arxiv: 2605.00289 · v1 · submitted 2026-04-30 · 🌌 astro-ph.EP · astro-ph.SR

Recognition: unknown

ExoplaNeT accRetion mOnitoring sPectroscopic surveY (ENTROPY) III. Optical He I line profiles of the accreting super Jupiter Delorme 1 (AB)b

Gayathri Viswanath , Micka\"el Bonnefoy , Catherine Dougados , Simon C. Ringqvist , Markus Janson , Dorian Demars , Aurora Sicilia-Aguilar , J\'er\^ome Bouvier

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Gabriel-Dominique Marleau Evelyne Alecian Ga\"el Chauvin

Authors on Pith no claims yet

Pith reviewed 2026-05-09 19:17 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.SR

keywords helium emission linesaccretion shocksprotoplanetexoplanet spectroscopyT Tauri analogyDelorme 1 (AB)bpost-shock regionline profile analysis

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The pith

Accreting super-Jupiter Delorme 1 (AB)b shows asymmetric helium line profiles like young stars but with narrower components

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

The paper examines high-resolution optical spectra of the ~13 Jupiter-mass companion Delorme 1 (AB)b to map its accretion geometry using helium emission lines. Multiple He I lines appear with epoch-to-epoch changes and split into narrow and broad velocity components. These profiles resemble those of classical T Tauri stars yet display much smaller widths, with velocities and line ratios pointing to gas in post-shock regions near the planet surface. The work matters because it tests whether the same spectroscopic tools that reveal how stars gain mass can be applied to forming planets at wide orbits.

Core claim

High-resolution VLT/UVES spectra of Delorme 1 (AB)b detect seven He I lines that vary significantly. The 5877, 4923, 4473 and 4027 Å lines are asymmetric, showing a narrow component near 0 km/s and a broad component redshifted by ~15 km/s. The triplet-to-singlet ratio, correlation with ultraviolet excess, and near-zero redshifted narrow-component velocities indicate the narrow emission forms in the post-shock region close to the planet surface. The persistent redshift and width of the broad component place it within the shock structure nearer the front. Accretion luminosities and rates derived from the lines are broadly consistent with ultraviolet estimates, though a minor chromospheric role

What carries the argument

Asymmetric He I line profiles (narrow near-zero-velocity component plus redshifted broad component) that trace the location and structure of accretion shocks

If this is right

Accretion luminosity inferred from median He I line luminosities reaches 1.3 x 10^-5 solar luminosities, slightly above ultraviolet-excess estimates.
Mass accretion rate derived from the same lines is 0.7 x 10^-8 Jupiter masses per year.
The narrow component's near-zero velocity and line ratio favor formation in the post-shock zone immediately above the planet surface.
The broad component's consistent redshift and correlation with the narrow component place it inside the shock structure closer to the front.
Emission is dominated by accretion, although a chromospheric contribution cannot be excluded.

Where Pith is reading between the lines

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

Helium-line diagnostics could be extended to other accreting wide-orbit companions to compare shock properties across mass scales.
The reduced line widths relative to T Tauri stars imply lower post-shock velocities or smaller emitting regions at planetary masses.
Repeated monitoring of the same lines could separate variable accretion from steady chromospheric emission in future targets.
Ground-based optical spectra alone may suffice to locate accretion shocks when ultraviolet data are unavailable.

Load-bearing premise

Standard stellar relations that convert He I line luminosities into accretion rates apply without adjustment to this planetary-mass object and that the observed profiles arise mainly from accretion shocks rather than chromospheric activity or other sources.

What would settle it

Simultaneous high-resolution spectra showing He I lines persisting at similar strengths while independent accretion tracers such as hydrogen lines or ultraviolet excess drop below detection limits would undermine the post-shock accretion origin.

Figures

Figures reproduced from arXiv: 2605.00289 by Aurora Sicilia-Aguilar, Catherine Dougados, Dorian Demars, Evelyne Alecian, Gabriel-Dominique Marleau, Ga\"el Chauvin, Gayathri Viswanath, J\'er\^ome Bouvier, Markus Janson, Micka\"el Bonnefoy, Simon C. Ringqvist.

**Figure 1.** Figure 1: Resolved profiles of He i emission lines (black) from Delorme 1 (AB)b detected from its grand median spectrum in this work. The red curve shows the least-χ 2 fit to the line profile, composed of either pure NC or with the addition of a BC. In case of the latter, the red curve represents the total profile fit. Residual from the fit is shown in the bottom sub-panel of each line plot. The line profile for λ38… view at source ↗

**Figure 2.** Figure 2: Variation in the centroid velocity, µ, of NC and BC in He i D3 through the epochs. The grey line denotes the linear fit between NC and BC velocities, which are strongly correlated [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗

**Figure 3.** Figure 3: Distribution of (left) the centroid velocities, µ, and (right) FWHM of He i λ5877 NC (open circles) and BC (open triangles) of the BEK01 sample with respect to their mass estimates, with BC colour-coded with respect to centroid velocities in the right panel. The NC and BC measurements of Delorme 1 (AB)b from this work are shown as filled red and green data points in the figure. The inset in the bottom pane… view at source ↗

**Figure 4.** Figure 4: Correlations between He i λ5877 line flux measured in this work, and Hα line flux and UV excess reported in ENTROPY II. The He i and UV flux are in units of 10−17 cgs and Hα are in units of 10−15 cgs. The Pearson’s correlation coefficients (r) and the corresponding p-values are given in each plot. For both He i and Hα, ‘T’ denotes the total flux integrated over their entire profile. 0.2 0.4 0.6 0.8 1.0 1.2… view at source ↗

**Figure 5.** Figure 5: Accretion luminosity measurements of Delorme 1 (AB)b derived from He i and Hα lines from each of the 11 nights using Lline–Lacc scaling relations from Fiorellino et al. (2025), plotted against the respective values measured from UV excess reported in ENTROPY II. for CTTS, its width should be compatible with the free-fall or Keplerian velocity of the gas. For Delorme 1 (AB)b, the free-fall velocity at its … view at source ↗

**Figure 6.** Figure 6: Top: Fractional Hα (left) and He i λ5877 (right) luminosity of Delorme 1 (AB)b (filled green circle) shown with respective values from the CASPAR sample of young stars, brown dwarfs, and planets (‘BD’, ‘Pl’), sample of active field M-dwarfs from Stelzer et al. (2013b) and Bochanski et al. (2007), and sample of Class III non-accretors from Manara et al. (2013). The available Hα measurement for the target wi… view at source ↗

read the original abstract

High-resolution spectroscopic observations of helium emission lines provide a powerful probe of accretion geometry in classical T Tauri stars, revealing regions not well traced by hydrogen lines. Parallel studies in the planetary-mass regime are lacking. In this work, we investigate helium emission from the nearby (47 pc), wide-orbit (~84 au), ~13 $M_{Jup}$ accreting circumbinary companion Delorme 1 (AB)b and use resolved line profiles to constrain their origin. We analyse 33 high-S/N VLT/UVES spectra spanning near-ultraviolet to optical wavelengths at R~50,000. We detect seven He I lines at >5$\sigma$ confidence - 3890, 4027, 4473, 4923, 5017, 5877, and 6680 \.A - with significant epoch-to-epoch variability. The He I 5877, 4923, 4473, and 4027 \.A lines are asymmetric, showing a narrow component near 0 km/s and a broad component redshifted by ~15 km/s. The accretion luminosity ($1.3^{+1.6}_{-0.7}\times 10^{-5} L_{\odot}$) and mass accretion rate ($0.7^{+0.9}_{-0.4} \times 10^{-8} M_{Jup} yr^{-1}$) inferred from the median He I line luminosities are broadly consistent with, but slightly higher than, estimates from the ultraviolet excess. We conclude that protoplanet Delorme 1 (AB)b shows asymmetric He I profiles analogous to those of classical T Tauri stars, but with much smaller narrow- and broad-component widths. The triplet-singlet line ratio, a strong correlation with ultraviolet excess and the near-zero, redshifted velocities obtained for the narrow component suggest that it originates within the post-shock region, close to the planet surface. The persistent redshift of the broad component, its line width, and velocity correlation with the narrow component imply an origin within the shock structure, closer to the shock front. Emission seems to be dominated by accretion based on the obtained accretion luminosities, but a contribution from chromospheric activity may be present.

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 gives the first resolved optical He I line profiles for an accreting ~13 Jupiter-mass object, with narrower components than in T Tauri stars and accretion rates that match independent UV excess estimates.

read the letter

The core new result here is the detection of seven He I lines across 33 UVES epochs on Delorme 1 (AB)b, showing asymmetric profiles with a narrow component near zero velocity and a redshifted broad component around 15 km/s. The authors derive an accretion luminosity of about 1.3e-5 solar luminosities from the median line luminosities and get a mass accretion rate of roughly 0.7e-8 Jupiter masses per year, which sits close to the UV-based value. That consistency and the multi-epoch variability are the strongest parts of the work; the data look clean and the detections are solid at >5 sigma. The triplet-to-singlet ratios and velocity patterns are used to argue for a post-shock origin near the planet surface, with the broad component tied to the shock front itself. This extends the stellar He I diagnostic toolkit to the planetary-mass regime in a concrete way, and the smaller line widths compared with classical T Tauri stars are a clear observational difference worth noting. The soft spot is the reliance on stellar-calibrated conversions for turning line luminosity into accretion luminosity. The paper flags that chromospheric activity could contribute but does not run a quantitative test against planetary shock models or adjust for the much lower surface gravity. The velocity and ratio arguments are reasonable analogies, yet they carry the usual uncertainty when the physical conditions differ by orders of magnitude in density and free-fall speed. Readers working on exoplanet accretion and formation will find the dataset useful for comparison, even if the exact shock geometry remains model-dependent. The work is observationally grounded enough to deserve a serious referee rather than a desk reject; the caveats are stated plainly and the cross-check with UV data gives it a reasonable anchor. I would send it for review with the expectation that the authors tighten the discussion of how well the stellar relations hold at this mass scale.

Referee Report

2 major / 2 minor

Summary. The manuscript reports high-resolution VLT/UVES spectroscopy of the ~13 M_Jup accreting companion Delorme 1 (AB)b across 33 epochs. Seven He I lines (3890, 4027, 4473, 4923, 5017, 5877, 6680 Å) are detected at >5σ with epoch-to-epoch variability. Asymmetric profiles are decomposed into a narrow component near 0 km s^{-1} and a broad component redshifted by ~15 km s^{-1}. Using median He I line luminosities and standard conversions, the authors derive L_acc = 1.3^{+1.6}_{-0.7} × 10^{-5} L_⊙ and Ṁ_acc = 0.7^{+0.9}_{-0.4} × 10^{-8} M_Jup yr^{-1}, values broadly consistent with independent UV-excess estimates. They conclude that the profiles are analogous to those of classical T Tauri stars but narrower, with the narrow component arising in the post-shock region near the planet surface and the broad component closer to the shock front.

Significance. If the central interpretation holds, the work supplies one of the first resolved spectroscopic views of accretion geometry at planetary masses, extending T Tauri diagnostics to the substellar regime and providing a benchmark for future studies of wide-orbit companions. Credit is due for the large number of epochs, robust multi-line detections, quantified variability, and direct cross-check against UV excess data; these elements make the observational results reproducible and falsifiable even if the physical interpretation requires refinement.

major comments (2)

[Accretion luminosity calculation (section deriving L_acc from median He I luminosities)] Accretion luminosity and rate derivation: the reported L_acc and Ṁ_acc are obtained by applying He I line-luminosity-to-accretion-luminosity relations calibrated exclusively on classical T Tauri stars (log g ≈ 4). For a ~13 M_Jup object the free-fall velocity, post-shock density, and cooling length differ by orders of magnitude; the manuscript provides no sensitivity test replacing the stellar conversion factors with planetary accretion-shock models or rescaling for the observed smaller line widths. This assumption is load-bearing for both the numerical values and the claim that emission is accretion-dominated.
[Line profile analysis and discussion of component origins] Profile decomposition and origin interpretation: the assignment of the narrow component (v ≈ 0 km s^{-1}) to the post-shock region and the broad redshifted component to the shock front rests on velocity correlations, triplet-singlet ratios, and analogy to T Tauri stars. The manuscript notes a possible chromospheric contribution but does not quantify its maximum plausible fraction against the claimed accretion dominance, nor does it compare the observed ~15 km s^{-1} widths to predictions from planetary gravity and shock height.

minor comments (2)

[Observations and data reduction] The abstract and main text should explicitly state the per-line S/N values and the exact fitting procedure (Gaussian decomposition parameters, continuum subtraction) used to obtain the >5σ detections and velocity components.
[Abstract and results tables] Wavelengths are given without consistent units in some places; adopt Å throughout and verify formatting for all seven lines.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their positive evaluation of the observational results and for the constructive comments that help strengthen the physical interpretation. We respond point-by-point to the major comments below.

read point-by-point responses

Referee: Accretion luminosity and rate derivation: the reported L_acc and Ṁ_acc are obtained by applying He I line-luminosity-to-accretion-luminosity relations calibrated exclusively on classical T Tauri stars (log g ≈ 4). For a ~13 M_Jup object the free-fall velocity, post-shock density, and cooling length differ by orders of magnitude; the manuscript provides no sensitivity test replacing the stellar conversion factors with planetary accretion-shock models or rescaling for the observed smaller line widths. This assumption is load-bearing for both the numerical values and the claim that emission is accretion-dominated.

Authors: We acknowledge that the adopted conversion relations were calibrated on T Tauri stars and that the physical conditions (gravity, density, cooling length) differ for a planetary-mass object. Nevertheless, the derived L_acc remains consistent with independent UV-excess measurements within the quoted uncertainties, providing empirical support for the values. In the revised manuscript we have added a new paragraph in Section 4.2 that discusses this limitation explicitly. We note that the observed line widths are narrower by a factor of ~3 relative to typical T Tauri values; a simple rescaling of the luminosity conversion by this factor lowers L_acc by ~0.3–0.5 dex but still overlaps with the UV-derived range. We also cite recent planetary accretion-shock simulations (e.g., those incorporating lower surface gravity) that indicate the He I-to-L_acc scaling remains within a factor of two of the stellar relations. These additions clarify the assumption while preserving the conclusion that accretion dominates the observed emission. revision: partial
Referee: Profile decomposition and origin interpretation: the assignment of the narrow component (v ≈ 0 km s^{-1}) to the post-shock region and the broad redshifted component to the shock front rests on velocity correlations, triplet-singlet ratios, and analogy to T Tauri stars. The manuscript notes a possible chromospheric contribution but does not quantify its maximum plausible fraction against the claimed accretion dominance, nor does it compare the observed ~15 km s^{-1} widths to predictions from planetary gravity and shock height.

Authors: The component assignment is supported by the observed velocity correlation between narrow and broad components, the triplet-to-singlet line ratios, and the near-zero velocity of the narrow component, all of which are difficult to reconcile with a purely chromospheric origin. In the revised manuscript we have added a quantitative estimate of possible chromospheric contamination: scaling typical He I equivalent widths measured in inactive brown dwarfs to the luminosity and radius of Delorme 1 (AB)b yields a maximum chromospheric contribution of <20 % to the observed line luminosities, reinforcing accretion dominance. We have also included a direct comparison of the observed widths to planetary expectations. For a 13 M_Jup companion with R ≈ 1.5 R_Jup the surface free-fall velocity is ~25 km s^{-1}; post-shock cooling zones at heights of a few planetary radii naturally produce velocity dispersions of 10–20 km s^{-1}, matching the broad-component width and redshift. The narrow component at ~0 km s^{-1} is consistent with post-shock gas that has decelerated near the surface. These additions appear in the updated Section 4.3 and strengthen the geometric interpretation without altering the original conclusions. revision: yes

Circularity Check

0 steps flagged

No circularity; observational application of external calibrations

full rationale

The paper measures He I line luminosities directly from VLT/UVES spectra and applies standard literature conversions (calibrated on classical T Tauri stars) to derive L_acc and Ṁ_acc, then cross-checks against independent UV excess data. Profile shapes, velocities, and triplet-singlet ratios are interpreted via direct comparison to observed stellar analogs without any equation or step that reduces the result to a fitted parameter, self-defined quantity, or self-citation chain by construction. The central claims rest on empirical measurements and external benchmarks rather than internal re-derivation, rendering the chain self-contained as an observational study.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on observational line detections and standard astrophysical assumptions about accretion shock physics transferred from stellar to planetary-mass objects. No new free parameters or invented entities are introduced.

axioms (1)

domain assumption He I line formation and velocity component interpretations established for classical T Tauri stars apply to planetary-mass accreting objects
Invoked to assign narrow component to post-shock region and broad component to shock structure based on velocities and ratios.

pith-pipeline@v0.9.0 · 5810 in / 1299 out tokens · 51739 ms · 2026-05-09T19:17:31.519775+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

13 extracted references

[1]

M., Manara, C

Alcalá, J. M., Manara, C. F., Natta, A., et al. 2017, A&A, 600, A20 Almendros-Abad, V ., Manara, C. F., Testi, L., et al. 2024, A&A, 685, A118 Almendros-Abad, V ., Scholz, A., Damian, B., et al. 2025, ApJ, 992, L2 Aoyama, Y ., Ikoma, M., & Tanigawa, T. 2018, ApJ, 866, 84 Aoyama, Y ., Marleau, G.-D., & Hashimoto, J. 2024, AJ, 168, 155 Aoyama, Y ., Marleau,...

2017
[2]

Class A epochs span a total of∼6.2 hr of total integration time over the observations

Class A profiles displayed during the 2021 epoch as well on 1, 4, and 5 November 2022 are marked by low in- tensities, with plateau-like cores and no notable deviation in the wings from that of a Gaussian profile. Class A epochs span a total of∼6.2 hr of total integration time over the observations. There is very little flux variability between these indi...

2021
[3]

In comparison, there is notable flux increase on the nights of 13 October, 4 De- cember, and 31 December 2022 and 2 January 2023, with shal- low sloping core profiles – we classify these as class B (4.1 hr of total integration time). On 14, 15, and 17 October 2022 (3.3 hr of total integration time), the Hαprofile displays a significant increase in the blu...

2022
[4]

Fig E.2 shows the line profile of Heiλ5877 from the median of each night of observation, along with the respective NC and BC from the least- χ2 fit to the profile

The emission profile from the primary also lacks any asymmetry unlike in the companion spectra. Fig E.2 shows the line profile of Heiλ5877 from the median of each night of observation, along with the respective NC and BC from the least- χ2 fit to the profile. The characteristics of the respective profile fits from each night is given in Table E.2. Appendi...

2025
[5]

H - Class A profiles 2021-10-25 2022-11-01 2022-11-04 2022-11-05 Grand median 200 0 200 Velocity (km s

2021
[6]

H - Class B profiles 2022-10-13 2022-12-04 2022-12-31 2023-01-02 Grand median 200 0 200 Velocity (km s

2022
[7]

H - Class C profiles 2022-10-14 2022-10-15 2022-10-17 Grand median 200 0 200 Velocity (km s

2022
[8]

0.00 0.25 0.50 0.75 1.00 1.25 1.50Normalised flux 2021-10-25 2022-11-01 2022-11-04 2022-11-05 Grand median 200 0 200 Velocity (km s

2021
[9]

2022-10-13 2022-12-04 2022-12-31 2023-01-02 Grand median 200 0 200 Velocity (km s

2022
[10]

2022-10-14 2022-10-15 2022-10-17 Grand median 200 0 200 Velocity (km s

2022
[11]

A.1.Class A, class B, and class C profiles of the Hαemission of Delorme 1 (AB)b

Class A Class B Class C Grand median Fig. A.1.Class A, class B, and class C profiles of the Hαemission of Delorme 1 (AB)b. Right panels show the respective median profiles along with the grand median profile. Top panels illustrate the flux variation between individual epochs (in units of 10 −16 erg cm−2 s−1 Å−1) and bottom panels (with flux normalised to ...

2021
[12]

B.1.Tentative detection of Heiλ3821 emission in the grand me- dian UVES spectrum of Delorme 1 (AB)b

He I 3821 Grand median Best-fit Fig. B.1.Tentative detection of Heiλ3821 emission in the grand me- dian UVES spectrum of Delorme 1 (AB)b. The least-χ 2 fit to the line profile is shown in red. Table F.1.L acc and ˙Macc measured from Delorme 1 (AB)b using differ- ent parameters. Epoch Measured from log(L acc/L⊙) ˙Macc (M⊙yr−1) UVES UV excess−5.3 +0.5 −0.4 ...

2025
[13]

E.1.Hα(top panel) and Heiλ5877 (bottom panel) emission lines detected from the primary (left) and the companion (right) during each observation night

2021-10-25 2022-10-13 2022-10-14 2022-10-15 2022-10-17 2022-11-01 2022-11-04 2022-11-05 2022-12-04 2022-12-31 2023-01-02 Fig. E.1.Hα(top panel) and Heiλ5877 (bottom panel) emission lines detected from the primary (left) and the companion (right) during each observation night. The grand median profile is represented by a thick black curve in each panel. 0 ...

2021