Alert! Nova Cas 2021 mag 9

[Joan Guarro Flo]

Hello,

The little changes continuing in NOVA Cas 2021, you can see details of that in this graphics and the test improvement on the NOU_T results
from SMM Remote Observatory.

Cheers, J.Guarro.

[Joan Guarro Flo]

Hello,

Nova Cas 2021 is follow showing variations in its blue region.


Cheers, J.Guarro.

[Christophe Boussin]

Hello all,

It's with great pleasure that I resume my "storytelling" of the Halpha line of Nova Cas 2021...which continues to make the show !

I obtained eight new high resolution spectra of the Halpha line on September 16 at 21 h 35 TU (resolution of 18183, JJ = 2459474.3993, 9 x 600s), on September 23 at 20 h 42 TU (resolution of 18118, JJ = 2459481.3622, 9 x 600s), on September 24 at 21 h 33 TU (resolution of 17108, JJ = 2459482.3982, 9 x 600s), on September 30 at 22 h 22 TU (resolution of 16869, JJ = 2459488.4322, 8 x 600s), on October 4 at 19 h 43 TU (resolution of 18860, JJ = 2459492.3213, 5 x 600s), on October 19 at 18 h 35 TU (resolution of 19383, JJ = 2459507.2741, 8 x 600s), on October 23 at 18 h 20 TU (resolution of 12885, JJ = 2459511.2641, 7 x 600s) and on October 27 at 20 h 34 TU (resolution of 19457, JJ = 2459515.3567, 9 x 600s) with my LHIRES III (grating of 2400 lines / mm).

Here are all the spectra I got between September 16th and October 27th :

Halpha line profile of the Nova CAS 2021 on September 16th, 23th, 24th, 30th and on October 4th, 19th, 23th and 27th 2021

novacas2021_20210916_20211027_Christophe Boussin.png (52.91 KiB) Viewed 11570 times

On the following graph, we can note that the shape of the Halpha line profile in the "blue" part has evolved very clearly during the last few days between October 23 and 27 !!

Halpha line profile of the Nova CAS 2021 on September 16th, 23th, 24th, 30th and on October 4th, 19th, 23th and 27th 2021 (zoom)

novacas2021_20210916_20211027_Christophe Boussin_zoom.png (48.22 KiB) Viewed 11570 times

According to the AAVSO website, the magnitude of the Nova Cas 2021 has continued to oscillate in recent weeks.

(Johnson V : green squares)

Light curve of the Nova CAS 2021 (AAVSO)

I wish you all very clear skies !!

Christophe BOUSSIN

[Joan Guarro Flo]

Hello,

It seems that Nitrogen bands have appareaded these last few days.

J.Guarro.

[Francois Teyssier]

Yes, Joan,
Just add [ ] as they are "forbidden" (more correctly: collisionally excited) lines.
It began to appear at the begining of the month.

RSOph_2021-11-19_[NII]5755.png (34.99 KiB) Viewed 10908 times

It means that some parts of the nebula form by the outburst have now a low electronic density, 8 months after the outburst!

What is strange:
- The first forbidden lines to appear in the classical development of a nova are [OI], still absent.
- We have a. [NII] : low density and b. P cygni profile for He I 5876 (i.e.: opacity, high density).
Very unusual.

novacas2021_NII.png (41.31 KiB) Viewed 10939 times

Correction to line identification of [NII] 6548, 6583:
A clue: Compare H alpha, H beta, He I profiles using PlotSpectra



Of course, more data are needed.
Nova Cas 2021 is very well placed in the evening night..
I got a spectrum this evening. To be process.

All the best,
François

[James Ley]

Thanks for your explanations François.
Are those not emissions for NIII at 4638 and HeII at 4686? Since the ionization potentials for N, N+ and He are all greater than for O, does one expect to see [OI]?

[Christophe Boussin]

Hello all,

Thank you for these explanations Francois !!
This nova is definitely very surprising !!
We were able to record five new spectra at high resolution around the Halpha line during this month of November which effectively show the appearance of the forbidden lines of nitrogen [NII] at 6548 and 6583 A.

These solution spectra were obtained on November 3 at 23 h 44 TU (resolution of 18848, JJ = 2459522.4888, 9 x 600s), on November 5 at 23 h 30 TU (resolution of 18015, JJ = 2459524.479, 12 x 600s), on November 8 at 22 h 10 TU (resolution of 18471, JJ = 2459527.4238, 9 x 600s), on November 22 at 20 h 39 TU (resolution of 18488, JJ = 2459541.3604, 5 x 600s) and on November 23 at 19 h 41 TU (resolution of 19284, JJ = 2459542.3198, 12 x 600s) with a LHIRES III (grating of 2400 lines / mm).

Here are all the spectra we got between November 3th and November 23th :

Halpha line profile of the Nova CAS 2021 on November 3th, 5th, 8th, 22th and 23th 2021

The appearance of the forbidden lines of nitrogen [NII] at 6548 and 6583 A seems to be between November 4 and 6...Note the blue shift in wavelength of these lines !
The Halpha line profile itself has changed dramatically compared to October (see previous post) !

Halpha line profile of the Nova CAS 2021 (zero velocity is on Halpha at rest) on November 3th, 5th, 8th, 22th and 23th 2021

novacas2021_20211103_20211123_Halpha_velocity_Marion Thomas et Christophe Boussin.png (60.56 KiB) Viewed 10782 times

According to the AAVSO website, the magnitude of Nova Cas 2021 is increasing with oscillations : has the decline begun ?

(Johnson V : green squares)

Light curve of the Nova CAS 2021 (AAVSO)

We wish you all a very clear sky to follow this new evolution of the Nova Cas 2021 !!

Marion THOMAS and Christophe BOUSSIN

[Francois Teyssier]

Correction to line identification of [NII] 6548, 6583:
A clue: Compare H alpha, H beta, He I profiles using PlotSpectra

Not a lot of comments ...

I recall the method: always compare the lines *between* them.

Well,

novacas2021_NII (002).png (20.41 KiB) Viewed 10763 times

[NII] or the shape of the ejecta revealed by the remove of opacity?

has the decline begun ?
Yes, it is now probably (almost) frozen.
But for such an object any prevision is highly speculative.


François

[Christophe Boussin]

Thank you for this comparison Francois !
Yes, indeed, the profiles of the Halpha and Hbeta lines are very similar...and the evolution of the shape of the Halpha line can give the same impression as the appearance of the [NII] lines at 6548 and 6583 A...To be continued !

Christophe

[Francois Teyssier]

The best way for a comparison of the profiles:
Normalisation of both the continuum and maximum intensity of the lines (here, resp: 1 & 10)

RSOph_Hbeta4861_Halpha6563_2021-11-09_741.png (85.04 KiB) Viewed 10694 times

For Balmer series, do not hesitate to check also the lower members as they show more details (due to radiative processes)
Note the absorption in H gamma profile. Large parts of the nebula are still optically thick.

RSOph_Hgamma4340_Hbeta4861_Halpha6563_2021-11-09_741.png (115.15 KiB) Viewed 10694 times

One can see easily from this sequence that H alpha is *not* the best line for the study of the phenomenon.


François