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REVIEW 1 major objections 1 minor 68 references

The CARMENES search for exoplanets around M dwarfs -- Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines

T0 review · 1 major / 1 minor · reviewed 2026-05-25 · grok-4.3

Pith's one-line read Parameters from visible spectra of M dwarfs agree better with literature than near-infrared spectra alone.

desk verdict The paper shows that for 282 CARMENES M dwarfs, parameters from visible and combined VIS+NIR spectra agree better with literature than NIR-only fits, using updated PHOENIX models and activity-insensitive lines. read the letter →

arxiv 1907.00807 v1 pith:FMPQAX55 submitted 2019-07-01 astro-ph.SR

classification astro-ph.SR
keywords MdwarfsphotosphericparametersPHOENIXmodelsCARMENESstellaractivityexoplanethostshigh-resolutionspectroscopy
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper determines effective temperature, surface gravity, and metallicity for 282 M dwarfs by fitting PHOENIX models to CARMENES spectra. It compares results from visible wavelengths, near-infrared, and both combined. The visible and combined fits match literature values more closely than near-infrared fits by themselves. Selecting lines insensitive to magnetic activity is key to avoiding biases from stellar activity. Accurate parameters help in characterizing planets around these stars.

What carries the argument

χ² minimization fitting of updated PHOENIX stellar atmosphere models to selected activity-insensitive spectral lines across visible and near-infrared ranges.

What would settle it

A direct comparison showing that near-infrared derived parameters match literature values as closely as visible ones would challenge the central finding.

Watch

Extended reading notes

Core claim

Fundamental parameters derived from visible spectra and visible plus near-infrared spectra combined are in better agreement with literature values than those derived from near-infrared spectra alone, when fitting to magnetically insensitive lines.

Load-bearing premise

Magnetically insensitive lines can be selected reliably so that stellar activity does not influence the fitted line profiles.

Editorial extensions

If this is right

  • Improved stellar parameters lead to better constraints on the properties of any orbiting exoplanets.
  • Multiwavelength modeling reduces systematic errors in metallicity and temperature estimates for cool stars.
  • Future observations can prioritize visible spectroscopy for more reliable results on M dwarfs.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The discrepancy in near-infrared fits may point to incomplete modeling of molecular features or activity effects in that range.
  • Simultaneous multiwavelength data could become standard for reducing uncertainties in stellar characterization.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

1 major / 1 minor

Summary. The paper derives effective temperature, surface gravity, and metallicity for 282 M dwarfs by χ²-fitting the latest PHOENIX models (with updated EOS and line lists) to simultaneous CARMENES high-resolution spectra. It stresses the selection of magnetically insensitive lines to mitigate stellar activity effects on line profiles and performs the first direct comparison of parameters obtained from the visible range (0.52–0.96 μm), near-infrared range (0.96–1.71 μm), and their combination, reporting that VIS and VIS+NIR results agree better with literature values than NIR-only results.

Significance. If the empirical comparison holds, the work supplies a large homogeneous parameter catalog useful for CARMENES exoplanet host characterization. The simultaneous multi-range observations and explicit use of activity-insensitive lines constitute a clear methodological advance over single-band analyses; the updated PHOENIX models are also a positive contribution.

major comments (1)
  1. [Methods / line selection] The central claim rests on the assertion that magnetically insensitive lines can be selected so that activity does not bias the χ² fits. The manuscript states the importance of this selection but does not specify the quantitative criteria, line list, or validation tests used; without these details the robustness of the VIS vs. NIR agreement comparison cannot be assessed.
minor comments (1)
  1. The abstract gives wavelength ranges but does not report the number of lines retained after selection or the typical χ² values per degree of freedom for the three fitting regimes.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their constructive review and positive assessment of the work's significance. We address the single major comment below and will revise the manuscript to incorporate the requested details.

read point-by-point responses
  1. Referee: [Methods / line selection] The central claim rests on the assertion that magnetically insensitive lines can be selected so that activity does not bias the χ² fits. The manuscript states the importance of this selection but does not specify the quantitative criteria, line list, or validation tests used; without these details the robustness of the VIS vs. NIR agreement comparison cannot be assessed.

    Authors: We agree that additional explicit documentation is needed. In the revised manuscript we will add a dedicated subsection (in Section 3) that (i) states the quantitative criteria used to identify magnetically insensitive lines (primarily the lack of detectable Zeeman broadening in the PHOENIX synthetic spectra and cross-references to published magnetic-sensitivity indices), (ii) provides the resulting line list (or a machine-readable table of the selected features), and (iii) reports validation tests, including fits performed with and without the activity-sensitive lines and comparisons against independent activity indicators. These additions will directly support the robustness of the VIS–NIR comparison. revision: yes

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity detected

full rationale

The derivation consists of direct χ² fitting of updated external PHOENIX atmosphere models (with new EOS and line lists) to observed CARMENES spectra across VIS, NIR, and combined ranges, followed by empirical comparison of the resulting Teff, log g, and [Fe/H] values against independent literature compilations. No equations reduce outputs to inputs by construction, no fitted parameters are relabeled as predictions, and no load-bearing self-citations or uniqueness theorems imported from prior author work are invoked to force the central agreement claim. The method is self-contained against external benchmarks.

Assumptions & free parameters 3 free parameters · 2 assumptions · 0 invented entities

The central claim rests on the fidelity of the updated PHOENIX models for low-temperature atmospheres and the assumption that activity-insensitive lines can be isolated; three fitted parameters are determined per star but no additional free parameters are introduced beyond the standard atmospheric parameters.

free parameters (3)
  • effective temperature
    Fitted via χ² minimization to match observed spectra in the stated wavelength ranges
  • surface gravity
    Fitted via χ² minimization to match observed spectra in the stated wavelength ranges
  • metallicity
    Fitted via χ² minimization to match observed spectra in the stated wavelength ranges
assumptions (2)
  • domain assumption Updated PHOENIX models with new equation of state and atomic/molecular line lists accurately represent M-dwarf photospheres at low temperatures
    Invoked as the basis for all model fits described in the abstract
  • domain assumption Magnetically insensitive lines exist and can be selected to eliminate activity effects from the line profiles
    Stated as a prerequisite for reliable fitting to avoid stellar activity bias

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Cite this review

Pith. "Pith review of The CARMENES search for exoplanets around M dwarfs -- Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines." pith.science (2026). https://pith.science/paper/FMPQAX55

@misc{pith2026190700807,
  author       = {Pith},
  title        = {Pith review of: The CARMENES search for exoplanets around M dwarfs -- Photospheric parameters of target stars from high-resolution spectroscopy. II. Simultaneous multiwavelength range modeling of activity insensitive lines},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/FMPQAX55}},
  note         = {Machine review of arXiv:1907.00807}
}
abstract

We present precise photospheric parameters of 282 M dwarfs determined from fitting the most recent version of PHOENIX models to high-resolution CARMENES spectra in the visible (0.52 - 0.96 $\mu$m) and near-infrared wavelength range (0.96 - 1.71 $\mu$m). With its aim to search for habitable planets around M dwarfs, several planets of different masses have been detected. The characterization of the target sample is important for the ability to derive and constrain the physical properties of any planetary systems that are detected. As a continuation of previous work in this context, we derived the fundamental stellar parameters effective temperature, surface gravity, and metallicity of the CARMENES M-dwarf targets from PHOENIX model fits using a $\chi^2$ method. We calculated updated PHOENIX stellar atmosphere models that include a new equation of state to especially account for spectral features of low-temperature stellar atmospheres as well as new atomic and molecular line lists. We show the importance of selecting magnetically insensitive lines for fitting to avoid effects of stellar activity in the line profiles. For the first time, we directly compare stellar parameters derived from multiwavelength range spectra, simultaneously observed for the same star. In comparison with literature values we show that fundamental parameters derived from visible spectra and visible and near-infrared spectra combined are in better agreement than those derived from the same spectra in the near-infrared alone.

Figures

Figures reproduced from arXiv: 1907.00807 by the authors.

Figure 1
Figure 1. Surface gravity log g as a function of effective temperature Teff. The left panel compares the Lyon group’s BCAH98 (Baraffe et al. 1998), BHAC15 (Baraffe et al. 2015) models, and PARSEC models for [M/H] = 0 and fixed age of 5 Gyr. The right panel shows the PARSEC models for [M/H] = 0 and variable age from 0.01 to 10 Gyr. The gray vertical lines indicate the temperature range of our PHOENIX-SESAM grid from 2900 K to … view at source ↗
Figure 2
Figure 2. Comparison of PHOENIX-ACES (blue) and PHOENIX-SESAM (red) models for a selection of lines. The parameters of the models are Teff=3500 K, log g=5.0 dex, and [Fe/H]=0.0 dex. The models are broadened corresponding to the spectral resolution in the VIS (R ≈ 94 600) and NIR (R ≈ 80 500) channel. For each wavelength region the residual between the two models are shown. 2014), which limits using these lines in spectroscopi… view at source ↗
Figure 3
Figure 3. CARMENES template spectrum of GJ 133 = J03213+799 (black) with best-fit model (blue and red). The fitting regions are marked in red. All lines are identified together with their Landé factors when available. Article number, page 10 of 30 [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗
Figures from the paper (5 more)
Figure 4
Figure 4. Figure 4: Comparison of stellar parameters derived from VIS and NIR ranges. The assumed stellar age is color-coded. The black line indicates the 1:1 relation, the gray lines represent the 1σ deviations for VIS of 51 K, 0.04 log g, and 0.16 [Fe/H]. Error bars for VIS and NIR are …
Figure 5
Figure 5. Figure 5: Comparison between results from VIS and literature values for Teff (top panel), log g (middle panel), and [Fe/H] (bottom panel). The 1:1 relation is indicated by the black line. The uncertainties of this work (black) are shown in the lower right corner of each panel to…
Figure 6
Figure 6. Figure 6: Comparison between results from NIR and literature values for Teff (top panel), log g (middle panel), and [Fe/H] (bottom panel). The 1:1 relation is indicated by the black line. The uncertainties of this work (black) are shown in the lower right corner of each panel to…
Figure 7
Figure 7. Figure 7: Comparison between results from VIS+NIR and literature values for Teff (top panel), log g (middle panel), and [Fe/H] (bottom panel). The 1:1 relation is indicated by the black line. The uncertainties of this work (black) are shown in the lower right corner of each pane…
Figure 8
Figure 8. Figure 8: Comparison of [Fe/H] (top panel), log g (middle panel), and Teff (bottom panel) between values of this work in VIS+NIR and literature. The age is color-coded; active star are plotted as asterisks. Outliers are identified with numbers; the green lines connect their diff…

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