GPI Spectra of HR 8799 c, d, and e from 1.5 to 2.4 μm with KLIP Forward Modeling

Abstract

We explore KLIP forward modeling spectral extraction on Gemini Planet Imager coronagraphic data of HR 8799,usingPyKLIP,and show algorithm stability with varying KLIP parameters. We report new and re-reducedspectrophotometry of HR 8799 c, d, and e in theHandKbands. We discuss a strategy for choosing optimal KLIPPSF subtraction parameters by injecting simulated sources and recovering them over a range of parameters. TheK1/K2spectra for HR 8799 c and d are similar to previously published results from the same data set. We alsopresent aK-band spectrum of HR 8799 e for thefirst time and show that ourH-band spectra agree well withpreviously published spectra from the VLT/SPHERE instrument. We show that HR 8799 c and d show significantdifferences in theirHandKspectra, but do notfind any conclusive differences between d and e, nor between c ande, likely due to large error bars in the recovered spectrum of e. Compared to M-, L-, and T-typefield brown dwarfs,all three planets are most consistent with mid- and late-L spectral types. All objects are consistent with low gravity,but a lack of standard spectra for low gravity limit the ability tofit the best spectral type. We discuss how dedicatedmodeling efforts can betterfit HR 8799 planets’near-IRflux, as well as how differences between the properties ofthese planets can be further explored.