spectro-aras.com

Une méthode simple pour mesurer la transmisson réelle de la fente d'un spectrographe (LISA, LHIRES, ...). La technique consiste à
comparer du signal d'une même étoile avec et sans fente. Le résultat va dépendre du seeing, de la qualité du suivi, de la focalisation de l'étoile... :

Here a simple method for evaluate real slit transmission for the conditions of observation (seeing, tracking, focusing, ...) - comparison of star signal with and without slit :



Full version:

http://www.astrosurf.com/buil/forum/pos ... ciency.png

Une transmission de fente comprise entre 0,3 et 0,7 peu être considérée comme typique et normale.

Slit transmission between 0.3 and 0.7 is typical.

Christuan Buil

the method is very simple:

1/ take a spectrum of a star with your spectrograph with the slit
2/ remove the slit, make sure no light foes through the new opening and record another spectrum

In ISIS, use the statistics and measure the "counts" within the same window/area for both images. Divide the count numbers and you get the slit efficiency. This inclused 92% of glass transmission you can remove by dividing your result with that figure.


For exemple:
image with slit: count C1 = 110500
Image without slit: count C2 = 182800

Slit transmission is C1/C2 = 0.60 (60%)

92% is due to glass and 0.60/0.92=65% is due to the geometry of the slit.


Slit transmission between 0.3 and 0.7 is typical.