pith. sign in

arxiv: 2604.10140 · v1 · submitted 2026-04-11 · 🌌 astro-ph.IM · astro-ph.EP

A seeing measurement device for the PoET solar telescope

Bachar Wehbe , Andr\'e Silva , Manuel Abreu , Alexandre Cabral , Nuno Santos , Pit S\"utterlin This is my paper

Pith reviewed 2026-05-10 15:49 UTC · model grok-4.3

classification 🌌 astro-ph.IM astro-ph.EP
keywords solar seeingscintillationdaytime turbulencePoET telescopeParanalseeing monitorsolar spectroscopyatmospheric characterization
0
0 comments X

The pith

We built and validated a dedicated solar seeing monitor that uses scintillation to measure daytime atmospheric turbulence at Paranal for the PoET telescope.

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

The paper presents the design, commissioning, and initial on-sky tests of a new instrument for measuring daytime atmospheric seeing at the Paranal site in Chile. The device exploits a 1993 quantitative link between seeing and scintillation, treating the Sun as a bright extended source to avoid needing a full telescope. Accurate daytime seeing data are required to choose the best observing aperture on PoET, which feeds high-resolution spectra of the Sun into ESPRESSO to study the noise sources that limit ultra-precise radial-velocity exoplanet searches.

Core claim

We have developed and implemented a dedicated solar seeing monitor for daytime deployment at Paranal, Chile, where PoET will operate. The instrument exploits the quantitative relationship between seeing and scintillation established in 1993, using the Sun as an extended bright source and non-telescopic optics. Commissioning and initial on-sky validation results demonstrate its readiness to support selection of optimal apertures between 1 and 55 arcseconds for PoET's spatially resolved solar spectroscopy.

What carries the argument

The solar seeing monitor, a compact non-telescopic instrument that converts measured solar scintillation intensity fluctuations into seeing estimates via the 1993 seeing-scintillation relation.

If this is right

  • The monitor supplies the seeing data needed to select the optimal 1-55 arcsecond aperture for each PoET observation.
  • It enables reliable characterization of daytime atmospheric turbulence at Paranal for solar-proxy studies of stellar noise.
  • Validated performance supports PoET's goal of feeding clean solar spectra into ESPRESSO for ultra-high-precision radial-velocity work.
  • The device provides a practical, low-cost tool for ongoing daytime seeing monitoring at the PoET site.

Where Pith is reading between the lines

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

  • Similar scintillation-based monitors could be replicated at other solar observatories to improve daytime site characterization.
  • Long-term data from the monitor might reveal seasonal or diurnal patterns in Paranal daytime seeing that affect solar spectroscopy planning.
  • Integration with real-time control systems could allow PoET to adjust aperture size dynamically as seeing changes.

Load-bearing premise

The 1993 quantitative relationship between seeing and scintillation applies accurately to this instrument configuration and Paranal daytime conditions without significant unaccounted systematics.

What would settle it

Independent daytime seeing measurements at Paranal that consistently disagree with simultaneous readings from this monitor would show the assumed scintillation-to-seeing conversion does not hold for the site or hardware.

Figures

Figures reproduced from arXiv: 2604.10140 by Alexandre Cabral, Andr\'e Silva, Bachar Wehbe, Manuel Abreu, Nuno Santos, Pit S\"utterlin.

Figure 1
Figure 1. Figure 1: Optical layout of a scintillometer tube. The components are (from left to right): Neutral Density filter, lens, bandpass filter, field stop, photodi￾ode. All components are off-the-shelf. prevailing seeing conditions. We point to Seykora (1993) for details on the principle. In the following subsections, we will detail the opto-mechanical design, the electronics design, and the software design of the instru… view at source ↗
Figure 2
Figure 2. Figure 2: General schematic of the PCB showing its main functions. Note that a more detailed design can be accessed upon request from the authors. The analog outputs from the six SHABAR scintillometers are connected to twelve single-ended analog input channels of the data acquisition board NI USB-6218 digitizer via high-quality, shielded coaxial cables, ensuring signal integrity and minimizing electromagnetic interf… view at source ↗
Figure 3
Figure 3. Figure 3: The geometry of the beams defined by the source and detectors intersecting the turbulence: 𝑜 and 𝑜 ′ are the height at which the cones from two detectors intersect. The separation between the detectors is denoted by 𝑟 and 𝑟 ′ . the top of the solar telescope tower (16 m above ground layer) where the 𝑆𝐻 𝐴𝐵𝐴𝑅𝑆 is installed (see [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: AC (top) and DC (bottom) raw signals over Box 0 for one day of observation (30𝑡ℎ of July, 2025). with a value of -9 V. For consistency sake, we fully rejected the data from box 3 for the seeing calculation that will be presented later on. The jumps in the DC signal, more clear on the last two days, are due to the meridian flip where we had to stop, perform the flip of the mount manually, and resume data co… view at source ↗
Figure 6
Figure 6. Figure 6: AC (top) and DC (bottom) raw signals over the full commissioning period. The difference in the amplitude of the AC signal is due to different jumper position across the days. validated the stability and uniformity of the detector channels, ensuring consistent normalization across scintillometers. On-sky commissioning at the Swedish Solar Telescope demon￾strated that the instrument delivers reliable and tem… view at source ↗
Figure 7
Figure 7. Figure 7: 𝑟0 (top) and seeing (bottom) time series obtained over one day (30𝑡ℎ of July, 2025). The binned data over a 1-minute period is also shown. Freitas, D. B., Delgado-Mena, E., Delisle, J.-B., Ehrenreich, D., Faria, J., Figueira, P., Fontinele, D. O., Forveille, T., Gagné, J., Genolet, L., Témich, F. G., Hernandez, O., Hobson, M. J., Hoeijmakers, J., Hubin, N., Jahandar, F., Jayawardhana, R., Käufl, H.-U., Ker… view at source ↗
Figure 10
Figure 10. Figure 10: Validation of the 𝑆𝐻 𝐴𝐵𝐴𝑅𝑃 vs 𝑆𝐻 𝐴𝐵𝐴𝑅𝑆. In the upper pannel, the raw seeing results are shown for the 𝑆𝐻 𝐴𝐵𝐴𝑅𝑃 and 𝑆𝐻 𝐴𝐵𝐴𝑅𝑆 (as reduced by SST). In the lower panel, we show a zoom in on the results. Besides the 1𝑠𝑡 one hour of observation, the two instruments are showing similar results in terms of variation and amplitude. The results are shown for one day of observation (30𝑡ℎ of July, 2025). A., 2000. Th… view at source ↗
Figure 9
Figure 9. Figure 9: top pannel: scatter plot of the 𝑆𝐻 𝐴𝐵𝐴𝑅𝑆 data reduced by the PoET pipeline vs 𝑆𝐻 𝐴𝐵𝐴𝑅𝑆 reduced by the SST; bottom pannel: scatter plot of the 𝑆𝐻 𝐴𝐵𝐴𝑅𝑃 data vs the 𝑆𝐻 𝐴𝐵𝐴𝑅𝑆 reduced by the SST. We also show the regression line with the corresponding slope of each plot. Mégevand, D., Molaro, P., Riva, M., Zapatero Osorio, M. R., Amate, M., Manescau, A., Pasquini, L., Zerbi, F. M., Adibekyan, V., Abreu, M., Af… view at source ↗
read the original abstract

Atmospheric seeing arises from stochastic fluctuations in the refractive index of the Earth's atmosphere, producing random variations in the apparent direction of incoming light from astronomical sources. Scintillation refers to the associated intensity fluctuations induced by these refractive index inhomogeneities. A quantitative relationship between seeing and scintillation was established in 1993, enabling daytime seeing measurements by exploiting the Sun as an extended, bright source and using non-telescopic instrumentation. PoET, the Paranal solar ESPRESSO Telescope, will feed the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, ESPRESSO, at the European Southern Observatory (ESO) Very Large Telescope (VLT). By using the Sun as a proxy for solar-type stars, PoET will facilitate detailed investigations of the physical processes that drive stellar noise in ultra-high-precision radial-velocity measurements for exoplanet studies. The instrument is capable of targeting any region on the solar disk and acquiring spatially resolved spectra over areas ranging from 1 to 55 arcseconds. Accurate characterization of daytime atmospheric seeing is therefore essential for selecting the optimal observing aperture and ensuring the scientific performance of PoET. To support this requirement, we have developed and implemented a dedicated solar seeing monitor for daytime deployment at Paranal, Chile, where PoET will operate. In this work, we describe the instrument design and present the results from commissioning and initial on-sky validation.

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 describes the design and implementation of a dedicated solar seeing monitor for the PoET solar telescope at Paranal, Chile. It exploits the quantitative relationship between seeing and scintillation established in 1993, using the Sun as an extended source for daytime measurements, and reports results from instrument commissioning and initial on-sky validation to support aperture selection for PoET's high-precision radial-velocity observations.

Significance. If the on-sky validation holds with demonstrated accuracy, the instrument would provide a practical, non-telescopic tool for routine daytime seeing characterization at a premier site, directly enabling optimized observing strategies for PoET and similar solar telescopes. The work fills a specific operational gap for solar astronomy at Paranal.

major comments (2)
  1. [On-sky validation] On-sky validation section: The central claim of successful commissioning and validation rests on the direct transfer of the 1993 seeing-scintillation relation to the monitor's pupil geometry, wavelength band, integration time, and Paranal daytime boundary-layer conditions. No independent cross-check (e.g., simultaneous comparison with a co-located DIMM or MASS) is described to isolate potential systematics, which is load-bearing for asserting that the device delivers accurate seeing values for PoET aperture selection.
  2. [Abstract and results] Results presentation: The abstract asserts quantitative commissioning and validation outcomes, yet the provided summary supplies no error bars, statistical metrics, comparison values, or exclusion criteria. This omission prevents verification that the measured scintillation-to-seeing conversion performs as required under the target conditions.
minor comments (2)
  1. [Instrument design] Clarify the exact pupil diameter, filter bandpass, and sampling cadence of the monitor in the instrument design section to allow readers to assess compatibility with the 1993 assumptions.
  2. The manuscript would benefit from a short table summarizing key performance metrics (e.g., seeing range, precision, comparison residuals) from the on-sky tests.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive and detailed comments, which help clarify the strengths and limitations of our work. We address each major point below and propose targeted revisions to improve the manuscript.

read point-by-point responses

  1. Referee: [On-sky validation] On-sky validation section: The central claim of successful commissioning and validation rests on the direct transfer of the 1993 seeing-scintillation relation to the monitor's pupil geometry, wavelength band, integration time, and Paranal daytime boundary-layer conditions. No independent cross-check (e.g., simultaneous comparison with a co-located DIMM or MASS) is described to isolate potential systematics, which is load-bearing for asserting that the device delivers accurate seeing values for PoET aperture selection.

    Authors: We acknowledge that the validation relies on transferring the 1993 relation without an independent cross-check against DIMM or MASS. Simultaneous observations with those instruments were not feasible during the initial commissioning due to site scheduling and resource constraints. In the revised version, we will expand the on-sky validation section with a new subsection explicitly discussing the assumptions in the transfer (pupil geometry, wavelength band, integration time, and daytime boundary-layer specifics), potential systematics, and quantitative uncertainty estimates from the available data. We will also clarify how these affect the reliability for PoET aperture selection. revision: partial

  2. Referee: [Abstract and results] Results presentation: The abstract asserts quantitative commissioning and validation outcomes, yet the provided summary supplies no error bars, statistical metrics, comparison values, or exclusion criteria. This omission prevents verification that the measured scintillation-to-seeing conversion performs as required under the target conditions.

    Authors: We agree that the abstract should include quantitative details for transparency. We will revise the abstract to report key commissioning and validation metrics, including measured seeing ranges with uncertainties, relevant statistical measures, and any comparison or exclusion criteria applied to the data. These will be drawn directly from the results section to allow readers to evaluate the scintillation-to-seeing conversion performance. revision: yes

standing simulated objections not resolved
  • We do not have simultaneous DIMM or MASS data for an independent cross-check and cannot add such a comparison without new observations.

Circularity Check

0 steps flagged

No circularity; instrument paper uses external 1993 relation and reports independent commissioning data.

full rationale

The manuscript is an instrument description and validation report. It cites the 1993 seeing-scintillation relation as an established external result (not derived or fitted here) to convert scintillation measurements to seeing values. No equations, parameters, or predictions within the paper reduce to self-definitions, self-citations, or fitted inputs by construction. Commissioning and on-sky results serve as external benchmarks rather than tautological outputs. The derivation chain is therefore self-contained with no load-bearing circular steps.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the validity of an external 1993 relationship and the unverified performance of the new hardware; no free parameters or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption A quantitative relationship between seeing and scintillation was established in 1993
    Invoked as the enabling principle for daytime seeing measurements using the Sun.

pith-pipeline@v0.9.0 · 5566 in / 1119 out tokens · 46862 ms · 2026-05-10T15:49:15.196040+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages

  1. [1]

    4853 ofSociety of Photo- Optical Instrumentation Engineers (SPIE) Conference Series, pp

    The1-meterSwedishsolartelescope,inInnovative Telescopes and Instrumentation for Solar Astrophysics, vol. 4853 ofSociety of Photo- Optical Instrumentation Engineers (SPIE) Conference Series, pp. 341–350. ed. Schroeder, D. J., 2000.Astronomical optics. Seykora, E. J., 1993. Solar Scintillation and the Monitoring of Solar Seeing, Sol. Phys.,145(2), 389–397. ...

    work page 2000

  2. [2]

    Seeing measurements with autonomous, short-baseline shadow bandrangers,inGround-based and Airborne Telescopes III,vol.7733of Society of Photo-Optical Instrumentation Engineers (SPIE) Confer- ence Series, p. 77334L. Thompson, S. J., Queloz, D., Baraffe, I., Brake, M., Dolgopolov, A., Fisher, M., Fleury, M., Geelhoed, J., Hall, R., González Hernández, J. I....

    work page 2016