Metallicity Estimates for Old Star Clusters in M33

Using the theoretical stellar population synthesis models of BC96, Kong et al. (2003) showed that some BATC colors and color indices could be used to disentangle the age and metallicity effect. They found that there is a very good relation between the flux ratio of L_{8510}/L_{9170} and the metallicity for stellar populations older than 1 Gyr. In this paper, based on the Kong et al. results and on the multicolor spectrophotometry of Ma et al. (2001, 2002a,b,c), we estimate the metallicities of 31 old star clusters in the nearby spiral galaxy M33, 23 of which are ``true'' globular clusters. The results show that most of these old clusters are metal poor. We also find that the ages and metal abundance for these old star clusters of M33 do not vary with deprojected radial position.Comment: Accepted for Publication in A&A, 13 pages, 7 figures (1 figure of jpg

The metallicity gradient as a tracer of history and structure : the Magellanic Clouds and M33 galaxies

Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO) DOI: 10.1051/0004-6361/200912138Context. The stellar metallicity and its gradient place constraints on the formation and evolution of galaxies. Aims. This is a study of the metallicity gradient of the LMC, SMC and M33 galaxies derived from their asymptotic giant branch (AGB) stars. Methods. The [Fe/H] abundance was derived from the ratio between C- and M-type AGB stars and its variation analysed as a function of galactocentric distance. Galaxy structure parameters were adopted from the literature. Results. The metallicity of the LMC decreases linearly as −0.047±0.003 dex kpc−1 out to ∼8 kpc from the centre. In the SMC, [Fe/H] has a constant value of ∼−1.25 ± 0.01 dex up to ∼12 kpc. The gradient of the M33 disc, until ∼9 kpc, is −0.078 ± 0.003 dex kpc−1 while the outer disc/halo, out to ∼25 kpc, has [Fe/H] ∼ −1.7 dex. Conclusions. The metallicity of the LMC, as traced by different populations, bears the signature of two major star forming episodes: the first one constituting a thick disc/halo population and the second one a thin disc and bar due to a close encounter with the Milky Way and SMC. The [Fe/H] of the recent episode supports an LMC origin for the Stream. The metallicity of the SMC supports star formation, ∼3 Gyr ago, as triggered by LMC interaction and sustained by the bar in the outer region of the galaxy. The SMC [Fe/H] agrees with the present-day abundance in the Bridge and shows no significant gradient. The metallicity of M33 supports an “insideout” disc formation via accretion of metal poor gas from the interstellar medium.Peer reviewe

Waves, bumps, and patterns in neural field theories

Neural field models of firing rate activity have had a major impact in helping to develop an understanding of the dynamics seen in brain slice preparations. These models typically take the form of integro-differential equations. Their non-local nature has led to the development of a set of analytical and numerical tools for the study of waves, bumps and patterns, based around natural extensions of those used for local differential equation models. In this paper we present a review of such techniques and show how recent advances have opened the way for future studies of neural fields in both one and two dimensions that can incorporate realistic forms of axo-dendritic interactions and the slow intrinsic currents that underlie bursting behaviour in single neurons