Nova Men 2022 (AT 2022ufh)

Alerts and Monitoring of Novae
Post Reply
Paul Luckas
Posts: 101
Joined: Tue Jun 24, 2014 5:08 pm
Location: Perth, Western Australia

Nova Men 2022 (AT 2022ufh)

Post by Paul Luckas »

Greetings all,

A nova for the 'southerners'. It's rising mid-evening, and I'm sure François will appreciate on-going observations.

https://www.astronomerstelegram.org/?read=15639

Paul
AT2022ufh_20221001_625_Paul_Luckas.png
Francois Teyssier
Posts: 1520
Joined: Fri Sep 23, 2011 1:01 pm
Location: Rouen
Contact:

Re: Nova Men 2022 (AT 2022ufh)

Post by Francois Teyssier »

Thanks, Paul!
I'm sure François will appreciate on-going observations.
Yes! One spectrum of a "new" star (in Human Knowledge) is nothing more than a new object in a collection.
It allows its classification and eventually stats.
This is the Aristotelian level of science.
Medium and long term monitoring, as our group is able, bring very new and useful information about the physics of the object, constrains the models, ... This the level which is expected by the specialists of these objects. This is at this level of involvement, thanks to our striking power, that we can act -at our modest level - to Human knowledge of the Universe. Just a little cent, in the money bank, but valuable.
I very pleased that some of us have understood this key point, well develop by some professionals we are working with.

I propose from this spectrum a

Basic introduction to the spectroscopic development of a classical CO nova.
1. Maximum luminosity

Paul' spectrum is typical of a very classical CO nova near its maximum luminosity.
The nova phenomenon is one of the results of the accretion of solar matter (H and He) at the surface of a white dwarf in a binary system from a late type companion .
It consists of :
1. thermo nuclear runaway,TNR, (CNO cool and hot) in the envelop of the degenerated accreted material (solar type, H + He) at the surface of a white dwarf. The increase of the temperature (until Fermi temperature) stops the degeneracy: at least in some parts of the envelop .
2. the expansion of the envelop (or a part of it) to giant dimension (~ 1 Rsol)
3. the ejection of a part this expended envelop during the expansion at a still unknown moment forming the ejecta
4. The ejecta expands freely in the interstellar medium acting as a passive medium while the remaining envelop retracts.

TD:
- Study evolutionary path of low mass stars (< 8 Msol) until the state of white dwarf (CO and ONe types)
- What is degenerated matter ? (vs Perfect gaz)
- From 2.: how does the effective temperature evolve during the expension of the envelop?


Observing note:
- The spectroscopic rise is not well documented due for its short duration.
- A well-known pre-maximum photometric halt about 1 mag under the maximum is often observed (see the work of Mc Laughlin). Just after the maximum a fast decline of about 1 mag and a short halt (with a faint re-brightening) was observed in some classical CO novae, for instance Nova Del 2013. The origin of these breaks of slopes is still not understood.
- Continuous spectroscopic as far as possible after the alert, during the very first moments of the rise and around the maximum luminosity during the photometric halts could provide very important information about the phenomenon (physics of the expansion of the envelop and expulsion of the ejecta (point 3.)
- Long monitoring observation during the first nights and 24 hours observations (for tropical objects) are highly encouraged (we performed that during the decline of Nova Del 2013 with a 24 hours monitoring from Europe, North America and Australia).
The spectrum near the maximum
The spectrum secured by Paul is typical:
1. Blue continuum (i.e. strong intensity of the blue part of the continuum) produced by the photosphere of the envelop, well modelized as a black body of temperature 10 000 K or lower as an order of magnitude.
2. Emission lines of HI (Balmer) lines and metal s(neutral as Na I D and singly ionized as Fe II) accompanied by a blue absorption.
Note: due to interstellar reddening for far object toward the disk of the galaxy, the slope of the continuum can tend to horizontal or even the red in extreme cases.

TD:
- Check Planck’s law, Wien’s law
- The temperature of the photosphere can by approximated using Planck’s law and/or BVR values (photometry) of B/V and V/B ratio from a spectrum even not calibrated in flux. One can use; a. convolution with the transmission curves of B, V, R filters or more simply the value of the continuum around the effective wavelength of the filter.
Emission lines
- As usual when studying a spectrum, begin by HI lines, which follow the classical Balmer decrement.
- The other lines are metal lines (in astrophysical language, metal is an element which is not H or He . In stellar A.P., they correspond respectively to the proportions Z, Y, X.
- The typical Fe II (42) multiplet is characteristic of the spectrum of a CO nova near the maximum.
- At this state of the development of the (permitted) lines are formed (in the ejecta) essentially by recombination, id est ionization followed by recombination and cascade and also by excitation from the ground level.
- The emission near 5900 A can not be He I. First: if He I 5876 is most often the stronger line of the He I spectrum, after lines (doublet 6678 or triplet 7085 A) should appear. This not the case. Second (physical reasoning) : He I requires more energetic radiation (about 25000 K) much above the effective temperature. He I helium will occur later at about + 2 V mag during the “Helium flash”.
Notes:
For this class of novae, the state is sometimes called “Iron Curtain” (S. Shore) due to the strong opacity of Fe+ (not numerous ions in comparison to H, but very efficient due to great number of lines)
The classification of “Fe II spectrum” (vs. He/N) is used in many publications following Williams’s classification (1991, 1994). The concept is contested by S. Shore.
TD:
- Knowing that it is not He I, what is the line at about 5900 angströms. What observation could more easily confirms the identification?
- The temperature of a ionizing source can be approximated by : ionization energy of the highest energetic lines (value in eV ) x 1000 K. From the observed lines in the spectrum, what is the temperature of the photosphere (order of magnitude) ? Is it consistent with the evaluation of the temperature of the ionizing source.
- Perhaps more difficult. Could you explain why the good agreement between the two rough evaluations of the temperature is well explain by the theory of a freely expanding and passive medium ionized by the photosphere?
at2022ufh_20221001_625_sp0.png
Velocities.

A rough evaluation of the velocity of the ejecta is obtained by the analysis of the profiles of the lines in the velocity space (transformation of the wavelength axis to velocity by application of the Doppler formula).

Observing note:
Due to the high velocity of the ejecta low resolution spectra produce very valuable results. For refinement, one can computed the effective velocity, knowing that Observed velocity (square) Vobs equals the sum of the square of the resolution of the spectroscope (Vspec) and physical velocity (Vreal): Vobs^2 = Vreal^2 + Vspec^2.
It is very important to know the resolution of a spectrum in units of km/s (depending of the wavelength).

A common evaluation is obtained by the measure of the FWHM. It should be perfect for a gaussian line on a linear continuum. It is a good approximation in many cases. But for novae near maximum it doesn’t work well due to the strong opacity in the blue part of the spectrum: a part of the emission is absorbed by the ejecta in the direction of the observer, producing asymmetry of the emission profile and at this state absorption resulting from two effects : P Cygni profiles and absorption by neutral gas (not yet ionized due to the opacity) in outer layers of the ejecta.
Thus, the measure of FWHM is a poor evaluation.

Two measures can provide information: the maximum velocity and the velocity at the maximum absorption.
at2022ufh_20221001_625_balmer.png
at2022ufh_20221001_625_balmer.png (19.05 KiB) Viewed 3609 times
Of course, these evaluations suppose a spherical shape and homogeneous velocity according to the radius at a first order.


TD:
- Knowing the resolution of your spectrum, compute some values of the resolution in units of km/s at various values from 3500 to 10000 A. Graph and table could accompanied you in further studies. Compute the values for typical values of X-rays, UV, near IR, radio.
- Have a glance to the formation of P Cygni profiles. But be careful with simple graphic explanations which do not explain the processes.
- Compare H alpha profile with its symmetric profile according to the rest wavelength and explain why FWHM is not a good tool.

Velocities of Balmer lines
at2022ufh_20221001_625_balmer.png
at2022ufh_20221001_625_balmer.png (19.05 KiB) Viewed 3609 times
- Compute maximal velocity and velocity at the maximum absorption for the 3 lines.
- Compare them
- Could you explain why H alpha is not the best line to be studied.
- Could you explain why the profiles of these 3 lines are different?

Velocities of Fe II lines
at2022ufh_20221001_625_feii.png
at2022ufh_20221001_625_feii.png (24.82 KiB) Viewed 3606 times
- Compute maximal velocity and velocity at the maximum absorption for the 3 lines.
- Compare to Balmer values.
- Fe II (42) are *very very very often * formed in similar physical conditions, thus the shape of the lines should be similar. Why the profile of Fe II 5169 so different ?

Well, this is a first attempt.
For me it is interesting to synthesize my knowledge and remember my first times in spectroscopy with so many obscure concepts. I have learned a lot these last 13 years, sufficiently to understand that what I don't know now is much more vast than what I learned (with many thanks again to Steve)

Say me if it is useful for you.
Say me about the expected level and information.
And do not hesitate to raise questions. I'll try to reply or find support.

François Teyssier
Tom Love
Posts: 64
Joined: Sun Apr 21, 2019 5:57 am

Re: Nova Men 2022 (AT 2022ufh)

Post by Tom Love »

Sadly, it's the third La Nina year in a row, and the weather has meant very little observing has been possible for many weeks now in New Zealand and Eastern Australia. Deeply frustrating!
-------------------------------------------------
Martinborough, New Zealand. Alpy, Lhires RC12
Francois Teyssier
Posts: 1520
Joined: Fri Sep 23, 2011 1:01 pm
Location: Rouen
Contact:

Re: Nova Men 2022 (AT 2022ufh)

Post by Francois Teyssier »

There will be many new novae, especially in Southern Sky.
Cloudy skies is a good opportunity to work on the data -;) and improve his (and OUR) knowledge.

All the best,
François
Post Reply