23 July 2014 - Mission Day: 6809 - DOY: 204

Twanging the Sun's Guitar

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Radiance and Doppler observations by SUMER

EIT 171 Å image of hot loops

Intensity (left) and velocity (right) variations of loops observed with a thin slit (time goes from left to right in each half). Red means receding material, blue means appraching.
High-resolution TIFF

An EIT 171 Å image of hot loops,
High-resolution TIFF

Caption: The latest news about the Sun's hot corona is the discovery of strong oscillations in very hot loops above active regions. The discovery is presented by Dr. Werner Curdt of Germany's Max-Planck-Institut für Aeronomie at a scientific meeting on the Greek island of Santorini this week.

"It's like twanging a guitar string, although one that's tuned to a very low bass note," according to Dr. Curdt, Principal Investigator for the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument on board SOHO.

The SUMER spectrometer observes emission lines from ionized gas (Fe XIX 1118 Å in this case), precisely determining the wavelength (or frequency) of the emission lines. Similar to the changing pitch of a whistle on a passing train, the "pitch" (or frequency/wavelength) of the emission lines change depending on the speed of the emitting material, towards or away from the observer.

This way, observations of hot loops above the limb have revealed powerful oscillations back and forth, usually in conjunction with flares observed by other instruments and/or spacecraft. The movie below (click on the image) shows SUMER spectra (inset on the left) on a background of EIT images. The SUMER slit position is indicated by the vertical line on the EIT image. One can clearly see the emission line oscillating back and forth (left-right) as the material is moving.

SUMER emission lines on EIT context image

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Picture credits: SOHO/SUMER,SOHO/EIT, (ESA & NASA)


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