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We present optical and near-IR spectroscopic observations of the luminousblue variable SN 2009ip during its remarkable photometric evolution of 2012.The spectra sample three key points in the SN 2009ip lightcurve, correspondingto its initial brightening in August (2012-A) and its dramatic rebrightening inearly October (2012-B). Based on line fluxes and velocities measured in ourspectra, we find a surprisingly low I(H-alpha)/I(H-beta) ~ 1.3-1.4 in the2012-B spectra. Such a ratio implies either a rare Case B recombinationscenario where H-alpha, but not H-beta, is optically thick, or an extremelyhigh density for the circumstellar material of n_e > 10^13 cm^(-3) The H-alphaline intensity yields a minimum radiating surface area of >~20,000 AU^2 inH-alpha at the peak of SN 2009ip's photometric evolution. Combined with thenature of this object's spectral evolution in 2012, a high circumstellardensity and large radiating surface area imply the presence of a thin diskgeometry around the central star (and, consequently, a possible binarycompanion), suggesting that the observed 2012-B rebrightening of SN 2009ip canbe attributed to the illumination of the disk's inner rim by fast-moving ejectaproduced by the underlying events of 2012-A.

The Peculiar Balmer Decrement of SN 2009ip: Constraints on Circumstellar Geometry