Mass-accreting White Dwarfs Research Articles

He-accreting Oxygen–Neon White Dwarfs and Accretion-induced Collapse Events

It has been widely accepted that mass-accreting white dwarfs (WDs) are the progenitors of Type Ia supernovae (SNe) or electron-capture supernovae. Previous work has shown that the accretion rate could affect the elemental abundance on the outer layers of CO WDs, and therefore affect the observational characteristics after they exploded as SNe Ia. However, it has not been well studied how elemental abundance changes on the outer layers of He-accreting ONe WDs as they approach the Chandrasekhar mass limit. In this paper, we investigated the evolution of He-accreting ONe WDs with MESA. We found that a CO-rich mantle will accumulate beneath the He layers resulting from the He burning, after which the ignition of the CO-rich mantle could transform carbon into silicon (Si). The amount of Si produced by carbon burning is strongly anticorrelated with the accretion rate. As the ONe WD nearly approaches the Chandrasekhar mass limit (M ch) through accretion, it is likely to undergo accretion-induced collapse, resulting in the formation of a neutron star.

Planetary nebulae hosting accreting white dwarfs: a possible solution for the mysterious cut-off of planetary nebula luminosity function?

ABSTRACTMany binary companions to the central stars of planetary nebulae (PNe) are found to be inflated, perhaps indicating that accretion onto the central star might occur during the planetary nebula (PN) phase. The discovery of a handful of nova eruptions and supersoft X-ray sources inside PNe supports this hypothesis. In this paper, we investigate the impact that hosting a steadily accreting white dwarf (WD) would have on the properties and evolution of a PN. By pairing the published accreting nuclear-burning WD models with radiation transfer simulations, we extract the time evolution of the emission line spectra and ionization properties of a PN that surrounds a 0.6$\, \rm M_{\odot }$ steadily nuclear-burning WD as a function of the mass accretion rate. We find that accreting WDs are able to form very extended, high excitation, [${\rm O\, \small {\rm III}}$]-bright PNe, which are characterized by high nebular electron temperatures. Their properties remain almost invariant with time and their visibility time can be much longer compared to PNe powered by single WDs. We discuss the implications of our findings in explaining specific characteristics observed in PNe. Finally, we examine how accreting WDs affect the planetary nebula luminosity function (PNLF) by covering WD masses in the range of 0.5–0.8$\, \rm M_{\odot }$ and for various accretion rates within the steady accretion regime. We find that for all but the lowest accretion rates, the [${\rm O\, \small {\rm III}}$] luminosities are almost constant and clustered very close to the PNLF cut-off value. Our results suggest that mass-accreting WDs in interacting binaries might play a role in understanding the invariant cut-off of the PNLF.

SHORTEST RECURRENCE PERIODS OF NOVAE

Stimulated by the recent discovery of the 1 yr recurrence period nova M31N 2008-12a, we examined the shortest recurrence periods of hydrogen shell flashes on mass-accreting white dwarfs (WDs). We discuss the mechanism that yields a finite minimum recurrence period for a given WD mass. Calculating the unstable flashes for various WD masses and mass accretion rates, we identified a shortest recurrence period of about two months for a non-rotating 1.38 M_sun WD with a mass accretion rate of 3.6 x 10^{-7} M_sun yr^{-1}. A 1 yr recurrence period is realized for very massive (> 1.3 M_sun) WDs with very high accretion rates (> 1.5 x 10^{-7} M_sun yr^{-1}). We revised our stability limit of hydrogen shell burning, which will be useful for binary evolution calculations toward Type Ia supernovae.

FINAL FATES OF ROTATING WHITE DWARFS AND THEIR COMPANIONS IN THE SINGLE DEGENERATE MODEL OF TYPE Ia SUPERNOVAE

Taking into account the rotation of mass-accreting white dwarfs (WDs) whose masses exceed the Chandrasekhar mass, we extend our new single degenerate model for the progenitors of Type Ia supernovae (SNe Ia), accounting for two types of binary systems, those with a main sequence companion and those with a red-giant (RG) companion. We present a mass distribution of WDs exploding as SNe Ia, where the WD mass ranges from 1.38 to 2.3 Msun. These progenitor models are assigned to various types of SNe Ia. A lower mass range of WDs (1.38 Msun < M_WD <~ 1.5 Msun), which are supported by rigid rotation, correspond to normal SNe Ia. A variety of spin-down time may lead to a variation of brightness. A higher mass range of WDs (M_WD >~ 1.5 Msun), which are supported by differential rotation, correspond to brighter SNe Ia such as SN 1991T. In this case, a variety of the WD mass may lead to a variation of brightness. We also show the evolutionary states of the companion stars at SN Ia explosions and pose constraints on the unseen companions. In the WD+RG systems, in particular, most of the RG companions have evolved to helium/carbon-oxygen WDs in the spin-down phase before the SN Ia explosions. In such a case, we do not expect any prominent signature of the companion immediately before and after the explosion. We also compare our new models with the recent stringent constraints on the unseen progenitors of SNe Ia such as SN 2011fe.

A SINGLE DEGENERATE PROGENITOR MODEL FOR TYPE Ia SUPERNOVAE HIGHLY EXCEEDING THE CHANDRASEKHAR MASS LIMIT

Recent observations of Type Ia supernovae (SNe Ia) suggest that some of the progenitor white dwarfs (WDs) had masses up to 2.4-2.8 M_sun, highly exceeding the Chandrasekhar mass limit. We present a new single degenerate (SD) model for SN Ia progenitors, in which the WD mass possibly reaches 2.3-2.7 M_sun. Three binary evolution processes are incorporated; optically thick winds from mass-accreting WDs, mass-stripping from the binary companion star by the WD winds, and WDs being supported by differential rotation. The WD mass can increase by accretion up to 2.3 (2.7) M_sun from the initial value of 1.1 (1.2) M_sun, being consistent with high luminosity SNe Ia such as SN 2003fg, SN 2006gz, SN 2007if, and SN 2009dc. There are three characteristic mass ranges of exploding WDs. In an extreme massive case, differentially rotating WDs explode as an SN Ia soon after the WD mass exceeds 2.4 M_sun because of a secular instability at T/|W|\sim 0.14. For a mid mass range of M_WD=1.5-2.4 M_sun, it takes some time (spinning-down time) until carbon is ignited to induce an SN Ia explosion after the WD mass has reached maximum, because it needs a loss or redistribution of angular momentum. For a lower mass case of rigidly rotating WDs, M_WD=1.38-1.5 M_sun, the spinning-down time depends on the timescale of angular momentum loss from the WD. The difference in the spinning-down time may produce the "prompt" and "tardy" components. We also suggest the very bright super-Chandrasekhar mass SNe Ia are born in a low metallicity environment.

Binary population synthesis study of the supersoft X-ray phase of single degenerate type Ia supernova progenitors

In the single degenerate (SD) scenario for type Ia supernovae (SNe Ia), a mass-accreting white dwarf is expected to experience a supersoft X-ray source (SSS) phase. However, some recent observations showed that the expected number of mass-accreting WDs is much lower than that predicted from theory, regardless of whether they are in spiral or elliptical galaxies. In this paper, we performed a binary population synthesis study on the relative duration of the SSS phase to their whole mass-increasing phase of WDs leading to SNe Ia. We found that for about 40% of the progenitor systems, the relative duration is shorter than 2% and the evolution of the mean relative duration shows that it is always smaller than 5%, both for young and old SNe Ia. In addition, before the SNe Ia explosions, more than 55% of the progenitor systems were experiencing a dwarf novae phase and no more than 10% were staying in the SSS phase. These results are consistent with the recent observations and imply that both in early- and late-type galaxies, only a small fraction of mass-accreting WDs resulting in SNe Ia contributes to the supersoft X-ray flux. So, although our results are not directly related to the X-ray output of the SN Ia progenitor, the low supersoft X-ray luminosity observed in early type galaxies may not be able to exclude the validity of the SD model. On the contrary, it is evidence to support the SD scenario.

Novae and Accreting White Dwarfs as Progenitors of Type Ia Supernovae

AbstractI review various phenomena associated with mass-accreting white dwarfs (WDs) in relation to progenitors of Type Ia supernovae (SNe Ia). The WD mass can be estimated from light curve analysis in multiwavelength bands based on the theory of optically thick winds. In the single degenerate scenario of SNe Ia, two main channels are known, i.e., WD + main sequence (MS) channel and WD + red giant (RG) channel. In each channel, a typical binary undergoes three evolutionary stages before explosion, i.e., the wind phase, supersoft X-ray source (SSS) phase, and recurrent nova phase, in this order because the accretion rate decreases with time as the companion mass decreases. For some accreting WDs we can identify the corresponding stage of evolution. Intermittent supersoft X-ray sources like RX J0513.9−6951 and V Sge correspond to wind phase objects. For the SSS phase, CAL 87-type objects correspond to the WD+MS channel. For the WD + RG channel, soft X-ray observations of early type galaxies give statistical evidence of SSS phase binaries. Recurrent novae of U Sco-type and RS Oph-type correspond to the WD + MS channel and WD + RG channel, respectively. The majority of recurrent novae host a very massive WD (≳ 1.35 M⊙) and often show a plateau phase in their optical light curves corresponding to the long-lasting supersoft X-ray phase. These properties are indications of increasing WD masses.

α-Induced Reaction Rates for Accreting Compact Stars

Studies have shown that alpha-induced nuclear reactions in the hot CNO cycles and on the waiting points of the rp-process play a principal role in energy production and nucleosynthesis on the surface of mass-accreting white dwarfs and neutron stars. This paper will present recent measurements at Notre Dame on the rate of 15O( α, γ) and new experiments for ( α,p) reactions on the waiting point nuclei of 14O and 26Si. Preliminary results and astrophysical implications will be discussed.

Accreting white dwarfs as supersoft X‐ray sources

AbstractI review various phenomena associated with mass‐accreting white dwarfs (WDs) in the view of supersoft X‐ray sources. When the mass‐accretion rate is low (Ṁacc &lt; a few × 10–7 M⊙yr–1), hydrogen nuclear burning is unstable and nova outbursts occur. A nova is a transient supersoft X‐ray source (SSS) in its later phase which timescale depends strongly on the WD mass. The X‐ray turn on/off time is a good indicator of the WD mass. At an intermediate mass‐accretion rate an accreting WD becomes a persistent SSS with steady hydrogen burning. For a higher mass‐accretion rate, the WD undergoes “accretion wind evolution” in which the WD accretes matter from the equatorial plane and loses mass by optically thick winds from the other directions. Two SSS, namely RX J0513‐6951 and V Sge, are corresponding objects to this accretion wind evolution. We can specify mass increasing WDs from light‐curve analysis based on the optically thick wind theory using multiwavelength observational data including optical, IR, and supersoft X‐rays. Mass estimates of individual objects give important information for the binary evolution scenario of type Ia supernovae (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The Delay-Time Distribution of Type Ia Supernovae and the Single-Degenerate Model

We present a theoretical delay-time distribution (DTD) of Type Ia supernovae on the basis of our new evolutionary models of single-degenerate (SD) progenitor systems. Our model DTD has almost a featureless power law shape (∝t−n with n ≈ 1) for the delay time from t ∼ 0.1 to 10 Gyr. This is in good agreement with the recent direct measurement of DTDs. The observed featureless property of the DTD has been suggested to be favorable for the double-degenerate (DD) scenario but not for the SD scenario. If the mass range of the companion star to the white dwarf (WD) were too narrow in the SD model, its DTD would be too limited around the companion's main-sequence lifetime to be consistent with the observed DTD. However, this is not the case in our SD model that consists of the two channels of WD+RG (red giant) and WD+MS (main-sequence star). In these channels, the companion stars have a mass range of ~0.9-3 M☉ (WD+RG) and ~2-6 M☉ (WD+MS). The combined mass range is wide enough to yield the featureless DTD. We emphasize that the SD scenario should include two important processes: the optically thick winds from the mass-accreting WD and the mass-stripping from the companion star by the WD wind.

Young and Massive Binary Progenitors of Type Ia Supernovae and Their Circumstellar Matter

We present new evolutionary models for Type Ia supernova (SN Ia) progenitors, introducing the mass-stripping effect on a main-sequence (MS) or slightly evolved companion star by winds from a mass-accreting white dwarf (WD). The mass stripping attenuates the rate of mass transfer from the companion to the WD. As a result, a very massive MS companion can avoid forming a common envelope and thus can increase the WD mass up until the SN Ia explosion. Including the mass-stripping effect, we follow binary evolutions of various WD + MS systems and obtain the parameter region in the initial donor mass-orbital period plane in which SNe Ia occur. The newly obtained SN Ia region extends to donor masses of 6-7 M☉, although its extension depends on the efficiency of the mass-stripping effect. The stripped matter would mainly be distributed on the orbital plane and would form very massive circumstellar matter (CSM) around the SN Ia progenitor. This can explain the massive CSM around the Type Ia/IIn(IIa) supernovae SN 2002ic and SN 2005gj, as well as the tenuous CSM around the normal Type Ia supernova SN 2006X. Our new model suggests the presence of very young (108 yr) populations of SNe Ia, which is consistent with recent observational indications of young-population SNe Ia.

A New Interpretation of the Low Radial Velocity Determined from the HeII Emission Line in the Galactic Supersoft X-Ray Source RX J0019.8+2156

We propose a new interpretation for the low radial velocity of He II emission line in the Galactic supersoft X-ray source RX J0019.8+2156 based on a 2-D numerical simulation of dynamical mass transfer in binary systems. A more massive main-sequence (MS) companion of ~ 2.0 M⊙ is derived for a ~ 0.6 M⊙ white dwarf (WD) primary.The Galactic supersoft X-ray source RX J0019.8+2156 (hereafter, RX J0019) with a 12.2 mag optical counterpart was discovered by ROSAT. The source is a binary with the period of 0.66 days and its X-ray luminosity is fairly constant, at least, for 7 yrs. Therefore RX J0019 seems to be a typical luminous supersoft X-ray source (SSS) with steady hydrogen shell-burning on a mass-accreting white dwarf (WD).

RX J0513.9-6951 and V Sagittae: Accretion Wind Evolution, A Key Evolutionary Process to Type IA Supernovae

AbstractA new self-sustained model for long-term light-curve variations of the supersoft X-ray sources RX J0513.9–6951 and V Sge is proposed based on an optically thick wind model of mass-accreting white dwarfs (WDs). When the mass accretion rale to a WD exceeds the critical rate of ~ 1 x 10–1M⊙. yr–1, optically thick strong winds begin to blow from the WD so that a formation of common envelope is avoided. The WD can accrete and burn hydrogen-rich matter on the surface of the WD at the critical rate. The excess matter transferred to the WD above the critical rate is expelled by winds. This is called “accretion wind evolution.” This ejection process, however, occurs intermittently because the mass transfer is attenuated by strong winds: the strong winds collide with the secondary surface and strip oil the surface layer of the secondary. Properly formulating the mass-stripping effect and the ensuing decay of mass-transfer rate, we are able to reproduce the transition between the optical high/X-ray off and optical low/X-ray -on states of the supersoft X-ray sources RX J0513.9–6951 and V Sge. Thus these two objects are the lirst examples of accretion wind evolution, which is a key evolutionary process in a recently developed evolutionary path to Type la supernovae.

RX J0513.9−6951: The First Example of Accretion Wind Evolution, a Key Evolutionary Process to Type Ia Supernovae

A new self-sustained model for long-term light-curve variations of RX J0513.9-6951 is proposed based on an optically thick wind model of mass-accreting white dwarfs (WDs). When the mass rate to a WD exceeds the critical rate of ~1 × 10-6 M☉ yr-1, optically thick strong winds begin to blow from the WD so that a formation of common envelope is avoided. The WD can accrete and burn hydrogen-rich matter on the surface of the WD at the critical rate. The excess matter transferred to the WD above the critical rate is expelled by winds. This is called accretion wind evolution. This ejection process, however, occurs intermittently because the mass transfer is attenuated by strong winds: the strong winds collide with the secondary surface and strip off the surface layer of the secondary. The stripped-off matter is lost from the binary system. Properly formulating this mass-stripping effect and the ensuing decay of mass-transfer rate, we are able to reproduce, in a self-sustained manner, the transition between the optical high/X-ray-off and optical low/X-ray-on states of RX J0513.9-6951. Thus RX J0513.9-6951 is the first example of wind evolution, which is a key evolutionary process in a recently developed evolutionary path to Type Ia supernovae.

A New Evolutionary Path to Type Ia Supernovae: A Helium‐rich Supersoft X‐Ray Source Channel

We have found a new evolutionary path to Type Ia supernovae (SNe Ia) that has been overlooked in previous work. In this scenario, a carbon-oxygen white dwarf (C+O WD) is originated not from an asymptotic giant branch star with a C+O core but from a red giant star with a helium core of ~0.8-2.0 M☉. The helium star, which is formed after the first common envelope evolution, evolves to form a C+O WD of ~0.8-1.1 M☉, transferring a part of the helium envelope onto the secondary main-sequence star. This new evolutionary path, together with the optically thick wind from mass-accreting white dwarf, provides a much wider channel to SNe Ia than previous scenarios. A part of the progenitor systems are identified as luminous supersoft X-ray sources or recurrent novae such as U Sco, which are characterized by the accretion of helium-rich matter. The white dwarf accretes hydrogen-rich, helium-enhanced matter from a lobe-filling, slightly evolved companion at a critical rate and blows excess matter into the wind. The white dwarf grows in mass to the Chandrasekhar mass limit and explodes as an SN Ia. A theoretical estimate indicates that this channel contributes a considerable part of the inferred rate of SNe Ia in our Galaxy, i.e., the rate is about 10 times larger than the previous theoretical estimates for white dwarfs with slightly evolved companions.

A New Model for Progenitor Systems of Type Ia Supernovae

We propose a new model for progenitor systems of Type Ia supernovae. The model consists of an accreting white dwarf and a lobe-filling, low-mass red giant. When the mass accretion rate exceeds a certain critical rate, there is no static envelope solution on the white dwarf. For this case, we find a new strong wind solution, which replaces the static envelope solution. Even if the mass-losing star has a deep convective envelope, the strong wind stabilizes the mass transfer until the mass ratio, q, between the mass-losing star and the mass-accreting white dwarf reaches 1.15, i.e., q < 1.15. A part of the transferred matter can be accumulated on the white dwarf at a rate that is limited to cr = 9.0 × 10-7 (MWD/M☉ - 0.50) M☉ yr-1, and the rest is blown off in the wind. The photospheric temperature is kept around T ~ 1 × 105-2 × 105 K during the wind phase. After the wind stops, the temperature quickly increases up to ~1 × 106 K. The white dwarf steadily burns hydrogen and accretes helium, thereby being able to increase its mass up to 1.38 M☉ and explode as a Type Ia supernova. The expected birth rate of this type of supernovae is consistent with the observed rate of Type Ia supernovae. The hot white dwarf may not be observed during the strong wind phase due to self-absorption by the wind itself. The Strong wind stops when the mass transfer rate decreases below cr. Then it can be observed as a supersoft X-ray source.

The final stages of evolution of cold, mass-accreting white dwarfs

view Abstract Citations (34) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Final Stages of Evolution of Cold, Mass-accreting White Dwarfs Hernanz, Margarita ; Isern, Jordi ; Canal, Ramon ; Labay, Javier ; Mochkovitch, Robert Abstract The evolution of solid C + O white dwarf models upon mass accretion is calculated up to the point of either explosive thermonuclear ignition or gravitational collapse. It is shown that both explosions and 'quiet' collapses to a neutron star are possible for each of two different phase diagrams for high-density C + O mixtures. The ranges of initial masses and temperatures and of accretion rates leading to the different outcomes are determined. Problems concerning the chemical composition of the accreted matter and the effects of tidal dissipation are discussed. Publication: The Astrophysical Journal Pub Date: January 1988 DOI: 10.1086/165898 Bibcode: 1988ApJ...324..331H Keywords: Cool Stars; Stellar Evolution; Stellar Mass Accretion; Stellar Models; Stellar Temperature; White Dwarf Stars; Gravitational Collapse; Neutron Stars; Stellar Composition; Stellar Interiors; Supernovae; Thermonuclear Reactions; Astrophysics; STARS: ACCRETION; STARS: INTERIORS; STARS: SUPERNOVAE; STARS: WHITE DWARFS full text sources ADS |

Solid white dwarfs as Type I supernova progenitors

Mass-accreting white dwarfs in close binary systems are generally thought to be Type I supernova (SN I) progenitors. Low-mass (Mtot≲5 M⊙) binary X-ray sources (also known as Type II sources) equally appear to be the descendants of cataclysmic variables (CV) and thus to have been produced by the collapse of a mass-accreting white dwarf. We point out here that a single process, thermonuclear ignition inside a partially solid, carbon–oxygen white dwarf, may account for the full range of phenomena: from mildly or non-explosive collapses leaving a condensed remnant up to ‘slow’ to ‘fast’ SN I outbursts with total disruption of the parent star.

Neutron star formation by collapse of white dwarfs

Mass-accreting carbon-oxygen white dwarfs become thermally and dynamically unstable when they reach high enough central densities. Carbon ignition at the star's center likely propagates subsonically and, in the case of an initially solid core, leads to collapse if the rate of increase of the core's mass is sufficiently fast. Recent results indicate, however, that solidification of the core induces carbon-oxygen separation. The central regions are then made of pure oxygen while carbon is rejected to lower-density layers. Carbon ignition happens only after neutronization of the central (oxygen) regions. Collapse to a neutron star is then independent from the rate of mass increase and the only possible restrictions are set by the behaviour of the outer, accreted layers. X-ray sources, pulsars and Type I supernovae are likely outcomes of this process.

Nova Explosion of Mass Accreting White Dwarfs

Evolution of a mass accreting white dwarf has been computed from the onset of accretion through nova explosion. We have considered a white dwarf of 1.3M⊙ with the accretion rate of 1×10-10M⊙ yr-1. Because the thermal structure during the accretion phase has been fully taken into computation, the mass of the accreted hydrogen-rich envelope and the corresponding temperature distribution in the envelope have been determined. When the hydrogen-rich envelope of mass ΔMH = 1.63 × 10-4M⊙ has been formed, a hydrogen-shell flashes commences. The flashing shell lies midway between the bottom of the envelope and the stellar surface; the mass lying above this shell is 5.7 × 10-5M⊙