Traitement alpy 200

Ask your questions, show your results
Post Reply
Vincent Marik
Posts: 36
Joined: Fri Aug 17, 2012 1:00 pm
Location: Tours (France)

Traitement alpy 200

Post by 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 :roll:
Une version de demetra ad hoc est-elle en cours d’élaboration ?
Bon ciel
Vincent
VMA/ TRS-FR/ T 200/ Alpy/ Atik 314L+
Jean-Pierre Masviel
Posts: 35
Joined: Thu Oct 06, 2011 12:54 pm

Re: Traitement alpy 200

Post by 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
LHIRES III # 24, ALPY 600, Atik 314
http://astrosurf.com/jpmasviel/
Vincent Marik
Posts: 36
Joined: Fri Aug 17, 2012 1:00 pm
Location: Tours (France)

Re: Traitement alpy 200

Post by Vincent Marik »

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

Vincent
VMA/ TRS-FR/ T 200/ Alpy/ Atik 314L+
Robin Leadbeater
Posts: 1936
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: Traitement alpy 200

Post by 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
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
Posts: 1936
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: Traitement alpy 200

Post by 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
isis_image_crop.png (26.34 KiB) Viewed 4271 times
Here is an example an image (the flat) and the area I crop.
flat_ATK428_alpy200_2bin_20240108_crop_area.jpg
flat_ATK428_alpy200_2bin_20240108_crop_area.jpg (31.16 KiB) Viewed 4271 times
Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
Posts: 1936
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: Traitement alpy 200

Post by 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
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
Posts: 1936
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: Traitement alpy 200

Post by 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
ALPY200_skysub.png (170.7 KiB) Viewed 4269 times
Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
Posts: 1936
Joined: Mon Sep 26, 2011 4:41 pm
Contact:

Re: Traitement alpy 200

Post by 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
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Vincent Marik
Posts: 36
Joined: Fri Aug 17, 2012 1:00 pm
Location: Tours (France)

Re: Traitement alpy 200

Post by Vincent Marik »

Thank you very much Robin.
Let’s go !
Vincent
VMA/ TRS-FR/ T 200/ Alpy/ Atik 314L+
Post Reply