Color 2D images with spectrograph

[Christian Buil]

How to take color images of nebulae with a spectrograph:

http://www.astrosurf.com/buil/scan/demo.htm



A direct application of spectroheliographic method to deep-sky object

Color images... but also possibility to construct temperature/density map and more...

The SCAN command is available in ISIS V5.2.5 version.

Christian B

[Olivier GARDE]

Here's a scan of M57 taken with a LISA and SCT 12 inchs whose imaging were made ​​precisely by Stéphane. Then I realized the data process via the "scan" function that Christian has developed in the latest version of ISIS software.

The color version of M57 is the assembly lines SII for red, Ha for green and OIII for blue (made with photoshop)

I then made ​​a "thermogram" of the NP according to the following formula :
  (Flux @ 5007 - Flux @ 4959) / flow @ 4363
Once colorized in false color, I get the following diagram

I'll try on other NP targets as soon as possible....


Voici un scan spectro de M57 dont les acquisitions ont été faite précisement par Stéphane. J'ai ensuite réalisé le traitement via la fonction "scan" que Christian a développé dans la dernière version d'ISIS.

La version couleur de M57 est l'assemblage des raies SII pour le rouge, Ha pour le vert et OIII pour le bleue.

J'ai ensuite réalisé un "thermogramme" de la la NP selon la formule suivante :
(Flux @5007- Flux@4959)/flux @4363
Une fois colorisé en fausse couleur, j'obtient le diagramme suivant

Je vais essayer prochainement sur d'autre cibles de NP....

[Francois Teyssier]

C'est vraiment excellent et très prometteur.
Olivier, la température électronique est proportionnelle à (5007+4959)/4363
[Dans les conditions normales 4959 = 1/3 x 5007]



François

[Paolo Berardi]

J'ai ensuite réalisé un "thermogramme" de la la NP...

Olivier, this is fantastic!
A question, how you compensate the instrumental response?

Paolo

[Olivier GARDE]

Olivier, this is fantastic!
A question, how you compensate the instrumental response?

Paolo

Hi Paolo,

For the instrumental response we do the same way as a normal target, a reference star near M57 (HD 174602) before and after M57 images.

To resume a session of spectro scan imaging we do :
- Ref star HD 174602
- M57 (we put the target first out of the slit, to have futur space on the final scan)
- We take 3 exposures of M57 (3 x 300s) for each position, then we move about 5 pixels (half the size of the slit, in this case, we use a LISA with 35u slit)
- After about 30 differents positions of M57 we do reference star again (the same as we do at the beginning)

[Olivier GARDE]

C'est vraiment excellent et très prometteur.
Olivier, la température électronique est proportionnelle à (5007+4959)/4363
[Dans les conditions normales 4959 = 1/3 x 5007]



François

François,

A ta connaissance, existe t'il dans la littérature sur les NP, un tel diagramme de température afin de comparer notre résultat et voir s'il est cohérent ?

[Paolo Berardi]

Thank you Olivier, it is a quite challenging procedure which also takes a long time...

I was wondering how do you use the reference star spectrum to correct intensity level at the three wavelength used for compute the thermogram (flux @ 4363A, 4959A and 5007A). I think the last two are close enough but 4363A could suffer a relative loss of efficiency for instrumental response. Is not necessary to scale the overall intensity of 2d spectra before combining the images? Maybe I'm missing something about the process.

Effectively the thermogram does not carry an absolute measure of temperature. Perhaps is this the reason why is not necessary an accurate balance of image intensities (that also should consider interstellar reddening)?

Ciao,
Paolo