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arxiv: 2606.06898 · v1 · pith:AOYNQGNVnew · submitted 2026-06-05 · 🌌 astro-ph.IM · astro-ph.SR

MOSES -- The MONET Star and Exoplanet Spectrograph

S. Sch\"afer , L. Schmidt , H. Anwand-Heerwart , D. Jones , A. Reiners This is my paper

Pith reviewed 2026-06-27 21:11 UTC · model grok-4.3

classification 🌌 astro-ph.IM astro-ph.SR
keywords radial velocityechelle spectrographexoplanet detectionFabry-Perot etalonwhite pupil designMONET telescopehigh-resolution spectroscopy
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The pith

MOSES is a new high-resolution echelle spectrograph for the MONET telescope designed to reach radial velocity precision below 2 m/s.

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

The paper introduces MOSES as the designated instrument for the 1.2 m MONET telescope, built specifically for radial velocity experiments and activity monitoring of Sun-like stars. It describes a white pupil optical layout covering 380-680 nm at resolution above 80,000 with 3.5 pixel sampling, dual-fiber injection for simultaneous calibration, and enclosure in a vacuum vessel under temperature control. A Fabry-Pérot etalon supplies the calibration reference. These choices are presented as the route to the target precision once the instrument is installed in late 2026. A reader would care because sub-2 m/s measurements on a modest telescope could expand access to precise stellar velocity work without requiring the largest facilities.

Core claim

MOSES features a white pupil design and aims for a spectral resolution greater than 80,000 over the 380-680 nm wavelength range. It incorporates a pixel sampling rate of 3.5 and uses two fibers to facilitate a simultaneous calibration mode. Encased within a vacuum vessel and operating in a temperature-stabilized environment, MOSES is expected to achieve a radial velocity precision below 2 m/s, aided by a Fabry-Pérot etalon calibration system.

What carries the argument

The white pupil layout with dual-fiber simultaneous calibration and Fabry-Pérot etalon reference, which supplies a stable wavelength scale while the vacuum and thermal enclosure maintain mechanical stability.

If this is right

  • The instrument will support radial velocity surveys and stellar activity monitoring on the MONET 1.2 m telescope starting in 2026.
  • Simultaneous calibration with the Fabry-Pérot etalon will provide a continuous wavelength reference during science exposures.
  • The vacuum vessel and temperature control are intended to minimize instrumental drifts over long observing campaigns.
  • The 380-680 nm coverage at resolution above 80,000 will capture multiple spectral lines for velocity extraction.

Where Pith is reading between the lines

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

  • If the design meets its targets, similar fiber-fed white-pupil instruments on other 1 m class telescopes could reach comparable precision without major new infrastructure.
  • The dual-fiber mode may allow direct comparison of activity-induced signals between target and reference fibers on the same exposure.
  • Success would demonstrate that moderate-aperture telescopes can contribute to exoplanet radial-velocity follow-up when equipped with vacuum-stabilized spectrographs.

Load-bearing premise

The assumption that the white pupil design, dual-fiber injection, vacuum enclosure, and temperature stabilization will together deliver the stated spectral resolution and RV precision once installed and commissioned.

What would settle it

On-sky measurement of radial velocity scatter on a set of stable reference stars after installation and commissioning in 2026.

Figures

Figures reproduced from arXiv: 2606.06898 by A. Reiners, D. Jones, H. Anwand-Heerwart, L. Schmidt, S. Sch\"afer.

Figure 1
Figure 1. Figure 1: Schematic overview of the instrument design. [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: The MONET/N telescope next to the planned MOSES building and the existing transformer station. [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The planned MOSES building: The instrument is located inside a commercial walk-in freezer (green [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Modes of operation of the FE: Optical setup between telescope focus (lower left), ADC, tip-tilt [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Left: Optical performance of the science mode for the center, 141 and 200 arcsec off center positions. [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: CAD image of the FE unit without the cover plates. [PITH_FULL_IMAGE:figures/full_fig_p010_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: CAD image of the instrument selction unit. [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Spectrograph configuration. 4.3 Ghost and Stray Light Considerations A comprehensive ghost analysis did detect some interesting features of the optical configuration. There are a couple of camera component ghosts of diameter 0.4 mm or greater which were not deemed to be problematic. These would be mitigated via good AR coatings on the lenses. In this system, CCD ghosts are a potential problem when the ghos… view at source ↗
Figure 9
Figure 9. Figure 9: Spectrograph performance. Orders from top to bottom are: 161, 148, 135, 116, 89. Rows span 1.0 [PITH_FULL_IMAGE:figures/full_fig_p013_9.png] view at source ↗
read the original abstract

We introduce MOSES, the new High-Resolution Echelle Spectrograph designated for the 1.2m MONET telescope at McDonald Observatory, Texas, USA. The science drivers are radial velocity experiments and activity monitoring in Sun-like stars. Set for installation in the final quarter of 2026, MOSES features a white pupil design and aims for a spectral resolution greater than 80,000 over the 380-680 nm wavelength range. It incorporates a pixel sampling rate of 3.5 and uses two fibers to facilitate a simultaneous calibration mode. Encased within a vacuum vessel and operating in a temperature-stabilized environment, MOSES is expected to achieve a radial velocity precision below 2 m/s, aided by a Fabry-P\'erot etalon calibration system. This paper outlines the implementation of the fiber injection unit, the optical layout of the spectrograph, and the present status of the various subsystems under development.

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 introduces MOSES, a new high-resolution echelle spectrograph for the 1.2 m MONET telescope at McDonald Observatory. It describes a white-pupil design with dual-fiber injection, vacuum enclosure, temperature stabilization, and Fabry-Pérot etalon calibration, targeting spectral resolution >80,000 over 380-680 nm and radial velocity precision below 2 m/s for Sun-like star RV experiments and activity monitoring. The paper outlines the fiber injection unit, optical layout, and development status of subsystems, with installation planned for late 2026.

Significance. If the stated performance targets are realized, MOSES would add a dedicated RV instrument to a 1.2 m telescope, enabling new exoplanet and stellar activity studies. The detailed subsystem descriptions are of practical value to the instrumentation community for similar white-pupil designs. However, the paper provides no machine-checked proofs, reproducible simulations, or empirical validation, limiting its immediate impact to a design overview.

major comments (2)
  1. [Abstract] Abstract: The central claim that MOSES 'is expected to achieve a radial velocity precision below 2 m/s' is stated as a design goal but is unsupported by any error budget (thermal, mechanical, optical, or calibration terms), end-to-end line-profile simulations, wavelength-solution residuals, or scaling from comparable instruments. This directly affects the soundness of the performance target.
  2. [Design and subsystems description] Throughout the manuscript (e.g., sections describing the vacuum vessel, temperature stabilization, and Fabry-Pérot system): No quantitative modeling or stability analysis is provided to show how the white-pupil layout, dual-fiber injection, and environmental controls combine to meet the <2 m/s target; the 2 m/s figure therefore remains an unanchored expectation rather than a derived prediction.
minor comments (2)
  1. [Abstract] The abstract and text refer to a 'pixel sampling rate of 3.5' without specifying the units or the rationale for this choice relative to the resolution target.
  2. [Present status of subsystems] The manuscript would benefit from a dedicated section or table summarizing the current development status of each subsystem (e.g., completed vs. in-progress) to clarify the timeline to the 2026 installation.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive review of our design overview for MOSES. The comments correctly note that the <2 m/s RV target is presented without supporting quantitative analysis in this pre-construction manuscript. We address the points below and have made targeted revisions to clarify the status of the performance goals while preserving the paper's scope as a design description.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central claim that MOSES 'is expected to achieve a radial velocity precision below 2 m/s' is stated as a design goal but is unsupported by any error budget (thermal, mechanical, optical, or calibration terms), end-to-end line-profile simulations, wavelength-solution residuals, or scaling from comparable instruments. This directly affects the soundness of the performance target.

    Authors: We agree the claim requires better anchoring. The manuscript is a design paper with installation planned for late 2026; full error budgets and simulations will appear in a future commissioning paper. In revision we have changed the abstract wording from 'is expected to achieve' to 'aims to achieve' and added a short paragraph in the introduction that scales the target from published performance of similar vacuum-stabilized white-pupil instruments (HARPS, ESPRESSO) that use dual-fiber FP calibration. This provides the requested scaling justification without claiming new modeling. revision: partial

  2. Referee: [Design and subsystems description] Throughout the manuscript (e.g., sections describing the vacuum vessel, temperature stabilization, and Fabry-Pérot system): No quantitative modeling or stability analysis is provided to show how the white-pupil layout, dual-fiber injection, and environmental controls combine to meet the <2 m/s target; the 2 m/s figure therefore remains an unanchored expectation rather than a derived prediction.

    Authors: We concur that no original quantitative stability analysis is included. As the instrument remains in the design phase, detailed thermal/mechanical modeling is still underway. We have added a brief qualitative subsection linking the vacuum enclosure (pressure stability), temperature control (<0.01 K), and simultaneous FP calibration to the RV goal, supported by references to equivalent subsystems in existing sub-2 m/s instruments. This makes the design rationale explicit while acknowledging the absence of new simulations. revision: partial

standing simulated objections not resolved
  • A complete quantitative error budget, end-to-end line-profile simulations, or wavelength-solution residuals cannot be supplied at present because the instrument has not been built and the associated engineering analyses are ongoing.

Circularity Check

0 steps flagged

No circularity: purely descriptive instrument design paper with no derivations

full rationale

The manuscript is a hardware design summary. It states design targets (R>80k, RV precision <2 m/s) and lists components (white-pupil layout, dual-fiber injection, vacuum vessel, Fabry-Pérot etalon) but contains no equations, no fitted parameters, no error budgets, no simulations, and no predictions derived from inputs. No self-citations, uniqueness theorems, or ansatzes appear. The <2 m/s figure is presented as an untested expectation rather than the output of any derivation chain, so no reduction to inputs exists. This is the normal case of a non-circular descriptive paper.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The paper rests on standard optical engineering assumptions about achievable resolution and stability in a white-pupil echelle design; no new physical principles or data-driven fits are introduced.

free parameters (2)
  • target radial velocity precision = <2 m/s
    Stated design goal of below 2 m/s without derivation from first principles or existing data.
  • target spectral resolution = >80,000
    Design specification of greater than 80,000 without supporting calculation in the abstract.
axioms (1)
  • domain assumption White pupil layout combined with vacuum and thermal stabilization will meet the resolution and stability targets
    Invoked as the basis for expected performance in the optical layout and environmental control description.

pith-pipeline@v0.9.1-grok · 5708 in / 1306 out tokens · 23527 ms · 2026-06-27T21:11:42.510365+00:00 · methodology

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Reference graph

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