arXiv subjects

Qiliang Fang

Publications and source records attributed to Qiliang Fang.

15 recordsLinked to original sources

arXiv2026

A Radiation-Hydrodynamic Light Curve Grid and Interpolation Framework for Stripped-Envelope Supernovae

We present a grid of 8,148 stripped-envelope supernovae (SESNe) light curves based on radiation hydrodynamic simulations of exploding helium-star progenitors. The grid spans an ejecta-mass range representative of typical SESNe, together with broad ranges of explosion energies, radioactive nickel masses, and degrees of material mixing. We systematically investigate how these physical parameters shape the light curves and develop an interpolation-based parameter inference framework that enables the application of the model grid to observational data. Using the simulated light curves as mock observations, we assess the reliability of the widely used Arnett model. Although it reproduces the overall light-curve morphology, the inferred ejecta masses show no significant correlation with the true values. Moreover, the analytical model produces a spurious correlation between explosion energy and nickel mass, despite these parameters being independent in the underlying model grid. These results demonstrate that good light-curve fits do not necessarily imply reliable physical parameter estimates and highlight the need for physically motivated radiation hydrodynamic models in population studies of SESNe.

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arXiv2026

WFST Supernovae in the First Year: III. Systematical Study of the Photometric Behavior of Early-phase Core-collapse Supernovae

We investigate the multiband photometric properties of seven supernovae (SNe) showing double-peaked light-curve evolution and prominent shock-cooling emission, observed by the Wide Field Survey Telescope (WFST) during its first year of operation. By jointly employing an analytic early shock-cooling model and the Arnett radioactive-diffusion model, we fit the bolometric light curves and infer ejecta masses in the range $1.1$-$2.6 M_\odot$, consistent with a transitional population between ultra-stripped supernovae (USSNe) and normal stripped-envelope supernovae (SESNe). The envelope masses are estimated to be $M_{\rm env}=0.1$-$0.4 M_\odot$, while the progenitors are constrained to be yellow or blue supergiants (YSGs/BSGs) with radii of $R=120$-$300 R_\odot$. Using empirical relations, we estimate progenitor luminosities of $L=10^{4.6}$-$10^{4.9} L_\odot$, corresponding to zero-age main-sequence (ZAMS) masses of $8$-$20 M_\odot$. Theoretical models suggest that such progenitors are more naturally produced through binary evolution channels, as single-star evolutionary pathways are unable to yield ejecta masses this low.

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arXiv2025

Reconciling the Tension Between Light Curve Modeling of Type II Supernovae and Neutrino-Driven Core-Collapse Supernovae Models with Late-Phase Spectroscopy

Type II supernovae (SNe II) are the most frequently observed outcome of core-collapse explosions and provide a valuable window into the physical mechanisms governing the deaths of massive stars. However, estimates of explosion properties based on optical light curve modeling often show tension with the predictions of modern neutrino-driven explosion models. In particular, when based on light curves from the explosions of red supergiant (RSG) tied to specific stellar wind models, many SNe II are found to originate from low-mass progenitors yet exhibit unusually high explosion energies ($E_{\rm K}$), far exceeding theoretical predictions. In this study, we incorporate late-phase (nebular) spectroscopy to estimate the helium core mass of the progenitor ($M_{\rm He\,core}$), which serves as an additional constraint to break degeneracies in light curve modeling. This approach is applied to a sample of 32 well-observed SNe II, using a light curve model grid constructed from RSGs with arbitrarily stripped hydrogen-rich envelopes, rather than assuming a fixed wind model. Examining the resulting correlations among the physical parameters, we find that the tension between the observed $M_{\rm He\,core}$-$E_{\rm K}$ and $E_{\rm K}$-$M_{\rm Ni}$ relations and those predicted by neutrino-driven explosion models has significantly lessened by incorporating nebular spectroscopy in light curve modeling. This study highlights the crucial role of nebular spectroscopy in interpreting SNe II observations and provides support to the neutrino-driven explosion mechanism as the dominant engine powering these events.

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arXiv2025

Diversity in Hydrogen-rich Envelope Mass of Type II Supernovae. (III). The mass-loss and evolutionary pathways of the red supergiant progenitors

We present a comprehensive analysis of 32 type II supernovae (SNe II) with plateau phase photometry and late phase ($nebular$) spectroscopy available, aiming to bridge the gap between the surface and core of their red supergiant (RSG) progenitors. Using \texttt{MESA}\,+\texttt{STELLA}, we compute an extensive grid of SN II light curve models originating from RSG with effective temperatures $T_{\rm eff}$ around 3650\,K and hydrogen-rich envelopes artificially stripped to varying degrees. These models are then used to derive the hydrogen-rich envelope masses $M_{\rm Henv}$ for SNe II from their plateau phase light curves. Nebular spectroscopy further constrains the progenitor RSG's luminosity log\,$L_{\rm prog}$, and is employed to remove the degeneracies in light curve modeling. The comparison between log\,$L_{\rm prog}$-$M_{\rm Henv}$ reveals that $M_{\rm Henv}$ spans a broad range at the same log\,$L_{\rm prog}$, and almost all SNe II have lower $M_{\rm Henv}$ than the prediction of the default stellar wind models. We explore alternative wind prescriptions, binary evolution models, and the possibility of more compact RSG progenitors. Although binary interaction offers a compelling explanation for the non-monotonicity and large scatter in the log\,$L_{\rm prog}$-$M_{\rm Henv}$ relation, the high occurrence rate of partially-stripped RSGs cannot be accounted for by stable binary mass transfer alone without fine-tuned orbital parameters. This highlights that, despite being the most commonly observed class of core-collapse SNe, SNe II likely originate from a variety of mass-loss histories and evolutionary pathways that are more diverse and complex than typically assumed in standard stellar evolution models.

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arXiv2025

Red Supergiant problem viewed from the nebular phase spectroscopy of type II supernovae

The red supergiant (RSG) problem refers to the observed dearth of luminous RSGs identified as progenitors of Type II supernovae (SNe II) in pre-SN imaging. Understanding this phenomenon is essential for studying pre-SN mass loss and the explodability of core-collapse SNe. In this work, we re-assess the RSG problem using late-phase spectroscopy of a sample of 50 SNe II. The [O I] $λλ$6300,6363 emission in the spectra is employed to infer the zero-age main sequence (ZAMS) mass distribution of the progenitors, which is then transformed into a luminosity distribution via an observation-calibrated mass-luminosity relation. The resulting luminosity distribution reveals an upper cutoff at log $L/L_{\odot} = 5.21^{+0.09}_{-0.07}$ dex, and the RSG problem is statistically significant at the 2$σ$ to 3$σ$ level. Assuming single RSG progenitors that follow the mass-luminosity relation of KEPLER models, this luminosity cutoff corresponds to an upper ZAMS mass limit of $20.63^{+2.42}_{-1.64}$ $M_{\odot}$. Comparisons with independent measurements, including pre-SN imaging and plateau-phase light curve modeling, consistently yield an upper ZAMS mass limit below about 25 $M_{\odot}$, with a significance level of 1-3$σ$. While each individual method provides only marginal significance, the consistency across multiple methodologies suggests that the lack of luminous RSG progenitors may reflect a genuine physical problem. Finally, we discuss several scenarios to account for this issue should it be confirmed as a true manifestation of stellar physics.

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arXiv2024

Diversity in hydrogen-rich envelope mass of type II supernovae (I): $V$-band light curve modeling

We present a systematic study of Type II supernovae (SNe II) originating from progenitors with effective temperatures ($T_{\rm eff}$) and luminosities closely resembling red supergiants (RSGs) observed in pre-SN images and in the Galaxy. Using $\texttt{MESA}$, we compute a large grid of massive stars with $T_{\rm eff}$ ranging from 3200 K to 3800 K at their RSG phases, with hydrogen envelopes artificially stripped to varying extents (3 to 10\,$M_{\odot}$). The light curves of SNe IIP resulting from the explosions of these Galactic-RSG-like progenitors are modeled using $\texttt{STELLA}$. Our survey of the light curves reveals that partial stripping of the hydrogen envelope creates diversity in the magnitude and duration of SNe IIP light curves, without affecting the position of the RSG progenitor on the Hertzsprung-Russell diagram (HRD). For these Galactic-RSG-like progenitor models, we establish an indicator based on the light-curve properties to estimate the hydrogen envelope mass. Additionally, we discuss the effects of material mixing and $^{56}$Ni heating. Applying our model grid to a large sample of approximately 100 observed SNe IIP reveals a considerably broader range of hydrogen-rich envelope masses than predicted by standard stellar wind models. This finding suggests that, if SNe IIP are explosions of Galactic-like RSGs, to explain the diversity in the observed light curves, a significant fraction of them must have experienced substantial mass loss beyond the standard mass-loss prescription prior to their explosions. This finding highlights the uncertainties involved in massive star evolution and the pre-SN mass-loss mechanism.

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arXiv2024

Diversity in hydrogen-rich envelope mass of type II supernovae (II): SN 2023ixf as explosion of partially-stripped intermediate massive star

SN 2023ixf is one of the most well-observed core-collapse supernova in recent decades, yet there is inconsistency in the inferred zero-age-main-sequence (ZAMS) mass $M_{\rm ZAMS}$ of its progenitor. Direct observations of the pre-SN red supergiant (RSG) estimate $M_{\rm ZAMS}$ spanning widely from 11 to 18 $M_{\rm \odot}$. Additional constraints, including host environment and the pulsation of its progenitor RSG, suggest a massive progenitor with $M_{\rm ZAMS}$ > 17 $M_{\rm \odot}$. However, the analysis of the properties of supernova, from light curve modeling to late phase spectroscopy, favor a relatively low mass scenario ($M_{\rm ZAMS}$ < 15 $M_{\rm \odot}$). In this work, we conduct systematic analysis of SN 2023ixf, from the RSG progenitor, plateau phase light curve to late phase spectroscopy. Using MESA+STELLA to simulate the RSG progenitor and their explosions, we find that, despite the ZAMS mass of the RSG models being varied from 12.0 to 17.5 $M_{\rm \odot}$, they can produce light curves that well match with SN 2023ixf if the envelope mass and the explosion energy are allowed to vary. Using late phase spectroscopy as independent measurement, the oxygen emission line [O I] suggests the ZAMS is intermediate massive (~16.0 $M_{\rm \odot}$), and the relatively weak H$α$ emission line indicates the hydrogen envelope has been partially removed before the explosion. By incorporating the velocity structure derived from the light curve modeling into an axisymmetric model, we successfully generated [O I] line profiles that are consistent with the [O I] line observed in late phase spectroscopy of SN 2023ixf. Bringing these analyses together, we conclude that SN 2023ixf is the aspherical explosion of an intermediate massive star ($M_{\rm ZAMS}$ = 15-16 $M_{\rm \odot}$) with the hydrogen envelope being partially stripped to 4-5 $M_{\rm \odot}$ prior to its explosion.

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arXiv2023

An aspherical distribution for the explosive burning ash of core-collapse supernovae

It is widely believed that asphericity in the explosion is the crucial ingredient leading to successful core-collapse (CC) supernovae. However, direct observational evidence for the explosion geometry and for the connection with the progenitor properties are still missing. Based on the thus-far largest late-phase spectroscopic sample of stripped-envelope CC supernovae, we demonstrate that about half of the explosions exhibit a substantial deviation from sphericity. For these aspherical CC supernovae, the spatial distributions of the oxygen-burning ash and the unburnt oxygen, as traced by the profiles of [Ca II] λλ7291,7323 and [O i] λλ6300,6363 emissions, respectively, appear to be anticorrelated, which can be explained if the explosion is bipolar and the oxygen-rich material burnt into two detached iron-rich bubbles. Our combined analysis of the explosion geometry and the progenitor mass further suggests that the degree of asphericity grows with the mass of the carbon-oxygen core, which may be used to guide state-of-the-art simulations of CC supernova explosions.

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arXiv2023

Inferring the progenitor mass-kinetic energy relation of stripped-envelope core-collapse supernovae from nebular spectroscopy

The relation between the progenitor mass and the kinetic energy of the explosion is a key toward revealing the explosion mechanism of stripped-envelope (SE) core-collapse (CC) supernovae (SNe). Here, we present a method to derive this relation using the nebular spectra of SESNe, based on the correlation between the [O~I]/[Ca~II], which is an indicator of the progenitor mass, and the width of [O~I], which measures the expansion velocity of the oxygen-rich material. To explain the correlation, the kinetic energy ($E_{\rm K}$) is required to be positively correlated with the progenitor mass as represented by the CO core mass ($M_{\rm CO}$). We demonstrate that SNe IIb/Ib and SNe Ic/Ic-BL follow the same $M_{\rm CO}$-$E_{\rm K}$ scaling relation, which suggests the helium-rich and helium-deficient SNe share the same explosion mechanism. The $M_{\rm CO}$-$E_{\rm K}$ relation derived in this work is compared with the ones from early phase observations. The results are largely in good agreement. Combined with early phase observation, the method presented in this work provides a chance to scan through the ejecta from the outermost region to the dense inner core, which is important to reveal the global properties of the ejecta and constrain the explosion mechanism of core-collapse supernovae.

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arXiv2022

Statistical properties of the nebular spectra of 103 stripped envelope core collapse supernovae

We present an analysis of the nebular spectra of 103 stripped envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O I] 6300, 6363. The line profile and width of [O I] are employed to infer the ejecta geometry and the expansion velocity of the inner core. These two measurements are then compared with the SN sub types, and further with the [O I]/[Ca II] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best fit results of the [O I] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at about 1 sigma level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O I] width and [O I]/[Ca II] ratio is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O I]/[Ca II] ratio increases, the fraction of objects with Gaussian [O I] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass.

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arXiv2021

Luminous Type II Short-Plateau Supernovae 2006Y, 2006ai, and 2016egz: A Transitional Class from Stripped Massive Red Supergiants

The diversity of Type II supernovae (SNe II) is thought to be driven mainly by differences in their progenitor's hydrogen-rich (H-rich) envelope mass, with SNe IIP having long plateaus ($\sim100$ days) and the most massive H-rich envelopes. However, it is an ongoing mystery why SNe II with short plateaus (tens of days) are rarely seen. Here, we present optical/near-infrared photometric and spectroscopic observations of luminous Type II short-plateau SNe 2006Y, 2006ai, and 2016egz. Their plateaus of about $50$-$70$ days and luminous optical peaks ($\lesssim-18.4$ mag) indicate significant pre-explosion mass loss resulting in partially stripped H-rich envelopes and early circumstellar material (CSM) interaction. We compute a large grid of MESA+STELLA single-star progenitor and light-curve models with various progenitor zero-age main-sequence (ZAMS) masses, mass-loss efficiencies, explosion energies, $^{56}$Ni masses, and CSM densities. Our model grid shows a continuous population of SNe IIP-IIL-IIb-like light-curve morphology in descending order of H-rich envelope mass. With large $^{56}$Ni masses ($\gtrsim0.05\,M_\odot$), short-plateau SNe II lie in a confined parameter space as a transitional class between SNe IIL and IIb. For SNe 2006Y, 2006ai, and 2016egz, our findings suggest high-mass red supergiant (RSG) progenitors ($M_{\rm ZAMS} \simeq 18$-$22\,M_{\odot}$) with small H-rich envelope masses ($M_{\rm H_{\rm env}} \simeq 1.7\,M_{\odot}$) that have experienced enhanced mass loss ($\dot{M} \simeq 10^{-2}\,M_{\odot}\,{\rm yr}^{-1}$) for the last few decades before the explosion. If high-mass RSGs result in rare short-plateau SNe II, then these events might ease some of the apparent underrepresentation of higher-luminosity RSGs in observed SN II progenitor samples.

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arXiv2018

Supernova Nebular Spectroscopy Suggests a Hybrid Envelope-Stripping Mechanism for Massive Stars

When nuclear fuel in the core of a massive star with a zero-age main-sequence mass $M_{\rm ZAMS} \gtrsim 8M_\odot$ is exhausted, the central part of the iron or magnesium core collapses and forms a neutron star or a black hole. At the same time, the material above the collapsing core is rapidly ejected, leading to a stripped-envelope supernova (SESN) explosion if the outer hydrogen envelope of the star was removed before its explosion. The envelope is presumably stripped either via strong stellar winds or due to mass transfer to a companion star in a close binary orbit. It is not clear which process is dominant, and whether different mechanisms are at work for different classes of SESNe; type IIb, Ib, and Ic SNe in order of increasing degree of envelope stripping. In this work, a new analysis of late-time nebular spectra of SESNe is presented, which is more sensitive to differences in the core structure than early-phase spectral analysis. The results show that the progenitors of SNe IIb and Ib are indistinguishable except for the residual amount of hydrogen envelope while the progenitors of SNe Ic are not only deficient in hydrogen and helium, but are also distinctly more massive than SNe IIb and Ib. These findings strongly suggest that more than one mechanism is responsible for the removal of the outer hydrogen envelope and the deeper helium layer, with the former most likely due to binary interaction, and the latter involving a mass-dependent process such as strong stellar winds or episodic pre-explosion mass ejection.

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arXiv2018

The origin of the H$α$-like structure in nebular spectra of type IIb supernovae

We investigate the origin of the H$α$-like structure seen in late-phase nebular spectra of type IIb supernovae (SNe IIb) at $\sim 200$ days after the explosion. We compare the luminosities of emission lines in the nebular spectra with the light curve peak magnitudes to reveal their power sources. In this work, we analyze 7 SNe IIb, as well as 2 SNe Ib (SN 2007Y and iPTF 13bvn) that show the H$α$-like emission in their nebular spectra. The luminosity of the H$α$-like emission shows a tight correlation with the light curve peak magnitude, sharing the same behavior with other nebular lines. This result indicates that the H$α$-like emission is powered by the radiative decay of $^{56}$Co. The line flux is then expected to roughly follow the mass of the emitting layer. The variation expected from the diversity of the H-rich envelope mass among SNe IIb (reaching nearly to an order of magnitude) is however not seen, suggesting that it is most likely contributed predominantly by [N II], not by H$α$. While further analysis is limited by the available sample size, we find a hint that SNe IIb with a double-peak light curve, which is interpreted as an outcome of the more extended and massive hydrogen envelope, tend to show excess in the luminosity of the H$α$-like feature than those with a single-peak light curve. This behavior indicates possible additional contribution from H$α$. Additionally, we also find a correlation between the [Ca II]/[O I] ratio and the post-maximum decline rate, indicating that the [Ca II]/[O I] can be used as a diagnostics for the progenitor mass.

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arXiv2017

Age spreads and the temperature dependence of age estimates in Upper Sco

Past estimates for the age of the Upper Sco Association are typically 11-13 Myr for intermediate-mass stars and 4-5 Myr for low-mass stars. In this study, we simulate populations of young stars to investigate whether this apparent dependence of estimated age on spectral type may be explained by the star formation history of the association. Solar and intermediate mass stars begin their pre-main sequence evolution on the Hayashi track, with fully convective interiors and cool photospheres. Intermediate mass stars quickly heat up and transition onto the radiative Henyey track. As a consequence, for clusters in which star formation occurs on a similar timescale as the transition from a convective to a radiative interior, discrepancies in ages will arise when ages are calculated as a function of temperature instead of mass. Simple simulations of a cluster with constant star formation over several Myr may explain about half of the difference in inferred ages versus photospheric temperature; speculative constructions that consist of a constant star formation followed by a large supernova-driven burst could fully explain the differences, including those between F and G stars where evolutionary tracks may be more accurate. The age spreads of low-mass stars predicted from these prescriptions for star formation are consistent with the observed luminosity spread of Upper Sco. The conclusion that a lengthy star formation history will yield a temperature dependence in ages is expected from the basic physics of pre-main sequence evolution and is qualitatively robust to the large uncertainties in pre-main sequence evolutionary models.

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arXiv2016

The low-mass population in the young cluster Stock 8: Stellar properties and Initial Mass Function

The evolution of HII regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6, 4.5 μm photometry from UKIDSS and Spitzer-IRAC. We use multi-color criteria to identify the candidate young stellar objects in the region. Using evolutionary models, we obtain a median log(age) of ~6.5 (~3.0 Myr) with an observed age spread of ~0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ~0.15 dex. The intrinsic age spread in the cluster is ~0.2 dex. The fraction of young stellar objects surrounded by disk is ~35%. The K-band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The IMF of Stock 8 has a Salpeter- like slope at >0.5 Msun and the IMF flattens and peaks at ~0.4 Msun, below which declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of IMF due to the proximity of massive stars around the cluster.

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