Volume 540, April 2012
|Number of page(s)||20|
|Section||Galactic structure, stellar clusters and populations|
|Published online||20 March 2012|
Metallicities for globular clusters from R97 on the Carretta et al. (2009) scale.
The sum of equivalent widths for the strongest two CaT lines measured with Gaussian-only fits are plotted here against the same quantity measured with Gaussian+Lorentzian fits. The latter are taken from the G09 paper, for stars in the clusters M 5 (+ signs), NGC 4372 (filled triangles), NGC 6752 (filled 5-point stars), NGC 6397 (open 5-point stars), NGC 6171 (open squares) and NGC 4590 (6-point stars). The interpolating line has slope f = 1.147, and it was obtained by minimizing residuals and imposing the passage through the origin.
|Open with DEXTER|
Same as Fig. A.1, for the stars observed for this work. The symbols identify NGC 3201 (open circles), M 10 (open triangles), M 4 (open diamonds), M 15 ( × signs) and M 71 (open squares). The fitting line has slope f = 1.090 and passes through the origin.
|Open with DEXTER|
We define the reduced equivalent width for a single star as W′ = S − a (V − VHB) where S = W8542 + W866210. So we can write for the (G)09 and (A)D91 systems: and the averaged reduced equivalent widths are: By comparing measurements of individual S made with the G09 or the AD91 method, we found that SG = f SA, and by imposing a linear fit that is passing through (0,0) we found for clusters of the Leo I paper f = 1.147 (see Fig. A.1) and for clusters in this run f = 1.090 (see Fig. A.2). So then in the G09 system:
then we have and with a substitution where for simplicity we wrote ΣHB = Σ(V − VHB). Rearranging and simplifying a bit more: which gives as a function of f (with f = 1.090 or f = 1.147), the number of stars N measured for each cluster, the averaged reduced equivalent width in the AD91 system, the slopes aA and aG of the S vs. V − VHB relations in the two systems, and the sum of the magnitude differences with respect to the HB, ΣHB. The difference in slopes f is probably due to the fact that older spectra had a better resolution (slit of instead of 1″), so it might be that the Gauss-only fit does a worse job with line wings in that case.
© ESO, 2012
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