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arxiv: 1907.06391 · v1 · pith:NPEBVL4Snew · submitted 2019-07-15 · 🌌 astro-ph.SR · astro-ph.GA

Stellar atmospheric parameters for 754 spectra from the X-shooter Spectral Library

Pith reviewed 2026-05-24 21:25 UTC · model grok-4.3

classification 🌌 astro-ph.SR astro-ph.GA
keywords X-shooter Spectral Librarystellar atmospheric parametersfull-spectrum fittingeffective temperaturesurface gravityiron abundanceMILES library
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The pith

A uniform set of effective temperatures, surface gravities and iron abundances is provided for 754 X-shooter spectra.

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

The paper derives effective temperatures, surface gravities and iron abundances for 754 spectra of 616 stars drawn from the X-shooter Spectral Library. Full-spectrum fitting is applied to the ultraviolet-blue and visible segments of each spectrum, with the empirical MILES library serving as the reference set. The resulting parameters span wide ranges in temperature, gravity and metallicity, and the work supplies type-dependent precision estimates. This dataset is intended to support the library's use as a benchmark for stellar population studies.

Core claim

We present a uniform set of stellar atmospheric parameters, effective temperatures, surface gravities, and iron abundances for 754 spectra of 616 XSL stars. We used the full-spectrum fitting package ULySS with the empirical MILES library as reference to fit the ultraviolet-blue (UVB) and visible (VIS) spectra. The stars cover a range of effective temperature 2900 < Teff < 38 000 K, surface gravity 0 < log g < 5.7, and iron abundance -2.5 < [Fe/H] < +1.0, with a couple of stars extending down to [Fe/H] = -3.9. The precisions of the measurements for the G- and K-type stars are 0.9%, 0.14, and 0.06 in Teff, log g, and [Fe/H], respectively.

What carries the argument

Full-spectrum fitting of UVB and VIS segments with ULySS, using the empirical MILES library as the reference set of spectra and parameters.

If this is right

  • The parameters cover the stated ranges in Teff, log g and [Fe/H] and are accompanied by type-specific precision estimates.
  • Internal consistency of the fits was tested and the results were compared with literature compilations.
  • The catalog supplies a consistent reference set intended for stellar population work.
  • Separate precisions are quoted for G/K stars, cool giants, other cool stars, and stars hotter than 6500 K.

Where Pith is reading between the lines

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

  • The catalog could be used to test whether population-synthesis models reproduce observed spectra when fed these parameters.
  • Applying the same fitting procedure to the near-infrared arm of the XSL spectra would allow a check on wavelength-dependent consistency.
  • The derived parameters could serve as an anchor for recalibrating other medium-resolution libraries that overlap with XSL.

Load-bearing premise

The MILES library supplies reference spectra and parameters accurate enough to serve as the basis for fitting across the full range of stellar types and metallicities present in the XSL sample.

What would settle it

A set of independent high-resolution spectroscopic parameters for a subset of the same stars that differ from the fitted values by more than the stated type-dependent precisions.

Figures

Figures reproduced from arXiv: 1907.06391 by Alejandro Vazdekis, Anais Gonneau, Anke Arentsen, Ariane Lan\c{c}on, Jes\'us Falc\'on Barroso, Mariya Lyubenova, Patricia S\'anchez Bl\'azquez, Philippe Prugniel, Reynier Peletier, Scott Trager, Yan-Ping Chen.

Figure 1
Figure 1. Figure 1: Distribution of the spectral types present in XSL, as retrieved from SIMBAD. We highlight the number of stars known as LPV objects in purple. The stars in the ‘LPV’ bin have no given spectral type but have object types labelling them as LPV objects. The stars in the blue bin ‘other’ do not have spectral types in SIMBAD, nor have object types which label them as LPV objects. full-spectrum fitting package pe… view at source ↗
Figure 2
Figure 2. Figure 2: Line spread function for the MILES interpolator, separated by colour for the UVB and VIS. HyperLeda4 (Makarov et al. 2014) and to a high resolution syn￾thetic spectrum. The resulting MILES interpolator LSF is rep￾resented in [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Distributions of ∆Pw for pairs of observations of the same star. The UVB and VIS analyses are presented in the top and bottom row, respectively. The Gaussians with a mean of zero and a standard deviation computed as described in the text are shown, the standard deviations of these Gaussians are given in the top right corner of each panel. 5000 10000 20000 Teff in K (MILES) 0.3 0.2 0.1 0.0 0.1 0.2 0.3 Teff … view at source ↗
Figure 4
Figure 4. Figure 4: Comparison between the MILES and ELODIE solutions in the UVB for the stars with Teff (MILES) > 4000 K. Each atmospheric parameter is shown in a separate panel, and the colour of the symbols identify two temperature ranges (dividing at 5500 K). Stars hotter than 7000 K are shown as crosses. In the Teff and log g panels, seven and two outliers, respectively, are not shown (all hot stars). The dispersion σ an… view at source ↗
Figure 5
Figure 5. Figure 5: Ratio of the internal errors between the UVB and VIS for each atmospheric parameter, in separate panels. The stars with Teff < 4000 K, 4000 < Teff < 5500 K, and Teff > 5500 K are shown with dark blue, orange, and light blue symbols, respectively. The dispersion σ and mean offset µ for the three temperature ranges are indicated. 4000 5000 7000 10000 Teff in K (UVB) 0.3 0.2 0.1 0.0 0.1 0.2 0.3 Teff (U V B VI… view at source ↗
Figure 6
Figure 6. Figure 6: Difference between the parameters determined from the UVB and VIS spectra for stars with 3500 K < Teff (UVB) < 10 000 K. The colour￾coding is the same as in [PITH_FULL_IMAGE:figures/full_fig_p008_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Final parameters in this paper for XSL. Top panel: Hertzsprung￾Russell diagram for XSL, colour-coded by [Fe/H]. Middle: Distribution in the Teff– [Fe/H] plane, colour-coded by log g. Bottom: Distribution in the [Fe/H]– log g plane, colour-coded by log Teff. One star with a log g error larger than 2.0 is not shown (carbon star [ABC89] Cir 18). 4.6. External precision: Comparisons with the general literature… view at source ↗
Figure 8
Figure 8. Figure 8: Comparison between our adopted parameters and the literature compilation. The standard deviation and mean of the differences are written and the corresponding curve is shown. The number of clipped observations compared to the total number of literature values is presented in the lower right corner of each of the panels. The colour of the points relates to Teff; the size of the points to [Fe/H], and giants … view at source ↗
Figure 9
Figure 9. Figure 9: Comparison of different ∆s (our adopted parameter minus the literature value) for Teff, log g, and [Fe/H]. Stars with multiple literature references are shown as circles, whereas stars with only one reference are shown as diamonds. The observations outside the boxes that have more than one literature reference are discussed in Sections 4.6.1–4.6.3. medium or low resolution spectra, using either synthetic s… view at source ↗
Figure 10
Figure 10. Figure 10: Comparison between our adopted parameters and the parameters from Wu et al. (2011b). One and three outliers are not shown for log g and [Fe/H], respectively, and one measurement at 29000 K is not shown (its ∆ Teff/ Teff lit is +0.027.). The axes and symbols are explained in [PITH_FULL_IMAGE:figures/full_fig_p012_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Same as [PITH_FULL_IMAGE:figures/full_fig_p012_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Same as [PITH_FULL_IMAGE:figures/full_fig_p012_12.png] view at source ↗
Figure 10
Figure 10. Figure 10: The standard deviations in Teff, log g, and [Fe/H] are 1.4%, 0.16, and 0.09, respectively (clipping with a sigma of 3.0). There do not appear to be any biases. Wu et al. (2011b) compared their determined parameters for FGK stars to many different lit￾erature compilations and determined robustly their external er￾rors. They claim a precision of 43 K, 0.13, and 0.05 for Teff, log g, and [Fe/H], respectively… view at source ↗
Figure 12
Figure 12. Figure 12: The standard deviations are 0.9%, 0.1, and 0.07 in [PITH_FULL_IMAGE:figures/full_fig_p013_12.png] view at source ↗
read the original abstract

The X-shooter Spectral Library (XSL) is an empirical stellar library at medium spectral resolution covering the wavelength range from 3000 \AA to 24 800 \AA. This library aims to provide a benchmark for stellar population studies. In this work, we present a uniform set of stellar atmospheric parameters, effective temperatures, surface gravities, and iron abundances for 754 spectra of 616 XSL stars. We used the full-spectrum fitting package ULySS with the empirical MILES library as reference to fit the ultraviolet-blue (UVB) and visible (VIS) spectra. We tested the internal consistency and we compared our results with compilations from the literature. The stars cover a range of effective temperature 2900 < Teff < 38 000 K, surface gravity 0 < log g < 5.7, and iron abundance -2.5 < [Fe/H] < +1.0, with a couple of stars extending down to [Fe/H] = -3.9. The precisions of the measurements for the G- and K-type stars are 0.9%, 0.14, and 0.06 in Teff, log g, and [Fe/H], respectively. For the cool giants with log g < 1, the precisions are 2.1%, 0.21, and 0.22, and for the other cool stars these values are 1%, 0.14, and 0.10. For the hotter stars (Teff > 6500 K), these values are 2.6%, 0.20, and 0.10 for the three parameters.

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 / 1 minor

Summary. The manuscript presents a uniform set of stellar atmospheric parameters (effective temperature Teff, surface gravity log g, and iron abundance [Fe/H]) for 754 spectra of 616 stars from the X-shooter Spectral Library (XSL). Parameters are derived via full-spectrum fitting of the UVB and VIS arms using the ULySS package with the empirical MILES library as reference. Internal consistency is tested and results are compared to literature compilations. The sample spans 2900 < Teff < 38000 K, 0 < log g < 5.7, and -3.9 < [Fe/H] < +1.0, with type-dependent precisions reported (e.g., 0.9% in Teff, 0.14 dex in log g, 0.06 dex in [Fe/H] for G/K stars).

Significance. If the results hold, this provides a valuable homogeneous parameter catalog for a large empirical stellar library spanning a wide wavelength range (3000–24800 Å), supporting its use as a benchmark for stellar population studies. The full-spectrum fitting method is standard, and the internal consistency tests plus literature comparisons offer moderate grounding, though the empirical tie to MILES limits independence at parameter extremes.

major comments (2)
  1. [Abstract] Abstract: The quoted precisions (0.9–2.6% in Teff, 0.14–0.22 dex in log g, 0.06–0.22 dex in [Fe/H] by stellar type) are presented without details on fitting residuals, covariance from ULySS, or post-fit adjustments; this is load-bearing for the central claim that these precisions are reliable across the full range including extremes.
  2. [Abstract] Abstract and results: Internal consistency tests and literature comparisons are described but not indicated to be stratified by the extreme subsets (e.g., [Fe/H] < -2.5, Teff > 20000 K, or log g < 1 cool giants), where MILES coverage is known to be sparse; this directly affects validation of uniformity for the full XSL sample.
minor comments (1)
  1. [Abstract] Abstract: The stated [Fe/H] range is -2.5 < [Fe/H] < +1.0 with a couple of stars to -3.9; clarify whether the quoted precisions apply to these outliers or if they are treated separately.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive feedback on our presentation of precision estimates and validation across the parameter range. We respond to each major comment below and agree that clarifications and additions will strengthen the manuscript.

read point-by-point responses
  1. Referee: [Abstract] Abstract: The quoted precisions (0.9–2.6% in Teff, 0.14–0.22 dex in log g, 0.06–0.22 dex in [Fe/H] by stellar type) are presented without details on fitting residuals, covariance from ULySS, or post-fit adjustments; this is load-bearing for the central claim that these precisions are reliable across the full range including extremes.

    Authors: The quoted precisions are the standard deviations obtained directly from our internal consistency tests (repeat observations of the same stars), as described in the results section. The methods section details the ULySS fitting procedure, including the use of the covariance matrix for formal errors and typical residual levels after fitting. No post-fit adjustments were applied. Due to abstract length constraints we did not repeat these details there, but we will revise the abstract to include a short clause stating that the precisions derive from internal consistency tests on repeat spectra. We agree this improves transparency for the full range, including extremes where MILES coverage is limited. revision: yes

  2. Referee: [Abstract] Abstract and results: Internal consistency tests and literature comparisons are described but not indicated to be stratified by the extreme subsets (e.g., [Fe/H] < -2.5, Teff > 20000 K, or log g < 1 cool giants), where MILES coverage is known to be sparse; this directly affects validation of uniformity for the full XSL sample.

    Authors: We agree that explicit stratification by the most extreme subsets is not shown. The number of stars in these regimes is small (only a couple with [Fe/H] < -2.5, limited hot stars above 20 000 K, and a modest number of cool giants with log g < 1), which restricts the utility of formal stratification. Nevertheless, the internal consistency tests encompass these objects, and the literature comparisons for the available extreme stars remain consistent with the quoted type-dependent precisions. In revision we will add a dedicated paragraph in the results section that separately discusses performance and limitations for the extreme subsets, explicitly noting the sparse MILES coverage at the boundaries. revision: yes

Circularity Check

0 steps flagged

No significant circularity; parameters derived from external reference library with literature validation

full rationale

The paper derives Teff, log g and [Fe/H] for XSL spectra by applying the ULySS full-spectrum fitting code to the independent MILES empirical library (explicitly stated in the abstract and methods). It reports internal consistency tests plus direct comparisons to external literature compilations. No self-definitional equations, no fitted inputs relabeled as predictions, and no load-bearing self-citations or uniqueness theorems appear in the derivation chain. Reliance on MILES is a standard empirical calibration step whose accuracy is externally checkable; the paper does not reduce its central claim to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that the MILES library is an adequate empirical reference and that the ULySS fitting procedure recovers unbiased parameters for the XSL wavelength coverage and resolution. No new free parameters or invented entities are introduced; the output parameters are the fitted results themselves.

axioms (1)
  • domain assumption The MILES library provides reliable reference spectra and parameters for full-spectrum fitting across the stellar parameter space covered by XSL.
    Invoked when the authors state they used MILES as the reference to fit the XSL spectra.

pith-pipeline@v0.9.0 · 5905 in / 1357 out tokens · 32202 ms · 2026-05-24T21:25:37.269454+00:00 · methodology

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    Xiang, M. S., Liu, X. W., Yuan, H. B., et al. 2015, MNRAS, 448, 822 Article number, page 14 of 15 Anke Arentsen et al.: Stellar atmospheric parameters for 754 spectra from the X-shooter Spectral Library , Appendix A: Tables with derived and literature stellar parameters Table A.1. Derived atmospheric parameters of the XSL stars Name Obs a UVB solution VIS...