Galactic vs. Extragalactic Origin of the Peculiar Transient SCP 06F6

We study four scenarios for the SCP 06F6 transient event that was announced recently. Some of these were previously briefly discussed as plausible models for SCP 06F6, in particular with the claimed detection of a z=0.143 cosmological redshift of a Swan spectrum of a carbon rich envelope. We adopt this value of z for extragalactic scenarios. We cannot rule out any of these models, but can rank them from most to least preferred. Our favorite model is a tidal disruption of a CO white dwarf (WD) by an intermediate-mass black hole (IMBH). To account for the properties of the SCP 06F6 event, we have to assume the presence of a strong disk wind that was not included in previous numerical simulations. If the IMBH is the central BH of a galaxy, this explains the non detection of a bright galaxy in the direction of SCP 06F6. Our second favorite scenario is a type Ia-like SN that exploded inside the dense wind of a carbon star. The carbon star is the donor star of the exploded WD. Our third favorite model is a Galactic source of an asteroid that collided with a WD. Such a scenario was discussed in the past as the source of dusty disks around WDs, but no predictions exist regarding the appearance of such an event. Our least favorite model is of a core collapse SN. The only way we can account for the properties of SCP 06F6 with a core collapse SN is if we assume the occurrence of a rare type of binary interaction.Comment: Accepted by New Astronom

An Analysis of Solution Properties of the Graph Coloring Problem

This paper concerns the analysis of solution properties of the Graph Coloring Problem. For this purpose, we introduce a property based on the notion of representative sets which are sets of vertices that are always colored the same in a set of solutions. Experimental results on well-studied DIMACS graphs show that many of them contain such sets and give interesting information about the diversity of the solutions. We also show how such an analysis may be used to improve a tabu search algorithm

An Evolutionary Annealing Approach to Graph Coloring

This paper presents a new heuristic algorithm for the graph coloring problem based on a combination of genetic algorithms and simulated annealing. Our algorithm exploits a novel crossover operator for graph coloring. Moreover, we investigate various ways in which simulated annealing can be used to enhance the performance of an evolutionary algorithm

Register allocation by optimal graph coloring

We here present new insights of properties of real-life interference graphs emerging in register allocation. These new insights imply good hopes for a possibility of improving the coloring approach towards optimal solutions. The conclusions axe based on measurements of nearly 28,000 real instances of such interference graphs. All the instances explored are determined to possess the so-called 1-perfectness property, a fact that seems to make them easy to color optimally. The exact algorithms presented not only produce better solutions than the traditional heuristic methods, but also, indeed, seem to perform surprisingly fast, according to the measurements on our implementations