Traitement alpy 200

[Vincent Marik]

Bonjour,

Nous sommes en train de régler l’alpy 200 et nous posons maintenant la question de savoir comment traiter les spectres obtenus en utilisant demetra ou Isis
Une version de demetra ad hoc est-elle en cours d’élaboration ?
Bon ciel
Vincent

[Jean-Pierre Masviel]

Bonjour Vincent,

Je pense que la réponse est donnée par François Cochard dans la vidéo de l'atelier sur l'ALPY 200:
https://youtu.be/0L6LLn9HjUY
C'est vers la fin ( 1H 48 mn).
Avec ISIS, on peut ouvrir le profil spectral (étoile de type A ou B pour avoir les raies de Balmer bien nettes) et sélectionner sur la droite "Dispersion", puis rentrer "à la main" les longueurs d'ondes avec en face le numéro de pixel correspondant. ISIS fera le calcul du polynome, qui pourra ensuite être aussi utilisé dans Demetra.

Jean-Pierre

[Vincent Marik]

Merci Jean-Pierre, en effet, tout est expliqué.
On va regarder ça de près.

Vincent

[Robin Leadbeater]

I use ISIS with 4 Balmer lines with my ALPY200 (Ha alpha to delta). A good tip is to rectify the spectrum first to make the lines easier to measure.

ISIS does something similar when using the standard ALPY600 and Balmer lines (Method 1)
ttp://www.astrosurf.com/buil/isis/guide_alpy/ ... onnage.htm
but with the ALPY200 it has to be done manually.

My version of the ALPY 200 needs a 2nd order fit but the Shelyak version is almost linear so you could probably find some lines in the calibration lamp spectrum which are not blended and use those instead.

Cheers
Robin

[Robin Leadbeater]

With ISIS it is also important to crop all the images before you process them so there is no large area of black. If you do not do this, the flat correction does not work correctly and you lose a lot of dynamic range which is very important on faint objects. ISIS has a good tool to do this easily

isis_image_crop.png (26.34 KiB) Viewed 1169 times

Here is an example an image (the flat) and the area I crop.

flat_ATK428_alpy200_2bin_20240108_crop_area.jpg (31.16 KiB) Viewed 1169 times

Cheers
Robin

[Robin Leadbeater]

Other good tips using ISIS are to make the binning zone as narrow as possible and select optimised binning in the general tab. This helps to minimise the sky and camera noise.

Cheers
Robin

[Robin Leadbeater]

Accurate sky background subtraction is also very important for faint objects. Check the sky subtracted image that ISIS produces and turn up the brightness. The sky background near the spectrum should be just noise with no features.

ALPY200_skysub.png (170.7 KiB) Viewed 1167 times

Cheers
Robin

[Robin Leadbeater]

I have opened a thread in the "spectroscopes and software" section for ALPY200 users
https://www.spectro-aras.com/forum/viewtopic.php?t=3117

[Vincent Marik]

Thank you very much Robin.
Let’s go !
Vincent