We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured ≈ 6,300 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 CaII 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; iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to both SEGUE-SDSS and degraded HR spectra totalling 6,451 low resolution (LR, R ∼ 2,000) spectra for 5,001 RRLs (3,439 RRab, 1,562 RRc). This resulted in an iron distribution with a median of -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.

On the Use of Field RR Lyrae as Galactic Probes. II. A new $Delta$S calibration to estimate their metallicity / CRESTANI RIBEIRO DE SOUZA, Juliana; Fabrizio, Michele; Braga, Vittorio F.; Sneden, Christopher; Preston, George W.; Ferraro, I.; Iannicola, G.; Bono, Giuseppe; Alves-Brito, Alan; Nonino, Mario; D'Orazi, Valentina; Inno, L.; Monelli, M.; Storm, J.; Altavilla, G.; Chaboyer, B.; Dall'Ora, Massimo; Fiorentino, Giuliana; Gilligan, C. K.; Grebel, Eva; Lemasle, B.; Marengo, Massimo; Marinoni, S.; Marrese, P. M.; Martínez-Vázquez, C. E.; Matsunaga, N.; Mullen, J. P.; Neeley, J.; Prudil, Z.; Stetson, Ronaldo da Silva P. B.; Thévenin, F.; Walker, Vitor Engrácia Valenti A. R.; Zoccali, M.; Lala, H.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 1538-4357. - (2021).

On the Use of Field RR Lyrae as Galactic Probes. II. A new $Delta$S calibration to estimate their metallicity

Juliana Crestani;Michele Fabrizio;Vittorio F. Braga;I. Ferraro;Massimo Dall'Ora;
2021

Abstract

We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured ≈ 6,300 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 CaII 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; iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to both SEGUE-SDSS and degraded HR spectra totalling 6,451 low resolution (LR, R ∼ 2,000) spectra for 5,001 RRLs (3,439 RRab, 1,562 RRc). This resulted in an iron distribution with a median of -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.
Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Astrophysics of Galaxies
01 Pubblicazione su rivista::01a Articolo in rivista
On the Use of Field RR Lyrae as Galactic Probes. II. A new $Delta$S calibration to estimate their metallicity / CRESTANI RIBEIRO DE SOUZA, Juliana; Fabrizio, Michele; Braga, Vittorio F.; Sneden, Christopher; Preston, George W.; Ferraro, I.; Iannicola, G.; Bono, Giuseppe; Alves-Brito, Alan; Nonino, Mario; D'Orazi, Valentina; Inno, L.; Monelli, M.; Storm, J.; Altavilla, G.; Chaboyer, B.; Dall'Ora, Massimo; Fiorentino, Giuliana; Gilligan, C. K.; Grebel, Eva; Lemasle, B.; Marengo, Massimo; Marinoni, S.; Marrese, P. M.; Martínez-Vázquez, C. E.; Matsunaga, N.; Mullen, J. P.; Neeley, J.; Prudil, Z.; Stetson, Ronaldo da Silva P. B.; Thévenin, F.; Walker, Vitor Engrácia Valenti A. R.; Zoccali, M.; Lala, H.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 1538-4357. - (2021).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1485686
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