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74 - Z. Fan 2009
We present the photometry of 30 globular clusters (GCs) and GC candidates in 15 intermediate-band filters covering from ~3000 to ~10000 AA using the archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan - Connecticut (BATC) Mu lticolour Sky Survey. We transform these intermediate-band photometric data to the photometry in the standard UBVRI broad-bands. These M31 GC candidates are selected from the Revised Bologna Catalogue (RBC V.3.5), and most of these candidates do not have any photometric data. Therefore the present photometric data are supplement to RBC V.3.5. We find that 4 out of 61 GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at their locations. By linear fit of the distribution in colour-magnitude diagram of blue GCs and GC candidates using the data from RBC V.3.5, and in this study we find the ``blue-tilt of blue M31 GCs with a high confidence at 99.95% or 3.47 sigma for the confirmed GCs, and >99.99% or 4.87 sigma for GCs and GC candidates.
249 - Z. Fan 2007
Using metallicities from the literature, combined with the Revised Bologna Catalogue of photometric data for M31 clusters and cluster candidates (the latter of which is the most comprehensive catalogue of M31 clusters currently available, including 3 37 confirmed globular clusters -- GCs -- and 688 GC candidates), we determine 443 reddening values and intrinsic colours, and 209 metallicities for individual clusters without spectroscopic observations. This, the largest sample of M31 GCs presently available, is then used to analyse the metallicity distribution of M31 GCs, which is bimodal with peaks at $rm {[Fe/H]}approx -1.7$ and -0.7 dex. An exploration of metallicities as a function of radius from the M31 centre shows a metallicity gradient for the metal-poor GCs, but no such gradient for the metal-rich GCs. Our results show that the metal-rich clusters appear as a centrally concentrated spatial distribution; however, the metal-poor clusters tend to be less spatially concentrated. There is no correlation between luminosity and metallicity among the M31 sample clusters, which indicates that self-enrichment is indeed unimportant for cluster formation in M31. The reddening distribution shows that slightly more than half of the GCs are affected by a reddening of $E(B-V) la 0.2$ mag; the mean reddening value is $E(B-V) = 0.28_{-0.14}^{+0.23}$ mag. The spatial distribution of the reddening values indicates that the reddening on the northwestern side of the M31 disc is more significant than that on the southeastern side, which is consistent with the conclusion that the northwestern side in nearer to us.
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