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arxiv: 1906.11956 · v1 · pith:GTBW4CF7new · submitted 2019-06-27 · 🌌 astro-ph.SR

Multiplicity of the Orion Trapezium stars

R. Costero This is my paper

Pith reviewed 2026-05-25 14:07 UTC · model grok-4.3

classification 🌌 astro-ph.SR
keywords Orion Trapeziumstellar multiplicityspectroscopic binariesradial velocityyoung stellar clustersmassive star formationinterferometric binaries
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The pith

Component D in the Orion Trapezium is a double star with a 53-day orbit and mass ratio 0.5, while Component F is probably unrelated.

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

The paper presents early spectroscopic results on the six brightest stars in the Orion Trapezium to map their multiplicities and assess the group's stability. It finds that Component D shows both spectroscopic and interferometric signatures of a companion with half the primary mass on a 52.9-day orbit. Component B has a third body with a period near 3.5 years. Component F, classified as a chemically peculiar B star, has a radial velocity well below the cluster mean and may be more evolved than other members of similar mass. These details point to an extremely young system whose binary properties can inform how massive stars form and interact.

Core claim

Component D is a spectroscopic and interferometric double star with a relatively high-mass companion (q=M2/M1=0.5) and period 52.90±0.05 d. Component F is a CP star (B7.5 p Si) whose radial velocity of 23.2±4.2 km s^{-1} is smaller than that of all other Trapezium members; its evolutionary stage may also be more advanced than that of members with similar mass. Consequently Component F is probably not physically related to the Trapezium. The orbit of the secondary in the eclipsing Component A is highly inclined relative to the primary's equator, and the eclipsing binary BM Ori (Component B) has a tertiary member with period about 3.5 years.

What carries the argument

Combined spectroscopic radial-velocity curves and interferometric data used to solve for orbital periods, mass ratios, and inclinations of the Trapezium subsystems.

If this is right

  • The Trapezium contains at least two confirmed binaries and one triple system whose orbits will influence the group's long-term dynamical evolution.
  • The extreme youth of the system follows from the presence of short-period massive binaries and the lack of more evolved members among the bright stars.
  • The high orbital inclination of the secondary around Component A implies that its formation involved processes that misaligned the orbit with the primary's spin.
  • Continued monitoring can test whether additional companions exist and whether the group will remain bound.

Where Pith is reading between the lines

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

  • If Component F is a foreground or background object, the Trapezium's total mass and binding energy estimates must exclude it.
  • The 3.5-year tertiary around Component B could be checked for consistency with the GRAVITY interferometric detection by searching for corresponding radial-velocity variations.
  • Similar multiplicity surveys in other young massive clusters could test whether short-period high-mass binaries are a common outcome of the formation process.

Load-bearing premise

All true physical members of the Trapezium share essentially the same radial velocity within the precision of the measurements.

What would settle it

A radial-velocity measurement of Component F that matches the mean velocity of the other Trapezium stars to within a few km/s would falsify the claim that it is not associated.

Figures

Figures reproduced from arXiv: 1906.11956 by R. Costero.

Figure 1
Figure 1. Figure 1: The Orion Trapezium in a two-second exposure image [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Velocity curve of θ 1 Ori A obtained during and around seven primary eclipses, showing the abnormal Rossiter-McLaughlin effect. The horizontal axis is the photometric phase (see text for details). Col￾ors and shapes of data points correspond to different observing seasons. for his BA thesis. All together, the spectra covered the complete ingress of the eclipse and well passed the minimum light. Adopting th… view at source ↗
Figure 3
Figure 3. Figure 3: Velocity curve of the center of mass of the eclipsing binary [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
read the original abstract

Preliminary results on the ongoing spectroscopic study of the six brightest Orion Trapezium stars is presented here. The main purpose of this work is to better understand the multiplicity and stability of each of these subsystems and the dynamical future of the group. So far the most interesting results reached are: 1) The orbit of the secondary star of the eclipsing Component A (V1016 Ori) is highly inclined with respect to the equatorial plane of its primary star. 2) The also eclipsing binary BM Ori (Trapezium Component B) does have a tertiary member with period about 3.5 years, as proposed by Vitrichenko & Klochkova (2004), and is the same as the companion recently found by the GRAVITY collaboration et al. (2018}. 3) Component D is indeed a spectroscopic and interferometric double star with a relatively high-mass companion ($q=M_2/M_1=0.5$) and period $52.90\pm0.05\,d$. 4) Component F, is a CP star (B7.5 p Si); its radial velocity, $23.2\pm4.2\,km\,s^{-1}$, is smaller than that of all other Trapezium members and, possibly, the evolutionary stage of the star is more advanced than that of members with similar mass. Consequently, Component F is probably not physically related to the Trapezium. Several evidences point to the extreme youth of this stellar group; its further study, most likely, will shed light on the formation processes of massive stars.

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.

Referee Report

2 major / 2 minor

Summary. The manuscript presents preliminary spectroscopic results on the multiplicity of the six brightest Orion Trapezium stars. It claims an inclined orbit for the secondary of the eclipsing Component A, a ~3.5-year tertiary for BM Ori (Component B) matching GRAVITY interferometry, Component D as a spectroscopic/interferometric binary with mass ratio q=0.5 and period 52.90±0.05 d, and that Component F (B7.5p Si) is likely not a physical member due to its RV of 23.2±4.2 km/s being lower than other members, plus possible advanced evolutionary stage.

Significance. Confirmation of the orbital parameters for Components B and D would add useful constraints on the multiplicity and dynamical evolution of this extremely young massive-star group. The non-membership suggestion for F, if substantiated, could refine Trapezium membership criteria, though the current evidence is insufficient to support it.

major comments (2)
  1. [Abstract] Abstract, point 4: The claim that Component F is probably not physically related rests solely on its RV (23.2±4.2 km/s) being smaller than that of all other Trapezium members. No radial velocities are reported for Components A–E, no cluster mean velocity is given, and no intrinsic velocity dispersion is estimated, so it is impossible to determine whether the offset exceeds the expected 2–5 km/s dispersion plus measurement error.
  2. [Abstract] Abstract: The quoted uncertainties and derived parameters (e.g., period and q for Component D) are presented without any description of the spectroscopic data reduction, radial-velocity extraction method, orbital fitting procedure, or error budget, which are required to assess the reliability of the central multiplicity claims.
minor comments (2)
  1. [Abstract] The abstract refers to 'several evidences' for the extreme youth of the group but does not list or cite them.
  2. [Abstract] The mass-ratio notation q=M2/M1 should be explicitly defined on first use.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful review and constructive comments on our preliminary results manuscript. We respond to each major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract, point 4: The claim that Component F is probably not physically related rests solely on its RV (23.2±4.2 km/s) being smaller than that of all other Trapezium members. No radial velocities are reported for Components A–E, no cluster mean velocity is given, and no intrinsic velocity dispersion is estimated, so it is impossible to determine whether the offset exceeds the expected 2–5 km/s dispersion plus measurement error.

    Authors: We agree the abstract claim is insufficiently supported as presented. This short note reports only the new RV for F; RVs for A–E come from our ongoing campaign but were omitted here. We will revise the abstract to qualify the non-membership statement as tentative, reference the expected 2–5 km/s dispersion, and state that a full RV dataset and statistical comparison will appear in the follow-up paper. revision: partial

  2. Referee: [Abstract] Abstract: The quoted uncertainties and derived parameters (e.g., period and q for Component D) are presented without any description of the spectroscopic data reduction, radial-velocity extraction method, orbital fitting procedure, or error budget, which are required to assess the reliability of the central multiplicity claims.

    Authors: Because the manuscript is a brief preliminary report, detailed methods were deferred. To address the concern we will insert a concise methods paragraph summarizing the spectrograph, reduction pipeline, cross-correlation RV technique, and basic error sources (including the quoted uncertainties for D). Full procedures and error budget remain for the comprehensive paper. revision: yes

Circularity Check

0 steps flagged

No circularity; purely observational reporting of measured parameters

full rationale

The manuscript reports direct spectroscopic and interferometric measurements: radial velocities (e.g., 23.2±4.2 km s^{-1} for Component F), orbital periods (52.90±0.05 d for D), mass ratios (q=0.5), and inclinations. These are presented as empirical results from ongoing observations without any claimed first-principles derivations, model predictions, or parameter fits that are then re-labeled as independent outputs. No self-citations are invoked to justify uniqueness or load-bearing premises. The non-membership inference for F rests on a comparative RV statement, but this is a straightforward observational comparison rather than a reduction to prior fitted values by construction. The work is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The claims rest on standard assumptions of spectroscopic radial-velocity analysis and the interpretation of velocity differences as membership indicators. No new entities are postulated.

free parameters (2)
  • orbital period of Component D = 52.90 d
    Fitted value 52.90 d derived from spectroscopic and interferometric data.
  • mass ratio q for Component D = 0.5
    Derived mass ratio 0.5 from orbital solution.
axioms (2)
  • domain assumption Stars with discrepant radial velocities are not physically associated with the cluster.
    Invoked to conclude Component F is probably unrelated.
  • domain assumption Orbital periods can be reliably extracted from combined spectroscopic and interferometric observations.
    Underlying the reported periods for components A, B, and D.

pith-pipeline@v0.9.0 · 5812 in / 1312 out tokens · 28086 ms · 2026-05-25T14:07:19.765079+00:00 · methodology

discussion (0)

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