Collaborative Research: Polarimetric Imaging and Spectroscopy of the Corona from 500-1500nm during Total Solar Eclipses

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The proposed four-year project will take advantage of unique opportunities offered by the total solar eclipses of 29 March 2006 (Libya) and 1 August 2008 (China-Russia) for imaging and spectroscopy of polarized coronal emissions at wavelengths spanning the visible to the near infrared. Polarized emission is a characteristic of some of the strongest coronal emission lines, while polarized fluorescence is a property of nanometer size dust particles. The near infrared polarimetric observations carried out by the PI during the eclipse of 21 June 2001 led to the serendipitous discovery of the signature of nanometer size dust particles in the inner corona. These 2001 observations also pointed to the potential existence of a discrete spectrum resulting from the fluorescence of these dust grains, and their spectrum is likely to be embedded within the spectrum of coronal ionic lines. By observing the next eclipses, the PI plans to infer the direction of the coronal magnetic field at different stages of the solar cycle, uncover the spectrum of nanometer size dust grains in the inner corona, and establish the relationship between interplanetary dust grains and the coronal magnetic field. In addition to the observations from Libya and China-Russia, simultaneous and identical observations will be made with the coronagraph in Hawaii. All the coronal observations will be compared with polarimetric laboratory measurements of fluorescence from silicon nanoparticles, which can be synthesized into stable and reproducible discrete sizes that fluoresce in the blue, green, yellow, and infrared part of the spectrum, under non-resonant UV or resonant excitation of their emission bands. Knowledge of the direction of the coronal field is critical for establishing the fraction of the solar magnetic flux that escapes into interplanetary space carrying the solar wind with it. Embedded in the solar wind, the interplanetary magnetic field shapes the environment of planets and defines the heliosphere. While the field also shapes cometary tails, it is likely to be responsible for the distribution of dust particles in the corona that may come from the sublimation of sun-grazing comets. The proposed program opens a new research direction by exploring the coupled signature of the coronal magnetic field direction and the fluorescence spectrum from nanoparticle dust grains in the inner corona. This effort will complement the laboratory experiments on polarized fluorescence from silicon nanoparticles.