arxiv: 2602.09777 · v1 · submitted 2026-02-10 · 🌌 astro-ph.SR

Recognition: no theorem link

Characterisation of an EXor outburst SPICY 97589

Aaron Labdon , Rik Claes

Authors on Pith no claims yet

Pith reviewed 2026-05-16 02:40 UTC · model grok-4.3

classification 🌌 astro-ph.SR

keywords EXor outburstaccretion rateyoung stellar objectemission linesdisk windsstellar parameters

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The pith

The 2023 outburst of SPICY 97589 is confirmed as an accretion event onto an M3 star at 2.38e-7 solar masses per year.

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

This paper establishes that the 2023 outburst of SPICY 97589 was an accretion outburst, with material from the disk flowing onto the central star at a rate of 2.38 times 10 to the minus 7 solar masses per year. This rate is two orders of magnitude higher than the quiescent level, as measured from emission line luminosities in multi-wavelength spectra taken during peak and after the event. The authors also determine the star to be an M3.0 type with a mass of 0.29 solar masses. A sympathetic reader cares because such events are believed to be common in the formation of stars and planets but have rarely been characterised in detail, providing insight into disk evolution.

Core claim

The 2023 outburst was driven by an influx of material from the surrounding environment to the central star, an accretion outburst. The accretion rate reaches 2.38 plus or minus 0.58 times 10 to the minus 7 solar masses per year. The spectral fingerprint of emission lines is also characteristic of an outbursting EXor-type source, including variable disk winds.

What carries the argument

Emission line luminosities from multi-waveband spectroscopy converted to mass-accretion rate via empirical relations, compared between outburst peak and post-outburst quiescent spectra.

If this is right

The central star is an M3.0 type with effective temperature 3410 K, luminosity 0.41 solar luminosities and mass 0.29 solar masses.
The outburst contributes to disk evolution by transporting material inward at an elevated rate.
Variable disk winds form part of the spectral signature during the outburst phase.

Where Pith is reading between the lines

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

Outbursts of this kind may represent a major channel for mass assembly in young stars across clusters.
Targeted spectroscopic monitoring of similar young objects could uncover additional EXor events.
Extended time-series data might reveal whether the outbursts repeat on predictable timescales.

Load-bearing premise

The conversion of observed emission-line luminosities to mass-accretion rate relies on empirical relations calibrated on other stars; if those relations do not apply to this object the quoted rate could be systematically off.

What would settle it

An independent measurement of accretion rate, such as through continuum veiling, showing no significant increase during the 2023 event would falsify the accretion-driven outburst claim.

Figures

Figures reproduced from arXiv: 2602.09777 by Aaron Labdon, Rik Claes.

**Figure 1.** Figure 1: Spectral energy distribution (SED) of SPICY 97589. Circles are the photometry from sources described in Appendix A. All photometry is taken during quiescence, pre-2017 outburst. The blue line is the binned X-Shooter flux calibrated 2023 outburst spectrum. The red line is the binned X-Shooter flux calibrated spectrum post-2023 outburst. Article number, page 2 of 11 [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗

**Figure 2.** Figure 2: Best fit of the X-Shooter spectrum of SPICY 97589. The observed spectrum is shown in black. The best fit photospheric template in yellow, and the slab model in green. The best fit is shown in light blue. The blue points indicate the wavelength ranges used to constrain the model. during quiescence as 18.66±0.12 magnitudes in the G band. The parameters of the outbursts can be measured by fitting simple mode… view at source ↗

**Figure 3.** Figure 3: Gaia G-band light curve over the past seven years. Highlighted in orange and red are the 2017 and 2023 outbursts, respectively. The black dashed lines are the data of the X-Shooter spectroscopic observations on 2023-04-19 and 2024-07-25. The mean quiescent magnitude is measured as 18.66 ± 0.12. 7000 7500 8000 8500 9000 9500 10000 10500 JD - 2450000 [days] 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 Magnitude 2017… view at source ↗

**Figure 4.** Figure 4: WISE light curves in the W1 (3.35 µm) and W2 (4.6 µm) shown in blue and red respectively. For each date of WISE observations, multiple images are taken, and the photometry of each image is averaged to provide the final values. The black dashed line represents the Gaia G band light curve, adjusted in magnitude scale by 7.5mag. Highlighted in orange and red are the 2017 and 2023 outbursts, respectively. Lacc… view at source ↗

**Figure 5.** Figure 5: Continuum-subtracted X-Shooter spectra across the three instrument arms. The three panels from top to bottom show the spectra from the UVB, VIS and NIR arms. In black is the outburst spectra and in red is the quiescent spectra. Highlighted as dashed lines are the prominent emission lines present in the spectra; a full list of the identified lines is presented in Appendix A. Article number, page 5 of 11 [P… view at source ↗

**Figure 6.** Figure 6: Heliocentric corrected P-Cygni profile of the Hα line at a rest wavelength of 656.28 nm (black dashed line). The blue line is the quiescent spectra taken, while red is the outburst line. The spectra are not continuum-subtracted or offset. 5. Conclusions Our spectroscopic characterisation has characterised the YSO SPICY 97589, adding it to an exclusive but growing list of accretion outbursting objects. We… view at source ↗

read the original abstract

Stellar outbursts from variable or periodic accretion are thought to be ubiquitous across young stellar populations. However, relatively few outbursting objects have been discovered to date. Here, we present the characterisation of a new EXor-type episodic accretor. We aim to characterise the nature of the 2023 outburst of SPICY 97589/Gaia23bab and characterise the stellar source for the first time, while exploring how an accretion outburst contributes to disk evolution. We employ multi-waveband medium-resolution spectroscopy with UVB-VIS-NIR coverage during the peak of the 2023 outburst and the post-outburst quiescent object. The broad wavelength coverage of the dataset allows for robust measurements of the accretion rate using known line tracers. The addition of quiescent spectra provides a good estimation of stellar parameters of the central star while also informing us on the evolution of the disk during outburst phases. We find the stellar source to be a 3410\,K, M3.0 type star with a luminosity of 0.41 $L_\odot$ and an estimated stellar mass of 0.29 $M_\odot$. We measure the accretion rate of SPICY 97589 to be $\dot M = 2.38\pm0.58\times10^{-7}\,\mathrm{M_\odot yr^{-1}}$. This value is at two orders of magnitude greater than the quiescent accretion rate. Thus, we confirm that the 2023 outburst was driven by an influx of material from the surrounding environment to the central star, an accretion outburst. The spectral fingerprint of emission lines is also characteristic of an outbursting EXor-type source, including variable disk winds.

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 provides solid new data on an EXor outburst but the accretion rates rest on empirical calibrations whose fit to this M3 star is untested.

read the letter

The main point for you is that this is a straightforward observational paper that gives us the first detailed characterization of SPICY 97589 as an EXor. They used multi-band spectroscopy during the 2023 peak and afterward to classify the star as M3.0 with effective temperature 3410 K, luminosity 0.41 solar luminosities, and mass around 0.29 solar masses. The accretion rate during outburst comes out to 2.38 plus or minus 0.58 times 10 to the minus 7 solar masses per year, which is about 100 times the quiescent level. That jump, plus the emission line patterns, backs up the accretion outburst interpretation. They handle the data reasonably well by covering UVB to NIR for good line coverage and using multiple tracers like H alpha, Pa beta, and Br gamma. The quiescent spectra let them pin down the stellar parameters separately, which is helpful for understanding the disk changes. It's the kind of work that slowly builds the sample of these episodic accretors. The soft spot is the dependence on empirical line-to-accretion-rate relations. These are calibrated mostly on T Tauri stars that are more massive than this M3 object. If the line formation or veiling behaves differently here, both the absolute rate and the contrast to quiescence could be off by some factor. The paper doesn't show a cross-check with something like continuum veiling or UV measurements to confirm. No major contradictions in the data as presented, and the uncertainties are quoted. The citation pattern looks standard for the field. This paper is for astronomers working on young stellar objects and accretion variability. It won't change the big picture but provides a solid new data point for statistical studies. The evidence is observational and direct enough that it merits a serious referee to go over the spectral extraction and calibration choices. I would recommend putting it through peer review rather than desk rejecting it.

Referee Report

1 major / 2 minor

Summary. The manuscript presents multi-wavelength (UVB-VIS-NIR) spectroscopic observations of SPICY 97589/Gaia23bab during the peak of its 2023 outburst and in quiescence. It classifies the central source as an M3.0 star (T_eff = 3410 K, L = 0.41 L_⊙, M_* = 0.29 M_⊙) and derives an outburst accretion rate Ṁ = 2.38 ± 0.58 × 10^{-7} M_⊙ yr^{-1} from emission-line luminosities, two orders of magnitude above the quiescent value, thereby confirming the event as an EXor-type accretion outburst with characteristic line emission and variable disk winds.

Significance. If the reported factor-of-100 increase in accretion rate holds, the work adds a well-observed low-mass EXor to the still-small sample of such objects and directly links the photometric outburst to enhanced accretion, with implications for disk evolution. The broad wavelength coverage enabling simultaneous use of multiple line tracers is a methodological strength.

major comments (1)

[§4] §4 (accretion-rate derivation): The mass-accretion rate is obtained from Hα, Paβ and Brγ luminosities via empirical calibrations (Alcalá et al.-style relations) derived on higher-mass T Tauri samples. No quantitative assessment is given of whether these relations remain valid for an M3.0 star at T_eff = 3410 K; if line-formation physics, veiling or extinction differ systematically, both the absolute Ṁ and the reported factor-of-100 contrast with quiescence become uncertain. An orthogonal check (e.g., continuum veiling or UV excess) is absent.

minor comments (2)

[Abstract and §3] The abstract and §3 state that 'known line tracers' were used but do not list the specific lines or equivalent-width measurements; adding a table of line luminosities and the exact calibration coefficients employed would improve reproducibility.
[Figures] Figure 2 (or equivalent spectral comparison plot) would benefit from explicit annotation of the lines used for the Ṁ calculation and a clear quiescent vs. outburst overlay to highlight the factor-of-100 change.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive review and recommendation for minor revision. The comment on the accretion-rate derivation is addressed point-by-point below.

read point-by-point responses

Referee: [§4] §4 (accretion-rate derivation): The mass-accretion rate is obtained from Hα, Paβ and Brγ luminosities via empirical calibrations (Alcalá et al.-style relations) derived on higher-mass T Tauri samples. No quantitative assessment is given of whether these relations remain valid for an M3.0 star at T_eff = 3410 K; if line-formation physics, veiling or extinction differ systematically, both the absolute Ṁ and the reported factor-of-100 contrast with quiescence become uncertain. An orthogonal check (e.g., continuum veiling or UV excess) is absent.

Authors: We agree that the Alcalá et al.-style empirical relations were calibrated on samples dominated by higher-mass T Tauri stars. For our M3.0 source (T_eff = 3410 K), systematic differences in veiling, extinction, or line-formation physics could affect the absolute Ṁ value. However, the reported factor-of-100 contrast remains robust because both the outburst and quiescent accretion rates are derived using identical relations and the same set of line tracers. We will revise §4 to add a quantitative discussion of the applicability of these calibrations to low-mass stars, including the typical scatter in the relations and references to prior applications on M-dwarfs and brown dwarfs. An orthogonal check via UV excess or continuum veiling is not feasible with the current UVB-VIS-NIR dataset, which lacks the necessary UV coverage for such measurements; the internal consistency across Hα, Paβ, and Brγ provides the primary validation. revision: partial

Circularity Check

0 steps flagged

No circularity: accretion rates derived from external empirical line-luminosity relations applied to independent outburst and quiescent spectra

full rationale

The paper measures stellar parameters (T_eff=3410 K, L=0.41 L_sun, M=0.29 M_sun) and accretion rates directly from UVB-VIS-NIR spectra using established external calibrations (Alcalá-style relations for Hα, Paβ, Brγ). The factor-of-100 contrast between outburst (2.38e-7 M_sun/yr) and quiescent rates follows from applying the identical external conversion to two independent epochs; no parameter is fitted to the present data and then re-used as a prediction, no self-citation supplies a uniqueness theorem or ansatz, and no step renames or re-derives its own input. The derivation chain is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on empirical calibrations that convert emission-line luminosities into mass-accretion rates and on standard pre-main-sequence evolutionary tracks used to convert effective temperature and luminosity into mass.

free parameters (1)

line-to-accretion-rate conversion factors
Empirical relations calibrated on other young stars; the exact numerical factors are taken from the literature and applied here.

axioms (1)

domain assumption Standard stellar spectral classification and pre-main-sequence evolutionary models apply to this source.
Used to assign T_eff = 3410 K, spectral type M3.0, L = 0.41 L_sun and M = 0.29 M_sun.

pith-pipeline@v0.9.0 · 5596 in / 1349 out tokens · 40744 ms · 2026-05-16T02:40:40.699309+00:00 · methodology

discussion (0)

Reference graph

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