+
Measuring the wavelength of the center of a line.
IN: wavelength - dblarr - wavelengths (angstroms); absolute values
flux - fltarr - fluxes
OUT: xmin - double - wavelength of the line bottom
ymin - double - flux at xmin
sigmax - double - sigma associated with the measurement of xmin
KEYWORDS: npoints- number of pixels around the minimum to enter the fit.
(default: 7) It has to be an even number.
order - order of the polynomial (defult: 3 = third order)
interp - when on, we use a spline interpolation to improve sampling
(step= 0.005 A)
minabs - min. central absorption of a line in order to be considered
(default: 0.98)
noisy - if set, we measure line shifts of lines with irregular
shapes close to the line center. Otherwise, we don't.
noplot - when set, it does not produce any plot
tpb - two-point-bisector tecnique (Hamilton & Lester 1999)
NOTE: when the measurement cannot be performed, -1000 is return in xmin,ymin
and sigmax
C. Allende Prieto, UT, 1999
C. Allende Prieto, UT, 2001 included spline interp. to improve sampling
C. Allende Prieto, UT, 2001 more rigorous determination of error in lambda
implementation of 'security' checks
C. Allende Prieto, UT, 2006 fixed a bug in the determination of the error
and added a 2nd error estimate, the average of
the two is kept as tests indicate it is more robust
than either method alone.