Though thousands of exoplanets have been discovered, only a few of the most massive, either at very close or very wide separations, are amenable to spectroscopic characterization. The rest are…

The National Aeronautics and Space Administration (NASA) awarded a $360,676.72 grant to the University of California, Santa Barbara (UCSB) to conduct research on exoplanet characterization. The research aims to use the SCExAO and CHARIS instruments on the Subaru Telescope to survey for new exoplanets around nearby young stars, obtain and characterize spectra of both newly discovered and known exoplanets, and use the spectra to infer the planets' properties and connect them to theories of giant planet formation. This fundamental research seeks to address challenges in calibrating and statistically analyzing exoplanet spectra obtained through high-contrast imaging in order to better understand exoplanet atmospheric chemistry, surface gravity, and heat supply. The research outcomes could provide much-needed validation of theoretical models of exoplanet and brown dwarf atmospheres, and the techniques developed will be applicable to future space-based observatories like the James Webb Space Telescope, WFIRST, HABEX, and LUVOIR. There was no set-aside designation for this grant, which was awarded directly to UCSB, a public research university, by NASA.

Though thousands of exoplanets have been discovered, only a few of the most massive, either at very close or very wide separations, are amenable to spectroscopic characterization. The rest are observed only through their effects on their host STARS: their orbits, masses and/or radii are all that is known. By obtaining spectra of massive, wide-separation planets, we can probe their atmospheric chemistry and abundances, constrain their surface gravities (and hence their masses), and infer their heat supply at formation. Spectroscopic characterization can resolve the controversy over how these planets formed and enable US to understand the physical state of their atmospheres, including temperature and pressure profiles and the formation of clouds and hazes. The same techniques will ultimately provide a way to search for nonequilibrium chemistry in the atmospheres of rocky planets, a potential signature of life. We propose to use the new instruments scexao and charis on the subaru telescope to (1) conduct a survey for new exoplanets around nearby young STARS visible from the northern hemisphere, (2) obtain, calibrate, and characterize spectra of known and newly-discovered planets, and (3) use these spectra to infer planet properties and connect them to theories of giant planet formation. Charis has the broadest simultaneous bandpass of any instrument in its class, which enables US to distinguish diffracted starlight from the light of faint exoplanets close to their STARS. Scexao's use of incoherent satellite spots (jovanovic ET AL. 2015) will enable US to accurately calibrate the position and brightness of planets. Spectra obtained with the aid of high-contrast imaging are, by their nature, difficult to calibrate and characterize. This makes proper statistical comparisons with theoretical spectra impossible, and makes IT difficult to infer the planets' chemistry and atmospheric conditions. Published exoplanet spectra have used high-pass filters (konopacky ET AL. 2013), generically omit covariances, and have used a range of extraction algorithms in an attempt to understand systematic uncertainties (macintosh ET AL. 2015). Our research program will combine new extraction algorithms with scexao's calibration capabilities to enable deeper searches for new planets, and statistically rigorous comparisons of observed spectra with theoretical models. These comparisons are the only way to infer the exoplanets' chemical abundances, which could point to the locations in the protoplanetary disk where the planets formed. Our observed and calibrated spectra will provide much-needed tests of theoretical models of exoplanet and brown dwarf atmospheres, while the algorithms and statistical techniques we develop will be applicable to data from jwst and from future missions like wfirst, habex and luvoir.