Eruption of the Recurrent Nova RS Oph!

[Pete Presland]

9 hours ago, robin_astro said:

That tallies with my notes from the 2006 outburst accompanying my Star Analyser spectra which described it as straw coloured a few days after outburst. If it follows the same trend as then it should change to a deep red over the next week or so as the H alpha emission comes to completely dominate the spectrum.  Over on CN Keith Geary describes it as blue  when he discovered it in outburst, now pale yellow last night and George Wallerstein describes it as purple initially at the outburst in 1958 in this interesting S&T article from 2005 published just before the 2006 outburst

https://skyandtelescope.org/observing/celestial-objects-to-watch/when-will-rs-ophiuchi-next-blow-its-stack/

 

Sorry if this is dumb question, but will this change in the Spectrum be visble to the naked eye?

[Captain Scarlet]

Dammit I wish I’d seen this thread yesterday. Last night was a lovely clear unforecast 21.6 night. Tonight I’m in the midst of low cloud and fog. Hopefully this nova will wait for me.

M

[Pixies]

Managed to get a view of it in the bins and then the ST80 before the clouds came over.

I'd say its dimmer than mag 4.8 Tau Ophiuchi but slightly brighter than nearby mag 5.4 HR 6686.  So mag 5.2 - ish.

[robin_astro]

4 hours ago, Pete Presland said:

Sorry if this is dumb question, but will this change in the Spectrum be visble to the naked eye?

Do you mean viewing visually through a spectroscope ?   While it is bright enough I would say quite possibly at low resolution but as it fades you would need a big telescope to view the spectrum visually as  the light is so spread out by the spectrograph. This is what the spectrum looked like tonight in a 30 second exposure at low resolution with an ALPY600 spectrograph

The spectrum covers the near UV (~3700 Angstrom) to the near IR (~7900 Angstrom) The bright spot right of centre is the H alpha emission. This is expected to increasingly dominate the spectrum in the days ahead turning the star  from its current straw colour to a deep red visually

Cheers

Robin

[robin_astro]

10 hours ago, rl said:

 

Looks like there is far more emission at the Hydrogen Beta wavelength (4861 angstrom) compared to the alpha (6563).

 

This is mainly due to the response of the instrument which is less sensitive at H alpha compared with H beta. To compare intensities of emission lines at different wavelengths you  first need to subtract the background and correct for the response of the instrument and atmospheric extinction (which is quite high for RS Oph here in the UK due to the low altitude) using a standard star.  Flattening the spectrum (rectifying it) allows you to compare the strength of absorption lines as they are a proportion of the total continuum but it distorts the differences in the relative strength of emission lines)  

Here is a  spectrum corrected for instrument and atmosphere (calibrated in relative flux) from tonight using the ALPY 600. 

Cheers

Robin

Edited August 11, 2021 by robin_astro
clarification

[robin_astro]

13 minutes ago, robin_astro said:

 

Here is a  spectrum corrected for instrument and atmosphere (calibrated in relative flux) from tonight using the ALPY 600. 

 

This paper describing the changes in the spectrum during the 2006 outburst is a good reference to compare with. 

https://academic.oup.com/mnras/article/474/3/4211/4768437

fig 1 which covers the first week is relevant at the moment and identifies the main lines in the spectrum (H ,Fe II, Ca II)

Cheers

Robin

[robin_astro]

11 hours ago, rl said:

The (possibly) Silicon lines roundabout 5000 ang look fairly prominent

These are Fe II, commonly seen in Nova spectra

Cheers

Robin

[Nik271]

There was a bit of haze last night but otherwise it was clear at 10:30pm and I managed to have a look with my Skymax 127. It was dimmer than Tau Oph but considerably brighter than the nearby Y Oph, so I will put it at mag 5.4 or thereabout. Hard to be more precise because the haze and low altitude was making everything dimmer than it should be. I took 20 photos with 85mm lens and stacked them. Here is the result. I have labelled the nearby bright stars from Ophiuci.

 

Edited August 11, 2021 by Nik271

[rl]

@robin_astro..

Robin

Thanks for the input; very helpful, with much food for thought. I checked the sensor response and there is indeed a bias towards the beta line:

The rest of the telescope optics are all reflective (and clean). The spectroscope has a resolution of 400 which isn't great....it probably is good enough for looking at known lines but less so for identifying unknowns. 

I did take some spectra of Altair and Vega with the intention of normalising the instrument response but attempts so far to complete the process in Vspec have failed. The workflow process is quite involved,  and the handbook is much better at explaining what the button do rather than explaining why I need them in the first place. Ken Harrison's book is the best "how to" reference I've found so far.  I've been meaning to sit down and sort this out since Nova Herculis last month..it's becoming something of an ogre now! 

The instrument is known to be slightly nonlinear, so was calibrated against a neon lamp using about 20 lines..this particular bulb has some weak argon lines that help in the blue. I tried a 3rd and 4th order fit. Both show higher residuals in the blue so I'm wondering if the argon lines are real or not. 

The reference paper looks very interesting...

[Pete Presland]

8 hours ago, robin_astro said:

Do you mean viewing visually through a spectroscope ?   While it is bright enough I would say quite possibly at low resolution but as it fades you would need a big telescope to view the spectrum visually as  the light is so spread out by the spectrograph. This is what the spectrum looked like tonight in a 30 second exposure at low resolution with an ALPY600 spectrograph

The spectrum covers the near UV (~3700 Angstrom) to the near IR (~7900 Angstrom) The bright spot right of centre is the H alpha emission. This is expected to increasingly dominate the spectrum in the days ahead turning the star  from its current straw colour to a deep red visually

Cheers

Robin

Thanks for the reply. No, i was thinking through binoculars or with a DSLR image

[JeremyS]

Still borderline NE visibility, but on the turn. Get those binoculars out and catch it while you can 🙂.

AAVSO light curve (circles = vis, green squares = CCD + V filter):

Edited August 11, 2021 by JeremyS

[JeremyS]

2 hours ago, Pete Presland said:

Thanks for the reply. No, i was thinking through binoculars or with a DSLR image

Some novae do appear coloured in binos and DSLR images. This colour is related to the prominent spectral emission bands. And this can change with time.

For example, have a look at these pics taken by Mazin Younis in Manchester of Nova Cas 2021 on 30.03.2021 and 19.05.2021. This shows a shift to red colour. He used a Skywatcher Quattro 200mm Newtonian f/4 and (colour) ZWO ASI 294MC-Pro

 

Edited August 11, 2021 by JeremyS

[JeremyS]

BTW Mazin Younis's fine image of RS Oph is here.

[lunator]

I managed to have a quick look last night. There was thin high cloud making it a less than perfect night. Using my ST80 with a 25mm ortho eyepiece giving x16' magnification approximately 2.75 degree field of view. 

I estimated the magnitude at 5.5. 

I hope for a few more clear night to watch it change colour.

Cheers

Ian

[robin_astro]

2 hours ago, rl said:

 I checked the sensor response and there is indeed a bias towards the beta line:

The sensor is only one part of the overall response though. The grating response is as important and also has a similar shape. Coatings on the optics and the atmosphere also have an  effect and if you are using a slit spectrograph the defocussing effects of any chromatism (including atmospheric dispersion) can affect the fraction of the light going through the slit depending on the wavelength. The trick to dealing with all these factors though is to measure a star with a known spectrum and use this to flux calibrate the unknown. There is a document on my website  which covers how I do this which you might find useful.

http://www.threehillsobservatory.co.uk/astro/spectroscopy_21.htm

Cheers

Robin

[robin_astro]

3 hours ago, Pete Presland said:

Thanks for the reply. No, i was thinking through binoculars or with a DSLR image

I remember in 2006 visually it looked straw coloured a few days after outburst turning to very red over about 2 weeks. The change might not be so obvious in a DSLR image though depending on the sensitivity to H alpha

 

Edited August 11, 2021 by robin_astro

[skybadger]

I had an extended session on this last night using my vixen na140. First to find it, next to image it without the centre being overexposed. I was taking 0.8 second images at 1x binning so I mostly lost the other fainter field stars. 

The Goldy straw colour was prominent even in the haze. 

I may try for a spectrum tonight..

 

Edited August 11, 2021 by skybadger
So.

[Paul M]

I'll be most annoyed if I don't get a weather window before this drops out of 10x50 bino range.

[Muc]

Looking at it again right now, possibly more orangey, and slightly closer to 6th mag. The most comparable star I could put it would be HD164064, the bottom left one in the triangle with Zeta Serpentis (5.94). Still brighter then Y Ophiuchi. Lovely orange tone 

[Muc]

Actually the comparable star would be HD163532 as my view in Stellarium is flipped!

[Malpi12]

Y Oph is also a variable, so perhaps not the best ref !
bit of a sporadic history on AAVSO, currently estimated visual between 5.8 and ~6.4, most clustering near 6.4

Edited August 12, 2021 by Malpi12

[Malpi12]

Sadly awol this night (11-12Aug) due to cloud&rain.
So I amused myself with a search of  my recent archives and, oh so close, I was in the region chasing asteroids and have this "pre" from 20June2021
where (with a bit of a stretch and imagination) in the noise lurks RS at about 10.5-10.8 ish ! [mags from Stellarium,]

Stack of 100x1sec iso6400, fixed tripod, vastly pixel cropped out of a 50mm f2.8 canon aps frame

Not a vastly significant obs in the grand scheme of things, but it amused me to find it

Edited August 12, 2021 by Malpi12

[lunator]

RS Oph is definitely fainter I estimate mag 6.5. It appeared slightly brighter than HD162713 and a similar colour. 

It was still very easy to find in the 10x50 binoculars and the ST80.

Cheers

Ian 

[Nik271]

I had a quick look yesterday about 10:30pm with my 9x50 finder. It seemed to be 6.3 to 6.5, slightly more red than 2 days ago and almost a magnitude dimmer.

[rl]

Turning a bit redder now (12 August 2300 UT) ,Bright star in centre of image:

60 seconds, TS65Q (420mm focal length, Canon 1100D modded, iso 1600), Skyglow Imaging filter, north at top.

Raw spectrum:

Hydrogen markers in green.