Spectroscopy - tooo difficult!

[Merlin66]

If you've thought of spectroscopy as being "tooo difficult" or too scientific, trust me - getting started is very easy.
I'd appreciate hearing any comments/ concerns/ issues which have put you off considering moving into the "final frontier"- amateur spectroscopy..
Let me know how we can help you...........

[Miaplacidus]

I will be a passive observer to this thread since I have the beginnings of an inkling of an interest in this very topic, but I am not far enough down the path to be able to contribute meaningfully. I will be interested to see what are costs of starting from scratch, too.

[LightningNZ]

Something that may entice a few extra people to give astronomical spectroscopy a go is that they can use their setup with relatively little modification for doing terrestrial spectroscopy - atmospheric (absorption) or plants and animals (reflection).

If anyone's interested in giving reflection spectroscopy a go, I'm happy to lend a few hints/tips/web resources. I actually have a publication in field spectroscopy from several years back, but no longer work in that area of biology.

Cheers,
Cam

[darrellx]

Well, this has been something that has been of interest to me for a long time. Some years ago I purchased a Star Analyser 100, and I have tried several times to get something out of it - with no success.

I have tried with a 200mm reflector and a 90mm refractor; with a dslr, an Atik314L+ and a DMK21. I get a spectrum bar (if thats the right term) but there are no absorption lines (or emission lines).

Initially, I thought the problem was in the way I was aquiring the image. So rather than just one, I took several and stacked them. No luck. So I took more, stacked them, did the flats and darks. No luck.

Then I suspected the issue might be in the processing. If I understand correctly, I need to stretch the image a fair bit to see the lines. But I just don't seem to be able to get it. Over the last few years, I have tried bright stars, not so bright stars, dim stars, but have not tried the Sun.

I am now beginning to think that the issue may be in the placement of the Star Analyser. I may not have it at an appropriate distance from the sensor.

There is obviously something I am missing. Frustrating!
Darrell

[Merlin66]

Miaplacidus,
A couple of hundred dollar will get you started with a Star Analyser grating (SA100)...Think of it as "Spectroscopy 101"
Darrell,
Unfortunately your situation isn't to uncommon. The SA100 usually comes with a DVD which explains the basics of setting it up and getting that first spectral image.
You really need to gain an understanding of what the grating is and what it does before letting it loose on a telescope.
The distance between the grating and the CCD chip should be around 50-60mm - this depends on the pixel size of the camera and the width of the chip.
The grating is a lo res "slitless" spectroscope - this means that the resolution (and height...) of the spectrum is controlled by the size of the star image. Seeing usually limits this to about 2-3 sec arc.
The basics:
-Around an f5 system is ideal.
-Align the grating so that the "lines" are parallel to the side of the chip. This should give you a spectrum horizontally across the CCD.
-Look at the first image you get...there should be a bright star image (zero order image) and a spectra on either side. One is much brighter than the other - that's the one you want to record.
-Position the zero order star close to the edge of the field and the brighter spectrum across the middle.
-Start with an A class star - the Hydrogen lines are much easier to see (and will help you with the calibration later)
initially focus on the star - but as soon as you have the framing correct - ignore the star image (!) and concentrate on the spectrum. Refocus to show the absorption bands and bring them into the best contrast you can.
If you can get this far you're about 10% there!!!

The rest, we can discuss, comes down to the background removal, wavelength calibration and instrument response correction.....
At this stage we can then seriously look at the spectrum and do some basic analysis.
Onwards and Upwards.

[darrellx]

Okay, I can see the issue.

I have always made sure that the image of the star has been in focus. I have not worried obout the spectrum until I got to the processing stage. This is probably why the spectrum has always appeared "fuzzy" and indistinct. The colours are there, but thats about it. I thought this must have just been a function of using the gratings.

Once this weather clears, I will give it another go.

Thanks for the tip.
Darrell