V5116 Sgr (Nova Sgr 2005 No. 2), discovered on 2005 July 4, was observed with XMM-Newton in March 2007, 20 months after the optical outburst. The X-ray spectrum shows that the nova had evolved to a pure supersoft X-ray source, with no significant emission at energies above 1 keV. The X-ray light-curve shows abrupt decreases and increases of the flux by a factor ~8. It is consistent with a periodicity of 2.97 h, the orbital period suggested by Dobrotka et al. (2007), although the observation lasted just a little more than a whole period. We estimate the distance to V5116 Sgr to be 11+/-3 kpc. A simple blackbody model does not fit correctly the EPIC spectra, with reduced chi^2>4. In contrast, ONe rich white dwarf atmosphere models provide a good fit, with nH=1.3(+/-0.1)e21 cm^-2, T=6.1(+/-0.1)e5 K, and L=3.9(+/-0.8)e37(D/10kpc)^2 erg/s (during the high-flux periods). This is consistent with residual hydrogen burning in the white dwarf envelope. The white dwarf atmosphere temperature is the same both in the low and the high flux periods, ruling out an intrinsic variation of the X-ray source as the origin of the flux changes. We speculate that the X-ray light-curve may result from a partial coverage by an asymmetric accretion disk in a high inclination system.
We searched for X-ray counterparts of optical novae detected in M 31 and M 33. We combined an optical nova catalogue from the WeCAPP survey with optical novae reported in the literature and correlated them with the most recent X-ray catalogues from ROSAT, XMM-Newton and Chandra, and - in addition - searched for nova correlations in archival data. We report 21 X-ray counterparts for novae in M 31 - mostly identified as supersoft sources (SSS) by their hardness ratios - and two in M 33. Our sample more than triples the number of known optical novae with supersoft X-ray phase. Most of the counter…
BeppoSAX detected luminous 0.2-2.0 keV supersoft X-ray emission from the recurrent nova U Sco ~19-20 days after the peak of the optical outburst in February 1999. U Sco is the first recurrent nova to be observed during a luminous supersoft X-ray phase. Non-LTE white dwarf atmosphere spectral models (together with a ~0.5 keV optically thin thermal component) were fitted to the BeppoSAX spectrum. We find that the fit is acceptable assuming enriched He and an enhanced N/C ratio. This implies that the CNO cycle was active during the outburst, in agreement with a thermonuclear runaway scenario. The…
Short supersoft X-ray source (SSS) states (durations < 100 days) of classical novae (CNe) indicate massive white dwarfs that are candidate progenitors of supernovae type Ia. We carry out a dedicated optical and X-ray monitoring program of CNe in the bulge of M 31. We discovered M31N 2007-11a and determined its optical and X-ray light curve. We used the robotic Super-LOTIS telescope to obtain the optical data and XMM-Newton and Chandra observations to discover an X-ray counterpart to that nova. Nova M31N 2007-11a is a very fast CN, exhibiting a very short SSS state with an appearance time of 6-…
Nova LMC 1995, previously detected during 1995-1998 with ROSAT, was observed again as a luminous supersoft X-ray source with XMM-Newton in December of 2000. This nova offers the possibility to observe the spectrum of a hot white dwarf, burning hydrogen in a shell and not obscured by a wind or by nebular emission like in other supersoft X-ray sources. Notwithstanding uncertainties in the calibration of the EPIC instruments at E<0.5 keV, using atmospheric models in Local Thermonuclear Equilibrium we derived T(eff)=400,000-450,000 K, L(bol)=2.3 x 110(-14) 0(37) erg cm(-2) s(-1) and we verified th…
We report on initial progress in a program of optical identification of supersoft X-ray sources in M31, pursued mainly with the WIYN telescope. We propose the identification of one supersoft X-ray source with a variable star, which we believe to have been a classical or recurrent nova in outburst in September 1990. The nova remnant must have been still a supersoft X-ray sources 5 years after this observation, when it was observed with ROSAT.
The recurrent nova CI Aquilae entered the final decline phase a bit before May of 2001, showing the slowest evolution among the recurrent novae. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have estimated the turn-off time of the CI Aql 2000 outburst in March of 2001, after a supersoft X-ray source (SSS) phase lasts 150 days from December of 2000 until May of 2001. Fitting our theoretical light curves with both the 1917 and 2000 outbursts, we also obtained the WD mass to be M_{WD}= 1.2 \pm 0.05 M_\sun, helium enrichment of ejecta, He/H ~ 0.5 by numb…
Classical novae (CNe) have been found to represent the major class of supersoft X-ray sources (SSS) in our neighbour galaxy M 31. We determine properties and evolution of the two first SSSs ever discovered in the M 31 globular cluster (GC) system. We have used XMM-Newton, Chandra and Swift observations of the centre region of M 31 to discover both SSS and to determine their X-ray light curves and spectra. We performed detailed analysis of XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and NLTE white dwarf (WD) atmosphere models. For the SSS in Bol 194 (SS2) we used o…
We have found a new clue to the transition mechanism between optical high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray source RX J0513.9-6951. A sharp ~1 mag drop is common to the CI Aql 2000 outburst. These drops are naturally attributed to cessation of optically thick winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that the size of a disk drastically shrinks when the wind stops. This causes ~1-2 mag drop in the optical light curve. In RX J0513.9-6951, the same mechanism reproduces sharp ~1 mag drop from optical high to low states. We predict…
We have been proposing two evolutionary paths to Type Ia supernovae (SNe Ia), which are called the supersoft X-ray source (SSS) channel and the symbiotic channel, depending on the orbital separation just prior to an SN Ia explosion. The essential difference of our treatment is inclusion of strong, optically thick winds on mass-accreting white dwarfs (WDs) in binary evolutions when the mass accretion rate on to WDs exceeds a critical rate of ~ 1 x 10^{-6} Mo/yr. Once optically thick winds blow from the WD, the binary can avoid forming a common envelope in some cases. So that the WDs are able to…
Recurrent nova CI Aquilae is still bright 300 days after the optical maximum, showing the slowest evolution among recurrent novae. We predict the turn-off time of CI Aql 2000 outburst coming in August 2001 after a supersoft X-ray source (SSS) phase lasts 250 days. We also predict helium enrichment of ejecta, He/H = 0.25 by number. Observational confirmations are urgently required. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have also estimated the WD mass to be 1.2 +- 0.05 Msun by fitting our theoretical light curves with the 1917 and 2000 outburst…
Recurrent nova CI Aquilae has entered the final decline phase a bit before May of 2001, about 300 days after the optical maximum, showing the slowest evolution among recurrent novae. Based on the optically thick wind mass-loss theory of the thermonuclear runaway model, we have estimated the turn-off time of the CI Aql 2000 outburst. It is in late March of 2001 after a luminous supersoft X-ray source phase lasts 150 days (from November of 2000 until March of 2001). We have also obtained, by fitting our theoretical light curves with the 1917 and 2000 outbursts, the white dwarf (WD) mass to be M_…
Optical novae have recently been identified as the major class of supersoft X-ray sources in M31 based on ROSAT and early XMM-Newton and Chandra observations. This paper reports on a search for X-ray counterparts of optical novae in M31 based on archival Chandra HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brig…
Nova Velorum 1999 (V382 Vel) was observed by BeppoSAX 6 months after optical maximum and was detected as a bright X-ray supersoft source, with a count rate 3.454+-0.002 cts/s in the LECS. It was the softest and most luminous supersoft source observed with this instrument. The flux in the 0.1-0.7 keV range was not constant during the observation. It dropped by a factor of 2 in less than 1.5 hour and then was faint for at least 15 minutes, without significant spectral changes. The observed spectrum is not well fit with atmospheric models of a hot, hydrogen burning white dwarf. This is due mainly…
X-ray data reveal that the supersoft X-ray binary CAL 83 exhibits 38.4 minute pulsations at some epochs. These X-ray variations are similar to those found in some novae and are likely to be caused by nonradial pulsations the white dwarf. This is the first detection of pulsations in a classical supersoft X-ray binary.
We report on three X-ray observations of Nova LMC 2000 with XMM at 17, 51 and 294 days after the maximum, respectively. X-ray spectral fits show a concordant decrease of the absorbing column and the X-ray luminosity. No supersoft X-ray emission is detected. The mass of the ejected shell is determined to be (less than) 7.5*E-5 msun. Though data are sparse, one interesting correlation becomes visible: sources with a long-duration supersoft X-ray phase have shorter orbital periods than those with short or no supersoft X-ray phase. This can be understood considering that (i) enough matter has to b…
Nova Vel 1999 (V382 Vel) was observed with BeppoSAX twice, 15 days and 6 months after the optical maximum. A hard X-ray source was detected in the first observation, while the second time also a very luminous supersoft X-ray source was detected. The continuum observed in the supersoft range with the BeppoSAX LECS cannot be fitted with atmospheric models of hot hydrogen burning while dwarfs. We suggest that we are observing instead mainly a ``pseudocontinuum'', namely a blend of very strong emission lines in the supersoft X-ray range.
The deepest X-ray images of M31, obtained with XMM-Newton, are examined in this paper to derive spectral and statistical properties of the population of the softest X-ray sources. Classifying supersoft X-ray sources (SSS) with criteria based on the same hardness ratios defined for recent Chandra observations, a quarter of the selected SSS turn out to be supernova remnants (SNR). Another quarter of SSS are spatially coincident with recent classical novae (but they are less than 10% of the nova population observed in the last 25 years). Only 3 among 15 non-SNR SSS show clear time variability, wi…
V4444 Sgr (Nova Sgr 1999) has been recently suggested to be a possible recurrent nova based on the detection of the preexisting dust, which may have been formed in a previous outburst. We examined this possibility using the available outburst observations, including the VSNET observations. We also noticed that this nova was recorded in the OGLE II public photometric database, which covered both preoutburst and late decline phases. The outburst light curve constructed from these observations showed a plateau phase, particularly in the OGLE II I-band light curve, which was followed by a more rap…
V617 Sgr is a V Sagittae star - a group of binaries thought to be the galactic counterparts of the Compact Binary Supersoft X-ray Sources - CBSS. To check this hypothesis, we measured the time derivative of its orbital period. Observed timings of eclipse minima spanning over 30,000 orbital cycles are presented. We found that the orbital period evolves quite rapidly: P/Pdot = 1.1 x 10^{6} years. This is consistent with the idea that V617 Sgr is a wind driven accretion supersoft source. As the binary system evolves with a time-scale of about one million years, which is extremely short for a low …
Classical novae occur in close binary systems (main-sequence star + white dwarf). V4743 Sgr is a very fast nova exhibiting a X-ray spectrum which is consistent with a view on the optically thick atmosphere of an extremely hot white dwarf (WD). It exhibits strong absorption features of the C V, C VI, N VI, N VII, and O VII resonance lines indicating an effective temperature of about 610 kK. We present preliminary results of a spectral analysis by means of line-blanketed non-LTE atmosphere models of a XMM-Newton RGS-1 spectrum of V4743 Sgr, taken about half a year after its outburst.
We present optical and near-infrared spectral evolution of the Galactic nova V5114 Sgr (2004) during few months after the outburst. We use multi-band photometry and line intensities derived from spectroscopy to put constrains on the distance and the physical conditions of the ejecta of V5114 Sgr. The nova showed a fast decline (t_2 \simeq 11 days) and spectral features of FeII spectroscopic class. It reached M_V = -8.7 \pm 0.2 mag at maximum light, from which we derive a distance of 7700 \pm 700 kpc and a distance from the galactic plane of about 800 pc. Hydrogen and Oxygen mass of the ejecta …
We propose the first association of an optical counterpart with a luminous supersoft X-ray source in M31, RX J0044.0+4118, observed with ROSAT in July 1991. The PSPC position is at 1.6" angular distance from a candidate nova in outburst in September of 1990. This is interesting because the incidence of classical novae among supersoft X-ray sources is an open question. The proposed optical counterpart was measured at R~17.7 in September of 1990, and it had faded to R>19.2 when it was observed again after 70 days. The light curve was too sparsely monitored for definite conclusions on the speed c…
We present the period analysis of unfiltered photometric observations of V5116 Sgr (Nova Sgr 2005 #2) and we search for superhump candidates in novae remnants. The PDM method for period analysis is used. The masses of the novae componets are estimated from the secondary mass -- orbital period and primary mass -- decline time relations. We found that 13 nights of V5116 Sgr observations in the year 2006 are modulated with a period of $0.1238 \pm 0.0001$ d ($2.9712 \pm 0.0024$ h). Following the shape of the phased light curves and no apparent change in the value of the periodicity in different su…
We present a radio survey of X-ray sources in the Large and Small Magellanic clouds with the Australia Telescope Compact Array at 6.3 and 3.5 cm. Specifically, we have observed the fields of five LMC and two SMC supersoft X-ray sources, the X-ray binaries LMC X-1, X-2, X-3 & X-4, the X-ray transient Nova SMC 1992, and the soft gamma-ray repeater SGR 0525-66. None of the targets are detected as point sources at their catalogued positions. In particular, the proposed supersoft jet source RXJ 0513-69 is not detected, placing constraints on its radio luminosity compared to Galactic jet sources. Li…
We report on recent near-IR observations of V4332 Sgr - the nova-like variable that erupted in 1994. Its rapid, post-outburst evolution to a cool M type giant/supergiant, soon after its outburst, had showed that it was an unusual object differing from other eruptive variables like classical/symbiotic novae or born-again AGB stars. The present study of V4332 Sgr was motivated by the keen interest in the recent eruption of V838 Mon - which along with V4332 Sgr - is believed to belong to a new class of objects (we propose they may be called "quasi-novae"). Our observations show new developments i…
A period analysis of CCD unfiltered photometry of V4745 Sgr (Nova Sgr 2003 #1) performed during 23 nights in the years 2003 - 2005 is presented. The photometric data are modulated with a period of 0.20782 +- 0.00003 d ($4.98768 +- 0.00072 h). Following the shape of the phased light curve and the presence of the periodicity in all data sets with no apparent change in its value, we interpret this periodicity as orbital in nature and this is consistent with a cataclysmic variable above the period gap. We found a probable short-term periodicity of 0.017238 +- 0.000037 d (24.82272 +- 0.05328 m) whi…
Photometric observations of V4633 Sgr (Nova Sagittarii 1998) during 1998-2005 reveal the presence of a stable photometric periodicity at P1=180.8 min which is probably the orbital period of the underlying binary system. A second period was present in the light curve of the object for six years. Shortly after the nova eruption it was measured as P2=185.6 min. It has decreased monotonically in the following few years reaching the value P2=183.9 min in 2003. In 2004 it was no longer detectable. We suggest that the second periodicity is the spin of the magnetic white dwarf of this system that rota…
We explore the formation and evolution of debris ejected around quark stars in the Quark Nova scenario, and the application to Soft Gamma-ray Repeaters (SGRs) and Anomolous X-ray Pulsars (AXPs). If an isolated neutron star explodes as a Quark Nova, an Iron-rich shell of degenerate matter forms out of the fall-back (crust) material. Our model can account for many of the observed features of SGRs and AXPs such as: (i) the two types of bursts (giant and regular); (ii) the spin-up and spin-down episodes during and following the bursts with associated persistant increases in $\dot{P}$; (iii) the en…
We present a spectroscopic monitoring of the transient nova V4745 Sagittarii (Nova Sgr 2003 #1) covering ten months after the discovery. During this period the light curve showed well expressed transient phase in the form of six rebrightenings, and the presented dataset is one of the best spectroscopic coverages of a classical nova during the transition phase. Low- and medium-resolution spectra revealed that the majority of spectral lines switched back to strong P-Cyg profiles during the mini-outbursts, similar to the spectra just after the major eruption. We interpret the observed phenomena a…
We have searched for the important radioactive isotope 26Al in the nova-like source V4332 Sgr. Recent results from gamma ray astronomy show that there is pervasive emission of the 1.809 MeV gamma ray photon, arising from the decay of 26Al to 26Mg, from all over the galactic plane. Though the sites from where this emission originates are not clearly established, novae are believed to be an important contributing source. In this context, V4332 Sgr presented a rare opportunity to observationally investigate whether novae or novae-like sources synthesize 26Al and to what extent. Strong AlO bands i…
The evolution of the soft X-ray emission of V1974 Cyg has been simulated by a white dwarf envelope model with steady hydrogen burning. The comparison of the results obtained from ROSAT observations with the results of our envelope models indicates that the post-outburst evolution of the nova can be explained by steady H-burning on either a 0.9 Msun white dwarf with 50% degree of mixing between solar-like accreted material and the ONe degenerate core, or on a 1.0 Msun ONe white dwarf with 25% mixing.
We present a unified model of infrared (IR), optical, ultraviolet (UV), and X-ray light curves for the 1983 outburst of GQ Muscae (Nova Muscae 1983) and estimate its white dwarf (WD) mass. Based on an optically thick wind model of nova outbursts, we model the optical and IR light curves with free-free emission, and the UV 1455 Åand supersoft X-ray light curves with blackbody emission. The best fit model that reproduces simultaneously the IR, optical, UV 1455 Å, and supersoft X-ray observations is a 0.7 \pm 0.05 M_\sun WD for an assumed chemical composition of the envelope, X=0.35-0.55, X_{CNO}…
I review X-ray observations of classical and recurrent novae in outburst. Significant X-ray flux is emitted by the nova shell, with a peak luminosity up to 10**35 erg/cm**2/s in the 0.2-10 keV range.In recurrent nova systems, or in novae hosting a red giant, the source of X-rays may be previous circumstellar matter shocked by the nova wind. However, for most classical novae, X-rays originate inside the nebula ejected in the outburst. The data indicate a very high fraction of shocked material, and a non-smooth, varying wind outflow. A nebular emission line spectrum is also observed at late phas…
We report on X-ray observations of Nova Sagittarius 1998 (V4633 Sgr), performed with XMM-Newton at three different epochs, 934, 1083 and 1265 days after discovery. The nova was detected with the EPIC cameras at all three epochs, with emission spanning the whole energy range from 0.2 to 10 keV. The X-ray spectra do not change significantly at the different epochs, and are well fitted for the first and third observations with a multi-temperature optically thin thermal plasma, while lower statistics in the second observations lead to a poorer fit. The thermal plasma emission is most probably orig…
We present a consistent model for the UV and supersoft X-ray emission from the symbiotic nova SMC3 (=RX J0048.4-7332). Following the present picture of symbiotic stars, the model consists of radiation from a hot star and an emission nebula excited by that star. The observations were compared to theoretical models in which the hot star's emission is calculated with the help of hydrostatic and Wolf-Rayet-type non-LTE model atmospheres. Our analysis clearly shows evidence for mass loss rates of several 10^{-6} Msolar/yr. The minimum effective temperature compatible with both the observed UV and X…
We report the results of observations of V4633 Sgr (Nova Sagittarii 1998) during 1998-2000. Two photometric periodicities were present in the light curve during the three years of observations: a stable one at P=3.014 h, which is probably the orbital period of the underlying binary system, and a second one of lower coherence, approximately 2.5 per cent longer than the former. The latter periodicity may be a permanent superhump, or alternatively, the spin period of the white dwarf in a nearly synchronous magnetic system. A third period, at P=5.06 d, corresponding to the beat between the two per…
V4643 Sagittarii or Nova Sagittarii 2001 was discovered in outburst at 7.7 mag. on 2001 February 24. Here, we present near-infrared results of this fast classical nova obtained in the early decline phase in 2001 March followed by optical observations about one month later. Subsequently we also present near-infrared spectra taken later in the nova's evolution, about four months after the outburst, when V4643 Sgr had entered the coronal phase. The spectra in the early decline phase are dominated by emission lines of the HI Brackett series and also the Paschen beta and gamma lines. We study the c…
RS Ophiuchi is one of the well-observed recurrent novae and also a candidate progenitor of Type Ia supernovae. Its sixth recorded outburst was discovered on 12 February 2006. Detection of a supersoft X-ray phase will provide a firm confirmation of hydrogen shell-burning on the white dwarf and its turn-on/turn-off dates strongly constrain a mass range of the white dwarf, which clarify whether or not RS Oph becomes a Type Ia supernova. For a timely detection of its supersoft X-ray phase, we have calculated outburst evolution of RS Oph based on the optically thick wind theory and predicted a supe…
The recurrent nova RS Ophiuchi, one of the candidates for Type Ia supernova progenitors, underwent the sixth recorded outburst in February 2006. We report a complete light curve of supersoft X-ray that is obtained for the first time. A numerical table of X-ray data is provided. The supersoft X-ray flux emerges about 30 days after the optical peak and continues until about 85 days when the optical flux shows the final decline. Such a long duration of supersoft X-ray phase can be naturally understood by our model in which a significant amount of helium layer piles up beneath the hydrogen burning…
We present the results of 11 nights of CCD unfiltered photometry of V4743 Sgr (Nova Sgr 2002 # 3) from 2003 and 2005. We find two periods of 0.2799 d ~ 6.7 h and 0.01642 d ~ 24 min in the 2005 data. The long period is also present in the 2003 data, but only weak evidence of the shorter period is found in this year. The 24-min period is somewhat longer than the 22-min period, which was detected from X-ray observations. We suggest that the 6.7-h periodicity represents the orbital period of the underlying binary system and that the 24-min period is the beat periodicity between the orbital period …
One of the candidates for Type Ia supernova progenitors, the recurrent nova RS Ophiuchi underwent the sixth recorded outburst in February 2006, and for the first time a complete light curve of supersoft X-ray has been obtained. It shows the much earlier emergence and longer duration of a supersoft X-ray phase than expected before. These characteristics can be naturally understood when a significant amount of helium layer piles up beneath the hydrogen burning zone during the outburst, suggesting that the white dwarf (WD) is effectively growing up in mass. We have estimated the WD mass in RS Oph…
We present new photometric and spectroscopic observations of the transient supersoft X-ray source RX J0537.7-7034 and find a periodicity of approximately 3.5 hrs. This establishes RX J0537.7-7034 as the supersoft X-ray source with the shortest orbital period. We furthermore derive an inclination of the binary system of 45<i<70 deg, and the masses of the two binary components: M_accretor = 0.6+-0.2 Msun, M_donor = 0.35+-0.02 Msun. This implies that the standard scenario of supersoft X-ray sources, in which the donor is thought to be more massive than the accreting white dwarf to ensure high mas…
We present a unified model for optical, ultraviolet (UV), and X-ray light curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model of nova outbursts, we have calculated light curves and searched for the best fit model that is consistent with optical, UV, and X-ray observations. Our best fit model is a white dwarf (WD) of mass 1.05 M_\sun with a chemical composition of X=0.46, C+N+O=0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and continuum UV 1455 Ålight curves are well reproduced. Supersoft X-rays emerged on day ~ 250 after outburst, which is naturally expla…
Short time scale photometric properties of eight faint Cataclysmic Variable (CV) stars are presented. Nova Carinae 1895 (RS Car) has a photometric modulation at 1.977 h which could be either an orbital or a superhump period. Nova Carinae 1948 (V365 Car) shows flickering, but any orbital modulation has a period in excess of 6 h. The nova-like variable and X-ray source V436 Car has an orbital modulation at P(orb) = 4.207 h, no detectable period near 2.67 h (which had previously given it a possible intermediate polar classification), and Dwarf Nova Oscillations (DNOs) at ~40 s. Nova Crucis 1936 (…
The central star V4334 Sgr (Sakurai's Nova) of the planetary nebula PN G010.4+04.4 underwent in 1995-1996 the rare event of a very late helium flash. It represents only one out of two such events during the era of modern astronomy (the second event was V605 Aql = Nova Aql 1919). All the other prominent objects of that type originate from events occurring several thousands of years ago (e.g. A30, A78). Thus it is of special interest for stellar evolution theory to model the detailed observations obtained during the last four years. Those models depend essentially on basic stellar parameters lik…
We report on time series of CCD photometry of V4140 Sgr between 1991 and 2001. The analysis reveals that the object was in the decline from an outburst in 1992 and again in outburst in 2001. The historical light curve collected by amateur astronomers shows low amplitude (1-2 mag) outbursts 5-10 days long, recurrent every 80-90 days, confirming its dwarf nova nature. We derive an outburst decline time scale of 1.2 days mag$^{-1}$. Eclipse mapping techniques were applied to data both in quiescence and in outburst to derive accretion disc surface brightness maps. A distance of $d = 170 \pm 30$ pc…
The classical nova V4743 Sgr was observed with XMM-Newton for about 10 hours on April 4 2003, 6.5 months after optical maximum. At this time, this nova had become the brightest supersoft X-ray source ever observed. We present the results of a time series analysis performed on the X-ray light curve obtained in this observation, and in a previous shorter observation done with Chandra 16 days earlier. Intense variability, with amplitude as large as 40% of the total flux, was observed both times. Similarities can be found between the two observations in the structure of the variations. Most of the…
Light curve analysis of decay phase of nova outburst are summarized. Nova duration is determined by the strong wind mass-loss which depends only on the white dwarf mass. Fast novae correspond very massive white dwarfs and very slow novae correspond almost lower mass limit of white dwarfs. This relation is shown in both of classical novae and recurrent novae. Light curves are theoretically reproduced for recurrent novae, U Sco, V394 CrA, CI Aql, V2487 Oph, RS Oph, T CrB, V745 Sco and V3890 Sgr, using binary model composed of a white dwarf, an irradiated accretion disk, and partly irradiated com…
The first results of a photometric survey of faint Cataclysmic Variables are presented. V359 Cen is an SU UMa star with a period of 112 min. Even though observed at quiescence, the mass transfer rate in this old nova may be sufficiently high that in such a short period system (with its implied small mass ratio) the disc may be excited into an elliptical shape with the result that the observed brightness modulation gives a superhump period rather than an orbital period. XZ Eri is an eclipsing dwarf nova with an orbital period (P(orb)) of 88.1 min. HY Lup has only slight variability. V351 Pup, t…
We present 1.2 mm continuum images and spectral line observations of CO(1--0) and SiO(3--2) rotational transitions of the recent nova V4743 Sgr. The nova is detected at 1.2 mm showing a variable millimetre emission. Only upper limits of T_A* = 0.06 K for CO and T_A* = 0.03 K for SiO could be derived. We discuss the results in terms the nature of the millimetre emission favouring dust from a phase before the recent outburst as the likely radiating source. We also comment on the possibility of free-free emission from the ionised shell as the source of the measured millimetre radiation.
We report the identification of cyclical changes in the orbital period of the eclipsing dwarf novae V2051 Ophiuchi and V4140 Sagitarii. We used sets of white dwarf mid-eclipse timings to construct observed-minus-calculated diagrams covering, respectively, 25 and 16 years of observations. The V2051 Oph data present cyclical variations that can be fitted by a linear plus sinusoidal function with period 22 +/- 2 yr and amplitude 17 +/- 3 s. The statistical significance of this period by an F-test is larger than 99.9 per cent. The V4140 Sgr data present cyclical variations of similar amplitude and…
L and M band observations of the nova-like variable V4332 Sgr are presented. Two significant results are obtained viz. the unusual detection of water ice at 3.05 microns and the fundamental band of 12CO at 4.67 microns in emission. The ice feature is a first detection in a nova-like variable while the CO emission is rarely seen in novae. These results, when considered together with other existing data, imply that V4332 Sgr could be a young object surrounded by a circumstellar disc containing gas, dust and ice. The reason for a nova-like outburst to occur in such a system is unclear. But since …
We report the results of two Chandra observations of the recurrent nova CI Aql at 14 and 16 months after its outburst in April 2000, respectively. The X-ray emission is faint in both cases, without any noticeable change in spectrum or intensity. Although the emission is very soft, it is not luminous enough to be due to late-time H-burning. This implies that the luminous supersoft phase ended even before the time predicted by the most recent calculations. The details of the X-ray spectrum, together with the fact that the observed X-ray intensity is brighter than pre-outburst (1992/1993), sugges…
We perform evolutionary calculations of binary stars to find progenitors of systems with parameters similar to the recurrent nova U Sco. We show that a U Sco-type system may be formed starting with an initial binary system which has a low-mass carbon-oxygen white dwarf as an accretor. Since the evolutionary stage of the secondary is not well known, we calculate sequences with hydrogen-rich and helium-rich secondaries. The evolution of the binary may be divided into several observable stages as: classical nova, supersoft X-ray source with stable hydrogen shell burning, or strong wind phase. It …
We present the first observational evidence for a collimated jet in a cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show bipolar components of H$α$ with velocities $\sim 1400 km/s$, very similar to those observed in the supersoft X-ray sources and in SS 433. We argue that a key ingredient of the formation of jets in the supersoft X-ray sources and T Pyx (in addition to an accretion disk threaded by a vertical magnetic field), is the presence of nuclear burning on the surface of the white dwarf.
The central star V4334 Sgr (Sakurai's Nova) of the planetary nebula PN G010.4+04.4 underwent in 1995-1996 the rare event of a very late helium flash. It is only one of two such events during the era of modern astronomy (the second event was V605 Aql = Nova Aql 1919). All other prominent objects of that type originate from events several thousands of years ago (e.g. A30, A78). Hence, only snapshots can be modeled for those objects. V4334 Sgr allows for the first time a dynamic consideration of the formation of the dust shell from the beginning. We present here a model which is able to describe …
V2540 Oph (Nova Oph 2002) is a classical nova discovered by Katsumi Haseda and Yuji Nakamura on 2002 January 24. The light curve of this nova shows strong post-outburst oscillations as were observed in V1178 Sco and V4361 Sgr. Accurate astrometry of the nova yeilded an upper limit of 21 mag for the nova precursor. In combination with the observed decline rate, We propose that the nova should have either a short orbital period or a high inclination. We suggest that V2540 Oph may be analogous to V2214 Oph, a presumed magnetic nova inside the period gap.
We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), done in a broad X-ray band covering 0.1-300 keV only 15 days after the discovery and again after 6 months. The nova was detected at day 15 with the BeppoSAX instruments in the energy range 1.8-10 keV and we attribute the emission to shocks in the ejecta. The plasma temperature was kT~6 keV and the unabsorbed flux was F(x)~4.3 x 10(-11) erg/cm**2/s. The nebular material was affected by high intrinsic absorption of the ejecta. 6 months after after the outburst, the intrinsic absorption did not play a role, the nova had turned into…
We describe recent theoretical work on the final stage of accretion when material passes from an accretion disk onto a white dwarf surface. Our calculations focus on understanding the latitudinal spreading and differentially rotating profile of this material, so we call it the ``spreading layer'' (SL) model. The SL typically extends to an angle of 0.01-0.1 radians, with respect to the equator. At low accretion rates ($\dot{M}\la10^{18} {\rm g s}^{-1}$) the amount of spreading is small, so that the dissipated energy is radiated back into the accretion disk. When the accretion rate is high, such…
We have modeled the unusual orbital light curve of V1494 Aquilae (Nova Aquilae 1999 No.2) and found that such an unusual orbital light curve can be reproduced when there exist two-armed, spiral shocks on the accretion disk. V1494 Aql is a fast classical nova and found to be an eclipsing system with the orbital period of 0.1346138 days in the late phase of the nova outburst. Its orbital light curve shows a small bump at orbital phase 0.2, a small dip at 0.3, sometimes a small bump at 0.4, and a large bump at 0.6-0.7 outside eclipse. Such a double- or triple-wave pattern outside eclipse has neve…
