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Bright nova in Perseus - N Per 2020

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#26 descott12

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Posted 25 December 2020 - 12:35 PM

I went back and following mwr's lead, I have identified a bunch more lines. Does the presence of these N, O and C lines indicate the nova is now in the "nebular" phase?

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  • Nova Per 2020 - 2020-12-21-3.png


#27 mwr

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Posted 26 December 2020 - 05:56 AM

 Does the presence of these N, O and C lines indicate the nova is now in the "nebular" phase?

Hi Dave,

 

in the nebular phase the forbidden lines like [O I] 6300, [O III] 5007 and N [II] 5755 become dominant and the Fe II lines fade away. The nebular phase starts when the maximum brightness of the nova has diminished by about 3.5 magnitudes. So the nova is not yet in the nebular phase and I estimate that the forbidden lines will become well visible around values of 12-13 mag - too faint for my setup :-(


Edited by mwr, 26 December 2020 - 05:58 AM.


#28 Bräumer

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Posted 26 December 2020 - 08:54 AM

Hi,

Does anyone have any information about how far the nova is from Earth?



#29 descott12

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Posted 26 December 2020 - 09:20 AM

Hi Dave,

 

in the nebular phase the forbidden lines like [O I] 6300, [O III] 5007 and N [II] 5755 become dominant and the Fe II lines fade away. The nebular phase starts when the maximum brightness of the nova has diminished by about 3.5 magnitudes. So the nova is not yet in the nebular phase and I estimate that the forbidden lines will become well visible around values of 12-13 mag - too faint for my setup :-(

Ah. Thanks for the explanation. Yes Walker explains a bit of this on page 134 but I did not realize the Fe II lines would disappear.  I will definitely keep a watch on this one. I wonder if I can capture it at Mag 12-13? I will certainly give it a try.

Very interesting stuff.



#30 robin_astro

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Posted 26 December 2020 - 10:42 AM

Hi,

Does anyone have any information about how far the nova is from Earth?

Novae vary quite a lot in absolute magnitude  so are not very good "standard candles" but we can make a very rough back of envelope estimate.

 

If we start with a typical absolute magnitude at maximum of say approximately -8 (from the reference in wikipedia) and then correct for the ~2.5 magnitudes of interstellar extinction estimated from from the strength of the interstellar lines,  E(B-V) ~0.8   

http://www.astronome...org/?read=14229

this gives a rough corrected absolute magnitude of  -5.5

 

From AAVSO data the apparent V magnitude at maximum was ~ 8.3

 

We can use these absolute and apparent magnitudes to estimate a distance of ~6kpc, though given the uncertainty in absolute magnitude, this could be a few times too large or small

 

Cheers

Robin


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#31 mwr

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Posted 26 December 2020 - 10:48 AM

Hi,

Does anyone have any information about how far the nova is from Earth?

Hi Kalle,

 

I haven't found yet a published distance but it can be estimated by using Cohen's formula for galactic novae (ASPC 4 (1988) 114-127; http://adsabs.harvar...ASPC....4..114C):

 

MV = -10.66 + 2.31*log t2 (in words: the absolute brightness can be calculated by the time (in days) that gives a decay of 2 mag in apparent brightness). t2 can be estimated from AAVSO data (Nova Per 2020 = V1112 Per) to be about 25 days (with mmax = 8.5 mag). This yields an absolute magnitude of MV = -7.43

 

The inverse square law for light tells us how an object's apparent brightness depends on its luminosity and distance and this allows us to calculate the distance of this nova by using the "photometric parallaxe":

 

d (parsec) = 10 exp ( (m-MV-AV+5) / 5 ) with AV = sum of circumstellar and interstellar extinction = 0.55 mag

 

This yields an estimation for the distance of 11912 parsec or 39708 light-years. 


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#32 mwr

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Posted 26 December 2020 - 11:13 AM

Novae vary quite a lot in absolute magnitude  so are not very good "standard candles" but we can make a very rough back of envelope estimate.

 

If we start with a typical absolute magnitude at maximum of say approximately -8 (from the reference in wikipedia) and then correct for the ~2.5 magnitudes of interstellar extinction estimated from from the strength of the interstellar lines,  E(B-V) ~0.8   

http://www.astronome...org/?read=14229

this gives a rough corrected absolute magnitude of  -5.5

 

From AAVSO data the apparent V magnitude at maximum was ~ 8.3

 

We can use these absolute and apparent magnitudes to estimate a distance of ~6kpc, though given the uncertainty in absolute magnitude, this could be a few times too large or small

 

Cheers

Robin

I haven't seen Robin's post that appeared almost simultaneously with my post. Robin's value for the interstellar extinction is certainly a much better estimation. Using 2.5 mag for AV yields a distance of 4.8 kpc or about 16000 light-years.


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#33 Bräumer

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Posted 26 December 2020 - 04:13 PM

Thank you both for your estimate!

You really help me in this thread to understand the nova :)

 

Kalle


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#34 robin_astro

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Posted 26 December 2020 - 07:59 PM

A brief foray into the IR with the LHIRES III and 600l/mm grating. A red (610nm long pass) filter was used to ensure no contamination from the 2nd order. beta Aur was used as a reference for response correction. 

 

novaper2020_20201223_916_Leadbeater.png

 

Cheers

Robin


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#35 descott12

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Posted 26 December 2020 - 09:33 PM

A brief foray into the IR with the LHIRES III and 600l/mm grating. A red (610nm long pass) filter was used to ensure no contamination from the 2nd order. beta Aur was used as a reference for response correction. 

 

attachicon.gifnovaper2020_20201223_916_Leadbeater.png

 

Cheers

Robin

Pretty cool that I was able to capture the two larger peaks with my SA-100 and there is actually a  hint of the central peak 8200 as well.



#36 mwr

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Posted 26 December 2020 - 10:28 PM

A brief foray into the IR with the LHIRES III and 600l/mm grating. A red (610nm long pass) filter was used to ensure no contamination from the 2nd order. beta Aur was used as a reference for response correction. 

 

attachicon.gifnovaper2020_20201223_916_Leadbeater.png

 

Cheers

Robin

Hi Robin,

 

a fascinating high resolution profile of the O I line at 8446 Angström !  It would be interesting to see if a suitable scaled velocity profile of this emission line can be somehow fitted to calculated profiles of ellipsoidal shells with equatorial and polar rings at different angles of inclination:

 

novae_profiles.jpg

 

Gill and O'Brian have presented numerous "Emission-line profiles from model nova shells" here: https://academic.oup...07/3/677/961689



#37 mwr

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Posted 27 December 2020 - 04:17 AM

 It would be interesting to see if a suitable scaled velocity profile of this emission line can be somehow fitted to calculated profiles of ellipsoidal shells with equatorial and polar rings at different angles of inclination:

 

 

I have just found Robin's spectrum in the BAA database and it seems that the calculated line profile for a simple ellipsoidal shell with an equatorial ring and polar rings of enhanced brightness with an inclination angle of 60° gives the best fit for the O I emission line:

 

 

_novaper2020_20201223_976_leadbeater.jpg

 

I haven't found out yet how to calculate a velocity profile from an emission line in VSpec but the maximum velocity for the ejecta that form the top ring should be around 900 km/sec.


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#38 mwr

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Posted 27 December 2020 - 05:49 AM

 

 

I haven't found out yet how to calculate a velocity profile from an emission line in VSpec but the maximum velocity for the ejecta that form the top ring should be around 900 km/sec.

Actually not that difficult:

 

_novaper2020_20201223_976_leadbeater_scaled.jpg

 

Richard Walker has written a very useful Tutorial that shows how to scale the x-axis in Doppler velocity:  https://www.ursusmaj...a_reduction.pdf



#39 robin_astro

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Posted 27 December 2020 - 07:51 AM

Tim Lester's PlotSpectra 

 

http://www.spectro-a....php?f=8&t=1596

 

(latest  version at end of thread)

 

can display any selected region of the spectrum in velocity space

 

Plotspectra_RV.png

 

You can even overlay different lines simultaneously eg as here in Nova Cas 2020

http://www.spectro-a...&p=15078#p15078

 

Cheers

Robin


Edited by robin_astro, 27 December 2020 - 07:54 AM.

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#40 robin_astro

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Posted 28 December 2020 - 05:39 PM

A brief foray into the IR with the LHIRES III and 600l/mm grating. 

Cranking up the resolution  on the OI 8446 line to R~7000 by moving to the 1200l/mm grating

 

novaper2020_20201228_742_Leadbeater.png

 

Robin


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#41 descott12

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Posted 28 December 2020 - 05:57 PM

Cranking up the resolution  on the OI 8446 line to R~7000 by moving to the 1200l/mm grating

 

attachicon.gifnovaper2020_20201228_742_Leadbeater.png

 

Robin

Beautiful! I am guessing your exposure has to get pretty long to support that resolution?



#42 Bräumer

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Posted 29 December 2020 - 08:10 AM

Hi,

 

It seems like I have a question again, I hope you can help me out again.

 

If we start with a typical absolute magnitude at maximum of say approximately -8 (from the reference in wikipedia) and then correct for the ~2.5 magnitudes of interstellar extinction estimated from from the strength of the interstellar lines,  E(B-V) ~0.8   

http://www.astronome...org/?read=14229

 

I have looked at the article and wonder, how is it possible to determine the E(B-V) just by looking at the interstellar lines? E(B-V) is a color excess, isn't it?

Wikipedia told me: "Also significant is that the strength of DIBs is broadly correlated with the interstellar extinction."

But why? And how exactly can you determine the color excess?

 

Kalle


Edited by Bräumer, 29 December 2020 - 08:11 AM.


#43 robin_astro

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Posted 29 December 2020 - 08:10 AM

 I am guessing your exposure has to get pretty long to support that resolution?

This was two hours (12x600s) but there was a lot of thin cloud around so I probably lost about half the signal. There seems to be quite a lot going on the in continuum that does not look like random noise. Fringes can be a problem at high resolution in the IR  but the flat seems pretty clear of them.



#44 robin_astro

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Posted 29 December 2020 - 02:51 PM

Hi,

 

It seems like I have a question again, I hope you can help me out again.

 

I have looked at the article and wonder, how is it possible to determine the E(B-V) just by looking at the interstellar lines? E(B-V) is a color excess, isn't it?

Wikipedia told me: "Also significant is that the strength of DIBs is broadly correlated with the interstellar extinction."

But why? And how exactly can you determine the color excess?

 

Kalle

E(B-V) is used as a shorthand for extinction but the interstellar medium has various properties which can be used to estimate empirically  how much there is between us and the object.

 

One is that it absorbs different wavelengths by different amounts, in general  absorbing less at longer wavelengths making objects look redder.  This is normally described as E(B-V), The difference between the expected (B-V) brightness values for a star (based on its spectral classification) compared with the measured B-V.

The actual absorption in the V band is ~3x E(B-V).  In this case we cannot use this however as we do not know what the spectrum should look like so we do not know what the (B-V) should be

 

The interstellar medium is made up of various substances however, some of which produce specific extra absorption lines in the spectrum of the nova. By measuring the depth of these lines we can estimate the amount of interstellar material. In this case lines produced by sodium and potassium in the interstellar medium were used to estimate the extinction.

 

Note these lines are different from the diffuse interstellar absorption bands which are thought to be produced by molecules in the interstellar medium. Their distribution of these varies so can only be used to approximately estimate extinction.

 

Robin


Edited by robin_astro, 29 December 2020 - 02:59 PM.


#45 Bräumer

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Posted 29 December 2020 - 05:01 PM

Oooh, ok. So the strength of interstellar absorption lines is directly related to the strength of the extinction?

#46 robin_astro

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Posted 29 December 2020 - 06:43 PM

Oooh, ok. So the strength of interstellar absorption lines is directly related to the strength of the extinction?

The strength of the interstellar absorption line in the spectrum of the target gives a measure of the amount of that particular  substance between us and the target. There is then an empirical relationship between that and the amount of dust causing the extinction. See here for example where the interstellar sodium D absorption line was used to track the extinction due to dust in the Milky Way

https://academic.oup...6/2/1465/975270

 

Cheers

Robin



#47 Bräumer

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Posted 30 December 2020 - 03:30 AM

Thank you Robin, I appreciate your explanation!



#48 robin_astro

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Posted 30 December 2020 - 11:08 AM

Cranking up the resolution  on the OI 8446 line to R~7000 by moving to the 1200l/mm grating

 

 

A lower noise version from last night. Lots of structure in the  line profile

 

Robin

 

novaper2020_20201229_751_Leadbeater.png


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#49 descott12

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Posted 30 December 2020 - 11:54 AM

A lower noise version from last night. Lots of structure in the  line profile

 

Robin

 

attachicon.gifnovaper2020_20201229_751_Leadbeater.png

Hey Robin, to get lower noise was that a longer exposure to boost SNR or was the previous curve simple smoothed a bit?



#50 mwr

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Posted 30 December 2020 - 02:37 PM

 Lots of structure in the  line profile

 

 

Hi Robin,

 

great spectrum! I have applied the low-pass filter function in VSpec to your spectrum and it looks like a six-peaked structure in a

classical-nova-shell line profile in the form of an inclined ellipsoidal shell with enhancements in equatorial and tropical rings. The similarity to the peak structures of the forbidden lines of the nova V705 Cas (inset) is really striking:

 

_novaper2020_20201228_742_leadbeater.jpg

 

The peaks in the profile are clearly brighter in the red than the blue but otherwise placed symmetrically about their rest wavelength.

 

Thanks for sharing your spectra. 




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