H-band temperature and metallicity indicators for cool giants empirical relations in bayesian framework

Abstract

ABSTRACT We explored here the near-infrared H-band atmospheric window aiming to provide quantitative diagnostic tools for deriving stellar parameters, for instance, effective temperature (Teff) and metallicity ([Fe/H]), of cool giants (Teff < 5000 K) using low-resolution spectra. We obtained 177 cool giants from the X-shooter spectral library covering a wider metallicity range (−2.35 dex < [Fe/H] < 0.5 dex) than in earlier works. Degrading the spectral resolution to R ∼ 1200, we estimated equivalent widths of several important spectral features, and the behaviour of spectral features with stellar parameters are studied. Also, the empirical relations for deriving Teff and [Fe/H] are established in the Bayesian framework. We found that 12CO at 1.56 and 1.62 $\mu$m, and 12CO + MgI at 1.71 $\mu$m are the best threeTeff indicators with a typical accuracy of 153, 123, and 107 K, respectively. The cubic Bayesian model provides the best metallicity estimator with a typical accuracy of 0.22, 0.28, and 0.24 dex for FeH at 1.62 $\mu$m, 12CO at 1.64 $\mu$m, and Fe I at 1.66 $\mu$m, respectively. We also showed a detailed quantitative metallicity dependence ofTeff–EWs correlations defining three metallicity groups, supersolar ([Fe/H] > 0.0 dex), solar (−0.3 dex < [Fe/H] < 0.3 dex), and subsolar ([Fe/H] <−0.3 dex), from Hierarchical Bayesian modelling. The difference between the solar and subsolar relationship is statistically significant, but such difference is not evident between the solar and supersolar groups.