000006659 001__ 6659
000006659 005__ 20240125123844.0
000006659 0247_ $$2DOI$$a10.1051/0004-6361/202347208
000006659 037__ $$aSCART-2024-0038
000006659 100__ $$aGiribaldi, R. E.
000006659 245__ $$aTITANS metal-poor reference stars. II. Red giants and CEMP stars
000006659 260__ $$c2023
000006659 520__ $$aContext. Representative samples of F-, G-, K-type stars located outside of the solar neighbourhood have started to become available in spectroscopic surveys. The fraction of metal-poor ([Fe/H] ≲ −0.8 dex) giants becomes increasingly relevant towards greater distances. In metal-poor stars, effective temperatures (Teff) based on local thermodynamic equilibrium (LTE) spectroscopy and on former colour-Teff relations - which are still widely used - have been reported to be inaccurate. It is necessary to recalibrate chemical abundances based on these Teff scales in the multiple available surveys in order to bring them to the same standard scale for their simultaneous use. To this end, a complete sample of standards is required, which until now has been restricted to a few stars with quasi-direct Teff measurements. Aims: We aim to provide a legacy sample of metal-poor standards with proven accurate atmospheric parameters. We add 47 giants to the TITANS metal-poor reference stars. Methods: We derived Teff using 3D non-LTE Hα modelling, the accuracy of which was tested against interferometry and with the Infra Red Flux Method (IRFM). We derived surface gravity (log ɡ) by fitting Mg I b triplet lines, and tested their accuracy against asteroseismology. Metallicity was derived using Fe II lines, and we find our results to be identical to the [Fe/H] derived from non-LTE spectral synthesis. Results: The Teff that we find using 3D non-LTE Hα is equivalent to interferometric and IRFM temperatures within a ±46 K uncertainty. We achieve precision of ~50 K for 34 stars with spectra with the highest signal-to-noise ratio (S/N). For log ɡ, we achieve a total uncertainty of ±0.15 dex. For [Fe/H], we obtain a total uncertainty of ±0.09 dex. We find that the ionisation equilibrium of Fe lines under LTE is not valid in metal-poor giants. LTE leads to a small but significant metallicity underestimation of ~0.1 dex when derived from weak Fe I lines, and only provided accurate Teff and log ɡ. This bias totally disappears under non-LTE. 
000006659 536__ $$aPrf-2020-033_BISTRO/$$cPrf-2020-033_BISTRO/$$fPrf-2020-033_BISTRO
000006659 594__ $$aNO
000006659 6531_ $$asurveys
000006659 6531_ $$atechniques: spectroscopic
000006659 6531_ $$astars: atmospheres
000006659 6531_ $$astars: fundamental parameters
000006659 6531_ $$astars: Population II
000006659 6531_ $$astars: carbon
000006659 6531_ $$aAstrophysics
000006659 6531_ $$aSolar and Stellar Astrophysics
000006659 6531_ $$aAstrophysics of Galaxies 
000006659 700__ $$aVan Eck, S.
000006659 700__ $$aMerle, T.
000006659 700__ $$aJorissen, A.
000006659 700__ $$aKrynski, P.
000006659 700__ $$aPlanquart, L.
000006659 700__ $$aValentini, M.
000006659 700__ $$aChiappini, C.
000006659 700__ $$aVan Winckel, H.
000006659 773__ $$pAstronomy & Astrophysics$$v679$$y2023
000006659 8560_ $$fthibault.merle@ksb-orb.be
000006659 85642 $$ahttps://ui.adsabs.harvard.edu/abs/2023A%26A...679A.110G/abstract
000006659 905__ $$apublished in
000006659 980__ $$aREFERD