Harald Paleske has double stacked two Lunt CaK modules: http://www.cloudynig.../Number/5171136
. Features do not seem to change as much as they do with H alpha DSing.
I received this PM from bob71741:
Bob - I got this from John Varsik at BBSO [Big Bear Solar Observatory] some time ago, and hopefully may provide some insight on what you observed.
“You can download the CaK absorption line spectra online to see the K1, K2, and K3 parts of the line. I have one, but cannot attach it.
The line at 3933 angstroms is called K because that's what Fraunhofer called it. The K1, K2 and K3 refer to specific parts of the line. The K line is very dark and wide, but at the center of it is an unusual "brightness reversal" -- the center of the line gets brighter. The very core of the line reverses again -- there is a dip in brightness again. The line arises from a transition between the 4p 2P 5/2 state to the 4s 2S 1/2 state (really need sub- and superscripts to write these correctly) of singly ionized calcium (Ca II). The Ca II K line is one of the most useful lines in the solar spectrum, but it is one of the most complicated lines in terms of its formation.
K1 = the point in the line wings where the reversal starts. There are two
points, called K1R and K1V on each side of the center of the line.
K2 = the point of maximum brightness in the reversal. There are two points, K2R
and K2V again on each side of the center of the line.
K3 = the dip at the very center of the line.
Note that in high resolution spectra the whole line (or parts of it) can be
Doppler shifted and thus vary in appearance depending on what's happening at that location on
These portions of the line arise at different heights in the upper photosphere
and chromosphere. K1 comes from near the temperature minimum, K2 from around1000
km above that, and K3 from higher in the chromosphere. See Mihalas' book _Stellar Atmospheres_ pg. 380 for the gory details.
Therefore the CaK line is actually composed of three differing layer heights. I believe that the layer imaged above is that of the higher K2 and possibly K3 portions of the CaK emission line, which while apparently faint, can be brought out with the right processing. Per the information above and the diagram below, the K2 portion of the CaK emission extends to the height of the H alpha core emission above the photosphere - thus the similarity to the "double limb" seen in H alpha filters with bandpasses over 0.5 Angstroms: