A Differential Measurement of Circumstellar Extinction for AA Tau’s 2011 Dimming Event*

Abstract AA Tau is a classical T Tauri star with highly inclined, warped circumstellar disk. For decades, exhibited photometric and spectroscopic variabilities that were successfully modeled as occultations of the primary by material. In 2011, entered an extended faint state, presumably due to enhanced levels dust. We use two sets contemporaneous optical–near-IR (NIR) spectra Tau, obtained in 2008 2014 December, directly measure wavelength-dependent extinction associated dust enhancement driving Tau’s 2011 optical fade. Taken alone, apparent optical–NIR increased curve cannot be fit well standard laws. At wavelengths, dimming event consistent predictions common models for increase A V = 2, but no such model reproduces color–color excess at NIR wavelengths. show veiling emission accounts anomalous extinction: after including this flux, 2 law across full range. also report mid-IR flux since its fade suggest height inner disk most likely explanation both IR brightening additional along line sight. addition informing our understanding analysis demonstrates caution should exercised when inferring (and stellar parameters) from young stars measurable fluxes.