Alert! Nova Cas 2021 mag 9

[Joan Guarro Flo]

Hello,

I apologize, the second picture in my last message the He ll 4685 position is wrong, you can see in this second graphic the exact position of this band.

So you can see too that there isn't any activity of He in this place on  September 10th,but you can appreciate a little beginning on  Sep. 12th.

Cheers, J. Guarro.

[Christophe Boussin]

Hello all,

A few days ago, data from the AAVSO website showed a new and very clear increase in the brightness of Nova Cas 2021...
The light curve shows that Nova Cas 2021 had a new maximum of luminosity around September 9-10 with a magnitude of about 6.5 !!
Since this date, the magnitude of the Nova is again at values comparable to those of early September...

Light curve of the Nova CAS 2021 (AAVSO)

Thanks to a sunny weather, I was able to follow the evolution of the Halpha line profile during this new maximum.
I obtained three new high resolution spectra of the Halpha line on September 11 at 21 h 47 TU (resolution of 18239, JJ = 2459469.4074, 12 x 600s), on September 12 at 21 h 17 TU (resolution of 16729, JJ = 2459470.3869, 6 x 600s) and on September 13 at 20 h 48 TU (resolution of 19614, JJ = 2459471.3668, 9 x 600s) with my LHIRES III (grating of 2400 lines / mm).

The set of my spectra obtained between August 27 and September 13 allows to see the global evolution of the Halpha line profile around the luminosity maximum :

Light curve (AAVSO) and Halpha line profile of the Nova CAS 2021 on August 27th, 31th and on September 2nd, 4th, 6th, 9th, 11th, 12th and 13th 2021

The position of the peak at +785 km/s on September 2 and 4 is noted on this graph.
We can notice the decrease of the relative intensity of the top of the Halpha line during the increase of luminosity between September 4 and 9 then its increase during the decrease of luminosity since September 9-10.
Following this episode, the Halpha line has "fully recovered" a profile and a relative intensity very similar to early August.

The next graphs allow to see in more detail the evolution of this profile between August 27 and September 13 :

Halpha line of Nova Cas 2021 on August 27th, 31th and on September 2nd, 4th, 6th, 9th, 11th, 12th and 13th 2021

novacas2021_20210827_20210913_Christophe Boussin.png (52.93 KiB) Viewed 11857 times

Halpha line of Nova Cas 2021 on August 27th, 31th and on September 2nd, 4th, 6th, 9th, 11th, 12th and 13th 2021 (zoom)

novacas2021_20210827_20210913_zoom_Christophe Boussin.png (57.33 KiB) Viewed 11857 times

and its animation :

Halpha line of Nova Cas 2021 from August 27th to September 13th 2021 (animation)

novacas2021_20210827_20210913_Christophe Boussin.gif (77.79 KiB) Viewed 11857 times

The return of rainy days forces me to take a break in this monitoring... I wish you all very clear skies !!

Christophe BOUSSIN

[Peter Somogyi]

Nice serie, Christophe!
Let me extend yours with my time serie (exceptional weather):

H-alpha at R~17000

NovaCas2021_0902_0912.png (56.82 KiB) Viewed 11824 times

All normalized for the 6520-6530A range.
Cheers,
Peter

[Wolfgang Vollmann]

Hi all,

great work you are doing here on the Nova!

I follow the brightness changes with a DSLR camera using 3-color photometry in RGB. My measures are available in AAVSO database (VOL).

Very interesting are the changes in color index green minus red which follow the brightness changes of the Nova quite closely. Near the bright maxima the color index is smallest (around +0.3..0.4mag), near the minima largest (+0.9mag). I attach the 2 diagrams with same timescale. TG = Tri-Color Green magnitude, TR = Tri-Color Red magnitude.

Am I right to interpret the changing intensity of the H-alpha emission relative to continuum causing this color index changes?
What drives these changes?

Best regards
Wolfgang Vollmann

[Christian Buil]

The appearance of nova Cas 2021, the September 28, 2021 with a Newton 200 mm f/5 and the Star'Ex spectrograph operated in low resolution (R = 2200) - 24 x 40 s exposure:





A description of the spectrograph setup is here (part 4.4): http://www.astrosurf.com/solex/sol-ex-stars-en.html

... and a video (!) of this observation (in French sorry), which also shows some tips for spectra calibrating:https://youtu.be/5nKucBo9Fys

Christian Buil

[Benjamin Mauclaire]

Hello Christian,
J'aime l'aspect très pédagogique de ta vidéo.
Cheers

[Christian Buil]

Merci Benji !

Christian

[Dubreuil Pierre]

Nova Cas 2021 très rouge !

Hier soir météo enfin favorable !

UVEX(4) poussé dans l'infrarouge jusqu'à 10000A !
Fente claire 25µ, RC8, plus aucun bout de verre !

Nova Cas 2021 IR

_novacas2021_20210929_872_Pierre Dubreuil.png (10.23 KiB) Viewed 11437 times

Pierre

[HughAllen]

I have continued to follow the evolution of the expansion velocity, using the blue shifted absorption minimum on the shoulder of many of the emission lines. At the resolution of my Alpy 600 spectroscope, such P Cygni profiles have remained strong for all of the Balmer lines Hβ and above. In Hα and HeI (5876Å) there have been brief periods of disappearance whilst the P Cygni profile on the FeII (5169Å) emission was not observable for much longer periods, particularly during August and early September. When observable the FeII (5169Å) absorption velocity has almost always been the lowest. On a given date the velocity sequence in the other lines has been quite variable but the overall trend in absorption velocity shows an inverse link to the Vmag of the nova:

Here is the latest spectrum in the sequence, with markers at the rest wavelengths of the emission lines monitored in this study:

novacas2021_101021.png (32.29 KiB) Viewed 10957 times

Cheers
Hugh

[Joan Guarro Flo]

Hello,

You can see here a comparison details in the blue.

Cheers, J. Guarro.