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arxiv: 2606.18804 · v1 · pith:2ZWI2H4Xnew · submitted 2026-06-17 · 🌌 astro-ph.IM

The atmospheric extinction curve at Lenghu site

Jin-Sheng Qiu , Xiao-Hui Xu , Qing-Feng Zhu , Xu Kong , Ting-Gui Wang , Lu-Lu Fan , Yong-Quan Xue , Ji-An Jiang
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Zheng Lou Xu Zhou Xu-Zhi Li Bo-Jun Tao Jun-Han Zhao Zhi-Yong Pu
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Pith reviewed 2026-06-26 19:41 UTC · model grok-4.3

classification 🌌 astro-ph.IM
keywords atmospheric extinction curveLenghu siteA0-type starsoptical wavelengthsastronomical site characterizationspectroscopic measurementsextinction curve comparison
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The pith

The atmospheric extinction curve at Lenghu has been derived using A0 star observations and compared to Mauna Kea and Cerro Paranal.

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

The paper uses low-resolution spectroscopy on a dedicated telescope to measure the optical extinction curve at the Lenghu site. Observations of A0-type stars at airmasses from 1.0 to 2.0 over multiple nights in 2024-2026 provide the data for wavelengths 400 to 800 nm. This establishes the site's extinction properties for comparison with other premier astronomical sites.

Core claim

The extinction curve for the Lenghu site is derived from the airmass-dependent attenuation of light from A0 stars in the optical range, and it is directly compared with the extinction curves from Mauna Kea and Cerro Paranal.

What carries the argument

Differential measurements of stellar flux as a function of airmass using low-resolution spectra of A0 stars to isolate the wavelength-dependent atmospheric extinction.

If this is right

  • The Lenghu site now has a characterized extinction curve for use in optical observations.
  • Quantitative comparisons can be made between Lenghu and other sites for site selection decisions.
  • The method demonstrates the use of spectroscopic data for extinction determination at new sites.
  • Data collected over several years provides a robust baseline for the curve.

Where Pith is reading between the lines

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

  • This could support planning for future telescope installations at Lenghu.
  • The results may help in modeling regional atmospheric effects on light transmission.
  • Similar measurements could be repeated to monitor changes in the extinction over time.
  • Connections to photometric calibration techniques using standard stars are strengthened.

Load-bearing premise

Observations of A0-type stars at airmasses 1.0-2.0 yield an extinction curve free from significant instrumental or other atmospheric contamination.

What would settle it

If independent observations at Lenghu produce a substantially different extinction curve, the derived values would be called into question.

Figures

Figures reproduced from arXiv: 2606.18804 by Bo-Jun Tao, Ji-an Jiang, Jin-Sheng Qiu, Jun-Han Zhao, Lu-Lu Fan, Qing-Feng Zhu, Ting-Gui Wang, Xiao-Hui Xu, Xu Kong, Xu-Zhi Li, Xu Zhou, Yong-Quan Xue, Zheng Lou, Zhi-Yong Pu.

Figure 1
Figure 1. Figure 1: The left panel shows the two-dimensional the stellar spectrum image after calibration. The target stellar spectrum is extracted from the region between the two green dashed lines (35 pixels). The sky background is measured by averaging the flux in the regions above and below the stellar spectrum (35 pixels, between the red dashed lines). The right panel displays the one-dimensional extracted spectrum, obta… view at source ↗
Figure 2
Figure 2. Figure 2: The image shows the normalized observed spectra at different airmasses, with different colors representing different airmass values. The green dash-dotted line presents the normalized A0 standard star spectrum for comparison. The red dashed vertical line indicates the wavelength of 670 nm. Beyond this wavelength, multiple absorption features are evident in the observed spectra that are absent in the A0 sta… view at source ↗
Figure 3
Figure 3. Figure 3: The stellar images at three different wavelengths (blue for 400 nm, orange for 500 nm, red for 700 nm), which are Gaussian PSFs with a FWHM of 2.5”. The positive direction of the y-axis represents the zenith direction, as indicated by the green arrow. The slit blue stripes are fixed at 3” width and the slit centers are randomly sampled from a Gaussian distribution (σ = 0.8”) around the center position. in … view at source ↗
Figure 4
Figure 4. Figure 4: The figure displays the relationship between ex￾tinction magnitudes and airmasses at four selected wave￾lengths. Blue dots represent the observed data, the red line denotes the best linear fit, and the light red shaded region indicates the ± 1 standard deviation interval. The corre￾sponding wavelengths and atmospheric extinctions k are la￾beled at upper-left corner. ∆λ =    10 nm, λ < 650 nm, 5 nm, λ > … view at source ↗
Figure 5
Figure 5. Figure 5: In upper panel, the gray dotted-lines with errorbars represent individual nights’ measurements, and gray dashed-lines indicate data excluded from averaging due to significant deviations. The red dashed line shows the average extinction curve, with a light-red shaded region for the standard deviation. For comparison, the green solid line shows the extinction curve of best-fitting MODTRAN model, the blue das… view at source ↗
read the original abstract

In this study, we use a dedicated spectroscopic telescope to carry out low-resolution measurements of the optical atmospheric extinction curve at Lenghu astronomical site in Qinghai Province, China. Observations of A0-type stars are conducted over multiple nights between 2024 and 2026, covering airmasses from 1.0 to 2.0 and wavelengths in the range of 400 to 800 nm. We derive the extinction curve for the Lenghu site and compare it with those from Mauna Kea and Cerro Paranal.

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

1 major / 0 minor

Summary. The manuscript reports low-resolution spectroscopic observations of A0-type stars at the Lenghu site over multiple nights in 2024-2026, covering airmasses 1.0-2.0 and wavelengths 400-800 nm, to derive the site's atmospheric extinction curve and compare it with those from Mauna Kea and Cerro Paranal.

Significance. If substantiated with data and analysis, the result would provide a useful characterization of a developing astronomical site in China, allowing direct comparison to established sites and informing observational planning. The conventional technique of A0-star spectroscopy across airmass is appropriate for this purpose.

major comments (1)
  1. [Abstract] Abstract: The abstract states that a curve was derived but supplies no data, fitting procedure, error analysis, or comparison details, preventing evaluation of whether the measurements support the claim.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for highlighting the lack of detail in the abstract. We agree this limits evaluation and will revise the abstract accordingly while ensuring the full manuscript already contains the supporting analysis.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The abstract states that a curve was derived but supplies no data, fitting procedure, error analysis, or comparison details, preventing evaluation of whether the measurements support the claim.

    Authors: We agree the abstract is overly concise and omits these elements. The full manuscript describes the A0-star observations across airmasses 1.0-2.0, the low-resolution spectroscopy from 400-800 nm, the derivation of the extinction curve via airmass-dependent fitting, associated uncertainties, and direct comparisons to Mauna Kea and Cerro Paranal. In revision we will expand the abstract to briefly summarize the dataset, fitting approach, error treatment, and key comparative results. revision: yes

Circularity Check

0 steps flagged

No significant circularity in direct observational report

full rationale

The paper presents a conventional empirical measurement: low-resolution spectroscopy of A0 stars at airmasses 1.0-2.0 to extract the extinction curve between 400-800 nm, followed by site comparisons. No equations, fitted models, self-definitions, or derivations are described that could reduce the claimed result to its own inputs by construction. The derivation chain consists solely of data reduction from observations, with no load-bearing self-citations or ansatzes. This is a standard site-characterization report whose central claim is an independent empirical output.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on standard domain assumptions for using A0 stars in extinction work and on the observational dataset itself; no free parameters or invented entities are described in the abstract.

axioms (1)
  • domain assumption A0-type stars have sufficiently well-known spectra to serve as standards for deriving atmospheric extinction.
    Invoked by the choice of target stars for the observations.

pith-pipeline@v0.9.1-grok · 5658 in / 958 out tokens · 34952 ms · 2026-06-26T19:41:53.472000+00:00 · methodology

discussion (0)

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Reference graph

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