Lorentz Covariant Theory of Light Propagation in Gravitational Fields of Arbitrary-Moving Bodies

The Lorentz covariant theory of propagation of light in the (weak) gravitational fields of N-body systems consisting of arbitrarily moving point-like bodies with constant masses is constructed. The theory is based on the Lienard-Wiechert presentation of the metric tensor. A new approach for integrating the equations of motion of light particles depending on the retarded time argument is applied. In an approximation which is linear with respect to the universal gravitational constant, G, the equations of light propagation are integrated by quadratures and, moreover, an expression for the tangent vector to the perturbed trajectory of light ray is found in terms of instanteneous functions of the retarded time. General expressions for the relativistic time delay, the angle of light deflection, and gravitational red shift are derived. They generalize previously known results for the case of static or uniformly moving bodies. The most important applications of the theory are given. They include a discussion of the velocity dependent terms in the gravitational lens equation, the Shapiro time delay in binary pulsars, and a precise theoretical formulation of the general relativistic algorithm of data processing of radio and optical astrometric measurements in the non-stationary gravitational field of the solar system. Finally, proposals for future theoretical work being important for astrophysical applications are formulated.Comment: 77 pages, 7 figures, list of references is updated, to be published in Phys. Rev. D6

Constraining corotation from shocks in tightly-wound spiral galaxies

We present a new method for estimating the corotation radius in tightly wound spiral galaxies, through analysis of the radial variation of the offset between arms traced by the potential (P-arms) and those traced by dust (D-arms). We have verified the predictions of semi-analytical theory through hydrodynamical simulations and have examined the uniqueness of the galactic parameters that can be deduced by this method. We find that if the range of angular offsets measured at different radii in a galaxy is greater than around pi/4, it is possible to locate the radius of corotation to within ~ 25%. We argue that the relative location of the P- and D-arms provides more robust constraints on the galactic parameters than can be inferred from regions of enhanced star formation (SF-arms), since interpretation of the latter involves uncertainties due to reddening and the assumed star formation law. We thus stress the importance of K-band studies of spiral galaxies.Comment: Accepted for publication in MNRAS. 15 pages, 23 figure

Spin and quadrupole contributions to the motion of astrophysical binaries

Compact objects in general relativity approximately move along geodesics of spacetime. It is shown that the corrections to geodesic motion due to spin (dipole), quadrupole, and higher multipoles can be modeled by an extension of the point mass action. The quadrupole contributions are discussed in detail for astrophysical objects like neutron stars or black holes. Implications for binaries are analyzed for a small mass ratio situation. There quadrupole effects can encode information about the internal structure of the compact object, e.g., in principle they allow a distinction between black holes and neutron stars, and also different equations of state for the latter. Furthermore, a connection between the relativistic oscillation modes of the object and a dynamical quadrupole evolution is established.Comment: 43 pages. Proceedings of the 524. WE-Heraeus-Seminar "Equations of Motion in Relativistic Gravity". v2: fixed reference. v3: corrected typos in eqs. (1), (57), (85

Holmberg II - A laboratory for studying the violent interstellar medium

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

A Multi-Wave length Survey of the ISM in NGC 628

Original paper can be found at http://www.astrosociety.org/pubs/cs/156-194.html--Copyright Astronomical Society of the PacificIs atomic hydrogen a precursor to or byproduct of the star formation process? Recent evidence suggests that a large percentage of the atomic hydrogen in spiral galaxies could be due to photodissociation of molecular gas by UV radiation from hot young stars

THINGS: The HI Nearby Galaxy Survey

Original article can be found at: http://www.iop.org/EJ/journal/aj Copyright American Astronomical Society DOI: 10.1088/0004-6256/136/6/2563We present “The HI Nearby Galaxy Survey (THINGS)”, a high spectral (≤5.2 kms−1) and spatial (~ 6′′) resolution survey of HI emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA). The overarching scientific goal of THINGS is to investigate fundamental characteristics of the interstellar medium (ISM) related to galaxy morphology, star formation and mass distribution across the Hubble sequence. Unique characteristics of the THINGS database are the homogeneous sensitivity as well as spatial and velocity resolution of the HI data which is at the limit of what can be achieved with the VLA for a significant number of galaxies.Peer reviewe