Current Science at NOAO

Solar Infrared Spectroheliograms

Alan Clark and Marcel Bergman,University of Calgary; Doug Rabin and Claude Plymate,NSO/National Science Foundation

Image at "moustache" peak intensity.

June, 1999  |  Alan Clark and Marcel Bergman (University of Calgary), and Doug Rabin and Claude Plymate (NSO) used the Near Infra-red Imaging Camera at the McMath-Pierce Telescope to image an active region on the Sun in the light of an infrared hydrogen line for the first time. These results are part of a broader infrared spectroscopic imaging program to explore the distribution across active regions and the limb of many metal and molecular lines in order to develop new diagnostic tests for atmospheric models of both quiet and active regions of the Sun.

The active region NOAA 8350 was observed during a period of excellent seeing on 8 October 1998, at a time when a bright Ellerman bomb appeared on a light bridge crossing the main sunspot. Images of small, bright Ellerman bombs on the fringe of the penumbra are about 1 arcsec in diameter, almost matching the limiting resolution of the telescope at these IR wavelengths. These features show the characteristic "moustache" spectral signature for spectral lines. The most interesting feature, a bright Ellerman bomb, can be seen on the light bridge which crosses the sunspot. The spectral frame centered on this feature, which is crossed by several N2O absorption lines from the Earth's atmosphere, clearly shows the moustache emission extending over most of the 3 cm-1 spectral range. A spectroheliogram at a wavelength near the peak of the emission clearly shows the intense brightness as well as the structure of the transient event, while a spectroheliogram centered on Br-alpha shows no brightening, as expected. The matching CaII K image also shows this bright feature.

Image at Br-alpha Line Center.

The appearance of the sunspot in Br-alpha is interesting in its own right. The dark umbra is surrounded by a bright penumbra, which itself is surrounded by plage regions which appear dark against the quiet photosphere. This behavior has been seen in subsequent observations of other sunspots.

For more information see:
   NOAO Newsletter

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