Chemical signatures of the first star clusters

The chemical abundance patterns of the oldest stars in the Galaxy are expected to contain residual signatures of the first stars in the early universe. Numerous studies attempt to explain the intrinsic abundance scatter observed in some metal-poor populations in terms of chemical inhomogeneities dispersed throughout the early Galactic medium due to discrete enrichment events. Just how the complex data and models are to be interpreted with respect to "progenitor yields" remains an open question. Here we show that stochastic chemical evolution models to date have overlooked a crucial fact. Essentially all stars today are born in highly homogeneous star clusters and it is likely that this was also true at early times. When this ingredient is included, the overall scatter in the abundance plane [Fe/H] vs. [X/Fe] (C-space), where X is a nucleosynthetic element, can be much less than derived from earlier models. Moreover, for moderately flat cluster mass functions (gamma < 2), and/or for mass functions with a high mass cut-off (M_max > 10^5 M_sun), stars exhibit a high degree of clumping in C-space that can be identified even in relatively small data samples. Since stellar abundances can be modified by mass transfer in close binaries, clustered signatures are essential for deriving the yields of the first supernovae. We present a statistical test to determine whether a given set of observations exhibit such behaviour. Our initial work focusses on two dimensions in C-space, but we show that the clustering signal can be greatly enhanced by additional abundance axes. The proposed experiment will be challenging on existing 8-10m telescopes, but relatively straightforward for a multi-object echelle spectrograph mounted on a 25-40m telescope.Comment: 24 pages, 17 figs; Astrophysical Journal (Sept 20 issue); a full copy is available at http://sydney.edu.au/science/physics/~jbh/share/firststarclusters.pd

A New Simplified Federated Single Sign-on System

The work presented in this MPhil thesis addresses this challenge by developing a new simplified FSSO system that allows end-users to access desktop systems, web-based services/applications and non-web based services/applications using one authentication process. This new system achieves this using two major components: an “Authentication Infrastructure Integration Program (AIIP) and an “Integration of Desktop Authentication and Web-based Authentication (IDAWA). The AIIP acquires Kerberos tickets (for end-users who have been authenticated by a Kerberos single sign-on system in one net- work domain) from Kerberos single sign-on systems in different network domains without establishing trust between these Kerberos single sign-on systems. The IDAWA is an extension to the web-based authentication systems (i.e. the web portal), and it authenticates end-users by verifying the end-users\u27 Kerberos tickets. This research also developed new criteria to determine which FSSO system can deliver true single sign-on to the end-users (i.e. allowing end-users to access desktop systems, web-based services/applications and non-web based services/applications using one authentication process). The evaluation shows that the new simplified FSSO system (i.e. the combination of AIIP and IDAWA) can deliver true single sign-on to the end- users. In addition, the evaluation shows the new simplified FSSO system has advantages over existing FSSO systems as it does not require additional modifications to network domains\u27 existing non-web based authentication infrastructures (i.e. Kerberos single sign- on systems) and their firewall rules