We present a new calibration of the Stromgren metallicity index m(1) using red giant (RG) stars in four globular clusters (GCs: M92, M13, NGC 1851, 47 Tuc) with metallicity ranging from - 2.2 to - 0.7, marginally affected by reddening [E( B - V) <= 0: 04] and with accurate (u, v, b, y) photometry. The main difference between the new metallicity-index-color (MIC) relations and similar relations available in the literature is that we have adopted the u - y and v - y colors instead of b - y. These colors present a stronger sensitivity to effective temperature, and the MIC relations show a linear slope. The difference between photometric estimates and spectroscopic measurements for RGs in M71, NGC 288, NGC 362, NGC 6397, and NGC 6752 is 0: 04 +/- 0: 03 dex (sigma = 0: 11 dex). We also apply the new MIC relations to 85 field RGs with metallicity ranging from - 2.4 to -0.5 and accurate reddening estimates. We find that the difference between photometric estimates and spectroscopic measurements is -0.14 +/- 0.01 dex (sigma = 0.17 dex). We also provide two sets of MIC relations based on evolutionary models that have been transformed into the observational plane by adopting either semiempirical or theoretical color-temperature relations. We apply the semiempirical relations to the nine GCs and find that the difference between photometric and spectroscopic metallicities is 0.04 +/- 0.03 dex (sigma = 0.10 dex). A similar agreement is found for the sample of field RGs, with a difference of -0.09 +/- 0.03 dex (with sigma = 0.19 dex). The difference between metallicity estimates based on theoretical relations and spectroscopic measurements is -0.11 +/- 0.03 dex (sigma = 0.14 dex) for the nine GCs and -0.24 +/- 0.03 dex (sigma = 0.15 dex) for the field RGs. Current evidence indicates that new MIC relations provide metallicities with an intrinsic accuracy better than 0.2 dex.

Calamida, A., Bono, G., Stetson, P.b., Freyhammer, L.m., Cassisi, S., Grundahl, F., et al. (2007). Stromgren photometry of galactic globular clusters. I. New calibrations of the metallicity index. THE ASTROPHYSICAL JOURNAL, 670(1), 400-422 [10.1086/521424].

Stromgren photometry of galactic globular clusters. I. New calibrations of the metallicity index

BONO, GIUSEPPE;BUONANNO, ROBERTO;
2007-01-01

Abstract

We present a new calibration of the Stromgren metallicity index m(1) using red giant (RG) stars in four globular clusters (GCs: M92, M13, NGC 1851, 47 Tuc) with metallicity ranging from - 2.2 to - 0.7, marginally affected by reddening [E( B - V) <= 0: 04] and with accurate (u, v, b, y) photometry. The main difference between the new metallicity-index-color (MIC) relations and similar relations available in the literature is that we have adopted the u - y and v - y colors instead of b - y. These colors present a stronger sensitivity to effective temperature, and the MIC relations show a linear slope. The difference between photometric estimates and spectroscopic measurements for RGs in M71, NGC 288, NGC 362, NGC 6397, and NGC 6752 is 0: 04 +/- 0: 03 dex (sigma = 0: 11 dex). We also apply the new MIC relations to 85 field RGs with metallicity ranging from - 2.4 to -0.5 and accurate reddening estimates. We find that the difference between photometric estimates and spectroscopic measurements is -0.14 +/- 0.01 dex (sigma = 0.17 dex). We also provide two sets of MIC relations based on evolutionary models that have been transformed into the observational plane by adopting either semiempirical or theoretical color-temperature relations. We apply the semiempirical relations to the nine GCs and find that the difference between photometric and spectroscopic metallicities is 0.04 +/- 0.03 dex (sigma = 0.10 dex). A similar agreement is found for the sample of field RGs, with a difference of -0.09 +/- 0.03 dex (with sigma = 0.19 dex). The difference between metallicity estimates based on theoretical relations and spectroscopic measurements is -0.11 +/- 0.03 dex (sigma = 0.14 dex) for the nine GCs and -0.24 +/- 0.03 dex (sigma = 0.15 dex) for the field RGs. Current evidence indicates that new MIC relations provide metallicities with an intrinsic accuracy better than 0.2 dex.
2007
Pubblicato
Rilevanza internazionale
Articolo
Sì, ma tipo non specificato
Settore FIS/05 - ASTRONOMIA E ASTROFISICA
English
Globular clusters: general; Globular clusters: individual (M13, M71, M92, NGC 288, NGC 362, NGC 1851, NGC 6397, NGC 6752, 47 Tucanae); Stars: abundances stars: evolution
Calamida, A., Bono, G., Stetson, P.b., Freyhammer, L.m., Cassisi, S., Grundahl, F., et al. (2007). Stromgren photometry of galactic globular clusters. I. New calibrations of the metallicity index. THE ASTROPHYSICAL JOURNAL, 670(1), 400-422 [10.1086/521424].
Calamida, A; Bono, G; Stetson, Pb; Freyhammer, Lm; Cassisi, S; Grundahl, F; Pietrinferni, A; Hilker, M; Primas, F; Richtler, T; Romaniello, M; Buonanno, R; Caputo, F; Castellani, M; Corsi, Ce; Ferraro, I; Iannicola, G; Pulone, L
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/56162
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