Stephen White's Research

Stephen White

Stephen White is primarily a solar radio astronomer. Radio emission can probe every part of the Sun's atmosphere, from the chromosphere just above the solar surface to the corona in which solar flares accelerate electrons to high energies and coronal mass ejections travelling at thousands of kilometers per second drive shocks. These phenomena can be seen with CARMA at millimeter wavelengths, with the Nobeyama Radio Heliograph and the Very Large Array at centimeter wavelengths, and with the Nancay Radio Heliograph and the Giant Metrewave Radio Telescope at meter wavelengths.

ADS Listing for past 5 years

Dynamics of the Solar Chromosphere
Observations of the quiet Sun at millimeter wavelengths are an important technique for studying the solar chromosphere. At these short wavelengths the Sun's atmosphere becomes optically thick in the chromosphere, and since the wavelength lies in the Rayleigh-Jeans limit, the measured radio brightness temperature is exactly the electron temperature in the layer being observed. Simulations of convection in the solar atmosphere indicate that waves with periods of 3 to 5 minutes propagate upwards into the chromosphere and will form shocks there, dissipating their energy by heating gas to temperatures of order 1000 K, and these features should be observable if we can map the chromosphere at 10 arcsecond resolution or better, which requires a millimeter interferometer. However, the solar chromosphere is the toughest possible target for an interferometer, since it completely fills the field of view with low-contrast but time-varying features. BIMA data have been used to demonstrate that in fact maps of the chromosphere can be made, and further that oscillations can be detected in time sequences of images, opening up a new method for studying heating in the Sun's atmosphere (references White et al 2006, Loukitcheva et al 2006).

Contours of 85 GHz emission overlaid on a Ca K image of a solar active region, showing the excellent correlation. This is the first successful millimeter interferometer map of the solar chromosphere.

A 30-minute movie of a solar active region at 85 GHz at 15 second cadence. The beam size is about 10 arcseconds and the field of view is about 200 arcseconds.

Green Bank Solar Radio Burst Spectrometer
Stephen White maintains the data archive and web site for the Green Bank Solar Radio Burst Spectrometer (GBSRBS), a solar radio burst patrol system located at the NRAO site at Green Bank and operating from 10 to 1070 MHz. GBSRBS provides research quality dynamic spectra of solar radio bursts at 1 second time resolution in western hemisphere time zones. Tim Bastian and Rich Bradley of NRAO are the lead investigators for this instrument.

The example at left is a high-frequency Type II burst observed on 2005 November 14.

Stephen White is also a participant in the Frequency Agile Solar Radiotelescope (FASR) project, a proposal to the NSF Atmospheric Sciences division of the National Science Foundation to build a radio telescope that will make images of the Sun at high spatial and temporal resolution from 100 to 20000 MHz.

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