Search

Aims. Cataclysmic variables (CVs) are compact binary systems in which a white dwarf accretes matter from a Roche-lobe-filling companion star. For this study we searched for new CVs in the Milky Way in the Chandra Source Catalog v2.0, cross-matched with Gaia Data Release 3 (DR3). Methods. We identified new CV candidates by combining X-ray and optical data in a color-color diagram called the X-ray main sequence. We used two different cuts in this diagram to compile pure and optically variable samples of CV candidates. We undertook optical spectroscopic follow-up observations with the Keck and Palomar Observatories to confirm the nature of these sources. Results. We assembled a sample of 25 887 Galactic X-ray sources and found 14 new CV candidates. Seven objects show X-ray and/or optical variability. All sources show X-ray luminosity in the 1029 − 1032 erg s−1 range, and their X-ray spectra can be approximated by a power-law model with photon indices in the Γ ∼ 1 − 3 range or an optically thin thermal emission model in the kT ∼ 1 − 70 keV range. We spectroscopically confirmed four CVs, discovering two new polars, one low accretion rate polar and a WZ Sge-like low accretion rate CV. X-ray and optical properties of the other nine objects suggest that they are also CVs (likely magnetic or dwarf novae), and one other object could be an eclipsing binary, but revealing their true nature requires further observations. Conclusions. These results show that a joint X-ray and optical analysis can be a powerful tool for finding new CVs in large X-ray and optical catalogs. X-ray observations such as those by Chandra are particularly efficient at discovering magnetic and low accretion rate CVs, which could be missed by purely optical surveys. [ABSTRACT FROM AUTHOR]

Context. Supersoft X-ray sources (SSSs) have been proposed as one of the progenitors for Type Ia supernovae. However, the exact origin of the quasi-periodic variability in the optical light curve remains a mystery. Aims. In this work, our goal is to investigate the effect of the feedback of an evolved main-sequence companion star on X-ray irradiation and find whether periodic X-ray irradiation of the companion star could reproduce periodic mass transfer. Methods. Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we modeled the evolutionary track of the companion star under the influence of supersoft X-ray irradiation, and we calculated the resulting mass transfer rate. Results. We find that the supersoft X-ray heating of the companion star can result in the expansion of the companion, causing it to greatly overflow its Roche lobe and thereby increasing the mass transfer rate. The periodic X-ray irradiation on the companion stars leads to periodic changes in the mass transfer rate. For a given companion star, higher irradiation efficiencies result in a higher mass transfer rate. Additionally, the mass transfer rate increases as the mass of the companion star decreases for a given irradiation efficiency. Conclusions. The companion star undergoing thermal timescale mass transfer is periodically irradiated by the X-rays from the WD, which can lead to periodic enhancement of the mass transfer rate. The mechanism could be the origin of the quasi-periodic optical light curve in supersoft X-ray sources. [ABSTRACT FROM AUTHOR]

We present X-ray and optical observations of nova V407 Lup (Nova Lup 2016), previously well monitored in outburst, as it returned to quiescent accretion. The X-ray light curve in 2020 February revealed a clear flux modulation with a stable period of 564.64 |$\pm$| 0.64 s, corresponding to the period measured in outburst and attributed to the spin of a magnetized white dwarf in an intermediate polar (IP) system. This detection in quiescence is consistent with the IP classification proposed after the nova eruption. The XMM–Newton EPIC X-ray flux is |${\simeq} 1.3 \times 10^{-12}$|  erg cm |$^{-2}$|  s |$^{-1}$| at a distance, most likely, larger than 5 kpc, emitted in the whole 0.2–12 keV range without a significant cut-off energy. The X-ray spectra are complex; they can be fitted including a power-law component with a relatively flat slope (a power-law index |$\simeq$| 1), although, alternatively, a hard thermal component at kT |$\ge$| 19 keV also yields a good fit. The SALT optical spectra obtained in 2019 March and 2022 May are quite typical of IPs, with strong emission lines, including some due to a high ionization potential, like He  ii at 4685.7 Å. Nebular lines of O [ iii ] were prominent in 2019 March, but their intensity and equivalent width appeared to be decreasing during that month, and they were no longer detectable in 2022, indicating that the nova ejecta dispersed. Complex profiles of the He  ii lines of V407 Lup are also characteristic of IPs, giving further evidence for this classification. [ABSTRACT FROM AUTHOR]

The eruption of Nova V2891 Cygni in 2019 offers a rare opportunity to explore the shock-induced processes in novae ejecta. The spectral evolution shows noticeable differences in the evolution of various oxygen emission lines such as O  i 7773 Å, O  i 8446 Å, O  i 1.1286  μ m, O  i 1.3164  μ m, etc. Here, we use spectral synthesis code cloudy to study the temporal evolution of these oxygen emission lines. Our photoionization model requires the introduction of a component with a very high density (⁠|$n \sim 10^{11}$| cm |$^{-3}$|⁠) and an enhanced oxygen abundance (O/H |$\sim$| 28) to produce the O  i 7773 Å emission line, suggesting a stratification of material with high oxygen abundance within the ejecta. An important outcome is the behaviour of the O  i 1.3164  μ m line, which could only be generated by invoking the collisional ionization models in cloudy. Our phenomenological analysis suggests that O  i 1.3164  μ m emission originates from a thin, dense shell characterized by a high density of about |$10^{12.5}\!-\!10^{12.8}$| cm |$^{-3}$|⁠ , which is most likely formed due to the strong internal collisions. If such is the case, the O  i 1.3164  μ m emission presents itself as a tracer of shock-induced dust formation in V2891 Cyg. The collisional ionization models have also been successful in creating the high-temperature conditions (⁠|$\sim 7.07\!-\!7.49 \times 10^5$|  K) required to reproduce the observed high ionization potential coronal lines, which coincide with the epoch of dust formation and evolution of the O  i 1.3164 μ m emission line. [ABSTRACT FROM AUTHOR]

We present time-dependent nova outburst models with optically thick winds for 1.2 and 1.35 |$\, M_{\odot }$| white dwarfs (WDs) with a mass-accretion rate of |$5 \times 10^{-9}\, M_{\odot }$|  yr−1 and for a 1.3 |$\, M_{\odot }$| WD with |$2 \times 10^{-9}\, M_{\odot }$|  yr−1. The X-ray flash occurs 11 d before the optical peak of the 1.2 |$\, M_{\odot }$| WD and 2.5 d before the peak of the 1.3 |$\, M_{\odot }$| WD. The wind mass-loss rate of the 1.2 |$\, M_{\odot }$| WD (1.3 |$\, M_{\odot }$| WD) reaches a peak of |$6.4 \times 10^{-5}\, M_{\odot }$| yr−1 (⁠|$7.4 \times 10^{-5}\, M_{\odot }$| yr−1) at the epoch of the maximum photospheric expansion with the lowest photospheric temperature of log  T ph (K) = 4.33 (4.35). The nuclear energy generated during the outburst is lost in the form of radiation (61% for the 1.2 |$\, M_{\odot }$| WD; 47% for the 1.3 |$\, M_{\odot }$| WD), gravitational energy of ejecta (39%; 52%), and kinetic energy of the wind (0.28%; 0.29%). We found an empirical relation for fast novae between the time to optical maximum from the outburst t peak and the expansion timescale τexp. With this relation, we are able to predict the time to optical maximum t peak from the ignition model (at t = 0) without following a time-consuming nova wind evolution. [ABSTRACT FROM AUTHOR]

We review the evolution of our understanding of the planetary nebulae phenomenon and their place in the scheme of stellar evolution. The historical steps leading to our current understanding of central star evolution and nebular formation are discussed. Recent optical imaging, X-ray, ultraviolet, infrared, millimeter wave, and radio observations have led to a much more complex picture of the structure of planetary nebulae. The optically bright regions have multiple shell structures (rims, shells, crowns, and haloes), which can be understood within the interacting winds framework. However, the physical mechanism responsible for bipolar and multipolar structures that emerged during the proto-planetary nebulae phase is yet to be identified. Our morphological classifications of planetary nebulae are hampered by the effects of sensitivity, orientation, and field-of-view coverage, and the fraction of bipolar or multipolar nebulae may be much higher than commonly assumed. The optically bright bipolar lobes may represent low-density, ionization-bounded cavities carved out of a neutral envelope by collimated fast winds. Planetary nebulae are sites of active synthesis of complex organic compounds, suggesting that planetary nebulae play a major role in the chemical enrichment of the Galaxy. Possible avenues of future advancement are discussed. [ABSTRACT FROM AUTHOR]

Accretion discs are fundamental to much of astronomy. They can occur around stars, both young and old, around compact objects they provide a window into the extremes of physics, and around supermassive black holes in galaxy centres, they generate spectacular luminosities that can outshine the entire galaxy. However, our understanding of the inner workings of accretion discs remains far from complete. Here, we revisit a conundrum in the observations of some of the simplest accreting systems: the cataclysmic variables (CVs). The high-accretion-rate states of (non-magnetic) CVs can be divided into the short-lived outbursts (∼a week), typical of dwarf novae (DNe), and the long-lived (and sometimes perpetual) high states of nova-like (NL) CVs. Since both sorts of high-state occur in approximately steady-state accretion discs with similar properties and accretors, we would expect them to display similar spectral energy distributions. However, previous analyses based on UV spectra from the International Ultraviolet Explorer have shown that their spectral energy distributions are different. We perform a re-analysis of the data using up to date calibrations and distance (and thus dereddening) estimates to test whether this difference persists and whether it is statistically significant over the sample. We find that it does persist, and it is statistically significant. We propose routes to investigating this discrepancy further and discuss the implications this has for other accreting systems, such as X-ray binaries, active galactic nuclei, and protoplanetary discs. [ABSTRACT FROM AUTHOR]

We present high‐resolution (0.06 Å px −1$$ {}^{-1} $$) spectroscopic observations of the recurrent nova T Coronae Borealis obtained during the last 1.5 years (September 2022–January 2024), with the 2.0‐m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria. Double‐peaked emission is visible in the Hα$$ {H}_{\alpha } $$ line after the end of the superactive state. We subtract the red giant contribution and measure the distance between the peaks (Δva$$ \Delta {v}_a $$) of the line. For the period July 2023–January 2024, we find that Δva$$ \Delta {v}_a $$ is in range 90<Δva<120$$ 90<\Delta {v}_a<120 $$ km s −1$$ {}^{-1} $$. Assuming that the emission is from the accretion disc around the white dwarf, we find average radius of the accretion disc Rdisc=89±19$$ {R}_{\mathrm{disc}}=89\pm 19 $$ R ⊙$$ {}_{\odot } $$, which is approximately equal to the Roche lobe size of the white dwarf. Our results indicate that tidal torque plays an important role but that the disc can extend up to the Roche lobe of the accreting star. [ABSTRACT FROM AUTHOR]

We report on spin variations in the intermediate polar and cataclysmic variable CC Scl, as seen by the Transiting Exoplanet Survey Satellite (TESS). By studying both the spin period and its harmonic, we find that the spin has varied since it was first observed in 2011. We find the latest spin value for the source to be 389.473(6) s, equivalent to 0.00450779(7) d, 0.02 s shorter than the first value measured. A linear fit to these and intermediate data give a rate of change of spin (Ṗ) ∼ −4.26(2.66)× 10−11 and a characteristic time-scale τ ∼ 2.90 × 105 yr, in line with other known intermediate polars with varying spin. The spin profile of this source also matches theoretical spin profiles of high-inclination intermediate polars, and furthermore, appears to have changed in shape over a period of three years. Such 'spin-up' in an intermediate polar is considered to be from mass accretion on to the white dwarf (the primary), and we note the presence of dwarf nova eruptions in this source as being a possible catalyst of the variations. [ABSTRACT FROM AUTHOR]

We present a systematic search for periodic X-ray sources in the bulge of M31, using ∼2 Ms of archival Chandra observations spanning a temporal baseline of 16 yr. Utilizing the Gregory–Loredo algorithm that is designed for photon-counting, phase-folded light curves, we detect seven periodic X-ray sources, among which four are newly discovered. Three of these sources are novae, the identified periods of which range between 1.3 and 2.0 h and are most likely the orbital period. The other four sources are low-mass X-ray binaries, the identified periods of which range between 0.13 and 19.3 h and are also likely orbital due to a clear eclipsing/dipping behaviour in the light curve. We address implications on the X-ray binaries population of the M31 bulge. Our study demonstrates the potential of using archival X-ray observations to systematically identify periodic X-ray sources in external galaxies, which would provide valuable information about the underlying exotic stellar populations. [ABSTRACT FROM AUTHOR]

Cataclysmic variables (CVs) that have evolved past the period minimum during their lifetimes are predicted to be systems with a brown dwarf donor. While population synthesis models predict that around 40–70 per cent of the Galactic CVs are post-period minimum systems referred to as 'period bouncers', only a few dozen confirmed systems are known. We report the study and characterization of a new eclipsing CV, SRGeJ041130.3+685350 (SRGeJ0411), discovered from a joint SRG/eROSITA and ZTF programme. The optical spectrum of SRGeJ0411 shows prominent hydrogen and helium emission lines, typical for CVs. We obtained optical high-speed photometry to confirm the eclipse of SRGeJ0411 and determine the orbital period to be P orb ≈ 97.530 min. The spectral energy distribution suggests that the donor has an effective temperature of ≲ 1800 K. We constrain the donor mass with the period–density relationship for Roche lobe-filling stars and find that M donor ≲ 0.04  M ⊙. The binary parameters are consistent with evolutionary models for post-period minimum CVs, suggesting that SRGeJ0411 is a new period bouncer. The optical emission lines of SRGeJ0411 are single-peaked despite the system being eclipsing, which is typically only seen due to stream-fed accretion in polars. X-ray spectroscopy hints that the white dwarf in SRGeJ0411 could be magnetic, but verifying the magnetic nature of SRGeJ0411 requires further investigation. The lack of optical outbursts has made SRGeJ0411 elusive in previous surveys, and joint X-ray and optical surveys highlight the potential for discovering similar systems in the near future. [ABSTRACT FROM AUTHOR]

We present a systematic search for periodic X-ray sources in 10 Galactic globular clusters (GCs) utilizing deep archival Chandra observations. By applying the Gregory–Loredo algorithm, we detect 28 periodic signals among 27 independent X-ray sources in 6 GCs, which include 21 newly discovered ones in the X-ray band. The remaining 4 GCs exhibit no periodic X-ray sources, mainly due to a relatively lower sensitivity of the data. Through analysis of their X-ray timing and spectral properties, complemented with available optical and ultraviolet information, we identify 21 of these periodic sources as cataclysmic variables (CVs). Combining with 11 periodic CVs in 47 Tuc similarly identified in the X-ray band, we compile the most comprehensive sample to date of GC CVs with a probable orbital period. The scarcity of old, short-period CVs in GCs compared to the Galactic inner bulge and solar neighbourhood, can be attributed to both a selection effect favouring younger, dynamically formed systems and the hindrance of CV formation through primordial binary evolution by stellar dynamical interactions common to the GC environment. Additionally, we identify a significant fraction of the GC CVs, most with an orbital period below or within the CV period gap, as probable magnetic CVs, but in the meantime there is a deficiency of luminous intermediate polars in the GC sample compared to the solar neighbourhood. [ABSTRACT FROM AUTHOR]

We conduct numerical simulations of multiple nova eruptions in detached, widely separated symbiotic systems that include an asymptotic giant branch (AGB) companion to investigate the impact of white dwarf (WD) mass and binary separation on the evolution of the system. The accretion rate is determined using the Bondi–Hoyle–Lyttleton method, incorporating orbital momentum loss caused by factors such as gravitational radiation, magnetic braking, and drag. The WD in such a system accretes matter coming from the strong wind of an AGB companion until it finishes shedding its envelope. This occurs on an evolutionary time-scale of ≈3 × 105 yr. Throughout all simulations, we use a consistent AGB model with an initial mass of 1.0 M⊙ while varying the WD mass and binary separation, as they are the critical factors influencing nova eruption behaviour. We find that the accretion rate fluctuates between high and low rates during the evolutionary period, significantly impacted by the AGB's mass loss rate. We show that unlike novae in cataclysmic variables, the orbital period may either increase or decrease during evolution, depending on the model, while the separation consistently decreases. Furthermore, we have identified cases in which the WDs produce weak, non-ejective novae and experience mass gain. This suggests that provided the accretion efficiency can be achieved by a more massive WD and maintained for long enough, they could potentially serve as progenitors for type Ia supernovae. [ABSTRACT FROM AUTHOR]

We present the first reliable determination of the orbital period of the recurrent nova V2487 Oph (Nova Oph 1998). We derived a value of 0.753 ± 0.016 d (18.1 ± 0.4 h) from the radial velocity curve of the intense He  ii  λ4686 emission line as detected in time-series X-shooter spectra. The orbital period is significantly shorter than earlier claims, but it makes V2487 Oph one of the longest period cataclysmic variables known. The spectrum of V2487 Oph is prolific in broad Balmer absorptions that resemble a white dwarf spectrum. However, we show that they come from the accretion disc viewed at low inclination. Although highly speculative, the analysis of the radial velocity curves provides a binary mass ratio q ≈ 0.16 and a donor star mass M 2 ≈ 0.21 M⊙, assuming the reported white dwarf mass M 1 = 1.35 M⊙. A subgiant M-type star is tentatively suggested as the donor star. We were lucky to inadvertently take some of the spectra when V2487 Oph was in a flare state. During the flare, we detected high-velocity emission in the Balmer and He  ii λ4686 lines exceeding −2000 km s−1 at close to orbital phase 0.4. Receding emission up to 1200 km s−1 at about phase 0.3 is also observed. The similarities with the magnetic cataclysmic variables may point to magnetic accretion on to the white dwarf during the repeating flares. [ABSTRACT FROM AUTHOR]

Superorbital signals and negative superhumps are thought to be related to the reverse precession of the nodal line in a tilted disc, but the evidence is lacking. Our results provide new evidence for the precession of the tilted disc. Based on the TESS and K2 photometry, we investigate the superorbital signals, negative superhumps, positive superhumps, and eclipse characteristics of the long-period eclipsing cataclysmic variable star SDSS J0812. We find superorbital signals, negative superhumps, and positive superhumps with periods of 3.0451(5) d, 0.152047(2) d, and 0.174686 (7) d, respectively, in the K2 photometry, but all disappear in the TESS photometry, where the positive superhumps are present only in the first half of the same campaign, confirming that none of them is permanently present in SDSS J0812. In addition, we find for the first time a cyclic variation of the O-C of minima, eclipse depth, and negative superhumps amplitudes for 3.045 (8) d, 3.040(6) d, and 3.053 (8) d in SDSS J0812, respectively, and all reach the maximum at ∼0.75 precession phases of the tilted disc, which provides new evidence for the precession of the tilted disc. We suggest that the O-C and eclipse depth variations may come from a shift of the brightness centre of the precession tilted disc. Our first finding on the periodic variation of negative superhumps amplitude with the superorbital signals is significant evidence that the origin of negative superhumps is related to the precession of the tilted disc. [ABSTRACT FROM AUTHOR]

Arthur Anthony Page was at the forefront of astronomy in Queensland, Australia, for much of the second half of the twentieth century. This paper explores his life and achievements. He was a talented amateur astronomer who played a key role in the evolution of astronomical societies in the southeastern corner of the State of Queensland. He also was interested in research, especially in flare stars and cataclysmic variables, and built and equipped two observatories so that he could carry out these studies. He had access to some advanced instrumentation, and was keen to adopt new technologies such as photoelectric photometry--which was very unusual for amateur astronomers at this time. One of his discoveries was the chance flaring of the Be star 66 Ophiuchi in 1969. This was significant as this type of star had not previously been known to generate flares. Arthur Page also attended national and international conferences, published research papers in national and international journals, and produced star catalogues and star charts. Over the years, he built an international reputation in the shadowy boundary between professional and amateur astronomy. A long-time Internatonal Astronomical Union (IAU) member, he was an inaugural member of the Astronomical Society of Australia (a rare honour for an amateur astronomer), and was awarded an honorary PhD by the University of Queensland. In 2008 the IAU named asteroid 11516 'Arthur Page' in his honour. [ABSTRACT FROM AUTHOR]

We extend a magnetic braking (MB) model, which has been used earlier to address the evolution of cataclysmic variables, to address the spin period P spin evolution of fully convective M-dwarf (FCMD) stars. The MB mechanism is an α–Ω dynamo, which leads to stellar winds that carry away angular momentum. We model our MB torque such that the FCMDs experience an MB torque, approximately scaling as |$P_\mathrm{spin}^{-1}$| at shorter periods, before transitioning into a Skumanich-type MB torque, scaling as |$P_\mathrm{spin}^{-3}$|⁠. We also implement a parametrized reduction in the wind mass-loss owing to the entrapment of winds in dead zones. We choose a set of initial conditions and vary the two free parameters in our model to find a good match of our spin trajectories with open clusters containing FCMDs such as NGC2547, Pleiades, NGC2516, and Praesepe. We find that our model can explain the long spin periods of field stars and that a spread in spin distribution persists till over 3 Gyr. An advantage of our model is in relating physically motivated estimations of the magnetic field strength and stellar wind to properties of the stellar dynamo, which other models often remain agnostic about. We track the spin dependence of the wind mass-losses, Alfvén radii, and surface magnetic fields and find good agreement with observations. We discuss the implications of our results on the effect of the host FCMD on any orbiting exoplanets and our plans to extend this model to explain solar-like stars in the future. [ABSTRACT FROM AUTHOR]

Here, we present the results of our multiwavelength campaign aimed at classifying Swift J170800−402551.8 as part of the Swift Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with the Neil Gehrels Swift Observatory, Chandra X-ray Observatory , Neutron star Interior Composition Explorer (NICER), X-ray Multi-Mirror Mission (XMM–Newton), Nuclear Spectroscopic Telescope Array (NuSTAR), and the Southern African Large Telescope (SALT), as well as multiwavelength archival observations from Gaia , VST Photometric Hα Survey, and VISTA Variables in the Via Lactea. The source displays a periodicity of 784 s in our XMM–Newton observation. The X-ray spectrum (XMM–Newton and NuSTAR) can be described by thermal bremsstrahlung radiation with a temperature of kT ≈ 30 keV. The phase-folded X-ray light curve displays a double-peaked, energy-dependent pulse profile. We used Chandra to precisely localize the source, allowing us to identify and study the multiwavelength counterpart. Spectroscopy with SALT identified a Balmer H α line, and potential He  i lines, from the optical counterpart. The faintness of the counterpart (r ≈ 21 AB mag) favours a low-mass donor star. Based on these criteria, we classify Swift J170800−402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s. [ABSTRACT FROM AUTHOR]

Using the Catalina Sky Survey and Gaia alert data bases, we have carried out a systematic search for long-term variability of the brightness of dwarf novae in quiescence. A small, but significant portion of them revealed variability on time-scales between 2 and 14 yr which can be fitted, in some of the targets, by linear slopes of 0.14 mag yr−1 on average and up to 0.6 mag yr−1 in extreme cases. Another group of dwarf novae showed quasi-periodic variations in their quiescent brightness, with periods of 3.7 yr on average and up to 13 yr in extreme cases, and mean amplitudes of 0.5 mag, reaching up to 1.3 mag. The observed slopes could be understood as portions of a quasi-sinusoidal variability with larger periods, not covered by our data. SU UMa stars have, on average, smaller slope values and longer periods, compared to other dwarf novae. These variations could be interpreted as caused by magnetic activity of the secondary companion star, similar to the 11-yr solar cycle, but one could consider also other origins of this phenomenon. [ABSTRACT FROM AUTHOR]

Continuing previous work on the identification and characterization of periodic and non-periodic variations in long and almost uninterrupted high cadence light curves of cataclysmic variables observed by the Transiting Exoplanet Survey Telescope mission, the results on 23 nova-like variables and old novae out of sample of 127 such systems taken from the Ritter & Kolb catalogue are presented. All of them exhibit at least at some epochs either positive or negative (or both) superhumps, and in 19 of them superhumps were detected for the first time. The basic properties of the superhumps such as their periods, their appearance and disappearance, and their waveforms are explored. Together with recent reports in the literature, this elevates the number of known nova-like variables and old novae with superhumps by more than 50 per cent. The previous census of superhumps and the Stolz–Schoembs relation for these stars are updated. Attention is drawn to superhump properties in some stars that behave differently from the average, as well as to positive superhumps in high-mass ratio systems that defy theory. As a by-product, the orbital periods of 13 stars are either improved or newly measured, correcting previously reported erroneous values. [ABSTRACT FROM AUTHOR]

T CrB is one of the most-famous and brightest novae known, and is a recurrent nova with prior eruptions in 1866 and 1946 that peak at V = 2.0. I have constructed light curves spanning 1842–2022 with 213 730 magnitudes, where the B and V magnitudes are fully corrected to the Johnson system. These light curves first reveal a unique complex high-state (with 20× higher accretion rate than the normal low-state) stretching from −10 to +9 yr after eruption, punctuated with a deep pre-eruption dip (apparently from dust formation in a slow mass ejection) and a unique enigmatic secondary eruption (with 10 per cent of the energy of the primary eruption), with the light curves identical for the 1866 and 1946 eruptions. Starting in 2015, T CrB entered the high-state, like in 1936, so a third eruption in upcoming years has been widely anticipated. With the pre-1946 light curve as a template, I predict a date of 2025.5 ± 1.3 for the upcoming eruption, with the primary uncertainty arising from a possible lengthening of the pre-eruption high-state. I use the large-amplitude ellipsoidal modulation to track the orbital phase of the binary from 1867–2022. I measure that the orbital period increased abruptly by +0.185 ± 0.056 d across the 1946 eruption, the 1947–2022 years had a steady period decrease of (−8.9 ± 1.6) × 10−6 d-per-day, and the 1867–1946 years had a steady period change consistent with zero, at (+1.75 ± 4.5) × 10−6 d-per-day. These large period changes cannot be explained by any published mechanism. [ABSTRACT FROM AUTHOR]

Using the Hubble Ultraviolet Globular Cluster Survey (HUGS) and additional HST archival data, we have carried out a search for optical counterparts to the low-luminosity Chandra X-ray sources in the globular cluster M4 (NGC 6121). We have also searched for optical or X-ray counterparts to radio sources detected by the VLA. We find 24 new confident optical counterparts to Chandra sources for a total of 40, including the 16 previously identified. Of the 24 new identifications, 18 are stellar coronal X-ray sources (active binaries, ABs), the majority located along the binary sequence in a V 606– I 814 colour–magnitude diagram and generally showing an H α excess. In addition to confirming the previously detected cataclysmic variable (CV, CX4), we identify one confident new CV (CX76), and two candidates (CX81 and CX101). One MSP is known in M4 (CX12), and another strong candidate has been suggested (CX1); we identify some possible MSP candidates among optical and radio sources, such as VLA20, which appears to have a white dwarf counterpart. One X-ray source with a sub-subgiant optical counterpart and a flat radio spectrum (CX8, VLA31) is particularly mysterious. The radial distribution of X-ray sources suggests a relaxed population of average mass |$\sim 1.2\!-\! 1.5\, \mbox{$\mathrm{ M_\odot} $}$|⁠. Comparing the numbers of ABs, MSPs, and CVs in M4 with other clusters indicates that AB numbers are proportional to cluster mass (primordial population), MSPs to stellar encounter rate (dynamically formed population), while CVs seem to be produced both primordially and dynamically. [ABSTRACT FROM AUTHOR]

We present follow-up spectroscopy of 21 cataclysmic variables (CVs) with evolved secondaries and ongoing or recently terminated mass transfer. Evolutionary models predict that the secondaries should have anomalous surface abundances owing to nuclear burning in their cores during their main-sequence evolution and subsequent envelope stripping by their companion white dwarfs. To test these models, we measure sodium (Na) abundances of the donors from the Fraunhofer 'D' doublet. Accounting for interstellar absorption, we find that all objects in our sample have enhanced Na abundances. We measure 0.3 dex ≲ [Na/H] ≲ 1.5 dex across the sample, with a median [Na/H]  = 0.956 dex, i.e. about an order of magnitude enhancement over solar values. To interpret these values, we run Modules for Experiments in Stellar Astrophysics binary evolution models of CVs in which mass transfer begins just as the donor leaves the main sequence. These generically predict Na enhancement in donors with initial donor masses |$\gtrsim 1\, {\rm M}_{\odot }$|⁠ , consistent with our observations. In the models, Na enrichment occurs in the donors' cores via the NeNa cycle near the end of their main-sequence evolution. Na-enhanced material is exposed when the binaries reach orbital periods of a few hours. Donors with higher initial masses are predicted to have higher Na abundances at fixed orbital period owing to their higher core temperatures during main-sequence evolution. The observed [Na/H] values are on average ≈0.3 dex higher than predicted by the models. Surface abundances of evolved CV donors provide a unique opportunity to study nuclear burning products in the cores of intermediate-mass stars. [ABSTRACT FROM AUTHOR]

The disc instability mechanism (DIM) is widely accepted to account for the transient behaviour of dwarf novae (DNe), which experience short outbursts separated by long quiescence. The duty cycle (the ratio between the outburst duration and the recurrence time) determines the amount of accreted mass by the white dwarf (WDs) during outbursts, thus playing an important role in the long-term binary evolution. Employing the code of Modules for Experiments in Stellar Astrophysics, we systemically investigate the influence of the duty cycles on the evolution of DNe and the mass growth of accreting carbon-oxygen (CO) WDs. Our calculations show that, while the DIM can considerably influence the accretion process, efficient WD-mass growth requires a particular range of the duty cycle. For WDs with the initial masses of 0.6, 0.7, and 1.1 M⊙, these duty cycles are 0.006 |$\, \le$| d |$\, \le$| 0.007, d   =  0.005, and , d   = 0.003 and the accumulated mass of the WDs can reach 0.1, 0.13, and 0.21 M⊙, respectively. In all of our simulations, no CO WDs can grow their masses to the explosion mass of Type Ia supernovae of about 1.38 M⊙. Because of a much short time-scale of the outburst state, the final donor-star masses and orbital periods are insensitive to the duty cycles. Therefore, we propose that the DIM in DNe could alleviate the WD mass problem to some extent. [ABSTRACT FROM AUTHOR]

We present near-infrared spectroscopy of the 2022 eruption of the recurrent nova U Sco, over the period from 5.4 to 45.6 d after outburst. This is the most intensive infrared study of this nova. Our observations started early after the outburst and extended almost to the end of the 'Super Soft' X-ray phase. A major find is the presence of coronal lines from day 9.41, one of the earliest appearances of these in any nova, classical, or recurrent. The temperature of the coronal gas is 7 × 105 K. There is also evidence for the presence of much cooler (⁠|$\lesssim 2.5\times 10^4$|  K) gas. Remarkable changes are seen in the He  i 1.083 |$\, \mu$| m line, the strength of which declines, then recovers, in anticorrelation with the X-ray behaviour. We conclude that shock ionization is the dominant excitation mechanism for the coronal line emission. There is evidence in the infrared spectra for the presence of black body emission at ∼20 000 K, which we tentatively identify with the irradiated secondary, and for free-free/free-bound emission. For the previously determined binary inclination of 82.7°, the implied ejection velocities are as high as 22 000 km s−1. These velocities appear unprecedented in nova outflows, and are comparable to those seen in supernovae, thereby marking U Sco as a truly remarkable object. [ABSTRACT FROM AUTHOR]

Superoutbursts in WZ Sge-type dwarf novae (DNe) are characterized by both early superhumps and ordinary superhumps originating from the 2 : 1 and 3 : 1 resonances, respectively. However, some WZ Sge-type DNe show a superoutburst lacking early superhumps; it is not well established how these differ from superoutbursts with an early superhump phase. We report time-resolved photometric observations of the WZ Sge-type DN V627 Peg during its 2021 superoutburst. The detection of ordinary superhumps before the superoutburst peak highlights that this 2021 superoutburst of V627 Peg, like that in 2014, did not feature an early superhump phase. The duration of stage B superhumps was slightly longer in the 2010 superoutburst accompanied by early superhumps than that in the 2014 and 2021 superoutbursts, which lacked early superhumps. This result suggests that an accretion disk experiencing the 2 : 1 resonance may have a larger mass at the inner part of the disk and hence needs more time for the inner disk to become eccentric. The presence of a precursor outburst in the 2021 superoutburst suggests that the maximum disk radius should be smaller than that of the 2014 superoutburst, even though the duration of quiescence was longer than that before the 2021 superoutburst. This could be accomplished if the 2021 superoutburst was triggered as an inside-out outburst or if the mass transfer rate in quiescence changes by a factor of two, suggesting that the outburst mechanism and quiescence state of WZ Sge-type DNe may have more variety than ever thought. [ABSTRACT FROM AUTHOR]

In this work, we search for negative superhumps (nSHs) in poorly studied cataclysmic variables using Transiting Exoplanet Survey Satellite data. We find three eclipsing binaries with nSH signatures: HBHA 4204−09, Gaia DR3 5931071148325476992, and SDSS J090113.51+144704.6. The last one exhibits IW And-like behaviour in archival Zwicky Transient Facility data, and appears to have shallow, grazing eclipses. In addition, we detect nSH signatures in two non-eclipsing systems: KQ Mon and Gaia DR3 4684361817175293440, by identifying the orbital period from the superorbital-dependent irradiation of the secondary. We discover nSH signatures in one more system, [PK2008] HalphaJ103959, by using an orbital period from another work. An improved mass ratio–nSH deficit relation q (ε−) is suggested by us, which agrees with independent measurements on nova-like variables. With this relation, we estimate the mass ratios of all systems in our sample, and determine the orbital inclinations for the three that are eclipsing. All systems with discovered nSHs in this work are excellent targets for follow-up spectroscopic studies. [ABSTRACT FROM AUTHOR]

We model cataclysmic variables (CVs) with solar metallicity donors (X  = 0.7 and  Z  = 0.02) that evolve to form AM CVn stars through the evolved CV formation channel using various angular momentum loss mechanisms by magnetic braking (AMLMB). We find that the time-scale for AMLMB in our double-dynamo (DD) model is shorter than that of previously used empirical formulae. Owing to the shorter time-scales, a larger parameter space of initial conditions evolves to form AM CVn stars with the DD model than with other models. We perform an analysis of the expected number of AM CVn stars formed through the Evolved CV channel and find about 3 times as many AM CVn stars as reported before. We evolve these systems in detail with the Cambridge stellar evolution code (stars) and show that evolved CVs populate a region with orbital period |$P_\mathrm{orb}\ge 5.5\, \mathrm{hr}$|⁠. We evolve our donors beyond their orbital period minimum and find that a significant number become extremely H-exhausted systems. This makes them indistinguishable from systems evolved from the He-star and the White Dwarf (WD) channels in terms of the absence of H in their spectra. We also compare the masses, mass-transfer rates of the donor, and the orbital period with observations. We find that the state of the donor and the absence of H in systems such as YZ LMi and V396 Hya match with our modelled trajectories, while systems such as CR Boo and HP Lib match with our modelled tracks if their actual donor mass lies on the lower-end of the observed mass range. [ABSTRACT FROM AUTHOR]

Aims. We performed a systematic analysis of X-ray point sources within 1.°5 of the Galactic centre using archival XMM-Newton data. While doing so, we discovered Fe Kα complex emission and pulsation in two highly variable sources, 4XMM J174917.7–283329 and 4XMM J174954.6–294336. In this work we report the findings of the X-ray spectral and timing studies. Methods. We performed detailed spectral modelling of the sources and searched for pulsation in the light curves using Fourier timing analysis. We also searched for multi-wavelength counterparts for the characterization of the sources. Results. The X-ray spectrum of 4XMM J174917.7–283329 shows the presence of complex Fe K emission in the 6–7 keV band. The equivalent widths of the 6.4 and 6.7 keV lines are 99−72+84 and 220−140+160 eV, respectively. The continuum is fitted by a partially absorbed apec model with a plasma temperature of kT = 13−2+10 keV. The inferred mass of the white dwarf (WD) is 0.9−0.2+0.3 M⊙. We detected pulsations with a period of 1212 ± 3 s and a pulsed fraction of 26 ± 6%. The light curves of 4XMM J174954.6–294336 display an asymmetric eclipse and dipping behaviour. To date, this is only the second known intermediate polar to show a total eclipse in X-rays. The spectrum of the sources is characterized by a power-law model with photon index Γ = 0.4 ± 0.2. The equivalent widths of the iron fluorescent (6.4 keV) and Fe XXV (6.7 keV) lines are 171−79+99 and 136−81+89 eV, respectively. The continuum is described by emission from optically thin plasma with a temperature of kT ∼ 35 keV. The inferred mass of the WD is 1.1−0.3+0.2 M⊙. We detect coherent pulsations from the source with a period of 1002 ± 2 s. The pulsed fraction is 66 ± 15%. Conclusions. The spectral modelling indicates the presence of intervening clouds with a high absorbing column density in front of both sources. The detected periodic modulations in the light curves are likely associated with the spin period of WDs in magnetic cataclysmic variables. The measured spin period, hard photon index, and equivalent width of the fluorescent Fe Kα line are consistent with the values found in intermediate polars. 4XMM J174954.6–294336 has already been classified as an intermediate polar, and we suggest that 4XMM J174917.7–283329 is a new intermediate polar. The X-ray eclipses in 4XMM J174954.6–294336 are most likely caused by a low-mass companion star obscuring the central X-ray source. The asymmetry in the eclipse is likely caused by a thick bulge that intercepts the line of sight during the ingress phase but not during the egress phase located behind the WD along the line of sight. [ABSTRACT FROM AUTHOR]

Superhumps are among the abundant variable phenomena observed in the light curves of cataclysmic variables (CVs). They come in two flavours as positive and negative superhumps, distinguished by periods slightly longer or shorter, respectively, than the orbital periods of these interacting binary systems. Positive superhumps are ubiquitous in superoutbursting short-period dwarf novae of the SU UMa type but are less common in longer period systems with accretion discs in a permanent bright state, such as novalike variables and most old novae. Negative superhumps do not seem to have a preference for a particular type of CV. Here, I take advantage of the long high-cadence light curves provided by TESS for huge number of stars, selecting all old novae and novalike variables with past reported superhumps for which TESS light curves are available and have not yet been analysed in previous publications in order to study their superhump behaviour. In combination with information taken from the literature, the results enable to compile the most complete census of superhumps in these stars so far. As a corollary, for the eclipsing systems in the present sample of objects, eclipse epochs derived from the TESS light curves and in some cases from archival light curves are listed and used to update orbital ephemeris and to discuss period changes. [ABSTRACT FROM AUTHOR]

The prototype dwarf nova SS Cyg unexpectedly exhibited an anomalous event in its light curve in the early few months of 2021 in which regular dwarf nova-type outbursts stopped, and only small-amplitude fluctuations occurred. Inspired by this event, we have performed numerical simulations of light curves of SS Cyg by varying mass transfer rates and varying viscosity parameters in the cool disk. We have also studied the effect of gas-stream overflows beyond the outer disk edge in the light curve simulations. We have confirmed that the enhanced mass transfer is not likely to be responsible for the 2021 anomalous event or its forerunner. We have found that the enhancement of the viscosity in the disk may reproduce the forerunner of that event but may not be sufficient to explain the 2021 anomalous event, although the latter result might be particular to the thermal equilibrium curve we used. Within our simulations, a model of the gas-stream overflow with a slightly higher mass transfer rate than that of our standard model reproduces light curves similar to the 2021 anomalous event. We suggest that the gas-stream overflow is necessary to reproduce that event. The gas-stream overflow may also be responsible for the abnormally high X-ray flux during the normal quiescent state in SS Cyg. [ABSTRACT FROM AUTHOR]

HS 2325+8205 is a long-period eclipsing dwarf nova with an orbital period above the period gap (P orb > 3 h) and is reported to be a Z Cam-type dwarf nova. We study the light variation and the quasi-periodic oscillations (QPOs) of HS 2325+8205 based on the photometry of the Transiting Exoplanet Survey Satellite (TESS). Using a continuous wavelet transform, a Lomb–Scargle periodogram (LSP), and sine fitting methods, we find for the first time that there is a QPO of ∼2160 s in the long outburst top light curves of HS 2325+8205. Moreover, we find that the oscillation intensity of the QPOs of HS 2325+8205 is related to the orbital phase, and the intensity in orbital phases 0.5–0.9 is stronger than in orbital phases 0.1–0.5. Therefore, the relationship between the oscillation intensity of QPOs and the orbital phase may become a topic of research into the origin of QPOs. In addition, we use the LSP to correct the orbital period of HS 2325+8205 to 0.19433475(6) d. [ABSTRACT FROM AUTHOR]

We present spectroscopic observations of Nova Cas 2020 (V1391 Cas) obtained using the Russian Turkish Telescope during different stages of its 2020 outburst. We followed the spectral evolution of the nova until it entered the nebular phase. The expansion velocity of the ejecta reached ∼ 780 km s − 1 . The fluxes of the neutral [O I] lines at wavelengths 6300, 6364, and 5577 ̊A were used to calculate the electron temperature and the mass of neutral oxygen in the ejecta. We found average values T e = 4890 K , M OI = 2.54 × 10 −5 M ⊙ which are consistent with the values calculated for other novae. We modeled the nova's ejected envelope 515 days after its discovery and found that the log elemental abundances by number relative to Hydrogen of the envelope are He = −0.7, C = −5.5, O = −2.5, N = −2.0 and Ne = −4.0. • Spectral Evolution of the classical Nova Cas 2020 was studied. • Neutral oxygen mass and electron temperature in the ejecta were derived. • The mass of Hydrogen and the total mass of the ejected envelope were calculated. • Elemental abundances in the ejected envelope were calculated. • The expansion velocity of the ejecta was calculated. [ABSTRACT FROM AUTHOR]

I report on a large-scale search for the orbital periods (P) of most known nova systems, by looking for significant, coherent, and stable optical photometric modulation in two or more independent light curves taken mostly from the large surveys of TESS ,  Kepler, AAVSO, SMARTS, OGLE, ASAS, and ZTF. I have discovered 31 new orbital periods. Further, I have measured new periods for 18 novae with evolved companions, to 30 per cent accuracy, as based on their spectral energy distribution. Also, I have confirmed, improved, and rejected prior claims for P in 46 novae. (As part of this effort, I recognize that 5 novae display 1–3 coherent, significant, and transient periodicities 0.12–4.1 d, with these being mysterious as not being the orbital, spin, or superhump periods). In all, I have compiled a comprehensive list of 156 reliable P values for novae. The histogram of nova periods shows a minimum P at 0.059 h (85 min), and a Period Gap from 0.071 to 0.111 d (1.70–2.66 h). The upper edge of the Period Gap is significantly different between novae (0.111 d), nova-like systems (0.131 d), and dwarf novae (0.141 d). A further issue from the histogram is that 31 per cent of nova systems have evolved companions, for which there has been no models or understanding for their current state or evolution. For the novae with red giant companions, 15-out-of-20 are in the bulge population, despite novae with main-sequence and subgiant companions having bulge fractions near 0.11–0.32. [ABSTRACT FROM AUTHOR]

We present the analysis of existing optical photometry and new optical spectroscopy of the candidate cataclysmic variable star OGLE-BLG504.12.201843. As was shown previously, this object has an orbital period of 0.523419 d and exhibits year-long outbursts with a mean period of 973 d. Using digitized photographic archives, we show that the earliest recorded outburst occurred in 1910. We propose that this object is a U Gem-type dwarf nova (DN) with extreme properties. The orbital variability of the system in outburst shows clear signs of an accretion disc, from which the outburst likely originates. During quiescence, the object slowly brightens by up to 0.75 mag in the I  band over 600 d before the outburst and exhibits small flares with amplitude ≲0.2 mag in the I  band. We interpret the gradual brightening as an increase in the luminosity and temperature of the accretion disc, which is theoretically predicted but only rarely seen in DNe. The origin of small flares remains unexplained. The spectra show Balmer absorption lines both in quiescence and outburst, which can be associated with a bright secondary star or a cold accretion disc. During outbursts, emission lines with full width at half-maximum of about 450 km s−1 appear; however, they lack typical double-peaked profiles. We suggest that either these lines originate in the disc winds or the orbital inclination is low, the latter being consistent with constrains obtained from the orbital variability of the system. Due to its extreme properties and peculiarities, OGLE-BLG504.12.201843 is an excellent object for further follow-up studies. [ABSTRACT FROM AUTHOR]

Luminous red novae (LRNe) are astrophysical transients believed to be caused by the partial ejection of a binary star's common envelope (CE) and the merger of its components. The formation of the CE is likely to occur during unstable mass transfer, initiated by a primary star which is evolving off the main sequence (a Hertzsprung gap star) and a lower mass companion. In agreement with observations, theoretical studies have shown that outflows from the pre-CE phase produce a detectable brightening of the progenitor system a few years before the ejection event. Based on these assumptions, we present a method to identify Galactic LRNe precursors, the resulting precursor candidates, and our follow-up analysis to uncover their nature. We begin by constructing a sample of progenitor systems, i.e. Hertzsprung gap stars, by statistically modelling the density of a colour magnitude diagram formed from 'well behaved' Gaia DR2 sources. Their time-domain evolution from the Zwicky Transient Facility (ZTF) survey is used to search for slowly brightening events, as pre-CE precursor candidates. The nature of the resulting candidates is further investigated using archival data and our own spectroscopic follow-up. Overall, we constructed a sample of ∼5.4 × 104 progenitor sources, from which 21 were identified as candidate LRNe precursors. Further analysis revealed 16 of our candidates to be Hα emitters, with their spectra often suggesting hotter (albeit moderately extincted) A-type or B-type stars. Because of their long-term variability in optical and mid-infrared wavelengths, we propose that many of our candidates are mass-transferring binaries with compact companions surrounded by dusty circumstellar discs or alternatively magnetically active stellar merger remnants. [ABSTRACT FROM AUTHOR]

Intermediate polars are a class of cataclysmic variables in which a white dwarf accretes material from a companion star. The intermediate polar nature confirmation usually derives from the detection of two periods in both X -ray and optical photometry. In this respect, the high-energy signal is often characterized by modulations on the white dwarf spin and the orbital period. However, noting that the periodograms may be characterized by strong features also at the synodic period and/or other sidebands, the timing analysis of the X -ray signal may offer the unique possibility to firmly discover an intermediate polar candidate. Here, we concentrate on a sample of five cataclysmic variable binary candidates: i.e. SAXJ1748.2-2808, 1RXS J211336.1 + 542226, CXOGC J174622.7-285218, CXOGC J174517.4-290650, and V381 Vel, listed in the IPHome catalogue. Our main aim is to confirm if they belong to the intermediate polar class or not. The results of our analysis show that we can safely assess the intermediate polar nature of all the considered sources, apart for the case of V381 Vel which instead behaves like a cataclysmic variable of the polar subclass. Moreover, the source SAXJ1748.2-2808, previously classified as an HMXB, appears to be, most likely, an intermediate polar variable. [ABSTRACT FROM AUTHOR]

U Sco is a recurrent nova with 11 observed eruptions, most recently in 2010.1 and 2022.4. I report on my program (running since 1989) of measuring eclipse times and brightnesses of U Sco in quiescence, from 2010 to 2022. The orbital period suddenly increased by +22.4 ± 1.0 parts-per-million across the 2010.1 eruption. This period change is greater than the near-zero period change (+3.9 ± 6.1 parts-per-million) across the 1999.2 eruption. This period change cannot come from any of the usual mechanisms, whereas the one remaining possibility is that the period changes are dominated by the little-known mechanism of the nova ejecting asymmetric shells. From 2010.1 to 2016.78, the O − C curve showed a steady period change that was large, with |$\dot{P}$|  = (−21.0 ± 3.2) × 10−9. This is greatly higher than the steady period changes in the two previous inter-eruption intervals (−3.2 ± 1.9 and −1.1 ± 1.1 × 10−9). This large, variable, and negative |$\dot{P}$| apparently comes from magnetic braking of the companion star's rotation. Starting in 2016.9 ± 0.6, the O − C curve showed a strong kink that is a unique characteristic of the sudden period change (+35.4 ± 7.1 parts-per-million) across a nova event. The brightness in quiescence after 2010.4 shows that the white dwarf accreted the trigger mass for the next nova event in the year 2017.1 ± 0.6. Photometric records show the only possible time for the eruption to peak (such that its total duration of 60 d was undetectable by any observation) is during a 75-d interval inside the 2016 solar gap, thus constraining the missed eruption to 2016.78 ± 0.10. [ABSTRACT FROM AUTHOR]

Polars are highly magnetic cataclysmic variables which have been long observed to have both high and low brightness states. The duration of these states has been previously seen to vary from a number of days up to years. Despite this, these states and their physical origin have not been explained in a consistent manner. We present observations of the shortest duration states of a number of Polars observed by ZTF and TESS. This has allowed us to determine that short-duration states are a relatively common feature across the population of Polars. Furthermore, we have been able to generalize the model of star-spot migration to explain both short-lived high and low states in Polars by incorporating the interaction between the magnetic field of the white dwarf and that of the star spots. [ABSTRACT FROM AUTHOR]

The unidentified infrared (UIR) bands, whose carriers are thought to be organics, have been widely observed in various astrophysical environments. However, our knowledge of the detailed chemical composition and formation process of the carriers is still limited. We have synthesized laboratory organics named Quenched Nitrogen-included Carbonaceous Composite (QNCC) by quenching plasma produced from nitrogen gas and hydrocarbon solids. Infrared and X-ray analyses of QNCC showed that infrared properties of QNCC well reproduce the UIR bands observed in novae and amine structures contained in QNCC play an important role in the origin of the broad 8 m feature, which characterizes the UIR bands in novae. QNCC is at present the best laboratory analog of organic dust formed around dusty classical novae, which carries the UIR bands in novae via thermal emission process [Endo et al.(2021)]. [ABSTRACT FROM AUTHOR]

We present a detailed photometric study of the bright cataclysmic variable, BG Triangulum (BG Tri), using ground-based observations mainly from the Rozhen Observatory, the All-Sky Automated Survey for Supernovae (ASAS-SN), the Transiting Exoplanet Survey Satellite (TESS) and the Wide Angle Search for Planets (WASP). We report on the discovery of a negative superhump with P −sh = 0.1515(2) d and a co-existing superorbital variation with P  = 3.94(53) d in data from 2019 and 2020. A positive superhump with P +sh = 0.1727(14) d is also discovered in data from 2006. The obtained negative superhump deficit ε− = 0.044(1) and the positive superhump excess ε+ = 0.090(9) give us an independent photometric evaluation of the mass ratio (q) of the system, which we find to be q − = 0.37(2) and q + = 0.40(5), respectively. We also present a study of the quasi-periodic oscillations and stochastic variability (flickering) in BG Tri. The light curves show a rich mixture of simultaneously overlapping quasi-periods ranging from 5 to 25 min. The multicolour (UBVRI) photometric observations from the Rozhen Observatory reveal the typical increase of the flickering amplitudes to the shorter wavelengths. The recently introduced A 60 amplitude of the flickering light source in all studied photometric bands is systematically lower when the negative superhump is gone in season 2021. [ABSTRACT FROM AUTHOR]

The growing number of multi-epoch optical and infrared sky surveys are uncovering unprecedented numbers of new variable stars, of an increasing number of types. The short interval between observations in adjacent near-infrared filters in the UKIDSS Galactic Plane Survey (UGPS) allows for the discovery of variability on the time-scale of minutes. We report on the nature of one such object, through the use of optical spectroscopy, time series photometry, and targeted X-ray observations. We propose that UGPS J194310.32+183851.8 is a magnetic cataclysmic variable star of novel character, probably featuring a longer than average spin period and an orbital period likely to be shorter than the period gap (i.e. P orb < 2 h). We reason that the star is likely a member of the short-period intermediate-polar subclass that exists below this period boundary, but with the additional feature that system's spectral energy distribution is fainter and redder than other members of the group. [ABSTRACT FROM AUTHOR]

Cataclysmic variables (CVs) exhibit a plethora of variable phenomena many of which require long, uninterrupted light curves to reveal themselves in detail. The month long data sets provided by TESS are well suited for this purpose. TESS has the additional advantage to have observed a huge number of stars, among them many CVs. Here, a search for periodic variations in a sample of CVs of the novalike and old novae subtypes is presented. In 10 of the 15 targets either previously unseen positive or negative superhumps or unusual features in known superhumps are identified. The TESS light curves demonstrate that the occurrence of superhumps in these types of CVs is not an exception but quite common. For 8 systems new or improved values for the orbital period are measured. In TV Col the long-sought optical manifestation of the white dwarf spin period is first seen in form of its orbital sideband. The mystery of multiple photometric periods observed in CP Pup in the past is explained by irregularly occurring anomalous states which are reflected in the light curve. [ABSTRACT FROM AUTHOR]

We give an updated version of the analytical equation of state used in the Cambridge stellar evolution code (stars) as a free to use open-source package that we have used to model cool white dwarfs (WDs) down to temperatures |$\log _{10}(T_\mathrm{eff}/\mathrm{K})\, =\, 3$|⁠. With this update in the stars code, we model the secular evolution of cataclysmic variable (CV) stars using a double dynamo model wherein there is an interplay between two α − Ω dynamos, one in the convective envelope and the other at the boundary of a slowly rotating shrinking radiative core and the growing convective envelope. We confirm that this model provides a physical formalism for the interrupted magnetic braking paradigm. In addition, our model also provides a mechanism for extra angular momentum loss below the period gap. We construct the relative probability distribution of orbital periods P orb using the mass distribution of WDs in CVs and find that our model excellently reproduces the period gap and the observed period minimum spike in CV distribution. We also compare the evolutionary trajectories from our model with those of other empirical models and find agreement between the two. We also report good agreement between our modelled systems and observational data. [ABSTRACT FROM AUTHOR]

This document is a correction to a paper titled "TESS light curves of cataclysmic variables – III – More superhump systems among old novae and nova-like variables" published in the Monthly Notices of the Royal Astronomical Society. The correction addresses an error in the calculation of the period excess of the star KIC 9406652, which was found to deviate from the general trend. The correct period excess value is -0.0593, and the corrected location of KIC 9406652 is indicated in Figure 1. The correction also includes updated equations related to the period excess. [Extracted from the article]

Accreting white dwarfs (WDs) in cataclysmic variables (CVs) provide crucial insights about the accretion of mass and angular momentum in all types of binaries, including accreting NSs and BHs. Accreting WDs are the critical component in the single degenerate pathway to SNe Ia, along with the double degenerate merger pathway, they are the standard candles of cosmology proving that the universe is accelerating and the existence of dark energy. Another key question is whether the WD in a CV can grow in mass despite the mass loss due to thousands of nova explosions in its lifetime. Angular momentum loss drives CV evolution and accreting WDs offer critically needed WD masses from Gaia distances and reliable surface temperatures to derive the most accurate accretion rates. We review the studies on accreting WDs, including WD masses, accurate rotational velocities and chemical abundances of elements. Most of the progress that has been made is based upon Hubble Space Telescope spectroscopy and FUSE spectroscopy in the UV spectral region during dwarf nova quiescence and the low states of novalike variables, when the accreting WD dominates the UV spectral range. [ABSTRACT FROM AUTHOR]

We report on our second campaign to search for old nova shells around cataclysmic variables (CVs). Our aim was to test the theory that nova eruptions cause cycles in the mass transfer rates of CVs. These mass transfer cycles change the behaviour of CVs during their intereruption periods. We examined H α images of 47 objects and found no new shells around any of the targets. Combining our latest results with those of our previous campaign (Sahman et al.), and the searches by Schmidtobreick et al. and Pagnotta & Zurek, we estimate that the nova-like phase of the mass transfer cycle lasts ∼3000 yr. [ABSTRACT FROM AUTHOR]

DW Cnc is an intermediate polar which has previously been observed in both high and low states. Observations of the high state of DW Cnc have previously revealed a spin period at ∼38.6 min, however, observations from the 2018 to 2019 low state showed no evidence of the spin period. We present results from our analysis of 12 s cadence photometric data collected by Next Generation Transit Survey of DW Cnc during the high state which began in 2019. Following the previously reported suppression of the spin period signal, we identify the return of this signal during the high state, consistent with previous observations of it. We identify this as the restarting of accretion during the high state. We further identified three short outbursts lasting ∼1 d in DW Cnc with a mean recurrence time of ∼60 d and an amplitude of ∼1 mag. These are the first outbursts identified in DW Cnc since 2008. Due to the short nature of these events, we identify them not as a result of accretion instabilities but instead either from instabilities originating from the interaction of the magnetorotational instability in the accretion disc and the magnetic field generated by the white dwarf or the result of magnetic gating. [ABSTRACT FROM AUTHOR]

During the outburst of the dwarf nova AY Lac in October 2020, the authors obtained more 2200 CCD-frames in UBVRcIc-bands of the variable. An analysis of the observed photometric series showed that superhumps were observed on this type SUWZ star both before early on and in the "B" stage, with periods of 0d.058074 and 0d.059418, respectively. The change in the shape of the superhumps during the outburst was studied, values of Pdot = P / P = 6.6 ∙10-5 and a period excess of ε = 0.024 were found, and a most probable ratio q = 0.11 of the masses of the components was estimated, as well as color temperatures and a number of other quantities. It is shown that AY Lac is a typical WZ Sge-type star in terms of all the characteristics that were studied. [ABSTRACT FROM AUTHOR]

The search for special and rare celestial objects has always played an important role in astronomy. Cataclysmic Variables (CVs) are special and rare binary systems with accretion disks. Most CVs are in the quiescent period, and their spectra have the emission lines of Balmer series, HeI, and HeII. A few CVs in the outburst period have the absorption lines of Balmer series. Owing to the scarcity of numbers, expanding the spectral data of CVs is of positive significance for studying the formation of accretion disks and the evolution of binary star system models. At present, the research for astronomical spectra has entered the era of Big Data. The Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) has produced more than tens of millions of spectral data. the latest released LAMOST-DR7 includes 10.6 million low-resolution spectral data in 4926 sky regions, providing ideal data support for searching CV candidates. To process and analyze the massive amounts of spectral data, this study employed the Light Gradient Boosting Machine (LightGBM) algorithm, which is based on the ensemble tree model to automatically conduct the search in LAMOST-DR7. Finally, 225 CV candidates were found and four new CV candidates were verified by SIMBAD and published catalogs. This study also built the Gradient Boosting Decision Tree (GBDT), Adaptive Boosting (AdaBoost), and eXtreme Gradient Boosting (XGBoost) models and used Accuracy, Precision, Recall, the F1-score, and the ROC curve to compare the four models comprehensively. Experimental results showed that LightGBM is more efficient. The search for CVs based on LightGBM not only enriches the existing CV spectral library, but also provides a reference for the data mining of other rare celestial objects in massive spectral data. [ABSTRACT FROM AUTHOR]