Probable SN in NGC 6946

Information about outbursts of eruptive stars, Be activity, ...
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Peter Somogyi
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Re: Probable SN in NGC 6946

Post by Peter Somogyi »

Result from this week:
sn2017eaw_cmp2.png
sn2017eaw_cmp2.png (49.58 KiB) Viewed 6917 times
Some deeper absorptions appear in the range of 5300-5850A (I can't identify at the moment).

- Peter
Francois Teyssier
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Re: Probable SN in NGC 6946

Post by Francois Teyssier »

Some deeper absorptions appear in the range of 5300-5850A (I can't identify at the moment).
Not easy
Main lines in SN Spectra http://supernova.lbl.gov/~dnkasen/tutor ... ectra.html
Also the shape of P Cygni depending of various parameters
http://supernova.lbl.gov/~dnkasen/tutor ... rties.html

François
Peter Somogyi
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Re: Probable SN in NGC 6946

Post by Peter Somogyi »

Thanks Francois. I'll hunt for another clear night soon, getting some changes on these features should make it easier to do a distinction.
James Foster
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Re: Probable SN in NGC 6946

Post by James Foster »

Here is LISA (35 micron slit) spectra of AT2017eaw taken from my high altitude site (2500 meters) on 19Jun17:
Image
This was shot with a 33 centimeter aperture classical cassegrain working at F/7.5 with a combined 35 minute exposure (7x300sec) binned 2x2 with an Atik 460ex CCD.
The only lines I could clearly identify were OI (telluric) at 5577A and (maybe) hydrogen epsilon at 3970A. I notice more "bumpiness" in the blue-end of the spectrum.

James
James Foster
eShel2-Zwo ASI6200MM Pro
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope
LISA IR/Visual Spectroscope (IR Configured)
Alpy 200/600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
Paolo Berardi
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Re: Probable SN in NGC 6946

Post by Paolo Berardi »

Hi all,

your spectra get better as time passes, despite the brightness (slight) decrease!

My last observation on June 26, compared with previous spectra (flux calibrated with simultaneous V photometry):

Image

We can also appreciate the P-Cygni absorption RV variations, showing the photosphere that recedes to the inner and more slowly layers of expanding ejecta. To make it quicker I used my observations but I think it would be nice to use all of our spectra, plotting in a graph the velocity development.

Image

Paolo
etienne bertrand
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Re: Probable SN in NGC 6946

Post by etienne bertrand »

Good results Paolo !
etienne bertrand
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Re: Probable SN in NGC 6946

Post by etienne bertrand »

Un spectre de la SN hier soir avec la lunette 102/714 et Alpy600
Le pic du minimum Ha doppler arrive à 6401.5A ce qui nous donnes :
z = -0.024775 et une vitesse de -7368.27 - 8.794 (vitesse helio) : V = -7377 km/s.
Image
Olivier GARDE
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Re: Probable SN in NGC 6946

Post by Olivier GARDE »

Etienne,

Ton calcul n'est pas rigoureusement exact car tu ne tient pas compte de la vitesse de la galaxie qui est de 45 Km/s (la Sn est dans NGC 6946)

de plus vue la précision que l'on peut obtenir avec un Alpy, on peut négliger sans problème les chiffres après la virgule qui ne sont pas significatif (précision de l'alpy +/- 50 km/s) et présenter les résultats comme l'a fait Paolo.

Plus simplement dans le cas d'un profil p Cyg, il suffit de mesurer la valeur de la raie en emission et la valeur de celle en absorption puis de calculer ainsi la vitesse par calcul Doppler, sans tenir compte de la vitesse hélio et de la vitesse propre de l'objet (ici on ne parle pas de z, juste d'une vitesse d'expansion de la Sn en km/s). Ou encore d'étalonner le graphe en vitesse en prenant comme origine le pic H Alpha et l'on trouve ainsi la vitesse d'expansion de la Sn (voir graphes de Paolo).
Voir également le lien qu'a indiqué François sur la vitesse :
http://supernova.lbl.gov/~dnkasen/tutor ... ocity.html
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
etienne bertrand
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Re: Probable SN in NGC 6946

Post by etienne bertrand »

Bonsoir Olivier,
Merci pour ton commentaire. Parfois je ne suis pas très rigoureux dans les appellations, tu as raison pour le redshift.
Compris pour la vitesse d'expansion. Merci pour le liens.
Peter Somogyi
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Re: Probable SN in NGC 6946

Post by Peter Somogyi »

Nice result, Etienne!
Last week I've also made a shot (11 x 20 min - once cloud in between), but reddening seems to have settled - some absorptions in the green have become deeper:
sn2017eaw_ 20170529_043_PSO.png
I would like to assess all RVs on a graph in the end (if manage to identify all lines), planning to shoot 1-2 weekly till possible.

- Peter
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