MAESTRO Flexure
Estimator
As objects are tracked over the sky, there is mechanical flexure of the
spectrograph, and as a result the spectrum shifts on the
CCD. Originally, we had plans to shift the spectrum
slightly with peizos attached to the grating, but these have not been
installed.
Depending on the observational program, flexure limits the length of
exposure times.
Flexure was measured on November 27, 2007, and then the measurements
were repeated on April 4, 2008 after modifications were made to the
grating mount and spectrograph space frame to minimize motion of the
spectral format on the detector. The results of these
measurements, as summarized by Morag Hastie, are shown HERE.
To estimate flexure for your exposure times, download the perl script flexure.pl.
To run the script, at a unix prompt type
chmod 777 flexure.pl
flexure.pl dec HA
where dec = the declination of your target, in decimal degrees and
HA = the
hour angle of the beginning of your observation.
The script returns the expected on-axis flexure based on the
measurements of April 2008, per 30 minute exposure, in binned pixels: where the
binning is assumed to be 3 pixels in the dispersion direction and 2
pixels in the spatial direction. This is the recommended binning
for most observations.
We'll update the script with new flexure measurements, including
flexure shifts from changes in rotation angle, as they become available.
Example:
for declination = 33.3 degrees and starting hour angle = -2.5, the
result is
% flexure.pl 33.3 -2.5
MAESTRO
Flexure Estimate
Target
Declination = 33.3 degrees
Hour Angle,
Airmass, Pixel shift per half hour in
Dispersion, Spatial Directions:
-2.500 1.173
0.000 0.000
-2.000 1.106
-0.234 -1.067
-1.500 1.058
-0.235 -1.072
-1.000 1.025
-0.235 -1.073
-0.500 1.007
-0.233 -1.065
0.000 1.000
0.184 0.842
0.500 1.007
-0.184 -0.842
1.000 1.025
-0.233 -1.065
1.500 1.058
-0.235 -1.073
Last update: May 24, 2013