M. Sundin

The Interaction between Spiral Galaxies IC 2163 and NGC 2207. I. Observations

Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/176374 [Full text of this article is not available in the UHRA]

The Interaction between Spiral Galaxies IC 2163 and NGC 2207. II. Models

Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/176375 [Full text of this article is not available in the UHRA]

Thermal depth profiling of materials for defect detection using hot disk technique

A novel application of the hot disk transient plane source technique is described. The new application yields the thermal conductivity of materials as a function of the thermal penetration depth which opens up opportunities in nondestructive testing of inhomogeneous materials. The system uses the hot disk sensor placed on the material surface to create a time varying temperature field. The thermal conductivity is then deduced from temperature evolution of the sensor, whereas the probing depth (the distance the heat front advanced away from the source) is related to the product of measurement time and thermal diffusivity. The presence of inhomogeneity in the structure is manifested in thermal conductivity versus probing depth plot. Such a plot for homogeneous materials provides fairly constant value. The deviation from the homogeneous curve caused by defects in the structure is used for inhomogeneity detection. The size and location of the defect in the structure determines the sensitivity and possibility of detection. In addition, a complementary finite element numerical simulation through COMSOL Multiphysics is employed to solve the heat transfer equation. Temperature field profile of a model material is obtained from these simulations. The average rise in temperature of the heat source is calculated and used to demonstrate the effect of the presence of inhomogeneity in the system.

The galactic habitable zone in barred galaxies

One of the criteria for the concept of a galactic habitable zone (GHZ) is that the pattern speed of the stars in the GHZ should be close to the pattern speed of the spiral arms. Another criteria is that the stars in it should have a high enough metallicity. In a barred galaxy, the GHZ will be more complicated to define since the bar can change stellar orbits. Many disc galaxies, including the Milky Way, are barred galaxies. The stars in the bar move in a number of fairly complicated orbits. However, the bar will also influence the orbits of stars in the whole galaxy. Stars passing close to the bar can either gain or lose angular momentum, due to a positive or negative torque by the bar. Some stars will therefore be captured by the bar while some stars eventually may reach the escape velocity from the galaxy. The bar will hence be able to relocate stars, and stars with low or high metallicity could be found far away from their original orbits. The ordinary evolution of a bar is to grow in length out to the co-rotation radius for the pattern speed of the bar. As the galaxy ages, and the bar grows in length, the bar will influence a larger part of the galaxy. The effect of moving stars inwards or outwards is greatest just outside the bar, and this region can eventually lose a high percentage of the stars. Received 6 July 2006, accepted 28 July 2006

John Bauer: Painter of a star-spangled fairy-tale world

Abstract Several generations of Swedish children have become acquainted with the world of fairy-tales through illustrations by the painter John Bauer in the Christmas magazine Goblins and Trolls . Next to his portrayal of grotesque but humorous trolls, his paintings of the Moon and the starry sky are among those best remembered. These pictures have inspired very many Swedes to take pleasure in the beauty of the stars and the movement of the Moon.

Sharp Edges Due to Close Interactions

Sharp edges of spiral arms, found in simulations and observations of galaxies in interaction, are explained kinematically using the impulse approximation. We investigate the kinematics of a galactic disc perturbed by a disturber on an unbound orbit. Such encounters can be expected to be common if galaxies are initially formed in weakly bound, low angular momentum systems. Here we shall be concerned with smaller disturbing masses (less than 10 % of the main galaxy) as larger disturbances will tend to disrupt the disc. We present results for the case of a 5 % disturber passing through the outer parts of a Kuzmin disc.