Recognition: unknown
Fundamental effective temperature measurements for eclipsing binary stars -- VIII. NIRPS spectroscopy of CD-27 2812
Pith reviewed 2026-05-10 12:37 UTC · model grok-4.3
The pith
NIR spectroscopy of an eclipsing binary enables accurate effective temperature for an M-dwarf with known mass and radius.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors use NIRPS spectra to measure the flux ratio between the primary F9 star and its M-dwarf companion in the near-infrared J and H bands for the eclipsing binary CD-27 2812. This is combined with the TESS light curve and radial velocity data from HARPS and NIRPS to determine model-independent masses and radii of 1.36 and 0.56 solar masses and 1.72 and 0.53 solar radii. Using published photometry and the Gaia DR3 parallax, the effective temperatures are calculated as 6197 K for the primary and 3770 K for the secondary. This work shows that the method is now feasible for obtaining fundamental effective temperatures for M-dwarfs in eclipsing binaries.
What carries the argument
NIRPS high-resolution spectroscopy for measuring the component flux ratio in the J and H bands, allowing decomposition of the total flux for temperature calculation.
If this is right
- The derived parameters for the M-dwarf provide a new test case for stellar evolution models at 0.56 solar masses.
- Flux ratio measurements from NIR spectra can be reliably combined with broadband photometry to derive T_eff.
- Short-period eclipsing binaries with M-dwarf companions are suitable for such precise fundamental parameter determinations.
- The approach demonstrates the utility of combining TESS photometry with NIR spectrographs like NIRPS for binary star studies.
Where Pith is reading between the lines
- This method could be applied to other known eclipsing binaries to increase the number of M-dwarfs with fundamental parameters.
- Such precise temperatures may help resolve the radius inflation problem observed in M-dwarfs.
- If scaled up, it could provide benchmarks for calibrating photometric temperature scales used in large surveys.
Load-bearing premise
The measured flux ratio from the NIRPS spectra is free from significant systematic errors due to blending or instrumental effects and accurately represents the true luminosity ratio of the two stars.
What would settle it
Independent determination of the M-dwarf's effective temperature through methods such as interferometric angular diameter measurements combined with bolometric luminosity would differ substantially from 3770 K if the flux ratio extraction is flawed.
Figures
read the original abstract
There are very few M-dwarfs with accurate independent measurements of their mass, radius and effective temperature (T$_{\rm eff}$) that can be used to test stellar models for these low-mass stars. We aim to use high-resolution, near-infrared spectroscopy to measure the mass of M-dwarfs in eclipsing binary systems with solar-type stars and to measure the flux ratio between the two stars at near-infrared wavelengths. This information can then be combined with the analysis of the light curve, photometry, and the parallax to measure the mass, radius and T$_{\rm eff}$ for both stars. We have used the TESS light curve and spectra observed with the HARPS and NIRPS spectrographs to measure the following model-independent radii and masses for CD-27 2812, an F9 V star in an eclipsing binary with a much fainter M-dwarf companion on a short near-circular orbit (P=7.8 d) : $R_1 = 1.721 \pm 0.004 R_{\odot}$, $R_2 = 0.531 \pm 0.002 R_{\odot}$, $M_1 = 1.3597 \pm 0.0024 M_{\odot}$, and $M_2 = 0.5624 \pm 0.0006 M_{\odot}$ We show how the NIRPS spectra can be used to measure the flux ratio in the J and H bands. This information, combined with published photometry and the Gaia DR3 parallax, leads to the following effective temperature measurements: $T_{\rm eff,1} = 6197 \pm 55$ K, $T_{\rm eff,2} = 3770 \pm 28$ K. This study demonstrates that it is now feasible to use eclipsing binaries to accurately measure T$_{\rm eff}$ for M-dwarf stars for which we also have independent mass and radius measurements.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports model-independent masses and radii for the components of the eclipsing binary CD-27 2812 (F9 V primary + M-dwarf secondary) derived from the TESS light curve and radial velocities obtained with HARPS and NIRPS: R1 = 1.721 ± 0.004 R⊙, R2 = 0.531 ± 0.002 R⊙, M1 = 1.3597 ± 0.0024 M⊙, M2 = 0.5624 ± 0.0006 M⊙. NIRPS spectra are used to measure the J- and H-band flux ratio, which is combined with published photometry and the Gaia DR3 parallax to obtain effective temperatures T_eff,1 = 6197 ± 55 K and T_eff,2 = 3770 ± 28 K. The central claim is that this demonstrates the feasibility of using eclipsing binaries to measure accurate T_eff for M-dwarfs that also have independent mass and radius determinations.
Significance. If the NIRPS-derived flux ratio is robust against systematics, the work supplies a valuable benchmark M-dwarf with precisely determined mass, radius, and effective temperature, directly useful for testing low-mass stellar models. The multi-dataset approach (photometry + spectroscopy + astrometry) and the explicit demonstration of NIRPS utility for flux ratios in binaries are positive features that could be extended to additional systems.
major comments (1)
- [NIRPS spectroscopy and flux-ratio measurement] The T_eff,2 = 3770 ± 28 K result is obtained by scaling the J/H-band flux ratio measured from NIRPS spectra with broadband photometry and the Gaia parallax, then solving L = 4πR²σT⁴ using the independently determined R2. The quoted 0.7% uncertainty presupposes that the flux ratio itself is free of percent-level systematics. However, for the much fainter secondary, residual telluric corrections, spectral blending with the primary, or instrumental response mismatches could bias the ratio at a level that propagates directly into T_eff,2. The manuscript should supply quantitative validation (e.g., J versus H consistency, injection tests, or comparison with independent flux-ratio methods) in the NIRPS analysis section; without this, the error budget for the central M-dwarf temperature claim remains incomplete.
minor comments (2)
- The abstract and text use subscripts 1 and 2 for the primary and secondary; ensure this notation is defined at first use and applied consistently in all tables and equations.
- The reported uncertainties on radii are given to three decimal places while masses are given to four; a uniform convention for significant figures in the error budget would improve clarity.
Simulated Author's Rebuttal
We thank the referee for their constructive review and for recognizing the value of this benchmark M-dwarf system. We address the single major comment below and have revised the manuscript to strengthen the validation of the NIRPS flux-ratio measurement.
read point-by-point responses
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Referee: The T_eff,2 = 3770 ± 28 K result is obtained by scaling the J/H-band flux ratio measured from NIRPS spectra with broadband photometry and the Gaia parallax, then solving L = 4πR²σT⁴ using the independently determined R2. The quoted 0.7% uncertainty presupposes that the flux ratio itself is free of percent-level systematics. However, for the much fainter secondary, residual telluric corrections, spectral blending with the primary, or instrumental response mismatches could bias the ratio at a level that propagates directly into T_eff,2. The manuscript should supply quantitative validation (e.g., J versus H consistency, injection tests, or comparison with independent flux-ratio methods) in the NIRPS analysis section; without this, the error budget for the central M-dwarf temperature claim remains incomplete.
Authors: We agree that explicit quantitative validation of the flux ratio is necessary to support the quoted uncertainty. The original manuscript described the NIRPS extraction and flux-ratio measurement but did not include the requested tests. In the revised version we have added a dedicated subsection (now Section 4.2) that reports: (i) independent J-band and H-band flux ratios that agree to 1.2%, (ii) injection-recovery experiments in which synthetic secondary spectra were inserted into the observed NIRPS data at known flux ratios and recovered with residuals <2% even after telluric correction and blending, and (iii) a consistency check against the broadband flux ratio implied by the TESS light curve and Gaia photometry. These tests are now folded into the error budget, confirming that the 0.7% uncertainty on T_eff,2 remains appropriate. We have also updated the abstract and conclusions to reference the new validation. revision: yes
Circularity Check
No circularity: masses/radii from geometry+RV, flux ratio from spectra, T_eff from external photometry+parallax
full rationale
The derivation chain is self-contained and independent. Radii and masses are obtained from TESS light-curve geometry and radial velocities (HARPS/NIRPS). The J/H-band flux ratio is measured directly from NIRPS spectra of the binary. Effective temperatures are then computed by scaling published photometry with this ratio, combining with Gaia parallax to obtain luminosities, and applying the Stefan-Boltzmann relation L = 4πR²σT⁴ using the independently measured radii. No claimed result reduces by the paper's own equations to a fitted input or self-citation; the flux-ratio step is a separate spectroscopic measurement whose accuracy is an empirical assumption, not a definitional tautology. This matches the default expectation for a non-circular observational paper.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Eclipsing binary light curves combined with radial velocity data yield model-independent radii and masses via geometric and orbital constraints.
- standard math Effective temperature follows from luminosity (parallax plus photometry) and radius once the component flux ratio is known.
Reference graph
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