The spectral energy distribution of YSES 1 b and its circumplanetary disc

Alexander D. Hedglen; Avalon L. McLeod; Eden A. McEwen; Jared R. Males; Jay K. Kueny; Jennifer Lumbres; Jialin Li; Joseph D. Long; Kyle Van Gorkom; Laird M. Close

REVIEW 2 major objections 1 minor 1 cited by

Modeling a circumplanetary disc around YSES 1 b revises its temperature to 2854 K and radius to 1.58 Jupiter radii.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

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T0 review · grok-4.3

2026-07-01 16:36 UTC pith:MSY2J5WQ

load-bearing objection New photometry plus a basic CPD model revises YSES 1 b to hotter, smaller, and higher-mass, but the disc proxy itself is the part that needs checking. the 2 major comments →

arxiv 2605.26805 v1 pith:MSY2J5WQ submitted 2026-05-26 astro-ph.EP

The spectral energy distribution of YSES 1 b and its circumplanetary disc

Michiel Darcis , Sebastiaan Y. Haffert , Tomas Stolker , Richelle F. van Capelleveen , Matthew A. Kenworthy , Pieter J. de Visser , Laird M. Close , Olivier Guyon

show 13 more authors

Alexander D. Hedglen Parker T. Johnson Maggie Y. Kautz Jay K. Kueny Jialin Li Joseph D. Long Jennifer Lumbres Jared R. Males Eden A. McEwen Avalon L. McLeod Logan A. Pearce Lauren Schatz Kyle Van Gorkom

This is my paper

classification astro-ph.EP

keywords YSES 1 bcircumplanetary discdirect imagingsubstellar companionspectral energy distributionbrown dwarfdust extinction

verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper tests whether adding a circumplanetary disc to the spectral energy distribution fit improves the physical parameters derived for the directly imaged companion YSES 1 b. Previous models without the disc produced an object that appeared too large for its luminosity. Including dust extinction and blackbody radiation from the disc yields a significantly better match to the combined r', i', z', and archival photometry. The revised parameters place the object at higher temperature and smaller size, shifting its mass estimate into the brown dwarf regime for the system's age range.

Core claim

The central claim is that a circumplanetary disc model, represented by dust extinction plus a blackbody component, provides a significantly better fit to the photometric data than a bare object model. This changes the derived effective temperature from 1727 K to 2854 K and the radius from 3.0 RJ to 1.58 RJ, while increasing the mass to 25.7 MJ or 41.6 MJ depending on whether the system age is taken as 17 Myr or 27 Myr.

What carries the argument

The forward-modeling procedure that combines the companion's atmosphere with a circumplanetary disc represented by a dust extinction law and an additional blackbody radiation term.

Load-bearing premise

The circumplanetary disc can be represented by a simple dust extinction model plus a blackbody component without missing important physical effects or introducing large biases.

What would settle it

An independent radius measurement, for example through high-resolution imaging or spectroscopy that isolates the object's photosphere, that matches 1.58 RJ rather than 3.0 RJ would support the revised parameters.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

The mass of YSES 1 b increases into the brown dwarf range for either 17 Myr or 27 Myr system ages.
Dust extinction from the disc accounts for the previously reported large radius anomaly.
Similar radius discrepancies in other wide-orbit companions may be resolved by adding circumplanetary disc extinction.
Accurate masses and temperatures for such objects become more reliable inputs for testing formation pathways.

Where Pith is reading between the lines

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

If the simple disc model works here, it may be worth testing on other directly imaged companions that show inflated radii.
Mid-infrared observations could isolate the blackbody emission from the disc and provide an independent check.
The revised smaller radius implies the object retains a disc at a later evolutionary stage than expected for its mass.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Desk Editor's Note

New photometry plus a basic CPD model revises YSES 1 b to hotter, smaller, and higher-mass, but the disc proxy itself is the part that needs checking.

read the letter

The paper's core result is that adding a circumplanetary disc term to the SED fit for YSES 1 b changes the inferred temperature from roughly 1700 K to 2850 K and the radius from 3 RJ down to 1.6 RJ, pushing the mass estimate into the brown-dwarf range once evolutionary tracks are applied. They supply new r', i', z' photometry from MagAO-X on Magellan and combine it with existing SPHERE and NACO points, then run forward models both with and without the disc component.

The new data and the direct comparison of the two fits are the useful parts. The radius reduction is presented as a possible fix for the previously noted radius anomaly, and the mass shift is quantified for two different system ages. That gives a concrete example of how an unseen disc can bias parameters for a wide-orbit companion.

The limitation is in how the disc is represented. The model adds a dust-extinction term and a single-temperature blackbody; the abstract reports a better fit but does not show comparisons to radiative-transfer disc spectra, checks on parameter degeneracies across the observed bands, or tests with different extinction laws. Without those, it is hard to know whether the large shift in Teff and radius is driven by the object's atmosphere or partly absorbed by the disc proxy. The free parameters listed for the disc make this a real concern rather than a minor detail.

This is a focused observational note on one system. People who model directly imaged companions or track CPD signatures will want the photometry and the revised numbers. It is not broad enough to change formation theory on its own.

It should go to peer review. The observations are new, the modeling is explicit, and the central claim can be tested against the data they release. A referee can ask for more validation on the disc component without the paper being rejected outright.

Referee Report

2 major / 1 minor

Summary. The paper presents new r', i', z' photometry of the directly imaged companion YSES 1 b obtained with MagAO-X, combines it with archival VLT/SPHERE and NACO data, and performs forward modeling of the SED both with and without a circumplanetary disc (CPD). The CPD is represented by a dust-extinction term plus a single-temperature blackbody; the CPD-inclusive model is reported to yield a significantly better fit, revising Teff upward from 1727 K to 2854 K and radius downward from 3.0 RJ to 1.58 RJ, increasing the inferred mass and moving the object into the brown-dwarf regime.

Significance. If the CPD representation is shown to be unbiased, the result would demonstrate that circumplanetary material can resolve the previously noted radius anomaly for young wide-orbit companions and materially affect mass estimates derived from evolutionary tracks, with direct consequences for formation scenarios and the planetary/brown-dwarf boundary.

major comments (2)

[Methods] Methods (CPD modeling paragraph): The central claim that the CPD model produces a significantly better fit and drives the large shift in Teff and radius rests on representing the disc by a simple dust-extinction law plus single blackbody; no comparison to radiative-transfer disc spectra, no alternative extinction laws, and no posterior-predictive checks on wavelength-dependent residuals are provided to demonstrate that this proxy does not absorb atmospheric degeneracies.
[Results] Results (parameter table or text): The revised values (Teff = 2854+110-94 K, R = 1.58+0.06-0.07 RJ) are obtained only after adding the two extra CPD parameters; without reported quantitative model-comparison statistics (Δχ², evidence ratios, or cross-validation) it is impossible to judge whether the improvement exceeds what is expected from the added degrees of freedom.

minor comments (1)

[Abstract] Abstract: the mass-estimate sentence ('increases from 14+-3 MJ (17 Myr) to either 25.7+4.1-3.6 (17 Myr) or 41.6+3.6-3.4 MJ (27 Myr)') is internally inconsistent in its age assignments and should be clarified.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed report. We address each major comment below and outline the revisions we will make to strengthen the manuscript.

read point-by-point responses

Referee: [Methods] Methods (CPD modeling paragraph): The central claim that the CPD model produces a significantly better fit and drives the large shift in Teff and radius rests on representing the disc by a simple dust-extinction law plus single blackbody; no comparison to radiative-transfer disc spectra, no alternative extinction laws, and no posterior-predictive checks on wavelength-dependent residuals are provided to demonstrate that this proxy does not absorb atmospheric degeneracies.

Authors: Our CPD representation was adopted as a minimal, computationally efficient proxy to isolate the first-order effects of extinction and re-radiation. We agree that full radiative-transfer calculations and alternative extinction curves would provide stronger validation. Because performing such modeling lies outside the scope of the present study, we will revise the Methods and Discussion sections to state this limitation explicitly and to recommend more detailed disc modeling as future work. We will also add residual plots versus wavelength so that readers can directly inspect any systematic trends. revision: partial
Referee: [Results] Results (parameter table or text): The revised values (Teff = 2854+110-94 K, R = 1.58+0.06-0.07 RJ) are obtained only after adding the two extra CPD parameters; without reported quantitative model-comparison statistics (Δχ², evidence ratios, or cross-validation) it is impossible to judge whether the improvement exceeds what is expected from the added degrees of freedom.

Authors: The manuscript already lists the χ² values obtained with and without the CPD component. To quantify the improvement relative to the two additional free parameters, we will add in the revised Results section the Δχ², the reduced χ² for each model, and an AIC comparison. These statistics will be presented alongside the parameter table so that the significance of the fit improvement can be evaluated directly. revision: yes

Circularity Check

0 steps flagged

No significant circularity; forward-model fit to photometry is independent of inputs

full rationale

The derivation consists of acquiring new r'i'z' photometry, combining it with archival data, and performing forward modeling to fit atmospheric parameters both with and without an added CPD component (dust extinction + single blackbody). No equations are presented that define a quantity in terms of itself, no fitted parameters are relabeled as predictions, and no load-bearing premise reduces to a self-citation chain. The central result (shifted Teff and radius) is the direct numerical output of the fit to external photometric measurements; the CPD representation is an explicit modeling choice whose validity can be tested against other data or models outside the present fit. This is the standard, non-circular workflow for SED parameter estimation.

Axiom & Free-Parameter Ledger

3 free parameters · 1 axioms · 0 invented entities

The central claim depends on the validity of the forward-modeling procedure, the specific representation of the CPD, and the evolutionary models used to convert luminosity to mass; several parameters are fitted directly to the photometric data.

free parameters (3)

effective temperature = 2854 K
Fitted parameter in the SED model with CPD component
radius = 1.58 RJ
Fitted parameter in the SED model with CPD component
CPD dust extinction and blackbody parameters
Additional parameters introduced to represent the circumplanetary disc and fitted to the data

axioms (1)

domain assumption Evolutionary models accurately convert the derived bolometric luminosity to mass for the assumed system ages (17 Myr or 27 Myr).
Invoked when estimating mass from luminosity after SED fitting.

pith-pipeline@v0.9.1-grok · 6003 in / 1459 out tokens · 44002 ms · 2026-07-01T16:36:55.631510+00:00 · methodology

0 comments

read the original abstract

Context. Direct imaging enables the characterisation of substellar companions on wide orbits. These objects provide a testbed for our formation theories; therefore, it is important to obtain accurate physical parameters for them. One of these objects is YSES 1 b. Aims. Our objective is to improve the spectral energy distribution (SED) modelling of YSES 1 b and determine the bulk and atmospheric parameters. Methods. We obtained observations in the r', i', and z' bands using MagAO-X on the 6.5 metre Magellan Clay telescope at Las Campanas Observatory. We combined this data with archival VLT/SPHERE and VLT/NACO data and used a forward modelling approach to estimate the physical parameters. We tested models both without and with a circumplanetary disc (CPD) model. We represented the CPD by including a dust extinction model and a blackbody radiation component. Using the derived bolometric luminosity, we estimated the mass of YSES 1 b by fitting evolutionary models. Results. Including the CPD model provides a significantly better fit to the photometric data, yielding an object that is considerably warmer (2854+110-94 K vs 1727+172-127 K) and smaller (1.58+0.06-0.07 RJ vs 3.0+0.2-0.7 RJ) than previous estimates. The newly determined radius suggests that the addition of dust extinction could resolve the large radius anomaly identified previously. Depending on the age of the system, the estimated mass increases from 14+-3 MJ (17 Myr) to either 25.7+4.1-3.6 (17 Myr) or 41.6+3.6-3.4 MJ (27 Myr). Conclusions. Dust extinction and blackbody radiation from a CPD can substantially change the estimated physical parameters of an object. For YSES 1 b, this moves it into the brown dwarf regime.

Figures

Figures reproduced from arXiv: 2605.26805 by Alexander D. Hedglen, Avalon L. McLeod, Eden A. McEwen, Jared R. Males, Jay K. Kueny, Jennifer Lumbres, Jialin Li, Joseph D. Long, Kyle Van Gorkom, Laird M. Close, Lauren Schatz, Logan A. Pearce, Maggie Y. Kautz, Matthew A. Kenworthy, Michiel Darcis, Olivier Guyon, Parker T. Johnson, Pieter J. de Visser, Richelle F. van Capelleveen, Sebastiaan Y. Haffert, Tomas Stolker.

**Figure 2.** Figure 2: YSES 1 SED fit. The photometric points are colour-coded [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 3.** Figure 3: Top: Spectral energy distribution (SED) fit of YSES 1 b using MagAO-X, SPHERE, and NACO data using only an at [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗

**Figure 4.** Figure 4: Top: Spectral energy distribution (SED) fit of YSES 1 b using MagAO-X, SPHERE, and NACO data using an atmospheric [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗

**Figure 5.** Figure 5: Comparison of ground-based photometry and our best-fit [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗

discussion (0)

Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

Parameter Effects in Circumplanetary Disk Spectra and Prospects for Spectral Fitting
astro-ph.EP 2026-06 unverdicted novelty 3.0

A parameter-grid radiative-transfer study maps the effects of CPD structure and dust properties on IR spectra and demonstrates spectral fitting to observations.

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages · cited by 1 Pith paper

[1]

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work page arXiv 2014

[1] [1]

2013, Proceedings of the International Astronomical Union, 8, 271 Allard, F., Homeier, D., & Freytag, B

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[2] [2]

C.1: The posterior distributions for the stellar SED fit using the BT-Settl-CIFIST model

Teff = 4708+30 33 K 3.5 4.0 4.5 5.0 log g log g = 4.46+0.38 0.46 0.98 1.00 1.02 1.04 R (R ) R = 1.02+0.01 0.01 R 10.615 10.630 10.645 10.660 (mas) = 10.63+0.01 0.01 mas 0.025 0.050 0.075 0.100 AV AV = 0.06+0.03 0.04 46404680472047604800 Teff (K) 0.36 0.35 0.34 0.33 log L /L 3.5 4.0 4.5 5.0 log g 0.98 1.00 1.02 1.04 R (R ) 10.61510.63010.64510.660 (mas) 0....

work page arXiv 2014