CONFIRMATION OF A GAPPED PRIMORDIAL DISK AROUND LkCa 15

摘要

Recently, analysis of near-infrared broadband photometry and Spitzer IRS spectra has led to the identification of a new "pre-transitional disk" class whose members have an inner optically thick disk separated from an outer optically thick disk by an optically thin gap. This is in contrast to the "transitional disks" that have inner disk holes (i.e., large reductions of small dust from the star out to an outer optically thick wall). In LkCa 15, one of these proposed pre-transitional disks, detailed modeling showed that although the near-infrared fluxes could be understood in terms of optically thick material at the dust sublimation radius, an alternative model of emission from optically thin dust over a wide range of radii could explain the observations as well. To unveil the true nature of LkCa 15's inner disk, we obtained a medium-resolution near-infrared spectrum spanning the wavelength range 2-5 μm using SpeX at the NASA Infrared Telescope Facility. We report that the excess near-infrared emission above the photosphere of LkCa 15 is a blackbody continuum that can only be due to optically thick material in an inner disk around the star. When this confirmation of a primordial inner disk is combined with earlier observations of an inner edge to LkCa 15's outer disk, it reveals a gapped structure. Forming planets emerge as the most likely mechanism for clearing the gap we detect in this evolving disk.