On the chemical abundances of Miras in clusters: V1 in the metal-rich globular NGC 5927

• Published in: arXiv.org 2018-02
• Main Authors: D'Orazi, V, Magurno, D, Bono, G, Matsunaga, N, Braga, V F, Elgueta, S S, Fukue, K, Hamano, S, Inno, L, Kobayashi, N, Kondo, S, Monelli, M, Nonino, M, Przybilla, P N, Sameshima, H, Saviane, I, Taniguchi, D, Thevenin, F, Urbaneja-Perez, M, Watase, A, Arai, A, Bergemann, M, Buonanno, R, Dall'Ora, M, Silva, R, Fabrizio, M, Ferraro, I, Fiorentino, G, Francois, P, Gilmozzi, R, Iannicola, G, Ikeda, Y, Jian, M, Kawakita, H, R -P Kudritzki, Lemasle, B, Marengo, M, Marinoni, S, Martinez-Vasquez, C, Minniti, D, Neeley, J, Otsubo, S, Prieto, J L, Proxauf, B, Romaniello, M, Sanna, N, Sneden, C, Takenaka, K, Tsujimoto, T, Valenti, E, Yasui, C, Yoshikawa, T, Zoccali, M
• Format: Article
• Language: English
• Subjects: Abundance; Alpha iron; Data analysis; Globular clusters; High resolution; Metallicity; Mira variables; Near infrared radiation; Organic chemistry; Photometry; Sodium; Spectra; Thermodynamic equilibrium; Titanium
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1802.07314

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~ 28,000), high signal-to-noise ratio (~200) spectra collected with WINERED, a near-infrared (NIR) spectrograph covering simultaneously the wavelength range 0.91--1.35 micron. 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.