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Lower Limits on Lorentz Factors in Gamma-Ray Bursts
As is well known, the requirement that gamma-ray bursts be optically thin to high-energy photons yields a lower limit on the Lorentz factor (γ) of the expansion. In this paper, we provide a simple
Densities and Eccentricities of 139 Kepler Planets from Transit Time Variations
We extract densities and eccentricities of 139 sub-Jovian planets by analyzing transit time variations (TTVs) obtained by the Kepler mission through Quarter 12. We partially circumvent the
Secular Dynamics in Hierarchical Three-Body Systems
The secular approximation for the evolution of hierarchical triple configurations has proven to be very useful in many astrophysical contexts, from planetary to triple-star systems. In this
Compressible Magnetohydrodynamic Turbulence in Interstellar Plasmas
Radio wave scintillation observations reveal a nearly Kolmogorov spectrum of density fluctuations in the ionized interstellar medium. Although this density spectrum is suggestive of turbulence, no
Planet formation by coagulation: A focus on Uranus and Neptune
Planets form in the circumstellar disks of young stars. We review the basic physical processes by which solid bodies accrete each other and alter each others' random velocities, and we provide
Most planet pairs in the Kepler data that have measured transit time variations (TTVs) are near first-order mean-motion resonances. We derive analytical formulae for their TTV signals. We separate
The Intrinsic Size of Sagittarius A* from 0.35 to 6 cm
We present new high-resolution observations of Sagittarius A* at wavelengths of 17.4-23.8 cm with the Very Large Array in the A configuration with the Pie Town Very Long Baseline Array (VLBA)
We analyze the transit timing variations (TTV) obtained by the Kepler mission for 22 sub-Jovian planet pairs (19 published, 3 new) that lie close to mean motion resonances. We find that the TTV
Final Stages of Planet Formation
We address three questions regarding solar system planets: What determined their number? Why are their orbits nearly circular and coplanar? How long did they take to form? Runaway accretion in a