DISENTANGLING THE ORIGIN AND HEATING MECHANISM OF SUPERNOVA DUST: LATE-TIME<i>SPITZER</i>SPECTROSCOPY OF THE TYPE IIn SN 2005ip

Abstract

This paper presents late-time near-infrared and {\\it Spitzer} mid-infrared\nphotometric and spectroscopic observations of warm dust in the Type IIn SN\n2005ip in NGC 2906. The spectra show evidence for two dust components with\ndifferent temperatures. Spanning the peak of the thermal emission, these\nobservations provide strong constraints on the dust mass, temperature, and\nluminosity, which serve as critical diagnostics for disentangling the origin\nand heating mechanism of each component. The results suggest the warmer dust\nhas a mass of $\\sim 5 \\times 10^{-4}~$\\msolar, originates from newly formed\ndust in the ejecta, or possibly the cool, dense shell, and is continuously\nheated by the circumstellar interaction. By contrast, the cooler component\nlikely originates from a circumstellar shock echo that forms from the heating\nof a large, pre-existing dust shell $\\sim 0.01 - 0.05$~\\msolar~by the late-time\ncircumstellar interaction. The progenitor wind velocity derived from the blue\nedge of the He 1 1.083 \\micron~P Cygni profile indicates a progenitor eruption\nlikely formed this dust shell $\\sim$100 years prior to the supernova explosion,\nwhich is consistent with a Luminous Blue Variable (LBV) progenitor star.\n