Details

Autor(en) / Beteiligte

• Crestani, J.
• Fabrizio, M.
• Braga, V. F.
• Sneden, C.
• Preston, G.
• Ferraro, I.
• Iannicola, G.
• Bono, G.
• Alves-Brito, A.
• Nonino, M.
• D’Orazi, V.
• Inno, L.
• Monelli, M.
• Storm, J.
• Altavilla, G.
• Chaboyer, B.
• Dall’Ora, M.
• Fiorentino, G.
• Gilligan, C.
• Grebel, E. K.
• Lala, H.
• Lemasle, B.
• Marengo, M.
• Marinoni, S.
• Marrese, P. M.
• Martínez-Vázquez, C. E.
• Matsunaga, N.
• Mullen, J. P.
• Neeley, J.
• Prudil, Z.
• Silva, R. da
• Stetson, P. B.
• Thévenin, F.
• Valenti, E.
• Walker, A.
• Zoccali, M.

Titel

On the Use of Field RR Lyrae as Galactic Probes. II. A New ΔS Calibration to Estimate Their Metallicity

Ist Teil von

• The Astrophysical journal, 2021-02, Vol.908 (1), p.20

Ort / Verlag

Philadelphia: IOP Publishing

Erscheinungsjahr

2021

Link zum Volltext

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• Abstract We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured ≈6300 high-resolution (HR, R ∼ 35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well-defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the Δ S method. This diagnostic, based on the equivalent widths of Ca ii K and three Balmer (H δ , γ , β ) lines, traces the metallicity of RRLs. For the first time, the new empirical calibration: (i) includes spectra collected over the entire pulsation cycle; (ii) includes RRc variables; (iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; and (iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to a data set of both SEGUE-SDSS and degraded HR spectra totalling 6451 low-resolution ( R ∼ 2000) spectra for 5001 RRLs (3439 RRab, 1562 RRc). This resulted in an iron distribution with a median η = −1.55 ± 0.01 and σ = 0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments.