Light+Echoes

Light Echoes

Tuesday 20 September 2011, 14:00-15:30

Organized by Howard E. Bond and Armin Rest

The phenomenon of a light echo occurs when light from a transient event, such as a supernova or other eruptive stellar outburst, scatters off nearby dust and reaches the Earth at later times. The first light echo was seen over a century ago, following the outburst of Nova Persei 1901. However, the subject has recently received renewed interest because of the spectacular light echo around V838 Monocerotis (which produced iconic Hubble Space Telescope images) and discoveries of light echoes from ancient supernovae and other luminous transients in the Magellanic Clouds and Milky Way, allowing spectroscopic observations with modern equipment of events that occurred centuries ago.

In extragalactic astronomy, "reverberation mapping" is a closely related technique used to study the structure of active galactic nuclei.

This workshop will start with brief summaries of the subject, including the geometry of light echoes, their use for astrophysical applications such as geometric distance determination, spectral typing and expansion velocities of the illuminating objects (as seen from different viewing angles), and obtaining 3-dimensional dust structure. We will then open a round-table discussion of various issues.

Outline for 90-minute session:

o Bond [~10-15 min]:

- Review of light-echo geometry - apparent superluminal expansion - Examples of light echoes imaged by HST - V838 Mon: an intermediate-luminosity red transient - Cepheid RS Puppis: nested light echoes - flaring young stellar object in IC 348 - Geometric distance determination from polarimetry

o Rest [~10 min]:

- Searching for echoes from historical events - LMC SNe - Galactic SNe - LBV's - classical novae - Spectral typing of ancient events & spectral evolution during outbursts - Asymmetries revealed by the different viewing angles - 3D dust structure

o Clayton [~10 min]:

- Light and shadow echoes around R CrB stars

o Bentz [~10 min]:

- Reverberation Mapping: Continuum Variability Echoes in the Broad-Line Region of AGNs

o General discussion; how can the scientific return from light echoes be enhanced?

- What are the challenges for full exploitation of light echoes? - Optimal telescope scheduling; TOO's; quick response scenarios - When new luminous transient event occurs, can we coordinate the search for light echoes? - Role of photographic archives - Recommendations for the future