arXiv subjects

Chengyuan Wu

Publications and source records attributed to Chengyuan Wu.

At least 19 recordsLinked to original sources

arXiv2026

Dynamically driven collapse of a thermally stable accretion disk in a nova-like system

While standard disk instability theory predicts thermal-steady, outburst-free disks in nova-like variables due to their high mass transfer rates, mass transfer variations are prevailingly invoked to explain the occasional flaring/fading phenomena observed in these systems. Here we report the observational evidence for a dynamical collapse of a thermally stable accretion disk, captured serendipitously by TESS during a fading episode of the VY Scl-type nova-like system MASTER OT J072703.91-631952.8, and traced by the emergence of an unusual negative superhump that evolves toward its orbital frequency. Simultaneously, the system underwent an anomalous eruptive event featuring a remarkably symmetric 45-day light-curve profile, indicative of a mild energy-release mechanism fundamentally distinct from documented eruptive events in cataclysmic variables. Notably, the concurrence of the eruption and the disk collapse is difficult to reconcile with the paradigm of mass transfer variations: the eruption implies enhanced mass transfer, whereas the disk collapse indicates a decline. The morphological disk evolution over $\sim 700$ days, characterized by both negative and positive superhumps, indicates a transition from a circular disk to an eccentric disk, followed by a tilted state and ultimately a minimal disk configuration. This evolutionary sequence provides evidence for a previously unrecognized dynamics-driven cycle operating in the thermally stable accretion disk of a VY Scl-type nova-like star.

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arXiv2026

The double white dwarf merger model for the progenitors of SN 2021yfj-like events

Context. Recently, a new class of supernovae with prominent narrow emission features of Si, S and Ar has been reported, i.e. SN 2021yfj-like events (SNe Ien). Their progenitor origin is still unknown. It has been suggested that a massive CO WD may evolve into a Si/S-rich WD when accreting He-rich matter at a high mass-transfer rate. If the He companion subsequently evolves into another more massive WD, the merger of this double WD system can generate Si/S-rich CSM through tidal stripping. Following the SN explosion, the interaction between the SN ejecta and the Si/S-rich CSM could produce the Si, S, and Ar emission lines characteristic of SN 2021yfj-like events. Aims. In this work, we aim to determine the initial parameter space of WD+He star systems that can lead to SN 2021yfj-like events via the double WD merger scenario, and to quantify their theoretical Galactic birthrate and delay-time distributions. Methods. We perform detailed binary evolution simulations of a large number of semidetached WD+He star systems to obtain the parameter space that leads to the formation of Si/S-rich WDs and subsequent double WD mergers. We then use binary population synthesis to calculate the Galactic birthrate and delay-time distribution of such events. Results. For the formation of SN 2021yfj-like events, we found that the initial CO WD and He companion masses must lie in the ranges of 1.0-1.2 M_sun and 2.2-2.5 M_sun, respectively. The derived merger rate for this scenario is ~(2.6-4.4)x10^-5 yr^-1 with delay times longer than 450 Myr, which is about 1% of the observed SN Ia rate. Conclusions. We suggest that the double WD merger scenario involving a Si/S-rich WD originating from a CO WD+He star system, represents a significant and competitive model for SN 2021yfj-like events, underscoring the need for further observations of similar events coupled with relevant theoretical investigations.

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arXiv2026

SN 2022erq: A Superluminous Thermonuclear Supernova with Escalating Preexplosion Mass Loss

We present a photometric and spectroscopic study of the superluminous Type Ia supernova SN 2022erq. Its early spectra, dominated by iron-group elements with weak intermediate-mass features, might indicate highly efficient nuclear burning, broadly similar to that inferred for some overluminous SNe Ia. The rapid emergence and persistence of narrow Balmer emission lines superposed on this iron-rich spectrum provide clear evidence of long-lived interaction with a hydrogen-rich circumstellar medium (CSM), establishing SN 2022erq as a member of the rare Ia-CSM class. SN 2022erq reached a peak bolometric luminosity of about 8 x 10^43 erg/s and exhibited an exceptionally slow post-peak decline, indicating that its light curve is dominated by long-duration ejecta-CSM interaction. By combining H-alpha diagnostics with bolometric light-curve modeling, we reconstruct the pre-explosion mass-loss history of the progenitor. The mass-loss rate escalated by one order of magnitude over the final decades, rising from about 0.04 to about 0.6 solar masses per year. This surge produced a massive, extended CSM shell of about 3 solar masses out to about 3.5 x 10^16 cm. The young stellar environment (about 100 Myr) together with this substantial, extensive CSM points to a progenitor system consisting of a white dwarf and an intermediate-mass companion that underwent increasing mass loss prior to explosion.

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arXiv2026

Surrogate models for type II supernovae: Probing low-energy explosions and interaction-free regimes

To address the computational bottleneck of analyzing type II supernova samples from surveys such as the Legacy Survey of Space and Time, we present two STELLA-based neural-network surrogates: an interaction model for low-energy explosions with possible circumstellar-material (CSM) interaction and a photospheric model for standard interaction-free SNe IIP. Each uses an autoencoder to compress spectral energy distributions and an emulator to map physical parameters to the latent space. Latent-mixup regularization improves latent-space continuity, with ResNet blocks used for the interaction model and 2D CNNs for the photospheric model. Their normalized test-set reconstruction MSEs are approximately 9.1e-5 and 1.0e-4, respectively. Applied to SN 2005cs, the interaction model favors a low-mass progenitor, M_ZAMS = 10.40(+0.04/-0.05) M_sun, and confined dense CSM, providing a scenario consistent with direct imaging and helping resolve the historical mass discrepancy. For SN 2012aw, it recovers M_ZAMS = 11.05(+0.06/-0.06) M_sun, consistent with previous studies. For SN 1999em, the photospheric model gives M_ZAMS = 10.05(+0.07/-0.04) M_sun, broadly consistent with preexplosion imaging limits without explicit CSM modeling. These surrogates reduce full Bayesian inference from days to minutes and enable rapid physical characterization of large supernova samples.

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arXiv2026

Elemental Abundances from Off-center Carbon Burning in Accreting CO White Dwarfs: Implications for SN 2021yfj-like events

SN 2021yfj is a recently discovered interacting supernova that exhibits narrow emission lines of Si, S, and Ar, indicating the presence of circumstellar material (CSM) enriched with these elements surrounding the progenitor prior to the explosion. The origin of SN 2021yfj-like events remains uncertain. Recent work proposed that the SN 2021yfj-like events may stem from the double WD merger scenario, in which the merger of a Si-rich WD with a more massive ONe WD tidally strips about 0.3Msun of Si-rich material to form the CSM. If the merger subsequently triggers a supernova explosion, the interaction between the ejecta and the CSM can reproduce the observed light curve of SN 2021yfj. In this scenario, the progenitor system is a CO WD + He star binary, in which the CO WD accretes He-rich material from the He star. The accumulated material can trigger off-center carbon burning, potentially leading to the formation of a Si-rich WD. However, it remains unclear whether such off-center carbon burning can produce Si, S, and Ar in amounts comparable to those inferred for the CSM of SN 2021yfj. In this work, we simulate the evolution of a CO WD accreting He-rich material using time-dependent mass-accretion rates. Our results show that off-center carbon burning in the accreting CO WD can produce significant amounts of Si and S. We further found that the resulting elemental abundances are strongly affected by the initial carbon abundance of the WD. Based on our results, we suggest that the double WD merger scenario may provide a viable progenitor channel for SN 2021yfj-like events.

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arXiv2026

Can dwarf novae produce type Ia supernovae?

Accreting white dwarfs (WDs) are considered one of the most promising progenitor candidates for Type Ia supernovae (SNe Ia). Dwarf novae (DNe), a subclass of cataclysmic variables (CVs), consist of a carbon--oxygen (CO) WD accretor and a low-mass donor star, which may be either a main-sequence (MS) star or a slightly evolved subgiant. Previous studies have suggested that, under the thermal--viscous disk instability mechanism, the time-averaged accretion rate in long-period DNe may approach the regime of stable hydrogen burning, potentially allowing the WD to grow toward the Chandrasekhar mass, (M_{\rm Ch}). However, whether such periodic accretion can sustain stable hydrogen burning and lead to WD mass growth remains uncertain. In this work, we explore whether high accretion rates on short periodic timescales can maintain stable hydrogen burning on the WD surface and drive the WD toward (M_{\rm Ch}). Using Modules for Experiments in Stellar Astrophysics (MESA), we investigate the mass-retention efficiency of WDs undergoing intermittent DN-like accretion and examine its dependence on duty cycle, accretion rate, and initial WD properties. We find that periodic accretion fails to maintain stable hydrogen burning. During quiescent phases, the WD cools and becomes increasingly degenerate, leading to nova outbursts with progressively decreasing mass-retention efficiency and ultimately preventing further WD mass growth. We therefore suggest that DNe are unlikely to be progenitors of SNe Ia.

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arXiv2026

Spectral Dataset of Stripped-Envelope Supernovae from the Tsinghua Supernova Group

The extent of envelope stripping in the progenitor stars is directly reflected in the diversity of spectral features observed in stripped-envelope supernovae (SESNe). Through extensive spectral observation and analysis, we aim to clarify the statistical differences between the subclasses of SESNe. The Tsinghua Supernova group obtained 249 optical spectra of 62 SESNe during the years from 2010 to 2020, covering phases from $-$16 to over 190 days relative to maximum light. Most spectra were obtained during the photospheric phases after the supernova explosion. For each spectrum, the pseudo-equivalent widths (pEWs) and blueshift velocities of principal lines were measured. We further investigated the common spectral features by analysing their velocity and strength correlations across all subtypes. We identify the feature near 6200~Å in SNe Ib as H$\mathrmα$ through comparison with SNe IIb and Ic, which resolves inconsistent literature interpretations. Our finding reveals prevalent residual hydrogen in SNe Ib, further supporting a continuous stripping sequence from SNe IIb to Ib. We observe a trend in increasing velocity among different subtypes of stripped-envelope SNe, with SNe IIb exhibiting the lowest line velocities, followed by Ib, Ic, and Ic-BL. Typically, the O~I lines in SNe Ic/Ic-BL are stronger than those seen in SNe IIb/Ib. In nebular phases, the [Ca II] emission dominates over [O I] in SNe IIb/Ib while [O I] is stronger in SNe Ic, including the He-rich SN 2016coi. This spectral dichotomy implies that progenitors of SNe Ic (BL) have more massive CO cores and hence higher initial masses.

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arXiv2026

Supernovae interacting with Si and S-rich circumstellar matter from double white dwarf mergers

We present that supernovae interacting with a dense Si and S-rich circumstellar matter like SN 2021yfj can originate from mergers of two white dwarfs. A C+O white dwarf accreting He from its non-degenerate He companion star can initiate a C burning frame at its surface propagating inward under certain conditions. Such a burning frame synthesizes intermediate mass elements such as Si and S, forming a hybrid WD with an outer Si+S-rich layer. After the He star companion becomes a white dwarf, the two white dwarfs can eventually merge. During the merger, the outer layers of the hybrid white dwarf can be tidally stripped, forming a dense Si and S-rich circumstellar matter. If a thermonuclear explosion is triggered in the merging white dwarfs, an explosion within a dense Si and S-rich circumstellar matter can be realized, resulting in SN 2021yfj-like events. We argue that the properties of SN 2021yfj can be reproduced by a dense Si and S-rich circumstellar matter having ~ 0.3 Msun within which an explosion having kinetic energy of ~ 4e50 erg and ejecta mass of ~ 0.3 Msun occurred. These properties are consistent with the double white dwarf merger scenario. This scenario can naturally explain the existence of He observed in SN 2021yfj. Because white dwarf mergers can also lead to the formation of He and C+O dense circumstellar matter, some Type Ibn and Icn supernovae may also originate from a similar evolutionary path.

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arXiv2025

Evolution Models of CO WD -- AGB Star Merger Remnants

Common envelope evolution is a critical but still poorly understood phase in binary evolution. It plays a key role in forming close binaries such as hot subdwarfs, double white dwarfs, X-ray binaries, and double neutron stars. However, its outcomes remain highly uncertain. Depending on the efficiency of envelope ejection, a system may either survive as a close binary or undergo a complete merger. In this work, we investigate the post merger evolution of systems where a CO WD mergers with the core of an AGB star. A grid of merger remnant models with various core and envelope masses is constructed. At the onset of evolution, the CO core contracts and undergoes off-center carbon ignition, producing an inwardly propagating carbon flame. For remnants with relatively low mass of CO core, the flame phase is followed by core contraction and subsequent H-shell burning. For more massive CO cores, the carbon flame reaches the center and is soon followed by off-center neon burning, which is expected to eventually lead to core-collapse supernovae. The merger remnants occupy nearly the same region on HR diagram as ordinary AGB or super-AGB stars, exhibiting similar surface properties. Although their surface abundance may differ slightly from those of normal AGB stars depending on the initial core and envelope masses, these differences are strongly reduced once mass-loss is taken into account. We suggest that some giant-like stars, including candidates for Thorne-Zytkow objects (e.g., HV 2112), might alternatively be explained as AGB-WD merger remnants.

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arXiv2025

Helium-burning blue large-amplitude pulsators: A Population Study with BPASS

Blue Large-Amplitude Pulsators (BLAPs) are a class of radially pulsating stars with effective temperatures ranging from 20,000 to 35,000 K and pulsation periods between 7 and 75 minutes. This study utilizes the Binary Population and Spectral Synthesis (BPASS) code to investigate helium-burning stars as a formation channel for BLAPs in the Milky Way. The progenitor stars have initial masses of 3-6 $M_{\odot}$, resulting in BLAPs with final masses of 0.5-1.2 $M_{\odot}$. Based on a constant star formation rate of 3 $ M_{\odot}\text{yr}^{-1}$ and solar metallicity (Z = 0.020), population synthesis predicts approximately 14,351 helium-burning BLAPs in the Milky Way: 12,799 with Main Sequence (MS) companions and 1,551 with evolved/compact-object companions. Helium-burning BLAPs show prolonged lifetimes in the pulsation region and a narrow stellar age range for entering this regime (log(t/yr) = 8.0-8.6), unlike pre-white dwarf models. BLAPs with MS companions typically form via Roche lobe overflow, leading to longer orbital periods ($\sim$100 days). Those with evolved/compact-object companions form through common envelope evolution, resulting in shorter periods. While Galactic extinction makes most BLAPs faint (apparent magnitudes $>$ 25), future surveys like WFST and VRO LSST are expected to detect approximately 500-900. This research establishes helium-burning stars as a significant BLAP contributor and offers testable predictions regarding their binary properties and Galactic distribution.

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arXiv2025

A post-common-envelope binary with double-peaked Balmer emission lines from TMTS

The dynamical method provides an efficient way to discover post-common-envelope binaries (PCEB) with faint white dwarfs (WDs), thanks to the development of time-domain survey projects. We perform a comprehensive analysis of the PCEB system TMTS J15530469+4457458 (J1553), discovered by the Tsinghua University-Ma Huateng Telescopes for Survey, to explore its physical origin and evolutionary fate. This system is characterized by double-peaked Balmer emission lines, and a cross-correlation function is applied to derive its radial velocity (RV) from a series of phase-resolved Keck spectra. Analyses with the cross-correlation function suggest that this system is a single-lined spectroscopic binary and only one star is optically visible. Further analysis through Doppler tomography indicates that J1553 is a detached binary without an accretion disk. Under such a configuration, the simultaneous light-curve and RV fitting reveal that this system contains an unseen WD with mass $M_{\rm A}=0.56\pm 0.09\, M_{\odot}$, and an M4 dwarf with mass $M_{\rm B}=0.37\pm 0.02\,M_{\odot}$ and radius $R_{\rm B}=0.403^{+0.014}_{-0.015}\,R_{\odot}$. The extra prominent Balmer emission lines seen in the spectra can trace the motion of the WD, which are likely formed near the WD surface as a result of wind accretion. According to the MESA simulation, J1553 could have evolved from a binary consisting of a 2.0-4.0 ${M}_{\odot}$ zero-age-main-sequence star and an M dwarf with an initial orbital period $P_i\approx 201-476$ d, and the system has undergone a common-envelope (CE) phase. After about $3.3\times10^6$ yr, J1553 should evolve into a cataclysmic variable, with a transient state as a supersoft X-ray source at the beginning. J1553 is an excellent system for studying wind accretion, CE ejection physics, and binary evolution theory.

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arXiv2025

Supernovae at Distances < 40 Mpc: II. Supernova Rate in the Local Universe

Context.This is the second paper of a series aiming to determine the birth rates of supernovae in the local Universe. Aims. In this paper, we aim to estimate the SN rates in the local universe and fit the delay-time distribution of SNe Ia to put constraints on their progenitor scenarios. Methods.We performed a Monte-Carlo simulation to estimate the volumetric rates with the nearby SN sample introduced in Paper I of the series. The rate evolution of core-collapse SNe well traces the evolution of cosmic star formation history; while that of SNe Ia involves the convolution of cosmic star-formation history and a two-component delay-time distribution including a power law and a Gaussian component. Results.The volumetric rates of type Ia, Ibc and II SNe are derived as $0.325\pm0.040^{+0.016}_{-0.010}$, $0.160\pm0.028^{+0.044}_{-0.014}$, and $0.528\pm0.051^{+0.162}_{-0.013}$ (in unit of $10^{-4} yr^{-1} Mpc^{-3} h^3_{70}$), respectively. The rate of CCSNe is consistent with previous estimates. The newly derived local SN Ia rate is larger than existing results given at redshifts 0.01 < z < 0.1, favoring an increased rate from the universe at z ~ 0.1 to the local universe. A two-component model can well fit the rate variation, with the power law component accounting for the rate evolution at larger redshifts and the Gaussian component with a delay time of 12.63$\pm$0.38 Gyr accounting for the local rate evolution. This delayed component with such a longer delay time suggests that the progenitors of these SNe Ia were formed at around 1 Gyr after the birth of the universe, which could only be explained by a double-degenerate progenitor scenario. This is evidenced by the comparison with the PTF sample of SNe Ia at z = 0.073, which reveals that the increase in SN Ia rate at z < 0.01 is primarily due to the SNe Ia of massive E and S0 galaxies with old stellar populations.

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arXiv2025

Binary Evolution Pathways to Blue Large-Amplitude Pulsators: Insights from HD 133729

Blue Large-Amplitude Pulsators (BLAPs) represent a recently identified class of pulsating stars distinguished by their short pulsation periods ($2 - 60$ minutes) and asymmetric light curves. This study investigated the evolutionary channel of HD 133729 which is the first confirmed BLAP in a binary system. Using the binary evolution code MESA, we explored various mass ratios and initial orbital periods. Our simulations suggest that a system with a mass ratio $q = 0.30$ undergoing non-conservative mass transfer ($β=0.15$) can reproduce the observed characteristics through the pre-white dwarf Roche lobe overflow channel. Meanwhile, we predict that there are significant helium and nitrogen enhancements on the surface of the main sequence (MS) star. The system will eventually undergo the common envelope phase, leading to a stellar merger. HD 133729 is a unique case as a benchmark, providing crucial insights into the formation mechanism and evolutionary fate of BLAPs with MS companions. This work constrains the elemental abundances of the MS star and has helped our understanding of non-conservative mass transfer in binary evolution.

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arXiv2024

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 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 anti-correlated with the accretion rate. As the ONe WD nearly approaches the Chandrasekhar mass limit (Mch) through accretion, it is likely to undergo accretion-induced collapse (AIC), resulting in the formation of the neutron star (NS).

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arXiv2024

Light curves of the explosion of ONe WD+CO WD merger remnant and type Icn supernovae

Type Icn supernovae (SNe Icn) are a newly detected rare subtype of interacting stripped-envelope supernovae which show narrow P-Cygni lines of highly ionized carbon, oxygen, and neon in their early spectra due to the interactions of the SNe ejecta with dense hydrogen- and helium-deficient circumstellar material (CSM). It has been suggested that SNe Icn may have multiple progenitor channels, such as the explosion of carbon-rich Wolf-Rayet stars, or the explosion of stripped-envelope SNe which undergo binary interactions. Among the SNe Icn, SN 2019jc shows unique properties, and previous work inferred that it may stem from the ultra-stripped supernova, but other possibilities still exist. In this work, we aim to simulate the light curves from the explosions of oxygen-neon and carbon-oxygen double white dwarf (WD) merger remnants, and to further investigate whether the corresponding explosions can appear as some particular SNe Icn. We generate the light curves from the explosive remnants and analyse the influence of different parameters on the light curves, such as the ejecta mass, explosion energy, mass of Ni56 and CSM properties. Comparing our results with some SNe Icn, we found that the light curves from the explosions of double WD merger remnants can explain the observable properties of SN 2019jc, which inferred that this special SN Icn may have a different progenitor. Our results indicated that double WD merger may be an alternative model in producing at least one of the SNe Icn.

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arXiv2024

A seven-Earth-radius helium-burning star inside a 20.5-min detached binary

Binary evolution theory predicts that the second common envelope (CE) ejection can produce low-mass (0.32-0.36 Msun) subdwarf B (sdB) stars inside ultrashort-orbital-period binary systems, as their helium cores are ignited under nondegenerate conditions. With the orbital decay driven by gravitational-wave (GW) radiation, the minimum orbital periods of detached sdB binaries could be as short as ~20 minutes. However, only four sdB binaries with orbital periods below an hour have been reported so far, while none of them has an orbital period approaching the above theoretical limit. Here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, TMTS J052610.43+593445.1, in which the visible star is being tidally deformed by an invisible carbon-oxygen white dwarf (WD) companion. The visible component is inferred to be an sdB star with a mass of ~0.33 Msun, approaching that of helium-ignition limit, although a He-core WD cannot be completely ruled out. In particular, the radius of this low-mass sdB star is only 0.066 Rsun, about seven Earth radii, possibly representing the most compact nondegenerate star ever known. Such a system provides a key clue to map the binary evolution scheme from the second CE ejection to the formation of AM CVn stars having a helium-star donor, and it will also serve as a crucial verification binary of space-borne GW detectors in the future.

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arXiv2024

A spectral data release for 104 Type II Supernovae from the Tsinghua Supernova Group

We present 206 unpublished optical spectra of 104 type II supernovae obtained by the Xinglong 2.16m telescope and Lijiang 2.4m telescope during the period from 2011 to 2018, spanning the phases from about 1 to 200 days after the SN explosion. The spectral line identifications, evolution of line velocities and pseudo equivalent widths, as well as correlations between some important spectral parameters are presented. Our sample displays a large range in expansion velocities. For instance, the Fe~{\sc ii} $5169$ velocities measured from spectra at $t\sim 50$ days after the explosion vary from ${\rm 2000\ km\ s^{-1}}$ to ${\rm 5500\ km\ s^{-1}}$, with an average value of ${\rm 3872 \pm 949\ km\ s^{-1}}$. Power-law functions can be used to fit the velocity evolution, with the power-law exponent quantifying the velocity decline rate. We found an anticorrelation existing between H$β$ velocity at mid-plateau phase and its velocity decay exponent, SNe II with higher velocities tending to have smaller velocity decay rate. Moreover, we noticed that the velocity decay rate inferred from the Balmer lines (i.e., H$α$ and H$β$) have moderate correlations with the ratio of absorption to emission for H$α$ (a/e). In our sample, two objects show possibly flash-ionized features at early phases. Besides, we noticed that multiple high-velocity components may exist on the blue side of hydrogen lines of SN 2013ab, possibly suggesting that these features arise from complex line forming region. All our spectra can be found in WISeREP and Zenodo.

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arXiv2023

Evolution of double oxygen-neon white dwarf merger remnant

Double white dwarf (WD) merger process and their post-merger evolution are important in many fields of astronomy, such as supernovae, gamma-ray bursts, gravitational waves, etc. The evolutionary outcomes of double ultra-massive WD merger remnants are still a subject of debate, though the general consensus is that the merger remnant will collapse to form a neutron star. In this work, we investigate the evolution of a 2.20Msun merger remnant stemmed from the coalescence of double 1.10Msun ONe WDs. We find that the remnant ignites off-centre neon burning at the position near the surface of primary WD soon after the merger, resulting in the stable inwardly propagating oxygen/neon (O/Ne) flame. The final outcomes of the merger remnant are sensitive to the effect of convective boundary mixing. If the mixing cannot stall the O/Ne flame, the flame will reach the centre within 20 years, leading to the formation of super Chandrasekhar mass silicon core, and its final fate probably be neutron star (NS) through iron-core-collapse supernova. In contrast, if the convective mixing is effective enough to prevent the O/Ne flame from reaching the centre, the merger remnant will undergo electron capture supernova to form an ONeFe WD. Meanwhile, we find that the wind mass loss process may hardly alter the final fate of the remnant due to its fast evolution. Our results imply that the coalescence of double ONe WDs can form short lived giant like object, but the final outcomes (NS or ONeFe WD) are influenced by the uncertain convective mixing in O/Ne flame.

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