In 2010/3, the Large Area Telescope on board Fermi revealed a transient gamma-ray source, positionally coincident with the optical nova in the symbiotic binary, V407Cyg. This event marked the first discovery of gamma-ray emission from a nova. We aimed to obtain resolved radio imaging of the material involved in the nova event; to determine the ejecta geometry and advance velocity directly in the image plane; to constrain the physical conditions of the system. We observed the source with the EVN and the VLBA over 16 epochs, between 20 days and 6 months after the optical discovery. The source is initially very dim but it later shows a substantial increase in brightness and a resolved shell-like structure 40 to 90 days after the optical event. The shell has a projected elliptical shape and is asymmetric in brightness and spectral index, being brighter and characterised by a rising spectrum at the S-E edge. We determine a projected velocity of ~3500 km/s in the initial phase, and ~2100 km/s between day 20 and 91. We also found an emitting feature about 350 mas (940 AU) to the N-W, advancing at a projected velocity of ~700 km/s along the polar axis of the binary. The total flux density in the VLBI images is significantly lower than that previously reported at similar epochs and over much wider angular scales with the VLA. Optical spectra demonstrated that in 2010 we were viewing V407Cyg along the equatorial plane and from behind the Mira. Our radio observations image the bipolar flow of the ejecta perpendicular to the orbital plane, where deceleration is much lower than through the equatorial plane probed by the truncated profile of optical emission lines. The separated polar knot at 350 mas and the bipolar flow strictly resemble the similar arrangement seen in Hen 2-104. The observed ~700 km/s expansion constrains the launch-date of the polar knot around 2004. [Abridged]
V476 Cyg (Nova Cyg 1920) is a bright, fast nova reaching a photographic magnitude of 2.0. Using the Zwicky Transient Facility (ZTF) public database, I found that this nova is currently a dwarf nova with a cycle length of ~24 d. Compared to other classical novae currently in dwarf nova-type states, outbursts of V476 Cyg are rapidly rising and short with durations of a few days. Based on the AAVSO observations, this nova was probably already in the dwarf nova-type phase in 2016, 96 years after the nova eruption. I found a possible orbital period of 0.1018002(6) d using the ZTF data, which would …
We present multi-frequency radio observations of the 2010 nova event in the symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array and spanning 1-45 GHz and 17-770 days following discovery. This nova---the first ever detected in gamma rays---shows a radio light curve dominated by the wind of the Mira giant companion, rather than the nova ejecta themselves. The radio luminosity grew as the wind became increasingly ionized by the nova outburst, and faded as the wind was violently heated from within by the nova shock. This study marks the first time that this physical mech…
Morphology of nova ejecta is essential for fully understanding the physical processes involved in nova eruptions. We studied the 3D morphology of the expanding ejecta of the extremely slow nova V1280 Sco with a unique light curve. Synthetic line profile spectra were compared to the observed [O III] 4959, 5007 and [N II] 5755 emission line profiles in order to find the best-fit morphology, inclination angle, and maximum expansion velocity of the ejected shell. We derive the best fitting expansion velocity, inclination, and squeeze as $V_{\rm exp} = 2100^{+100}_{-100}$ \,km\,s$^{-1}$, $i = 80^{+…
We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. A very soft blackbody-like component peaking at 0.5 keV indicates that either we observe remaining, localized hydrogen burning on the surface of the white dwarf, or accretion onto a magnetized polar cap. In the second case, V2491 Cyg is a candidate "soft intermediate polar". We obtained the best fit for the X-ray spectra with several components: two of thermal plasm…
Nova V2491 Cyg was discovered on April 10.72 UT 2008 (Nakano, 2008). Here we present spectrophotometric premises that V2491 Cyg can be a good candidate for recurrent nova (RNe). Its properties are compared to five well known RNe with red dwarf secondaries (U Sco, V394 Cra, T Pyx, CI Aql, IM Nor) and recently confirmed as recurrent nova V2487 Oph (Pagnotta et al.,2008). Photometric $U, B, V, R_C, I_C$ and moderate resolution (R$\sim 1500$) spectral observations of V2491 Cyg were carried out in the Torun Observatory (Poland) between April 14 and May 20 2008.
Q Cygni (Nova Cygni 1876) is the third oldest old novae (after WY Sge and V841 Oph) with a long orbital period of 10.08 hours and spectroscopic peculiarities in the optical including the presence of variable wind outflow revealed by optical P Cygni profiles in the HeI lines and H alpha beta (Kafka et al. 2003). We have carried out a synthetic spectral analysis of a far ultraviolet IUE archival spectrum of Q Cygni using our optically thick, steady state, accretion disk models and model white dwarf photospheres. We find that the accretion light of a luminous accretion disk dominates the FUV flux…
V2491 Cygni (Nova Cygni 2008 No.2) was detected as a transient supersoft X-ray source with the Swift XRT as early as 40 days after the outburst, suggesting a very massive white dwarf (WD) close to the Chandrasekhar limit. We present a unified model of near infrared, optical, and X-ray light curves for V2491 Cyg, and have estimated, from our best-fit model, the WD mass to be 1.3 \pm 0.02 M_\sun with an assumed chemical composition of the envelope, X=0.20, Y= 0.48, X_{CNO} =0.20, X_{Ne} =0.10, and Z = 0.02 by mass weight. We strongly recommend detailed composition analysis of the ejecta because …
The classical nova V2491 Cyg was once suggested to be a recurrent nova. We have broadly reproduced the light curve of V2491 Cyg by a nova outburst model on a cold $1.36~M_\odot$ white dwarf (WD), which strongly suggests that V2491 Cyg is a classical nova outbursting on a cold very massive WD rather than a recurrent nova outbursting on a warmer WD like the recurrent nova RS Oph. In a long-term evolution of a cataclysmic binary, an accreting WD has been settled down to a thermal equilibrium state with the balance of gravitational energy release and neutrino loss. The central temperature of the W…
The photometric and spectroscopic evolution of the He/N and very fast Nova Cyg 2008 N2 (V2491 Cyg) is studied in detail. A primary maximum was reached at V=7.45 +/-0.05 on April 11.37 (+/-0.1) 2008 UT, followed by a smooth decline characterized by t2(V)=4.8 days, and then a second maximum was attained at V=9.49 +/-0.03, 14.5 days after the primary one. This is the only third nova to have displayed a secondary maximum, after V2362 Cyg and V1493 Aql. The development and energetics of the secondary maximum is studied in detail. The smooth decline that followed was accurately monitored until day +…
The optical spectroscopic observations of ASASSN-18fv observed from 2018 March 24 to 2019 Jan 26 are presented. The optical spectra are obtained from Mirranook, Vainu Bappu and South African Astronomical observatories. The spectra are dominated by hydrogen Balmer, Fe II and O I lines with P-Cygni profiles in the early phase, typical of an Fe II class nova. The spectra show He I lines along with H I and O I emission lines in the decline phase placing the nova in the hybrid class of novae. The spectra show rapid development in high ionization lines in this phase. Analysis of the light curve indi…
We continue our study of the physical properties of the recurrent nova T Pyx, focussing on the structure of the ejecta in the nebular stage of expansion during the 2011 outburst. The nova was observed contemporaneously with the Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R ~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration), and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar. 28 (absolute fluxes). We use standard plasma diagnostics (e.g.…
The shock interaction and evolution of nova ejecta with a wind from a red giant star in a symbiotic binary system are investigated via three-dimensional hydrodynamics simulations. We specifically model the March 2010 outburst of the symbiotic recurrent nova V407~Cygni from the quiescent phase to its eruption phase. The circumstellar density enhancement due to wind-white dwarf interaction is studied in detail. It is found that the density-enhancement efficiency depends on the ratio of the orbital speed to the red giant wind speed. Unlike another recurrent nova, RS~Ophiuchi, we do not observe a …
In this paper we analyzed the behavior of the unusual dwarf nova EM Cyg using the data obtained in April-October, 2007 in Vyhorlat observatory (Slovak Republic) and in September, 2006 in Crimean Astrophysical Observatory (Ukraine). During our observations EM Cyg has shown outbursts in every 15-40 days. Because on the light curves of EM Cyg the partial eclipse of an accretion disc is observed we applied the eclipse mapping technique to reconstruct the temperature distribution in eclipsed parts of the disc. Calculations of the accretion rate in the system were made for the quiescent and the outb…
The radio light curves of novae rise and fall over the course of months to years, allowing for detailed observations of the evolution of the nova shell. However, the main parameter determined by radio models of nova explosions - the mass of the ejecta - often seems to exceed theoretical expectations by an order of magnitude. With the recent technological improvements on the Karl G. Jansky Very Large Array (VLA), new observations can test the assumptions upon which ejecta mass estimates are based. Early observations of the classical nova V1723 Aql showed an unexpectedly rapid rise in radio flux…
Synoptic spectroscopic observations of the U Sco 2010 outburst from maximum light to quiescence as well as a contemporaneous X-ray observation are presented and analyzed. The X-ray spectrum 52 days after outburst indicates a hot source (kTbb ~ 70 eV). . Narrow line components from the irradiated companion atmosphere were observed in hydrogen and helium optical recombination lines. The formation of a nebular spectrum is seen for the first time in this class of recurrent novae, allowing a detailed study of the ejecta using photoionization models. Unusual [OIII] auroral-to-nebular line ratios wer…
The total masses ejected during classical nova eruptions are needed to answer two questions with broad astrophysical implications: Can accreting white dwarfs be pushed towards the Chandrasekhar mass limit to yield type Ia supernovae? Are Ultra-luminous red variables a new kind of astrophysical phenomenon, or merely extreme classical novae? We review the methods used to determine nova ejecta masses. Except for the unique case of BT Mon (nova 1939), all nova ejecta mass determinations depend on untested assumptions and multi-parameter modeling. The remarkably simple assumption of equipartition b…
We present X-ray observations of novae V2491 Cyg and KT Eri about 9 years post-outburst, of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM-Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times10^{-9}-10^{-8}M_\odot/yr$, while for KT…
The formation of bimodal dust species (that is, both of silicate and amorphous carbon dust grains are observed in a nova eruption) in nova ejecta is still debated. Using the Modules for Experiments in Stellar Astrophysics code and considering the effects of WD's mass, mass-accretion rate and the chemical profiles of WD which are described by new parameter --- mixing depth on the chemical abundances of nova ejecta, we investigate the possibility that bimodal dust species are produced in a nova eruption. We find that $C/O$ (the ratio of carbon number density to oxygen number density) of nova eje…
Context. Classical novae are thermonuclear explosions hosted by accreting white dwarfs in stellar binary systems. Material piles up on top of the white dwarf star under mildly degenerate conditions, driving a thermonuclear runaway. The energy released by the suite of nuclear processes operating at the envelope (mostly proton-capture reactions and beta-decays) heats the material up to peak temperatures ranging from 100 to 400 MK. In these events, about 10-3 - 10-7 Msun, enriched in CNO and, sometimes, other intermediate-mass elements (e.g., Ne, Na, Mg, Al), are ejected into the interstellar med…
We conducted an X-ray spectroscopic study of the classical nova V2491 Cygni using our target-of-opportunity observation data with the Suzaku and XMM-Newton satellites as well as archived data with the Swift satellite. Medium-resolution (R~10-50) spectra were obtained using the X-ray CCD spectrometers at several post-nova epochs on days 9, 29, 40, 50, and 60-150 in addition to a pre-nova interval between days -322 and -100 all relative to the time when the classical nova was spotted. We found remarkable changes in the time series of the spectra: (a) In the pre-nova phase and on day 9, the 6.7 k…
Of all the light elements, the evolution of lithium (Li) in the Milky Way is perhaps the most difficult to explain. Li is difficult to synthesize and is easily destroyed, making most stellar sites unsuitable for producing Li in sufficient quantities to account for the proto-solar abundance. For decades, novae have been proposed as a potential explanation to this 'Galactic Li problem', and the recent detection of 7Be in the ejecta of multiple nova eruptions has breathed new life into this theory. In this work, we assess the viability of novae as dominant producers of Li in the Milky Way. We pre…
Hubble Space Telescope} images of the ejecta surrounding the nova T Pyxidis resolve the emission into more than two thousand bright knots. We simulate the dynamical evolution of the ejecta from T Pyxidis during its multiple eruptions over the last 150 years using the adaptive mesh refinement capability of the gas dynamics code Ramses. We demonstrate that the observed knots are the result of Richtmeyer-Meshkov gas dynamical instabilities (the equivalent of Rayleigh-Taylor instabilities in an accelerated medium). These instabilities are caused by the overrunning of the ejecta from the classical …
According to the nova model from \citet{Yaron2005} and \citet{Jose1998} and using Monte Carlo simulation method, we investigate the contribution of chemical abundances in nova ejecta to the interstellar medium (ISM) of the Galaxy. We find that the ejected mass by classical novae (CNe) is about $2.7\times10^{-3}$ $ \rm M_\odot\ {\rm yr^{-1}}$. In the nova ejecta, the isotopic ratios of C, N and O, that is, $^{13}$C/$^{12}$C, $^{15}$N/$^{14}$N and $^{17}$O/$^{16}$O, are higher about one order of magnitude than those in red giants. We estimate that about 10$\%$, 5$\%$ and 20$\%$ of $^{13}$C, $^{1…
Classical nova events in symbiotic stars, although rare, offer a unique opportunity to probe the interaction between ejecta and a dense environment in stellar explosions. In this work, we use X-ray data obtained with Swift and Suzaku during the recent classical nova outburst in V407 Cyg to explore such an interaction. We find evidence of both equilibrium and non-equilibrium ionization plasmas at the time of peak X-ray brightness, indicating a strong asymmetry in the density of the emitting region. Comparing a simple model to the data, we find that the X-ray evolution is broadly consistent with…
We present optical and near-infrared (NIR) photometry of a classical nova, V2362 Cyg (= Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening with a long duration from 100 to 240 d after the maximum of the nova. Our multicolor observation indicates an emergence of a pseudophotosphere with an effective temperature of 9000 K at the rebrightening maximum. After the rebrightening maximum, the object showed a slow fading homogeneously in all of the used bands for one week. This implies that the fading just after the rebrightening maximum ( less or equal 1 week ) was caused by a slowly sh…
The X-ray flux of Nova V2491 Cyg reached a maximum some forty days after optical maximum. The X-ray spectrum at that time, obtained with the RGS of XMM-Newton, shows deep, blue-shifted absorption by ions of a wide range of ionization. We show that the deep absorption lines of the X-ray spectrum at maximum, and nine days later, are well described by the following phenomenological model with emission from a central blackbody and from a collisionally ionized plasma (CIE). The blackbody spectrum (BB) is absorbed by three main highly-ionized expanding shells; the CIE and BB are absorbed by cold cir…
Nova Mon 2012 was the first classical nova to be detected as a high energy $γ$-ray transient, by Fermi-LAT, before its optical discovery. We study a time sequence of high resolution optical echelle spectra (Nordic Optical Telescope) and contemporaneous NOT, STIS UV, and CHIRON echelle spectra (Nov 20/21/22). We use [O III] and H$β$ line fluxs to constrain the properties of the ejecta. We derive the structure from the optical and UV line profiles and compare our measured line fluxes for with predictions using Cloudy with abundances from other ONe novae. Mon 2012 is confirmed as an ONe nova. We …
The nova outburst experienced in 2010 by the symbiotic binary Mira V407 Cyg has been extensively studied at optical and infrared wavelengths with both photometric and spectroscopic observations. This outburst, reminiscent of similar events displayed by RS Oph, can be described as a very fast He/N nova erupting while being deeply embedded in the dense wind of its cool giant companion. The hard radiation from the initial thermonuclear flash ionizes and excites the wind of the Mira over great distances (recombination is observed on a time scale of 4 days). The nova ejecta is found to progressivel…
V906 Carinae was one of the best observed novae of recent times. It was a prolific dust producer and harboured shocks in the early evolving ejecta outflow. Here, we take a close look at the consequences of these early interactions through study of high-resolution UVES spectroscopy of the nebular stage and extrapolate backwards to investigate how the final structure may have formed. A study of ejecta geometry and shaping history of the structure of the shell is undertaken following a spectral line SHAPE model fit. A search for spectral tracers of shocks in the nova ejecta is undertaken and an a…
The formation of bimodal dust species (namely the silicate and amorphous carbon dust grains coexistent) in a nova eruption is an open problem. According to the nova model simulated by Modules for Experiments in Stellar Astrophysics code, we calculate the formation and growth of carbon (C) and forsterite (Mg2SiO4) dust grains purely in nova ejecta for the fee-expansion model and the radiative shock model by assuming spherical geometry of the nova ejecta. In these models, the chemical properties of pre-existing circumstellar medium are not taken into account. In the free-expansion model, the nov…
The nova outburst of V407 Cyg in 2010 Mar. 10 was the first observed for this star but its close resemblance to the well known symbiotic-like recurrent nova RS Oph suggests that it is also a member of this rare type of Galactic novae. The nova was the first detected at $γ$-ray energies and is the first known nova explosion for this system. The extensive multiwavelength coverage of this outburst makes it an ideal comparison with the few other outbursts known for similar systems. We extend our previous analysis of the Mira and the expanding shock from the explosion to detail the time development…
Despite being the prototype of its class, T Pyx is arguably the most unusual and poorly understood recurrent nova. Here, we use radio observations from the Karl G. Jansky Very Large Array to trace the evolution of the ejecta over the course of the 2011 outburst of T Pyx. The radio emission is broadly consistent with thermal emission from the nova ejecta. However, the radio flux began rising surprisingly late in the outburst, indicating that the bulk of the radio-emitting material was either very cold, or expanding very slowly, for the first ~50 days of the outburst. Considering a plausible ran…
Available data for novae show that the X-ray and visible spectral regions correlate with each other as they evolve. Large differences in ionization exist simultaneously in the two wavelength regimes, and a straightforward model is proposed that explains the characteristics observed in both spectral regimes. Its key features are (1) ejected blobs of very high density gas from the white dwarf that expand to create within each clump a wide range of emitting density, ionization, and velocity, and (2) a more homogeneous circumbinary envelope of gas that is produced by secondary star mass loss. The …
A fraction of classical novae form dust during the early stages of their outbursts. The classical CO nova V5668 Sgr (Nova Sgr. 2015b) underwent a deep photometric minimum about 100 days after outburst that was covered across the spectrum. A similar event was observed for an earlier CO nova, V705 Cas (Nova Cas 1993) and a less optically significant event for the more recent CO nova V339 Del (Nova Del 2013). This study provides a "compare and contrast" of these events to better understand the very dynamical event of dust formation. We show the effect of dust formation on multiwavelength high res…
We report on the time variation of SiO maser emission from the symbiotic stellar system V407 Cyg after the classical nova outburst on 2010 March 10. Although both the SiO $J=1$--0 $v=1$ and 2 lines at 43.122 and 42.821 GHz were found previously in the envelope of a mira in the binary system, only weak emission of the $J=1$--0 $v=2$ line has continuously been detectable after the nova outburst. The line profile exhibited a dramatic change several weeks after the burst; the component on the higher-velocity side of the systemic velocity disappeared two weeks after the burst, and a new persistent …
Pre-outburst 2MASS and WISE photometry of Nova Sco 2014 (V1534 Sco) have suggested the presence of a cool giant at the location of the nova in the sky. The spectral evolution recorded for the nova did not however support a direct partnership because no flash-ionized wind and no deceleration of the ejecta were observed, contrary to the behavior displayed by other novae which erupted within symbiotic binaries like V407 Cyg or RS Oph. We have therefore obtained an 0.8-2.5 micron spectra of the remnant of Nova Sco 2014 in order to ascertain if a cool giant is indeed present and if it is physically…
We present some results of an ongoing study of the long-term spectroscopic variations of AG Dra, a prototypical eruptive symbiotic system. We discuss the effects of the environment and orbital modulation in this system and some of the physical processes revealed by a comparison with the nova outburst of the symbiotic-like recurrent nova V407 Cyg 2010.
Nova Cen 2013 (V1369 Cen) is the fourth bright nova observed panchromatically through high resolution UV+optical multi epoch spectroscopy. It is also the nova with the richest set of spectra (both in terms of data quality and number of epochs) thanks to its exceptional brightness. Here, we use the late nebular spectra taken between day ~250 and day ~837 after outburst to derive the physical, geometrical and kinematical properties of the nova. We compare the results with those determined for the other panchromatic studies in this series: T Pyx, V339 Del (nova Del 2013), and V959 Mon (nova Mon 2…
Previously, Nova Puppis 1991 (V351 Pup) was measured to host one of the most massive ejections claimed in the literature. Multi-frequency radio detections from one epoch were published for this nova in the 1990's, and yet, the remaining data collected by the Very Large Array (VLA) have remained unpublished. In this paper, we analyze the remaining unpublished data sets for V351 Pup at frequencies of 4.9, 8.4, 14.9, and 22.5 GHz. We fit the resulting light curve to a model of expanding thermal ejecta, under the assumption that the radio emission is dominated by free-free radiation and accounting…
We have imaged the ejecta of GK Persei (Nova Persei 1901 A.D.) with the Hubble Space Telescope (HST), revealing hundreds of cometary-like structures. One or both ends of the structures often show a brightness enhancement relative to the structures' middle sections, but there is no simple regularity to their morphologies (in contrast with the Helix nebula). Some of the structures' morphologies suggest the presence of slow-moving or stationary material with which the ejecta is colliding, while others suggest shaping from a wind emanating from GK Per itself. A detailed expansion map of the nova's…
We report on the evidence of highly blue-shifted resonance lines of the singly ionised isotope of 7BeII in high resolution UVES spectra of Nova Sagittarii 2015 No. 2 (V5668 Sgr). The resonance doublet lines 7BeII at lambda 313.0583, 313.1228 nm are clearly detected in several non saturated and partially resolved high velocity components during the evolution of the outburst. The total absorption identified with Beryllium has an equivalent width much larger than all other elements and comparable to hydrogen. We estimate an atomic fraction N(7Be)/N(Ca) ~ 53-69 from unsaturated and resolved absorp…
We identify a new class of novae characterized by the post-eruption quiescent light curve being more than roughly a factor of ten brighter than the pre-eruption light curve. Eight novae (V723 Cas, V1500 Cyg, V1974 Cyg, GQ Mus, CP Pup, T Pyx, V4633 Sgr, and RW UMi) are separated out as being significantly distinct from other novae. This group shares a suite of uncommon properties, characterized by the post-eruption magnitude being much brighter than before eruption, short orbital periods, long-lasting supersoft emission following the eruption, a highly magnetized white dwarf, and secular declin…
V959 Mon (Nova Mon 2012) was first detected by the Fermi Large Area Telescope in June 2012, as a transient gamma-ray source. Subsequent optical observations showed that this gamma-ray emission was due to a classical nova explosion. Multi-frequency observations of V959 Mon with the VLA between June and September 2012 revealed dramatic brightening, and a spectrum that steepened with increasing frequency. High resolution radio images of V959 Mon using e-MERLIN are presented here, at six epochs between September 2012 and February 2014 which show morphological evolution of the source. While early e…
The expanding ejecta from a classical nova remains hot enough ($\sim10^{4}\, {\rm K}$) to be detected in thermal radio emission for up to years after the cessation of mass loss triggered by a thermonuclear instability on the underlying white dwarf (WD). Nebular spectroscopy of nova remnants confirms the hot temperatures observed in radio observations. During this same period, the unstable thermonuclear burning transitions to a prolonged period of stable burning of the remnant hydrogen-rich envelope, causing the WD to become, temporarily, a super-soft X-ray source. We show that photoionization …
It has recently been discovered that some, if not all, classical novae emit GeV gamma rays during outburst, but the mechanisms involved in the production of the gamma rays are still not well understood. We present here a comprehensive multi-wavelength dataset---from radio to X-rays---for the most gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we show that V1324 Sco is a canonical dusty Fe-II type nova, with a maximum ejecta velocity of 2600 km s$^{-1}$ and an ejecta mass of few $\times 10^{-5}$ M$_{\odot}$. There is also evidence for complex shock interactions, inclu…
The recurrent nova and symbiotic binary RS Oph erupted again in August 2021 for its eighth known outburst. As part of a multi-epoch and frequency campaign, we observed RS Oph 34 days after the outburst at 5 GHz with the European VLBI Network (EVN). The radio image is elongated over the east-west direction for a total extension of about 90 mas (or about 240 AU at the Gaia DR3 distance d=2.68 [-0.15/+0.17] kpc), and shows a bright and compact central component coincident with the Gaia astrometric position, and two lobes east and west of it, expanding perpendicular to the orbital plane. By compar…
Morpho-kinematic modeling allows us to disentangle the morphology and kinematics of an object. The technique has been applied to a number of novae where resolved imaging, or lack of, and spectroscopic line profile fitting, show how we may retrieve important parameters of the system, such as the maximum expansion velocity, inclination angle and the morphology of the ejected shell. Furthermore, this technique may be used as a predictor for searches of eclipses which will then provide us further information on the system parameters, such as the orbital period and the white dwarf mass.
We present multi-epoch optical and near-infrared observations of the highly reddened, \pion{Fe}{ii} class slow nova V2891 Cygni. The observations span 15 months since its discovery. The initial rapid brightening from quiescence, and the presence of a $\sim$35 day long pre-maximum halt, is well documented. The evidence that the current outburst of V2891 Cyg has undergone several distinct episodes of mass ejection is seen through time-varying P Cygni profiles of the O\,{\sc i} 7773\,$Å$ line. A highlight is the occurrence of a dust formation event centred around $\sim$+273d, which coincides with…
We present infrared spectroscopic and photometric observations of the nova V2468 Cyg covering the period from 2008 March 13 till 2008 November 11. The JHK spectra of the object have been taken from the Mount Abu Infrared Observatory using the Near-Infrared Imager/Spectrometer. Spectra from 0.8-5.2 micron are also presented that were obtained using the NASA Infrared Telescope Facility and the SPEX instrument. The spectra are dominated by strong H I lines from the Brackett and Paschen series, Fe II, OI and CI lines in the initial days, typical of an Fe II type nova. The lines were broader in the…
We report on the detection of the linear rms-flux relation in two accreting white dwarf binary systems: V1504 Cyg and KIC 8751494. The rms-flux relation relates the absolute root-mean-square (rms) variability of the light curve to its mean flux. The light curves analysed were obtained with the Kepler satellite at a 58.8 s cadence. The rms-flux relation was previously detected in only one other cataclysmic variable, MV Lyr. This result reenforces the ubiquity of the linear rms-flux relation as a characteristic property of accretion-induced variability, since it has been observed in several blac…
We present the results of our studies of the aperiodic optical flux variability for SS Cyg, an accreting binary systemwith a white dwarf. The main set of observational data presented here was obtained with the ANDOR/iXon DU-888 photometer mounted on the RTT-150 telescope, which allowed a record(for CCD photometers) time resolution up to 8 ms to be achieved. The power spectra of the source's flux variability have revealed that the aperiodic variability contains information about the inner boundary of the optically thick flow in the binary system. We show that the inner boundary of the optically…
We present Spitzer Space Telescope mid-infrared IRS spectra, supplemented by ground-based optical observations, of the classical novae V1974 Cyg, V382 Vel, and V1494 Aql more than 11, 8, and 4 years after outburst respectively. The spectra are dominated by forbidden emission from neon and oxygen, though in some cases, there are weak signatures of magnesium, sulfur, and argon. We investigate the geometry and distribution of the late time ejecta by examination of the emission line profiles. Using nebular analysis in the low density regime, we estimate lower limits on the abundances in these nova…
A massive millisecond magnetar may survive a merger of a neutron star (NS) binary, which would continuously power the merger ejecta. We develop a generic dynamic model for the merger ejecta with energy injection from the central magnetar. The ejecta emission (the "merger-nova") powered by the magnetar peaks in the UV band and the peak of lightcurve progressively shifts to an earlier epoch with increasing frequency. A magnetar-powered mergernova could have an optical peak brightness comparable to a supernova, which is a few tens or hundreds times brighter than the radioactive-powered merger-nov…
SS Cyg has long been recognized as the prototype of a group of dwarf novae that show only outbursts. However, this object has entered a quite anomalous event in 2021, which at first appeared to be standstill, i.e., an almost constant luminosity state, observed in Z Cam-type dwarf novae. This unexpected event gives us a great opportunity to reconsider the nature of standstill in cataclysmic variables. We have observed this anomalous event and its forerunner, a gradual and simultaneous increase in the optical and X-ray flux during quiescence, through many optical telescopes and the X-ray telesco…
T Pyxidis is the only recurrent nova surrounded by knots of material ejected in previous outbursts. Following the eruption that began on 2011 April 14.29, we obtained seven epochs (from 4 to 383 days after eruption) of Hubble Space Telescope narrowband Ha images of T Pyx . The flash of radiation from the nova event had no effect on the ejecta until at least 55 days after the eruption began. Photoionization of hydrogen located north and south of the central star was seen 132 days after the beginning of the eruption. That hydrogen recombined in the following 51 days, allowing us to determine a h…
Determining the evolution of the ejecta morphology of novae provides valuable information on the shaping mechanisms in operation at early stages of the nova outburst. Understanding such mechanisms has implications for studies of shaping for example in proto-Planetary Nebulae. Here we perform morpho-kinematical studies of V2491 Cyg using spectral data to determine the likely structure of the ejecta and its relationship to the central system and shaping mechanisms. We use Shape to model different morphologies and retrieve their spectra. These synthetic spectra are compared with observed spectra …
