PNV J20233073+2046041 mag 6.8

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Re: PNV J20233073+2046041 mag 6.8

Postby Robin Leadbeater » Sat Aug 31, 2013 6:14 pm

Ernst Pollmann wrote:an increase of the continuum brightness (below Halpha) leads to a smaller EW and vice versa, proven with the correlation coefficient of better than 0.9.


Hi Ernst,

This is a correlation, not causation. The correlation is high because the H alpha EW is generally increasing as the nova fades. We already know that. What we are trying to establish is what the flux in the H alpha line is doing independent of the continuum level. To do this we need to express the continuum at Halpha (used as a reference for the EW measurement) in terms of flux. We can do this (as you have done) using the Vmag values as a reference. Your treatment however does not take into account the fact that the mean flux level in the Vmag passband changes with time relative to the continuum level at H alpha. That is what my correction factor takes into account. (This correction factor fell from ~1.7:1 to ~1.2:1 currently as the continuum flattened)

Cheers
Robin
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Re: PNV J20233073+2046041 mag 6.8

Postby Olivier GARDE » Sat Aug 31, 2013 8:24 pm

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Re: PNV J20233073+2046041 mag 6.8

Postby Christian Buil » Sun Sep 01, 2013 3:46 pm

Cette nova est l'occasion d'aller plus loin dans les techniques d'analyses

J’ai donc fait une page qui détaille la manière d’étalonner en flux nos
chers spectres :

http://www.astrosurf.com/buil/calibration2/absolute_calibration.htm

La méthode 2 est quasi celle évoquée par Steve Shore dans le
dernier message journalier de compte rendu qu’a fait passer François T.
sur la nova.

D'autres existent (François Teyssier teste une méthode mixte photométrie/spectrométrie
par exemple).

Si vous vous appropriez cela, vous serez de vrais champions de la spectro !
Et cela signifie que vous savez quasiment tout faire ;)

En vérité ce n’est pas très compliqué, et assez amusant.
Faites une tentative pour voir.

La chose peut rapporter gros aussi, car le résultat est bien plus riche
que la photométrie BVR classique sur le plan astrophysique. Il Faudrait
même que les photométristes si mettre... !

On touche vraiment au coeur de la spectro ici.

Pas trop le courage de traduire anglais, ni l’aptitude pour écrire les subtilités
de ces choses sans erreurs. S’il y a des volontaires (Robin, Olivier, ...).

J'ai ouvert un autre fil sur le forum pour discussion eventuelle car cela ne
concerne pas que la nova :

http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=695&p=2900#p2900

-----------------------------------

A page about techniques for convert spectra un flux unit. Two methods are
proposed (4 spectra techniques, 2 spectre techniques – i.e. the classical).
Sorry the text is in french (but illustration in english). It is too difficult for
me to translate. Procedures are not really complex... but have a
great interest for some astrophysical studies:

http://www.astrosurf.com/buil/calibration2/absolute_calibration.htm


A new topic in the forum because it is a general problem and question in spectrography:

http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=695&p=2900#p2900


Christian
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Re: PNV J20233073+2046041 mag 6.8

Postby Christian Buil » Tue Sep 03, 2013 1:26 am

A direct application of flux conversion :

- comparison of Aug. 29.83 and Sept. 1.98 spectra in flux unit (erg/cm2/s/A)
- comparison of Aug. 29.83 and Sept. 1.98 spectra in relative intensity (normalization zone 66650-6680 A)

The magnitude difference between the two date measured from flux spectra is (numerical Bessel filters set):

0.51 in B
0.56 in V
0.45 in R

To be confirmed (new measures this night).

Christian
Attachments
_compa_flux_3.png
_compa_flux_3.png (7.99 KiB) Viewed 3366 times
_compa_flux_2.png
_compa_flux_2.png (12.67 KiB) Viewed 3366 times
_compa_flux_1.png
_compa_flux_1.png (8.79 KiB) Viewed 3366 times
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Re: PNV J20233073+2046041 mag 6.8

Postby Robin Leadbeater » Tue Sep 03, 2013 11:25 am

Hello Christian,

The change in calculated V mag in 3 days seems larger than expected compared with the AAVSO data which is showing a slope of about 0.1 mag/day currently
Like Francois, I am also experimenting with flux calibration using V mag values. Is it possible to post the fits files of your flux calibrated spectra?

Cheers
Robin
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Re: PNV J20233073+2046041 mag 6.8

Postby Kevin Alton » Tue Sep 03, 2013 1:05 pm

I've been monitoring Nova Del 2013 since 21Aug2013 using a low resolution SBIG DSS-7/ST-402ME spectrophotometer and would like to share some of my results. Typical exposure times on a 20 cm SCT ranged between 40-50 sec using the narrowest slit (50 µm). Data reduction using HD 196544 as a reference was performed using RSpec. BTW, many thanks to Robin for helping me through the process. So far spectra have been generated on four separate days and can be seen below.
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Re: PNV J20233073+2046041 mag 6.8

Postby Francois Teyssier » Tue Sep 03, 2013 8:02 pm

Excellent results Kevin.
I wainting for the fit files as soon as you'll have fix the head issues.
Welcom on the forum, the camapaign and spectroscopy world
Best regards
François
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Re: PNV J20233073+2046041 mag 6.8

Postby Jacques Montier » Tue Sep 03, 2013 9:12 pm

Bonjour,

Dans la nuit du 2 au 3 septembre, le spectre au Lhires 2400 de H alpha montre un pic montant péniblement à 11 environ en valeur relative.

20130902_930_nova_del.png
20130902_930_nova_del.png (4.79 KiB) Viewed 3320 times


Vous confirmez ou c'est une fausse manip de ma part ?

Merci à vous,
Last edited by Jacques Montier on Wed Sep 04, 2013 8:15 am, edited 1 time in total.
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Re: PNV J20233073+2046041 mag 6.8

Postby Christian Buil » Tue Sep 03, 2013 11:24 pm

Jacques, regarde ta ligne de base (le continuum) : il n'est pas normalisé à 1, et donc
tu ne peux trouver la bonne valeur au pic. Faut commencer par normaliser, puis ensuite
on pourra évaluer.

Christian
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Re: PNV J20233073+2046041 mag 6.8

Postby Jacques Montier » Wed Sep 04, 2013 8:20 am

Christian Buil wrote:Jacques, regarde ta ligne de base (le continuum) : il n'est pas normalisé à 1, et donc
tu ne peux trouver la bonne valeur au pic. Faut commencer par normaliser, puis ensuite
on pourra évaluer.

Christian


Si, si Christian, la ligne de base était bien normalisée à 1, mais dans Isis -> Gnuplot, j'avais fait démarrer l'ordonnée Y1 à 0.5 au lieu de 0.
Ça induit en erreur car quelle que soit l'origine des y choisie dans Isis, Gnuplot affiche 0 sur l'axe des y...
C'est corrigé sur le post en mettant cette fois l'origine des Y à 0.

Amitiés,
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