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We present our optical photometric observations of the 2022 eruption of the recurrent nova U Scorpii (U Sco) using 49152 data points over 70 d following the optical peak. We have also analyzed its soft X-ray (0.3–1 keV) light curve by the Neil Gehrels Swift Observatory. During the 2022 eruption, the optical plateau stage started 13.8–15.0 d and ended 23.8–25.0 d after the optical peak. The soft X-ray stage started 14.6–15.3 d and ended 38.7–39.5 d after the optical peak. Both stages started later and had shorter durations, and the soft X-ray light curve peaked earlier and was less luminous compared to those during the U Sco 2010 eruption. These points suggest that there were differences in the envelope mass between the different cycles of the nova eruption. Furthermore, we have analyzed the optical eclipses during the 2022 eruption. The primary eclipse was first observed 10.4–11.6 d after the optical peak, earlier than the beginning of the optical plateau stage. This sequence of events can be explained by the receding ejecta photosphere associated with the expanding nova ejecta. We have determined the ingress and egress phases of the primary eclipses and estimated the outer radius of the optical light source centered at the white dwarf (WD). During the optical plateau stage, the source radius remained ∼1.2 times larger than the Roche volume radius of the primary WD, being close to the L1 point. When the optical plateau stage ended, the source radius drastically shrank to the tidal truncation radius within a few orbital periods. This previously unresolved phenomenon can be interpreted as a structural change in U Sco where the temporarily expanded accretion disk due to the nova wind returned to a steady state. [ABSTRACT FROM AUTHOR]

This document is an erratum for an article titled "Optical and soft X-ray light-curve analysis during the 2022 eruption of U Scorpii: Structural changes in the accretion disk." The erratum corrects an error in the email address that was mistakenly typed during the production process. The PDF and HTML versions of the original article have been updated with the correct email address. The article is authored by a diverse group of individuals from various institutions. [Extracted from the article]

The star KIC 8462852 (Boyajian's Star) displays both fast dips of up to 20 per cent on time-scales of days and long-term secular fading by up to 19 per cent on time-scales from a year to a century. We report on CCD photometry of KIC 8462852 from 2015.75 to 2018.18, with 19 176 images making for 1866 nightly magnitudes in BVRI. Our light curves show a continuing secular decline (by 0.023 ± 0.003 mags in the B band) with three superposed dips with duration 120–180 d. This demonstrates that there is a continuum of dip durations from a day to a century, so the secular fading is seen to be by the same physical mechanism as the short-duration Kepler dips. The BVRI light curves all have the same shape, with the slopes and amplitudes for VRI being systematically smaller than in the B band by factors of 0.77 ± 0.05, 0.50 ± 0.05, and 0.31 ± 0.05. We rule out any hypothesis involving occultation of the primary star by any star, planet, solid body, or optically thick cloud. But these ratios are the same as that expected for ordinary extinction by dust clouds. This chromatic extinction implies dust particle sizes going down to ∼0.1 micron, suggesting that this dust will be rapidly blown away by stellar radiation pressure, so the dust clouds must have formed within months. The modern infrared observations were taken at a time when there was at least 12.4 per cent ±1.3per cent dust coverage (as part of the secular dimming), and this is consistent with dimming originating in circumstellar dust. [ABSTRACT FROM AUTHOR]

We present optical photometry of superoutbursts that occurred in 2016 of two WZ Sge-type dwarf novae (DNe), ASASSN-16dt and ASASSN-16hg. Their light curves showed a dip in brightness between the first plateau stage with no ordinary superhumps (or early superhumps) and the second plateau stage with ordinary superhumps. We find that the dip is produced by the slow evolution of the 3 : 1 resonance tidal instability and that it would likely be observed in low mass-ratio objects. An estimated mass ratio (q ≡ M2/M1) from the period of developing (stage A) superhumps [0.06420(3) d] was 0.036(2) in ASASSN-16dt. Additionally, its superoutburst has many properties similar to those in other low-q WZ Sge-type DNe: long-lasting stage-A superhumps, small superhump amplitudes, long delay of ordinary-superhump appearances, and a slow decline rate in the plateau stage with superhumps. Its very small mass ratio and observational characteristics suggest that this system is one of the best candidates for a period bouncer--a binary accounting for the missing population of post-period minimum cataclysmic variables. Although it is not clearly verified due to the lack of detection of stage-A superhumps, ASASSN-16hg might be a possible candidate for period bouncers on the basis of the morphology of its light curves and the small superhump amplitudes. Many outburst properties of period bouncer candidates would originate from the small tidal effects of their secondary stars. [ABSTRACT FROM AUTHOR]

V1017 Sgr is a classical nova (from 1919) that displayed an earlier dwarf nova eruption (from 1901) and underwent two more dwarf nova events (in 1973 and 1991). Previous work on this bright system in quiescence (V = 13.5) has consisted only of a few isolated magnitudes, a few spectra and an ambiguous claim of an orbital period of 5.714 d based on nine radial velocities. To test this period, we have collected 2896 magnitudes (plus 53 in the literature) in the UBVRIJHKL bands from 1897-2016, making an essentially complete photometric history of this unique cataclysmic variable. We find that the light curve in all bands is dominated by the ellipsoidal modulations of a G giant companion star, with a post-eruption (after the 1919 nova event) orbital period of 5.786290 #&177; 0.000032 d. This is the longest period for any classical nova; the accretion must be powered by the nuclear evolution of the companion star and dwarf nova events occur only because the outer parts of the large disc are cool enough to be unstable. Further, we measure the pre-eruption orbital period (from 1907-1916). The orbital period has decreased by 273 #&177; 61 parts per million across the 1919 eruption, with the significance of the period change being at the 5.7σ confidence level. This is startling and mystifying for nova theory, because the three known period-change effects cannot account for a period decrease in V1017 Sgr, much less one of such a large size. [ABSTRACT FROM AUTHOR]

We present optical photometry of aWZ Sge-type dwarf nova (DN), ASASSN-15jd. Its light curve showed a small dip in the middle of the superoutburst in 2015 for the first time among WZ Sge-type DNe. The unusual light curve implies a delay in the growth of the 3 : 1 resonance tidal instability. Also, the light curve is similar to those of two other WZ Sge-type stars, SSS J122221.7-311523 and OT J184228.1+483742, which are believed to be the best candidates for period bouncers on the basis of their small values of the mass ratio (q ≡ M2/M1). Additionally, the small mean superhump amplitude (<0.1mag) and the long duration of no ordinary superhumps at the early stage of its superoutburst are common to the best candidates for period bouncers. Its average superhump period was Psh = 0.0649810(78) d and no early superhumps were detected. Although we could not estimate a mass ratio of ASASSN-15jd with high accuracy, this object is expected to be a candidate for a period bouncer--a binary accounting for the missing population of post-period minimum cataclysmic variables--based on the above characteristics. [ABSTRACT FROM AUTHOR]

We observed the first-ever recorded outburst of PM J03338+3320, the cataclysmic variable selected by proper-motion survey. The outburst was composed of a precursor and the main superoutburst. The precursor outburst occurred at least 5 d before the maximum of the main superoutburst. Despite this separation, long-period superhumps were continuously seen between the precursor and main superoutburst. The period of these superhumps is longer than its orbital period by 6.0(1)% and can be interpreted to reflect the dynamical precession rate at the 3 : 1 resonance for a mass ratio of 0.172(4). These superhumps smoothly evolved into those in the main superoutburst. These observations provide the clearest evidence that the 3 : 1 resonance is triggered by the precursor outburst, even if it is well separated, and the resonance eventually causes themain superoutburst as predicted by the thermaltidal instability model. The presence of superhumps well before the superoutburst cannot be explained by alternative models (the enhanced mass-transfer model and the pure thermal instability one) and the present observations clearly support the thermaltidal instability model. [ABSTRACT FROM AUTHOR]

In 2015 March, the notable WZSge-type dwarf nova ALCom exhibited an unusual outburst with a recurrence time of ~1.5 yr, which is the shortest interval of superoutbursts among WZSge-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 WZSge-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 following the precursor. The initial part of the outburst is indistinguishable from those of superoutbursts of ordinary SUUMa-type dwarf novae. This observation supports the interpretation that the 2:1 resonance suppresses a growth of ordinary superhumps. The estimated superhump period and superhump period derivative are Psh = 0.0573185(11) d and Pdot=+1.5(3.1)?10-5, respectively. These values indicate that the evolution of ordinary superhumps is the same as that in past superoutbursts with much larger extent. Although the light curve during the plateau stage was typical for an SUUMa-type dwarf nova, this superoutburst showed a rebrightening, together with a regrowth of the superhumps. The overall light curve of the rebrightening was the almost the same as those observed in previous rebrightenings. This implies that the rebrightening type is inherent in the system. [ABSTRACT FROM AUTHOR]

We report on photometric observations of two dwarf novae, OT J075418.7+381225 and OT J230425.8+062546, which showed superoutbursts in 2013 (OT J075418) and in 2011 (OT J230425). Their mean periods of the superhump were 0.0722403(26) d (OT J075418) and 0.067317(35) d (OT J230425). These objects showed a very long growth stage of the superhump (stage A) and a large period decrease in the stage A–B transition. The long stage A suggests slow evolution of the superhump due to the very small mass ratio of these objects. The declining rates during the plateau phase in the superoutburst of these objects were lower than those of SU UMa-type dwarf novae (DNe) with a similar superhump period. These properties were similar to those of SSS J122221.7−311523, the most likely candidate for the period bouncer. Therefore, these two DNe are regarded as likely candidates for the period bouncer. We estimated the number density of period bouncers roughly from our observations for the last five years. There is a possibility that these WZ Sge-type DNe with unusual outburst properties might account for the missing population of the period bouncer suggested by the evolutionary scenario. [ABSTRACT FROM AUTHOR]