Periodic masers in massive star forming regions

The first periodic Class II methanol maser was reported on in 2003. Since that time, a number of different monitoring programmes have found periodic masers, as well as other modes of variability. In a few cases, periodicity has been found in other maser species such as formaldehyde and water. Several distinct characteristics of light curves have been noted, possibly pointing to different underlying mechanisms for periodicity if one assumes a linear response to incoming radiation. I will give a brief overview of the known periodic sources, discuss current theories, and present new results obtained from monitoring mainline hydroxyl masers using the seven-element Karoo Array Telescope (KAT-7) during its science verification phase.

CLASS IV BEHAVIOR IN CELLULAR AUTOMATA MODELS OF PHYSICAL SYSTEMS

Wolfram’s cellular automata [1986] can be classified according to their asymptotic behavior: class I (homogeneous), class II (periodic), class III (chaotic) and class IV (“undecidable”, i.e. erratically changing between periodicity and chaos). While these automata are purely number-theoretical and suffer from ill-defined parametrization, we present here examples of automata describing actual physical systems and governed by well-defined control parameters: resting states between earthquakes, pigmentation on the shells of molluscs, and two-dimensional reaction–diffusion systems. We find that the dynamics of these three systems can be classified analogously to Wolfram’s automata. Moreover, we find agreement between class IV simulations and real shell patterns, indicating that these shells indeed present evidence for class IV behavior in nature. In addition, we performed an intuitively appealing quantification by averaging the fluctuations of the borders of error-propagation patterns.