Xu et al., ApJ 607, L131, 2004:or, how do flare footpoints work?

• First flare observations in the infrared

• 1.56 nominally is as deep as deep can be (the opacity minimum)

• Lucky to get an X10 flare (Oct. 29, 2003; good RHESSI observations)

Left: speckle WL preflare; right, flare image at 1.56

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20:52:1520:42:4620:39:45

Nice Sa”m Krucker RHESSI images

Footpoints and ribbons

• Anchor flaring coronal loops and interface with the mass reservoir there

• Traditional modeling in 1D radiation hydro approximation

• Hard X-ray (beam?) and UV-O-IR (deep atmosphere?) morphology significantly different

Nitty-gritty of the observations

• Dunn Solar Telescope @ near diffraction limit, high-order AO

• 10242 NIR array, 5nm passband @ 1.56, 13 ms sampling, 91 arc s FOV

• IR has better seeing (-6/5) but should have lower contrast

Ancient history! Ohki & Hudson, 1975

Blue: RHESSI 50-100 keV; Red: IR

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Bruzek, 1964

Maltby models for sunspot umbraand particle ranges

Flare spectroscopy: Shoji & Kurokawa 1995

Annotated conclusions

• Backwarming response (theory somewhat confused)

• V x B @ 45 V/cm, but is this really a relevant E?

• Weak photospheric lines in the passband - do they contribute?