"Using Simulations of the X-ray Emission from Black Holes to Dissect the Inner Regions of Accretion Flow"
Janie Hoormann (Washington U., St. Louis)
X-ray observations of black holes provide an opportunity to probe the strong gravity regime of General Relativity (GR) and the properties of inner accretion flow. To this end, a ray tracing code was developed to simulate the X-ray spectral, timing, and polarization signatures surrounding stellar and supermassive black holes for both the thermal disk and power-law emission. These simulations can be used to study the recently observed reverberation between the direct coronal emission and the reflected emission forming the Iron K alpha line and the Compton hump with particular attention taken to examine the effect the ionization of the disk will have on the reverberation observations. In addition, these calculations can also be performed for various spacetime backgrounds (both GR and non-GR) to constrain potential deviations from the No-Hair theorem which states black holes are only described by their mass, spin, and charge.
"Asteroseismic Tests of Stellar Isochrones"
Jamie Tayar (Astronomy)
With the combination of APOGEE spectroscopic data and asteroseismology from Kepler, there are now thousands of evolved stars with known masses, metallicities, temperatures, gravities, compositions, and evolutionary states. We find strong evidence for metallicity dependent offsets between the actual HR diagram position of evolved stars and that predicted by isochrones. Such offsets have been suggested previously, but they are particularly obvious in our uniquely well characterized data set. We compare this to results from 3D atmosphere calculations and discuss consistency with convection theory. We also show that these temperature offsets can cause large errors in the ages derived from HR diagram position.