Precision Orbit of $\delta$ Delphini and Prospects for Astrometric Detection of Exoplanets

Combining visual and spectroscopic orbits of binary starsleads to a determination of the full 3D orbit, individual masses, and distance to the system. We present a full analysis of the evolved binary system $\delta$ Delphini using astrometric data from the MIRC and PAVO instruments on the CHARAlong-baseline interferometer, 97 new spectra from the Fairborn Observatory, and 87 unpublished spectra from LickObservatory. We determine the full set of orbital elementsfor $\delta$ Del, along with masses of $1.78 \pm 0.07$ $M_{\odot}$ and $1.62 \pm 0.07$ $M_{\odot}$ for each component, and a distance of $63.61 \pm 0.89$ pc. These results are important in two contexts: for testing stellar evolutionmodels and defining the detection capabilities for future planet searches. We find that the evolutionary state of this system is puzzling, as our measured flux ratios, radii, and masses imply a $\sim$ 200 Myr age difference between the components using standard stellar evolutionmodels. Possible explanations for this age discrepancy include mass transfer scenarios with a now ejected tertiary companion. For individual measurements taken over a span of 2 years we achieve $ 2$ M$_{J}$ on orbits $>0.75$ AU around individual components of hot binary starsvia differential astrometry.