329 research outputs found
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
Continuum Spectra of Quasar Accretion Disk Models
We have calculated the spectrum and polarization of a standard thin accretion
disk with parameters appropriate for a bright quasar. This model improves upon
previous work by including ultraviolet metal line opacities, assumed for now to
be in LTE. Though not yet fully self-consistent, our calculations demonstrate
that metal lines can change the spectral slope, reduce the polarization, and
reduce the Lyman edge feature in accretion disk spectra. Some observational
differences between quasar spectra and accretion disk models might be
reconciled with the inclusion of metal lines.Comment: 4 pages, 3 figures, to appear in "Accretion Processes in
Astrophysical Systems: Some Like it Hot," proceedings of the 8th Annual
October Astrophysics Conference in Marylan
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