We are now clearly in an age of full-blown exoplanet discovery and characterization. Over 1700 exoplanets are known and confirmed, and there are thousands of additional, probable exoplanet…

We are now clearly in an age of full-blown exoplanet discovery and characterization. Over 1700 exoplanets are known and confirmed, and there are thousands of additional, probable exoplanet candidates from the results of the kepler mission. However, atmospheric detection and characterization understandably lags behind. Nevertheless, there is a nontrivial list of known exoplanetary atmospheres. This list includes a small handful of hydrogen-based detections, either ground-state (n=1) hydrogen detected in lyman alpha absorption, or excited (n=2) hydrogen detected in h-alpha (i.e., balmer alpha) absorption. These detections reveal extended atmospheres and possibly interactions between STARS and their planets. The proposing team made the first detection of h-alpha in an exoplanet's atmosphere (HD 189733B; jensen ET AL. 2012) through highresolution transmission spectroscopy---the differencing of a star's spectrum with the planet in- and out-of-transit. The team also has observations of additional targets in-hand (primarily the 9.2M hobby-eberly telescope, but also with the keck i/hires), with significant continued access to necessary observing resources through the hobby-eberly telescope. We are proposing a two-pronged approach to study exoplanetary exospheres. First, we propose to continue our observing program with the HET and keck i to study the h-alpha transition in extended atmospheres, and expand on our previous work by searching for evidence of additional balmer absorption (primarily h-beta); our original work (redfield ET AL. 2008; jensen ET AL. 2011, 2012) did not include spectral coverage at these wavelengths, but our in-hand keck and most recent HET observations do. We will specifically target systems that are more likely to show exospheric absorption, taking advantage of upgrades that the HET is currently undergoing. The second approach we will use is to theoretically explore the possibility that a semi-opaque exosphere has an impact on white light transits. Some preliminary work on this has been already done (barbosa DE souza, redfield,&jensen 2014), and the theoretical models can be compared to existing kepler data and future data from the recently-approved K2 mission, of which one member of the proposing team (redfield) has made successful campaign 0 and 1 proposals. The proposed work has significant relevance to the NASA strategic science question: "what are the characteristics of planetary systems orbiting other STARS, and do they harbor life?" and the NASA science area objective: "generate a census of extra-solar planets and measure their properties."