NAME

zeropt -- determine the zero point in wavelength for each band in the cube

USAGE

zeropt cube_image dispersion neon_pars

PARAMETERS

cube_image

the name of the image cube to be updated

dispersion

the text file containing the dispersion solution, usually from FITRING, but may be any text file containing 1 line with the constants A, B, and C

neon_pars

the text file containing the parameters for the neon or other standard lamp taken nearby in time to the actual data, and to be used to determine the zero points.

bands =

the band numbers, given either in a range format (1-3,4,5).

DESCRIPTION

Because the instrument may drift in wavelength while the B and C dispersion constants remain the same, it is advisable to obtain a calibration frame prior to each series of observations, or during a series as well. The parameters of the calibrations may be derived using RINGPARS and placed in the "neon_pars" file.

ZEROPT then takes those parameters, plus the prior solution contained in the "dispersion" file, to derive the constant A appropriate to the current series. The optical center is also determined. Both the wavelength and optical center are added to the image header of the cube using keywords LAMBDA01 through LAMBDAnn, and XC01, YC01 through XCnn, YCnn. The constants A, B, and C are also added to the cube header using keywords COEF1, COEF2, and COEF3.

Note that although the dispersion file produced by FITRING contains more information than used by ZEROPT. Only the first line of the file is used.

EXAMPLES

Update the cube header "cube" using the dispersion file "disp" for the three ring parameters in file "rings" appropriate to bands 1-3, 4-6, and 7-9.

cl> zeropt cube disp rings

The user will be asked to enter the range of bands appropriate to each calibration image contained in "rings".

TIME REQUIREMENTS

Fast

SEE ALSO

RINGPARS, FITRING