSS J173047.59+554518.5. The average spectrum shows strong double-peaked helium emission lines, as well as a variety of metal lines, including neon; this is the second detection of neon in an AM CVn binary, after the much brighter system GP Com. We detect no calcium in the accretion disc, a puzzling feature that has been no…
The AM Canum Venaticorum (AM CVn) binaries are a rare group of ultra-short period, mass-transferring white dwarf binaries, some of which may be Type Ia supernova progenitors. More than a third of the total known population of AM CVn binaries have been discovered via the Sloan Digital Sky Survey (SDSS). Here, we discuss our search for new AM CVns in the SDSS spectroscopic data base, and present two new AM CVns discovered in SDSS-III spectroscopy, SDSS J113732.32+405458.3 and SDSS J150551.58+065948.7. The AM CVn binaries exhibit a connection between their spectral appearance and their orbital pe…
We present our observational results of AM CVn star CR Boo in the UBVR bands. Our observational campaign includes data obtained over 5 nights with the National Astronomical Observatory Rozhen, Belogradchik and the AS Vidojevica telescopes. During the whole time of our observations the brightness of the system varied between $13.95 - 17.23$ in B band. We report the appearance of humps during the period of quiescence and superhumps during the active state of the object, (where the latter are detected in two nights). We obtain the superhumps periodicity for two nights, $P_{sh}\approx 24.76 - 24.9…
We report on PTF1 J191905.19+481506.2, a newly discovered, partially eclipsing, outbursting AM CVn system found in the Palomar Transient Factory synoptic survey. This is only the second known eclipsing AM CVn system. We use high-speed photometric observations and phase-resolved spectroscopy to establish an orbital period of 22.4559(3) min. We also present a long-term light curve and report on the normal and super-outbursts regularly seen in this system, including a super-outburst recurrence time of 36.8(4) d. We use the presence of the eclipse to place upper and lower limits on the inclination…
We present the results of a two and a half year optical photometric monitoring programme covering 16 AM CVn binaries using the Liverpool Telescope on La Palma. We detected outbursts in seven systems, one of which (SDSS J0129) was seen in outburst for the first time. Our study coupled with existing data shows that ~1/3 of these helium-rich accreting compact binaries show outbursts. The orbital period of the outbursting systems lie in the range 24-44 mins and is remarkably consistent with disk-instability predictions. The characteristics of the outbursts seem to be broadly correlated with their …
We present the latest results from a spectroscopic survey designed to uncover the hidden population of AM Canum Venaticorum (AM CVn) binaries in the photometric database of the Sloan Digital Sky Survey (SDSS). We selected ~2000 candidates based on their photometric colours, a relatively small sample which is expected to contain the majority of all AM CVn binaries in the SDSS (expected to be ~50). We present two new candidate AM CVn binaries discovered using this strategy: SDSS J104325.08+563258.1 and SDSS J173047.59+554518.5. We also present spectra of 29 new cataclysmic variables, 23 DQ white…
We report on two superoutbursts of the AM CVn-type object CR Boo in 2014 April--March and 2015 May--June. A precursor outburst acompanied both of these superoutbursts. During the rising branch of the main superoutburst in 2014, we detected growing superhumps (stage A superhumps) whose period was $0.017669(24)$ d. Assuming that this period reflects the dynamical precession rate at the radius of the 3:1 resonance, we could estimate the mass ratio ($q=M_2/M_1$) of 0.101(4) by using the stage A superhump period and the orbital one of 0.0170290(6) d. This mass ratio is consistent with that expected…
We report on a superoutburst of the AM CVn-type object SDSS J090221.35+381941.9 [J0902; orbital period 0.03355(6) d] in 2014 March-April. The entire outburst consisted of a precursor outburst and the main superoutburst, followed by a short rebrightening. During the rising branch of the main superoutburst, we detected growing superhumps (stage A superhumps) with a period of 0.03409(1) d. During the plateau phase of the superoutburst, superhumps with a shorter period (stage B superhumps) were observed. Using the orbital period and the period of the stage A superhumps, we were able to measure the…
Using Zwicky Transient Facility (ZTF) data, I noticed that MGAB-V240 = PS1-3PI J185529.82+323017.8 showed two different states: regularly outbursting state with a cycle length of 12 d and standstills. I found that the regularly outbursting state was in fact a sequence of superoutburst and intervening normal outbursts comprising a 12 d supercycle. During one of the superoutbursts, superhumps with a period of 0.015824(9) d (=22.79 min) were detected in the ZTF time-resolved data. This period and behavior have confirmed that MGAB-V240 is an AM CVn-type object with the shortest known supercycle an…
SDSS J141118.31+481257.6 is an ultracompact white dwarf binary (or AM CVn system) with an orbital period of 46 min. We analyze ~23 ks of X-ray and UV data taken with the Neil Gehrels Swift Observatory during its first ever recorded outbursts. The events took place 13 years after the system was discovered. We detected 3 events in our UV data, all with amplitudes of ~7 mags with respect to quiescence, the largests detected for an AM CVn system so far. The first 2 events correspond to a superoutburst and the third one to another detected outburst. The 3 episodes that we identified occurred in a p…
Ultracompact accreting binary systems each consist of a stellar remnant accreting helium-enriched material from a compact donor star. Such binaries include two related sub-classes, AM CVn-type binaries and helium cataclysmic variables, in both of which the central star is a white dwarf. We present a spectroscopic and photometric study of six accreting binaries with orbital periods in the range of 40--70 min, including phase-resolved VLT spectroscopy and high-speed ULTRACAM photometry. Four of these are AM CVn systems and two are helium cataclysmic variables. For four of these binaries we are a…
We identified that ASASSN-14cc is a very active dwarf nova spending approximately 60% of the time in outburst. Our long-term photometry revealed that the object shows long outbursts recurring with a period of 21-33 d and very brief short outbursts lasting less than 1 d. The maximum decline rate exceeds 2.8 mag/d. The duration of long outbursts is 9-18 d, comprising 50-60% of the recurrence time of long outbursts. We detected 0.01560-0.01562 d (22.5 min) modulations during long outbursts, which we identified to be superhumps. These features indicate that ASASSN-14cc has outburst parameters very…
We present three new candidate AM CVn binaries, plus one confirmed new system, from a spectroscopic survey of color-selected objects from the Sloan Digital Sky Survey. All four systems were found from their helium emission lines in low-resolution spectra taken on the Hale telescope at Palomar, and the Nordic Optical Telescope and the William Herschel Telescope on La Palma. The ultra-compact binary nature of SDSS J090221.35+381941.9 was confirmed using phase-resolved spectroscopy at the Keck-I telescope. From the characteristic radial velocity `S-wave' observed in the helium emission lines we m…
We report the discovery and characterisation of a deeply eclipsing AM CVn-system, Gaia14aae (= ASSASN-14cn). Gaia14aae was identified independently by the All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al. 2014) and by the Gaia Science Alerts project, during two separate outbursts. A third outburst is seen in archival Pan-STARRS-1 (PS1; Schlafly et al. 2012; Tonry et al. 2012; Magnier et al. 2013) and ASAS-SN data. Spectroscopy reveals a hot, hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting double degenerate classification. We use …
Phase-resolved spectroscopy of four AM CVn systems obtained with the William Herschel Telescope and the Gran Telescopio de Canarias (GTC) is presented. SDSS\,J120841.96+355025.2 was found to have an orbital period of 52.96$\pm$0.40\,min and shows the presence of a second bright spot in the accretion disc. The average spectrum contains strong Mg\,{\sc i} and Si\,{\sc i/ii} absorption lines most likely originating in the atmosphere of the accreting white dwarf. SDSS\,J012940.05+384210.4 has an orbital period of 37.555$\pm$0.003 min. The average spectrum shows the Stark broadened absorption lines…
{\it Kepler} satellite photometry and phase-resolved spectroscopy of the ultracompact AM CVn type binary SDSS J190817.07+394036.4 are presented. The average spectra reveal a variety of weak metal lines of different species, including silicon, sulphur and magnesium as well as many lines of nitrogen, beside the strong absorption lines of neutral helium. The phase-folded spectra and the Doppler tomograms reveal an S-wave in emission in the core of the He I 4471 Å\,absorption line at a period of $P_{\rm orb}=1085.7\pm2.8$\,sec identifying this as the orbital period of the system. The Si II, Mg II …
Recent work by Levitan et al has expanded the long-term photometric database for AM CVn stars. In particular, their outburst properties are well-correlated with orbital period, and allow constraints to be placed on the secular mass transfer rate between secondary and primary if one adopts the disk instability model for the outbursts. We use the observed range of outbursting behavior for AM CVn systems as a function of orbital period to place a constraint on mass transfer rate versus orbital period P. We infer a rate ~5 x 10^{-9} Msun/yr (P/1000 s)^{-5.2}. We show the functional form so obtaine…
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 optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141.18$-$014120.9 (J0751) is an eclipsing double WD binary containing a 0.19 Msol WD with a 0.97 Msol companion in a 1.9 h orbit. J0751 becomes the fifth eclipsing double WD system currently known. SDSS J174140.49+652638.7 (J1741) is another binary containing a 0.17 Msol WD with an unseen M > 1.11 Msol WD companion in a 1.5 h orbit. With a mass ratio of ~0.1, J1741 …
SDSS J080710+485259 is the longest period outbursting ultracompact white dwarf binary. Its first ever detected superoutburst started in November of 2018 and lasted for a year, the longest detected so far for any short orbital period accreting white dwarf. Here we show that the superoutburst duration of SDSS J080710+485259 exceeds the 2 months viscous time of its accretion disk by a factor of about 5. Consequently it follows neither the empirical relation nor the theoretical relation between the orbital period and the superoutburst duration for AM CVn systems. Six months after the end of the su…
We report unfiltered photometry during the first confirmed superoutburst of the recently discovered dwarf nova, SDSS J073208.11+413008.7 and conclude that it is a member of the SU UMa family. At its brightest, the star was magnitude 15.7. The outburst amplitude was nearly 5 magnitudes and it lasted about 14 days. We determined the mean superhump period from our first 3 nights of observations as Psh = 0.07979(19) d, however analysis of the O-C residuals showed a dramatic evolution in Psh during the outburst. During the first part of the plateau phase the period increased with dPsh/dt = +2.81(9)…
SDSS J080434.20+510349.2 is the 13th dwarf nova containing a pulsating white dwarf. Among the accreting pulsators that have experienced a dwarf novae outburst, SDSS J0804 has the most dramatic history of events within a short time scale: the 2006 outburst with 11 rebrightenings, series of December 2006 - January 2007 mini-outbursts, the 2010 outburst with 6 rebrightenings. Over 2006-2011, SDSS J080434.20+510349.2 in addition to positive 0.060^d superhumps during the outburst and 1-month post-outburst stage, 0.059005^d orbital humps in quiescence, displayed a significant short-term variations w…
Cataclysmic variable SDSS J143317.78+101123.3 with P=0.054241 d (78.1-min) was suspected to be a possible dwarf nova of WZ Sge type with the sub-stellar donor, but without detected outbursts so far. Checking the newly available data from ATLAS survey has revealed the outburst by at least 6 magnitudes in September 2020, thus confirming the dwarf nova nature of this object with the brown dwarf secondary. Other projects and individual observers have stopped their monitoring of this target several days before the outburst. This finding strengthens the value of observing the twilight zone by the pr…
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…
By cross matching blue objects from SDSS with GALEX and the astrometric catalogues USNO-B1.0, GSC2.3 and CMC14, 64 new dwarf nova candidates with one or more observed outbursts have been identified. 14 of these systems are confirmed as cataclysmic variables through existing and follow-up spectroscopy. A study of the amplitude distribution and an estimate of the outburst frequency of these new dwarf novae and those discovered by the Catalina Real-time Transient Survey (CRTS) indicates that besides systems that are faint because they are farther away, there also exists a population of intrinsica…
We present an ultraviolet spectrum and light curve of the short orbital period cataclysmic variable EZ Lyn obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope 14 months after its dwarf nova outburst, along with ground-based optical photometry. The UV spectrum can be fit with a 13,100K, log g=8 white dwarf using 0.5 solar composition, while fits to the individual lines are consistent with solar abundance for Si and Al, but only 0.3 solar for C. The Discrete Fourier Transforms of the UV and optical light curves at 14 months following outburst show a prominent period at 25…
AM Canum Venaticorum (AM CVn) stars belong to a class of ultra-compact, short period binaries with spectra dominated largely by helium. SDSS J0926+3624 is of particular interest as it is the first observed eclipsing AM CVn system. We observed SDSS J0926+3624 with the \textbf{Ar}ray \textbf{C}amera for \textbf{O}ptical to \textbf{N}ear-IR \textbf{S}pectrophotometry (ARCONS) at the Palomar 200" telescope. ARCONS uses a relatively new type of energy-resolved photon counters called Microwave Kinetic Inductance Detectors (MKIDs). ARCONS, sensitive to radiation from 350 to 1100 nm, has a time resolu…
COPAS: Compact Objects and the Physics of Accretion Survey I. Accreting Binaries with P < 83 Minutes
University of Texas Rio Grande Valley（德克萨斯大学里奥格兰德河谷分校）；South Texas Space Science Institute, University of Texas Rio Grande Valley（南德克萨斯空间科学研究所，德克萨斯大学里奥格兰德河谷分校）；Universidad de La Laguna（拉帕鲁纳大学）；Instituto de Astrofísica de Canarias (IAC)（加那利群岛天体物理研究所）；Texas Tech University（德克萨斯理工大学）；Universidad Nacional Autónoma de México, Instituto de Astronomía（墨西哥国立自治大学，天文研究所）；Durham University（杜伦大学）；Institute of Space Sciences (ICE, CSIC)（空间科学研究所（ICE，CSIC））
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 unfiltered CCD photometry of the eclipsing dwarf nova SDSS J093249.57+472523.0 obtained during its first confirmed outburst in 2011 March. The outburst amplitude was at least 3.0 magnitudes above mean quiescence and it lasted at least 11 days, although we missed the beginning of the outburst. Superhumps having peak-to-peak amplitude up to 0.3 magnitudes were present during the outburst, thereby establishing it to be a member of the SU UMa family. The mean superhump period was Psh = 0.06814(11) d. Analysis of our measurements of eclipse times of minimum, supplemented with data from ot…
On April 23, 2014, the Swift satellite responded to a hard X-ray transient detected by its Burst Alert Telescope, which turned out to be a stellar flare from a nearby, young M dwarf binary DG~CVn. We utilize observations at X-ray, UV, optical, and radio wavelengths to infer the properties of two large flares. The X-ray spectrum of the primary outburst can be described over the 0.3-100 keV bandpass by either a single very high temperature plasma or a nonthermal thick-target bremsstrahlung model, and we rule out the nonthermal model based on energetic grounds. The temperatures were the highest s…
We report unfiltered photometry of SDSS J112003.40+663632.4 during the 2011 February outburst which revealed the presence of superhumps with peak-to-peak amplitude of up to 0.22 magnitudes showing this to be an SU UMa type dwarf nova. The outburst amplitude was 5.4 magnitudes above mean quiescence and it lasted at least 12 days. The mean superhump period during the plateau phase was Psh = 0.07057(19) d.
We present time resolved photometry of the cataclysmic variable SDSS J081610.84+453010.2 and have established for the first time that it is an eclipsing dwarf nova. We observed an outburst of the system which lasted about 11 days and had an amplitude of 3.4 magnitudes above mean quiescence. From an analysis of the eclipse times of minimum during the outburst, we determined the orbital period as Porb = 0.2096(4) d or 5.030(10) h. The orbital period places it above the period gap in the distribution of orbital periods of dwarf novae. The eclipses are of short duration (average FWHM = 10.7 min or…
We present the discovery of SDSS J135154.46-064309.0, a short-period variable observed using 30-minute cadence photometry in K2 Campaign 6. Follow-up spectroscopy and high-speed photometry support a classification as a new member of the rare class of ultracompact accreting binaries known as AM CVn stars. The spectroscopic orbital period of $15.65 \pm 0.12$\,minutes makes this system the fourth-shortest period AM CVn known, and the second system of this type to be discovered by the Kepler spacecraft. The K2 data show photometric periods at $15.7306 \pm 0.0003$\,minutes, $16.1121 \pm 0.0004$\,mi…
The majority of cataclysmic variables are predicted to be post-period minimum systems with degenerate donor stars, the period bouncers. Owing to their intrinsic faintness, however, only a handful of these systems have so far been securely identified. We want to study the X-ray properties of two eclipsing period bouncers, OV Bootis and SDSS J103533.02+055158.3, that were selected for this study due to their proximity to Earth. We have obtained XMM-Newton phase-resolved X-ray and ultraviolet observations of the two objects for spectral and timing analysis. Owing to a recent dwarf nova outburst O…
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…
Gaia22ayj (=ZTF19aagmvuk) was detected as a transient on 2022 March 3 both by the Gaia satellite and the Zwicky Transient Facility (ZTF). I analyzed the past public ZTF data and found that Gaia22ayj showed coherent large-amplitude double-wave variations with a period of 0.00649910257(13) d = 9.36 min. The period can be either from the spin period of the white dwarf or the orbital period of the binary. I consider the latter possibility more likely based on the light curve resembling an eclipsing binary and on the stability of the profile. The presence of an outburst lasting at least ~1 d sugges…
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…
Using a machine learning (ML) method, we mine DB white dwarfs (DBWDs) from the Sloan Digital Sky Survey (SDSS) Data Release (DR) 12 and DR14. The ML method consists of two parts: feature extraction and classification. The least absolute shrinkage and selection operator (LASSO) is used for the spectral feature extraction by comparing high quality data of a positive sample group with negative sample groups. In both the training and testing sets, the positive sample group is composed of a selection of 300 known DBWDs, while the negative sample groups are obtained from all types of SDSS spectra. I…
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 present photometry of 11 and spectroscopy of 35 potential cataclysmic variables from the Sloan Digital Sky Survey, the Catalina Real-Time Transient Survey and vsnet-alerts. The photometry results include quasi-periodic oscillations during the decline of V1363 Cyg, nightly accretion changes in the likely Polar (AM Herculis binary) SDSS J1344+20, eclipses in SDSS J2141+05 with an orbital period of 76+/-2 min, and possible eclipses in SDSS J2158+09 at an orbital period near 100 min. Time-resolved spectra reveal short orbital periods near 80 min for SDSS J0206+20, 85 min for SDSS J1502+33, and …
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…
A New WZ Sagittae-type Dwarf Nova KSP-OT-202104a Near the Period Minimum from the KMTNet Supernova Program
Korea Astronomy and Space Science Institute（韩国天文与空间科学研究所）；Korea University of Science and Technology (UST)（韩国科学技术院）；Chungnam National University（忠南国立大学）；University of Toronto（多伦多大学）；University of California, Santa Barbara（加州大学圣塔芭芭拉分校）；Las Cumbres Observatory（拉斯孔布雷斯天文台）
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…
