Variability of Disk Emission in Pre-main-sequence and Related Stars. IV. Investigating the Structural Changes in the Inner Disk Region of MWC 480

Abstract

We present five epochs of near-IR observations of the protoplanetary disk around MWC 480 (HD 31648) obtained with the SpeX spectrograph on NASA's Infrared Telescope Facility between 2007 and 2013, inclusive. Using the measured line fluxes in the Pa beta and Br gamma lines, we found the mass accretion rates to be (1.26-2.30) x 10(-7) M-circle dot yr(-1) and (1.4-2.01) x 10(-7) M-circle dot yr(-1), respectively, but which varied by more than 50% from epoch to epoch. The spectral energy distribution reveals a variability of about 30% between 1.5 and 10 mu m during this same period of time. We investigated the variability using of the continuum emission of the disk in using the Monte-Carlo Radiative Transfer Code HOCHUNK3D. We find that varying the height of the inner rim successfully produces a change in the NIR flux but lowers the far-IR emission to levels below all measured fluxes. Because the star exhibits bipolar flows, we utilized a structure that simulates an inner disk wind to model the variability in the near-IR, without producing flux levels in the far-IR that are inconsistent with existing data. For this object, variable near-IR emission due to such an outflow is more consistent with the data than changing the scale height of the inner rim of the disk.