A SPATIALLY RESOLVED INNER HOLE IN THE DISK AROUND GM AURIGAE

Abstract

We present 0.3 arcsec resolution observations of the disk around GM Aurigae\nwith the Submillimeter Array (SMA) at a wavelength of 860 um and with the\nPlateau de Bure Interferometer at a wavelength of 1.3 mm. These observations\nprobe the distribution of disk material on spatial scales commensurate with the\nsize of the inner hole predicted by models of the spectral energy distribution.\nThe data clearly indicate a sharp decrease in millimeter optical depth at the\ndisk center, consistent with a deficit of material at distances less than ~20\nAU from the star. We refine the accretion disk model of Calvet et al. (2005)\nbased on the unresolved spectral energy distribution (SED) and demonstrate that\nit reproduces well the spatially resolved millimeter continuum data at both\navailable wavelengths. We also present complementary SMA observations of CO\nJ=3-2 and J=2-1 emission from the disk at 2" resolution. The observed CO\nmorphology is consistent with the continuum model prediction, with two\nsignificant deviations: (1) the emission displays a larger CO J=3-2/J=2-1 line\nratio than predicted, which may indicate additional heating of gas in the upper\ndisk layers; and (2) the position angle of the kinematic rotation pattern\ndiffers by 11 +/- 2 degrees from that measured at smaller scales from the dust\ncontinuum, which may indicate the presence of a warp. We note that\nphotoevaporation, grain growth, and binarity are unlikely mechanisms for\ninducing the observed sharp decrease in opacity or surface density at the disk\ncenter. The inner hole plausibly results from the dynamical influence of a\nplanet on the disk material. Warping induced by a planet could also potentially\nexplain the difference in position angle between the continuum and CO data\nsets.\n