ESO
SINFONI Pipeline User Manual
Doc:
VLT-MAN-ESO-19500-3600
Issue:
Issue 1.0
Date:
Date 2005-10-19
Page:
73 of 88
Finally a wavelength map is built by associating with each image pixel a wavelength corresponding to
the value resulting from the polynomial fit of degree n_a_coefficients. The intensity
7
?1
>
!
at each
image point
1
>
is given by
7
?1
>
!
$
?1
>
!
where:
?1
>
!
$
8
_
_
6
6
8
6
+
'
6
3
?>
4
+/'0'
!
6
and
+/'0'$
0>
4
!
where
0>
is the number of raws of the image.
10.1.10
Line shift computation
The recipe searches for the five brightest lines in each column of the input arc lamp. The shift between each line
position on the frame and the one resulting from the polynomial dispersion relation of degree n_a_coefficients
obtained in 10.1.9 is computed. Finally the overall wavelength calibration error is computed as the clean average
of the shifts obtained after removing 10% of the outliers. Then the wavelength positioning error at different
wavelengths is computed in a similar way. This value is monitored for quality control.
10.1.11
Dispersion relation adjustment
If a dispersion relation and a wavelength map are already available one may still want to adjust them to properly
match the given arc lamp frame.
The positions of the slitlets’ edges are initially determined by checking that the values of the zero order coeffi-
cient
+
'
for adjacent image columns differ by more than guess_disp1
pixel_dist.
An artificial spectrum is generated by convolving each entry of the reference line list with a Gaussian of position
and intensity as given by the reference line table and a sigma equal to
_
4
!
.
Bad and negative pixels are filtered out from the input image and a low-pass filter of half width mag_factor is
applied. The resulting cleaned and smoothed image is convolved with the artificial spectrum to compute their
shift, the maximum of the correlation value and the position at which this maximum is reached.
A new value of the zero order dispersion coefficients
+
'
is determined. A clean mean is performed on the
dispersion coefficients
+
'
and new values for the clean dispersion coefficients
+
'
are determined with
a single value decomposition fit over each slitlet spatial domain.
Finally a new wavelength map is generated using the clean dispersion coefficients
+
'
as described at the
end of section 10.1.9.
