paper

Observability of Scattered-Light Echoes Around Variable Stars and Cataclysmic Events

arXiv:astro-ph/0307245 · doi:10.1086/378358

Abstract

Scattered light echoes from variable and cataclysmic stars offer one of the most effective means to probe the structure and composition of circumtellar and interstellar media. I build a simple model of light-echo surface brightness by considering the source spectrum, and the dust density, geometry, and scattering efficiency. I use this model to investigate whether echoes should be observable around short and long-period giants, cataclysmic variables, and supernovae. Only supernovae are expected to illuminate material on both circumstellar and interstellar scales. Giant and post-AGB stars (e.g. Cepheids and Miras) with high mass-loss rates can produce observable echoes within their circumstellar envelopes. Echoes from novae and dwarf novae are probably detectable only from nearby material, and only in unusually dense gas. I present characteristic exposure times to image such echoes over a wide range of wavelengths for ground-based and {\em Hubble Space Telescope} observations. I apply these results to analyze the dust properties of the recently-reported echoes around SN 1993J, finding the dust in M81 to have a grain-size distribution and chemical composition consistent with Galactic dust. Optimal observing strategies for echo detection are also discussed.

43 pages, 18 figures; Accepted for publication in the AJ

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