About evaluation of instrument response

[Robin Leadbeater]

Hi Benji,

... ou d'utiliser un trou à la place de la fente.

Benjamin

This is not much better than a slit I think. You can never collect all the dispersed light with a hole matched to the star size. The fraction will perhaps be constant independent of parallactic angle but will still change with altitude.

Cheers
Robin

[Forrest Sims]

Hi Christian,

At the end of last year I installed a rotator in front of my LISA spectrograph. This allows me to rotate the spectrograph such that I can always orient the spectrograph slit perpendicular to the horizon when I am shooting the Reference star or the Target star. This appears to work very well to mitigate the issues of atmospheric dispersion, especially when it is necessary due to obstacles or declination to shoot targets that are at altitudes between 30 and 45 degrees. As a general rule so far, I always rotate the slit to this orientation below 60 degrees altitude and sometimes below 70 degrees. It is an extra burden in my nightly procedures to have to do this for each target pair but I am convinced I am getting better response corrected data. Determining the Parallactic Angle is not the problem for the target but determining to what position to rotate the spectrograph remotely is something I am still working on. For now I walk out to the observatory each time and using your "plumb bob" idea, rotate by eye until I have the correct orientation of the slit. We have also explored the AOD idea, but it also has an issue I believe as it too may have to be rotated/adjusted to the correct setting each time.

Best,

Woody

[James Foster]

I hope I purchased the correct halogen light bulbs to "shake"
in front of mt scope for the new instrument response procedures:



Purchased on Amazon, German design made in China......no US sources seem to stock Halogen
bulbs like these; only flood-type that have a flat light face.

James

[etienne bertrand]

2950K c'est peut être pas assez en température non ?

[Christian Buil]

James, 2950 K it is nearly max. temperature for the tungsten. The choice is excellent and a fine reference.

Etienne, 2950 K c'est déjà une très haute température pour une lampe halogène standard. Il n'est pas possible de monter plus haut car le filament ne tiens plus ou la durée de vie est très brève (il fond). Certes c'est toujours insuffisant pour étalonner le bleu confortablement, mais c'est déjà pas mal et on arrive à faire des choses avec une telle lampe (voir ma page). A part utiliser une très couteuse et dangereuse lampe plasma, on ne peut pas aller plus moins avec nos moyen (les lampes dites "musée", trichent sur la température en réduisant le rayonnement rouge, ce ne sont pas de vraies corps noir).

Christian

[James Foster]

To: Christian,

RE:"James, 2950 K it is nearly max. temperature for the tungsten. The choice is excellent and a fine reference."
Thanks for the confirmation! Will experiment with this new Instrument response procedure soon!

James