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| Paper: |
The horizontal branch luminosity-metallicity relation - Preliminary work |
| Volume: |
13, The Formation and Evolution of Star Clusters |
| Page: |
293 |
| Authors: |
Sarajedini, Ata; Lederman, Andrew |
| Abstract: |
Using the Yale Luminosity Functions, we parameterize the absolute magnitude of the RGB 'bump' in terms of (Fe/H) and age. Assuming a linear relation between horizontal branch (HB) luminosity and metallicity, we derive a simple algebraic expression that describes the slope of the HB luminosity-metallicity relation in terms of relative metallicities, relative ages, and relative observed magnitudes of the RGB 'bump' for Y = 0.24. Using available values for these quantities in seven globular clusters all relative to NGC 104 (47 Tuc), we compute a slope of 0.15 +/- 0.05 (s.d.) for the variation of HB luminosity with metallicity. Since the absolute level of the 'bump' as predicted by theoretical luminosity functions is known to be too bright when compared to the observational data, we use the recent determinations of RR Lyrae absolute magnitudes in NGC 6121 (M4) via the Baade-Wesselink Method to set our zeropoint. This gives a value of 1.00 +/- 0.08 mag for the zeropoint. In general, a slope of 0.32 or greater is ruled out by this analysis unless a majority of the clusters considered here are younger than 47 Tuc by about 2 Gyr. |
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