Program: GN-2008B-DD-4

The young A star Fomalhaut hosts a belt of dusty material with a morphology that implies the presence of a shepherding planet (Kalas et al. 2005). We request DDT to follow up the exciting discovery of a common proper motion companion to Fomalhaut, which appears to be the predicted exoplanet. We estimate that the mass of Fomalhaut b is less than three Jupiter masses: a more massive object would disrupt the dust belt and would be hotter than the 400 K effective temperature estimated from the HST/ACS F814W flux. Despite deep imaging with Keck AO, Fomalhaut b is not detected in H. This suggests either an error in the model exoplanet spectra or that reflected starlight contributes to the detected signal in the HST bands. NIRI provides very sensitive imaging at Lp, thus, we propose to observe Fomalhaut b at this wavelength. This measurement offers the best opportunity to measure the thermal emission from Fomalhaut b, to check the fidelity of the exoplanet model spectra, and to place limits on the fraction of scattered/reflected light at shorter wavelengths.