FLUXSTAR computes a flux calibration curve from a standard star spectrum
and a file containing the correct flux levels as a function of wavelength.
The input spectrum must be wavelength calibrated, be corrected for
atmospheric extinction, and have its intensities on an uncalibrated
F-lambda scale. The routine locates the flux points given in the input
file, and finds the star's average flux over the specified wavelength bin
of the flux point. A set of correction points are thus defined, which
consist of the correct fluxes, reduced to the Hayes-Latham Vega calibration
(Hayes
The FLUX command takes the correction points defined above, and uses a
spline (or polynomial) to define a flux calibration buffer for the input
spectrum. The spectrum is then calibrated by multiplication by this
buffer. The separate FLUXSTAR and FLUX commands permit the calibration of
spectra on different wavelength scales than the standard star spectrum.
The standard star's flux measurements are read in from a file, which is
assumed to be in the spectrum directory (see PRINT DIRECTORIES), with
extension .FLX unless specified otherwise. The file is headed by the stars
apparent V magnitude, and then its magnitude at 5556 A. Generally these
are identical, and will only be different if a (grey) change in the Vega
calibration is made. Each line of the file will contain a flux point
specified by its wavelength, magnitude per unit frequency, and bin width in
angstroms. The points must be in order of increasing wavelength, but there
is no strict format that must be observed.
Below is an example of a standard star flux file:
The keywords 'AVE' and 'WT=' allow the averaging with weights of multiple
flux curves. The default weighting, used for the first flux curve as well
as for those using 'AVE', is 1. Anytime neither keyword is specified a
fresh flux curve is started (again, with a weight of 1.). Note that the
averaging can handle two flux curves which overlap (but do not necessarily
match perfectly) in wavelength, and can even create a flux curve from two
curves with completely disjoint wavelength scales, but it cannot insert
flux points in the midst of an existing flux curve.
The SYSA keyword produces a point-by-point flux curve instead of a smooth,
spline fitted flux curve. This is done by removing the known stellar
absorption lines from the observed standard star spectrum. The atmospheric
bands, however, are not removed. The result is that you end up with a flux
curve which can correct for the atmospheric bands. A drawback for SYSA is
that any ;SPMquot;anomalous;SPMquot; absorption lines not known to the program will appear
in the response curve and can lead to extraneous features in the data.
The SYSC keyword produces a compromise response curve with the best
features of both ;SPMquot;system A;SPMquot; and (the default) ;SPMquot;system B;SPMquot;. In this option
the system A curve is smoothly fitted by a spline (at the usual knot
points) while the B and A atmospheric bands (+/- 65 Angstroms) are
retained. The curve is piecewise continuous. It is free from glitches
introduced by spurious absorption features in the stellar spectra, retains
a higher accuracy outside the extreme knot points, and compensates for the
atmospheric bands in the data.
<#5983#>Examples:<#5983#>
11.48
11.48
;SPMnbsp;
3200.0
13.17
40.0
3350.0
12.87
40.0
3400.0
12.64
40.0
3862.0
12.32
40.0
4036.0
12.12
40.0
.... ETC.
;SPMnbsp;
;SPMnbsp;