T Pyx is a luminous recurrent nova that accretes at a much higher rate than is expected for its photometrically determined orbital period of about 1.8 hours. We here provide the first spectroscopic confirmation of the orbital period, P =1.829 hours (f=13.118368(11) c/d), based on time-resolved optical spectroscopy obtained at the VLT and the Magellan telescopes. We also derive an upper limit of the velocity semi-amplitude of the white dwarf, K1 = 17.9 +/- 1.6 km/s, and estimate a mass ratio of q = 0.20 +/- 0.03. If the mass of the donor star is estimated using the period-density relation and theoretical main-sequence mass-radius relation for a slightly inflated donor star, we find M2 = 0.14 +/- 0.03 Msun. This implies a mass of the primary white dwarf M1 = 0.7 +/- 0.2 Msun. If the white-dwarf mass is > 1 Msun, as classical nova models imply, the donor mass must be even higher. We therefore rule out the possibility that T Pyx has evolved beyond the period minimum for cataclysmic variables. We find that the system inclination is constrained to be approximately 10 degrees, confirming the expectation that T Pyx is a low-inclination system. We also discuss some of the evolutionary implications of the emerging physical picture of T Pyx. In particular, we show that epochs of enhanced mass transfer (like the present) may accelerate or even dominate the overall evolution of the system, even if they are relatively short-lived. We also point out that such phases may be relevant to the evolution of cataclysmic variables more generally.
We discuss the nebular phase emission during the 2011 outburst of the recurrent nova T Pyxidis and present preliminary results on the analysis of the line profiles. We also present some discussions about the binary system configurations and the X-ray emission, showing that the white dwarf mass should be larger than 0.8 M$\odot$.
We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx - either during previous eruptions or by a wind - rather than the accumulation of dust produced during eruptions.
T Pyxidis is the prototypical recurrent nova (RN) with a mysterious nova shell. We report new observations of the shell with HST. The knots in the shell are expanding with velocities 500-715 km/s, for a distance of 3500 pc. The fractional expansion of the knots is constant, and this implies no significant deceleration. Hence, the knots were ejected by an eruption close to the year 1866. Knots have turned on after 1995, and this demonstrates that the knots are powered by shocks from the collision of the 1866 ejecta with fast ejecta from later RN eruptions. The 1866 ejecta has a total mass of 10…
The recurrent nova T Pyxidis (T Pyx) is well known for its small binary separation, its unusually high luminosity in quiescence, and the spectacular Hubble Space Telescope (HST) images of its surrounding remnant. In 2011 April, T Pyx erupted for the first time since 1966. Here we describe HST observations in late 2011 of a transient reflection nebula around the erupting white dwarf (WD). Our observations of this light echo in the pre-existing remnant show that it is dominated by a clumpy ring with a radius of about 5", and an inclination of 30 to 40 degrees, with the eastern edge tilted toward…
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…
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…
We present our observational results of the recurrent nova T Pyxidis at its early stage of 2011 outburst, using a low-resolution spectrograph ($R\approx400$) attached to a 28cm telescope. Total nights of our observation are 11, among which 9 nights are during the pre-maximum stage. As a result we have obtained a detailed evolutional feature of this recurrent nova on the way to its maximum light. At first, on the earliest three nights ($-25 \sim -21$ days before maximum), broad and prominent emission lines such as Balmer series, He I, He II, N II, N III and O I together with P Cygni profile are…
T Pyx is a recurrent nova which has undergone eruptions on an almost regular basis every 20 years until reaching a long lasting quiescence between 1967 and 2011. We observed the long awaited 2011 explosion in the optical and near infrared with intermediate spectral resolution. In this paper we report on the change in the spectral type of the nova (both during its rise and during its fading), as well as the observed changes in the expansion velocities. We also present an interpretation of these changes and set them in the general framework of a new understanding of nova classification.
A distinguishing trait of the three known Galactic recurrent novae with the shortest orbital periods, T Pyx, IM Nor, and CI Aql, is that their optical decline time-scales are significantly longer than those of the other recurrent systems. On the other hand, some estimates of the mass of the ejecta, the velocity of the ejecta, and the duration of the soft X-rays emission of these systems are of the order of those of the other recurrent systems and the fast classical novae. We put forth a tentative explanation of this phenomenon. We propose that in these systems part of the material transferred …
With six recorded nova outbursts, the prototypical recurrent nova T Pyxidis is the ideal cataclysmic variable system to assess the net change of the white dwarf mass within a nova cycle. Recent estimates of the mass ejected in the 2011 outburst ranged from a few 1.E-5 sollar mass to 3.3E-4 sollar mass, and assuming a mass accretion rate of 1.E-8 to 1.E-7 Sollar mass/yr for 44yrs, it has been concluded that the white dwaf in T Pyx is actually losing mass. Using NLTE disk modeling spectra to fit our recently obtained Hubble Space Telescope (HST) COS and STIS spectra, we find a mass accretion rat…
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 …
We study the spectroscopic and ionized structural evolution of T Pyx during its 2011 outburst, and also study the variation in degree of polarization during its early phase. Optical spectroscopic data of this system obtained from day 1.28--2415.62 since discovery, and optical, broadband imaging polarimetric observations obtained from day 1.36--29.33 during the early phases of the outburst are used in the study. The physical conditions and the geometry of the ionized structure of the nova ejecta has been modelled for a few epochs using the photo-ionization code, CLOUDY in 1D and pyCloudy in 3D.…
The recurrent nova T Pyx was observed with the X-ray gratings of Chandra and XMM-Newton, 210 and 235 days, respectively, after the discovery of the 2011 April 14 outburst. The X-ray spectra show prominent emission lines of C, N, and O, with broadening corresponding to a full width at half maximum of ~2000-3000 km/s, and line ratios consistent with high-density plasma in collisional ionization equilibrium. On day 210 we also measured soft X-ray continuum emission that appears to be consistent with a white dwarf (WD) atmosphere at a temperature ~420,000 K, partially obscured by anisotropic, opti…
We report the discovery by M. Linnolt on JD 2455665.7931 (UT 2011 April 14.29) of the sixth eruption of the recurrent nova T Pyxidis. This discovery was made just as the initial fast rise was starting, so with fast notification and response by observers worldwide, the entire initial rise was covered (the first for any nova), and with high time resolution in three filters. The speed of the rise peaked at 9 mag/day, while the light curve is well fit over only the first two days by a model with a uniformly expanding sphere. We also report the discovery by R. Stubbings of a pre-eruption rise start…
Linear Spectropolarimetry of the 2011 Eruption of the Recurrent Nova T Pyx
Universidad Internacional de Valencia (VIU)（瓦伦西亚国际大学）；Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Unidad Asociada al CSIC（阿拉贡宇宙物理研究中心（CEFCA），CSIC联合单位）
The recurrent nova T Pyx underwent its sixth historical outburst in 2011, and became the subject of an intensive multi-wavelength observational campaign. We analyze data from the Swift and Suzaku satellites to produce a detailed X-ray light curve augmented by epochs of spectral information. X-ray observations yield mostly non-detections in the first four months of outburst, but both a super-soft and hard X-ray component rise rapidly after Day 115. The super-soft X-ray component, attributable to the photosphere of the nuclear-burning white dwarf, is relatively cool (~45 eV) and implies that the…
We report on near-IR interferometric observations of the outburst of the recurrent nova T Pyx. We obtained near-IR observations of T Pyx at dates ranging from t=2.37d to t=48.2d after the outburst, with the CLASSIC recombiner, located at the CHARA array, and with the PIONIER and AMBER recombiners, located at the VLTI array. These data are supplemented with near-IR photometry and spectra obtained at Mount Abu, India. Slow expansion velocities were measured (<300km/s) before t=20d (assuming D=3.5kpc). From t=28d on, the AMBER and PIONIER continuum visibilities (K and H band, respectively) are be…
The nova T Pyx was observed with high resolution spectroscopy (R ~ 65000) spectroscopy, beginning 1 day after discovery of the outburst and continuing through the last visibility of the star at the end of May 2011. The interstellar absorption lines of Na I, Ca II, CH, CH$^+$, and archival H I 21 cm emission line observations have been used to determine a kinematic distance. Interstellar diffuse absorption features have been used to determine the extinction independent of previous assumptions. Sample Fe-peak line profiles show the optical depth and radial velocity evolution of the discrete comp…
In recent years, recurrent nova eruptions are often observed very intensely in wide range of wavelengths from radio to optical to X-rays. Here I present selected highlights from recent multi-wavelength observations. The enigma of T Pyx is at the heart of this paper. While our current understanding of CV and symbiotic star evolution can explain why certain subset of recurrent novae have high accretion rate, that of T Pyx must be greatly elevated compared to the evolutionary mean. At the same time, we have extensive data to be able to estimate how the nova envelope was ejected in T Pyx, and it t…
We report a 20-year campaign to track the 1.8 hour photometric wave in the recurrent nova T Pyxidis, using the global telescope network of the Center for Backyard Astrophysics. During 1996-2011, that wave was highly stable in amplitude and waveform, resembling the orbital wave commonly seen in supersoft binaries. The period, however, was found to increase on a timescale P/P-dot=3x10^5 years. This suggests a mass transfer rate in quiescence of ~10^-7 M_sol/yr, in substantial agreement with the accretion rate based on the star's luminosity. This is ~2000x greater than is typical for cataclysmic …
We present Hubble Space Telescope ultraviolet spectroscopy of the recurrent nova T Pyxidis obtained more than 5 years after its 2011 outburst indicating that the system might not have yet reached its deep quiescent state. The ultraviolet data exhibit a 20% decline in the continuum flux from the pre-outburst deep quiescence state to the post-outburst near quiescent state. We suggest that a decline across each recurring nova eruption might help explain the proposed 2mag steady decline of the system since 1866. Using an improved version of our accretion disk model as well as International Ultravi…
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.…
Recurrent novae are star systems in which a massive white dwarf accretes material at such a high rate that it undergoes thermonuclear runaways every 1 - 100 years. They are the only class of novae in which the white dwarf can grow in mass, making some of these systems strong Type Ia supernova progenitor candidates. Almost all known recurrent novae are long-period (P_orb > 12 hrs) binary systems in which the requisite mass supply rate can be provided by an evolved (sub-)giant donor star. However, at least two recurrent novae are short-period (P_orb < 3 hrs) binaries in which mass transfer would…
We investigated the optical lightcurve of T Pyx during its 2011 outburst by compiling a database of SMEI and AAVSO observations. The SMEI lightcurve, providing unprecedented detail covering 1.5-49d post-discovery, was divided into four phases based on the idealised CN optical lightcurve; the initial rise (1.5-3.3d), the pre-maximum halt (3.3-13.3d), the final rise (14.7-27.9d), and the early decline (27.9d-). The SMEI lightcurve contains a strongly detected period of 1.44+/-0.05d during the pre-maximum phase. These oscillations resemble those found in TNR models arising from instabilities in t…
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.
We report a long campaign to track the 1.8 hr photometric wave in the recurrent nova T Pyxidis, using the global telescope network of the Center for Backyard Astrophysics. During 1996-2011, that wave was highly stable in amplitude and waveform, resembling the orbital wave commonly seen in supersoft binaries. The period, however, was found to increase on a timescale P/P-dot=3x10^5 yr. This suggests a mass transfer rate of ~10^-7 M_sol/yr in quiescence. The orbital signal became vanishingly weak (<0.003 mag) near maximum light of the 2011 eruption. After it returned to visibility near V=11, the …
The reported positions of 964 suspected nova eruptions in M31 recorded through the end of calendar year 2013 have been compared in order to identify recurrent nova candidates. To pass the initial screen and qualify as a recurrent nova candidate two or more eruptions were required to be coincident within 0.1', although this criterion was relaxed to 0.15' for novae discovered on early photographic patrols. A total of 118 eruptions from 51 potential recurrent nova systems satisfied the screening criterion. To determine what fraction of these novae are indeed recurrent the original plates and publ…
We have examined the optical/X-ray light curves of seven well-observed recurrent novae, V745 Sco, M31N 2008-12a, LMC N 1968, U Sco, RS Oph, LMC N 2009a, T Pyx, and one recurrent nova candidate LMC N 2012a. Six novae out of the eight show a simple relation that the duration of supersoft X-ray source (SSS) phase is 0.70 times the total duration of the outburst ($=$ X-ray turnoff time), i.e., $t_{\rm SSS}=0.70 t_{\rm off}$, the total duration of which ranges from 10 days to 260 days. These six recurrent novae show a broad rectangular X-ray light curve shape, first half a period of which is highly…
A spectrum of the quiescent counterpart of the Recurrent Nova candidate M31N 1966-08a (= M31N 1968-10c) obtained with LRS2 on the Hobby-Eberly Telescope reveals the object to be a foreground Galactic dMe flare star, and not a nova in M31.
Recurrent novae are binaries harboring a very massive white dwarf (WD), as massive as the Chandrasekhar mass, because of their short recurrence periods of nova outbursts of 10-100 years. Thus, recurrent novae are considered as candidates of progenitors of Type Ia supernovae (SNe Ia). In fact, the SN Ia PTF11kx showed evidence that its progenitor is a symbiotic recurrent nova. The binary parameters of recurrent novae have been well determined, especially for the ones with frequent outbursts, U Sco and RS Oph, which provide useful information on the elementary processes in binary evolution towar…
In this review, I present our current state of knowledge regarding both Classical Nova and Recurrent Nova systems. Two particular objects (V1974 Cyg and RS Oph) are chosen to illustrate the range of phenomena that may be associated with their outbursts. The wider importance of nova research is emphasised and some of the most pressing unsolved problems are summarised.
M31 is an ideal laboratory for observing and studying recurrent novae. To date, there have been 18 recurrent nova discovered in M31, six of which have recurrence periods less than nine years. M31N 2017-12a (AT2017jdm) is a transient that was reported near the center of M31, with the time of outburst estimated to be 2017 December 24.141 +/- 0.42 based on constraints from previous data. Here we present the photometric observations of M31N 2017-12a, which we confirm as a recurrence of M31N 2007-10b.
Over the last 40 years, multi-frequency observations, coupled with advances in theoretical modelling, have led to a much fuller understanding of the nova phenomenon. Here I give a brief review of the current state of knowledge of Classical and Recurrent Novae including their central systems; the causes and consequences of their outbursts; sub-types, and possible relationships to Type Ia Supernovae. Particular attention is paid to the Recurrent Nova RS Ophiuchi as it shows a wealth of phenomena associated with its 2006 outburst. Finally, some open questions and avenues for future work are summa…
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…
This review concentrates on the multifrequency behaviour of RS Ophiuchi and in particular during its latest outburst. Confirmation of the 1945 outburst, bipolar outflows and its possible fate as a Type Ia Supernova are discussed.
Models have long predicted that the frequency-averaged masses of white dwarfs in Galactic classical novae are twice as large as those of field white dwarfs. Only a handful of dynamically well-determined nova white dwarf masses have been published, leaving the theoretical predictions poorly tested. The recurrence time distributions and mass accretion rate distributions of novae are even more poorly known. To address these deficiencies, we have combined our extensive simulations of nova eruptions with the Strope et al (2010) and Schaefer et al (2010) databases of outburst characteristics of Gala…
Aims. We present optical spectra of the fast recurrent nova U Sco during its recent outburst, obtained within 24 hr of maximum light. Methods. We use medium resolution (R~4000) spectra taken with the with the MagE spectrograph on the Magellan (Clay) 6.5m telescope of the Las Campanas Observatories. Results. The spectrum is notable for its lack of a low ionization transient heavy element absorption system that is visible in the large majority of novae near maximum light. We suggest that this may be due to the dominance of inner Lagrangian L1 mass transfer and the absence of a circumbinary gas r…
We report combined optical and X-ray observations of nova M31N 2007-12b. Optical spectroscopy obtained 5 days after the 2007 December outburst shows evidence of very high ejection velocities (FWHM H$α\simeq 4500$ km s$^{-1}$). In addition, Swift X-ray data show that M31N 2007-12b is associated with a Super-Soft Source (SSS) which appeared between 21 and 35 days post-outburst and turned off between then and day 169. Our analysis implies that $M_{\rm WD} \ga 1.3 $M$_{\odot}$ in this system. The optical light curve, spectrum and X-ray behaviour are consistent with those of a recurrent nova. Hubbl…
VLT and SALT spectroscopy of U Sco were obtained $\sim$18 and $\sim$30 months after the 2010 outburst. From these spectra the accretion disc is shown to take at least 18 months to become fully reformed. The spectral class of the companion is constrained to be F8$^{+5}_{-6}$\,IV-V at the 95% confidence level when the irradiated face of the companion is visible.
We revisit hydrogen shell burning on white dwarfs (WDs) with higher mass accretion rates than the stability limit, \dot M_stable, above which hydrogen burning is stable. Novae occur with mass accretion rates below the limit. For an accretion rate > \dot M_stable, a first hydrogen shell flash occurs followed by steady nuclear burning, so the shell burning will not be quenched as long as the WD continuously accretes matter. On the basis of this picture, some persistent supersoft X-ray sources can be explained by binary models with high accretion rates. In some recent studies, however, the claim …
We report spectroscopic observations of the $Hα$ emission line of the recurrent nova RS~Oph obtained between 12 and 23 August 2021 during the recent outburst. On the basis of the sharp P~Cyg profile superimposed onto the strong H-alpha emission, we estimate that the outflowing velocity of the material surrounding RS Oph is in the range 32 km/s < V_{out} < 68 km/s. The new GAIA distance indicates that the red giant should be probably classified in between II and III luminosity class. The spectra are available upon request from the authors and on Zenodo.
CCD BVRcIc photometric observations of the 2010 outburst of the recurrent nova U Scorpii are presented. The light-curve has a smooth development characterized by t2(V)=1.8 and t3(V)=4.1 days, close to the t2(V)=2.2 and t3(V)=4.3 days of 1999 outburst. The plateau phase in 2010 has been brighter, lasting shorter and beginning earlier than in the 1999 outburst. Flickering, with an amplitude twice larger in $I_{\rm C}$ than in $B$ band, was absent on day +4.8 and +15.7, and present on day +11.8, with a time scale of about half an hour.
We analyse long-term optical photometry for two Galactic recurrent novae (V745 Sco and V3890 Sgr) and one Large Magellanic Cloud object (Nova LMC 1990b) observed over several years by the Optical Gravitational Lensing Experiment (OGLE) sky survey. We do not find variability with the previously claimed orbital period of V745 Sco. This voids previous findings based on this value (e.g. the distance determination). The quiescence variability of this object is dominated by semiregular pulsations of the red giant secondary (with periods of 136.5 and 77.4 d). The photometry of Nova LMC 1990b reveals …
Recurrent novae are binary stars in which a white dwarf accretes matter from a less evolved companion, either a red giant or a main-sequence star. They have dramatic optical brightenings of around 5-6 mag in V in less than a day, several times a century. These occur at variable and unpredictable intervals, and are followed by an optical decline over several weeks, and activity from the X-ray to the radio. The unpredictability of recurrent novae and related stellar types can hamper systematic study of their outbursts. Here we analyse the long-term lightcurve of RS Ophiuchi, a recurrent nova wit…
On 28 January 2010, the recurrent nova U Scorpii had its long predicted eruption; prior preparation allowed for this to become the all-time best observed nova event. The coverage included daily and hourly spectra in the X-ray, ultraviolet, optical, and infrared, plus daily and hourly photometry in the X-ray, ultraviolet, U, B, V, y, R, I, J, H, K, and middle infrared, including roughly 35,000 V-band magnitudes (an average of better than once every three minutes) throughout the entire 67 days of the eruption. This unprecedented coverage has allowed for the discovery of three new phenomena; the …
Optical (BVRI) photometry of the first three weeks of the 2016 outburst of the recurrent Nova LMC 1968 is presented and discussed. The 2016 I-band light-curve is an exact replica, even in the most minute details, of that for the 2010 eruption. The maximum is inferred to have occurred on 2016 Jan 21.2 at I=11.5 mag, corresponding to an absolute magnitude M(I)=-7.15. A ~1 day plateau is present in all bands about six days past optical maximum, simultaneous with the emergence of super-soft X-ray emission in Swift observations, signalling the widespread ionization of the ejecta. The nova entered a…
We present an analysis of the red giant component of the recurrent nova V3890 Sgr, using data obtained before and after its 2019 eruption. Its effective temperature is $T_{\rm eff}=3050\pm$200 K for $\log{g}=0.7$, although there are modest changes in $T_{\rm eff}$. There is an overabundance of both carbon ($0.20\pm0.05$~dex) and sodium ($1.0\pm0.3$~dex) relative to their solar values, possibly the result of ejecta from the 1990 nova eruption being entrained into the red giant photosphere. We find $^{12}$C/$^{13}$C $=25\pm2$, a value similar to that found in red giants in other recurrent novae.…
T CrB is a symbiotic recurrent nova known to exhibit active phases, characterised by apparent increases in the hot component temperature and the appearance of flickering, i.e. changes in the observed flux on the time-scale of minutes. Historical UV observations have ruled out orbital variability as an explanation for flickering and instead suggest flickering is caused by variable mass transfer. We have analysed optical and X-ray observations to investigate the nature of the flickering as well as the active phases in T CrB. The spectroscopic and photometric observations confirm that the active …
The mass growth rate of mass-accreting white dwarfs (WDs) is a key factor in binary evolution scenarios toward Type Ia supernovae. Many authors have reported very different WD mass increasing rates. In this review, we clarify the reasons for such divergence, some of which come from a lack of numerical techniques, usage of old opacities, different assumptions for binary configurations, inadequate initial conditions, and unrealistic mass-loss mechanisms. We emphasize that these assumptions should be carefully chosen in calculating the long-term evolution of accreting WDs. Importantly, the mass-l…
We report the determination of abundances and isotopic ratios for C, O and Si in the photosphere of the red giant component of the recurrent nova T Coronae Borealis from new 2.284--2.402 $μ$m and 3.985--4.155 $μ$m spectroscopy. Abundances and isotopic ratios in the photosphere may be affected by (i) processes in the red giant interior which are brought to the surface during dredge-up, (ii) contamination of the red giant, either during the common envelope phase of the binary evolution or by material synthesised in recurrent nova eruptions, or a combination of the two. We find that the abundance…
The orbital period of the recurrent nova U Sco has been observed to decrease during the 1999 outburst. In an outburst mass is ejected from the surface of the white dwarf. The separation of the binary system widens and the orbital period increases. We find that magnetic braking between outbursts, mass transfer to the companion, and frictional angular momentum losses during outbursts are all too small to account for this unexpected change. We find, however, that if the secondary has a sufficiently strong magnetic field, B=8x10^3 G, then the ejected material can couple to it and corrotate with th…
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…
