Files in this directory:

TFP?.gif:
    Plots of transmission of a triple-FP system, i.e. the Queensgate
    etalon blocked with a vernier-spaced tandem etalon such as the
    Scientific Solutions liquid crystal device. Two vernier choices
    and two choices of finesse are shown. The conservative N=15
    finesse has probably unacceptable leakage from outside the principal
    order of the Queensgate, though it can be improved by reducing
    the total finesse.

    With these choices, the fraction of total light coming through the
    desired order ranges from 40% to 80%. The overall FSR is 48 nm or
    63 nm; neither is quite enough to use a blocker which would transmit
    both the C and D lines: if the 90% points of a 4-period filter are
    at 656 and 589 nm, the cwl is at 622 nm and the fwhm would be 71 nm.
    With the prefilters tuned to 656, the transmission of the blocker
    at 656 - 63 = 593 would be over 90% of peak. The 1% point is at
    622 - 0.83*71 = 563, so the overall fsr of the prefilter would need
    to be 656 - 563 = 93 nm. We can try it. . .

    
ivmfilters.gif:
    A model of the IVM Fabry-Perot tunable filter (showing 7 orders with
    the central one placed at 6302.00 A), together with a model of the
    blocking filter used for the Data camera. The models are based on
    manufacturers' data for the filters, plus our observations of the
    solar spectrum (see below). The blocker is a two-cavity interference
    filter. The blocker transmission is multiplied by the Liege atlas
    solar spectrum.

ivm_spec.gif:
    The Liege solar atlas spectrum at 630 nm is multiplied by the transmission
    of the blocker (see above) with the blocker passband centered at 6302.1 A.
    The blocker wavelength depends on temperature. The result is convolved
    with five orders of the Fabry-Perot to produce a prediction for the
    observed spectrum, shown in the top solid curve. A convolution with a
    single order of the FP is shown as the next solid curve, and the
    difference, representing the parasitic light from adjacent FP orders
    is plotted at the bottom. It amounts to a nearly constant 7% of the
    continuum. Observed spectra in the photosphere, shown as + points, and
    in a spot, shown as diamonds, are shown for comparison. The observed
    spectra are scaled to match the model at the continuum point at 6302.16 A.

960730_2108_NaIV.gif
    Sample images from Sodium D1 (5896) magnetogram of AR7981 on
    1996 July 30. Upper images are I, in far wing and line center;
    lower images are V in blue and red wings, about 120 mA from center.

standard_img.gif:
    Comparison of 'standard image' derived in two different ways,
    (1) computing coefficient arrays for mapping of an arbitrary
    test image to each of a series of 40 images, then averaging the
    coefficients and applying the resulting correction to the test
    image to get the standard; and (2) adding all 40 images and calling
    that the standard. In the figure, the data are from a file with
    less than terrific seeing, including quite a bit of squirming,
    file IMGR950312.1754. The first frame is the sample image, #160.
    The middle frame is the standard from method (1), using frames 40-79
    to obtain an ensemble of mapping coefficients. The right frame is
    the mean of frames 40-79. Scaling is 2800-3600 for all three.

950329_1820GM.gif:
    Mean signal in 50x50 area outside of spots but with some plage.
    Uses 6-frame modulation. Taken from raw data file.

950329_2023GM.gif:
    Same subframe as above, but in later dataset using 4-frame modulation.
    The period-4 variation also showed up in the March 1996 data,
    indicating that it represents a small instrumental polarization,
    maybe in fact a polarization in the LC retarders themselves.

950329_1820GPol.gif:
    Subframe mean, raw data, demodulated to see behavior of 'instrumental
    polarization' with wavelength step. Q and U are constant, with a scatter
    of about 1.5e-4; V has wavelength-dependent structure at the 3E-4
    level. This latter *may* be polarization fringes from somewhere.

950329_1820V.gif:
    The V instrumental polarization from the geometry camera (as above),
    multiplied by 20 and shifted up by .032; and the V polarization from
    the same region in the data camera. This still looks like polarization
    fringes; the geom camera will be less sensitive since the order
    spacing is not likely to be commensurate with the fringes.

deblur_interp.gif:
    Difference of two geometry-camera images, scaled to +/- 40 counts.
    First, uncorrected. The others are deblurred, with (2) replication
    of corrector coefficients, (3) bilinear interpolation, and (4) cubic
    spline interpolation. Replication works best, but when we apply
    this to the corresponding data-camera images, the spline-interpolated
    ones may work just a little better. There is little difference.

specvar_quiet.gif:
    histogram of std dev in twenty wavelength points at a single
    spatial point, of V(spectrum 1) - v(spectrum 2). The histogram
    includes stdev values for 10000 spatial points in a quiet region.

specvar_spot.gif:
    Same histogram, in spot region. Similar peak position and width,
    but there are a few larger values.