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Nova in Hercules

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Nova in Hercules

Patrick Schmeer has just posted this message on the BAA VSS Alert email system:

TCP J18573095+1653396 = ZTF19aasfsjq  (N:)
(submitted to VSX)

Discovered on 2021 June 12.537 UT at mag. 8.4 by Seiji Ueda (Kushiro, Hokkaido, Japan):
http://www.cbat.eps.harvard.edu/unconf/followups/J18573095+1653396.html

ZTF light curve, data, and images (via Lasair):
https://lasair.roe.ac.uk/object/ZTF19aasfsjq/

Possibly recorded on the rise (gmag. ~16.3 on June 12.192 UT) by the ASAS-SN Sky Patrol:
https://asas-sn.osu.edu/sky-patrol/coordinate/a611fda3-59f1-42fd-8e6d-386b21100256

Source No. 4514092717838547584 in Gaia EDR3 (Gmag. 19.95).

Spectroscopy and multiband photometry are urgently required.

Clear skies,
Patrick
-------
References:
All-Sky Automated Survey for Supernovae (ASAS-SN) Sky Patrol:
- Shappee et al., 2014ApJ...788...48S
- Kochanek et al., 2017PASP..129j4502K
Lasair:
- Smith et al., 2019RNAAS...3...26S
Zwicky Transient Facility (ZTF):
- Masci et al., 2019PASP..131a8003M

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Confirmation from W Australia

Latest on CBAT transients page

2021 06 12.642 - Visually confirmed this nova suspect at reported position. Magnitude 6.4 at June 12.642 UT.

2021 06 12.642 -Visual observation on June 12.642 UT by Andrew Pearce (Nedlands, W.Australia)

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Charts available from the

Charts available from the AAVSO chart plotter. Here is a 5 deg chart. And here is 10 deg.

Note that it's almost in Aql: it is between epsilon Aql and 111 Her

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Nova

In the twilight using opticron 15x70 binoculars I estimate the magnitude as 5.8

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Nova Her

Observed with 10x50B and a 5 degree chart drawn with VSP using the 61 star, I get 6.2 on June 12 at 22h 06m UT.

Gary

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Got it here at 6.3 vis, Jun

Got it here at 6.3 vis, Jun 12 at 22h 12m, using 8 x 42 bins 

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Photo of nova

Here is a photo just taken from Walmer, Kent. A 20 second exposure with a FujiFilm X-T10 and kit lens at 3200 ISO.

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Photo of nova

And here as an attachment.

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Nova or something else?

Intriguingly a low resolution Star Analyser spectrum by Rob Kaufman in Australia earlier today failed to show any significant emission

https://hosting.photobucket.com/images/ww271/Rob_Kau/TCP_J18573095_16533...

After clear blue skies all afternoon the clouds have rolled in here but no doubt we will have better spectra tonight

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Possible Nova Her 2021

Here is a low resolution R~1000 spectrum of the new bright object in Her. Taken with a LISA on a 0.28m SCT.

This has been instrument and atmospheric response corrected.

David

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Another bright nova! Here's

Another bright nova! Here's my image https://britastro.org/observations/observation.php?id=20210612_231222_b0ed29be83050b55. I've taken some 1s exposures too which I'll measure later.

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Wide-field image

A short 5 second exposure with 35mm lens.

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Nova Hercules image

5 seconds exposure - Canon 450d - Zenistar 73mm f=430mm APO - ISO 800 - Chesham UK

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Visual observation

At 23:45 UT I’m getting 6.4 (+/-0.2)V in my 10x50 binos, with reference to the 10deg chart. Transparency not great here so I only had a brief window to make an estimate - I seem to be in the one part of the country with cloud! But a really easy binocular target. Great to see the spectra on here.

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Nova Her 2021 - Alpy spectrum

It's wonderful that a 'new star' appears in the sky when the weather is ideal! The BAA notification system worked perfectly and I was able to observe the possible Nova Her 2021 after first capturing another spectrum of Nova Cas 2021. This is an extraordinary spectrum the like of which I haven't seen before

Cheers

Hugh

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spectrum

Very broad P Cygni H and He by the looks. Almost overlapping with the high velocity. Almost a supernova like spectrum

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Nova in Hercules

Whilst test running a new 2nd main telescope (16", F:6 Newt)  I was able to image the new Nova in Hercules, using a Moravian MkII 3200ME camera, 2x binning and a 1 sec exposure

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Now confirmed as a Nova by

Now confirmed as a Nova by Munari, Valisa and Dellaporta in an ATEL 14704: "Spectroscopic classification of TCP J18573095+1653396 as a nova bordering naked-eye brightness"

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Ignorance

In simple terms, what does the spectrum of the nova tell us about what is going on?

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description of spectrum evolution

Prof Steve Shore comments on the evolution of Nova Del 2013 based on amateur spectra here. Not simple though !

http://www.astrosurf.com/aras/novae/Nova2013Del-1.html

Cheers

robin

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Interpretation of Nova Her 2021 spectrum

After a little sleep I've attempted to interpret last night's spectrum. I estimate an explosion velocity of about 3450 km/sec based on the P Cygni profile of the Hα emission. I've annotated the spectrum with the rest wavelengths of the first seven H Balmer lines, where at the shortest wavelengths the P Cygni profiles are not consistently positioned based on my estimated explosion velosity. I also added  couple of the HeI l lines where the positions are consistent. Using my explosion velocity, several of the deepest absorption lines appear more consistent with some specific metal P Cygni profiles. It's certainly a fascinating spectrum

Cheers

Hugh

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Nova Hercules

Observed with Binos in a bright sky approx estimate 6th mag. Easy to find.

Image was taken at 22.52 UT Canon 600D 10sec exposure undriven

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Nova

It’s faded quickly, this time last night (21:50UT) I could easily see it in 15x70 binocular, now I can’t pick it up. I’ll wait until it gets a bit darker 

abandoned at 22:38UT as a bank of cloud has appeared 

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the view last night

Picked it up quite easily in our RC8 :) 

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Spectrum

I also had a go at a spectrum. As another poster noted, there doesnt seem to be much excess red.

This is the raw spectrum, not corrected for IR or atmosphere, compared to the refreence star Okab (type A0IV)

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I've just measured it as 7.54

I've just measured it as 7.54 (2021 June 13 22:51) compared to 5.94 at this time last night. Both unfiltered ref to Gaia DR2 G so somewhere between V and R. That's a fall of 1.6 mags in day. That's pretty fast. I remember photographing V838 Her (George Alcock's last nova) in 1991 but only getting it on one occasion since it faded so fast. 

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Low res spectrum

Yes, much fainter than I was hoping for but still bright enough for a low resolution spectrum:

Very broad hydrogen lines dominated by H alpha emission.

Mike.

[26cm, 3 degree objective prism on 30cm F/6.8 astrograph.  6 x 15 seconds at ~23:30BST 13th June 2021]

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Nova Her 2021

The spectrum now looks very different from last night with strong and very wide Balmer emission lines.

David

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Don’t go, Nova Her 2021

I have it at around 7.5V in 10x50 binoculars tonight (00:10 UT) - strikingly dimmer than comp. star 71 in the AAVSO chart (mag. 7.1), and only visible with averted vision although transparency isn’t perfect here. I had got my Star Analyser and C8 at the ready to capture a lo-res spectrum, but the clouds have promptly rushed in each time I have made an attempt.

I am intrigued by how quickly the spectrum seems to have changed from P Cygni profiles to hydrogen emission. I‘m guessing we were looking through the initial expanding envelope of ejected material yesterday and now we’re seeing ’deeper’ into the nova, to emission from runaway fusion etc? The pace at which these things can evolve amazes me.

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Photo from this morning

I took an unguided 10-second exposure at 0057 UT today with a FujiFilm X-T10 and 85mm Samyang lens. The nova had clearly faded. It appeared quite reddish compared to other stars. This image is reduced in size. 

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V1674 Her

CBET 4977 has designated this nova as V1674 Her.

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Nov Her

Mon June 14 23:35UT I get the Nova at 9.0m using the 8.5 and 9.4 comparison stars IRIS was used for Aperture photometry

Peter

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Nova in Hercules, V1674 Her

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Observed the nova last night,

Observed the nova last night, I made it  about 9.4.  I also noted a strong reddish colour- possibly the reddest nova I've ever observed!

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spectrum evolution

A nice collection of spectra building up here in the Spectroscopy Database showing the evolution 

The shift in the H alpha line from predominantly blue to red while still centred on the rest wavelength is curious. I wonder what that means physically

Cheers

Robin

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Evolution of Nova Her 2021 in flux

Further to Robin's posting, the following plot shows the change in absolute flux of the nova over the last 4 days. These R~1000 spectra have been calibrated in absolute flux using concurrently recorded V magnitudes of 6.35, 8.38 and 9.77 respectively as described here.

David

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Interpreting spectra

I’ve been dusting off the cobwebs concerning this very fascinating but confusing topic and found a nice – if older – overview in http://articles.adsabs.harvard.edu//full/1992AJ....104..725W/0000726.000... that I have been reading. I found it very helpful and I've summarized its main points here. What I like about this article is it does a nice job of trying to connect the squiggly lines found in spectra to the real world physics. Here's a very light (no pun intended) summary...

 

Spectroscopically, novae can be divided into two main types – those with ionized iron lines (FeII) and those with Helium/Nitrogen lines.

 

A given nova can have a spectrum that changes from one type to another.

Like certain supernovae, a nova forms in a binary system where matter builds up on a white dwarf – stolen from a companion star. If this accreted material ignites in a nuclear sense, it can form a nova. If the WD is sufficiently massive, (about 1.4 Msun) it can totally destroy itself and become a supernova. This kind of supernova, formed by the explosion of the same amount of matter (e.g., same number of sticks of dynamite since it always blows at 1.4 Msun), has a standard energy output and can then serve as a standard candle. In a nova, the WD is not destroyed.

The ejected material is in the form of a shell with a wind.

The shell has a high velocity and so its density drops rapidly.

Residual accreted material on the surface of the WD can continue burning gently.

Emission lines form in both the shell and the wind. Shell lines tend to be flat-topped; wind lines tend to be sharper and can have absorption line components.

If the winds are weak, the photosphere is close to the radius of the WD and its effective temperature is high. This creates higher ionization rates in the shell and produces He/N emission lines.

If the winds are strong, the photosphere is expanded, so its effective temperature is reduced, so the shell is less ionized, and much of the emission is from the wind (Fe II lines)

Different energies are needed to excite the different lines in the Balmer spectrum with H-alpha requiring the least. The closer the source region is to the hot surface, the higher the excitation possibility, so H-gamma is from deeper into the star than H-alpha etc.

As temperature is increased from zero… Collisions among atoms can bump electrons to higher orbits, from which they can fall and emit discrete line spectra. Hotter, and the atoms can be ionized – one or more electrons torn from atoms. As density drops, electrons can recombine with atoms and then cascade down through different lower levels; at higher densities, collisions might be driving electron back up, only to cascade back down.

From wikipedia… the Clasic P Cygnii line profile is essentially caused by the doppler effect acting on regions with different velocities. Emission lines coming from the wind, closer to the star and therefore with reduced velocity have minimal doppler change, while absorption from the shell – further out, closer to the observer, and approaching faster – involve shorter wavelengths; so a ‘line’ has both an emission part, and an absorption part at a slightly reduced wavelength. The separation between the absorption and the emission parts tell about the velocity differences. (More comprehensive explanations are available, but this seems good enough for now; the larger point is P Cygnii line profiles indicate the presence of an outflow of material.)

 

So, with this very brief summary, we can see the shapes of lines (P Cygnii, Flat, Narrow) informs us about whether the light is coming from a shell or the wind, and the presence of mass outflows. The presence of FeII vs He/N about winds and shells, and whether the winds are strong or weak, and the changes in the spectrum track how the nova is evolving with time.

So, there is a very strong connection between the wiggly lines of spectra and the underlying physics!

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Kato-san (VSnet) notes that

Kato-san (VSnet) notes that t3 (time to drop 3 mags) is ~ 2.3 days. Appears to be record breakingly fast!

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Nova in Hercules

Jeremy Shears gave us a great round up on the Nova at the start of our local society meeting tonight. Watch it at https://youtu.be/OhWkoHpXnBg Also James Dawson and Sandra Brantingham gave a talk on noctilucent clouds. 

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NAS talk

I have just watched it. Very interesting. Also the presentation on the Unistellar eVscope.

Thanks

Alan

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Fading quickly

As of 2021-06-15T22:11:36 i measured it at mag 9.8 which is quite a drop in brightness! 

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Down to about mag 11 as of

Down to about mag 11 as of today (June 20)

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Evolution of Nova Her 2021 = V1674 Her

Those following the class of this nova may be interested to know that the recent ATel 14728 has reported that it now looks more like a He/N nova than Fe II as was being reported by ATels up until June 16th. This change actually happened within 36 hours of its discovery on June 12.54 UT as this compilation of amateur spectra shows. Compare these with the spectrum of Nova Sgr 1991 in figure 2 of Williams, The Formation of Novae Spectra, AJ, 104, 725 (1992).

David

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Found it!

After hearing of the discovery of another nova and with the best chance I'd had in two weeks, I went hunting for it last night 27 June.  This was a lesson in the value of good polar alignment as I ended up using co-ordinates rather than star hopping.  After comparing my image with charts I managed to locate it and with Jeremy Shears magnitude estimate from last week I can see I almost missed this one.

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Still worth following this

Still worth following this nova in her while the field is well placed. Fading the mag 15 now, though, but perhaps leveling off:

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A spectrum at mag 16

Now at mag 16 but still within range of a very low resolution spectrum with the ALPY200.

The spectrum with several forbidden nebula lines looks similar to that of  another very fast nova Sgr 1991 at similar age in Gray & Corbally , where the tentative line identifications come from

Cheers

Robin