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Poor weather condition since a few days…This is an opportunity to spend more time on my previous observations. To better understand the changes in lines intensity, I am using the excellent example from François Tessier and observers team for Nova Monocerotis 2012. If my understanding is right , the Hbeta emission is used as reference to compute the intensity ratio of others lines (Hbeta, He I 5876 and Ne III 3869 in my modest and limited trial). A quick and dirty evaluation is done using a graphical chart initially done to compare velocities. Each line intensity is adjusted to Hbeta level (defined as 100) . See following example for july04,2021, the adjustment factor for each line is shown in the legend box) :



Same rough computation for my 3 others observations which allows to show a kind of trend for the past few days. Obviously there is not enough data here to come to a solid conclusion, however it looks like the Halpha and He I 5876 has started to decrease (versus Hbeta) 15days after discovery while Ne III 3869 shows a strong increase :



Not sure it make good sense...
Clear sky.
daniel

An other observation yesterday night July09.
The magnitude (source AAVSO) is now near 14 with obvious impact on S/N level. Result is shown in the chart below (blue curve). Compared to previous observation of July04, there is no major change. The intensity of the neon bands (NeIII 3869 / 3968) versus Hbeta, is still increasing (NeIII3869 / Hbeta = 1.5) while the Halpha/Hbeta ratio is showing small changes around 8.



Velocity and adjusted intensity to Hbeta level now impacted by poor S/N level :


Ratio to Hbeta :


At this magnitude (near 14) I have probably reached the limit of my capability for such measurement.
Clear sky.
Daniel

While most of the emission lines appear as large rectangular bands, there is a strange triangular structure moving from 4640A on june15 to 4680A on my last spectra on july09. After some doubts regarding a possible shift in calibration I came to the conclusion it could be the result of a blending effect between NIII 4640 and HeII 4686 lines with an increasing relative intensity of the 4686 side. All that, merged by expansion velocity and low resolution spectra, could explain the observed moving structure. Any comment will be more than welcome.



Cheers,
Daniel

I have obtained five spectra of Nova Herculis 2021 with the idea of seeing if there is any evolution as the luminosity of the nova decreases (current magnitude below +14). The only variation observed, at low resolution, is the increase in the line located approximately 468 nm, which seems to correspond to species with higher ionization. However, and because it is low resolution, I cannot specify what is happening. Has anyone interpreted the reason for the growth of that line over time? JJ

Has anyone interpreted the reason for the growth of that line over time? JJ

It is He II 4686 and/or NIII/CIII blend
The envelop recedes and its temperature is rising (perfect gas law): the ionization strengthen (~ 50 000 K), thus He II is doubly ionized and recombination produces the increase of He II emission and other high ionized lines. See: http://spectro-aras.com/forum/viewtopic.php?f=33&t=2703
With higher resolution spectra, I suggest a comparison of He II and H beta profiles in order to decide if He II is alone or blended with CIII/NIII. The further sequence of spectra will also help to decide.
The identification of lines often requires to take a step back ...

Congratulation to Juan José for the spectra at magnitude 14. Not an easy task... Many thanks to "admin" for the comments and advise helping us to better understand what we see in low resolution. At this level of magnitude it may be difficult to get additional data in high resolution. As per my previous image and comment above, the frequency shift of the apparent shape of that complex structure could provide an idea of the blending level between NIII 4640 and He II 4686 but I may be wrong.
It may also interesting to underline the relative (to Hbeta) increase of what colud be the neon lines (Ne III 3869, 3968). Here also our low definition observations are subject to interpretation errors...
Thanks again for these fascinating surveys and opportunities to learn through the Aras forum and data base.
Clear sky.
Daniel

Hola Juan José,

Very nice serie ! Very nice job !

Saludos, Joan.

Hello,
I took a sixth spectrum of Nova Her 2021 with a double purpose: to follow its evolution as the nova fades, and to check what is the practical limit of my spectrograph (an Alpy600). I think that this limit will probably not be conditioned by the camera that captures the spectrum, but by the guiding system. I am using an Atik Titan at binning x3 and 10s of individual exposure. How could I improve this system to be able to track dimly objects? At the time of the spectrum acquisition, the magnitude of the nova was approximately +14.7 and the Moon, located in Capricornus, was practically full (97%). Its effect can be seen in the upper 2D spectrum (individual 600s spectrum without sky background and instrumental correction). I added a rough evolution of the 468 nm line along time (42 days).
Regards. JJ Pueyo

Hello Juan,
Congratulation for that impressive result with a magnitude near 15 at full moon ! Apparently your sky is showing almost no pollution. Excellent site for observation.
Not sure to unsdestand your question regarding the guiding camera. Why to increase the exposure time above a few seconds ? At such low luminosity you should not expect to see the target within the slit. What really matter is the guiding star, not the target.... But I may have misunderstood your point.
Cheers,
Daniel

Now mag 16 so time to use the ALPY200 at R~130
Line identifications are based on a spectrum of another very fast nova Sgr 1991 in Gray and Corbally at similar date which looks very similar but should be treated with caution at this resolution.
If it is the same as nova Sgr 1991 there could be very strong [Ne V] lines at 3346/3428 A . Too far into the UV for me but perhaps a good target for the UVEX ?

Cheers
Robin