SPATIALLY RESOLVED 3 μm SPECTROSCOPY OF ELIAS 1: ORIGIN OF DIAMONDS IN PROTOPLANETARY DISKS

We present spatially resolved 3 μm spectra of Elias 1 obtained with an adaptive optics system. The central part of the disk is almost devoid of polycyclic aromatic hydrocarbon (PAH) emission at 3.3 μm; it shows up only at 30 AU and beyond. The PAH emission extends up to 100 AU, at least to the outer boundary of our observation. The diamond emission, in contrast, is more centrally concentrated, with the column density peaked around 30 AU from the star. There are only three Herbig Ae/Be stars known to date that show diamond emission at 3.53 μm. Two of them have low-mass companions likely responsible for the large X-ray flares observed toward the Herbig Ae/Be stars. We speculate on the origin of diamonds in circumstellar disks in terms of the graphitic material being transformed into diamond under the irradiation of highly energetic particles.