Estimating <i>T</i>eff, radius, and luminosity of M-dwarfs using high-resolution optical and NIR spectral features

Khata, Dhrimadri; Mondal, Soumen; Das, Ramkrishna; Baug, Tapas

doi:10.1093/mnras/stab2211

Cited by 7 publications

(3 citation statements)

References 80 publications

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“…It cannot be excluded that these deviations contribute to the disagreements in derived stellar parameters found in this work. However, we were able to shed some light on deficiencies of some methods, for instance, showing that the DL method would benefit from the use of multiple wavelength ranges and that ODUSSEAS could improve the T eff determination by using different sets of lines or, most importantly, by using a new reference T eff scale based on interferometry (Khata et al 2021). This possibility is currently being explored and is expected to be implemented as an option in an upgraded version of the tool.…”

Section: Discussionmentioning

confidence: 97%

Metallicities in M dwarfs: Investigating different determination techniques

Passegger

Bello-García

Ordieres-Meré

et al. 2022

A&A

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Deriving metallicities for solar-like stars follows well-established methods, but for cooler stars such as M dwarfs, the determination is much more complicated due to forests of molecular lines that are present. Several methods have been developed in recent years to determine accurate stellar parameters for these cool stars (Teff ≲ 4000 K). However, significant differences can be found at times when comparing metallicities for the same star derived using different methods. In this work, we determine the effective temperatures, surface gravities, and metallicities of 18 well-studied M dwarfs observed with the CARMENES high-resolution spectrograph following different approaches, including synthetic spectral fitting, analysis of pseudo-equivalent widths, and machine learning. We analyzed the discrepancies in the derived stellar parameters, including metallicity, in several analysis runs. Our goal is to minimize these discrepancies and find stellar parameters that are more consistent with the literature values. We attempted to achieve this consistency by standardizing the most commonly used components, such as wavelength ranges, synthetic model spectra, continuum normalization methods, and stellar parameters. We conclude that although such modifications work quite well for hotter main-sequence stars, they do not improve the consistency in stellar parameters for M dwarfs, leading to mean deviations of around 50–200 K in temperature and 0.1–0.3 dex in metallicity. In particular, M dwarfs are much more complex and a standardization of the aforementioned components cannot be considered as a straightforward recipe for bringing consistency to the derived parameters. Further in-depth investigations of the employed methods would be necessary in order to identify and correct for the discrepancies that remain.

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Section: Discussionmentioning

confidence: 97%

Metallicities in M dwarfs: Investigating different determination techniques

Passegger

Bello-García

Ordieres-Meré

et al. 2022

A&A

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“…For the very high resolutions of ESPRESSO and HARPS, the results derived by ODUSSEAS are essentially the same either by using directly the original highest-resolution spectra of ESPRESSO, or by convolving first the ESPRESSO spectra to the lower, but still high, resolution of HARPS. We ran ODUSSEAS by considering a reference data set composed of 47 stars with interferometry-based T eff (Rabus et al 2019;Khata et al 2021), and [Fe/H] derived through the photometric calibration by Neves et al (2012) using the Gaia DR3 parallaxes. We obtain T eff = 3419 ± 92 K and [Fe/H] = −0.03 ± 0.11 dex.…”

Section: Stellar Atmospheric Parametersmentioning

confidence: 99%

An unusually low-density super-Earth transiting the bright early-type M-dwarf GJ 1018 (TOI-244)

Castro-González¹,

Lillo-Box²,

Lavie³

et al. 2023

A&A

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Context. Small planets located at the lower mode of the bimodal radius distribution are generally assumed to be composed of iron and silicates in a proportion similar to that of the Earth. However, recent discoveries are revealing a new group of low-density planets that are inconsistent with that description. Aims. We intend to confirm and characterize the TESS planet candidate TOI-244.01, which orbits the bright (K = 7.97 mag), nearby (d = 22 pc), and early-type (M2.5 V) M-dwarf star GJ 1018 with an orbital period of 7.4 days. Methods. We used Markov chain Monte Carlo methods to model 57 precise radial velocity measurements acquired by the ESPRESSO spectrograph together with TESS photometry and complementary HARPS data. Our model includes a planetary component and Gaussian processes aimed at modeling the correlated stellar and instrumental noise. Results. We find TOI-244 b to be a super-Earth with a radius of Rp = 1.52 ± 0.12 R⊕ and a mass of Mp = 2.68 ± 0.30 M⊕. These values correspond to a density of ρ = 4.2 ± 1.1 g cm−3, which is below what would be expected for an Earth-like composition. We find that atmospheric loss processes may have been efficient to remove a potential primordial hydrogen envelope, but high mean molecular weight volatiles such as water could have been retained. Our internal structure modeling suggests that TOI-244 b has a 479−96+128 km thick hydrosphere over a 1.17 ± 0.09 R⊕ solid structure composed of a Fe-rich core and a silicate-dominated mantle compatible with that of the Earth. On a population level, we find two tentative trends in the density-metallicity and density-insolation parameter space for the low-density super-Earths, which may hint at their composition. Conclusions. With a 8% precision in radius and 12% precision in mass, TOI-244 b is among the most precisely characterized super-Earths, which, together with the likely presence of an extended hydrosphere, makes it a key target for atmospheric observations.

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“…The modeling of M dwarfs has advanced in recent years. Several works adopting high-resolution spectrum synthesis techniques (Lindgren et al 2016;Lindgren & Heiter 2017;Souto et al 2017Souto et al , 2018bSouto et al , 2020Souto et al , 2022Veyette et al 2017;Passegger et al 2018Passegger et al , 2019aPassegger et al , 2019bPassegger et al , 2020aPassegger et al , 2020bRajpurohit et al 2018aRajpurohit et al , 2018bLópez-Valdivia et al 2019;Birky et al 2020;Khata et al 2021;Marfil et al 2021;Sarmento et al 2021) have demonstrated that reliable stellar parameters for M dwarfs can be obtained, although there are certainly systematic differences between the metallicity results that still need to be evaluated in detail. The study of M dwarfs in open clusters as benchmarks offers the possibility to test the metallicity scale as a function of the M-dwarf effective temperature and also quantify possible systematic metallicity differences between the M dwarfs and the hotter FGK stars.…”

Section: Introductionmentioning

confidence: 99%

Stellar Characterization and Radius Inflation of Hyades M-dwarf Stars from the APOGEE Survey

Wanderley¹,

Cunha²,

Souto³

et al. 2023

ApJ

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We present a spectroscopic analysis of a sample of 48 M-dwarf stars (0.2 M ⊙ < M < 0.6 M ⊙) from the Hyades open cluster using high-resolution H-band spectra from the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Our methodology adopts spectrum synthesis with LTE MARCS model atmospheres, along with the APOGEE Data Release 17 line list, to determine effective temperatures, surface gravities, metallicities, and projected rotational velocities. The median metallicity obtained for the Hyades M dwarfs is [M/H] = 0.09 ± 0.03 dex, indicating a small internal uncertainty and good agreement with optical results for Hyades red giants. Overall, the median radii are larger than predicted by stellar models by 1.6% ± 2.3% and 2.4% ± 2.3%, relative to a MIST and DARTMOUTH isochrone, respectively. We emphasize, however, that these isochrones are different, and the fractional radius inflation for the fully and partially convective regimes have distinct behaviors depending on the isochrone. Using a MIST isochrone there is no evidence of radius inflation for the fully convective stars, while for the partially convective M dwarfs the radii are inflated by 2.7% ± 2.1%, which is in agreement with predictions from models that include magnetic fields. For the partially convective stars, rapid rotators present on average higher inflation levels than slow rotators. The comparison with SPOTS isochrone models indicates that the derived M-dwarf radii can be explained by accounting for stellar spots in the photosphere of the stars, with 76% of the studied M dwarfs having up to 20% spot coverage, and the most inflated stars with ∼20%–40% spot coverage.

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Estimating Teff, radius, and luminosity of M-dwarfs using high-resolution optical and NIR spectral features

Cited by 7 publications

References 80 publications

Metallicities in M dwarfs: Investigating different determination techniques

Metallicities in M dwarfs: Investigating different determination techniques

An unusually low-density super-Earth transiting the bright early-type M-dwarf GJ 1018 (TOI-244)

Stellar Characterization and Radius Inflation of Hyades M-dwarf Stars from the APOGEE Survey

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