Using data from the Complete Nearby (z_host<0.02) sample of Type Ia Supernovae (CNIa0.02), we discover a linear relation between two parameters derived from the B-V color curves of Type Ia supernovae: the "color stretch" s_BV and the rising color slope s_0^*(B-V) after the peak, and this relation applies to the full range of s_BV. The s_BV parameter is known to be tightly correlated with the peak luminosity, and especially for "fast decliners" (dim Type Ia supernovae), and the luminosity correlation with s_BV is markedly better than with the classic light-curve width parameters such as Δm_15(B). Thus our new linear relation can be used to infer peak luminosity from s_0^*. Unlike s_BV (or Δm_15), the measurement of s_0^*(B-V) does not rely on the well-determined time of light-curve peak or color maximum, making it less demanding on the light-curve coverage than past approaches.

The CNIa0.02 project aims to collect a complete, nearby sample of Type Ia supernovae (SNe Ia) light curves, and the SNe are volume-limited with host-galaxy redshifts z host < 0.02. The main scientific goal is to infer the distributions of key properties (e.g., the luminosity function) of local SNe Ia in a complete and unbiased fashion in order to study SN explosion physics. We spectroscopically classify any SN candidate detected by the All-Sky Automated Survey for Supernovae (ASAS-SN) that reaches a peak brightness <16.5 mag. Since ASAS-SN scans the full sky and does not target specific galaxies, our target selection is effectively unbiased by host-galaxy properties. We perform multiband photometric observations starting from the time of discovery. In the first data release (DR1), we present the optical light curves obtained for 247 SNe from our project (including 148 SNe in the complete sample), and we derive parameters such as the peak fluxes, Δ m 15 , and s BV .

V909 Cas is a little-studied example of a e̱ṯa̱ Cep pulsating variable located in the OB association Cas OB8 in the Perseus spiral arm of the Milky Way. Photometric observations in 2016-7 provided 30 new times of pulsation extrema and enabled its mean pulsation period to be determined as 0.2067798(1) d. From spectroscopic observations we determined its interstellar extinction and absolute magnitude and luminosity, and located it with other e̱ṯa̱ Cep stars in the OB instability region of the H-R diagram.

We report a long-term (1961-2017) study of the eclipse times in the dwarf nova WZ Sagittae, in an effort to learn its rate of orbital-period change. Some wiggles with a time scale of 20-50 years are apparent, and a connection with the 23-year interval between dwarf-nova eruptions is possible. These back-and-forth wiggles dominate the O-C diagram, and prevent a secure measurement of the steady rate of orbital-period change. The line, it is drawn, the curse, it is cast. The slow one now will later be fast... For the times, they are a-changin'. - Dylan (1963)

We summarize the results of a 20-yr campaign to study the light curves of BK Lyn, a nova-like star strangely located below the 2 to 3 h orbital-period gap in the family of cataclysmic variables (CVs). Two apparent superhumps dominate the nightly light curves, with periods 4.6 per cent longer, and 3.0 per cent shorter, than the orbital period. The first appears to be associated with the star's brighter states (V similar to 14), while the second appears to be present throughout and becomes very dominant in the low state (V similar to 15.7). It is plausible that these arise, respectively, from a prograde apsidal precession and a retrograde nodal precession of the star's accretion disc. Starting in the year 2005, the star's light curve became indistinguishable from that of a dwarf nova - in particular, that of the ER UMa subclass. No such clear transition has ever been observed in a CV before. Reviewing all the star's oddities, we speculate: (a) BK Lyn is the remnant of the probable nova on 101 December 30, and (b) it has been fading ever since, but it has taken similar to 2000 yr for the accretion rate to drop sufficiently to permit dwarf-nova eruptions. If such behaviour is common, it can explain other puzzles of CV evolution. One: why the ER UMa class even exists (because all members can be remnants of recent novae). Two: why ER UMa stars and short-period nova-likes are rare (because their lifetimes, which are essentially cooling times, are short). Three: why short-period novae all decline to luminosity states far above their true quiescence (because they are just getting started in their post-nova cooling). Four: why the orbital periods, accretion rates and white dwarf temperatures of short-period CVs are somewhat too large to arise purely from the effects of gravitational radiation (because the unexpectedly long interval of enhanced post-nova brightness boosts the mean mass-transfer rate). And maybe even five: why very old, post-period-bounce CVs are hard to find (because the higher mass-loss rates have 'burned them out'). These are substantial rewards in return for one investment of hypothesis: that the second parameter in CV evolution, besides orbital period, is time since the last classical-nova eruption.

In 2011 October an optical transient was reported in Pegasus as a possible nova. The object had an ultraviolet counterpart, GALEX J215818.5+241924. In this paper we present follow-up photometry of the object which revealed the presence of superhumps, with peak-to-peak amplitude of up to 0.22 magnitudes, diagnostic of it being a member of the SU UMa family of dwarf novae. The outburst amplitude was 4.6 magnitudes and it lasted at least 10 days, with a maximum brightness of magnitude 14.3. We determined the mean superhump period from our first 5 nights of observations as Psh = 0.06728(21) 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 = +2.67(15) x 10-4. There was then an abrupt change following which the period decreased with dPsh/dt = -2.08(9)x 10-4. We found a signal in the power spectrum of the photometry which we tentatively interpret as the orbital signal with Porb = 0.06606(35) d. Thus the superhump period excess was epsilon = 0.020(8), such value being consistent with other SU UMa systems of similar orbital period.

Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected the times of superhump maxima for 51 SU UMa-type dwarf novae, mainly observed during the 2010-2011 season. Although most of the new data for systems with short superhump periods basically confirmed the findings by Kato et al. (ibid.) and Kato et al. (2010, PASJ, 62, 1525), the long-period system GX Cas showed an exceptionally large positive-period derivative. An analysis of public Kepler data of V344 Lyr and V1504 Cyg yielded less-striking stage transitions. In V344 Lyr, there was a prominent secondary component growing during the late stage of superoutbursts, and this component persisted for at least two more cycles of successive normal outbursts. We also investigated the superoutburst of two conspicuous eclipsing objects: HT Cas and the WZ Sge-type object SDSS J080434.20+510349.2. Strong beat phenomena were detected in both objects, and late-stage superhumps in the latter object had an almost constant luminosity during repeated rebrightenings. The WZ Sge-type object SDSS J133941.11+484727.5 showed a phase reversal around the rapid fading from the superoutburst. The object showed a prominent beat phenomenon, even after the end of the superoutburst. A pilot study of superhump amplitudes indicated that the amplitude of superhumps is strongly correlated with the orbital period, and the dependence on the inclination is weak in systems with inclinations smaller than 80 degrees.

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 show that another AM CVn system, SDSS J124058.03-015919.2, has also undergone at least one outburst, with an amplitude of ~4.6 magnitudes.

During the outburst of V713 Cephei in August 2009 the times of 8 eclipses were measured and these, together with 5 eclipse timings obtained during quiescence in August 2007, provide an improved orbital period of 0.085418432(4)d. No superhumps were observed in the light curve indicating this was a normal UG-type dwarf nova outburst. We found the eclipse depth decreased linearly with rising system excitation level, falling from ~3 magnitudes in quiescence to ~2 magnitudes during outburst. The depth and totality of eclipses in quiescence suggests a high orbital inclination. We saw no variation in the FWHM of eclipses between quiescence and outburst despite a significant change in shape of the eclipse profile.

We report the results of a worldwide observing campaign in 2007 April, which covered the second known outburst of the dwarf nova GW Librae, as well as the aftermath in 2008 and 2010. The data consist of time-series photometry obtained from several locations around the Earth. The main eruption lasted 26 days. It began with a sharp 1 day rise to maximum light at V = 8.3, after which the star dimmed slowly for a while, then dropped off suddenly, landing at V = 15. The main eruption was followed by a slow, shallow drop toward quiescence. As expected, GW Lib showed powerful and long-lasting superhumps in its light curve at a period slightly longer than P-orb. These superhumps took a long time (10 days) to appear and continued for at least 90 days after the initial eruption. This time frame agrees with the general idea that cataclysmic variables (CVs) of very short P-orb are actually quite old, with small secondaries that have been exhausted by mass transfer over eons of evolution. A superhump period excess of 1.3% suggests a secondary star mass near 0.06 M-circle dot. A bolometric accounting of accretion light during the outburst yields a fairly good estimate of the time-averaged accretion rate; for the measured distance of 100 pc, we estimate L-bol = 8(+/- 2)10(31) ergs s(-1), which suggests dM/dt = 1.3(+/- 0.3)10(-11) M-circle dot yr(-1). We obtained an additional 102 nights of photometry during 2008 and 2010. During both years of posteruption observation, the star was near quiescence at V similar to 16.7. Its white dwarf pulsations, famous before outburst, were missing in both years. However, in 2008 a new pulsation appeared, with a period of similar to 20 minutes (similar to 73 cycles day(-1)) and properties not previously seen in any other stars of this type. The signal wandered slightly in frequency and amplitude, suggesting an underlying poor coherence and/or unresolved multiplet structure. This might signal a new type of pulsation in the heated white dwarf, or it could arise from the accretion disk itself. The star also commonly showed the famous but mysterious 2.1 hr signal in posteruption data. It appears, however, that the dominant (fundamental) signal is actually at 4.2 hr (similar to 5.5 cycles day(-1)). The origin of this signal remains as obscure as ever. This clock seems to lose phase in a few days or less; such a low coherence suggests an origin in the accretion disk.