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arxiv: 2604.24466 · v1 · submitted 2026-04-27 · 🌌 astro-ph.IM · astro-ph.SR

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An archive of reduced and telluric-corrected CRIRES+ L- and M-band spectra with slit-tilt and wavelength calibrations

Thomas Marquart , Alexis Lavail
Authors on Pith no claims yet

Pith reviewed 2026-05-07 17:20 UTC · model grok-4.3

classification 🌌 astro-ph.IM astro-ph.SR
keywords CRIRES+telluric correctionwavelength calibrationL-bandM-banddata archivenear-infrared spectroscopyVLT
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The pith

A public archive supplies 5649 wavelength-calibrated and telluric-corrected CRIRES+ spectra in the L and M bands.

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

Standard calibration sources fail beyond the K band on CRIRES+, leaving L and M band observations without reliable wavelength scales or slit-tilt measurements. The paper shows how fitting a dense set of atmospheric absorption lines with the viper tool on nodding A and B frames supplies both the missing wavelength solutions and the slit inclination for every observation. The authors re-reduce more than eleven thousand raw frames from 68 ESO programmes, producing 5649 extracted AB nod-pair spectra for 156 distinct targets. These data products, together with quality-assessment figures, are released through an interactive web interface. A sympathetic reader cares because the archive removes a major barrier to using high-resolution thermal-infrared spectra that were previously difficult to place on an absolute wavelength scale.

Core claim

We present a uniformly reprocessed archive of all public CRIRES+ L/M science observations obtained between September 2021 and March 2025, totalling 11 131 raw frames. We use the telluric modelling tool viper that fits a model to the plethora of atmospheric absorption features that exist around these wavelengths. We calibrate the slit tilt from the wavelength solutions for the nodding A and B frames and update the static inputs to the data reduction system. Subsequently, we derive new wavelength scales for each observation from telluric fits on the spectra themselves, additionally interpolating the solutions for spectra that have no tellurics. The resulting 5649 extracted, calibrated and tell

What carries the argument

The viper telluric-modelling tool that fits atmospheric absorption features to derive both wavelength solutions and slit-tilt corrections for L- and M-band nodding observations.

If this is right

  • Astronomers obtain ready-to-use calibrated spectra for 156 targets without repeating the telluric fitting step themselves.
  • The updated slit-tilt values can be adopted as new static inputs for future reductions of CRIRES+ L/M data with the standard pipeline.
  • The public web archive allows immediate inspection of data quality for every dataset before download.
  • Observations lacking sufficient tellurics now inherit interpolated wavelength solutions from nearby frames that do contain them.

Where Pith is reading between the lines

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

  • The same telluric-fitting approach could be tested on other high-resolution infrared spectrographs that lack calibration lamps in their longest bands.
  • The archive may shorten the time needed to combine multiple L/M-band epochs for variability or orbital-motion studies.
  • Future public releases could automatically incorporate new observations as they enter the ESO archive.

Load-bearing premise

Fitting telluric absorption lines with viper produces wavelength and slit-tilt calibrations that are accurate enough for scientific use and free of systematic offsets that would need separate verification.

What would settle it

A comparison of the viper-derived wavelength scales against the known rest wavelengths of a set of isolated telluric or stellar lines in a bright standard star observed in the same bands would reveal whether residual offsets exceed the claimed precision.

Figures

Figures reproduced from arXiv: 2604.24466 by Alexis Lavail, Thomas Marquart.

Figure 1
Figure 1. Figure 1: Slit tilt measured from the A–B wavelength difference of telluric standard stars, as a function of wavelength. Different symbols denote the three detector chips. Solid and dashed lines show the linear fits for L and M bands (Eqs. 1 and 2), which interpolate across the CO2 gap near 4.2–4.5 µm. Grey points are 3σ outliers excluded from the fit view at source ↗
Figure 2
Figure 2. Figure 2: Extracted spectrum of β Pic in the M4368 setting (order 7, all three detector chips), reduced with flat-fielding (blue) and without (red, offset vertically). The black lines show the corresponding viper telluric model for each case. 2.2. Better default wavelengths The viper fits to the telluric standards produce wavelength solu￾tions. For traces where the fit converged well (percentage RMS residual < 10 an… view at source ↗
Figure 3
Figure 3. Figure 3: Wavelength precision of the viper fits to science spectra, assessed via four metrics. Top left: absolute repeatability of the wavelength at pixel 1024 per (setting, chip, order) group, with symbol size proportional to the number of measurements. Top centre: distribution of per-group RMS for groups with RMS < 5 km s−1 . Top right: A–B difference scatter, the tightest metric (median 249 m s−1 ). Bottom left … view at source ↗
Figure 4
Figure 4. Figure 4: Residual between the measured median A–B wavelength shift and the shift predicted by the slit tilt model, as a function of wavelength. Blue and red points denote L- and M-band groups, respectively. The RMS residual of 1177 m s−1 and median offset of 40 m s−1 are consistent with a correctly measured tilt. 3500 3750 4000 4250 4500 4750 5000 wavelength (nm) 5 0 v (k m/s) o8 o7 o6 o5 o4 o3 M4318: _tw.fits vs a… view at source ↗
Figure 5
Figure 5. Figure 5: Velocity offset between the reference tracing table wavelengths and the median science viper solution for the M4318 setting, shown as a representative example. Each curve segment corresponds to one detector order, coloured by chip (blue: CHIP1, orange: CHIP2, green: CHIP3). Dotted segments mark orders that retained pipeline wave￾lengths; solid segments have viper wavelengths from the telluric stan￾dard. Th… view at source ↗
Figure 6
Figure 6. Figure 6: 12CO v = 1 − 0 fundamental P-branch toward the Herbig Ae transition-disk star MWC 758 (M4368, order 04, spanning the three de￾tector chips). Each panel shows the observed spectrum (black) with the viper forward model of the telluric transmission times the fitted stel￾lar continuum overlaid (red), plus the telluric-corrected spectrum (blue, offset vertically for clarity). Narrow CO emission peaks from the i… view at source ↗
Figure 7
Figure 7. Figure 7: Same as view at source ↗
Figure 9
Figure 9. Figure 9: Brα at 4.052 µm in GQ Lup, in order 06 of the same M4368 observation as view at source ↗
Figure 10
Figure 10. Figure 10: Brα at 4.052 µm in strong emission in the spectrum of β Ori (Rigel) 3.660 3.665 3.670 3.675 3.680 0 20000 40000 Flux [ADU] CHIP1 Car setting L3262 order 03 observed telluric model 12000 + obs / tell 3.685 3.690 3.695 3.700 3.705 0 20000 40000 Flux [ADU] CHIP2 3.715 3.720 3.725 3.730 3.735 Wavelength [ m] 0 20000 40000 Flux [ADU] CHIP3 view at source ↗
Figure 11
Figure 11. Figure 11: A Humphreys recombination line at 3.693 µm in emission in the spectrum of ωCar. 111.24V2.001, 111.24VY.001, 111.24VY.002, 111.24XW.003, 111.250R.001, 111.250R.002, 111.250Y.001, 111.250Y.002, 111.254J.004, 112.25MR.001, 112.25MU.001, 112.25MU.002, 112.25PX.001, 112.25PX.002, 112.25PX.003, 112.26WN.001, 112.26WN.002, 113.269C.002, 113.269T.001, 113.26AX.002, 113.26F9.001, 113.26PE.001, 113.26VH.001, 114.27… view at source ↗
read the original abstract

The high-resolution near-infrared spectrograph CRIRES+ at ESO VLT covers the Y, J, H, K, L and M bands. The U-Ne and Fabry-Perot calibration light sources, however, only work up to the K-band, leaving the bands L and M without wavelength calibration, and without a way to measure the inclination of the long slit relative to the detector frame. To remedy this, we present here a uniformly reprocessed archive of all public CRIRES+ L/M science observations obtained between September 2021 and March 2025, totalling 11 131 raw frames. We use the telluric modelling tool viper that fits a model to the plethora of atmospheric absorption features that exist around these wavelengths. We calibrate the slit tilt from the wavelength solutions for the nodding A and B frames that have the target in the lower and upper half of the slit, respectively. We then update the static inputs to the data reduction system with the slit tilt information and reduce the data with the standard pipeline recipes. Subsequently, we derive new wavelength scales for each observation from telluric fits on the spectra themselves, additionally interpolating the solutions for spectra that have no tellurics from the ones that have. The resulting 5649 extracted, calibrated and telluric-fitted AB nod-pair spectra, spanning 156 unique targets from 68 ESO programmes, are served through an interactive web archive at https://www.astro.uu.se/crires-lm that offers data downloads and figures for all datasets that allow an initial judgement of the data quality.

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 / 2 minor

Summary. The paper describes a uniform reprocessing of all public CRIRES+ L- and M-band observations (11 131 raw frames from September 2021 to March 2025) to produce an archive of 5649 extracted, telluric-corrected AB nod-pair spectra for 156 targets. Wavelength calibration and slit-tilt corrections are derived by fitting telluric absorption features with the viper tool on the science frames themselves (since U-Ne and Fabry-Perot calibrators do not reach these bands), with interpolation for frames lacking sufficient tellurics; the resulting products are served via an interactive web archive at https://www.astro.uu.se/crires-lm.

Significance. If the viper-derived calibrations prove accurate at the level required for high-resolution work, the archive supplies a substantial, uniformly processed resource that enables scientific exploitation of CRIRES+ L/M data previously limited by the absence of standard wavelength solutions. The public release with per-dataset figures for quality inspection is a clear strength and directly addresses community needs for accessible infrared spectroscopy.

major comments (1)
  1. [Calibration and reduction procedure (abstract and associated methods description)] The central claim that the delivered spectra are scientifically usable rests on the accuracy of the viper telluric fits for wavelength solutions and the derived A/B-nod slit-tilt corrections. However, the manuscript supplies no quantitative validation: no RMS residuals of the fits, no error budgets on the wavelength scales, no comparison against independent standards or other instruments, and no cross-checks on the interpolated solutions. This omission is load-bearing for the usability assertion.
minor comments (2)
  1. [Abstract] The abstract states the total numbers of frames and spectra but does not break them down by band (L vs. M) or by the fraction of observations that required interpolation; adding such a summary table would improve transparency.
  2. [Archive description] The web archive is described as offering 'figures for all datasets that allow an initial judgement of the data quality,' but the manuscript does not specify what diagnostic plots (e.g., fit residuals, telluric model overlays) are included; a brief enumeration would help readers anticipate the quality-assessment tools.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their positive summary and recommendation of minor revision. The single major comment identifies a genuine gap in the current manuscript that we will address through targeted additions.

read point-by-point responses

  1. Referee: [Calibration and reduction procedure (abstract and associated methods description)] The central claim that the delivered spectra are scientifically usable rests on the accuracy of the viper telluric fits for wavelength solutions and the derived A/B-nod slit-tilt corrections. However, the manuscript supplies no quantitative validation: no RMS residuals of the fits, no error budgets on the wavelength scales, no comparison against independent standards or other instruments, and no cross-checks on the interpolated solutions. This omission is load-bearing for the usability assertion.

    Authors: We agree that the absence of quantitative validation metrics weakens the usability claim. In the revised manuscript we will add a dedicated validation subsection (or expand the methods) that reports: (i) RMS residuals from the viper telluric fits across a representative sample of the 5649 spectra, (ii) a concise error budget for the derived wavelength scales that includes contributions from telluric-model uncertainties, line-list precision, and interpolation, (iii) direct cross-checks of interpolated solutions against neighbouring frames that possess sufficient tellurics for independent fits, and (iv) quantitative assessment of the A/B-nod slit-tilt corrections via the reduction in residual misalignment after correction. We will also discuss the inherent limitation that no laboratory or standard-lamp wavelength references exist for CRIRES+ in the L and M bands; where feasible we will include comparisons to high-resolution synthetic telluric spectra and to any overlapping observations from other facilities. These additions will be supported by new figures showing residual distributions and example wavelength-solution overlays. revision: yes

Circularity Check

0 steps flagged

No circularity: empirical data archive produced by external-tool pipeline

full rationale

The paper describes an observational data-reduction pipeline that ingests public raw CRIRES+ frames, applies the external viper tool to fit telluric absorption for wavelength solutions and slit-tilt calibration, updates pipeline static inputs, runs standard ESO recipes, and interpolates solutions where needed. The delivered archive of 5649 spectra is the direct empirical output of this processing applied to 11131 frames. No derived quantity is defined in terms of itself, no fitted parameter is relabeled as a prediction, and no load-bearing premise rests on self-citation. The work is self-contained against external benchmarks (raw ESO data and the viper code base) and contains no theoretical derivation chain that could reduce to its inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the domain assumption that telluric modeling provides reliable wavelength solutions in the L and M bands and on the use of the standard ESO data-reduction pipeline.

axioms (1)
  • domain assumption Telluric absorption features can be modeled accurately enough by the viper tool to derive wavelength scales and slit tilts in the L and M bands.
    This assumption underpins the entire calibration procedure described in the abstract.

pith-pipeline@v0.9.0 · 5594 in / 1424 out tokens · 117063 ms · 2026-05-07T17:20:04.470533+00:00 · methodology

discussion (0)

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Reference graph

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