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allenhugh10's picture
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Alpy spectrum of Nova Cas 2021 near maximum

Amazingly there was a hole in the weather here in Somerset last night. The nova was incredibly bright! I had to drop the camera exposure from 300 to 90sec to avoid over exposing the H alpha emission. It is now putting on a complex display of emission lines with beautiful P Cygni profiles. The H Balmer series is still prominent whilst helium emission lines have now disappeared to be replaced by a forest of singly ionised iron emission lines some of which I've marked. Also very striking is the pair of singly ionised calcium emission lines down in the violet, their associated blue-shifted absorption reminiscent of the solar spectrum. A wonderful spectrum!

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Objective prism spectrum

Ideal conditions last night to try for a higher res. spectrum; no wind and low humidity.  The result is on my members page and shows some nice detail at the blue end of the spectrum.

Mike.

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Here's a plot from the BAA

Here's a plot from the BAA Variable Star Section database. Looks like it is past the peak, BUT this type of nova might have a second (or third) peak. Keep watching!

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Rapid fading of Nova

Kato-san posted the following on VSnet overnight:

"V1405 Cas rapid fading

   Several observers have noted rapid fading.

   Itoh-san's data:

May 14  V=6.11, B-V=+0.57
May 15  V=6.95, B=V=+0.27

 This fading is apparently not caused by dust formation."

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Latest plot from VSS database

Latest plot from VSS database

mike harlow's picture
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Recent spectra

I'm still taking spectra of the nova whenever possible and the latest one from last night seems to suggest that the helium lines are coming back.  Can anyone confirm this?  I'm no expert on novae but I can't remember seeing one like this before.  Can anyone explain what it's doing and has this sort of behaviour been seen before? And it appears to be creeping up in magnitude again!

Thanks,

Mike.

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Nova Cas 2021 remarkable spectral evolution

Yes Mike, the HeI emission has returned amongst a few other significant changes in this wonderful nova. I've captured a dozen spectra since Mar 22, here's an offset relative flux plot of a few of them showing the disappearnce and then return of the HeI emission:

I've also been monitoring the expansion velocity. Until May 24 it was showing a perhaps expected gradual decline, but then briefly increased in my spectrum of May 24 around the time the nova began to brighten again. My latest spectrum from last night May 30 suggests the decline in expansion velocity has resumed accompanied by a strengthening again of the P Cygni profiles:

The spectrum is dominated by the overwhelming relative brightness of the H alpha emission line. Here is the spectrum from May 24:

A truly remarkable object and great fun to follow in a spectroscope!

Cheers

Hugh

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Recent spectral changes

Thanks Hugh, that's a really interesting summary of recent changes...I'm glad I was seeing something real!  It will be fascinating to see what it does next...

Mike.

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V1405

Couldn’t see it without my 15x70 binoculars, at 22:30ut last night I estimated it was around 7.5, typo error not 5.5 as I previously wrote. Observed it in 31st through haze and it seemed about the same as the previous night. But not the best conditions to observe 

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Light curve 1 June

The BAA VSS light curve indicates the nova has been gradually brightening again over the last few days. 

May 31.208  7.24 TG (Gary Poyner)

May 31.995  7.1 vis (Paul Abel)

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Brightened?

I had a quick look last night at around 21:45ut and it seemed around mag7 but sky conditions weren’t that good due to haze. I wonder if that’s it for the second peak and it will fade or even if we will see more peaks, very interesting article in the latest vas circular about it being miss- classified ages ago. Thinking about it how accurate was the position as it’s a crowded star field 

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Gradual brightening continue.

Gradual brightening continue. Now brighter than 7.0

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fading

Reasonably clear a few high altitude clouds, hindered by my neighbours washing setting off her security light in a the gentle breeze. So wait 5 minutes until it goes out.

Seems to be fading when compared to the weekend, last night I estimated it at mag7.9

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Recent brightening trend

Recent brightening trend continues

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Brightened

I’ve had 9 continuous nights of clear skies but last night the transparency was awful, doesn’t look a lot better tonight so far. I hope to follow this one for some time in Binoculars and a 10 inch Newt. Skies around here suffer from a lot of LED street lights. 

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nova cass

This morning the BBC  Weather  reporter  was blaming our very poor  sky conditions on  high  altitude smoke  from the USA  wild fires. For the last  two nights  ie 21/22 July and 22/23 July  the  moon has looked as if it was in Eclipse and very few  stars  dimmer than  second Magnitude were  visible naked  eye. Thunder Storms in Forecast  for the  next 48 hours ..  So not much chance  of getting an upto date image of this  long lasting Nova. 

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V1405 Broadband linear polarisation

I wondered if there might be evidence of any asymmetry in the nova due to shocks or clumping of fast/slow ejecta and if it might show up in linear polarisation and wavelength dependence. Measurements from 21-22/07/2021 [file attached] don't seem to show much other than interstellar polarisation characteristic.

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iTEL 18 results a bit of a disappointment

I thought I would give this bright nova a try with iTEL 18 (300 mm) in Spain. Even with only a 5 sec exposure the images were saturating. Then all iTEL images are charged as if they were 60 sec exposures - not economical. 

So I will stick to fainter objects unless someone can point out a workaround.

Stewart

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Stewart, Yes, it's back up to

Stewart, Yes, it's back up to 5.6 unfiltered tonight (July 26) which is not far short of its brightest at the previous peak. I'm doing 1s exposures and it is not far off saturating my camera. It is very hazy here but I think I'll get the binoculars out again.

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iTEL 18

The good news is that iTEL are  forgiving of my mistakes in setting up runs. They have refunded my account which I think is very good of them.

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Faded

seems to be fading quickly, easily visible in my 20x70 binoculars on Wednesday 28th but last night the 1st August  I couldn’t see it. Was going to get my telescope out but clouds rolled in just as I set up. 

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Nova Cas 2021

Here is a spectrum of Nova Cas 2021 taken on 6th August with a LISA (R~1065) and calibrated in absolute flux using a concurrently measured V magnitude of 7.70. There are broad emission lines of H I Balmer and He I, all with P-Cygni absorption dips, and weak Fe II emission lines with double peaks. The H-alpha line is so strong that exposures had to be kept to 40 sec to avoid saturating. Further information about the spectrum and more plots can be found on the ARAS Forum at

http://www.spectro-aras.com/forum/viewtopic.php?f=36&t=2744&p=15888#p15888

David

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This nova is still showing

This nova is still showing lots of interesting activity. And it's still 8th mag

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The nova that keeps on giving

The nova that keeps on giving!

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V1405

Never ceases to amaze me each night I observe it. I hope it continues for a long time. I hope there will be a paper on what is going on with iy.

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