We present the first spectroscopic abundance determination of iron , \alpha -elements ( Si , Ca and Ti ) and sodium for the Mira variable V1 in the metal-rich globular cluster NGC 5927 .
We use high-resolution ( R \sim 28 , 000 ) , high signal-to-noise ratio ( \sim 200 ) spectra collected with WINERED , a near-infrared ( NIR ) spectrograph covering simultaneously the wavelength range 0.91–1.35 \mu m. The effective temperature and the surface gravity at the pulsation phase of the spectroscopic observation were estimated using both optical ( V ) and NIR time-series photometric data .
We found that the Mira is metal-rich ( [ Fe/H ] = -0.55 \pm 0.15 ) and moderately \alpha -enhanced ( [ \alpha /Fe ] = 0.15 \pm 0.01 , \sigma =0.2 ) .
These values agree quite well with the mean cluster abundances based on high-resolution optical spectra of several cluster red giants available in the literature ( [ Fe/H ] = -0.47 \pm 0.06 , [ \alpha /Fe ] = +0.24 \pm 0.05 ) .
We also found a Na abundance of +0.35 \pm 0.20 that is higher than the mean cluster abundance based on optical spectra ( +0.18 \pm 0.13 ) .
However , the lack of similar spectra for cluster red giants and that of corrections for departures from local-thermodynamical equilibrium prevents us from establishing whether the difference is intrinsic or connected with multiple populations .
These findings indicate a strong similarity between optical and NIR metallicity scales in spite of the difference in the experimental equipment , data analysis and in the adopted spectroscopic diagnostics .