[julianh72 (Julian)]

The following really belongs in a sub-forum for "Spectroscopy Beginners Start Here", but I thought I would post here to share my beginner's excitement, and as an encouragement to anybody who is thinking of dabbling in spectroscopy. (If you are, my advice is "Do It!" - you won't be disappointed!)

There are no great scientific revelations here, but it is really quite exciting to be able to re-discover for yourself some of the fundamental physics of the universe, using only very affordable hobby-grade equipment. I am using a Meade 8" LX-90 (although a more modest telescope can be used just as effectively - I've grabbed some nice spectra with my 90 mm Mak), a mono QHY5 camera, and a Star Analyser SA-100 eyepiece filter grating.

I took a range of spectra last night on some favourably positioned stars (and one emission nebula – Eta Carinae), and then stacked and scaled the spectra to compare them with each other. Some trends become very apparent:

• The position of the peak of each spectrum correlates with the surface temperature of the star.
o Acrux and Becrux are super-hot (> 20000 K surface temperature)
o Sirius has a surface temperature of ~ 9900 K
o Procyon has a surface temperature of ~ 6500 K
o Gacrux is a red giant with a surface temperature of “only” about 3400 K.

• The strong dips in the near-infra-red are visible in all of the plots
o This is atmospheric absorption, rather than being an intrinsic feature of the stars’ spectra. (I guess that's why all the best infra-red observatories are in space, above the Earth's atmosphere!)
o This will limit the amount of useful “fine detail” I will be able to collect in the infra-red, although I can still see the fact that red giants such as Gacrux emit well into the infra-red compared with the hotter stars.

• Hydrogen absorption is visible in all of the stars - but look at the strong hydrogen emission lines from the Eta Carinae nebula!!!
o There is not as much relative hydrogen absorption visible in Gacrux, but lots of other strong absorption lines around 6000 to 7000 Angstroms. I believe these are associated with absorption of other metals such as Calcium and Titanium, reflecting the fact that as a red giant, it has burnt most of its hydrogen, and is now burning helium and even higher elements.

Not bad! Real Science, all done with a decent hobby-class telescope, a cheap astro-camera (~$200), and a diffraction grating filter (~$150)!

Next step: Chase down some interesting spectroscopy targets - maybe a red-shifted Quasar or two, and a couple of Wolf-Rayet stars. Any suggestions for some interesting (but not TOO challenging!) targets?