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LkCa 15 is an extensively studied star in the Taurus region known for itspre-transitional disk with a large inner cavity in dust continuum and normalgas accretion rate. The most popular hypothesis to explain the LkCa 15 datainvokes one or more planets to carve out the inner cavity, while gas continuesto flow across the gap from the outer disk onto the central star. We presentspatially unresolved HCO+ J=4-3 observations of the LkCa 15 disk from the JCMTand model the data with the ProDiMo code. We find that: (1) HCO+ line-wings areclearly detected, certifying the presence of gas in the cavity within <50 AU ofthe star. (2) Reproducing the observed line-wing flux requires both asignificant suppression of cavity dust (by a factor >10^4 compared to the ISM)and a substantial increase in the gas scale-height within the cavity (H_0/R_0 ~0.6). An ISM dust-to-gas ratio (d:g=10^-2) yields too little line-wing fluxregardless of the scale-height or cavity gas geometry, while a smallerscale-height also under predicts the flux even with a reduced d:g. (3) Thecavity gas mass is consistent with the surface density profile of the outerdisk extended inwards to the sublimation radius (corresponding to mass M_d ~0.03 M_sun), and masses lower by a factor >10 appear to be ruled out.

HCO+ Detection of Dust-Depleted Gas in the Inner Hole of the LkCa 15 Pre-Transitional Disk