We present a new method to determine the star formation and metal enrichment histories of any resolved stellar system. This method is based on the fact that any observed star in a colour-magnitude diagram will have a certain probability of being asso
ciated with an isochrone characterised by an age t and metallicity [Fe/H] (i.e. to have formed at the time and with the metallicity of that isochrone). We formulate this as a maximum likelihood problem that is then solved with a genetic algorithm. We test the method with synthetic simple and complex stellar populations. We also present tests using real data for open and globular clusters. We are able to determine parameters for the clusters (t, [Fe/H]) that agree well with results found in the literature. Our tests on complex stellar populations show that we can recover the star formation history and age-metallicity relation very accurately. Finally, we look at the history of the Carina dwarf galaxy using deep BVI data. Our results compare well with what we know about the history of Carina.
The connection between long GRBs and supernovae is now well established. I briefly review the evidence in favor of this connection and summarise where we are observationally. I also use a few events to exemplify what should be done and what type of d
ata are needed. I also look at what we can learn from looking at SNe not associated with GRBs and see how GRBs fit into the broad picture of stellar explosions.
We present the results from a multi-epoch survey of two regions of M33 using the 3.5m WIYN telescope. The inner field is located close to the centre of the galaxy, with the outer region situated about 5.1 kpc away in the southern spiral arm, allowing
us to sample a large metallicity range. We have data for 167 fundamental mode Cepheids in the two regions. The reddening-free Wesenheit magnitude Wvi period-luminosity relations were used to establish the distance modulus of each region, with mu_{inner} = 24.37 +- 0.02 mag and mu_{outer} = 24.54 +- 0.03 mag. The apparent discrepancy between these two results can be explained by the significant metallicity gradient of the galaxy. We determine a value for the metallicity parameter of the Period--Luminosity relation gamma = d(m-M)/d log(Z) = -0.29 +- 0.11 mag/dex, consistent with previous measurements. This leads to a metallicity corrected distance modulus to M33 of 24.53 +- 0.11 mag.
We have started a survey of M 33 in order to find variable stars and Cepheids in particular. We have obtained more than 30 epochs of gri data with the CFHT and the one-square-degree camera MegaCam. We present first results from this survey, including
the search for variable objects and a basic characterization of the various groups of variable stars.
