arXiv subjects

Chuan-Jui Li

Publications and source records attributed to Chuan-Jui Li.

17 recordsLinked to original sources

arXiv2026

A MUSE View of the Optical Torus within the Supernova Remnant 1E 0102.2-7219

We present new MUSE Narrow Field Mode with Adaptive Optics observations of the optical torus surrounding a Central Compact Object (CCO) candidate within the oxygen-rich supernova remnant 1E 0102.2-7219 (E0102) located in the Small Magellanic Cloud. These data provide nearly an order-of-magnitude improvement in spatial resolution over previous MUSE Wide Field Mode observations. The improved spatial resolution resolved the previously identified torus into a cavity-like structure with a sharply defined inner edge and diffuse, outer filamentary substructure. The emission shows continuous velocity connectivity, broad intrinsic line widths, and co-spatial contributions from neutral and partially ionized species, including O I, Ne I, [O I], [O II], and [O III]. Spatially resolved line-ratio maps indicate that the emission arises from a multiphase, non-equilibrium medium rather than a single homogeneous component. Comparison with photoionization and shock models shows that no single-component model within the explored parameter space can simultaneously reproduce both the strong neutral and high-ionization diagnostics, indicating that multiple physical conditions must coexist. We favor an interpretation in which shocks propagating through density inhomogeneities in the ejecta shape the observed morphology and excitation, while also considering alternative mechanisms linked to the central source, binary evolution, or interaction with an embedded object within the remnant.

astro-ph.HE↗

arXiv2026

Decadal pre-explosion activity and circumstellar interaction in a supernova

When a massive star explodes as a supernova, crucial information about its immediate environment is lost within hours. Here we report rapid optical observations from Lulin Observatory of the broad-lined Type Ic supernova SN 2026gzf, beginning 1.25 hours after Einstein Probe detected the X-ray transient EP260321a. Our data led to the discovery of the optical counterpart and showed a luminous blue first-day excess that cannot be reproduced by standard radioactive models. We find that interaction between the ejecta and $\approx 0.02$ M$_{\odot}$ of circumstellar material accounts for the early excess. Archival Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) images show variability at the explosion site over the previous $\sim 12$ years, with the source brightening by a factor of $\sim 1.5$ in the final $\sim 3$ years before explosion, providing rare evidence for pre-explosion activity in a stripped-envelope progenitor system. The precursor brightening suggests enhanced eruptive mass loss during late-stage oxygen burning before core collapse, while an additional silicon-burning episode shortly before explosion may have created the compact nearby material responsible for the X-ray shock-breakout signal. SN 2026gzf therefore offers the first view of how a stripped progenitor modifies its immediate environment shortly before death, linking long-term precursor variability, circumstellar interaction and the explosion itself.

astro-ph.HE↗

arXiv2025

Intertwined birth and death: a Herbig-Haro outflow resolves the distance to Vela Junior

The distance to the Vela Junior supernova remnant (RX J0852.0-4622 or G266.2-1.2) has long remained uncertain, limiting our understanding of its physical properties. Using VLT/MUSE integral field spectroscopy, we uncover chemical and kinematic connections between the nebula surrounding its Central Compact Object (CXOU J085201.4-461753) and the nearby Herbig-Haro outflow of Ve 7-27 (Wray 16-30), indicating a shared nitrogen-rich, Fe-peak-enhanced environment. This link ties stellar birth and death, with the young star Ve 7-27 embedded in material expelled by Vela Junior's massive progenitor, and the remnant's blast wave is expanding through the same medium. Adopting the Gaia-based distance to Ve 7-27, we revise Vela Junior's distance to $1.41\pm0.14$ kpc. At this distance, the remnant's physical radius is $23.3\pm2.3$ pc, and X-ray proper motions of the northwestern rim correspond to shock speeds of $(2.8\pm0.7)\times10^3$ to $(5.6\pm1.5)\times10^3$ km s$^{-1}$. These imply an age of $\sim$1.6-3.3 kyr and a very low ambient density, indicating that Vela Junior is expanding within a highly rarefied wind-blown cavity carved by a massive progenitor -- consistent with the non-detection of strong thermal X-ray emission. This distance update also resolves long-standing inconsistencies, with major implications for its energy budget, particle acceleration efficiency, and compact object evolution.

astro-ph.HE↗

arXiv2025

The Altered Chaplygin Model as a Model for Dark Energy

We present a scalar-field formulation of the generalized Chaplygin gas (GCG) and modified Chaplygin gas (MCG) models, in which the cosmic fluid dynamics are reproduced by canonical Lagrangians with analytically derived energy density $ρ(ϕ)$, pressure $p(ϕ)$, and scalar potential $V(ϕ)$. This framework provides a unified description of dark matter and dark energy, transitioning naturally from a matter-dominated phase at early times to a negative-pressure dark-energy phase at late times. In this scalar-field formulation, the GCG and MCG models are naturally applicable to both theoretical analyses and numerical simulations. Extending this approach, we develop a systematic method to obtain a class of integrable scalar-field cosmological models. In this study, we use this method to construct a new scalar-field altered Chaplygin gas (ACG) model. To investigate the viability of Chaplygin-type models, we perform a likelihood analysis using the Pantheon+ Type Ia supernova compilation together with Cepheid-calibrated distances. We examine four models, $Λ$CDM, GCG, MCG, and ACG, obtaining posterior constraints on the Hubble constant $H_0$, the present-day effective equation of state $ω_0$, the transition redshift $z^\star$, and the cosmic age $t_0$. With the Cepheid calibration fixing the absolute distance scale, the inferred $H_{0}$ remains nearly model-independent. The Chaplygin-type models predict an earlier onset of cosmic acceleration than $Λ$CDM and give a broader range for the inferred age of the Universe, reflecting their greater flexibility in late-time expansion histories. Among them, the ACG model provides tighter parameter constraints, while the GCG and MCG models produce broader posteriors due to parameter degeneracies.

astro-ph.CO↗

arXiv2024

The Dark Energy Camera Magellanic Clouds Emission-Line Survey

We have used the Dark Energy Camera (DECam) on the CTIO Blanco 4-m telescope to perform a new emission-line survey of the Large Magellanic Cloud (LMC) using narrow-band H-alpha and [SII] filters in addition to a continuum band for use in creating pure emission-line images. We refer to this new survey as DeMCELS, to distinguish it from the earlier Magellanic Cloud Emission Line Survey (MCELS) that has been in service for nearly 25 years. DeMCELS covers $\sim 54$ degrees$^{2}$, encompassing most of the bright optical disk of the LMC. With DECam's pixel size of only 0.27", our DeMCELS survey provides a seeing-limited improvement of 3-5 times over MCELS and is comparable in depth, with surface brightness limits of 3.3E-17 erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ in H-alpha and 2.9E-17 erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ in H-alpha and [SII], respectively. DeMCELS provides detailed morphological information on nebulae of all scales, from the largest supershells to individual [HII] regions and supernova remnants, to bubbles of emission surrounding individual stars, and even to faint structures in the diffuse ionized gas of the LMC. Many complex regions of emission show significant variations in the ratio of [SII] to H-alpha, a sign of the mixture of shocks from stellar winds and/or supernovae with photoionization by embedded hot, young stars. We present the details of the observing strategy and data processing for this survey, and show selected results in comparison with previous data. A companion project for the Small Magellanic Cloud is in progress and will be reported separately. We are making these new data available to the community at large via the NOIRLab's Data Lab site.

astro-ph.GA↗

arXiv2024

Stellar Population near NGC 2021: Procession of Star Formation in the South Rim of Supergiant Shell LMC 4

Supergiant shells (SGSs) are the largest interstellar structures where heated and enriched gas flows into the host galaxy's halo. The SGSs in the Large Magellanic Cloud (LMC) are so close that their stars can be resolved with ground-based telescopes to allow studies of star formation history. Aiming to study the star formation history and energy budget of LMC 4, we have conducted a pilot study of the cluster NGC 2021 and the OB associations in its vicinity near the south rim of LMC 4. We use the Magellanic Cloud Photometric Survey data of the LMC to establish a methodology to examine the stellar population and assess the massive star formation history. We find a radial procession of massive star formation from the northwest part of the OB association LH79 through NGC 2021 to the OB association LH78 in the south. Using the stellar content of NGC 2021 and the assumption of Salpeter's initial mass function, we estimate that $\sim$4 supernovae have occurred in NGC 2021, injecting at least $4\times10^{51}$ ergs of kinetic energy into the interior of LMC 4.

astro-ph.GA↗

arXiv2023

MUSE observations of the optical nebula surrounding the central compact object in the Vela Junior Supernova Remnant

Central Compact Objects (CCOs), neutron stars found near the centre of some Supernova Remnants (SNRs), have been almost exclusively studied in X-rays and are thought to lack the wind nebulae typically seen around young, rotation-powered pulsars. We present the first, spatially-resolved, morphological and spectroscopic study of the optical nebula observed at the location of CXOU J085201.4-461753, the CCO in the heart of the Vela Junior SNR. It is currently the only Galactic CCO with a spatially coincident nebula detected at optical wavelengths, whose exact nature remains uncertain. New MUSE integral field spectroscopy data confirm that the nebula, shaped like a smooth blob extending 8" in diameter, is dominated by [N II]$λλ$6548,6583 emission. The data reveals a distinct and previously unobserved morphology of the H$α$ emission, exhibiting an arc-like shape reminiscent of a bow shock nebula. We observe a significantly strong [N II] emission relative to H$α$, with the [N II]$λλ$6548,6583 up to 34 times the intensity of the H$α$ emission within the optical nebula environment. Notably, the [N II] and H$α$ structures are not spatially coincident, with the [N II] nebula concentrated to the south of the CCO and delimited by the H$α$ arc-like structure. We detect additional emission in [N I], He I, [S II], [Ar III], [Fe II], and [S III]. We discuss our findings in the light of a photoionization or Wolf-Rayet nebula, pointing to a very massive progenitor and further suggesting that very massive stars do not necessarily make black holes.

astro-ph.HE↗

arXiv2023

New Insights on 30 Dor B Revealed by High-Quality Multi-wavelength Observations

The supernova remnant (SNR) 30 Dor B is associated with the \ion{H}{2} region ionized by the OB association LH99. The complex interstellar environment has made it difficult to study the physical structure of this SNR. We have used Hubble Space Telescope H$α$ images to identify SNR shocks and deep Chandra X-ray observations to detect faint diffuse emission. We find that 30 Dor B hosts three zones with very different X-ray surface brightnesses and nebular kinematics that are characteristic of SNRs in different interstellar environments and/or evolutionary stages. The ASKAP 888 MHz map of 30 Dor B shows counterparts to all X-ray emission features except the faint halo. The ASKAP 888 MHz and 1420 MHz observations are used to produce a spectral index map, but its interpretation is complicated by the background thermal emission and the pulsar PSR J0537$-$6910's flat spectral index. The stellar population in the vicinity of 30 Dor B indicates a continuous star formation in the past 8--10 Myr. The observed very massive stars in LH99 cannot be coeval with the progenitor of 30 Dor B's pulsar. Adopting the pulsar's spin-down timescale, 5000 yr, as the age of the SNR, the X-ray shell would be expanding at $\sim$4000 km\,s$^{-1}$ and the post-shock temperature would be 1--2 orders of magnitude higher than that indicated by the X-ray spectra. Thus, the bright central region of 30 Dor B and the X-ray shell requires two separate SN events, and the faint diffuse X-ray halo perhaps other older SN events.

astro-ph.GA↗

arXiv2021

The Shellless SNR B0532-67.5 in the Large Magellanic Cloud

The supernova remnant (SNR) B0532$-$67.5 in the Large Magellanic Cloud (LMC) was first diagnosed by its nonthermal radio emission and its SNR nature was confirmed by diffuse X-ray emission; however, no optical SNR shell is detected. The OB association LH75, or NGC 2011, is projected within the boundary of this SNR. We have analyzed the massive star population in and around SNR B0532$-$67.5: using optical photometric data to construct color-magnitude diagrams (CMDs), using stellar evolutionary tracks to estimate stellar masses, and using isochrones to assess the stellar ages. From these analyses, we find a 20-25 Myr population in LH75 and a younger population less than 10 Myr old to the southwest of LH75. The center of SNR B0532$-$67.5 is located closer to the core of LH75 than the massive stars to its southwest. We conclude that the SN progenitor was probably a member of LH75 with an initial mass $\sim$15 $M_\odot$. The SN exploded in an H I cavity excavated by the energy feedback of LH75. The low density of the ambient medium prohibits the formation of a visible nebular shell. Despite the low density in the ambient medium, physical properties of the hot gas within the SNR interior do not differ from SNRs with a visible shell by more than a factor of 2-3. The large-scale H I map shows that SNR B0532$-$67.5 is projected in a cavity that appears to be connected with the much larger cavity of the supergiant shell LMC-4.

astro-ph.GA↗

arXiv2021

Search for Surviving Companions of Progenitors of Young LMC Type Ia Supernova Remnants

We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants (SNRs) in the Large Magellanic Cloud: 0519-69.0, 0505-67.9 (DEM L71), and 0548-70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color-magnitude diagrams (CMDs), and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main sequence or helium star companions. No obvious candidates of surviving companion are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi-Unit Spectroscopic Explorer (MUSE) observations of 0519-69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519-69.0 and a star in DEM L71 moving at radial velocities of 182 $\pm$ 0 km s$^{-1}$ and 213 $\pm$ 0 km s$^{-1}$, more than 2.5$σ$ from the mean radial velocity of the underlying stellar population, 264 km s$^{-1}$ and 270 km s$^{-1}$, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the SN progenitors.

astro-ph.SR↗

arXiv2021

Searching for Surviving Companion in the Young SMC Supernova Remnant 1E 0102.2-7219

1E 0102.2--7219 (hereafter E0102) is a young supernova remnant (SNR) in the Small Magellanic Cloud (SMC). It contains oxygen-rich SN ejecta, a possible neutron star (NS), and a small amount of fast-moving H-rich ejecta material. These properties are also seen in Cas A, it has thus been suggested that E0102 is also a Type IIb SNR, whose SN progenitor's hydrogen envelope was stripped off possibly via interactions with a companion star. To search for a surviving companion of E0102's SN progenitor, we have used archival Hubble Space Telescope (HST) continuum images to make photometric measurements of stars projected in the SNR to construct color-magnitude diagrams and compare the stars with those expected from surviving companions of Type IIb SNe. We have also used the Multi-Unit Spectroscopic Explorer observations taken with the Very Large Telescope to perform spectroscopic analyses of stars and search for peculiar radial velocities as diagnostics of surviving companions. We further use the HST and Gaia data to inspect proper motions of stars for complementary kinetic studies. No plausible companion candidates are found if the SN explosion site was near the NS, while the B3 V star 34a may be a plausible companion candidate if the SN explosion site is near the SN ejecta's expansion center. If the NS is real and associated with E0102, it needs a ~1000 km/s runaway velocity, which has been observed in other SNRs and can be acquired from an asymmetric SN explosion or a kick by the SN explosion of a massive companion.

astro-ph.SR↗

arXiv2021

Forbidden Line Emission from Type Ia Supernova Remnants Containing Balmer-Dominated Shells

Balmer-dominated shells in supernova remnants (SNRs) are produced by collisionless shocks advancing into a partially neutral medium, and are most frequently associated with Type Ia supernovae. We have analyzed Hubble Space Telescope (HST) images and VLT/MUSE or AAT/WiFeS observations of five Type Ia SNRs containing Balmer-dominated shells in the LMC: 0509-67.5, 0519-69.0, N103B, DEM L71, and 0548-70.4. Contrary to expectations, we find bright forbidden line emission from small dense knots embedded in four of these SNRs. The electron densities in some knots are higher than 10$^4$ cm$^{-3}$. The size and density of these knots are not characteristic for interstellar medium (ISM) -- they most likely originate from a circumstellar medium (CSM) ejected by the SN progenitor. Physical property variations of dense knots in the SNRs appear to reflect an evolutionary effect. The recombination timescales for high densities are short, and HST images of N103B taken 3.5 yr apart already show brightness changes in some knots. VLT/MUSE observations detect [Fe XIV] line emission from reverse shocks into SN ejecta as well as forward shocks into the dense knots. Faint [O III] line emission is also detected from the Balmer shell in 0519-69.0, N103B, and DEM L71. We exclude the postshock origin because the [O III] line is narrow. For the preshock origin, we considered three possibilities: photoionization precursor, cosmic ray precursor, and neutral precursor. We conclude that the [O III] emission arises from oxygen that has been photoionized by [He II] $λ$304 photons and is then collisionally excited in a shock precursor heated mainly by cosmic rays.

astro-ph.HE↗

arXiv2021

Discovery of Double-Ring Structure in the Supernova Remnant N103B: Evidence for Bipolar Winds from a Type Ia Supernova Progenitor

The geometric structure of supernova remnants (SNR) provides a clue to unveiling the pre-explosion evolution of their progenitors. Here we present an X-ray study of N103B (0509-68.7), a Type Ia SNR in the Large Magellanic Cloud, that is known to be interacting with dense circumstellar matter (CSM). Applying our novel method for feature extraction to deep Chandra observations, we have successfully resolved the CSM, Fe-rich ejecta, and intermediate-mass element (IME) ejecta components, and revealed each of their spatial distribution. Remarkably, the IME ejecta component exhibits a double-ring structure, implying that the SNR expands into an hourglass-shape cavity and thus forms bipolar bubbles of the ejecta. This interpretation is supported by more quantitative spectroscopy that reveals a clear bimodality in the distribution of the ionization state of the IME ejecta. These observational results can be naturally explained if the progenitor binary system had formed a dense CSM torus on the orbital plane prior to the explosion, providing further evidence that the SNR N103B originates from a single-degenerate progenitor.

astro-ph.HE↗

arXiv2021

A Multiwavelength Survey of Wolf-Rayet Nebulae in the Large Magellanic Cloud

Surveys of Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) have yielded a fairly complete catalog of 154 known stars. We have conducted a comprehensive, multiwavelength study of the interstellar/circumstellar environments of WR stars, using the Magellanic Cloud Emission Line Survey (MCELS) images in the H$α$, [O III], and [S II] lines; Spitzer Space Telescope 8 and 24 $μ$m images; Blanco 4m Telescope H$α$ CCD images; and Australian Telescope Compact Array (ATCA) + Parkes Telescope H I data cube of the LMC. We have also examined whether the WR stars are in OB associations, classified the H II environments of WR stars, and used this information to qualitatively assess the WR stars' evolutionary stages. The 30 Dor giant H II region has active star formation and hosts young massive clusters, thus we have made statistical analyses for 30 Dor and the rest of the LMC both separately and altogether. Due to the presence of massive young clusters, the WR population in 30 Dor is quite different from that from elsewhere in the LMC. We find small bubbles ($<$50 pc diameter) around $\sim$12% of WR stars in the LMC, most of which are WN stars and not in OB associations. The scarcity of small WR bubbles is discussed. Spectroscopic analyses of abundances are needed to determine whether the small WR bubbles contain interstellar medium or circumstellar medium. Implications of the statistics of interstellar environments and OB associations around WR stars are discussed. Multiwavelength images of each LMC WR star are presented.

astro-ph.GA↗

arXiv2020

Searching for Balmer-dominated Type Ia Supernova Remnants in M33

We have searched for Balmer-dominated Type Ia SNRs in M33 by selecting thermal X-ray sources with $L_{\rm X} \ge 5\times10^{35}$ ergs s$^{-1}$, identifying associated H$α$ emission features, and checking their [S II] and [O III] emission properties. Our search did not find any Balmer-dominated Type Ia SNRs in M33. This result is puzzling because M33 is 2-3 times more massive than the LMC, yet the LMC hosts five Balmer-dominated Type Ia SNRs and M33 has none. We have considered observational biases, interstellar densities and ionization conditions, Type Ia SN rate expected from the star formation history and Type Ia SN delay time distribution function, and metallicity effect. None of these can explain the absence of X-ray-bright Balmer-dominated Type Ia SNRs in M33. It is intriguing that the Galaxy has X-ray-bright and thermal Type Ia SNRs (Kepler and Tycho) as well as X-ray-faint and nonthermal Type Ia SNRs (G1.9+0.3, SN1006, and RCW86), while the LMC does not have the X-ray-faint and nonthermal ones and M33 does not have the X-ray-bright and thermal ones.

astro-ph.GA↗

arXiv2018

X-Ray Luminosity and Size Relationship of Supernova Remnants in the LMC

The Large Magellanic Cloud (LMC) has $\sim$60 confirmed supernova remnants (SNRs). Because of the known distance, 50 kpc, the SNRs' angular sizes can be converted to linear sizes, and their X-ray observations can be used to assess X-ray luminosities ($L_X$). We have critically examined the LMC SNRs' sizes reported in the literature to determine the most plausible sizes. These sizes and the $L_X$ determined from \emph{XMM-Newton} observations are used to investigate their relationship in order to explore the environmental and evolutionary effects on the X-ray properties of SNRs. We find: (1) Small LMC SNRs, a few to 10 pc in size, are all of Type Ia with $L_X>10^{36}$ ergs s$^{-1}$. The scarcity of small core-collapse (CC) SNRs is a result of CCSNe exploding in the low-density interiors of interstellar bubbles blown by their massive progenitors during their main sequence phase. (2) Medium-sized (10-30 pc) CC SNRs show bifurcation in $L_X$, with the X-ray-bright SNRs either in an environment associated with molecular clouds or containing pulsars and pulsar wind nebulae and the X-ray-faint SNRs being located in low-density interstellar environments. (3) Large (size$>$30 pc) SNRs show a trend of $L_X$ fading with size, although the scatter is large. The observed relationship between $L_X$ and sizes can help constrain models of SNR evolution.

astro-ph.HE↗

arXiv2017

Physical Structures of the Type Ia Supernova Remnant N103B

N103B is a Type Ia supernova remnant (SNR) projected in the outskirt of the superbubble around the rich cluster NGC 1850 in the Large Magellanic Cloud (LMC). We have obtained H$α$ and continuum images of N103B with the $\textit{Hubble Space Telescope}$ ($\textit{HST}$) and high-dispersion spectra with 4m and 1.5m telescopes at Cerro Tololo Inter-American Observatory. The $\textit{HST}$ H$α$ image exhibits a complex system of nebular knots inside an incomplete filamentary elliptical shell that opens to the east where X-ray and radio emission extends further out. Electron densities of the nebular knots, determined from the [S II] doublet, reach 5300 cm$^{-3}$, indicating an origin of circumstellar medium, rather than interstellar medium. The high-dispersion spectra reveal three kinematic components in N103B: (1) a narrow component with [N II]6583/H$α$ $\sim$ 0.14 from the ionized interstellar gas associated with the superbubble of NGC 1850 in the background, (2) a broader H$α$ component with no [N II] counterpart from the SNR's collisionless shocks into a mostly neutral ambient medium, and (3) a broad component, $ΔV$ $\sim$ 500 km s$^{-1}$, in both H$α$ and [N II] lines from shocked material in the nebular knots. The Balmer-dominated filaments can be fitted by an ellipse, and we adopt its center as the site of SN explosion. We find that the star closest to this explosion center has colors and luminosity consistent with a 1 $M_\odot$ surviving subgiant companion as modelled by Podsiadlowski. Follow-up spectroscopic observations are needed to confirm this star as the SN's surviving companion.

astro-ph.SR↗