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Chandra HETG observations of RS Ophiuchi at day 13.9 of the 2006 outburst reveal a rich spectrum of emission lines from abundant ions formed over a wide temperature range (∼ 3 × 10 6 to 60 × 10 6 K) indicative of shock heating of the circumstellar medium by the expanding blast wave. Lines are asymmetric and strongly broadened (v ∼ 2400 km s −1 at zero intensity). Using simple analytical model profiles, we show how the lines are shaped by differential absorption in the red giant wind and explosion ejecta, and that shock heating to multimillion degree temperatures appears to have occurred preferentially in the direction perpendicular to the line of sight. We conclude that the asymmetric nature of the offset 1/r 2 density profile and likely equatorial circumstellar density enhancement in which the explosion occurred are responsible for both the shock collimation and broad range in plasma temperature observed. The ejecta mass deduced from X-ray absorption is more easily reconciled with the expected mass accretion rate for material enhanced in metals by up to an order of magnitude.

The phase of Super-Soft-Source (SSS) emission of the sixth recorded outburst of the recurrent nova RS Oph was observed twice with Chandra and once with XMM-Newton. The observations were taken on days 39.7, 54.0, and 66.9 after outburst. We confirm a 35-sec period on day 54.0 and found that it originates from the SSS emission and not from the shock. We discus the bound-free absorption by neutral elements in the line of sight, resonance absorption lines plus self-absorbed emission line components, collisionally excited emission lines from the shock, He-like intersystem lines, and spectral changes during an episode of high-amplitude variability. We find a decrease of the oxygen K-shell absorption edge that can be explained by photoionization of oxygen. The absorption component has average velocities of -1286+-267 km/s on day 39.7 and of -771+-65 km/s on day 66.9. The wavelengths of the emission line components are consistent with their rest wavelengths as confirmed by measurements of non-self absorbed He-like intersystem lines. We have evidence that these lines originate from the shock rather than the outer layers of the outflow and may be photoexcited in addition to collisional excitations. We found collisionally excited emission lines that are fading at wavelengths shorter than 15A that originate from the radiatively cooling shock. On day 39.5 we find a systematic blue shift of -526+-114 km/s from these lines. We found anomalous He-like f/i ratios which indicates either high densities or significant UV radiation near the plasma where the emission lines are formed. During the phase of strong variability the spectral hardness light curve overlies the total light curve when shifted by 1000sec. This can be explained by photoionization of neutral oxygen in the line of sight if the densities of order 10^{10}-10^{11} cm^{-3}., Comment: 16 pages, 10 figures, 4 tables. Accepted by ApJ; v2: Co-author Woodward added

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 variability is well represented as a combination of oscillations at a set of discrete frequencies lower than 1.7 mHz. At least five frequencies are constant over the 16 day time interval between the two observations. We suggest that a periods in the power spectrum of both light curves at the frequency of 0.75 mHz and its first harmonic are related to the spin period of the white dwarf in the system, and that other observed frequencies are signatures of nonradial white dwarf pulsations. A possible signal with a 24000 sec period is also found in the XMM-Newton light curve: a cycle and a half are clearly identified. This period is consistent with the 24278 s periodicity discovered in the optical light curve of the source and thought to be the orbital period of the nova binary system.

Astronomy and Astrophysics 556 (2013): A85 reproduced with permission from Astronomy & Astrophysics, RR Telescopii is the prototype of the symbiotic novae class. Since its outburst in 1944, it has been slowly fading, and its emission-line spectrum has evolved significantly. In this paper we discuss XMM-Newton observations of RR Tel taken in April 2009. These are the first X-ray high-resolution spectra of this system, and they provide important information about the physical conditions of the emitting gas. We have estimated the temperature and the luminosity of the hot star to be 154 kK and 5000 L•, respectively, from the comparison of model atmospheres with the X-ray spectra. Normalisation of the models with the far ultraviolet flux leads to similar values. Both the shape of the low-resolution X-ray spectrum and the spectral diagnostics that make use of the emission lines present in the RGS spectrum indicate the existence of collisionally ionised gas. At least two components are present, with temperatures of ≈0.6 and 1.7 MK. The existence of a wind from the hot star is unequivocally confirmed by HST-STIS observations taken in 2000, which showed displaced absorption components for the N V 1240 Å and C IV 1550 Å doublets. These components have terminal velocities of the order of 400 km s-1, which is consistent with the temperature of the gas detected in X-rays., Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts.

The 10th recorded outburst of the recurrent eclipsing nova USco was observed simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9 after outburst. Two full passages of the companion in front of the nova ejecta were observed, witnessing the reformation of the accretion disk. On day 22.9, we observed smooth eclipses in UV and optical but deep dips in the X-ray light curve which disappeared by day 34.9, then yielding clean eclipses in all bands. X-ray dips can be caused by clumpy absorbing material that intersects the line of sight while moving along highly elliptical trajectories. Cold material from the companion could explain the absence of dips in UV and optical light. The disappearance of X-ray dips before day 34.9 implies significant progress in the formation of the disk. The X-ray spectra contain photospheric continuum emission plus strong emission lines, but no clear absorption lines. Both continuum and emission lines in the X-ray spectra indicate a temperature increase from day 22.9 to day 34.9. We find clear evidence in the spectra and light curves for Thompson scattering of the photospheric emission from the white dwarf. Photospheric absorption lines can be smeared out during scattering in a plasma of fast electrons. We also find spectral signatures of resonant line scattering that lead to the observation of the strong emission lines. Their dominance could be a general phenomenon in high-inclination systems such as Cal87., Comment: Submitted to ApJ. 16 pages, 16 figures

Aims. We compare the observed and theoretical parameters for the quiescent and outburst phases of the recurring nova T Pyx. Methods. IUE data were used to derive the disk luminosity and the mass accretion rate, and to exclude the presence of quasi-steady burning at the WD surface. XMM-NEWTON data were used to verify this conclusion. Results. By various methods, we obtained L disk ∼ 70 L ⊙ and M ∼ 1.1 x 10 -8 M ⊙ yr -1 . These values were about twice as high in the pre-1966-outburst epoch. This allowed the first direct estimate of the total mass accreted before outburst, M accr = M pre -OB ·Δt, and its comparison with the critical ignition mass M ign . We found M accr and M ign to be in perfect agreement (with a value close to 5 x 10 -7 M ⊙ ) for M 1 ∼ 1.37 M ⊙ , which provides a confirmation of the thermonuclear runaway theory. The comparison of the observed parameters of the eruption phase, with the corresponding values in the grid of models by Yaron and collaborators, provides satisfactory agreement for values of M 1 close to 1.35 M ⊙ and log M between -8.0 and -7.0, but the observed value of the decay time t 3 is higher than expected. The long duration of the optically thick phase during the recorded outbursts of T Pyx, a spectroscopic behavior typical of classical novae, and the persistence of P Cyg profiles, constrains the ejected mass M ign to within 10 -5 -10 -4 M ⊙ . Therefore, T Pyx ejects far more material than it has accreted, and the mass of the white dwarf will not increase to the Chandrasekhar limit as generally believed in recurrent novae. A detailed study based on the UV data excludes the possibility that T Pyx belongs to the class of the supersoft X-ray sources, as has been postulated. XMM-NEWTON observations have revealed a weak, hard source and confirmed this interpretation.

The recurrent nova RS Ophiuchi was observed five times with Chandra and XMM‐Newton, on four different dates after the 2006 outburst. In the first month we detected an emission spectrum with prominent lines of H and He‐like ions of metals including O, N, Si, Fe, Ne and Mg, showing a large range of plasma temperatures. At this stage the emission was originated in the red giant wind material shocked by the nova ejecta. Later spectra show a large increase in emission at longer wavelengths, peaking two months after the outburst. We attribute this to the emergence of the underlying white dwarf. Preliminary fits with NLTE white dwarf atmospheric models yield log g = 9, and T ∼800,000K, appropriate a white dwarf mass of >1.2 M⊙. The constant bolometric luminosity phase was very short, less than three months, as expected for a white dwarf mass ≈ 1.35 M⊙. We detected an oscillation with a period ∼35 s in March and April light curves, which may be due to the spin of the white dwarf and may represents further evidenc...

A lot more work is needed to properly understand the spectra of classical novae near outburst due to their complexity, especially in the ultraviolet range. The detailed IUE monitoring data of V1974 Cyg 1992 allow, anyhow, to put some constraints on model spectra, and are expected to provide important information about the dynamics of the ejected envelope. The problems here addressed are related with the identification of the absorption systems in this nova and with the interpretation of the “emission” features in the early spectra.

The recent 1994-1995 active phase of AG Draconis has given us for the first time the opportunity to follow the full X-ray behaviour of a symbiotic star during two successive outbursts and to compare with its quiescence X-ray emission. With \ros observations we have discovered a remarkable decrease of the X-ray flux during both optical maxima, followed by a gradual recovering to the pre-outburst flux. In the UV the events were characterized by a large increase of the emission line and continuum fluxes, comparable to the behaviour of AG Dra during the 1980-81 active phase. The anticorrelation of X-ray/UV flux and optical brightness evolution is shown to very likely be due to a temperature decrease of the hot component. Such a temperature decrease could be produced by an increased mass transfer to the burning compact object, causing it to slowly expand to about twice its original size., Comment: 12 pages postscript incl. figures, Proc. of Workshop on Supersoft X-Ray Sources, to appear in Lecture Notes in Physics vol. 472 (1996)

In this paper we describe the evolution of Nova Cas 1993 over the first few months of its outburst. We discuss the ultraviolet light curve that covers the period from announcement to just after dust began forming in the ejecta (1994 Feb.15) and IUE spacecraft constraints forced us to halt our observations. The dust formed very quickly despite the initially high temperature of the ejecta. Our results suggest that high energy photons are absorbed efficiently by the innermost material in the ejecta, lowering the temperature while it is still dense. This allows molecules to form and then condense into dust. We used IUE data to obtain an extinction curve as a function of time during the dust formation phase. This curve shows that the dust was large - much larger than typical dust in the ISM.