Progenitors Of Type Ia Supernovae Research Articles

Irradiation-driven mass transfer for massive companion stars in supersoft X-rays sources

Supersoft X-ray sources (SSSs) have been proposed as one of the progenitors for Type Ia supernovae. However, the exact origin of the quasi-periodic variability in the optical light curve remains a mystery. In this work, our goal is to investigate the effect of the feedback of an evolved main-sequence companion star on X-ray irradiation and find whether periodic X-ray irradiation of the companion star could reproduce periodic mass transfer. Using the Modules for Experiments in Stellar Astrophysics (MESA) code, we modeled the evolutionary track of the companion star under the influence of supersoft X-ray irradiation, and we calculated the resulting mass transfer rate. We find that the supersoft X-ray heating of the companion star can result in the expansion of the companion, causing it to greatly overflow its Roche lobe and thereby increasing the mass transfer rate. The periodic X-ray irradiation on the companion stars leads to periodic changes in the mass transfer rate. For a given companion star, higher irradiation efficiencies result in a higher mass transfer rate. Additionally, the mass transfer rate increases as the mass of the companion star decreases for a given irradiation efficiency. The companion star undergoing thermal timescale mass transfer is periodically irradiated by the X-rays from the WD, which can lead to periodic enhancement of the mass transfer rate. The mechanism could be the origin of the quasi-periodic optical light curve in supersoft X-ray sources.

Type Ia Supernova Progenitor Properties and their Host Galaxies

We present an eigenfunction method to analyze 161 visual light curves (LCs) of Type Ia supernovae (SNe Ia) obtained by the Carnegie Supernova Project to characterize their diversity and host-galaxy correlations. The eigenfunctions are based on the delayed-detonation (DD) scenario using three parameters: the LC stretch s determined by the amount of deflagration burning governing the 56Ni production, the main-sequence mass M MS of the progenitor white dwarf controlling the explosion energy, and its central density ρ c shifting the 56Ni distribution. Our analysis tool (Supernova Parameter Analysis Tool) extracts the parameters from observations and projects them into physical space using their allowed ranges (M MS ≤ 8 M ⊙, ρ c ≤ 7–8 × 109 g cm−3). The residuals between fits and individual LC points are ≈1%–3% for ≈92% of objects. We find two distinct M MS groups corresponding to a fast (≈4–65 Myr) and a slow(≈200–500 Myr) stellar evolution. Most underluminous SNe Ia have hosts with low star formation but high M MS, suggesting slow evolution times of the progenitor system. 91T-like SNe show very similar LCs and high M MS and are correlated to star formation regions, making them potentially important tracers of star formation in the early Universe out to z ≈ 4–11. Some ∼6% outliers with nonphysical parameters using DD scenarios can be attributed to superluminous SNe Ia and subluminous SNe Ia with hosts of active star formation. For deciphering the SNe Ia diversity and high-precision SNe Ia cosmology, the importance is shown for LCs covering out to ≈60 days past maximum. Finally, our method and results are discussed within the framework of multiple explosion scenarios, and in light of upcoming surveys.

Tracing back the birth environments of Type Ia supernova progenitor stars: a pilot study based on 44 early-type host galaxies

ABSTRACT The environmental dependence of Type Ia supernova (SN Ia) luminosities is well established, and efforts are being made to find its origin. Previous studies typically use the currently observed status of the host galaxy. However, given the delay time between the birth of the progenitor star and the SN Ia explosion, the currently observed status may differ from the birth environment of the SN Ia progenitor star. In this paper, employing the chemical evolution and accurately determined stellar population properties of 44 early-type host galaxies, we, for the first time, estimate the SN Ia progenitor star birth environment, specifically [Fe/H]Birth and [α/Fe]Birth. We show that [α/Fe]Birth has a $30.4^{\text{+10.6}}_{-10.1}{{\ \rm per\ cent}}$ wider range than the currently observed [α/Fe]Current, while the range of [Fe/H]Birth is not statistically different ($17.9^{\text{+26.0}}_{-27.1}{{\ \rm per\ cent}}$) to that of [Fe/H]Current. The birth and current environments of [Fe/H] and [α/Fe] are sampled from different populations (p-values of the Kolmogorov–Smirnov test <0.01). We find that light-curve fit parameters are insensitive to [Fe/H]Birth (<0.9σ for the non-zero slope), while a linear trend is observed with Hubble residuals (HRs) at the 2.4σ significance level. With [α/Fe]Birth, no linear trends (<1.1σ) are observed. Interestingly, we find that [α/Fe]Birth clearly splits the SN Ia sample into two groups: SN Ia exploded in [α/Fe]Birth-rich or [α/Fe]Birth-poor environments. SNe Ia exploded in different [α/Fe]Birth groups have different weighted-means of light-curve shape parameters: 0.81 ± 0.33 (2.5σ). They are thought to be drawn from different populations (p-value = 0.01). Regarding SN Ia colour and HRs, there is no difference (<1.0σ) in the weighted-means and distribution (p-value > 0.27) of each [α/Fe]Birth group.

The physical properties of T Pyx as measured by MUSE. I. The geometrical distribution of the ejecta and the distance to the remnant

T Pyx is one of the most enigmatic recurrent novae, and it has been proposed as a potential Galactic type-Ia supernova progenitor. Using spatially resolved data obtained with MUSE, we characterized the geometrical distribution of the material expelled in previous outbursts surrounding the white dwarf progenitor. We used a 3D model for the ejecta to determine the geometric distribution of the extended remnant. We also calculated the nebular parallax distance ($d = 3.55 0.77$ kpc) based on the measured velocity and spatial shift of the 2011 bipolar ejecta. Our findings confirm previous results, including the data from the GAIA mission. The remnant of T Pyx can be described by a two-component model consisting of a tilted ring at $i = 63.7$ relative to its normal vector and fast bipolar ejecta perpendicular to the plane of the equatorial ring. We found an upper limit for the bipolar outflow ejected mass in 2011 of the bipolar outflow of $M_ ej,b $ M$_ odot $, which is lower than previous estimates given in the literature. However, only a detailed physical study of the equatorial component can provide an accurate estimate of the total ejecta of the last outburst, a fundamental step to understanding if T Pyx will end its life as a type-Ia supernova.

The Common Envelope Evolution Outcome. II. Short-orbital-period Hot Subdwarf B Binaries Reveal a Clear Picture

Common envelope evolution (CEE) is vital for forming short-orbital-period compact binaries. It covers many objects, such as double compact merging binaries, Type Ia supernovae progenitors, binary pulsars, and X-ray binaries. Knowledge of the common envelope (CE) ejection efficiency still needs to be improved, though progress has been made recently. Short-orbital-period hot subdwarf B star (sdB) plus white dwarf (WD) binaries are the most straightforward samples with which to constrain CEE physics. We apply the known orbital period–WD mass relation to constrain the sdB progenitors of seven sdB+WD binaries with a known inclination angle. The average CE efficiency parameter is 0.32. This is consistent with previous studies. However, the CE efficiency need not be constant, but a function of the initial mass ratio, based on well-constrained sdB progenitor mass and evolutionary stage. Our results can be used as physical inputs for binary population synthesis simulations of related objects. A similar method can also be applied to study other short-orbital-period WD binaries.

Eruptive novae in symbiotic systems

ABSTRACT We conduct numerical simulations of multiple nova eruptions in detached, widely separated symbiotic systems that include an asymptotic giant branch (AGB) companion to investigate the impact of white dwarf (WD) mass and binary separation on the evolution of the system. The accretion rate is determined using the Bondi–Hoyle–Lyttleton method, incorporating orbital momentum loss caused by factors such as gravitational radiation, magnetic braking, and drag. The WD in such a system accretes matter coming from the strong wind of an AGB companion until it finishes shedding its envelope. This occurs on an evolutionary time-scale of ≈3 × 105 yr. Throughout all simulations, we use a consistent AGB model with an initial mass of 1.0 M⊙ while varying the WD mass and binary separation, as they are the critical factors influencing nova eruption behaviour. We find that the accretion rate fluctuates between high and low rates during the evolutionary period, significantly impacted by the AGB’s mass loss rate. We show that unlike novae in cataclysmic variables, the orbital period may either increase or decrease during evolution, depending on the model, while the separation consistently decreases. Furthermore, we have identified cases in which the WDs produce weak, non-ejective novae and experience mass gain. This suggests that provided the accretion efficiency can be achieved by a more massive WD and maintained for long enough, they could potentially serve as progenitors for type Ia supernovae.

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.

A helium nova in the Large Magellanic Cloud – the faint supersoft X-ray source [HP99]159

ABSTRACT We propose a helium nova model for the Large Magellanic Cloud (LMC) supersoft X-ray source (SSS) [HP99]159. This object has long been detected as a faint and persistent SSS for about 30 yr, and recently been interpreted to be a source of steady helium-shell burning, because no hydrogen lines are observed. We find that the object can also be interpreted as in a decaying phase of a helium nova. The helium nova is slowly decaying toward the quiescent phase, during which the observed temperature, luminosity, and SSS lifetime (≳30 yr) are consistent with a massive white dwarf model of ∼1.2 M⊙. If it is the case, this is the second discovery of a helium nova outburst after V445 Pup in our Galaxy, and also the first identified helium nova in the LMC. We also discuss the nature of the companion helium star in relation to Type Ia supernova progenitors.

The Progenitors of Type Ia Supernovae with Asymptotic Giant Branch Donors

Type Ia supernovae (SNe Ia) are among the most energetic events in the universe. They are excellent cosmological distance indicators due to the remarkable homogeneity of their light curves. However, the nature of the progenitors of SNe Ia is still not well understood. In the single-degenerate model, a carbon–oxygen white dwarf (CO WD) could grow its mass by accreting material from an asymptotic giant branch (AGB) star, leading to the formation of SNe Ia when the mass of the WD approaches to the Chandrasekhar-mass limit, known as the AGB donor channel. In this channel, previous studies mainly concentrate on the wind-accretion pathway for the mass-increase of the WDs. In the present work, we employed an integrated mass-transfer prescription for the semidetached WD+AGB systems, and evolved a number of WD+AGB systems for the formation of SNe Ia through the Roche-lobe overflow process or the wind-accretion process. We provided the initial and final parameter spaces of WD+AGB systems for producing SNe Ia. We also obtained the density distribution of circumstellar matter at the moment when the WD mass reaches the Chandrasekhar-mass limit. Moreover, we found that the massive WD+AGB sample AT 2019qyl can be covered by the final parameter space for producing SNe Ia, indicating that AT 2019qyl is a strong progenitor candidate of SNe Ia with AGB donors.

White Dwarf—Red Giant Star Binaries as Type Ia Supernova Progenitors: With and without Magnetic Confinement

Various white-dwarf (WD) binary scenarios have been proposed trying to understand the nature and the diversity of type Ia supernovae (SNe Ia). In this work, we study the evolution of carbon–oxygen WD—red giant (RG) binaries (including the role of magnetic confinement) as possible SN Ia progenitors (the so-called symbiotic progenitor channel). Using the mesa stellar evolution code, we calculate the time dependence of the structure of the RG star, the wind mass loss, the Roche lobe-overflow mass-transfer rate, the polar mass-accretion rate (in the case of magnetic confinement), and the orbital and angular-momentum evolution. We consider cases where the WD is nonmagnetic and cases where the magnetic field is strong enough to force accretion onto the two small polar caps of the WD. Confined accretion onto a small area allows for more efficient hydrogen burning, potentially suppressing nova outbursts. This makes it easier for the WD to grow in mass toward the Chandrasekhar-mass limit and explode as a SN Ia. With magnetic confinement, the initial parameter space of the symbiotic channel for SNe Ia is shifted toward shorter orbital periods and lower donor masses compared to the case without magnetic confinement. Searches for low-mass He WDs or relatively low-mass giants with partially stripped envelopes that survived the supernova explosion and are found in SN remnants will provide crucial insights for our understanding of the contribution of this symbiotic channel.

Hydrodynamical simulations for the common-envelope wind model for Type Ia supernovae

Context. The single-degenerate (SD) model is one of the leading models for the progenitors of Type Ia supernovae (SNe Ia). Recently, a new version of the SD model, the common-envelope wind (CEW) model, has been proposed, which, in principle, has the potential to resolve most of the difficulties encountered by previous SD models. This model is still being developed and a number of open issues remain, such as the details of the mass-loss mechanism from the surface of the common envelope (CE), the main observational properties, and the spiral-in timescale of the binary inside the envelope. Aims. In this article, we aim to address these issues by considering hydrodynamical effects on the CE. Methods. Using the stellar evolution code MESA, we carried out a series of 1D hydrodynamical simulations of an asymptotic giant branch (AGB) star undergoing a common-envelope phase with different envelope masses (0.0007 M⊙–0.06 M⊙). The effect of the immersed binary was mimicked by changing the gravitational constant throughout the envelope and injecting an extra heating source at the location of the binary orbit. Results. We found that the envelopes are always dynamically unstable, leading to regular mass ejection events if the envelope is more massive than the critical value of ∼0.003 M⊙. The κ mechanism can naturally explain this phenomenon. We also found that, due to the low mass of the CE, the estimated frictional luminosity caused by the spiral-in of the immersed binary is much less than the nuclear luminosity, and therefore will not affect the structure of the CE significantly. Conclusions. Our results imply that the CE in the CEW model cannot be very massive. We also present a rough estimate for the spiral-in timescale based on a simplified model. We found that, for reasonable assumptions, the timescale may be longer than a few 105 yr; therefore, the white dwarf (WD) may have enough time to increase its mass toward the Chandrasekhar mass, avoiding a merger with the companion.

Probe for Type Ia Supernova Progenitor in Decihertz Gravitational Wave Astronomy

It is generally believed that Type Ia supernovae are thermonuclear explosions of carbon–oxygen white dwarfs (WDs). However, there is currently no consensus regarding the events leading to the explosion. A binary WD (WD–WD) merger is a possible progenitor of Type Ia supernovae. Space-based gravitational wave (GW) detectors with considerable sensitivity in the decihertz range such as the DECi-hertz Interferometer Gravitational wave Observatory (DECIGO) can observe WD–WD mergers directly. Therefore, access to the decihertz band of GWs would enable multi-messenger observations of Type Ia supernovae to determine their progenitors and explosion mechanism. In this paper, we consider the event rate of WD–WD mergers and the minimum detection range to observe one WD–WD merger per year, using a nearby galaxy catalog and the relation between Ia supernovae and their host galaxies. Furthermore, we calculate DECIGO’s ability to localize WD–WD mergers and to determine the masses of binary mergers. We estimate that a decihertz GW observatory can detect GWs with amplitudes of h ∼ 10−20 [Hz−1/2] at 0.01–0.1 Hz, which is 1000 times higher than the detection limit of DECIGO. Assuming the progenitors of Ia supernovae are merging WD–WD (1 M ⊙ and 0.8 M ⊙), DECIGO is expected to detect 6600 WD–WD mergers within z = 0.08, and identify the host galaxies of such WD–WD mergers within z ∼ 0.065 using GW detections alone.

A robust model for the origin of optical quasi-periodic variability in supersoft X-ray sources

Supersoft X-ray sources (SSSs) are known as possible progenitors of Type Ia supernovae. The quasi-periodic variability has been detected in the optical light curves of SSSs. However, the exact origin of such quasi-periodic observable features remains a mystery. In this paper, we aim to reproduce the observed optical quasi-periodic variability of SSSs by proposing a white dwarf (WD) accretion model with a periodic mass transfer caused by the irradiation of supersoft X-ray onto the companion star. Methods. Assuming that a periodic mass transfer from the companion star to the WD can be caused while the supersoft X-ray irradiates the companion star, we used MESA to simulate the WD accretion process and the subsequent WD evolution by adopting a periodic jagged accretion rate. Comparing our results to the optical light curves of a well-observed SSS RX J0513.9-6951, we find that our models can reproduce the quasi-periodic transition between the optical high and low states of RX J0513.9-6951 because the periodic accretion rate can lead to the WD photosphere expands and contracts periodically in our models. In addition, we find that the transitional periods of the SSSs in our models strongly depend on the mass of the accreting WDs. The more massive the WD mass is, the shorter the transitional period. Based on our results, we suggest that the periodic mass transfer caused by the irradiation of supersoft X-ray onto the companion star may be the origin of the observed optical quasi-periodic variability in SSSs. In addition, our results indicate that the observed optical transition period of a SSS may be useful for the rough estimate of the mass of an accreting WD.

The viability of the optically thick wind model in accreting white dwarfs at high accretion rates

ABSTRACT The single degenerate (SD) model is one of the leading models for the progenitors of Type Ia supernovae (SNe Ia). The optically thick wind (OTW) model is considered to be essential for the SD model. In this article, we aim to constrain the condition for the occurrence of the OTW. Using the stellar evolution code, Modules for Experiments in Stellar Astrophysics, we carried out a series of one-dimensional hydrodynamical simulations with different accretion rates and different white dwarf (WD) masses to simulate the dynamical ejection process on the accreting WDs. We find that, by neglecting interaction with the accreted material, we can get a similar result to the previous works using steady-state method, i.e. the OTW occurs. However, if we consider the interaction between the accreted and the outflowing materials, whether the OTW can occur or not becomes strongly dependent on the accretion rate. For a given WD mass, the higher the accretion rate, the less likely the OTW can occur. In addition, the WD masses can also affect the occurrence of the OTW, i.e. the higher the WD mass, the easier the OTW can occur. As a result, the OTW in novae may occur because the accretion rate is low enough, while in the SD progenitor system of SNe Ia, a high accretion rate is likely to prevent the occurrence of the OTW.

A Roche lobe-filling hot subdwarf and white dwarf binary: possible detection of an ejected common envelope

ABSTRACTBinaries consisting of a hot subdwarf star and an accreting white dwarf (WD) are sources of gravitational wave radiation at low frequencies and possible progenitors of Type Ia supernovae if the WD mass is large enough. Here, we report the discovery of the third binary known of this kind: It consists of a hot subdwarf O (sdO) star and a WD with an orbital period of 3.495 h and an orbital shrinkage of 0.1 s in 6 yr. The sdO star overfills its Roche lobe and likely transfers mass to the WD via an accretion disc. From spectroscopy, we obtain an effective temperature of $T_{\mathrm{eff}}=54\, 240\pm 1840$ K and a surface gravity of log g = 4.841 ± 0.108 for the sdO star. From the light curve analysis, we obtain an sdO mass of MsdO = 0.55 M⊙ and a mass ratio of q = MWD/MsdO = 0.738 ± 0.001. Also, we estimate that the disc has a radius of $\sim\!0.41\ \mathrm{R}_\odot$ and a thickness of $\sim\!0.18\ \mathrm{R}_\odot$. The origin of this binary is probably a common envelope ejection channel, where the progenitor of the sdO star is either a red giant branch star or, more likely, an early asymptotic giant branch star; the sdO star will subsequently evolve into a WD and merge with its WD companion, likely resulting in an R Coronae Borealis (R CrB) star. The outstanding feature in the spectrum of this object is strong Ca H&amp;K lines, which are blueshifted by ∼200 km s−1 and likely originate from the recently ejected common envelope, and we estimated that the remnant common envelope (CE) material in the binary system has a density $\sim\!6\times 10^{-10}\ {\rm g\, cm}^{-3}$.

Y Gem: A White Dwarf Symbiotic Star?

In this work we conduct a thorough investigation of the X-ray and ultraviolet (UV) properties of Y Gem based on six archival XMM-Newton and Chandra observations to explore the nature of the system. The results show that Y Gem has strong (1032–34 erg s−1) X-ray emission, including a hard (with a maximum emission temperature of 8–16 keV) and a soft (with emission temperatures of 0.02–0.2 and 0.2–0.9 keV) component. The integrated UV luminosity of Y Gem reaches ∼1035 erg s−1. We show that the previous asymptotic giant branch-main-sequence (AGB-MS) Roche-lobe overflow (RLOF) scenario is dynamically unstable and can hardly explain the ∼10 keV X-ray emission temperature. We propose Y Gem as a symbiotic star, where a white dwarf (WD) accretes from its AGB companion based on its X-ray and UV properties. We make numerical simulations to examine the evolutionary history of this system. The simulations can produce the observed properties of Y Gem in the wind WRLOF scenario. An ∼0.8M ⊙ WD with a ∼1.0–1.8M ⊙ companion in a ∼2000–32,000 day initial orbit may evolve to a Y Gem-like system. Our finding implies a potential population of symbiotic stars that may have been misclassified as AGB-MS binaries. What is more, their high mass accretion rates may enable mass accumulation to the WD and makes them candidates of Type Ia supernovae progenitors.

A triple star origin for T Pyx and other short-period recurrent novae

ABSTRACT Recurrent novae are star systems in which a massive white dwarf accretes material at such a high rate that it undergoes thermonuclear runaways every 1–100 yr. They are the only class of novae in which the white dwarf can grow in mass, making some of these systems strong Type Ia supernova progenitor candidates. Almost all known recurrent novae are long-period ($P_{\mathrm{orb}} \gtrsim 12\, \mathrm{h}$) binary systems in which the requisite mass supply rate can be provided by an evolved (sub-)giant donor star. However, at least two recurrent novae are short-period ($P_{\mathrm{orb}} \lesssim 3\, \mathrm{h}$) binaries in which mass transfer would normally be driven by gravitational radiation at rates three to four orders of magnitude smaller than required. Here, we show that the prototype of this class – T Pyxidis – has a distant proper motion companion and therefore likely evolved from a hierarchical triple star system. Triple evolution can naturally produce exotic compact binaries as a result of three-body dynamics, either by Kozai–Lidov eccentricity cycles in dynamically stable systems or via mass-loss-induced dynamical instabilities. By numerically evolving triple progenitors with physically reasonable parameters forward in time, we show explicitly that the inner binary can become so eccentric that mass transfer is triggered at periastron, driving the secondary out of thermal equilibrium. We suggest that short-period recurrent novae likely evolved via this extreme state, explaining their departure from standard binary evolution tracks.

A spectroscopic quadruple as a possible progenitor of sub-Chandrasekhar type Ia supernovae

Binaries have received much attention as possible progenitors of Type Ia supernova (SNIa) explosions, but long-term gravitational effects in tight triple or quadruple systems could also play a key role in producing SNIa. Here we report on the properties of a spectroscopic quadruple (SB4) found within a star cluster: the 2+2 hierarchical system HD 74438. Its membership in the open cluster IC 2391 makes it the youngest (43 My) SB4 discovered so far and among the quadruple systems with the shortest outer orbital period. The eccentricity of the 6 y outer period is 0.46 and the two inner orbits, with periods of 20.5 d and 4.4 d, and eccentricities of 0.36 and 0.15, are not coplanar. Using an innovative combination of ground-based high resolution spectroscopy and Gaia/Hipparcos astrometry, we show that this system is undergoing secular interaction that likely pumped the eccentricity of one of the inner orbits higher than expected for the spectral types of its components. We compute the future evolution of HD 74438 and show that this system is an excellent candidate progenitor of sub-Chandrasekhar SNIa through white dwarf (WD) mergers. Taking into account the contribution of this specific type of SNIa better accounts for the chemical evolution of iron-peak elements in the Galaxy than considering only near Chandrasekhar-mass SNIa.

Close detached white dwarf + brown dwarf binaries: further evidence for low values of the common envelope efficiency

ABSTRACT Common envelope evolution is a fundamental ingredient in our understanding of the formation of close binary stars containing compact objects that include the progenitors of type Ia supernovae, short gamma-ray bursts, and most stellar gravitational wave sources. To predict the outcome of common envelope evolution, we still rely to a large degree on a simplified energy conservation equation. Unfortunately, this equation contains a theoretically rather poorly constrained efficiency parameter (αCE) and, even worse, it is unclear if energy sources in addition to orbital energy (such as recombination energy) contribute to the envelope ejection process. In previous works, we reconstructed the evolution of observed populations of post-common envelope binaries (PCEBs) consisting of white dwarfs with main-sequence star companions and found indications that the efficiency is rather small (αCE ≃ 0.2–0.3) and that extra energy sources are only required in very few cases. Here, we used the same reconstruction tool to investigate the evolutionary history of a sample of observed PCEBs with brown dwarf companions. In contrast to previous works, we found that the evolution of observationally well-characterized PCEBs with brown dwarf companions can be understood assuming a low common envelope efficiency (αCE = 0.24–0.41), similar to that required to understand PCEBs with main-sequence star companions, and that contributions from recombination energy are not required. We conclude that the vast majority of PCEBs form from common envelope evolution that can be parametrized with a small efficiency and without taking into account additional energy sources.

Signatures of a Surviving Helium-star Companion in Type Ia Supernovae and Constraints on the Progenitor Companion of SN 2011fe

Abstract Single-degenerate (SD) binary systems composed of a white dwarf and a nondegenerate helium (He)-star companion have been proposed as the potential progenitors of Type Ia supernovae (SNe Ia). The He-star companions are expected to survive the SN Ia explosion in this SD progenitor model. In the present work, we map the surviving He-star companion models computed from our previous three-dimensional hydrodynamical simulations of ejecta–companion interaction into the one-dimensional stellar evolution code Modules for Experiments in Stellar Astrophysics to follow their long-term evolution to make predictions of their post-impact observational properties, which can be helpful in searches for such surviving He-star companions in future observations. By comparing with the very-late-epoch light curve of the best observed SN Ia, SN 2011fe, we find that our surviving He-star companions become significantly more luminous than SN 2011fe about 1000 days after maximum light. This suggests that an He star is very unlikely to be a companion to the progenitor of SN 2011fe.