Context. The disk instability model attributes the outbursts of dwarf novae to a thermal-viscous instability of their accretion disk, an instability to which nova-like stars are not subject. Aims. We aim to test the fundamental prediction of the disk instability model: the separation of cataclysmic variables (CVs) into nova-likes and dwarf novae depending on orbital period and mass transfer rate from the companion. Methods. We analyse the lightcurves from a sample of ≈ 130 CVs with a parallax distance in the Gaia DR2 catalogue to derive their average mass transfer rate. The method for converting optical magnitude to mass accretion rate is validated against theoretical lightcurves of dwarf novae. Results. Dwarf novae (resp. nova-likes) are consistently placed in the unstable (resp. stable) region of the orbital period -mass transfer rate plane predicted by the disk instability model. None of the analysed systems present a challenge to the model. These results are robust against the possible sources of error and bias that we investigated. Lightcurves from Kepler or, in the future, the LSST or Plato surveys, could alleviate a major source of uncertainty, the irregular sampling rate of the lightcurves, assuming good constraints can be set on the orbital parameters of the CVs that they happen to target. Conclusions. The disk instability model remains the solid base on which to construct the understanding of accretion processes in cataclysmic variables.

We present a statistical study of all measurable photometric features of a large sample of dwarf novae during their outbursts and superoutbursts. We used all accessible photometric data for all our objects to make the study as complete and up-to-date as possible. Our aim was to check correlations between these photometric features in order to constrain theoretical models which try to explain the nature of dwarf novae outbursts. We managed to confirm a few of the known correlations, that is the Stolz and Schoembs Relation, the Bailey Relation for long outbursts above the period gap, the relations between the cycle and supercycle lengths, amplitudes of normal and superoutbursts, amplitude and duration of superoutbursts, outburst duration and orbital period, outburst duration and mass ratio for short and normal outbursts, as well as the relation between the rise and decline rates of superoutbursts. However, we question the existence of the Kukarkin-Parenago Relation but we found an analogous relation for superoutbursts. We also failed to find one presumed relation between outburst duration and mass ratio for superoutbursts. This study should help to direct theoretical work dedicated to dwarf novae.

Context. The fast temporal evolution of the ejecta morphology of novae can be considered as an important test bench for studying the shaping of many kinds of nebulae. V1280 Sco is one of the slowest dust-forming nova ever historically observed that has experienced a particularly long common-envelope phase. Aims. We performed multi-epoch high-spatial resolution observations of the circumstellar dusty environment of V1280 Sco to investigate the level of asymmetry of the ejecta. Methods. We observed V1280 Sco in 2009, 2010 and 2011 (from t = 877 days after discovery until t = 1664 d) using unprecedented high angular resolution techniques. We used the NACO/VLT adaptive optics system in the J, H and K bands, together with contemporaneous VISIR/VLT mid-IR imaging that resolved the dust envelope of V1280 Sco, and SINFONI/VLT observations secured in 2011. Results. We report the discovery of a dusty hourglass-shaped bipolar nebula. The apparent size of the nebula increased from 0.30 × 0.17 in July 2009 to 0.64 × 0.42 in July 2011. The aspect ratio suggests that the source is seen at high inclination. The central source shines efficiently in the K band and represents more than 56 ± 5% of the total flux in 2009, and 87 ± 6% in 2011. A mean expansion rate of 0.39 ± 0.03 milliarcsec per day is inferred from the VISIR observations in the direction of the major axis, which represents a projected upper limit. Assuming that the dust shell expands in that direction as fast as the low-excitation slow ejecta detected in spectroscopy, this yields a lower limit distance to V1280 Sco of ∼1 kpc; however, the systematic errors remain large due to the complex shape and velocity field of the dusty ejecta. The dust seems to reside essentially in the polar caps and no infrared flux is detected in the equatorial regions in the latest dataset. This may imply that the mass-loss was dominantly polar. Conclusions. V1280 Sco is an excellent test case for studying the temporal evolution of dusty bipolar ejecta. As the nebula expands, observations will be easier and we advocate a yearly monitoring of the source using high angular resolution techniques.

We present and analyze optical photometry and high resolution SALT spectra of the symbiotic recurrent nova V3890 Sgr at quiescence. The orbital period, P = 747.6 days has been derived from both photometric and spectroscopic data. Our double-line spectroscopic orbits indicate that the mass ratio is q = Mg/MWD = 0.78 ± 0.05, and that the component masses are MWD ≈ 1.35 ± 0.13 M⊙ and Mg ≈ 1.05 ± 0.11 M⊙. The orbit inclination is ≈67 − 69○. The red giant is filling (or nearly filling) its Roche lobe, and the distance set by its Roche lobe radius, d ≈ 9 kpc, is consistent with that resulting from the giant pulsation period. The outburst magnitude of V3890 Sgr is then very similar to those of RNe in the Large Magellanic Cloud. V3890 Sgr shows remarkable photometric and spectroscopic activity between the nova eruptions with timescales similar to those observed in the symbiotic recurrent novae T CrB and RS Oph and Z And-type symbiotic systems. The active source has a double-temperature structure which we have associated with the presence of an accretion disc. The activity would be then caused by changes in the accretion rate. We also provide evidence that V3890 Sgr contains a CO WD accreting at a high, ∼ a few× 10−8–10−7 M⊙ yr−1, rate. The WD is growing in mass, and should give rise to a Type Ia supernova within $\lesssim 10^6$ yrs - the expected lifetime of the red giant.

We present observational evidence that supercycle lengths of the most active SU UMa-type stars are increasing during the past decades. We analysed a large number of photometric measurements from available archives and found that this effect is generic for this class of stars, independently of their evolutionary status. This finding is in agreement with previous predictions and the most recent work of Patterson et al.(2012) on BK Lyn.

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 Draconis 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 star varied in the range 14.6−18.2 mag. Superoutbursts occur regularly with the supercycle length (P sc ) of 58.5±0.5 d. When analysing data over the past 20 years, we found that P sc is increasing at a rate ofṖ = 1.8 × 10 −3 . Normal outbursts appear to be irregular, with typical occurrence times in the range 3.1 − 4.1 d. We detected a double-peaked structure of superhumps during superoutburst, with the secondary maximum becoming dominant near the end of the superoutburst. The mean superhump period observed during superoutbursts is P sh = 0.066982(36) d (96.45 ± 0.05 min), which is constant over the last two decades of observations. Based on the power spectrum analysis, the evaluation of the orbital period was problematic. We found two possible values: the first one, 0.06641(3) d (95.63 ± 0.04 min), which is in agreement with previous studies and our O − C analysis (0.06646(2) d, 95.70 ± 0.03 min), and the second one, 0.06482(3) d (93.34 ± 0.04 min), which is less likely. The evolutionary status of the object depends dramatically on the choice between these two values. A spectroscopic determination of the orbital period is needed. We updated available information on ER UMa-type stars and present a new set of their basic statistics. Thereby, we provide evidence that this class of stars is not uniform.

We present a new upgraded version of the code for the study of dynamical evolution of globular clusters and its first application to the study of evolution of multiple stellar populations. We explore a range of initial conditions spanning different structural parameters for the first (FG) and second population (SG) and we analyze their effect on the binary dynamics and survival. The set of simulations shown here represents the first phase of the new --2 project which will be further extended. Here, we focus our attention on the number ratio of FG and SG binaries, its variation with the distance from the cluster center, and the way their abundances are affected by various cluster initial properties. We find that SG stars more abundant in clusters that were initially tidally filling. Conversely, FG stars stay more abundant in clusters that were initially tidally underfilling. We also find that the ratio between binary fractions is not affected by the way we calculate these fractions (e.g. with the use of all binaries, only main-sequence binaries or observational binaries, i.e. main-sequence stars > 0.4𝑀 , mass ratios > 0.5). We find also that the evolution of mixing between populations presents the same features even if we take into account all single stars too. This implies that the main-sequence stars themselves are a very good proxy for probing entire populations of FG and SG in star clusters.We also discuss how our findings relate to the observations of Milky Way GCs. We show that with MOCCA models we are able to reproduce the observed range of SG fractions for any Milky Way GC for which we know this fraction. We show how the SG fractions depend on the initial conditions. We provide also an explanation what could be the initial conditions of star clusters, which at the Hubble time, have more numerous FG, and which more numerous SG stars.

We present an upgraded version of the mocca code for the study of dynamical evolution of globular clusters (GCs) and its first application to the study of evolution of multiple stellar populations. We explore initial conditions spanning different structural parameters for the first (FG) and second generation of stars (SG) and we analyse their effect on the binary dynamics and survival. Here, we focus on the number ratio of FG and SG binaries, its spatial variation, and the way their abundances are affected by various cluster initial properties. We find that present-day SG stars are more abundant in clusters that were initially tidally filling. Conversely, FG stars stay more abundant in clusters that were initially tidally underfilling. We find that the ratio between binary fractions is not affected by the way we calculate these fractions (e.g. only main-sequence binaries (MS) or observational binaries, i.e. MS stars >0.4M⊙ mass ratios >0.5). This implies that the MS stars themselves are a very good proxy for probing entire populations of FG and SG. We also discuss how it relates to the observations of Milky Way GCs. We show that moccamodels are able to reproduce the observed range of SG fractions for Milky Way GCs for which we know these fractions. We show how the SG fractions depend on the initial conditions and provide some constraints for the initial conditions to have more numerous FG or SG stars at the Hubble time.