Imaging planets around nearby white dwarfs

We suggest that Jovian planets will survive the late stages of stellar evolution, and that white dwarfs will retain planetary systems in wide orbits (≳5 au). Utilizing evolutionary models for Jovian planets, we show that infrared imaging with 8-m class telescopes of suitable nearby white dwarfs should allow us to resolve and detect companions ≳3 M _JUP. Detection of massive planetary companions to nearby white dwarfs would prove that such objects can survive the final stages of stellar evolution, place constraints on the frequency of main-sequence stars with planetary systems dynamically similar to our own and allow direct spectroscopic investigation of their composition and structure.     

Statistical Analysis of the Fluctuations Detected in High-Altitude Neutron Monitor,Solar and Interplanetary Parameters

Galactic cosmic ray fluctuations from six mountain altitude neutron monitors around the world are analyzed during the period 1990–1999. The period comprises the maximum and declining phase of solar cycle 22 and the beginning of cycle 23. The evolution of the most significant periodicities and comparisons with solar activity and interplanetary indicators are presented. We found a 38-day variation present in all neutron monitors, solar activity parameters, and IMF fluctuations. The possible origin of this and other stable periodicities of cosmic ray variations in the analyzed period are discussed.     

The Cosmology of Extra Dimensions and Varying Fundamental Constants

I briefly present the Organizing Committee's and my own motivation for organizing this workshop, and I suggest a few key questions for which we will try to find possible answers in the coming days. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamics of a satellite orbiting a planet with an inhomogeneous gravitational field

We study the dynamics of a satellite (artificial or natural) orbiting an Earth-like planet at low altitude from an analytical point of view. The perturbation considered takes into account the gravity attraction of the planet and in particular it is caused by its inhomogeneous potential. We begin by truncating the equations of motion at second order, that is, incorporating the zonal and the tesseral harmonics up to order two. The system is formulated as an autonomous Hamiltonian and has three degrees of freedom. After three successive Lie transformations, the system is normalised with respect to two angular co-ordinates up to order five in a suitable small parameter given by the quotient between the angular velocity of the planet and the mean motion of the satellite. Our treatment is free of power expansions of the eccentricity and of truncated Fourier series in the anomalies. Once these transformations are performed, the truncated Hamiltonian defines a system of one degree of freedom which is rewritten as a function of two variables which generate a phase space which takes into account all of the symmetries of the problem. Next an analysis of the system is achieved obtaining up to six relative equilibria and three types of bifurcations. The connection with the original system is established concluding the existence of various families of invariant 3-tori of it, as well as quasiperiodic and periodic trajectories. This is achieved by using KAM theory techniques.     

Is Ursa Major II the progenitor of the Orphan Stream?

Prominent in the 'Field of Streams'– the Sloan Digital Sky Survey map of substructure in the Galactic halo – is an 'Orphan Stream' without obvious progenitor. In this numerical study, we show a possible connection between the newly found dwarf satellite Ursa Major II (UMa II) and the Orphan Stream. We provide numerical simulations of the disruption of UMa II that match the observational data on the position, distance and morphology of the Orphan Stream. We predict the radial velocity of UMa II as −100 km s⁻¹, as well as the existence of strong velocity gradients along the Orphan Stream. The velocity dispersion of UMa II is expected to be high, though this can be caused both by a high dark matter content or by the presence of unbound stars in a disrupted remnant. However, the existence of a gradient in the mean radial velocity across UMa II provides a clear-cut distinction between these possibilities. The simulations support the idea that some of the anomalous, young halo globular clusters like Palomar 1 or Arp 2 or Ruprecht 106 may be physically associated with the Orphan Stream.     

Active galactic nuclei heating in the centres of galaxy groups: a statistical study

We present gas temperature, density, entropy and cooling time profiles for the cores of a sample of 15 galaxy groups observed with Chandra . We find that the entropy profiles follow a power-law profile down to very small fractions of R ₅₀₀. Differences between the gas profiles of groups with radio-loud and radio-quiet brightest group galaxies are only marginally significant, and there is only a small difference in the   L _X: T _X  relations, for the central regions we study with Chandra , between the radio-loud and radio-quiet objects in our sample, in contrast to the much larger difference found on scales of the whole group in earlier work. However, there is evidence, from splitting the sample based on the mass of the central black holes, that repeated outbursts of active galactic nuclei (AGN) activity may have a long-term cumulative effect on the entropy profiles. We argue that, to first order, energy injection from radio sources does not change the global structure of the gas in the cores of groups, although it can displace gas on a local level. In most systems, it appears that AGN energy injection serves primarily to counter the effects of radiative cooling, rather than being responsible for the similarity breaking between groups and clusters.