Galactic Center ADAF Ruled out By Polarization

Recent observations of linear polarization at high frequency towards the galactic center radio source, Sgr A*, place strong constraints on the nature of the radio emission region. We discuss how these constraints rule out the larger accretion rate need for low efficiency accretion flows, such as advection-dominated accretion flows, and we present a toy model which can explain the radio to sub-mm spectrum and polarization of Sgr A*

Transit timing to first order in eccentricity

Characterization of transiting planets with transit timing variations (TTVs) requires understanding how to translate the observed TTVs into masses and orbital elements of the planets. This can be challenging in multi-planet transiting systems, but fortunately these systems tend to be nearly plane-parallel and low eccentricity. Here we present a novel derivation of analytic formulae for TTVs that are accurate to first order in the planet-star mass ratios and in the orbital eccentricities. These formulae are accurate in proximity to first order resonances, as well as away from resonance, and compare well with more computationally expensive N-body integrations in the low eccentricity, low mass-ratio regime when applied to simulated and to actual multi-transiting Kepler planet systems. We make code available for implementing these formulae.Comment: Revised to match published version; associated code may be found at https://github.com/ericagol/TTVFaste