Supernova in M82...was cloudy!

[jnp]

Somehow managed to get some shots of the supernova in M82 last night despite the best efforts of the clouds. Needed to use 2x2 binning as there was no opportunity for longer exposures.

I know nothing of supernova spectra, apparently the big absorption dip is Silicon.

Thanks for looking
John

[DaveNicko]

Nice spectrum!

Are you using a diffraction grating? (I say this as someone who knows very little about astro spectroscopy). I guess the spectrum is directly horizontally right of the SN in the image? At some point a long time in the future I would like to get into spectroscopy - but not for a while!

Dave.

[jnp]

Hi Dave,

Yes a diffraction grating is used in front of the CCD sensor and the SN spectrum is to the right.

Most people start in spectroscopy by getting a 'star analyser 100' (sa100) grating. This is a low resolution 100 lines per mm transmission diffraction grating that sits about 40 to 80mm in front of the CCD. The grating aligned  so the spectrum is horizontal. 

Don't be put off by the term 'low resolution' sometimes that is exactly what is needed. There was no opportunity to use a slit spectrometer yesterday, so I dug out the sa100 that I haven't used in ages.

John

[Kedvenc]

Great stuff, love to see people capturing spectra (being a scientist) and was wondering if someone would get one for this SN. I've been wanting to do this for a while myself but not got round to it yet. I'll start with the SA100 I think as well.

[DaveNicko]

Hi Dave,

Yes a diffraction grating is used in front of the CCD sensor and the SN spectrum is to the right.

Most people start in spectroscopy by getting a 'star analyser 100' (sa100) grating. This is a low resolution 100 lines per mm transmission diffraction grating that sits about 40 to 80mm in front of the CCD. The grating aligned  so the spectrum is horizontal. 

Don't be put off by the term 'low resolution' sometimes that is exactly what is needed. There was no opportunity to use a slit spectrometer yesterday, so I dug out the sa100 that I haven't used in ages.

John

Thanks!

My future plans include: Mount, imaging scope, and CCD for what will likely be variable star observing rather than pretty pictures. Followed by (possibly at the same time) a diffraction grating. This won't be for a few years though - at first I plan on starting getting some visual variable star observing in. But at the moment I'm just enjoying my new scope (200mm dob)!

Dave.

[Gasman]

Nice catch John, you did much better than me last night! failed dismally with my Alpy to get a decent spectrum

Steve

[robin_astro]

Nice one John 

Did you notice the image of the galaxy core in the spectrum too at H alpha ?

Here is my one from last night using a new prototype high dispersion version of the Star Analyser designed for use in filter wheels. (The grating was just 26mm from  the camera sensor which is to close for the standard SA100)   The spectrum is corrected for instrument response and atmospheric extinction and i have overlaid Paolo Beradi's higher resolution spectrum from the day before for comparison. The downward slope towards the red and the narrow Na D line visible in Paolo's spectrum mean that there is quite a bit of absorption from interstellar material so it is unlikely that this supernova will reach its theoretical apparent brightness of around vmag 8.5. I suspect it could struggle to reach mag 10.

Cheers

Robin

[robin_astro]

Sorry, I meant downward slope towards the blue end of course. Extinction from interstellar dust is higher at the blue end 

Robin

[nytecam]

Congrats to jpn, Steve and Robin for SN2014J spectra that all show the classic absorption 'band' of silicon for type I SN :-) The M82 core in Ha is nice bonus - well done everyone :-)

[jnp]

Did you notice the image of the galaxy core in the spectrum too at H alpha ?

Robin - yes I did, it was useful to give me some idea for calibration.  I would have annotated the Ha, but that would draw attention to some hot pixels that need attention. That's a top notch result you got with the prototype grating, very consistent result.  Might give the supernova a go with my unwieldy 300 l/mm transmission spectrometer.

26mm will be easier to manage than ~75mm which can lead to  back focus issues (on Newtonians). How will it compare with the Rainbow Optics 200?

What is the significance of the Silicon absorption lines in a supernova?

best regards

John

[robin_astro]

Hi John,

26mm will be easier to manage than ~75mm which can lead to  back focus issues (on Newtonians). How will it compare with the Rainbow Optics 200?

What is the significance of the Silicon absorption lines in a supernova?

Yes that's part of the idea with the prototype SA-HD. Telescopes and cameras have got bigger and more people are using close coupled filter wheels since the SA100 came out back in 2005 so there are more situations where the space to get enough dispersion is limited.  You don't get any better performance though in the converging beam setup by going to a higher dispersion grating  provided you have enough space and too high dispersion is still a problem for small video type cameras so it is not an SA100 replacement.  

As far as I have seen over the past 8 years, the performance of the RO 200  seems to roughly match (but not better) the SA100  when used at the same dispersion and the preliminary tests  are showing very similar results  for the prototype with the SA100 perhaps having a slight edge due to the more forgiving shallower dispersion angle so there is no need to bin your SA100        The new model will have some extra features designed for filter wheel applications as well but more about that when it comes out which hopefully  should be soon.

In a type 1a supernova, the Si line is a by product of the nuclear explosion when the white dwarf acreted too much material from its binary companion, exceeded critical mass and went bang.  In the type II core collapse  supernova, which implode when the core runs out of fuel, the main spectral feature is H alpha so you can easily tell apart the two main mechanisms from a low resolution spectrum.  

Cheers

[Jack Martin]

John,

A good result I am taking spectra tonight as we have a clear spell.

Jack

[jnp]

Here are two more days of data. The 25th Jan was particularity windy with the 8" Newt behaving like a sail.

The profiles were scaled relative to the peak intensity of a nearby star (above and to the right in the pic at the start of this post). Assuming the nearby star is unchanging, this shows the brightness increasing, but I can't see any significant changes in the spectra?

Thanks for looking

John

[nytecam]

Hi Robin - so the SA HD will be similar dispersion to my faithful RO200 which performed well last night on SN2014J :-)

[robin_astro]

Hi Robin - so the SA HD will be similar dispersion to my faithful RO200 which performed well last night on SN2014J :-)

Hi Maurice,

Yes it should give a similar result. Here is my SN2014J image taken with the SA200 13rd January for example

and the calibrated spectrum

http://www.spectro-aras.com/forum/download/file.php?id=1370

(the blue line)

 I found that provided you adjust the spacing to give the same length spectrum  100 line and 200 gratings give similar resolution (with  a slight edge to the 100 line grating, presumably because of the smaller angle of dispersion)  but the 200 grating will work where space is restricted eg in filter wheel applications.

Here are my test results for SA100 v S200 using P Cygni

http://www.threehillsobservatory.co.uk/astro/spectroscopy_16.htm#SA200_filter_wheel

Cheers

Robin

[robin_astro]

Sorry, I just realised I have already posted some of this information up the thread.

(How do I edit my posts, I cannot find an edit button ? )

Robin

[michael.h.f.wilkinson]

Interesting stuff. Love those clear silicon features in the spectra

[nytecam]

Robin - I did, in the past, try to get RO200 like trans grating included in the filter-wheel in some of the automated scopes but with little response eg they were not 'real' spectrographs as pros expect. I'm glad the scene is improving :-)