Thermonuclear Event Research Articles

Mass-loss and composition of wind ejecta in type I X-ray bursts

Context. X-Ray bursts (XRBs) are powerful thermonuclear events on the surface of accreting neutron stars (NSs) where nucleosynthesis of intermediate-mass elements occurs. The high surface gravity of an NS prevents the ejection of material by the XRB thermonuclear explosion. However, the predicted and observed XRB luminosities sometimes exceed Eddington’s value, and some of the material may escape by means of stellar wind. Aims. This work aims to determine the mass-loss and chemical composition of the material ejected through radiation-driven winds and its significance for Galactic abundances. It also reports on the evolution of observational quantities during the wind phase, which can help constrain the mass-radius relation in NSs. Methods. A non-relativistic radiative wind model was implemented, with modern opacity tables and treatment of the critical point, and linked through a new technique to a series of XRB hydrodynamic simulations that include over 300 isotopes. This allowed us to construct a quasi-stationary time evolution of the wind during the XRB. Results. In the models we studied, the total mass ejected by the wind was about 6 × 1019 g; the average ejected mass per burst represented 2.6% of the accreted mass between bursts, with 0.1% of the envelope mass ejected per burst; and approximately 90% of the ejecta was composed by 60Ni, 64Zn, 68Ge, and 58Ni. The ejected material also contained a small fraction (10−4 − 10−5) of some light p-nuclei, but not enough to account for their Galactic abundances. Additionally, the observable magnitudes during the wind phase showed remarkable correlations, partly due to the fact that photospheric luminosity stays close to the Eddington limit. Some of these correlations involve wind parameters, such as energy and mass outflows, that are determined by the conditions at the base of the wind envelope. Conclusions. The simulations resulted in the first realistic quantification of mass-loss for each isotope synthesized in the XRB. The photospheric correlations we found could be used to link observable magnitudes to the physics of the innermost parts of the envelope, close to its interface with the NS crust. This is a promising result regarding the issue of NS radius determination.

Iron-rich Metal-poor Stars and the Astrophysics of Thermonuclear Events Observationally Classified as Type Ia Supernovae. I. Establishing the Connection

The progenitor systems and explosion mechanisms responsible for the thermonuclear events observationally classified as Type Ia supernovae are uncertain and difficult to uniquely constrain using traditional observations of Type Ia supernova host galaxies, progenitors, light curves, and remnants. For the subset of thermonuclear events that are prolific producers of iron, we use published theoretical nucleosynthetic yields to identify a set of elemental abundance ratios infrequently observed in metal-poor stars but shared across a range of progenitor systems and explosion mechanisms: [Na, Mg, Co/Fe] < 0. We label stars with this abundance signature “iron-rich metal-poor,” or IRMP stars. We suggest that IRMP stars formed in environments dominated by thermonuclear nucleosynthesis and consequently that their elemental abundances can be used to constrain both the progenitor systems and explosion mechanisms responsible for thermonuclear explosions. We identify three IRMP stars in the literature and homogeneously infer their elemental abundances. We find that the elemental abundances of BD +80 245, HE 0533–5340, and SMSS J034249.53–284216.0 are best explained by the (double) detonations of sub-Chandrasekhar-mass CO white dwarfs. If our interpretation of IRMP stars is accurate, then they should be very rare in globular clusters and more common in the Magellanic Clouds and dwarf spheroidal galaxies than in the Milky Way’s halo. We propose that future studies of IRMP stars will quantify the relative occurrences of different thermonuclear event progenitor systems and explosion mechanisms.

Development of a solar radiation sensor system with pyranometer

&lt;span&gt;Solar energy is a result of the nuclear fusion process in the form of a series of thermonuclear events that occur in the Sun's core. Solar radiation has a significant impact on the lives of all living things on earth. The uses, as mentioned earlier, are when the solar radiation received requires a certain amount and vice versa. As a result, a more accurate instrument of solar radiation is required. A specific instrument is typically used to measure solar radiation parameters. There are four solar radiation parameters: diffusion radiation, global radiation, direct radiation, and solar radiation duration. Thus, it needs to use many devices to measure radiation data. The paper designs to measure all four-radiation data by pyranometer with particular modification and shading device. This design results have a high correlation with a global standard with a value of R=0.73, diffusion with a value of R=0.60 and a sufficiently strong direct correlation with a value of R=0.56. It can be said that the system is much simpler, making it easier to monitor and log the various solar radiation parameters.&lt;/span&gt;

SDSS J124043.01+671034.68: the partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?

ABSTRACT The white dwarf SDSS J124043.01+671034.68 (SDSS J1240+6710) was previously found to have an oxygen-dominated atmosphere with significant traces of neon, magnesium, and silicon. A possible origin via a violent late thermal pulse or binary interactions has been suggested to explain this very unusual photospheric composition. We report the additional detection of carbon, sodium, and aluminium in far-ultraviolet and optical follow-up spectroscopy. No iron-group elements are detected, with tight upper limits on titanium, iron, cobalt, and nickel, suggesting that the star underwent partial oxygen burning, but failed to ignite silicon burning. Modelling the spectral energy distribution and adopting the distance based on the Gaia parallax, we infer a low white dwarf mass, $M_\mathrm{wd}=0.41\pm 0.05\, \mathrm{M}_\odot$. The large space velocity of SDSS J1240+6710, computed from the Gaia proper motion and its radial velocity, is compatible with a Galactic rest-frame velocity of ≃ 250 km s−1 in the opposite direction with respect to the Galactic rotation, strongly supporting a binary origin of this star. We discuss the properties of SDSS J1240+6710 in the context of the recently identified survivors of thermonuclear supernovae, the D6 and LP 40−365 stars, and conclude that it is unlikely related to either of those two groups. We tentatively suggest that SDSS J1240+6710 is the partially burned remnant of a low-mass white dwarf that underwent a thermonuclear event.

The Supersoft X-Ray Transient ASASSN-16oh as a Thermonuclear Runaway without Mass Ejection

Abstract The supersoft X-ray and optical transient ASASSN-16oh has been interpreted by Maccarone et al. as having been induced by an accretion event on a massive white dwarf (WD), resembling a dwarf nova super-outburst. These authors argued that the supersoft X-ray spectrum had a different origin than in an atmosphere heated by shell nuclear burning, because no mass was ejected. We find instead that the event’s timescale and other characteristics are typical of non-mass-ejecting thermonuclear runaways, as already predicted by Shara et al. and the extensive grid of nova models by Yaron et al. We suggest that the low X-ray and bolometric luminosity in comparison to the predictions of the models of nuclear burning are due to an optically thick accretion disk, hiding most of the WD surface. If this is the case, we calculated that the optical transient can be explained as a non-ejective thermonuclear event on a WD of ≃1.1 M ⊙ accreting at the rate of ≃3.5–5 × 10−7 M ⊙ yr−1. We make predictions that should prove whether the nature of the transient event was due to thermonuclear burning or to accretion; observational proof should be obtained in the next few years, because a new outburst should occur within ≃10–15 yr of the event.

Gamma-ray line measurements from supernova explosions

AbstractGamma ray lines are expected to be emitted as part of the afterglow of supernova explosions, because radioactive decay of freshly synthesised nuclei occurs. Significant radioactive gamma ray line emission is expected from56Ni and44Ti decay on time scales of the initial explosion (56Ni, τ ~days) and the young supernova remnant (44Ti,τ ~90 years). Less specific, and rather informative for the supernova population as a whole, are lessons from longer lived isotopes such as26Al and60Fe. From isotopes of elements heavier than iron group elements, any interesting gamma-ray line emission is too faint to be observable. Measurements with space-based gamma-ray telescopes have obtained interesting gamma ray line emissions from two core collapse events, Cas A and SN1987A, and one thermonuclear event, SN2014J. We discuss INTEGRAL data from all above isotopes, including all line and continuum signatures from these two objects, and the surveys for more supernovae, that have been performed by gamma ray spectrometry. Our objective here is to illustrate what can be learned from gamma-ray line emission properties about the explosions and their astrophysics.

PRELUDE TO A DOUBLE DEGENERATE MERGER: THE ONSET OF MASS TRANSFER AND ITS IMPACT ON GRAVITATIONAL WAVES AND SURFACE DETONATIONS

We present the results of a systematic numerical study of the onset of mass transfer in double degenerate binary systems and its impact on the subsequent evolution. All investigated systems belong to the regime of direct impact, unstable mass transfer. In all of the investigated cases, even those considered unstable by conventional stability analysis, we find a long-lived mass transfer phase continuing for as many as several dozen orbital periods. This settles a recent debate sparked by a discrepancy between earlier SPH calculations that showed disruptions after a few orbital periods and newer grid-based studies in which mass transfer continued for tens of orbits. As we show that these binaries can survive at small separation for hundreds of orbital periods, their associated gravitational wave signal should be included when calculating the gravitational wave foreground (although expected to below LISA's sensitivity at these high frequencies). We also show that the inclusion of the entropy increase associated with shock-heating of the accreted material reduces the number of orbits a binary survives given the same initial conditions, although the effect is not as pronounced when using the appropriate initial conditions. The use of accurate initial conditions and a correct treatment of shock heating allows for a reliable time evolution of the temperature, density, and angular momentum, which are important when considering thermonuclear events that may occur during the mass transfer phase and/or after merger. Our treatment allows us to accurately identify when surface detonations may occur in the lead-up to the merger, as well as the properties of final merger products.

RS Ophiuchi: thermonuclear explosion or disc instability?

Abstract Sokoloski, Rupen &amp; Mioduszewski have recently reported evidence that the recurrent nova RS Ophiuchi produced a pair of highly collimated radio jets within days of its 2006 outburst. This suggests that an accretion disc must be present during the outburst. However, in the standard picture of recurrent novae as thermonuclear events, any such disc must be expelled from the white dwarf vicinity, as the nuclear energy yield greatly exceeds its binding energy. We suggest instead that the outbursts of RS Oph are thermal-viscous instabilities in a disc irradiated by the central accreting white dwarf. The distinctive feature of RS Oph is the very large size of its accretion disc. Given this, it fits naturally into a consistent picture of systems with unstable accretion discs. This picture explains the presence and speed of the jets, the brightness and duration of the outburst, and its rise time and linear decay, as well as the faintness of the quiescence. By contrast, the hitherto standard picture of recurrent thermonuclear explosions has a number of severe difficulties. These include the presence of jets, the faintness of quiescence, and the fact the accretion disc must be unstable unless it is far smaller than any reasonable estimate.

On the distance, reddening and progenitor of V838 Mon

Extensive optical and infrared photometry as well as low and high resolution spectroscopy are used as inputs in deriving robust estimates of the reddening, distance and nature of the progenitor of V838 Mon, the 2002 outbursting event that produced a most spectacular light-echo. The reddening affecting V838 Mon is found to obey the RV = 3.1 law and amounts to (i) EB−V = 0.86 from the interstellar NaI and KI lines; (ii) EB−V = 0.88 from the energy distribution of the B3 V component; and (iii) EB−V = 0.87 from the progression of extinction along the line of sight. The adopted EB−V = 0.87 ± 0.01 is also the amount required by fitting the progenitor with theoretical isochrones of appropriate metallicity. The distance is estimated from (a) the galactic kinematics of the three components of the interstellar lines; (b) the amount of extinction vs. the HI column density and vs. the dust emission through the whole Galaxy in that direction; from (c) spectrophotometric parallax to the B3 V companion; from (d) comparison of the observed color−magnitude diagram of field stars with 3D stellar population models of the Galaxy; from (e) comparison of theoretical isochrones with the components of the binary system in quiescence and found to be around 10 kpc. Pre-outburst optical and IR energy distributions show that the component erupting in 2002 was brighter and hotter than the B3 V companion. The best fit is obtained for a 50 000 K source, 0.5 mag brighter than the B3 V companion. The latter passed unaffected through the outburst, which implies an orbital separation wide enough to avoid mass exchange during the evolution of the binary system, and to allow a safe comparison with theoretical isochrones for single stars. Such a comparison suggests that the progenitor of the outbursting component had an initial mass ∼65 M� ,t hat it was approaching the carbon ignition stage in its core at the time it erupted in 2002 and that the age of the V838 Mon binary system is close to 4 million yr. The 2002 event is probably just a shell thermonuclear event in the outer envelope of the star.

Distributions of Pu isotopes and137Cs in soil from Semipalatinsk Nuclear Test Site detonations throughout southern districts

Soil samples collected mainly from the southern areas, including Kainar and Karaul settlements, around the Semipalatinsk Nuclear Test Site of the former USSR were analyzed for 137Cs and Pu isotopes (238Pu,239Pu and 240Pu) by γ-ray and α-ray spectrometry and ICP-MS. The 137Cs inventories varied widely from 170 to 13,600 Bq/m2. The 239,240Pu inventories, values of which are scare in the literature, also varied in the range of 34-2,050 Bq/m2 (most of date being 100-300 Bq/m2). In the areas around Tailan, Sarzal and Karaul settlements where the radioactive cloud related to the first thermonuclear explosion passed through, higher inventories of these nuclides were observed and especially their 238Pu/239,240Pu activity ratios (0.0064-0.0076) were markedly lower than those attributed to global fallout (0.03-0.04). The observed ratios might be used as a fingerprint to identify the Pu source of the first thermonuclear event. Most of the 240Pu/239Pu atomic ratios were lower than those of global fallout (0.18) commonly accepted. The contribution of local fallout 239,240Pu was higher (more than 80-90%) in the areas around the Tailan, Sarzal and Karaul settlements than that (30-ca. 60%) in the other areas. This high Pu contribution was related to the Pu source from the first thermonuclear event.

HST studies of cataclysmic variable white dwarfs

HST spectroscopy of faint exposed white dwarfs (WDs) in cataclysmic variables (CVs) has provided fundamental new information on white dwarf rotation rates, T eff, log g, chemical abundances of their accreted atmospheres, cooling response to heating of the white dwarf by boundary layer irradiation, compression and shear mixing in consequence of dwarf nova outburst events, and determined WD masses independent of disk emission line velocities. The first spectroscopic evidence of an accretion belt, predicted by Kippenhahn and Thomas, was uncovered in VW Hydri. The abundances and mix of nuclei in two white dwarfs in dwarf nova systems show signs of thermonuclear events in the recent past. In one of the cases, contamination of the secondary during a common envelope stage and re-accretion by the white dwarf, of its processed material, may be indicated. Although the detailed studies are few in number thus far, we have many promising indications of breakthroughs I would like to report at this conference. My focus will be on the essentially non-magnetic or weakly magnetic, tangentially accreting systems.

A photometric and spectroscopic study of the symbiotic binary BF Cyg

We present the historical 1890-1996 photographiclB-band light curve of the symbiotic binary BF Cyg for the first time. It displays three types of eruption: (i) a slow, symbiotic nova outburst (1895-1960), probably caused by a thermonuclear event; (ii) short-term flares dependent on the orbital phase, possibly triggered by accretion events, and (iii) outbursts (1920, 1989) such as are observed in classical symbiotic stars. Analyses of the deep minimum in the optical continuum during the last outburst, the observed bolo metric luminosity of the cool component, and elements of the hot component orbit [Kh =25.9 km s-l,fh(m) = 1.4 M0 ] indicate the system to be 4.6-5.4 kpc distant, and show that the binary consists of an M bright giant (Mg ' 2 M0 Rg~240-280 R 0 Lg~5000 L 0 ), filling up or being close to its Roche lobe, and a hot, luminous, compact object (Mh , 0.3-0.4 M0 Lh ~ 1.4Lg ) with an orbital inclination i~70-90°. Our parameters are very different from those previously published.

Gamma-ray lines from cosmic radioactivity

Gamma-ray spectroscopy holds great promise for probing nucleosynthesis in individual stellar explosions via short-lived radioactivity, and for measuring current global Galactic nucleosynthesis with longer-lived radioactivity. The former case was realized first for a Type II supernova when both 56Co and 57Co were detected in SN 1987A. These provide unprecedented constraints on models of core-collapse explosions. In the second category, 26Al in the Galaxy is now well observed and comes from massive stars, either before or during core collapse explosions, or from relatively massive AGB stars. We currently try to use these observations to constrain massive star evolution, supernova nucleosynthesis, and the Galactic supernova rate. Type Ia supernovae, thought to be entirely thermonuclear events, have not yet been definitively detected in γ-rays (although there is a hint of a signal from SN 1991T.) Ultimately, γ-ray measurements will confirm or disprove their thermonuclear character, probe the nuclear burning conditions, and help evaluate their contributions to Galactic nucleosynthesis. Positron annihilation radiation is also well-observed from the Galactic plane and bulge. All types of supernovae are plausibly significant contributors via their ejected positron emitters. By sorting out the contributions of the many possible sources, we can use these observations to constrain supernova nucleosynthesis, and we might obtain important clues to the progenitors of thermonuclear supernovae. All supernova types might contribute to a diffuse glow of 60Fe γ-ray lines. Current limits are very close to expected emission levels. Remnants of any type of age less that a few centuries might be detectable as individual spots of 44Ti γ-ray line emission. It is quite surprising that the brightest such spot is apparently the Cas A remnant, a relatively old one. That younger ones are not detected provides constraints on the combination of nucleosynthesis yields and supernova rates. Here we review the status of observations of γ-ray lines from these sources, discuss their implications, and briefly outline prospects for the future.

THE HOT STARS IN SYMBIOTIC SYSTEMS

ABSTRACT Symbiotic stars are interacting binaries, consisting of a late giant and a very hot companion, whose radiation ionizes the wind from the cool star. They strike the observers by their complex spectra and variability. A small subgroup, the symbiotic novae, undergo outbursts with an amplitude of several magnitudes and a duration of several decades. The ionizing binary component is usually too hot to be observed in the optical light. It emits mainly EUV photons, and in spectral regions better accessible to observers, nebula and cool star are much brighter than the hot star. Direct observations of hot components have therefore been restricted to special cases. Consequently, our knowledge about the hot components was poor. This thesis presents indirect methods allowing to extract crucial information on the ionizing star from the spectrum of the ionized nebula. Fundamental characteristics such as temperature, radius, and outburst energy are determined. They characterize the nature of the hot star, its outbursts, and the evolutionary status of the system. The IUE archive proved best suited as observational base. It contains thousands of far UV spectra of symbiotic stars. The UV continuum and the He II lambda-1640 recombination line turned out to be particularly sensitive to the hot star's parameters. For one object ROSAT observations of photospheric X-ray emission exist. They confirm the results obtained from IUE spectra. Unfortunately, only a subset of the symbiotics are bright enough to be observable in the UV, and moreover, the outburst of most symbiotic novae started long before the advent of space observatories. Possibilities to use optical spectroscopy are explored for these cases. T* can be derived from the observed ionization stages, and L* can be estimated from UBV magnitudes. The main result is displayed in Figure 1. Typically, the hot component of a symbiotic system has a radius ~0.1~R⊙, a surface temperature ~100,000~K, and a luminosity ~1000~L⊙. They occupy the same portion of the HR diagram as nova remnants and central stars of planetary nebulae. Like these, they seem to be basically white dwarfs with a hot atmosphere. They have not yet cooled or have been re-heated due to accretion of matter from the red giant. In particular, the results for the outbursts of symbiotic novae confirm the commonly adopted scenario of a thermo-nuclear event in an accreted layer on the surface of a white dwarf, largely analogous to a classical nova outburst. Unlike in classical novae, the cool component remains outside the outburst event, and the accreted matter slowly burns out over decades. While classical novae are hard to investigate when fading, the evolution of symbiotic novae can be tracked with the help of the subsisting nebular emission from the ionized part of the red giant's wind. The evolutionary paths roughly follow the theoretical models for novae. During the outburst of a symbiotic nova an energy around ~1047~erg is released, i.e. ~10-5 M⊙ of hydrogen is burnt. Besides supernovae, the outburst of symbiotic novae are the most energetic stellar events. The thesis is written in German.

Gamma-ray constraints on supernova nucleosynthesis

Gamma-ray spectroscopy holds great promise for probing nucleosynthesis in individual supernova explosions via short-lived radioactivity, and for measuring current global Galactic supernova nucleosynthesis with longer-lived radioactivity. It was somewhat surprising that the former case was realized first for a Type II supernova, when both Co-56 and Co-57 were detected in SN 1987A. These provide unprecedented constraints on models of Type II explosions and nucleosynthesis. Live Al-26 in the Galaxy might come from Type II supernovae, and if it is eventually shown to be so, can constrain massive star evolution, supernova nucleosynthesis, and the Galactic Type II supernova rate. Type Ia supernovae, thought to be thermonuclear explosions, have not yet been detected in gamma-rays. This is somewhat surprising given current models and recent Co-56 detection attempts. Ultimately, gamma-ray measurements can confirm their thermonuclear nature, probe the nuclear burning conditions, and help evaluate their contributions to Galactic nucleosynthesis. Type Ib/c supernovae are poorly understood. Whether they are core collapse or thermonuclear events might be ultimately settled by gamma-ray observations. Depending on details of the nuclear processing, any of these supernova types might contribute to a detectable diffuse glow of Fe-60 gamma-ray lines. Previous attempts at detection have come very close to expected emission levels. Remnants of any type of age less that a few centuries might be detectable as individual spots of Ti-44 gamma-ray line emission. It is in fact quite surprising that previous surveys have not discovered such spots, and the constraints on the combination of nucleosynthesis yields and supernova rates are very interesting. All of these interesting limits and possibilities mean that the next mission, International Gamma-Ray Astrophysics Laboratory (INTEGRAL), if it has sufficient sensitivity, is very likely to lead to the realization of much of the great potential of gamma-ray spectroscopy for understanding supernovae.

Spectra of low-mass helium star models and the type IC supernova SN 1987M

The question of whether the low-mass helium star models reproduce the helium-poor Type Ic spectrum of SN 1987M is investigated by comparing the theoretical spectrum from the 3.3-solar-mass model of Shigeyama et al. (1990) to observations of SN 1987M reported by Filippenko et al. (1990). The results indicate a number of positive correlations between the observed and the computed spectra. In both types of spectra, Ca II, O I, and Mg I emission lines dominate at late times, and, if extensive composition mixing is imposed, good fits can be made to the shapes of the emission features and good agreement can be found with the observed ratio of the forbidden and IR triplet blends of Ca II. The former indicates that the 3.3-solar-mass model predicts the proper density/velocity structure, and the latter indicates that the computed temperature structure is consistent with the observation though the lines are too strong relative to the continuum. This result is roughly independent of the He abundance. The computed and observed spectra are consistent with a small Ni-56 production in contrast to Type Ia thermonuclear events whose spectra are dominated by Fe-group lines at late times.

AG Dra a Symbiotic Star With an Uncommon Cool Component

SummaryAG Dra is probably a metal poor symbiotic binary of the galactic halo. The luminosity of the cool component is uncertain, which contributes to doubts about the correct model. Behaviour in activity is non classical with high ionization emission lines still having been seen then in the spectrum. This may perhaps most easily be explained by a weak thermonuclear event.

The historical record for Sirius: evidence for a white-dwarf thermonuclear runaway?

Schlosser and Bergmann1 recently presented evidence that in medieval times Sirius was a bright red star, rather than the present bluish-white star, from which they have suggested that Sirius B is a recently born white dwarf. However, their model poses severe evolutionary problems. We present the results of our attempts to detect possible planetary nebula ejecta toward Sirius, using data obtained by the International Ultraviolet Explorer (IUE) satellite. Based upon these results and in the light of recent advances in understanding white-dwarf evolution, we propose that Sirius B underwent a recent thermonuclear runaway event, triggered by a diffusion-induced CN reaction, to explain the historical behaviour of this star.

X-ray observations of symbiotic stars

AbstractObservations are reported of 19 symbiotic stars made with the imaging proportional counter of the Einstein Observatory. Three of the objects (HM Sge, V 1016 Cyg and RR Tel) were detected as soft X-ray sources. All three have shown slow-nova eruptions in the past 40 years. The data are interpreted as support of a model for slow novae involving thermonuclear events on white dwarfs which accrete from M giant companions. Symbiotic stars in their steady state, not being detected X-ray sources, are presumed to be powered by the accretion process alone.

X-ray observations of symbiotic stars

Observations are reported of 19 symbiotic stars made with the imaging proportional counter of the Einstein Observatory. Three of the objects (HM Sge, V 1016 Cyg and RR Tel) were detected as soft X-ray sources. All three have shown slow-nova eruptions in the past 40 years. The data are interpreted as support of a model for slow novae involving thermonuclear events on white dwarfs which accrete from M giant companions. Symbiotic stars in their steady state, not being detected X-ray sources, are presumed to be powered by the accretion process alone.