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Spectrum of the Ring Nebula
Posted: Wed Jul 21, 2021 5:35 am
by oopfan
An interesting NASA APOD today:
https://apod.nasa.gov/apod/ap210721.html
The identity of the three rings:
Left side: Ha + NII
Middle: OIII
Right side: Normal visual appearance
OIII is very strong in Planetary Nebulae, even stronger than Ha in many cases. However, OIII tends to be weak in regular Emission Nebulae.
Brian
Re: Spectrum of the Ring Nebula
Posted: Fri Jul 30, 2021 9:45 am
by timh
Interesting picture Brian. I have noticed that you can buy a diffraction grating eyepiece
https://www.rspec-astro.com/star-analyser/
and have wondered how well it would perform in practice. Could be interesting comparing carbon stars with types O and A etc?
Tim
Re: Spectrum of the Ring Nebula
Posted: Fri Jul 30, 2021 6:51 pm
by oopfan
Hi Tim,
Centuries ago when I was a teenager, I built a spectrograph for my telescope using a grating and some simple optics. My first subject was Vega. The Ha absorption band was very broad. It indicates that the atoms are super-heated, and bouncing around at high velocity, some moving towards us and others away from us. When they emit photons after absorption, there is a massive red shift and blue shift, therefore the broad absorption band. I would imagine that the absorption lines of Carbon stars are narrower, but you will pick up the heavier elements.
It's been a while since I visited the Rspec website, but I think their software can identify the spectral type of a star from its spectrum.
Brian
Re: Spectrum of the Ring Nebula
Posted: Fri Jul 30, 2021 11:31 pm
by timh
Hi Brian,
That was a good project for a lad..unfortunately as a teenager my hobby was chemistry and I used to make explosives - until a short stay in hospital cured me of that and I switched to amateur electronics and radio which was less destructive.
Your mention of Doppler line broadening led me to this
http://www-star.st-and.ac.uk/~kw25/teac ... widths.pdf
Most of of the broadening probably is collisional at high temperatures in stars ...I guess that the emission lines from relatively cool and low density emission nebulae are much narrower then than the corresponding absorption lines in stellar atmospheres?
Tim
Re: Spectrum of the Ring Nebula
Posted: Sat Jul 31, 2021 1:36 am
by oopfan
Tim,
Interesting. The red/blue shift was the explanation given in the 1970s, as best I can remember. Science does evolve!
Brian