Nova Ejecta Research Articles

Broad [O iii] in the globular cluster RZ 2109: X-ray ionized nova ejecta

We study the possibility that the very broad (~1500 km/s) and luminous (L_5007 ~ 1.4e37 erg/s) [OIII] line emission observed in the globular cluster RZ 2109 might be explained with the photoionization of nova ejecta by the bright (L_X ~ 4e39 erg/s) X-ray source hosted in the same globular cluster. We find that such scenario is plausible and explains most of the features of the RZ 2109 spectrum (line luminosity, absence of H emission lines, peculiar asymmetry of the line profile); on the other hand, it requires the nova ejecta to be relatively massive (>~ 0.5e-3 Msun}), and the nova to be located at a distance <~ 0.1 pc from the X-ray source. We also predict the time evolution of the RZ 2109 line emission, so that future observations can be used to test this scenario.

X-RAY EMISSION FROM AN ASYMMETRIC BLAST WAVE AND A MASSIVE WHITE DWARF IN THE GAMMA-RAY EMITTING NOVA V407 Cyg

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 nova ejecta driving a forward shock into the dense wind of the Mira companion. We detect a highly absorbed soft X-ray component in the spectrum during the first 50 days of the outburst that is consistent with supersoft emission from the nuclear burning white dwarf. The high temperature and short turn off time of this emission component, in addition to the observed breaks in the optical and UV lightcurves, indicate that the white dwarf in the binary is extremely massive. Finally, we explore the connections between the X-ray and GeV gamma-ray evolution, and propose that the gamma ray turn-off is due to the stalling of the forward shock as the ejecta reach the red giant surface.

FROM X-RAY DIPS TO ECLIPSE: WITNESSING DISK REFORMATION IN THE RECURRENT NOVA U Sco

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.

Unbound states of32Cl and the31S(p,γ)32Cl reaction rate

The 31S(p,\gamma)32Cl reaction is expected to provide the dominant break-out path from the SiP cycle in novae and is important for understanding enrichments of sulfur observed in some nova ejecta. We studied the 32S(3He,t)32Cl charge-exchange reaction to determine properties of proton-unbound levels in 32Cl that have previously contributed significant uncertainties to the 31S(p,\gamma)32Cl reaction rate. Measured triton magnetic rigidities were used to determine excitation energies in 32Cl. Proton-branching ratios were obtained by detecting decay protons from unbound 32Cl states in coincidence with tritons. An improved 31S(p,\gamma)32Cl reaction rate was calculated including robust statistical and systematic uncertainties.

PRESOLAR GRAINS FROM NOVAE: EVIDENCE FROM NEON AND HELIUM ISOTOPES IN COMET DUST COLLECTIONS

Presolar grains in meteorites and interplanetary dust particles (IDPs) carry non-solar isotopic signatures pointing to origins in supernovae, giant stars, and possibly other stellar sources. There have been suggestions that some of these grains condensed in the ejecta of classical nova outbursts, but the evidence is ambiguous. We report neon and helium compositions in particles captured on stratospheric collectors flown to sample materials from comets 26P/Grigg-Skjellerup and 55P/Tempel-Tuttle that point to condensation of their gas carriers in the ejecta of a neon (ONe) nova. The absence of detectable 3He in these particles indicates space exposure to solar wind (SW) irradiation of a few decades at most, consistent with origins in cometary dust streams. Measured 4He/20Ne, 20Ne/22Ne, 21Ne/22Ne and 20Ne/21Ne isotope ratios, and a low upper limit on 3He/4He, are in accord with calculations of nucleosynthesis in neon nova outbursts. Of these, the uniquely low 4He/20Ne and high 20Ne/22Ne ratios are the most diagnostic, reflecting the large predicted 20Ne abundances in the ejecta of such novae. The correspondence of measured Ne and He compositions in cometary matter with theoretical predictions is evidence for the presence of presolar grains from novae in the early solar system.

X-RAY AND ULTRAVIOLET EMISSION FROM THE RECURRENT NOVA RS OPHIUCHI IN QUIESCENCE: SIGNATURES OF ACCRETION AND SHOCKED GAS

RS Ophiuchi is a recurrent nova system that experiences outbursts every ~20 years, implying accretion at a high rate onto a massive white dwarf. However, previous X-ray observations of the system in quiescence have detected only faint emission that is difficult to reconcile with the high accretion rate predicted by nova theory for such frequent outbursts. Here, we use new Chandra and XMM-Newton observations obtained 537 and 744 days after the 2006 outburst to constrain both the accretion rate onto the white dwarf and the properties of the nova ejecta at these times. We detect low level UV variability with the XMM-Newton Optical Monitor on day 744 that is consistent with accretion disk flickering, and use this to place a lower limit on the accretion rate. The X-ray spectra in both observations are well described by a two component thermal plasma model. The first component originates in the nova shell, which can emit X-rays for up to a decade after the outburst. The other component likely arises in the accretion disk boundary layer, and can be equally well fit by a single temperature plasma or a cooling flow model. Although the flux of the single temperature model implies an accretion rate that is 40 times lower than theoretical predictions for RS Oph, the best fit cooling flow model implies Mdot < 1.2x10^-8 M_sol/yr 537 days after the outburst, which is within a factor of 2 of the theoretical accretion rate required to power an outburst every 20 years. Furthermore, we place an upper limit on the accretion rate through an optically thick region of the boundary layer of 2.0x10^-8 M_sol/yr. Thus, the X-ray emission in quiescence is consistent with the accretion rate expectations of nova theory. Finally, we discuss the possible origins of the low temperature associated with the accretion component, which is a factor of 10 lower than in T CrB, an otherwise similar recurrent nova.

The Asymmetric Outflow of RS Ophiuchi

AbstractRS Ophiuchi (RS Oph) is a symbiotic binary consisting of a hot white dwarf accreting from the slow, dense stellar wind of a cool, red giant companion. The system belongs to, and is one of the best studied examples of, an even smaller subclass of binaries known as recurrent novae in which the white dwarf undergoes repeated thermonuclear outbursts. We present 3D smoothed particle hydrodynamics (SPH) models of mass transfer from the red giant to the white dwarf, followed by a nova outburst. We show that the outflow in the former is strongly concentrated towards the binary orbital plane. The nova ejecta is thus constrained in the equatorial directions, resulting in a bipolar outflow. The white dwarf in RS Oph is thought to be close to the Chandrasekhar mass, making the system a likely Type Ia supernova candidate. We discuss the role that such a highly structured circumstellar medium will play in the evolution of the supernova remnant.

High Resolution XMM-Newton Data of Nova Outbursts using Warm &amp; Hot Absorber Models

AbstractWe reanalyze a selection of the XMM-Newton RGS (Reflection Grating Spectrometer) data of two classical novae; V4743 Sgr and V2491 Cyg. The high resolution nova spectra in the X-ray wavelengths show existence of absorption features (e.g., blue shifted). Our main aim is to model the absorption components detected in the high resolution spectra independently from the assumed continuum model. We assume that there is complex absorption of interstellar, photospheric, and of collisionally and/or photoionized gas origin in the moving material along the line of sight from a nova wind or ejecta. In addition to deriving the absorption properties, we obtain CNO abundances of elements in the ejecta/nova wind.

Episodic Mass Transfer: A Trigger for Nova Outbursts?

AbstractHigh resolution spectra of post-outburst novae show multiple components of ejected gas that are kinematically distinct. We interpret the observations in terms of episodes of enhanced mass transfer originating from the secondary star that result in the formation of discrete components of circumbinary gas and accretion onto the white dwarf (WD) that trigger nova outbursts. In this picture the concordance between absorption line velocities and emission line widths in most novae occurs as a result of the collision of the expanding nova ejecta with a larger mass of surrounding circumbinary gas. One implication of this model is that much of the accreted gas remains on the WD, leading to a secular increase in WD mass over each outburst event. Alternative scenarios to explain nova spectral evolution are possible that do not invoke circumbinary gas and a possible test of different models is proposed.

The RAINY3D Code: The Treatment of Condensation in Nova Remnants during Nebular Phase

ABSTRACTClassical nova remnants are important scenarios for improving the photoionization modeling. This work describes the pseudo-three-dimensional code RAINY3D, which drives the photoionization code Cloudy as a subroutine. Photoionization simulations of old nova remnants are also presented and discussed. In these simulations we analyze the effect of condensation in the remnant spectra. The condensed mass fraction affects the Balmer lines by a factor of greater than 4 when compared with homogeneous models, and this directly impacts the shell mass determination. The He II 4686/Hβ ratio decreases by a factor of 10 in clumpy shells. These lines are also affected by the clump size and density distributions. The behavior of the strongest nebular line observed in nova remnants is also analyzed for heterogeneous shells. The gas diagnoses in novae ejecta are thought to be more accurate during the nebular phase, but we have determined that at this phase the matter distribution can strongly affect the derived shell physical properties and chemical abundances.

A very luminous, highly extinguished, very fast nova – V1721 Aquilae

Studies indicate that fast novae are primarily located within the plane of the Milky Way and slow novae are found within its bulge. Because of high interstellar extinction along the line of sight many novae lying close to the plane are missed and only the brightest seen. One nova lying very close to the Galactic plane is V1721 Aquilae, which was discovered in outburst on 2008 September 22.5 UT. Examination of spectra obtained 2.69 days after outburst revealed very high expansion velocities (FWHM of the Hα emission ≈6450 km s-1). In this paper we have used available pre- and post-outburst photometry and post-outburst spectroscopy to conclude that the object is a very fast, luminous, and highly extinguished (AV = 11.6 ± 0.2) nova system with an average ejection velocity of ≈ 3400 km s-1. Pre-outburst near-IR colours from the 2MASS point source catalogue indicate that at quiescence the object is similar to many quiescent classical novae and appears to have a main sequence/sub-giant secondary rather than a giant counterpart. Based on the speed of decline of the nova and its emission line profiles we hypothesise that the axis ratio of the nova ejecta is ~1.4 and that its inclination is such that the central binary accretion disc is face-on to the observer. As such, the accretion disc’s blue contribution to the system’s near-IR quiescent colours may be significant. Simple models of the nova ejecta have been constructed using the morphological modelling code XS5, and the results support the above hypothesis. Precise spectral classification of this object has been exceptionally difficult owing to low signal-to-noise levels and high extinction, which has eliminated all evidence of any He/N or Fe II emission within the spectra. We suggest two possibilities for the nature of V1721 Aql: that it is a U Sco type RN with a sub-giant secondary or, less likely, that it is a highly energetic bright and fast classical nova with a main sequence secondary. Future monitoring of the object for possible RN episodes may be worthwhile, as would archival searches for previous outbursts.

CLEARING THE GAS FROM GLOBULAR CLUSTERS AND DWARF SPHEROIDALS WITH CLASSICAL NOVAE

Observations of the intra-cluster medium (ICM) in galactic globular clusters (GCs) show a systematic deficiency in ICM mass as compared to that expected from accumulation of stellar winds in the time available between galactic plane crossings. In this paper, we reexamine the original hypothesis of Scott and Durisen that hydrogen-rich explosions on accreting white dwarfs, classical novae (CNe), will sweep out the ICM from the cluster more frequently than galactic plane crossings. From the CNe rate and stellar mass-loss rate, this clearing mechanism predicts that ~ 0.03 M_sun should be present in <= 10^5 M_sun GCs. We model the expanding remnant made from the 10^-4 M_sun nova ejecta and show that it escapes long before it has cooled. We discuss the few positive ICM measurements and use a Monte-Carlo simulation of the accumulation and CNe recurrence times to reveal the possible variance in the ICM masses for the higher mass (> 5x10^5 M_sun) GCs. We find that nova shells are effective at clearing the ICM in low-mass GCs (<= 10^5 M_sun), whereas higher-mass clusters may experience a quiescent time between novae long enough to prevent the next nova shell from escaping. The nova clearing mechanism will also operate in ultra-faint Milky Way satellites, where many upper limits on gas masses are available.

The morphology of the expanding ejecta of V2491 Cygni (2008 N.2)

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 to determine the most likely morphology giving rise to them, including system inclination and expansion velocity of the nova ejecta. We find the best-fitting remnant morphology to be that of polar blobs and an equatorial ring with an implied inclination of 80+3−12 degrees and an maximum expansion velocity of the polar blobs of 3100+200−100 km s−1 and for the equatorial ring 2700+200−100 km s−1. This inclination would suggest that we should observe eclipses which will enable us to determine more precisely important parameters of the central binary. We also note that the amplitude of the outburst is more akin to the found in recurrent nova systems.

The 2010 nova outburst of the symbiotic Mira V407 Cyg

Abstract 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 d). The nova ejecta is found to progressively decelerate with time as it expands into the Mira wind. This is deduced from linewidths which change from a FWHM of 2760 km s−1 on day +2.3 to 200 km s−1 on day +196. The wind of the Mira is massive and extended enough for an outer neutral and unperturbed region to survive at all outburst phases.

Atypical dust species in the ejecta of classical novae

A classical nova outburst arises from a thermonuclear run- away in the hydrogen-rich material accreted onto the surface of a white dwarf in a binary system. These explosions can produce copious amounts of heavy element enriched material that are ejected violently into the surrounding interstellar medium. In some novae, conditions in the ejecta are suitable for the formation of dust of various compositions, including silicates, amorphous carbon, silicon carbide, and hydrocar- bons. Multiple dust grain types are sometimes produced in the same system. CO formation in novae may not reach saturation, thus in- validating the usual paradigm in which the C:O ratio determines the dust species. A few novae, such as V705 Cas and DZ Cru, have ex- hibited emission features near 6, 8, and 11 µm that are similar to Unidentified Infrared (UIR) features, but with significant differences in position and band structure. Here, we present Spitzer IRS spectra of two recent dusty novae, V2361 Cyg and V2362 Cyg, that harbor similar peculiar emission structures superimposed on features arising from carbonaceous grains. In other astronomical objects, such as star forming regions and young stellar objects, emission peaks at 6.2, 7.7, and 11.3 µm have been associated with polycyclic aromatic hydro- carbon (PAH) complexes. We suggest that hydrogenated amorphous carbon (HAC) may be the source of these features in novae based upon the spectral behavior of the emission features and the conditions under which the dust formed.

Direct Measurements ofNa22(p,γ)Mg23Resonances and Consequences forNa22Production in Classical Novae

The radionuclide 22Na is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the 22Na(p,γ)23Mg reaction. We have measured the strengths of low-energy 22Na(p,γ)23Mg resonances directly and absolutely using a radioactive 22Na target. We find the strengths of resonances at Ep=213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4-3.2, and we exclude important contributions to the rate from proposed resonances at Ep=198, 209, and 232 keV. The 22Na abundances expected in the ejecta of classical novae are reduced by a factor of ≈2.

Optical and Near-Infrared Photometry of Nova V2362 Cyg: Rebrightening Event and Dust Formation

Abstract We present optical and near-infrared (NIR) photometry of a classical nova, V2362 Cyg ($=$ Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening during the period between 100 and 240 d after the maximum of the nova. Our multicolor observation indicates the emergence of a pseudophotosphere with an effective temperature of $\sim\ $9000 K at the rebrightening maximum. After the rebrightening maximum, the object showed a slow fading homogeneously in all of the used bands for one week. This implies that the fading soon after the rebrightening maximum ($\lesssim\ $1 week) was caused by a slowly shrinking pseudophotosphere. Then, the NIR flux drastically increased, while the optical flux steeply declined. The optical and NIR fluxes were consistent with blackbody radiation with a temperature of $\sim\ $1500 K during this NIR rising phase. These facts are likely to be explained by dust formation in the nova ejecta. Assuming an optically thin case, we estimated the dust mass to be 10$^{-10}$–10$^{-8}\ M_{\odot}$, which is less than those in typical dust-forming novae. These results support the senario that a second, long-lasting outflow which caused the rebrightening interacted with a fraction of the initial outflow and formed dust grains.

AUTOMATED NanoSIMS MEASUREMENTS OF SPINEL STARDUST FROM THE MURRAY METEORITE

We report new O isotopic data on 41 presolar oxide grains, 38 MgAl2O4 (spinel) and 3 Al2O3 from the CM2 meteorite Murray, identified with a recently developed automated measurement system for the NanoSIMS. We have also obtained Mg-Al isotopic results on 29 of the same grains (26 spinel and 3 Al2O3). The majority of the grains have O isotopic compositions typical of most presolar oxides, fall well into the four previously defined groups, and are most likely condensates from either red giant branch or asymptotic giant branch stars. We have also discovered several grains with more unusual O and Mg compositions suggesting formation in extreme astrophysical environments, such as novae and supernovae. One of these grains has massive enrichments in 17O, 25Mg, and 26Mg, which are isotopic signatures indicative of condensation from nova ejecta. Two grains of supernova origin were also discovered: one has a large 18O/16O ratio typical of Group 4 presolar oxides; another grain is substantially enriched in 16O, and also contains radiogenic 44Ca from the decay of 44Ti, a likely condensate from material originating in the O-rich inner zones of a Type II supernova. In addition, several Group 2 presolar spinel grains also have large 25Mg and 26Mg isotopic anomalies that are difficult to explain by standard nucleosynthesis in low-mass stars. Auger elemental spectral analyses were performed on the grains and qualitatively suggest that presolar spinel may not have higher-than- stoichiometric Al/Mg ratios, in contrast to SIMS results obtained here and reported previously.

NON-EQUIPARTITION OF ENERGY, MASSES OF NOVA EJECTA, AND TYPE Ia SUPERNOVAE

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 between kinetic and radiated energy (E_kin and E_rad, respectively) in nova ejecta has been invoked as a way around this conundrum for the ultra-luminous red variable in M31. The deduced mass is far larger than that produced by any classical nova model. Our nova eruption simulations show that radiation and kinetic energy in nova ejecta are very far from being in energy equipartition, with variations of four orders of magnitude in the ratio E_kin/E_rad being commonplace. The assumption of equipartition must not be used to deduce nova ejecta masses; any such "determinations" can be overestimates by a factor of up to 10,000. We data-mined our extensive series of nova simulations to search for correlations that could yield nova ejecta masses. Remarkably, the mass ejected during a nova eruption is dependent only on (and is directly proportional to) E_rad. If we measure the distance to an erupting nova and its bolometric light curve then E_rad and hence the mass ejected can be directly measured.

Novae ejecta as colliding shells

Following on our initial absorption-line analysis of fifteen novae spectra we present additional evidence for the existence of two distinct components of novae ejecta having different origins. As argued in Paper I one component is the rapidly expanding gas ejected from the outer layers of the white dwarf by the outburst. The second component is pre-existing outer, more slowly expanding circumbinary gas that represents ejecta from the secondary star or accretion disk. We present measurements of the emission-line widths that show them to be significantly narrower than the broad P Cygni profiles that immediately precede them. The emission profiles of novae in the nebular phase are distinctly rectangular, i.e., strongly suggestive of emission from a relatively thin, roughly spherical shell. We thus interpret novae spectral evolution in terms of the collision between the two components of ejecta, which converts the early absorption spectrum to an emission-line spectrum within weeks of the outburst. The narrow emission widths require the outer circumbinary gas to be much more massive than the white dwarf ejecta, thereby slowing the latter's expansion upon collision. The presence of a large reservoir of circumbinary gas at the time of outburst is suggestive that novae outbursts may sometime be triggered by collapse of gas onto the white dwarf, as occurs for dwarf novae, rather than steady mass transfer through the inner Lagrangian point.