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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!

mike harlow's picture
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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

mike harlow's picture
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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)

Daryl's picture
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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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