Benchmarking the effective temperature scale of red giant branch stellar models: the case of the metal-poor halo giant HD 122563

Abstract

There is plenty of evidence in the literature of significant discrepancies between the observations and models of metal-poor red giant branch stars, in particular regarding the effective temperature, teff, scale. We revisit the benchmark star HD 122563 using the most recent observations from Gaia Data Release 3, to investigate if these new constraints may help in resolving this discrepancy. We review the most recent spectroscopic determinations of the metallicity of HD 122563 [Fe/H], and provide a new assessment of its fundamental parameters, i.e. bolometric luminosity, teff, surface gravity, plus a photometric determination of its metal content. Using these constraints, we compare the position of the star in the Hertzsprung-Russell (H-R) diagram with various recent sets of stellar evolution tracks. The H-R diagram analysis reveals a significant disagreement between observed and theoretical teff values, when adopting the most recent spectroscopic estimate of [Fe/H]. On the other hand, by using the photometric determination of [Fe/H] some of the selected sets of stellar tracks appear in fair agreement with observations. The sets with discrepant teff can be made to agree with observations either by modifying the prescription adopted to calculate the models' outer boundary conditions, and/or by reducing the adopted value of the mixing length parameter with respect to the solar-calibration. A definitive assessment of whether the teff scale of metal-poor stellar red giant branch models is consistent with observations requires an even more accurate determination of the fundamental parameters of HD 122563 and also a larger sample of calibrators. From the theoretical side, it is crucial to minimise the current uncertainties in the treatment (boundary conditions, temperature gradient) of the outer layers of stellar models with convective envelopes.

accepted for publication in A&A

References in corpus (29)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Gaia Data Release 3: Analysis of RVS spectra using the General Stellar Parametriser from spectroscopy
• Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I -- methods and content overview
• Observational constraints on the origin of the elements. IV: The standard composition of the Sun
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• Gaia Data Release 3: External calibration of BP/RP low-resolution spectroscopic data
• Improvements to stellar structure models, based on a grid of 3D convection simulations. II. Calibrating the mixing-length formulation
• The Stagger-grid: A grid of 3D stellar atmosphere models - III. The relation to mixing-length convection theory
• The brightness of the Red Giant Branch tip: Theoretical framework, a set of reference models, and predicted observables
• First Results From The Hertzsprung Song Telescope: Asteroseismology Of The G5 Subgiant Star {\Mu}Her
• Age dating of an early Milky Way merger via asteroseismology of the naked-eye star $\nu$ Indi
• Changing the ${\nu }_{\max }$ Scaling Relation: The Need For a Mean Molecular Weight Term
• Improvements to Stellar Structure Models, Based on a Grid of 3D Convection Simulations. I. $T(\tau )$-Relations
• Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
• On the Use of Blanketed Atmospheres as Boundary Conditions for Stellar Evolutionary Models
• Benchmark stars for Gaia: fundamental properties of the Population II star HD140283 from interferometric, spectroscopic and photometric data
• Accurate effective temperatures of the metal-poor benchmark stars HD 140283, HD 122563 and HD 103095 from CHARA interferometry
• Stellar models with mixing length and T(tau) relations calibrated on 3D convection simulations
• Fundamental stellar parameters of benchmark stars from CHARA interferometry. I. Metal-poor stars
• Stellar models with the ML2 theory of convection
• Asteroseismic versus Gaia distances: a first comparison
• Detections of solar-like oscillations in dwarfs and subgiants with Kepler DR25 short-cadence data
• Evidence of structural discontinuities in the inner core of red-giant stars
• Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. V. Oxygen abundance in the metal-poor giant HD 122563 from OH UV lines
• First detection of oscillations in the Halo giant HD 122563: validation of seismic scaling relations and new fundamental parameters
• Models for Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. III. Grids of Isochrones for $-2.5\le$ [Fe/H] $\le -0.5$ and Helium Abundances $Y=0.25$ and $0.29$ at Each Metallicity
• M92 (NGC~6341) Is a Metal-Complex Globular Cluster with an Atypical Primordial Population

Cited by in corpus (1)

• Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) II. Unveiling the formation and evolution of the kinematically selected Thick and Thin Discs