Fundamental effective temperature measurements for eclipsing binary stars -- VIII. NIRPS spectroscopy of CD-27 2812

TL;DR

This study demonstrates the use of high-resolution near-infrared spectroscopy to accurately measure the mass, radius, and effective temperature of stars in an eclipsing binary system, especially M-dwarfs, combining spectroscopic, photometric, and parallax data.

Contribution

It introduces a method to determine T$_{ m eff}$ for M-dwarfs using NIR spectroscopy and eclipsing binary data, improving stellar model testing.

Findings

Measured masses and radii for both stars in the binary system.

Derived effective temperatures with high precision for both stars.

Showed the feasibility of using NIR spectra to determine flux ratios and T$_{ m eff}$.

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.