CFHT operating manual - Homepage Usask
CFHT operating manual - Homepage Usask
CFHT operating manual - Homepage Usask
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ESPaDOnS: viewing, guiding and exposure meter facilities http://webast.ast.obs-mip.fr/magnetisme/espadons_new/guiding.html<br />
As a by-product, the guiding algorithm also produces in real time the width<br />
and flux of the stellar image (and thus the average seeing and magnitude), as<br />
well as an estimate of the fraction of the total flux that was fitted into the<br />
central pinhole. The guiding agent displays this information in the status<br />
server and can (on users’ request) plot it as a function of time on a graphical<br />
window, an example of which is shown on the right (recorded in arbitrary<br />
guiding conditions).<br />
Exposure meter<br />
To check that the flux entring the spectrograph is maximum<br />
and corresponds to the expectations, the observer can use the<br />
exposure meter implemented within the spectrograph, picking<br />
off a small fraction of the beam (of order 0.1% of the total flux)<br />
on its way from the main collimator to the grating. The<br />
detected count rate (in the range of about 10 counts/s to 2<br />
million counts/s) corresponds to stellar V magnitudes of about<br />
4 to 18 (depending on the color of the star of interest).<br />
The detected count rate, as well as the number of counts<br />
accumulated during an exposure, are displayed in real time in<br />
the status server. The observer can also activate, on request, a<br />
graphical window (see example panel on the right) displaying<br />
the count rate information, both on a linear scale (top graph)<br />
and on a logarithmic magnitude scale (bottom graph). Both<br />
graphs include both the instantaneous meaurements (light blue<br />
curve) and values averaged over the last 30 measurements<br />
(green curve). The standard deviation on the same sample of 30<br />
measurements is also indicated in the appropriate box and<br />
updated in real time.<br />
This tool is very useful to check how much the observing<br />
conditions are varying with time, and to potentially correct the<br />
situation (eg by refocussing the telescope or fine tuning the<br />
guiding zone) if necessary.<br />
© Jean-François Donati, last update May 18 2004<br />
2 of 2 08/07/04 11:32 PM
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