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arxiv: 2604.27086 · v1 · submitted 2026-04-29 · 🌌 astro-ph.SR · astro-ph.GA· astro-ph.IM

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A high-resolution K-band spectral atlas of massive stars

V. M. Kalari , W. D. Vacca
Authors on Pith no claims yet

Pith reviewed 2026-05-07 10:27 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GAastro-ph.IM
keywords K-band spectroscopymassive starsO-type starsspectral atlasinfrared observationssupergiantstelluric correction
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The pith

A high-resolution K-band spectral atlas of 81 massive stars has been compiled and released.

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

The paper compiles and publicly releases a collection of high-resolution spectra in the K-band for 81 massive stars. These stars are chosen as known standards from optical observations and cover spectral types from O2 to O9 and luminosity classes up to supergiants of type B1. The spectra have been corrected for atmospheric absorption lines and offer high signal-to-noise ratios. This resource supports the classification and study of massive stars in environments where visible light is blocked by dust.

Core claim

We present a high-resolution (~45000), high signal-to-noise (>100) K-band spectral atlas of massive stars. It includes 81 stars consisting of known optical standards, spanning spectral and luminosity subclasses from O2 to O9, and supergiant luminosity and spectral subclasses from O2-B1. The telluric-corrected reduced spectra are publicly available, and are discussed here.

What carries the argument

A curated set of 81 optically classified massive star standards observed at high resolution in the K-band, after telluric correction and reduction.

Load-bearing premise

The selected stars serve as reliable standards for K-band classification without significant differences from their optical types, and that the telluric corrections introduce no artifacts that affect the spectra's usability.

What would settle it

Independent high-resolution K-band observations of the same stars showing major discrepancies after telluric correction, or residual atmospheric features mimicking stellar lines, would question the atlas reliability.

Figures

Figures reproduced from arXiv: 2604.27086 by V. M. Kalari, W. D. Vacca.

Figure 1
Figure 1. Figure 1: Spectral atlas of O dwarf luminosity classes, of known optical standards given in view at source ↗
Figure 2
Figure 2. Figure 2: Same as Fig.1, but for giants. Note that the spectra of the O3 and O3.5 giants ALS 19312 and ALS 18752 are not shown (listed in view at source ↗
Figure 3
Figure 3. Figure 3: Same as Fig.1, but for sub-giants. N III lines at 2.2471 and 2.2513 µm are also shown. Another key line in the NIR is the He I 2.058µm line. Unlike other He lines in the NIR, this line de￾scends from the 21P level and so depends strongly on the far-UV 584˚A resonance line. In fact, modeling has had difficulties reproducing the observed profiles T. Re￾polust et al. (2005). In addition, this line is located … view at source ↗
Figure 4
Figure 4. Figure 4: Same as Fig.1, but for supergiant Iab/a subclasses. features, and only few strong emission lines. For the ear￾liest stars, even He II 2.189µm can be in emission. For O2–O3 stars we suggest classification based on observ￾ing the former line. The C IV line appears in absorption at O3. The N III 2.115 µm triplet is usually seen as a broad emission feature. 3.2. Line widths As discussed in Section 3.1, we find… view at source ↗
Figure 5
Figure 5. Figure 5: Same as Fig.1, but for low luminosity supergiant Ib subclasses. 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 Wavelength 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Normalized Flux + Offset BIab HD91316 B0.5Ia HD77581 B05.Ia HD115842 B0Ia HD156359 B0Ib HD150898 CIV NIII NIII view at source ↗
Figure 6
Figure 6. Figure 6: Similar to Fig.1, but for early B supergiants. The wavelength is curtailed, and regions with poor corrections are removed, which were particularly strong for some targets, and caused issues during normalization. Additional He I lines (from view at source ↗
Figure 8
Figure 8. Figure 8: He I 2.1126µm to He I 2.1891µm line ratios versus the optical spectral type are shown for optical standard stars. Dwarfs are shown by circles, while giants are given by open squares. The dashed line is the best least-squares fit to the data. Limits where a given spectral line could not be clearly measured are shown by top (where the He I is not clearly identified), or down carets (here, the limits are on t… view at source ↗
Figure 7
Figure 7. Figure 7: Ratio of the He I singlet (2.113 µm) to triplet (2.112 µm) which serves as an indicator of spectral type for late type O stars. the optical lines, as found by recent analysis of statistical sample of optical spectra in the 1/5Z⊙ Small Magellanic Cloud by J. S. Vink et al. (2023); J. M. Bestenlehner et al. (2025), and also by F. Tramper et al. (2014) in local group galaxies, especially given the NIR lines a… view at source ↗
Figure 10
Figure 10. Figure 10: Top: Multi-epoch spectra of HD 93129A. Bottom: Brγ line profile variations observed in HD 93129A 2.05 2.10 2.15 2.20 2.25 2.30 2.35 Wavelength 1.0 1.1 1.2 1.3 Normalized Flux + Offset 2024-02-25 2024-04-17 view at source ↗
Figure 11
Figure 11. Figure 11: Multi-epoch spectra of SS 215/WR20aa. strength of two line profiles in the He II feature. Based on these features, the star cannot be considered a representative of it’s type in the near-infrared. HD 152590/V1297 Sco is a known eclipsing binary (S. A. Otero & F. Claus 2004) SB2, which is seen in the K-band data. Both epochs are shown in view at source ↗
Figure 12
Figure 12. Figure 12: Top:Multi-epoch spectra of WR21a/THA 35-II-42. Bottom left: Zoom-in of the Brγ profile. Bottom right: Zoom-in of the He II line profile. 2.110 2.115 2.120 2.125 Wavelength 1.0 1.1 1.2 1.3 Normalized Flux + Offset 2024-02-25 2024-04-17 2.165 2.170 Wavelength 1.0 1.1 1.2 1.3 Normalized Flux + Offset 2024-02-25 2024-04-17 2.1850 2.1875 2.1900 2.1925 2.1950 Wavelength 1.0 1.1 1.2 1.3 Normalized Flux + Offset … view at source ↗
Figure 13
Figure 13. Figure 13: Left: Multi-epoch spectra of ALS 15210 centered on the N III triplet, Middle: Brγ profile, and Right: the He II line. 2.05 2.10 2.15 2.20 2.25 2.30 2.35 Wavelength 0.9 1.0 1.1 1.2 1.3 1.4 Normalized Flux + Offset 2023-06-14 2022-07-31 view at source ↗
Figure 14
Figure 14. Figure 14: Multi-epoch spectra of HD 152590. ALS 4067/CD-38 11748 Single-epoch spectroscopy of this target suggests it is a suitable spectral standard, as a O4.5I star. It shows an inverse P Cygni profile in the He II line, the N III lines are visible, and their ratio, along with the strong N III emission are clear ( view at source ↗
Figure 15
Figure 15. Figure 15: Similar to Fig.1, but for the non-spectral standards, along with their literature classification. ALS 1216/CD-47 4551 The spectrum is affected by normalization issues, and shows strong He Iemission, with the 2.113 µm feature in emission. He IIis in absorption consistent with its spectral type, and the line ratio of He I/He IIis consistent with an O5 or O5.5I classification. ALS 19692/[N78] 49 Marked as an… view at source ↗
Figure 16
Figure 16. Figure 16: Sky spectrum at Cerro Pach´on. Gray shaded regions are where the sky lines significantly affect the observed spectrum, where the transmission is < 0.4. Spectral atlases shown have only regions of transmission >0.2 marked for clarity view at source ↗
read the original abstract

A high-resolution ($\sim$45000), high signal-to-noise ($>$100) K-band spectral atlas of massive stars is presented. It includes 81 stars consisting of known optical standards, spanning spectral and luminosity subclasses from O2 to O9, and supergiant luminosity and spectral subclasses from O2-B1. The telluric-corrected reduced spectra are publicly available, and are discussed here.

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 manuscript presents a high-resolution (R ~ 45,000), high S/N (>100) K-band spectral atlas of 81 massive stars drawn from known optical standards. The sample spans O2–O9 spectral types and O2–B1 supergiant luminosity classes. Telluric-corrected, reduced spectra are released publicly and discussed in the text.

Significance. If the data reductions are shown to be free of significant artifacts, the atlas would fill a clear gap in the literature by supplying K-band standards for massive-star classification and population studies, where optical templates are often insufficient. The public release of the spectra is a concrete strength that enables immediate community use.

major comments (1)
  1. [Data reduction and validation section] Data reduction and validation section: The central claim that the atlas provides reliable K-band standards rests on the assertion of clean telluric corrections, yet no quantitative validation is supplied (e.g., rms residuals measured in line-free windows, direct comparison of corrected vs. uncorrected spectra, or consistency checks on diagnostic features such as Br γ at 2.166 μm and He I 2.112 μm). Without these metrics it is impossible to assess whether residuals at the few-percent level remain near classification lines.
minor comments (2)
  1. [Abstract] The abstract and introduction should explicitly state the wavelength coverage and the exact instrument/telescope used for the observations.
  2. [Figures] Figure captions for the atlas spectra should include the S/N measured per resolution element and the airmass range of the observations for each star.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive review and for recognizing the potential value of the atlas in filling a gap in K-band standards for massive stars. We address the single major comment below and will incorporate the requested quantitative validation in the revised manuscript.

read point-by-point responses

  1. Referee: Data reduction and validation section: The central claim that the atlas provides reliable K-band standards rests on the assertion of clean telluric corrections, yet no quantitative validation is supplied (e.g., rms residuals measured in line-free windows, direct comparison of corrected vs. uncorrected spectra, or consistency checks on diagnostic features such as Br γ at 2.166 μm and He I 2.112 μm). Without these metrics it is impossible to assess whether residuals at the few-percent level remain near classification lines.

    Authors: We agree that quantitative validation of the telluric corrections is essential to substantiate the atlas as reliable standards. The current manuscript emphasizes the public release of the reduced spectra and their discussion but does not include the specific metrics suggested. In the revised version we will expand the data reduction and validation section to report: RMS residuals measured in multiple line-free windows across the K-band; direct comparisons of corrected versus uncorrected spectra for representative targets; and consistency checks on key diagnostic features including Br γ at 2.166 μm and He I at 2.112 μm. These additions will allow readers to evaluate residual artifacts at the few-percent level near classification lines. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational data release with no derivations or predictions

full rationale

The paper presents a K-band spectral atlas of 81 massive stars based on observational data collection, reduction, and public release of telluric-corrected spectra. No equations, model fits, predictions, or derivation chains are claimed or present. The central claim reduces only to the empirical spectra themselves and their public availability, with no self-referential steps, fitted parameters renamed as predictions, or load-bearing self-citations that would create circularity. This is a standard observational catalog paper whose validity rests on data quality rather than any internal logical loop.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an observational data atlas paper. No free parameters, axioms, or invented entities are required or introduced.

pith-pipeline@v0.9.0 · 5357 in / 1015 out tokens · 79399 ms · 2026-05-07T10:27:58.512549+00:00 · methodology

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Reference graph

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