arxiv: 2603.12604 · v1 · submitted 2026-03-13 · 🌌 astro-ph.HE · astro-ph.SR

Recognition: no theorem link

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

Danfeng Xiang , Xiaofeng Wang , Jujia Zhang , Shengyu Yan , Han Lin , Liming Rui , Jun Mo , Xinghan Zhang

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Hanna Sai Cheng Miao Gaobo Xi Zhihao Chen Fangzhou Guo Xiaoran Ma Gaici Li Tianmeng Zhang Liyang Chen Jialian Liu Wenxiong Li Xulin Zhao Fang Huang Yongzhi Cai Weili Lin Jie Lin Chengyuan Wu Maokai Hu Cuiying Song Jicheng Zhang Qiqi Xia Zhitong Li Linyi Li Kaicheng Zhang Qian Zhai Juncheng Chen Zhou Fan Jianning Fu Shengbang Qian Hong Wu Xue-Bing Wu Huawei Zhang Junbo Zhang Liyun Zhang Jie Zheng

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Pith reviewed 2026-05-15 12:13 UTC · model grok-4.3

classification 🌌 astro-ph.HE astro-ph.SR

keywords stripped-envelope supernovaeSNe IbHα identificationspectral featuresenvelope strippingSNe IIbSNe Icprogenitor evolution

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The pith

The 6200 Å feature in SNe Ib is identified as Hα, showing residual hydrogen and a continuous envelope-stripping sequence from IIb to Ib to Ic.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper compiles 249 spectra of 62 stripped-envelope supernovae and measures line velocities and pseudo-equivalent widths across photospheric and nebular phases. By direct comparison of the 6200 Å feature with known Hα in IIb and its absence in Ic, the authors conclude this line is Hα in Ib events as well. This finding indicates that most SNe Ib retain some hydrogen, placing them as an intermediate stage between IIb and Ic. The data also show rising line velocities and shifting nebular line ratios from IIb through Ib to Ic-BL, consistent with progressively greater envelope loss and larger CO cores in the progenitors.

Core claim

The feature near 6200 Å in SNe Ib is identified as Hα through comparison with SNe IIb and Ic, which resolves inconsistent literature interpretations. This reveals prevalent residual hydrogen in SNe Ib, further supporting a continuous stripping sequence from SNe IIb to Ib. Line velocities increase from IIb to Ib to Ic to Ic-BL, O I lines are stronger in Ic/Ic-BL, and nebular [O I] dominates over [Ca II] in Ic events, implying progenitors of SNe Ic and Ic-BL have more massive CO cores and higher initial masses.

What carries the argument

Measurements of pseudo-equivalent widths and blueshift velocities of principal lines (Hα, He I, O I) across subtypes, used to compare feature strengths and velocities and establish the Hα identification in Ib spectra.

If this is right

SNe Ib retain detectable hydrogen, placing them between IIb and Ic in the stripping sequence.
Progenitors of Ic and Ic-BL events have larger CO cores than those of IIb and Ib events.
Nebular [O I] versus [Ca II] dominance provides a spectroscopic classifier for Ic versus Ib events.
Line-velocity trends can be used to estimate relative envelope masses in future observations.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The dataset could test whether single-star wind stripping or binary interaction better explains the observed sequence.
If the velocity trends hold in larger samples, they may constrain the initial-mass thresholds separating supernova subtypes.
Automated spectral classifiers for upcoming surveys could incorporate the 6200 Å Hα template to reduce misclassification of Ib events.

Load-bearing premise

The observed differences in line velocities and strengths across subtypes are driven mainly by the amount of envelope stripping and core mass rather than by differences in explosion energy, asymmetry, or viewing angle.

What would settle it

High-resolution spectra showing the 6200 Å feature in SNe Ib with velocity and profile behavior inconsistent with Hα, or nebular spectra where [O I] and [Ca II] ratios do not separate Ic from Ib events, would undermine the identification and the stripping-sequence claim.

read the original abstract

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 $-$16 to over 190 days relative to maximum light. Most spectra were obtained during the photospheric phases after the supernova explosion. For each spectrum, the pseudo-equivalent widths (pEWs) and blueshift velocities of principal lines were measured. We further investigated the common spectral features by analysing their velocity and strength correlations across all subtypes. We identify the feature near 6200~\AA\ in SNe Ib as H$\mathrm{\alpha}$ 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.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper's real value is the new 249-spectrum dataset with line measurements, but the progenitor mass claims rest on untested assumptions about what drives the velocity and strength trends.

read the letter

The main deliverable is a collection of 249 optical spectra from 62 stripped-envelope supernovae observed between 2010 and 2020, with straightforward measurements of pseudo-equivalent widths and blueshift velocities for the principal lines. That sample size and phase coverage is new and will be useful to anyone who needs a larger comparison set for SESNe work. The identification of the 6200 Å feature in SNe Ib as Hα, reached by direct comparison to IIb and Ic spectra, is a reasonable move that could clarify some earlier conflicting reports in the literature. The reported trends—velocities increasing from IIb through Ib to Ic and Ic-BL, stronger O I in the Ic group, and the nebular [Ca II] versus [O I] dichotomy—are presented clearly from the data they have. Those are the parts that hold up on the evidence given. The softer part is the jump from those measurements to statements about continuous envelope stripping and higher CO-core masses for Ic progenitors. The abstract does not describe any checks against independent estimates of explosion energy or 56Ni mass, even though Ic-BL events are known to be systematically more energetic and that alone can affect line velocities. No error bars, sample selection details, or tests for asymmetry or viewing-angle effects appear in the summary, so the central inferences about progenitor initial masses are only partially supported. This is the sort of paper supernova spectroscopists will want to consult for the raw measurements and line trends. If the full tables and spectra are released with uncertainties, it becomes a practical reference. It deserves a serious referee because the data effort is substantial and the line-identification point addresses a real inconsistency, even if the physical interpretation will need tightening on the confounders.

Referee Report

3 major / 3 minor

Summary. The manuscript presents a dataset of 249 optical spectra for 62 stripped-envelope supernovae (SESNe) observed by the Tsinghua Supernova Group from 2010-2020. It measures pseudo-equivalent widths (pEWs) and blueshift velocities of principal lines across photospheric and nebular phases. Key findings include identifying the ~6200 Å feature in SNe Ib as Hα by comparison to IIb and Ic, supporting residual hydrogen and a continuous stripping sequence; observing increasing line velocities from IIb to Ib to Ic to Ic-BL; stronger O I in Ic/Ic-BL vs IIb/Ib; and [O I] dominating [Ca II] in Ic, implying more massive CO cores for Ic progenitors.

Significance. If the interpretations hold after addressing potential confounders, this provides a substantial homogeneous spectral dataset valuable for the community and observational constraints on envelope stripping and progenitor core masses in SESNe. The public measurements of pEWs and velocities constitute a clear strength.

major comments (3)

[Section discussing the 6200 Å feature identification] The identification of the 6200 Å feature in SNe Ib as Hα (central to the residual-hydrogen claim) relies on qualitative comparison with IIb and Ic spectra. No quantitative line-profile fitting, alternative identification tests (e.g., against Si II λ6355), or Monte Carlo robustness checks against noise and blending are reported.
[Section on velocity trends across subtypes] The velocity ordering (IIb < Ib < Ic < Ic-BL) and inference of higher CO-core masses for Ic progenitors assumes velocities primarily trace envelope/core properties. No regression or control against independent explosion-energy indicators (E_kin, 56Ni mass) is presented, despite known higher energies in Ic-BL events.
[Nebular-phase analysis section] The O I strength dichotomy and nebular [O I] vs [Ca II] dominance used to infer core-mass differences similarly lack controls for temperature, density, asymmetry, or viewing-angle effects that could dominate the observed trends.

minor comments (3)

[Abstract and methods] Abstract and methods section should explicitly state sample selection criteria, completeness, and any biases in subtype distribution.
[Measurement methodology] All pEW and velocity measurements must include reported uncertainties and the method used to derive them (e.g., Gaussian fitting or direct integration).
[Figures] Figures showing example spectra should include clear subtype labels, phase information, and wavelength/flux scales for reproducibility.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the thoughtful and detailed report. The comments highlight important areas where our interpretations can be strengthened with additional discussion and analysis. We have revised the manuscript to incorporate quantitative checks on the 6200 Å identification, expanded discussion of velocity trends with reference to explosion energies, and added caveats on nebular line ratios. Below we respond point by point to the major comments.

read point-by-point responses

Referee: The identification of the 6200 Å feature in SNe Ib as Hα (central to the residual-hydrogen claim) relies on qualitative comparison with IIb and Ic spectra. No quantitative line-profile fitting, alternative identification tests (e.g., against Si II λ6355), or Monte Carlo robustness checks against noise and blending are reported.

Authors: We agree that the original identification was based on direct spectral comparison. In the revised manuscript we have added velocity measurements of the 6200 Å feature for all SNe Ib in the sample and compared them statistically to the Hα velocities measured in SNe IIb. We also explicitly test the Si II λ6355 alternative by noting the absence of the stronger Si II λ5972 line in the same spectra and discuss blending with other species. While a full Monte Carlo noise simulation is beyond the scope of this observational paper, the consistency of the feature across 62 events and multiple epochs provides supporting robustness. The relevant section has been expanded with these details and a brief discussion of limitations. revision: partial
Referee: The velocity ordering (IIb < Ib < Ic < Ic-BL) and inference of higher CO-core masses for Ic progenitors assumes velocities primarily trace envelope/core properties. No regression or control against independent explosion-energy indicators (E_kin, 56Ni mass) is presented, despite known higher energies in Ic-BL events.

Authors: The observed velocity trend is a direct result of our measurements. We acknowledge that kinetic energy and 56Ni mass can influence line velocities, especially for Ic-BL events. In revision we have added a new paragraph referencing available literature values of E_kin and 56Ni for overlapping events in our sample and note that the subtype ordering remains after accounting for the systematically higher energies of Ic-BL. A full multivariate regression is not feasible without complete energy data for every object, but we have clarified that the trend is consistent with increasing progenitor core mass while explicitly stating the possible contribution of explosion energy. revision: partial
Referee: The O I strength dichotomy and nebular [O I] vs [Ca II] dominance used to infer core-mass differences similarly lack controls for temperature, density, asymmetry, or viewing-angle effects that could dominate the observed trends.

Authors: We recognize that nebular line strengths depend on temperature, density, and geometry. Our inference rests on the clear statistical dichotomy observed in a homogeneous dataset of 249 spectra. In the revised text we have added discussion of these potential confounders, citing nebular modeling literature, and argue that the systematic difference between IIb/Ib and Ic subtypes is most naturally explained by CO-core mass given the parallel trends in photospheric velocities. Sample size and presumed random viewing angles help mitigate asymmetry effects. We have inserted explicit caveats on the interpretation while retaining the core-mass conclusion as the most straightforward reading of the data. revision: partial

Circularity Check

0 steps flagged

No significant circularity in observational spectral analysis

full rationale

The paper consists of new observational data collection (249 spectra of 62 SESNe) and direct measurements of pEWs and blueshift velocities, followed by empirical comparisons across subtypes. No mathematical derivations, equations, fitted parameters renamed as predictions, or self-citation chains appear in the provided text. The identification of the 6200 Å feature as Hα and the reported velocity/line-strength trends are presented as observational results without reduction to inputs by construction. This is the expected outcome for a dataset paper whose central content is measurement and classification rather than theoretical derivation.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an observational data-release paper; no new free parameters, axioms, or invented entities are introduced beyond standard astrophysical line identifications and progenitor interpretations.

pith-pipeline@v0.9.0 · 5793 in / 1158 out tokens · 55270 ms · 2026-05-15T12:13:55.345754+00:00 · methodology